Ilyashenko A.V. – Associate Professor of the Department of Structural Mechanics
Moscow State Construction University,
candidate of technical sciences

The study of the bearing capacity of compressed thin-walled elastic rods that have an initial deflection and have undergone local buckling is associated with the determination of the reduced cross section rod. The main provisions adopted for the study of the stress-strain state in the supercritical stage of compressed non-ideal thin-walled rods are given in the works. This article discusses the supercritical behavior of rods, which are presented as a set of jointly working elements - plates with an initial loss, simulating the work of shelves of angle, tee and cruciform profiles. These are the so-called shelves-plates with one elastically pinched edge and the other free (see figure). In the works, such a plate is referred to as type II.

It was found that the breaking load, which characterizes the bearing capacity of the rod, significantly exceeds the load P cr (m), at which there is a local buckling of the imperfect profile. From the graphs presented in , it can be seen that the deformations of the longitudinal fibers along the perimeter of the cross section in the supercritical stage become extremely unequal. In fibers far from the ribs, compressive strains decrease with increasing load, and at loads close to the limit, due to the sharp curvature of these fibers due to initial bends and ever-increasing arrows of longitudinal half-waves formed after local buckling, strains appear and grow rapidly. stretching.

Sections of the cross section with curved longitudinal fibers release stresses, as if they are switched off from the work of the rod, weakening the effective section and reducing its rigidity. So, the bearing capacity of a thin-walled profile is not limited to local buckling. The full load, perceived by more rigid (less curved) sections of the cross section, can significantly exceed the value of P cr (m) .

We will obtain an effective, reduced section, excluding non-working sections of the profile. To do this, we use the expression for the stress function Ф k (x, y), which describes the stress state of the kth plate of type II (see).

Let's move on to supercritical stresses σ kx (in the direction of the external compressive force), determined in the most unfavorable section of the rod (x=0). Let's write them in general form:

σ kx =∂ 2 Ф k (A km ,y, f kj , f koj , β c,d , β c,d,j ,ℓ, s) ∕ ∂ y 2 , (1)

where the integration constants А km (m=1,2,…,6) and the arrows of the acquired deflection components f kj (j=1,2) are determined from the solution of the system of resolving equations . This system of equations includes nonlinear variational equations and boundary conditions that describe the joint operation of non-ideal profile plates. Arrows f koj (j=1,2,…,5) components of the initial deflection of the k-th plate are determined experimentally for each type of profile;
ℓ is the length of the half-wave formed during local buckling;
s is the plate width;

β c,d = cs 2 + dℓ 2 ;

β c,d,j = cs 4 + dl 2 s 2 + gl 4 ;

c, d, j are positive integers.

The reduced or effective width of the reduced section of the plate-shelf (type II) is denoted by s p. To determine it, we write out the conditions for the transition from the actual cross section of the rod to the reduced one:

1. The stresses in the longitudinal fibers at the initial face of the plate (at y=0) adjacent to the rib (see figure) remain the same as those obtained by the nonlinear theory (1):

where F 2 kr =f 2 kr +2f k0r f kr .

To determine the stress σ k2 =σ k max it is necessary to substitute in (1) the ordinate of the most loaded longitudinal fiber, which is found from the condition: ∂σ kx /∂y=0.

2. The sum of internal forces in the plate during the transition to the reduced section in the direction of the compressive force does not change:

3. The moment of internal forces relative to the axis passing through the initial face (y=0) perpendicular to the plane of the plate remains the same:

From the figure, it is obvious that

σ ′ k2 = σ k1 + y p (σ k2 -σ k1) / (y p + s p). (5)

We write down the system of equations for determining the reduced width of the plate s p. To do this, we substitute (1) and (5) into (3) and (4):

where α=πs/ℓ ; F kr,ξ =f kr f koξ +f kr f kξ +f kor f kξ ;
r, ξ are positive integers.

The resulting system of equations (6) and (7) makes it possible to determine the reduced width s p of each of the plates-shelves that make up a compressed thin-walled rod that has undergone local buckling. Thus, the actual cross section of the profile was replaced by a reduced one.

The proposed technique seems to be useful both in theoretical and practical terms when calculating the bearing capacity of compressed pre-curved thin-walled rods, in which local wave formation is permissible according to operational requirements.

Bibliographic list

1. Ilyashenko A.V., Efimov I.B. Stress-strain state after local buckling of compressed thin-walled rods, taking into account the initial deflection. Stroitel'nye konstruktsii i materialy. Corrosion protection. - Ufa: Works of in-ta NIIpromstroy, 1981. - P.110-119.
2. Ilyashenko A.V. To the calculation of thin-walled tee, angle and cruciform profiles with initial camber // Pile foundations. - Ufa: Sat. scientific tr. Niipromstroy, 1983. - S. 110-122.
3. Ilyashenko A.V., Efimov I.B. Experimental study of thin-walled rods with curved lamellar elements // Organization and production of construction works. - M .: Tsentr.Buro n.-t. Information of Minpromstroy, 1983.

480 rub. | 150 UAH | $7.5 ", MOUSEOFF, FGCOLOR, "#FFFFCC",BGCOLOR, "#393939");" onMouseOut="return nd();"> Thesis - 480 rubles, shipping 10 minutes 24 hours a day, seven days a week and holidays

Kholkin Evgeny Gennadievich. Study local sustainability thin-walled trapezoidal profiles with longitudinal-transverse bending: dissertation... candidate of technical sciences: 01.02.06 / Kholkin Evgeniy Gennadievich; [Place of protection: Ohm. state tech. un-t].- Omsk, 2010.- 118 p.: ill. RSL OD, 61 10-5/3206

Introduction

1. Overview of Stability Studies of Compressed Plate Structural Members 11

1.1. Basic definitions and methods for studying the stability of mechanical systems 12

1.1.1, Algorithm for studying the stability of mechanical systems by the static method 16

1.1.2. static approach. Methods: Euler, nonideality, energetic 17

1.2. Mathematical model and main results of analytical studies of Euler stability. Stability factor 20

1.3. Methods for studying the stability of plate elements and structures made of them 27

1.4. Engineering methods for calculating plates and composite plate elements. The concept of the reduction method 31

1.5. Numerical studies of Euler stability by the finite element method: opportunities, advantages and disadvantages 37

1.6. Overview of experimental studies of the stability of plates and composite plate elements 40

1.7. Conclusions and tasks of theoretical studies of the stability of thin-walled trapezoidal profiles 44

2. Development of mathematical models and algorithms for calculating the stability of thin-walled plate elements of trapezoidal profiles: 47

2.1. Longitudinal-transverse bending of thin-walled plate elements of trapezoidal profiles 47

2.1.1. Problem statement, main assumptions 48

2.1.2. Mathematical model in ordinary differential equations. Boundary conditions, imperfection method 50

2.1.3. Algorithm for numerical integration, determination of critical

yarn and its implementation in MS Excel 52

2.1.4. Calculation results and their comparison with known solutions 57

2.2. Calculation of critical stresses for an individual plate element

in profile ^..59

2.2.1. A model that takes into account the elastic conjugation of the lamellar profile elements. Basic assumptions and tasks of numerical research 61

2.2.2. Numerical study of the stiffness of conjugations and approximation of the results 63

2.2.3. Numerical study of the buckling half-wavelength at the first critical load and approximation of the results 64

2.2.4. Calculation of the coefficient k(/3x,/32). Approximation of calculation results (A,/?2) 66

2.3. Assessment of the adequacy of calculations by comparison with numerical solutions by the finite element method and known analytical solutions 70

2.4. Conclusions and tasks of the pilot study 80

3. Experimental studies on local stability of thin-walled trapezoidal profiles 82

3.1. Description of prototypes and experimental setup 82

3.2. Sample testing 85

3.2.1. Methodology and content of tests G..85

3.2.2. Compressive test results 92

3.3. Findings 96

4. Accounting for local stability in the calculations of load-bearing structures made of thin-walled trapezoidal profiles with a flat longitudinal - transverse bending 97

4.1. Calculation of critical stresses of local buckling of plate elements and the limiting thickness of a thin-walled trapezoidal profile 98

4.2. Region allowable loads without taking into account local loss of stability 99

4.3. Reduction factor 101

4.4. Accounting for local buckling and reduction 101

Findings 105

Bibliographic list

Introduction to work

The relevance of the work.

Creating light, strong and reliable structures is an urgent task. One of the main requirements in mechanical engineering and construction is the reduction of metal consumption. This leads to the fact that structural elements must be calculated according to more accurate constitutive relations, taking into account the danger of both general and local buckling.

One of the ways to solve the problem of minimizing the weight is the use of high-tech thin-walled trapezoidal rolled profiles (TTP). Profiles are made by rolling thin sheet steel with a thickness of 0.4 ... 1.5 mm in stationary conditions or directly on the assembly site as flat or arched elements. Structures with the use of load-bearing arched coatings made of thin-walled trapezoidal profiles are distinguished by their lightness, aesthetic appearance, ease of installation and a number of other advantages compared to traditional types of coatings.

The main type of profile loading is longitudinal-transverse bending. Tone-

jfflF dMF" plate elements

profiles experiencing
compression in the middle plane
bones may lose space
new stability. local
buckling

Rice. 1. Example of local buckling

Yam,

^J

Rice. 2. Scheme of the reduced section of the profile

(MPU) is observed in limited areas along the length of the profile (Fig. 1) at significantly lower loads than the total buckling and stresses commensurate with the allowable ones. With MPU, a separate compressed plate element of the profile completely or partially ceases to perceive the load, which is redistributed between the other plate elements of the profile section. At the same time, in the section where the LPA occurred, the stresses do not necessarily exceed the allowable ones. This phenomenon is called reduction. reduction

is to reduce, in comparison with the real one, the cross-sectional area of ​​​​the profile when reduced to an idealized design scheme (Fig. 2). In this regard, the development and implementation of engineering methods for taking into account the local buckling of plate elements of a thin-walled trapezoidal profile is an urgent task.

Prominent scientists dealt with issues of plate stability: B.M. Broude, F. Bleich, J. Brudka, I.G. Bubnov, V.Z. Vlasov, A.S. Volmir, A.A. Ilyushin, Miles, Melan, Ya.G. Panovko, SP. Timoshenko, Southwell, E. Stowell, Winderberg, Khwalla and others. Engineering approaches to the analysis of critical stresses with local buckling were developed in the works of E.L. Ayrumyan, Burggraf, A.L. Vasilyeva, B.Ya. Volodarsky, M.K. Glouman, Caldwell, V.I. Klimanov, V.G. Krokhaleva, D.V. Martsinkevich, E.A. Pavlinova, A.K. Pertseva, F.F. Tamplona, ​​S.A. Timashev.

In the indicated engineering calculation methods for profiles with a cross section of a complex shape, the danger of MPU is practically not taken into account. At the stage of preliminary design of thin-walled structures, it is important to have a simple apparatus for assessing the bearing capacity of a particular size. In this regard, there is a need to develop engineering calculation methods that allow, in the process of designing structures from thin-walled profiles, to quickly assess their bearing capacity. The verification calculation of the bearing capacity of a thin-walled profile structure can be performed using refined methods using existing software products and, if necessary, adjusted. Such a two-stage system for calculating the bearing capacity of structures made of thin-walled profiles is the most rational. Therefore, the development and implementation of engineering methods for calculating the bearing capacity of structures made of thin-walled profiles, taking into account the local buckling of plate elements, is an urgent task.

The purpose of the dissertation work: study of local buckling in plate elements of thin-walled trapezoidal profiles during their longitudinal-transverse bending and development of an engineering method for calculating the bearing capacity, taking into account local stability.

To achieve the goal, the following research objectives.

Extension of analytical solutions for the stability of compressed rectangular plates to a system of conjugated plates as part of a profile.

Numerical study of the mathematical model of the local stability of the profile and obtaining adequate analytical expressions for the minimum critical stress of the MPC of the plate element.

Experimental evaluation of the degree of reduction in the section of a thin-walled profile with local buckling.

Development of an engineering technique for the verification and design calculation of a thin-walled profile, taking into account local buckling.

Scientific novelty work is to develop an adequate mathematical model of local buckling for a separate lamellar

element in the composition of the profile and obtaining analytical dependencies for calculating critical stresses.

Validity and reliability the obtained results are provided by basing on fundamental analytical solutions of the problem of stability of rectangular plates, correct application of the mathematical apparatus, sufficient for practical calculations, coincidence with the results of FEM calculations and experimental studies.

Practical significance is to develop an engineering methodology for calculating the bearing capacity of profiles, taking into account local buckling. The results of the work are implemented in LLC "Montazhproekt" in the form of a system of tables and graphical representations of the areas of permissible loads for the entire range of profiles produced, taking into account local buckling, and are used for preliminary selection of the type and thickness of the profile material for specific design solutions and types of loading.

Basic provisions for defense.

Mathematical model of flat bending and compression of a thin-walled profile as a system of conjugated plate elements and a method for determining the critical stresses of the MPU in the sense of Euler on its basis.

Analytical dependencies for calculating the critical stresses of local buckling for each lamellar profile element in flat longitudinal-transverse bending.

Engineering method for verification and design calculation of a thin-walled trapezoidal profile, taking into account local buckling. Approbation of work and publication.

The main provisions of the dissertation were reported and discussed at scientific and technical conferences of various levels: International Congress "Machines, technologies and processes in construction" dedicated to the 45th anniversary of the faculty "Transport and technological machines" (Omsk, SibADI, December 6-7, 2007); All-Russian scientific and technical conference, "RUSSIA YOUNG: advanced technologies - in industry" (Omsk, Om-GTU, November 12-13, 2008).

Structure and scope of work. The dissertation is presented on 118 pages of text, consists of an introduction, 4 chapters and one appendix, contains 48 figures, 5 tables. The list of references includes 124 titles.

Mathematical model and main results of analytical studies of Euler stability. Stability factor

Any engineering project relies on a solution differential equations mathematical model of motion and balance mechanical system. The drafting of a structure, mechanism, machine is accompanied by some tolerances for manufacturing, in the future - imperfections. Imperfections can also occur during operation in the form of dents, gaps due to wear and other factors. All variants of external influences cannot be foreseen. The design is forced to work under the influence of random perturbing forces, which are not taken into account in the differential equations.

Factors not taken into account in the mathematical model - imperfections, random forces or perturbations can make serious adjustments to the results obtained.

Distinguish between the unperturbed state of the system - the calculated state at zero disturbances, and the perturbed - formed as a result of disturbances.

In one case, due to the perturbation, there is no significant change in the equilibrium position of the structure, or its motion differs little from the calculated one. This state of the mechanical system is called stable. In other cases, the equilibrium position or the nature of the movement differs significantly from the calculated one, such a state is called unstable.

The theory of the stability of motion and equilibrium of mechanical systems is concerned with the establishment of signs that make it possible to judge whether the considered motion or equilibrium will be stable or unstable.

A typical sign of the transition of a system from a stable state to an unstable one is the achievement by some parameter of a value called critical - critical force, critical speed, etc.

The appearance of imperfections or the impact of unaccounted for forces inevitably lead to the motion of the system. Therefore, in the general case, one should investigate the stability of the motion of a mechanical system under perturbations. This approach to the study of stability is called dynamic, and the corresponding research methods are called dynamic.

In practice, it is often enough to confine ourselves to a static approach, i.e. static methods for studying stability. In this case, the end result of the perturbation is investigated - a new established equilibrium position of the mechanical system and the degree of its deviation from the calculated, unperturbed equilibrium position.

The static statement of the problem assumes not to consider the forces of inertia and the time parameter. This formulation of the problem often makes it possible to translate the model from the equations of mathematical physics into ordinary differential equations. This significantly simplifies the mathematical model and facilitates the analytical study of stability.

A positive result of the analysis of equilibrium stability by the static method does not always guarantee dynamic stability. However, for conservative systems, the static approach in determining critical loads and new equilibrium states leads to exactly the same results as the dynamic one.

In a conservative system, the work of the internal and external forces of the system, performed during the transition from one state to another, is determined only by these states and does not depend on the trajectory of motion.

The concept of "system" combines a deformable structure and loads, the behavior of which must be specified. This implies two necessary and sufficient conditions for the conservatism of the system: 1) the elasticity of the deformable structure, i.e. reversibility of deformations; 2) conservatism of the load, i.e. independence of the work done by it from the trajectory. In some cases, the static method gives satisfactory results for non-conservative systems as well.

To illustrate the above, let's consider several examples from theoretical mechanics and strength of materials.

1. A ball of weight Q is in a recess in the support surface (Fig. 1.3). Under the action of the perturbing force 5P Q sina, the equilibrium position of the ball does not change, i.e. it is stable.

With a short-term action of the force 5P Q sina, without taking into account rolling friction, a transition to a new equilibrium position or oscillations around the initial equilibrium position is possible. When friction is taken into account, the oscillatory motion will be damped, that is, stable. The static approach allows to determine only the critical value of the perturbing force, which is equal to: Рcr = Q sina. The nature of the movement when the critical value of the perturbing action is exceeded and the critical duration of the action can be analyzed only by dynamic methods.

2. The rod is long / compressed by the force P (Fig. 1.4). From the strength of materials based on the static method, it is known that under loading within the limits of elasticity, there is a critical value of the compressive force.

The solution of the same problem with a follower force, the direction of which coincides with the direction of the tangent at the point of application, by the static method leads to the conclusion about the absolute stability of the rectilinear form of equilibrium.

Mathematical model in ordinary differential equations. Boundary conditions, imperfection method

Engineering analysis is divided into two categories: classical and numerical methods. Using classical methods, they try to solve the problems of distribution of stress and strain fields directly, forming systems of differential equations based on fundamental principles. An exact solution, if it is possible to obtain equations in a closed form, is possible only for the simplest cases of geometry, loads and boundary conditions. A fairly wide range of classical problems can be solved using approximate solutions to systems of differential equations. These solutions take the form of series in which the lower terms are discarded after convergence has been examined. Like exact solutions, approximate ones require a regular geometric shape, simple boundary conditions, and convenient application of loads. Accordingly, these solutions cannot be applied to most practical problems. The principal advantage of classical methods is that they provide a deep understanding of the problem under study. With the help of numerical methods, a wider range of problems can be investigated. Numerical methods include: 1) energy method; 2) method of boundary elements; 3) finite difference method; 4) finite element method.

Energy methods make it possible to find the minimum expression for the total potential energy structures throughout the given area. This approach only works well for certain tasks.

The boundary element method approximates the functions that satisfy the system of differential equations being solved, but not the boundary conditions. The dimension of the problem is reduced because the elements represent only the boundaries of the modeled area. However, the application of this method requires knowledge of the fundamental solution of the system of equations, which can be difficult to obtain.

The finite difference method transforms the system of differential equations and boundary conditions into the corresponding system of algebraic -equations. This method allows solving problems of analysis of structures with complex geometry, boundary conditions and combined loads. However, the finite difference method often turns out to be too slow due to the fact that the requirement for a regular grid over the entire study area leads to systems of equations of very high orders.

The finite element method can be extended to an almost unlimited class of problems due to the fact that it allows using elements of simple and various forms to obtain partitions. The sizes of the finite elements that can be combined to obtain an approximation to any irregular boundaries in the partition sometimes differ by dozens of times. It is allowed to apply an arbitrary type of load to the elements of the model, as well as to impose any type of fastening on them. The main problem is the increase in costs to obtain results. One has to pay for the generality of the solution with the loss of intuition, since a finite element solution is, in fact, a set of numbers that are applicable only to a specific problem posed using a finite element model. Changing any significant aspect of the model usually requires a complete re-solving of the problem. However, this is not a significant cost, since the finite element method is often the only possible way her decisions. The method is applicable to all classes of field distribution problems, which include structural analysis, heat transfer, fluid flow, and electromagnetism. The disadvantages of numerical methods include: 1) the high cost of finite element analysis programs; 2) long training to work with the program and the possibility of full-fledged work only for highly qualified personnel; 3) quite often it is impossible to check the correctness of the result of the solution obtained by the finite element method by means of a physical experiment, including in nonlinear problems. t Review of experimental studies of the stability of plates and composite plate elements

Currently used for building structures profiles are made from metal sheets with a thickness of 0.5 to 5 mm and are therefore considered thin-walled. Their faces can be either flat or curved.

The main feature of thin-walled profiles is that faces with a high width-to-thickness ratio experience large buckling deformations under loading. A particularly intensive growth of deflections is observed when the magnitude of the stresses acting in the face approaches a critical value. There is a loss of local stability, deflections become comparable with the thickness of the face. As a result, the cross section of the profile is strongly distorted.

In the literature on the stability of plates, a special place is occupied by the work of the Russian scientist SP. Timoshenko. He is credited with developing an energy method for solving problems of elastic stability. Using this method, SP. Timoshenko gave a theoretical solution to the problems of stability of plates loaded in the middle plane under different boundary conditions. The theoretical solutions were verified by a series of tests on freely supported plates under uniform compression. Tests confirmed the theory.

Assessment of the adequacy of calculations by comparison with numerical solutions by the finite element method and known analytical solutions

To check the reliability of the obtained results, numerical studies were carried out by the finite element method (FEM). Recently, numerical studies of the FEM have been increasingly used due to objective reasons, such as the lack of test problems, the impossibility of observing all conditions when testing on samples. Numerical methods make it possible to conduct research under "ideal" conditions, have a minimum error, which is practically unrealizable in real tests. Numerical studies were carried out using the ANSYS program.

Numerical studies were carried out with samples: a rectangular plate; U-shaped and trapezoidal profile element, having a longitudinal ridge and without a ridge; profile sheet (Fig. 2.11). We considered samples with a thickness of 0.7; 0.8; 0.9 and 1mm.

To the samples (Fig. 2.11), a uniform compressive load sgsh was applied along the ends, followed by an increase by a step Det. The load corresponding to the local buckling of the flat shape corresponded to the value of the critical compressive stress ccr. Then, according to the formula (2.24), the stability coefficient & (/? i, /? g) was calculated and compared with the value from table 2.

Consider a rectangular plate with a length a = 100 mm and a width 6 = 50 mm, compressed at the ends by a uniform compressive load. In the first case, the plate has a hinged fastening along the contour, in the second - a rigid seal along the side faces and a hinged fastening along the ends (Fig. 2.12).

In the ANSYS program, a uniform compressive load was applied to the end faces, and the critical load, stress, and stability coefficient &(/?],/?2) of the plate were determined. When hinged along the contour, the plate lost stability in the second form (two bulges were observed) (Fig. 2.13). Then the resistance coefficients k,/32) of the plates, found numerically and analytically, were compared. The calculation results are presented in Table 3.

Table 3 shows that the difference between the results of the analytical and numerical solutions was less than 1%. Hence, it was concluded that the proposed stability study algorithm can be used in calculating critical loads for more complex structures.

To extend the proposed method for calculating the local stability of thin-walled profiles to the general case of loading, numerical studies were carried out in the ANSYS program to find out how the nature of the compressive load affects the coefficient k(y). The research results are presented in a graph (Fig. 2.14).

The next step in checking the proposed calculation methodology was the study of a separate element of the profile (Fig. 2.11, b, c). It has a hinged fastening along the contour and is compressed at the ends by a uniform compressive load USZH (Fig. 2.15). The sample was studied for stability in the ANSYS program and according to the proposed method. After that, the results obtained were compared.

When creating a model in the ANSYS program, in order to uniformly distribute the compressive load along the end, a thin-walled profile was placed between two thick plates and a compressive load was applied to them.

The result of the study in the ANSYS program of the U-shaped profile element is shown in Figure 2.16, which shows that, first of all, the loss of local stability occurs at the widest plate.

Permissible load area without taking into account local buckling

For load-bearing structures made of high-tech thin-walled trapezoidal profiles, the calculation is carried out according to the methods of allowable stresses. An engineering method is proposed for taking into account local buckling in the calculation of the bearing capacity of structures made of thin-walled trapezoidal profiles. The technique is implemented in MS Excel, available for wide application and can serve as the basis for the corresponding additions to the regulatory documents regarding the calculation of thin-walled profiles. It is built on the basis of research and the obtained analytical dependences for calculating the critical stresses of local buckling of plate elements of a thin-walled trapezoidal profile. The task is divided into three components: 1) determining the minimum thickness of the profile (limiting t \ at which there is no need to take into account local buckling in this type of calculation; 2) determining the area of ​​​​allowable loads of a thin-walled trapezoidal profile, inside which the bearing capacity is provided without local buckling; 3) determination of the range of permissible values ​​NuM, within which the bearing capacity is provided in case of local buckling of one or more plate elements of a thin-walled trapezoidal profile (taking into account the reduction of the profile section).

At the same time, it is considered that the dependence of the bending moment on the longitudinal force M = f (N) for the calculated structure was obtained using the methods of resistance of materials or structural mechanics (Fig. 2.1). The allowable stresses [t] and the yield strength of the material cgt are known, as well as the residual stresses cst in plate elements. In calculations after local loss of stability, the "reduction" method was applied. In case of buckling, 96% of the width of the corresponding plate element is excluded.

Calculation of critical stresses of local buckling of plate elements and limiting thickness of a thin-walled trapezoidal profile A thin-walled trapezoidal profile is divided into a set of plate elements as shown in Fig.4.1. At the same time, the angle of mutual arrangement of neighboring elements does not affect the value of the critical stress of the local

Profile H60-845 CURVED buckling. It is allowed to replace curvilinear corrugations with rectilinear elements. Critical compressive stresses of local buckling in the sense of Euler for a separate /-th plate element of a thin-walled trapezoidal profile with width bt at thickness t, modulus of elasticity of the material E and Poisson's ratio ju in the elastic stage of loading are determined by the formula

The coefficients k(px, P2) and k(v) take into account, respectively, the influence of the rigidity of the adjacent plate elements and the nature of the distribution of compressive stresses over the width of the plate element. The value of the coefficients: k(px, P2) is determined according to Table 2, or calculated by the formula

Normal stresses in a plate element are determined in the central axes by the well-known formula for the resistance of materials. The area of ​​permissible loads without taking into account local buckling (Fig. 4.2) is determined by the expression and is a quadrilateral, where J is the moment of inertia of the section of the profile period during bending, F is the sectional area of ​​the profile period, ymax and Umіp are the coordinates of the extreme points of the profile section (Fig. 4.1).

Here, the sectional area of ​​the profile F and the moment of inertia of the section J are calculated for a periodic element of length L, and the longitudinal force iV and the bending moment Mb of the profile refer to L.

The bearing capacity is provided when the curve of actual loads M=f(N) falls within the range of allowable loads minus the area of ​​local buckling (Fig. 4.3). Fig 4.2. Permissible load area without taking into account local buckling

The loss of local stability of one of the shelves leads to its partial exclusion from the perception of workloads - reduction. The degree of reduction is taken into account by the reduction factor

The bearing capacity is provided when the actual load curve falls within the range of permissible loads minus the load area of ​​local buckling. At smaller thicknesses, the line of local buckling reduces the area of ​​permissible loads. Local buckling is not possible if the actual load curve is placed in a reduced area. When the curve of actual loads goes beyond the line of the minimum value of the critical stress of local buckling, it is necessary to rebuild the area of ​​permissible loads, taking into account the reduction of the profile, which is determined by the expression

INTRODUCTION

1 STATUS OF THE ISSUE ON THE THEORY AND TECHNOLOGY OF PROFILING MULTIFACETED PIPES BY DRAWING WITHOUT DRAWING (LITERARY REVIEW).

1.1 Range profile pipes with flat edges and their use in technology.

1.2 The main methods for the production of profile pipes with flat edges.

1.4 Drawing shaped tool.

1.5 Drawing multifaceted helical-twisted pipes.

1.6 Conclusions. Purpose and objectives of research.

2 DEVELOPMENT OF A MATHEMATICAL MODEL OF PIPE PROFILING BY DRAWING.

2.1 Basic provisions and assumptions.

2.2 Description of the deformation zone geometry.

2.3 Description of the power parameters of the profiling process.

2.4 Evaluation of the fillability of the corners of the drawing die and the tightening of the profile faces.

2.5 Description of the algorithm for calculating profiling parameters.

2.6 Computer analysis of profiling force conditions square pipes uncorrected drawing.

2.7 Conclusions.

3 CALCULATION OF THE TOOL FOR STRENGTH FOR DRAWING PROFILE PIPES.

3.1 Statement of the problem.

3.2 Determination of the stress state of the die.

3.3 Construction of mapping functions.

3.3.1 Square hole.

3.3.2 Rectangular hole.

3.3.3 Plano-oval hole.

3.4 An example of calculating the stress state of a drawing die with a square hole.

3.5 An example of the calculation of the stress state of a drawing die with a round hole.

3.6 Analysis of the obtained results.

3.7 Conclusions.

4 EXPERIMENTAL STUDIES ON PROFILING OF SQUARE AND RECTANGULAR PIPES BY DRAWING.

4.1 Methodology of the experiment.

4.2 Profiling a square pipe by drawing in one transition into one die.

4.3 Profiling a square tube by drawing in one pass with counter tension.

4.4 Three-factor linear mathematical model of profiling square pipes.

4.5 Determination of the fillability of the corners of the drawing die and the tightening of the faces.

4.6 Improving the calibration of die channels for rectangular pipes.

4.7 Conclusions.

5 DRAWING OF PROFILE HELICALLY TWISTED PIPES.

5.1 Choice of technological parameters of drawing with torsion.

5.2 Determination of torque.

5.3 Determination of pulling force.

5.4 Experimental studies.

5.5 Conclusions.

Recommended list of dissertations

• Drawing thin-walled pipes with a rotating tool 2009, candidate of technical sciences Pastushenko, Tatyana Sergeevna

• Improving the technology of mandrelless drawing of thin-walled pipes into a block of drawing dies with a guaranteed wall thickness 2005, candidate of technical sciences Kargin, Boris Vladimirovich

• Improvement of processes and machines for the manufacture of cold profiled pipes based on the simulation of the deformation zone 2009, Doctor of Technical Sciences Parshin, Sergey Vladimirovich

• Modeling the process of profiling multifaceted pipes in order to improve it and select the parameters of the mill 2005, candidate of technical sciences Semenova, Natalya Vladimirovna

• Drawing pipes from anisotropic hardening material 1998, Ph.D. Chernyaev, Alexey Vladimirovich

Introduction to the thesis (part of the abstract) on the topic "Improving the process of profiling polyhedral pipes by mandrelless drawing"

Relevance of the topic. The active development of the production sector of the economy, stringent requirements for the economy and reliability of products, as well as for production efficiency require the use of resource-saving types of equipment and technology. For many sectors of the construction industry, mechanical engineering, instrument making, and the radio engineering industry, one of the solutions is the use of economical types of pipes (heat-exchange and radiator pipes, waveguides, etc.), which allows you to: increase the power of installations, strength and durability of structures, reduce their metal consumption, save materials , improve appearance. A wide range and a significant volume of consumption of profile pipes made the development of their production in Russia necessary. At present, the bulk of shaped pipes are manufactured in pipe drawing shops, since cold rolling and drawing operations are sufficiently developed in the domestic industry. In this regard, the improvement of existing production is especially important: the development and manufacture of tooling, the introduction of new technologies and methods.

The most common types of shaped pipes are multifaceted (square, rectangular, hexagonal, etc.) high-precision pipes obtained by drawing without a mandrel in one pass.

The relevance of the topic of the dissertation is determined by the need to improve the quality of multifaceted pipes by improving the process of their profiling without a mandrel.

The aim of the work is to improve the process of profiling multifaceted pipes by drawing without a mandrel by developing methods for calculating technological parameters and tool geometry.

To achieve this goal, it is necessary to solve the following tasks:

1. Create a mathematical model for profiling polyhedral pipes by mandrelless drawing to assess the force conditions, taking into account the nonlinear hardening law, the anisotropy of properties, and the complex geometry of the die channel.

2. Determine the force conditions depending on the physical, technological and structural parameters of profiling in the case of drawing without a mandrel.

3. To develop a method for assessing the fillability of die corners and face tightening when drawing multifaceted pipes.

4. Develop a method for calculating the strength of shaped dies to determine the geometric parameters of the tool.

5. Develop a methodology for calculating technological parameters with simultaneous profiling and torsion.

6. Conduct experimental studies of the technological parameters of the process that ensure high accuracy of the dimensions of polyhedral pipes and check the adequacy of the calculation of the technological parameters of profiling using a mathematical model.

Research methods. Theoretical studies were based on the main provisions and assumptions of the theory of drawing, the theory of elasticity, the method of conformal mappings, and computational mathematics.

Experimental studies were carried out in laboratory conditions using the methods of mathematical planning of the experiment on a universal testing machine TsDMU-30.

The author defends the results of calculating the technological and structural parameters of profiling multifaceted pipes by mandrelless drawing: a method for calculating the strength of a shaped die, taking into account normal loads in the channel; method for calculating the technological parameters of the process of profiling polyhedral pipes by mandrelless drawing; methodology for calculating technological parameters with simultaneous profiling and torsion during mandrelless drawing of helical thin-walled polyhedral pipes; results of experimental studies.

Scientific novelty. Regularities are established for changing the force conditions during profiling of multifaceted pipes by drawing without a mandrel, taking into account the nonlinear hardening law, the anisotropy of properties, and the complex geometry of the die channel. The problem of determining the stress state of a shaped die, which is under the action of normal loads in the channel, is solved. A complete record of the equations of the stress-strain state with simultaneous profiling and torsion of a polyhedral pipe is given.

The reliability of the research results is confirmed by a rigorous mathematical formulation of problems, the use of analytical methods for solving problems, modern methods of conducting experiments and processing experimental data, reproducibility of the experimental results, satisfactory convergence of calculated, experimental data and practical results, compliance of the simulation results with the manufacturing technology and the characteristics of finished polyhedral pipes.

The practical value of the work is as follows:

1. Modes for obtaining square pipes 10x10x1mm from D1 alloy of high precision are proposed, which increase the yield by 5%.

2. The dimensions of the shaped dies are determined, ensuring their performance.

3. Combining the operations of profiling and torsion shortens the technological cycle for the manufacture of helical polyhedral pipes.

4. Improved die channel calibration for profiling 32x18x2mm rectangular pipes.

Approbation of work. The main provisions of the dissertation work were reported and discussed at the international scientific and technical conference dedicated to the 40th anniversary of the Samara Metallurgical Plant "New directions for the development of production and consumption of aluminum and its alloys" (Samara: SSAU, 2000); 11th Interuniversity Conference "Mathematical Modeling and Boundary Problems", (Samara: SSTU, 2001); the second international scientific and technical conference "Metal Physics, Mechanics of Materials and Deformation Processes" (Samara: SSAU, 2004); XIV Tupolev readings: international youth scientific conference (Kazan: KSTU, 2006); IX Royal Readings: International Youth Scientific Conference (Samara: SSAU, 2007).

Publications Materials reflecting the main content of the dissertation were published in 11 papers, including 4 leading peer-reviewed scientific publications, determined by the Higher Attestation Commission.

Structure and scope of work. The dissertation consists of basic symbols, introduction, five chapters, bibliography and appendix. The work is presented on 155 pages of typewritten text, including 74 figures, 14 tables, a bibliography of 114 titles and an appendix.

The author expresses his gratitude to the staff of the Department of Metal Forming for their assistance, as well as to the supervisor, Professor of the Department, Doctor of Technical Sciences. V.R. Kargin for valuable comments and practical assistance in the work.

Similar theses in the specialty "Technologies and machines for pressure treatment", 05.03.05 VAK code

• Improvement of technology and equipment for the production of stainless steel capillary pipes 1984, candidate of technical sciences Trubitsin, Alexander Filippovich

• Improving the technology of assembly by drawing composite pipes of complex cross sections with a given level of residual stresses 2002, candidate of technical sciences Fedorov, Mikhail Vasilyevich

• Improving the technology and design of drawing dies for the manufacture of hexagonal profiles based on modeling in the "workpiece-tool" system 2012, candidate of technical sciences Malakanov, Sergey Aleksandrovich

• Investigation of models of the stress-strain state of metal during pipe drawing and development of a method for determining the power parameters of drawing on a self-aligning mandrel 2007, candidate of technical sciences Malevich, Nikolai Aleksandrovich

• Improvement of equipment, tools and technological means for drawing high-quality straight-seam pipes 2002, candidate of technical sciences Manokhina, Natalia Grigoryevna

Dissertation conclusion on the topic "Technologies and machines for pressure treatment", Shokova, Ekaterina Viktorovna

MAIN RESULTS AND CONCLUSIONS OF THE WORK

1. It follows from the analysis of scientific and technical literature that one of the rational and productive processes for manufacturing thin-walled polyhedral pipes (square, rectangular, hexagonal, octagonal) is the process of drawing without a mandrel.

2. A mathematical model of the process of profiling multifaceted pipes by mandrelless drawing has been developed, which makes it possible to determine the force conditions taking into account the nonlinear hardening law, the anisotropy of the properties of the pipe material and the complex geometry of the die channel. The model is implemented in the Delphi 7.0 programming environment.

3. With the help of a mathematical model, the quantitative influence of physical, technological and structural factors on the power parameters of the process of profiling polyhedral pipes by mandrelless drawing is established.

4. Techniques have been developed for assessing the fillability of die corners and face tightening during mandrelless drawing of polyhedral pipes.

5. A method has been developed for calculating the strength of shaped dies, taking into account normal loads in the channel, based on the Airy stress function, the method of conformal mappings and the third theory of strength.

6. A three-factor mathematical model for profiling square pipes has been experimentally built, which makes it possible to select technological parameters that ensure the accuracy of the geometry of the resulting pipes.

7. A method for calculating technological parameters with simultaneous profiling and twisting of polyhedral pipes by mandrelless drawing has been developed and brought to the engineering level.

8. Experimental studies of the process of profiling polyhedral pipes by mandrelless drawing showed satisfactory convergence of the results of theoretical analysis with experimental data.

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99. Trusov, P.V. Study of the profiling process of grooved pipes Text. / P.V. Trusov, V.Yu. Stolbov, I.A. Kron//Processing of metals by pressure. - Sverdlovsk, 1981. No. 8. - P.69-73.

100. Hooken, V. Preparation of tubes for drawing, drawing methods and equipment used in drawing Text. / V. Hooken // Production of pipes. Dusseldorf, 1975. Per. with him. M.: Metallurgizdat, 1980. - 286s.

101. Shevakin, Yu.F. Computers in the production of pipes Text. / Yu.F. Shevakin, A.M. Rytikov. M.: Metallurgy, 1972. -240s.

102. Shevakin Yu.F. Calibration of a tool for drawing rectangular pipes Text. / Yu.F. Shevakin, N.I. Kasatkin// Study of non-ferrous metal forming processes. -M.: Metallurgy, 1971. Issue. No. 34. - P.140-145.

103. Shevakin Yu.F. Pipe production Text./ Yu.F. Shevakin, A.Z. Gleyberg. M.: Metallurgy, 1968. - 440s.

104. Shevakin Yu.F. Production of pipes from non-ferrous metals Text. / Yu.F. Shevakin, A.M. Rytikov, F.S. Seidaliev M.: Metallurgizdat, 1963. - 355p.

105. Shevakin, Yu.F., Rytikov A.M. Improving the efficiency of production of pipes from non-ferrous metals Text./ Yu.F. Shevakin, A.M. Rytikov. M.: Metallurgy, 1968.-240s.

106. Shokova, E.V. Calibration of a tool for drawing rectangular pipes Text. / E.V. Shokov // XIV Tupolev Readings: International Youth Scientific Conference, Kazan State University. tech. un-t. Kazan, 2007. - Volume 1. - S. 102103.

107. Shurupov, A.K., Freiberg, M.A. Manufacture of pipes of economical profiles Text./A.K. Shurupov, M.A. Freiberg.-Sverdlovsk: Metallurgizdat, 1963-296s.

108. Yakovlev, V.V. Drawing of rectangular pipes of increased accuracy Text. / V.V. Yakovlev, B.A. Smelnitsky, V.A. Balyavin and others // Steel.-1981.-No. 6-S.58.

109. Yakovlev, V.V. Contact stresses during mandrelless pipe drawing. Text./ V.V. Yakovlev, V.V. Ostryakov // Sat: Production of seamless pipes. - M .: Metallurgy, 1975. - No. 3. - P. 108-112.

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Please note that the scientific texts presented above are posted for review and obtained through original dissertation text recognition (OCR). In this connection, they may contain errors related to the imperfection of recognition algorithms. There are no such errors in the PDF files of dissertations and abstracts that we deliver.

THESIS ON THE TOPIC:

Pipe production

1. ASSORTMENT AND REQUIREMENTS OF REGULATORY DOCUMENTATION FOR PIPES

1.1 Pipe schedule

JSC "KresTrubZavod" is one of the largest manufacturers of pipe products in our country. Its products are successfully sold both domestically and abroad. The products manufactured at the plant meet the requirements of domestic and foreign standards. International quality certificates are issued by such organizations as: the American Petroleum Institute (API), the German certification center TUV - Reiland.

Workshop T-3 is one of the main workshops of the enterprise, its products meet the standards presented in Table. 1.1.

Table 1.1 - Standards for manufactured pipes

The shop produces pipes from carbon, alloyed and highly alloyed steel grades with diameter D=28-89mm and wall thickness S=2.5-13mm.

Basically, the workshop specializes in the production of tubing, general purpose pipes and pipes intended for subsequent cold processing.

The mechanical properties of the produced pipes must correspond to those indicated in Table. 1.2.

1.2 Requirement of regulatory documentation

The production of pipes in the T-3 KresTrubZavod workshop is carried out according to various regulatory documents such as GOST, API, DIN, NFA, ASTM and others. Consider the requirements of DIN 1629.

1.2.1 Assortment

This standard applies to seamless round pipes from unalloyed steels. Chemical composition steels used for the production of pipes are given in Table 1.3.

Table 1.2 - Mechanical properties of pipes

Table 1.3 - Chemical composition of steels

Pipes manufactured according to this standard are used primarily in various apparatus in the manufacture of tanks and pipelines, as well as in general mechanical engineering and instrument making.

Dimensions and limit deviations pipes are given in Table 1.4., Table 1.5., Table 1.6.

The length of the pipe is determined by the distance between its ends. Types of pipe lengths are given in Table 1.4.

Table 1.4 - Length types and length tolerances

Table 1.5 - Permissible diameter deviations

Table 1.6 - Wall thickness tolerances

Pipes should be as round as possible. The roundness deviation must be within the outside diameter tolerances.

Pipes should be straight to the eye, if necessary, special requirements for straightness can be established.

Pipes must be cut perpendicular to the pipe axis and must be free of burrs.

The values ​​for linear masses (weights) are given in DIN 2448. The following deviations from these values ​​are allowed:

for a single pipe + 12% - 8%,

for deliveries weighing at least 10 tons +10%–5%.

The standard designation for pipes corresponding to DIN 1629 indicates:

Name (pipe);

The main number of the DIN dimensional standard (DIN 2448);

The main dimensions of the pipe (outer diameter × wall thickness);

Main number of technical delivery conditions (DIN 1629);

Abbreviated name of the steel grade.

An example of a symbol for a pipe according to DIN 1629 with an outer diameter of 33.7 mm and a wall thickness of 3.2 mm made of steel St 37.0:

Pipe DIN 2448–33.7×3.2

DIN 1629-St 37.0.

1.2.2 Technical requirements

Pipes must be manufactured in accordance with the requirements of the standard and according to the technological regulations approved in the prescribed manner.

On the outer and inner surfaces of pipes and couplings there should be no captivity, shells, sunsets, delaminations, cracks and sand.

Punching and cleaning of the indicated defects is allowed, provided that their depth does not exceed the limiting minus deviation along the wall thickness. Welding, caulking or sealing of defective places is not allowed.

In places where the wall thickness can be measured directly, the depth of defective places may exceed the specified value, provided that the minimum wall thickness is maintained, defined as the difference between the nominal pipe wall thickness and the maximum minus deviation for it.

Separate minor nicks, dents, risks, a thin layer of scale and other defects due to the production method are allowed, if they do not take the wall thickness beyond the limits of minus deviations.

Mechanical properties (yield strength, tensile strength, elongation at break) must correspond to the values ​​given in Table 1.7.

Table 1.7 - Mechanical properties

1.2.3 Acceptance rules

Pipes are presented for acceptance in batches.

The batch must consist of pipes of the same nominal diameter, the same wall thickness and strength group, of the same type and version, and be accompanied by a single document certifying that their quality complies with the requirements of the standard and containing:

Name of the manufacturer;

Nominal pipe diameter and wall thickness in millimeters, pipe length in meters;

Type of pipes;

Strength group, heat number, mass fraction of sulfur and phosphorus for all heats included in the batch;

Pipe numbers (from - to for each heat);

Test results;

Standard designation.

Checking appearance, the size of the defects and the geometric dimensions and parameters must be subjected to each pipe of the batch.

The mass fraction of sulfur and phosphorus must be checked from each heat. For pipes made from metal of another enterprise, the mass fraction of sulfur and phosphorus must be certified by a document on the quality of the metal manufacturer.

To check the mechanical properties of the metal, one pipe of each size is taken from each heat.

To check for flattening, one pipe is taken from each heat.

Each pipe shall be subjected to a leak test by internal hydraulic pressure.

If unsatisfactory test results are obtained for at least one of the indicators, repeated tests are carried out on it on a double sample from the same batch. The retest results apply to the entire lot.

1.2.4 Test methods

Inspection of the outer and inner surfaces of pipes and couplings is carried out visually.

The depth of defects should be checked by sawing or in another way in one to three places.

Checking the geometric dimensions and parameters of pipes and couplings should be carried out using universal measuring instruments or special devices, providing the necessary measurement accuracy, in accordance with the technical documentation approved in the prescribed manner.

The bending at the end sections of the pipe is determined based on the size of the deflection arrow, and is calculated as the quotient of dividing the deflection arrow in millimeters by the distance from the place - the measurement to the nearest end of the pipe in meters.

Testing of pipes by weight should be carried out on special means for weighing with an accuracy that meets the requirements of this standard.

The tensile test must be carried out according to DIN 50 140 on short longitudinal specimens.

To check the mechanical properties of the metal, one sample is cut from each selected pipe. Specimens shall be cut along either end of the pipe in a manner that does not alter the structure and mechanical properties of the metal. It is allowed to straighten the ends of the sample to be gripped by the clamps of the testing machine.

The duration of the hydraulic pressure test shall be at least 10 s. During the test, no leaks shall be detected in the pipe wall.

1.2.5 Marking, packaging, transport and storage

Pipe marking should be carried out in the following volume:

Each pipe at a distance of 0.4-0.6 m from its end must be clearly marked by impact or knurling:

Pipe number;

Trademark of the manufacturer;

Month and year of issue.

The place of marking should be circled or underlined with stable light paint.

The height of the marking signs should be 5-8 mm.

With the mechanical method of marking pipes, it is allowed to arrange it in one row. It is allowed to mark the heat number on each pipe.

Next to the marking by impact or knurling, each pipe must be marked with a stable light paint:

Nominal pipe diameter in millimeters;

Wall thickness in millimeters;

Type of execution;

Name or trademark of the manufacturer.

The height of the marking signs should be 20-50 mm.

All markings must be applied along the generatrix of the pipe. It is allowed to apply marking signs perpendicular to the generatrix using the knurling method.

When loading in one car, there should be pipes of only one batch. Pipes are transported in packages, firmly tied in at least two places. The mass of the package should not exceed 5 tons, and at the request of the consumer - 3 tons. Shipment of packages of pipes of different lots in one car is allowed, provided they are separated.

2. TECHNOLOGY AND EQUIPMENT FOR PIPE PRODUCTION

2.1 Description of the main equipment of shop T-3

2.1.1 Description and brief technical characteristics of the walking hearth furnace (PSHP)

The walking hearth furnace of the T-3 shop is designed for heating round billets with a diameter of 90...120 mm, a length of 3...10 m from carbon, low-alloy and stainless steels before piercing on the TPA-80.

The furnace is located in shop T-3 on the second floor in bays A and B.

The project of the furnace was carried out by Gipromez of the city of Sverdlovsk in 1984. Commissioning was carried out in 1986.

The furnace is a rigid metal structure, lined from the inside with refractory and heat-insulating materials. Inner dimensions kilns: length - 28.87 m, width - 10.556 m, height - 924 and 1330 mm, the performance characteristics of the furnace are presented in Table 2.1. Under the furnace is made in the form of fixed and movable beams, with the help of which the workpieces are transported through the furnace. The beams are lined with heat-insulating and refractory materials and framed with a special set of heat-resistant castings. Top part beams are made of mullite-corundum mass MK-90. The roof of the furnace is made suspended from shaped refractory materials and insulated with heat-insulating material. To maintain the furnace and conduct the technological process, the walls are equipped with working windows, a loading window and a metal unloading window. All windows are equipped with shutters. The heating of the furnace is carried out by natural gas, which is burned with the help of burners of the GR type (low pressure radiation burner) installed on the roof. The furnace is divided into 5 thermal zones with 12 burners each. Combustion air is supplied by two VM-18A-4 fans, one of which serves as a backup. Flue gases are removed through a smoke collector located on the roof at the beginning of the furnace. Further, flue gases are emitted into the atmosphere through a system of metal lined chimneys and flues with the help of two VGDN-19 smoke exhausters. A loop two-way tubular 6-section loop heat exchanger (CP-250) is installed on the chimney for heating the air supplied to combustion. For a more complete utilization of waste gas heat, the smoke exhaust system is equipped with a single-chamber mandrel heating furnace (PPO).

The issuance of the heated workpiece from the furnace is carried out using an internal water-cooled roller table, the rollers of which have a heat-resistant nozzle.

The oven is equipped with an industrial television system. Loud-speaking communication is provided between the control panels and the instrumentation panel.

The furnace is equipped with systems for automatic control of the thermal regime, automatic safety, units for monitoring operation parameters and signaling deviations from the norm. The following parameters are subject to automatic regulation:

Furnace temperature in each zone;

Gas-to-air ratio by zones;

Gas pressure in front of the furnace;

Pressure in the working space of the furnace.

In addition to automatic modes, a remote mode is provided. The automatic control system includes:

Furnace temperature by zones;

Temperature across the width of the furnace in each zone;

The temperature of the gases leaving the furnace;

Air temperature after the heat exchanger by zones;

Flue gas temperature in front of the heat exchanger;

The temperature of the smoke in front of the smoke exhauster;

Consumption of natural gas for the furnace;

Air consumption for the furnace;

Vacuum in the hog in front of the smoke exhauster;

Gas pressure in the common manifold;

Gas and air pressure in zone collectors;

Furnace pressure.

The furnace is provided with natural gas cut-off with light and sound alarm in case of gas and air pressure drop in the zone collectors.

Table 2.1 - Operating parameters of the furnace

Consumption of natural gas for the furnace (maximum) nm 3 / hour	5200
1 zone	1560
2 zone	1560
3 zone	1040
4 zone	520
5 zone	520
Natural gas pressure (maximum), kPa before
oven	10
burner	4
Air consumption for the furnace (maximum) nm 3 / hour	52000
Air pressure (maximum), kPa before
oven	13,5
burner	8
Pressure under the dome, Pa	20
Metal heating temperature, °С (maximum)	1200...1270
Chemical composition of combustion products in the 4th zone, %
CO 2	10,2
About 2	3,0
SO	0
Temperature of combustion products in front of the heat exchanger, °C	560
Air heating temperature in the heat exchanger, °C	Up to 400
The rate of issuance of blanks, sec	23,7...48
Furnace capacity, t/h	10,6... 80

The emergency sound alarm is also triggered when:

Temperature increase in the 4th and 5th zones (t cp = 1400°C);

Increasing the flue gas temperature in front of the heat exchanger (t with p = 850°С);

Increasing the flue gas temperature in front of the smoke exhauster (t cp =400°C);

Cooling water pressure drop (p cf = 0.5 atm).

2.1.2 Brief technical characteristics of the hot cutting line

The line for hot cutting of the workpiece is intended for the task of a heated rod into the shears, cutting the workpiece to the required length, and removing the cut workpiece from the shears.

A brief technical description of the hot cutting line is presented in Table 2.2.

The equipment of the hot cutting line includes the shears themselves (SKMZ designs) for cutting the workpiece, a movable stop, a transport roller table, a protective screen to protect the equipment from thermal radiation from the unloading window of the PSHP. Shears are designed for non-waste cutting of metal, however, if residual trimming is formed as a result of any emergency reasons, then a chute and a box in the pit, near the shears, are installed to collect it. In any case, the work of the line for hot cutting of the workpiece must be organized in such a way as to exclude the formation of offcuts.

Table 2.2 - Brief technical characteristics of the hot cutting line

Parameters of the bar to be cut
Length, m	4,0…10,0
Diameter, mm	90,0…120,0
Maximum weight, kg	880
Length of blanks, m	1,3...3.0
Rod temperature, ОС	1200
Productivity, piece/h	300
Transportation speed, m/s	1
Travel stop, mm	2000
Video clip
Barrel diameter, mm	250
Barrel length, mm	210
Rolling diameter, mm	195
Roller pitch, mm	500
Water consumption per water-cooled roller, m 3 / h	1,6
Water consumption per water-cooled roller with water-cooled axle boxes, m 3 / h	3,2
Water consumption on the screen, m 3 / h	1,6
Sound level, dB, no more	85

After heating the rod and issuing it, it passes through a thermostat (to reduce the temperature drop along the length of the workpiece), reaches the movable stop and is cut into workpieces of the required length. After the cut is made, the mobile stop is lifted with the help of a pneumatic cylinder, the workpiece is transported along the roller table. After it passes over the stop, it lowers to the working position and the cutting cycle is repeated. To remove scale from under the rollers of the roller table, hot cutting shears, a descaling system is provided, to remove trimmings - a chute and a receiving box. After leaving the roller table of the hot cutting line, the billet enters the receiving roller table of the piercing mill.

2.1.3 The device and technical characteristics of the main and auxiliary equipment of the piercing mill section

The piercing mill is designed for piercing a solid workpiece into a hollow sleeve. On the TPA-80, a 2-roll piercing mill with barrel-shaped or cup-shaped rolls and guide lines is installed. Technical specifications piercing mill is presented in Table 2.3.

There is a water-cooled roller table in front of the piercing mill, designed to receive the workpiece from the hot cutting line and transport it to the centerer. The roller table consists of 14 individually driven water-cooled rollers.

Table 2.3 - Technical characteristics of the piercing mill

Dimensions of the workpiece to be sewn:
Diameter, mm	100…120
Length, mm	1200…3350
Sleeve size:
Outer diameter, mm	98…126
Wall thickness, mm	14…22
Length, mm	1800…6400
Number of revolutions of the main drive, rpm	285…400
Gear ratio of the gear cage	3
Engine power, kW	3200
Feed angle, °	0…14
Rolling force:
Maximum radial, kN	784
Maximum axial, kN	245
Maximum torque on the roll, kNm	102,9
Work roll diameter, mm	800…900
Pressure screw:
Maximum stroke, mm	120
Travel speed, mm/s	2

The centering tool is designed for knocking out a center recess with a diameter of 20…30 mm and a depth of 15…20 mm at the end face of a heated workpiece and is a pneumatic cylinder in which a striker with a tip slides.

After centering, the heated billet enters the grate for its subsequent transfer to the chute of the front table of the piercing mill.

The front table of the piercing mill is designed to receive a heated billet rolling down the grate, align the axis of the billet with the axis of the piercing and hold it during the piercing.

On the output side of the mill, roller centralizers of the mandrel rod are installed, which support and center the rod, both before piercing and during piercing, when high axial forces act on it and its longitudinal bending is possible.

Behind the centralizers there is a stationary thrust-adjusting mechanism with an opening head, it serves to perceive the axial forces acting on the rod with the mandrel, adjust the position of the mandrel in the deformation zone and pass the sleeve outside the piercing mill.

2.1.4 Arrangement and technical characteristics of the main and auxiliary equipment of the continuous mill section

The continuous mill is designed for rolling rough pipes with a diameter of 92 mm and a wall thickness of 3…8 mm. Rolling is carried out on a long floating mandrel 19.5 m long. Brief technical characteristics of the continuous mill are given in Table 2.4., Table 2.5. gear ratios are given.

During rolling, the continuous mill works as follows: the sleeve is transported by a roller table behind the piercing mill to a mobile stop and, after stopping, is transferred to the grate in front of the continuous mill with the help of a chain conveyor and rolled back onto the dispenser levers.

Table 2.4 - Brief technical characteristics of the continuous mill

Name		Value
Outer diameter of the draft pipe, mm		91,0…94,0
Rough pipe wall thickness, mm		3,5…8,0
Maximum length of the draft pipe, m		30,0
Continuous mill mandrels diameter, mm		74…83
Mandrel length, m		19,5
Wolves diameter, mm		400
Roll barrel length, mm		230
Roll neck diameter, mm		220
Distance between axes of stands, mm		850
The course of the upper pressure screw with new rolls, mm	Up	8
	Down	15
The course of the lower pressure screw with new rolls, mm	Up	20
	Down	10
Top roll lifting speed, mm/s		0,24
Frequency of rotation of main drive engines, rpm		220…550

If there are defects on the sleeve, the operator, by manually turning on the blocker and pushers, directs it into the pocket.

With the dispenser levers lowered, the good sleeve rolls into the chute, is pressed by the clamping levers, after which a mandrel is inserted into the sleeve using the setting rollers. When the front end of the mandrel reaches the front edge of the sleeve, the clamp is released, and the sleeve is set into a continuous mill with the help of push rollers. At the same time, the speed of rotation of the pulling rollers of the mandrel and the sleeve is set in such a way that by the time the sleeve is captured by the first stand of the continuous mill, the front end of the mandrel is extended by 2.5 ... 3 m.

After rolling on a continuous mill, a rough pipe with a mandrel enters the mandrel extractor, a brief technical characteristic is presented in Table 2.6. After that, the pipe is transported by a roller table to the area of ​​cutting the rear end and approaches the stationary stop at the section of cutting the rear end of the pipe, the technical characteristics of the equipment of the POZK section are given in Table 2.7. Having reached the stop, the pipe is thrown by a screw ejector onto the grate in front of the leveling roller table. Next, the pipe rolls down the grate onto the leveling roller table, approaches the stop that determines the length of the cut, and is transferred piece by piece from the leveling roller table to the grate in front of the outlet roller table, while during the movement, the rear end of the pipe is cut off.

The cut end of the pipe is transferred by a scrap conveyor to a scrap bin located outside the workshop.

Table 2.5 - Gear ratio of continuous mill gearboxes and motor power

Table 2.6 - Brief technical characteristics of the mandrel extractor

Table 2.7 - Brief technical characteristics of the cutting section of the rear end of the pipe

2.1.5 The principle of operation of the main and auxiliary equipment of the section of the reduction mill and the cooler

The equipment of this section is designed to transport the draft pipe through the installation induction heating, rolling on a reduction mill, cooling and further transportation to the section of cold saws.

Heating of draft pipes in front of the reduction mill is carried out in the INZ-9000/2.4 heating unit, which consists of 6 heating blocks (12 inductors) located directly in front of the reduction mill. The pipes enter the induction plant one after the other in a continuous flow. In the absence of the receipt of pipes from the continuous mill (when the rolling is stopped), it is allowed to supply the deposited "cold" pipes to the induction installation individually. The length of the pipes specified in the installation should not exceed 17.5 m.

Type of reduction mill - 24-stand, 3-roll with two bearing position of rolls and individual drive of stands.

After rolling on the reducing mill, the pipe enters either the sprayer and the cooling table, or directly to the cooling table of the mill, depending on the requirements for the mechanical properties of the finished pipe.

The design and technical characteristics of the sprayer, as well as the parameters of the cooling of the pipes in it, are a trade secret of OAO KresTrubZavod and are not given in this work.

In table 2.8. the technical characteristics of the heating installation are presented, in Table 2.9. - a brief technical characteristic of the reduction mill.

Table 2.8 - Brief technical characteristics of the heating installation INZ-9000 / 2.4

2.1.6 Equipment for cutting pipes to length

For cutting pipes to lengths in the T-3 workshop, a Wagner batch cutting saw of the WVC 1600R model is used, the technical characteristics of which are given in Table. 2.10. KV6R model saws are also used - technical characteristics in table 2.11.

Table 2.9 - Brief technical characteristics of the reduction mill

Table 2.10 - Technical characteristics of the saw WVC 1600R

Parameter name		Value
Diameter of cut pipes, mm		30…89
Width of cut packages, mm		200…913
Wall thickness of cut pipes, mm		2,5…9,0
Pipe length after cutting, m		8,0…11,0
Length of pipe ends to be cut	Front, mm	250…2500
	Rear, mm
Saw blade diameter, mm		1600
Number of teeth on the saw blade, pcs	Segment	456
	Carbide	220
Cutting speed, mm/min		10…150
Minimum saw blade diameter, mm		1560
Circular saw support feed, mm		5…1000
Maximum tensile strength of pipes, N / mm 2		800

2.1.7 Pipe straightening equipment

Pipes cut to length according to the order are sent for straightening. Straightening is carried out on straightening machines РВВ320х8, designed for straightening pipes and rods made of carbon and low-alloy steel grades in a cold state with an initial curvature of up to 10 mm per 1 linear meter. Technical specifications straightening machine RVV 320x8 is given in table. 3.12.

Table 2.11 - Technical characteristics of the saw model KV6R

Parameter name	Value
Width of a single-row package, mm	No more than 855
Workpiece clamp opening width, mm	20 to 90
Pass in the vertical direction of the workpiece clamp, mm	No more than 275
Saw blade support stroke, mm	650
Saw blade feed speed (stepless) mm/min	no more than 800
Fast reverse motion of the saw blade, mm/min	No more than 6500
Cutting speed, m/min	40; 15; 20; 30; 11,5; 23
Clamped length of the pipe package on the inlet side, mm	At least 250
Clamping length of the pipe package on the discharge side, mm	At least 200
Saw blade diameter, mm	1320
Number of segments on the saw blade, pcs	36
Number of teeth per segment, pcs	10
Processed pipes diameter, mm	20 to 90

Table 2.12 - Technical characteristics of the straightening machine RVV 320x8

Parameter name		Value
Diameter of straightened pipes, mm		25...120
Wall thickness of straightened pipes, mm		1,0...8,0
Straightened pipes length, m		3,0...10,0
The yield strength of the metal of straightened pipes, kgf / mm 2	Diameter 25…90 mm	Up to 50
	Diameter 90…120 mm	up to 33
Pipe straightening speed, m/s		0,6...1,0
Pitch between roll axes, mm		320
Diameter of rolls in the neck, mm		260
Number of rolls, pcs	Driven	4
	single	5
Roll angles, °		45°...52°21'
The greatest stroke of the upper rolls from the upper edge of the lower ones, mm		160
Roll rotation drive	engine's type	D-812
	Voltage, V	440
	power, kWt	70
	Rotation speed, rpm	520

2.2 The existing technology for the production of pipes on the TPA-80 JSC "KresTrubZavod"

The workpiece in the form of rods entering the workshop is stored in the internal warehouse. Before being put into production, it is subjected to selective inspection on a special rack, and if necessary, repair. Scales were installed at the billet preparation site to control the weight of the metal put into production. The blanks from the warehouse are fed by an electric overhead crane to the loading grate in front of the furnace and loaded into the heating furnace with a walking hearth in accordance with the schedule and rate of rolling.

Compliance with the scheme of laying blanks is carried out visually by the metal planter. The workpiece is loaded into the furnace one by one into each, through one or more steps of the guide plates of the movable beams, depending on the rate of rolling and the multiplicity of the cut. When changing the steel grade, heat and pipe size, the fitter separates the steel grades, heats as follows: with a billet length of 5600-8000 mm, the heats are separated by shifting the first two rods along the width of the furnace; steel grades are separated by shifting the first four rods along the width of the furnace; with a billet length of 9000-9800mm, the separation of steel grades, heats from each other is carried out during planting with an interval of 8-10 steps, as well as counting the number of planted in the PSHP and issued billets, which are controlled by the PSHP metal heater and the hot cutting shear cutter by checking with control panels . TPA-80; when changing the size (transshipment of the mill) of the rolled pipes, the planting of metal in the furnace stops “5-6 steps” before the mill stops, when stopping for transshipment, the metal “steps back 5-6 steps” back. The movement of workpieces through the furnace is carried out by three movable beams. During the pauses of the movement cycle, the movable beams are set at the level of the hearth. The necessary heating time is provided by measuring the step cycle time. Excessive pressure in the working space should be from 9.8 Pa to 29.4 Pa, air flow coefficient =1.1 - 1.2.

When billets of various steel grades are heated in a furnace, the duration of heating is determined by the metal that has the longest residence time in the furnace. High-quality heating of the metal is ensured by the uniform passage of workpieces along the entire length of the furnace. Heated workpieces are delivered to the internal unloading roller table, and they are delivered to the hot cutting line.

To reduce the cooling of workpieces during downtime, a thermostat is provided on the roller table for transporting heated workpieces to the shears, as well as the possibility of returning (turning on the reverse) an uncut workpiece to the furnace and finding it during downtime.

During operation, a hot stop of the furnace is possible. A hot shutdown of a furnace is considered to be a shutdown without shutting off the natural gas supply. During hot shutdowns, the movable beams of the furnace are set at the level of the fixed ones. The download and upload windows are closed. The air flow rate is reduced from 1.1-1.2 to 1.0:-1.1 using the "fuel-air" adjuster. The pressure in the furnace at the level of the hearth becomes positive. When the mill stops: up to 15 minutes - the temperature by zones is set at the lower limit, and the metal is “stepped back” by two steps; from 15 minutes to 30 minutes - the temperature in zones III, IV, V is reduced by 20-40 0 С, in zones I, II by 30-60 0 С from lower limit; over 30 minutes - the temperature in all zones is reduced by 50-150 0 C compared to the lower limit, depending on the duration of downtime. The blanks "step back" 10 steps back. With a downtime of 2 to 5 hours, it is necessary to free the IV and V zones of the furnace from blanks. Blanks from zones I and II are unloaded into the pocket. The unloading of metal is carried out by a metal planter with PU-1. The temperature in the V and IV zones is reduced to 1000-I050 0 C. When stopping for more than 5 hours, the entire furnace is freed from metal. The temperature rise is carried out stepwise by 20-30 0 C, at a temperature rise rate of 1.5-2.5 0 C/min. With an increase in the heating time of the metal due to the low rate of rolling, the temperature in zones I, II, III is reduced by 60 0 C, 40 0 ​​C, 20 0 C, respectively, from the lower limit, and the temperature in zones IV, V at the lower limits. In general, with stable operation of the entire unit, the temperature is distributed among the zones as follows (Table 2.13).

After heating, the workpiece enters the hot cutting line of the workpiece. The equipment of the hot cutting line includes the shears themselves for cutting the workpiece, a movable stop, a transport roller table, a protective screen to protect the equipment from thermal radiation from the unloading window of the walking hearth furnace. After heating the rod and issuing it, it passes through the thermostat, reaches the movable stop and is cut into blanks of the required length. After the cut is made, the mobile stop is lifted with the help of a pneumatic cylinder, the workpiece is transported along the roller table. After it passes over the stop, it lowers to the working position and the cutting cycle continues.

Table 2.13 - Temperature distribution in the furnace by zones

The measured workpiece is transferred by roller table behind the shears to the centerer. The centered workpiece is transferred by the ejector to the grate in front of the piercing mill, along which it rolls to the delay and, when the output side is ready, is transferred to the chute, which is closed with a lid. With the help of the pusher, with the stop raised, the workpiece is set into the deformation zone. In the deformation zone, the workpiece is pierced on a mandrel held by the rod. The rod rests against the glass of the thrust head of the thrust-adjusting mechanism, the opening of which does not allow the lock. Longitudinal bending of the rod from axial forces arising during rolling is prevented by closed centralizers, the axes of which are parallel to the axis of the rod.

In the working position, the rollers are brought around the rod by a pneumatic cylinder through a system of levers. As the front end of the sleeve approaches, the centralizer rollers are sequentially separated. After the end of the workpiece piercing, the first rollers are reduced by the pneumatic cylinder, which move the sleeve from the rolls so that the rod interceptor can be captured by the rod interceptor levers, then the lock and the front head are folded, the dispensing rollers are brought together and the sleeve at an increased speed is issued at an increased speed by the thrust head onto the roller table behind the piercing mill .

After flashing, the sleeve is transported along the roller table to the mobile stop. Further, the sleeve is moved by a chain conveyor to the input side of the continuous mill. After the conveyor, the sleeve rolls along the inclined grate to the dispenser, which holds the sleeve in front of the inlet side of the continuous mill. Under the guides of the inclined grille there is a pocket for collecting defective cartridges. From the inclined grating, the sleeve is dropped into the receiving chute of the continuous mill with clamps. At this time, a long mandrel is inserted into the sleeve using one pair of friction rollers. When the front end of the mandrel reaches the front end of the sleeve, the sleeve clamp is released, two pairs of pulling rollers are brought onto the sleeve, and the sleeve with the mandrel is set into a continuous mill. At the same time, the speed of rotation of the pulling rollers of the mandrel and the pulling rollers of the sleeve is calculated in such a way that at the moment the sleeve is captured by the first stand of the continuous mill, the extension of the mandrel from the sleeve is 2.5-3.0 m. In this regard, the linear speed of the pulling rollers of the mandrels should be 2.25-2.5 times higher linear speed sleeve pull rollers.

Rolled pipes with mandrels are alternately transferred to the axis of one of the mandrels. The head of the mandrel passes through the steady rest of the extractor and is captured by the gripper insert, and the pipe into the steady rest ring. When the chain moves, the mandrel leaves the pipe and enters the chain conveyor, which transfers it to a double roller table, which transports the mandrel from both extractors to the cooling bath.

After removing the mandrel, the draft pipe enters the saws for trimming the rear disheveled end.

After induction heating, the tubes are fed into a reduction mill with twenty-four three-roll stands. In the reduction mill, the number of working stands is determined depending on the dimensions of the rolled pipes (from 9 to 24 stands), and stands are excluded, starting from 22 in the direction of decreasing numbers of stands. Stands 23 and 24 participate in all rolling programs.

During rolling, the rolls are continuously cooled with water. When moving pipes along the cooling table, each link should contain no more than one pipe. When rolling pig hot-worked pipes intended for the manufacture of tubing pipes of strength group "K" from steel grade 37G2S, after the reduction mill, accelerated controlled cooling of the pipes in sprayers is carried out.

The speed of pipes passing through the sprayer must be stabilized with the speed of the reduction mill. Control over the stabilization of speeds is carried out by the operator in accordance with the operating instructions.

After reduction, the pipes enter the rack-mounted cooling table with walking beams, where they are cooled.

At the cooling table, the pipes are collected in single-layer bags for trimming the ends and cutting to length on cold saws.

Finished pipes are delivered to the QCD inspection table, after inspection, the pipes are bundled into packages and sent to the finished product warehouse.

2.3 Justification of design decisions

In the case of piecewise reduction of pipes with tension on the PPC, a significant longitudinal difference in wall thickness of the ends of the pipes occurs. The reason for the end difference in wall thickness of the pipes is the instability of axial tensions in non-stationary deformation modes when filling and releasing the working stands of the mill with metal. The end sections are reduced under conditions of significantly lower longitudinal tensile stresses than the main (middle) part of the pipe. The increase in wall thickness at the end sections, exceeding the allowable deviations, makes it necessary to trim a significant part of the finished pipe

The norms for the end trimming of reduced pipes for TPA-80 JSC "KresTrubZavod" are given in Table. 2.14.

Table 2.14 - Norms for cutting pipe ends on TPA-80 JSC "KresTrubZavod"

2.4 Justification of design decisions

In the case of piecewise reduction of pipes with tension on the PPC, a significant longitudinal difference in wall thickness of the ends of the pipes occurs. The reason for the end difference in wall thickness of the pipes is the instability of axial tensions in non-stationary deformation modes when filling and releasing the working stands of the mill with metal. The end sections are reduced under conditions of significantly lower longitudinal tensile stresses than the main (middle) part of the pipe. The increase in wall thickness at the end sections, which exceeds the allowable deviations, makes it necessary to trim a significant part of the finished pipe.

The norms for the end trimming of reduced pipes for TPA-80 JSC "KresTrubZavod" are given in Table. 2.15.

Table 2.15 - Norms for cutting pipe ends on TPA-80 JSC "KresTrubZavod"

where PC is the front thickened end of the pipe; ZK - rear thickened end of the pipe.

Approximately annual loss of metal in the thickened ends of the pipes in the shop T-3 JSC "KresTrubZavod" is 3000 tons. With a reduction in the length and weight of cut thickened pipe ends by 25%, the annual profit increase will be about 20 million rubles. In addition, there will be savings in the cost of stack saw blades, electricity, etc.

In addition, in the production of a conversion billet for drawing shops, it is possible to reduce the longitudinal difference in wall thickness of pipes, and the saved metal by reducing the longitudinal difference in wall thickness can be used to further increase the volume of production of hot-rolled and cold-formed pipes.

3. DEVELOPMENT OF ALGORITHMS FOR CONTROL OF THE REDUCING MILL TPA-80

3.1 Status of the issue

Continuous tube-rolling units are the most promising high-performance plants for the production of hot-rolled seamless pipes of the corresponding range.

The composition of the units includes piercing, continuous mandrel and reducing stretching mills. The continuity of the technological process, the automation of all transport operations, the large length of rolled pipes provide high productivity, good quality pipes by surface and geometric dimensions

In recent decades, the intensive development of the production of pipes by continuous rolling has continued: built and put into operation (in "" Italy, France, USA, Argentina), reconstructed (in Japan) continuous rolling shops, supplied equipment for new shops (in China), developed and projects for the construction of workshops have been implemented (in France, Canada, USA, Japan, Mexico).

Compared to the units commissioned in the 1960s, the new mills have significant differences: they mainly produce oil country tubular goods, which is why large sections are built in the shops for finishing these pipes, including equipment for upsetting them. ends, heat treatment, pipe cutting, coupling production, etc.; the range of pipe sizes has significantly expanded: the maximum diameter has increased from 168 to 340 mm, the wall thickness - from 16 to 30 mm, which became possible due to the development of the rolling process on a long mandrel moving at an adjustable speed instead of a floating one on continuous mills. The new pipe-rolling units use continuously cast billets (square and round), which ensured a significant improvement in the technical and economic performance of their work.

Annular furnaces (TPA 48-340, Italy) are still widely used to heat billets, along with this, walking hearth furnaces (TPA 27-127, France, TPA 33-194, Japan) are being used. In all cases, the high productivity of a modern unit is ensured by installing one furnace of large unit capacity (capacity up to 250 t/h). Walking beam furnaces are used to heat pipes before reduction (calibration).

The main mill for the production of sleeves continues to be a two-roll screw rolling mill, the design of which is being improved, for example, by replacing the fixed rulers with driven guide disks. In the case of square blanks, the helical rolling mill in the technical line is preceded by either a press roll mill (TPA 48-340 in Italy, TPA 33-194 in Japan) or an edge calibration mill and a deep centering press (TPA 60-245, France).

One of the main directions further development method of continuous rolling is the use of mandrels that move at a controlled speed during the rolling process, instead of floating ones. Using a special mechanism that develops a holding force of 1600-3500 kN, the mandrel is set to a certain speed (0.3-2.0 m/s), which is maintained either until the pipe is completely removed from the mandrel during rolling (retained mandrel), or up to a certain the moment from which the reference moves as a floating (partially held mandrel). Each of these methods can be used in the production of pipes of a certain diameter. So, for pipes of small diameter, the main method is rolling on a floating mandrel, medium (up to 200 mm) - on a partially held, large (up to 340 mm and more) - on a held one.

The use on continuous mills of mandrels moving at an adjustable speed (held, partially held) instead of floating ones provides a significant expansion of the assortment, an increase in the length of pipes and an increase in their accuracy. Individual constructive solutions are of interest; for example, the use of a piercing mill rod as a partially retained mandrel of a continuous mill (TPA 27-127, France), out-of-station insertion of a mandrel into a sleeve (TPA 33-194, Japan) .

New units are equipped with modern reducing and sizing mills, and one of these mills is most often used. Cooling tables are designed to receive pipes after reduction without prior cutting.

Assessing the current general state of automation of pipe mills, the following features can be noted.

Transport operations associated with the movement of rolled products and tools through the unit are fully automated using traditional local (mainly non-contact) automation devices. On the basis of such devices, it became possible to introduce high-performance units with a continuous and discrete-continuous technological process.

Actually, technological processes and even individual operations on pipe mills are clearly insufficiently automated so far, and in this part their level of automation is noticeably inferior to that achieved, for example, in the field of continuous sheet mills. If the use of control computers (CCM) for sheet mills has become practically a widely recognized norm, then for pipe mills examples are still rare in Russia, although at present the development and implementation of process control systems and automated control systems has become the norm abroad. So far, on a number of pipe mills in our country, there are mainly examples of industrial implementation of individual subsystems of automated process control using specialized devices made using semiconductor logic and computer technology elements.

This state of affairs is mainly due to two factors. On the one hand, until recently, the requirements for quality, and above all, for dimensional stability of pipes, were satisfied relatively simple means(in particular, rational designs of mill equipment). These conditions did not stimulate more perfect and, of course, more complex developments, for example, using relatively expensive and not always sufficiently reliable CCMs. On the other hand, the use of special non-standard technical means of automation turned out to be possible only for simpler and less efficient tasks, while significant time and money were required for development and manufacture, which did not contribute to progress in the area under consideration.

However, the increasing modern requirements for pipe production, including the quality of pipes, cannot be satisfied by traditional solutions. Moreover, as practice shows, a significant proportion of efforts to meet these requirements falls on automation, and, at present, it is necessary to automatically change these modes during pipe rolling.

Modern advances in the field of control of electric drives and various technical means of automation, primarily in the field of minicomputers and microprocessor technology, make it possible to radically improve the automation of pipe mills and units, to overcome various production and economic limitations.

The use of modern technical means of automation implies a simultaneous increase in the requirements for the correctness of setting tasks and choosing ways to solve them, and in particular, for choosing the most effective ways to influence technological processes. The solution of this problem can be facilitated by an analysis of the existing most effective technical solutions for automating pipe mills.

Studies of continuous pipe-rolling units as automation objects show that there are significant reserves for further improvement of their technical and economic indicators by automating the technological process of pipe rolling on these units.

When rolling in a continuous mill on a long floating mandrel, an end longitudinal difference in wall thickness is also induced. The wall thickness of the rear ends of the draft pipes is greater than the middle by 0.2-0.3 mm. The length of the posterior end with a thickened wall is equal to 2-3 interstand spaces. The thickening of the wall is accompanied by an increase in diameter in the area separated by one interstand gap from the rear end of the pipe. Due to transient conditions, the wall thickness of the front ends is 0.05-0.1 mm less than the middle. When rolling with tension, the walls of the front ends of the pipes also thicken. The longitudinal variation in the thickness of the rough pipes is preserved during subsequent reduction and leads to an increase in the length of the rear cut off thickened ends of the finished pipes.

When rolling in reduction stretching mills, the wall of the ends of the pipes thickens due to a decrease in tension in comparison with the steady state, which occurs only when 3-4 stands of the mill are filled. The ends of pipes with a wall thickened beyond the tolerance are cut off, and the metal waste associated with this determines the main share of the total consumption coefficient on the unit.

The general nature of the longitudinal variation of the pipes after the continuous mill is almost completely transferred to the finished pipes. This is confirmed by the results of rolling pipes with dimensions of 109 x 4.07 - 60 mm at five tension modes on the reducing mill of the YuTZ installation 30-102. During the experiment, 10 pipes were selected at each speed mode, the end sections of which were cut into 10 parts 250 mm long, and three branch pipes were cut from the middle, located at a distance of 10, 20 and 30 m from the front end. After measuring the wall thickness on the device, deciphering the thickness difference diagrams and averaging the data, graphical dependences were plotted, shown in Fig. 54 .

Thus, the noted components of the total wall thickness of pipes have a significant impact on the technical and economic performance of continuous units, are associated with the physical features of the rolling processes in continuous and reduction mills, and can be eliminated or significantly reduced only through special automatic systems that change the setting of the mill during pipe rolling. The natural nature of these components of the difference in wall thickness makes it possible to use the program control principle in the basis of such systems.

There are other technical solutions to the problem of reducing end waste during reduction using automatic control systems for the process of rolling pipes in a reduction mill with an individual drive of the stands (Germany patents No. 1602181 and Great Britain 1274698). Due to the change in the speed of the rolls during the rolling of the front and rear ends of the pipes, additional tension forces are created, which leads to a decrease in the end longitudinal difference in wall thickness. There is evidence that such software speed correction systems for the main drives of the reduction mill operate on seven foreign pipe-rolling units, including two units with continuous mills in Mülheim (Germany). The units were supplied by Mannesmann (Germany).

The second unit was launched in 1972 and includes a 28-stand reduction mill with individual drives, equipped with a speed correction system. Speed ​​changes during the passage of pipe ends are carried out in the first ten stands in steps, as additions to the operating speed value. The maximum speed change takes place on stand No. 1, the minimum - on stand No. 10. Photo relays are used as sensors for the position of the pipe ends in the mill, which give commands to change speed. In accordance with the adopted speed correction scheme, the individual drives of the first ten stands are supplied according to an anti-parallel reversing scheme, the subsequent stands - according to a non-reversing scheme. It is noted that the correction of the speeds of the drives of the reduction mill allows to increase the yield on the unit by 2.5% with a mixed production program. With an increase in the degree of reduction in diameter, this effect increases.

There is similar information about equipping a twenty-eight-stand reduction mill in Spain with a speed correction system. Speed ​​changes are carried out in the first 12 stands. In this regard, various drive power schemes are also provided.

It should be noted that equipping reduction mills as part of continuous pipe-rolling units with a speed correction system does not completely solve the problem of reducing end waste during reduction. The efficiency of such systems should decrease with decreasing degree of reduction in diameter.

Programmatic process control systems are the easiest to implement and give a great economic effect. However, with their help, it is possible to improve the accuracy of pipe dimensions only by reducing one of its three components - the longitudinal difference in wall thickness. Studies show that the main specific weight in the total variation in the wall thicknesses of finished pipes (about 50%) falls on the transverse wall thickness. Fluctuations in average pipe wall thicknesses in batches are about 20% of the total variation.

At present, the reduction of the transverse wall variation is possible only by improving the technological process of pipe rolling on the mills that are part of the unit. Examples of the use of automatic systems for these purposes are unknown.

Stabilization of the average pipe wall thickness in batches is possible both by improving the rolling technology, the design of the stands and the electric drive, and by using automatic process control systems. Reducing the spread of pipe wall thicknesses in a batch can significantly increase the productivity of units and reduce metal consumption due to rolling in a field of minus tolerances.

Unlike software systems, systems designed to stabilize average pipe wall thicknesses must include sensors for controlling the geometric dimensions of pipes.

Technical proposals for equipping reduction mills with systems for automatic stabilization of pipe wall thickness are known. The structure of the systems does not depend on the type of unit, which includes a reduction mill.

A complex of control systems for the process of pipe rolling in continuous and reduction mills, designed to reduce end waste during reduction and increase the accuracy of pipes by reducing the longitudinal difference in wall thickness and the spread of average wall thicknesses, forms the process control system of the unit.

The use of computers to control production and automate the technological process of pipe rolling was first implemented on a continuous pipe rolling plant 26-114 in Mulheim.

The unit is designed for rolling pipes with a diameter of 26-114 mm, wall thickness of 2.6-12.5 mm. The unit includes a ring furnace, two piercing mills, a 9-stand continuous mill and a 24-stand reduction mill individually driven by 200 kW motors.

The second unit with a continuous mill in Mulheim, launched in 1972, is equipped with a more powerful computer, which is assigned to more extensive functions. The unit is designed for rolling pipes with a diameter of up to 139 mm, a wall thickness of up to 20 mm and consists of a piercing mill, an eight-stand continuous mill and a twenty-eight-stand reduction mill with an individual drive.

The continuous pipe rolling plant in the UK, launched in 1969, is also equipped with a computer, which is used to plan the loading of the plant and, as an information system, continuously monitors the parameters of rolled products and tools. The quality control of pipes and blanks, as well as the accuracy of mill settings, is carried out at all stages of the technological process. Information from each mill is sent to a computer for processing, after which it is issued to the mills for operational management.

In a word, many countries are trying to solve the problems of automating rolling processes, incl. and ours. To develop a mathematical model for controlling continuous mills, it is necessary to know the effect of the specified technological parameters on the accuracy of finished pipes; for this, it is necessary to consider the features of continuous rolling.

A feature of reducing pipes with tension is a higher product quality as a result of the formation of a smaller transverse wall difference, in contrast to rolling without tension, as well as the possibility of obtaining pipes of small diameters. However, with piece-by-piece rolling, an increased longitudinal variation in wall thickness is observed at the ends of the pipes. Thickened ends during reduction with tension are formed due to the fact that the front and rear ends of the pipe when passing through the mill are not subjected to the full effect of tension.

Tension is characterized by the tensile stress in the pipe (x). The most complete characteristic is the coefficient of plastic tension, which is the ratio of the longitudinal tensile stress of the pipe to the deformation resistance of the metal in the stand.

Typically, the reduction mill is set up in such a way that the coefficient of plastic tension in the middle stands is evenly distributed. Tension rises and falls in the first and last stands.

To intensify the reduction process and obtain thin-walled pipes, it is important to know the maximum tension that can be created in the reduction mill. The maximum value of the coefficient of plastic tension in the mill (z max) is limited by two factors: the pulling capacity of the rolls and the conditions of pipe rupture in the mill. As a result of the research, it was found that with a total reduction of the pipe in the mill up to 50-55%, the value of z max is limited by the pulling capacity of the rolls.

Workshop T-3, together with EF VNIPI "Tyazhpromelektroproekt" and the enterprise "ASK", created the basis of the ACS-TP system on the TPA-80 unit. Currently, the following components of this system are functioning: UZN-N, UZN-R, ETHERNET communication line, all AWPs.

3.2 Calculation of the rolling table

The basic principle of constructing the technological process in modern installations is to obtain pipes of the same constant diameter on a continuous mill, which allows the use of a billet and a sleeve of also a constant diameter. Obtaining pipes of the required diameter is ensured by reduction. Such a system of work greatly facilitates and simplifies the setting of the mills, reduces the stock of tools and, most importantly, allows you to maintain high productivity of the entire unit even when rolling pipes of a minimum (after reduction) diameter.

We calculate the rolling table against the rolling progress according to the method described in. The outer diameter of the pipe after reduction is determined by the dimensions of the last pair of rolls.

D p 3 \u003d (1.010..1.015) * D o \u003d 1.01 * 33.7 \u003d 34 mm

where D p is the diameter of the finished pipe after the reduction mill.

The wall thickness after continuous and reduction mills must be equal to the wall thickness of the finished pipe, i.e. S n \u003d Sp \u003d S o \u003d 3.2 mm.

Since a pipe of the same diameter comes out after a continuous mill, we take D n \u003d 94 mm. In continuous mills, the calibration of the rolls ensures that in the last pairs of rolls the inner diameter of the pipe is 1-2 mm larger than the diameter of the mandrel, so that the diameter of the mandrel will be equal to:

H \u003d d n - (1..2) \u003d D n -2S n -2 \u003d 94-2 * 3.2-2 \u003d 85.6 mm.

We take the diameter of the mandrels equal to 85 mm.

The inner diameter of the sleeve must ensure the free insertion of the mandrel and is taken 5-10 mm larger than the diameter of the mandrel

d g \u003d n + (5..10) \u003d 85 + 10 \u003d 95 mm.

We accept the wall of the sleeve:

S g \u003d S n + (11..14) \u003d 3.2 + 11.8 \u003d 15 mm.

The outer diameter of the sleeves is determined based on the value of the inner diameter and wall thickness:

D g \u003d d g + 2S g \u003d 95 + 2 * 15 \u003d 125 mm.

The diameter of the used workpiece D h =120 mm.

The diameter of the mandrel of the piercing mill is selected taking into account the amount of rolling, i.e. rise in the inner diameter of the sleeve, which is from 3% to 7% of the inner diameter:

P \u003d (0.92 ... 0.97) d g \u003d 0.93 * 95 \u003d 88 mm.

The drawing coefficients for piercing, continuous and reduction mills are determined by the formulas:

,

The overall draw ratio is:

The rolling table for pipes 48.3×4.0 mm and 60.3×5.0 mm in size was calculated in a similar way.

The rolling table is presented in Table. 3.1.

Table 3.1 - TPA-80 rolling table

Size of finished pipes, mm		Workpiece diameter, mm	Piercing mill				Continuous mill				reduction mill				Overall elongation ratio
Outside diameter	Wall thickness		Sleeve size, mm		Mandrel diameter, mm	Draw ratio	Pipe dimensions, mm		Mandrel diameter, mm	Draw ratio	Pipe size, mm		Number of stands	Draw ratio
			Diameter	Wall thickness			Diameter	Wall thickness			Diameter	Wall thickness
33,7	3,2	120	125	15	88	2,20	94	3,2	85	5,68	34	3,2	24	2,9	36,24
48,3	4,0	120	125	15	86	2,2	94	4,0	84	4,54	48,6	4,5	16	1,94	19,38
60,3	5,0	120	125	18	83	1,89	94	5,0	82	4,46	61,2	5,0	12	1,52	12,81

3.3 Calculation of the calibration of the reduction mill rolls

Roll calibration is important integral part calculation of the operating mode of the mill. It largely determines the quality of the pipes, tool life, load distribution in the working stands and the drive.

Roll calibration calculation includes:

a) the distribution of partial deformations in the stands of the mill and the calculation of the average diameters of the calibers;

b) determination of the dimensions of the calibers of the rolls.

3.3.1 Partial strain distribution

According to the nature of the change in partial deformations, the stands of the reduction mill can be divided into three groups: the head one at the beginning of the mill, in which the reductions increase intensively during rolling; calibrating (at the end of the mill), in which the deformations are reduced to a minimum value, and a group of stands between them (middle), in which partial deformations are maximum or close to them.

When rolling pipes with tension, the values ​​of partial deformations are taken on the basis of the stability condition of the pipe profile at a plastic tension value that ensures the production of a pipe of a given size.

The coefficient of total plastic tension can be determined by the formula:

,

where are axial and tangential strains taken in logarithmic form; T is the value determined in the case of a three-roll caliber by the formula

T= ,

where (S/D) cp is the average ratio of wall thickness to diameter over the period of pipe deformation in the mill; k-factor taking into account the change in the degree of thickness of the pipe.

,

,

where m is the value of the total deformation of the pipe along the diameter.

.

,

.

The value of the critical partial reduction at such a coefficient of plastic tension, according to , can reach 6% in the second stand, 7.5% in the third stand and 10% in the fourth stand. In the first cage, it is recommended to take in the range of 2.5-3%. However, to ensure a stable grip, the amount of compression is generally reduced.

In the pre-finishing and finishing stands of the mill, the reduction is also reduced, but to reduce the load on the rolls and improve the accuracy of the finished pipes. In the last stand of the sizing group, the reduction is taken equal to zero, the penultimate one - up to 0.2 from the reduction in the last stand of the middle group.

In the middle group of stands, a uniform and uneven distribution of partial deformations is practiced. With a uniform distribution of compression in all stands of this group, they are assumed to be constant. The uneven distribution of particular deformations can have several variants and be characterized by the following patterns:

compression in the middle group is proportionally reduced from the first stands to the last - falling mode;

in the first few stands of the middle group, partial deformations are reduced, while the rest are left constant;

compression in the middle group is first increased and then reduced;

in the first few stands of the middle group, partial deformations are left constant, and in the rest they are reduced.

With decreasing deformation modes in the middle group of stands, the differences in the magnitude of the rolling power and the load on the drive decrease, caused by an increase in the resistance to deformation of the metal during rolling, due to a decrease in its temperature and an increase in the strain rate. It is believed that reducing the reduction towards the end of the mill also improves the quality of the outer surface of the pipes and reduces the transverse wall variation.

When calculating the calibration of the rolls, we assume a uniform distribution of reductions.

The values ​​of partial deformations in the stands of the mill are shown in fig. 3.1.

Crimp Distribution

Based on the accepted values ​​of partial deformations, the average diameters of the calibers can be calculated by the formula

.

For the first stand of the mill (i=1) d i -1 =D 0 =94 mm, then

mm.

Calculated by this formula, the average diameters of the calibers are given in Appendix 1.

3.3.2 Determination of roll gauges

The form of calibers of three-roll mills is shown in fig. 3.2.

An oval pass is obtained by outlining it with a radius r with a center displaced relative to the rolling axis by an eccentricity e.

Caliber form

The values ​​of the radii and eccentricity of the calibers are determined by the width and height of the calibers according to the formulas:

To determine the dimensions of the caliber, it is necessary to know the values ​​of its semiaxes a and b, and to determine them, the value of the ovality of the caliber

To determine the ovality of the caliber, you can use the formula:

The exponent q characterizes the possible value of broadening in the caliber. When reducing in three-roll stands, q = 1.2 is taken.

The values ​​of the semi-axes of the caliber are determined by the dependencies:

where f is the correction factor, which can be calculated using the approximate formula

We will calculate the dimensions of the caliber according to the above formulas for the first stand.

For the remaining stands, the calculation is carried out in a similar way.

At present, the grooves of the rolls are carried out after the installation of the rolls in the working stand. Boring is carried out on special machines with a round cutter. The boring scheme is shown in fig. 3.3.

Rice. 3.3 - Caliber bore pattern

To obtain a caliber with given values ​​of a and b, it is necessary to determine the cutter diameter D f and its displacement relative to the plane of the roll axes (parameter X). D f and X are determined by the following mathematically exact formulas:

For three-roll mills, the angle a is 60°. Di is the ideal roll diameter, Di=330mm.

The values ​​calculated according to the above formulas are summarized in Table. 3.2.

Table 3.2 - Roll calibration

Stand number	d, mm	m,%	a, mm	b, mm	r, mm	e, mm	D f, mm	X, mm
1	91,17	2,0	45,60	45,50	45,80	0,37	91,50	8,11
2	87,07	4,5	43,60	43,40	43,80	0,35	87,40	8,00
3	82,71	5,0	41,40	41,20	41,60	0,33	83,00	7,87
4	78,58	5,0	39,30	39,20	39,50	0,32	78,80	7,73
5	74,65	5,0	37,40	37,20	37,50	0,3	74,90	7,59
6	70,92	5,0	35,50	35,40	35,70	0,28	71,20	7,45
7	67,37	5,0	33,70	33,60	33,90	0,27	67,60	7,32
8	64,00	5,0	32,00	31,90	32,20	0,26	64,20	7,18
9	60,80	5,0	30,40	30,30	30,60	0,24	61,00	7,04
10	57,76	5,0	28,90	28,80	29,00	0,23	58,00	6,90
11	54,87	5,0	27,50	27,40	27,60	0,22	55,10	6,76
12	52,13	5,0	26,10	26,00	26,20	0,21	52,30	6,62
13	49,52	5,0	24,80	24,70	24,90	0,2	49,70	6,48
14	47,05	5,0	23,60	23,50	23,70	0,19	47,20	6,35
15	44,70	5,0	22,40	22,30	22,50	0,18	44,80	6,21
16	42,46	5,0,	21,30	21,20	21,30	0,17	42,60	6,08
17	40,34	5,0	20,20	20,10	20,30	0,16	40,50	5,94
18	38,32	5,0	19,20	19,10	19,30	0,15	38,50	5,81
19	36,40	5,0	18,20	18,10	18,30	0,15	36,50	5,69
20	34,77	4,5	17,40	17,30	17,50	0,14	34,90	5,57
21	34,07	2	17,10	17,00	17,10	0,14	34,20	5,52
22	34,07	0	17,10	17,00	17,10	0,14	34,20	5,52
23	34,00	0	17,00	17,00	17,00	0	34,10	5,52
24	34,00	0	17,00	17,00	17,00	0	34,10	5,52

3.4 Calculation speed limit

The calculation of the speed mode of the mill consists in determining the number of revolutions of the rolls and, according to them, the number of revolutions of the engines.

When rolling pipes with tension, the change in wall thickness is greatly influenced by the value of plastic tension. In this regard, first of all, it is necessary to determine the coefficient of total plastic tension on the mill - ztot, which would ensure the required wall. The calculation of ztot is given in clause 3.3.

,

where is the coefficient taking into account the influence of non-contact deformation zones:

;

l i is the length of the capture arc:

;

- grip angle:

;

f is the coefficient of friction, we accept f=0.5; a is the number of rolls in the stand, a=3.

In the first working stand z c1 =0. In subsequent stands, you can take z p i -1 = z s i .

,

;

;

.

Substituting the data for the first stand into the above formulas, we obtain:

mm;

;

;

;

; ;

mm.

Having carried out similar calculations for the second stand, the following results were obtained: z p2 = 0.42, S 2 = 3.251 mm, z p3 = 0.426, S 3 = 3.252 mm, z p4 = 0.446, S 4 = 3.258 mm. On this, we stop the calculation of z p i according to the above method, because the condition z n2 >z total is fulfilled.

From the condition of complete slip, we determine the maximum possible tension z z in the last deforming stand, i.e. z s21 . In this case, we assume that z p21 =0.

.

mm;

;

;

The wall thickness in front of the 21st stand, i.e. S 20, can be determined by the formula:

.

;

; ;

mm.

Having carried out similar calculations for the 20th stand, the following results were obtained: z z 20 = 0.357, S 19 = 3.178 mm, z z 19 = 0.396, S 18 = 3.168 mm, z z 18 = 0.416, S 17 = 3.151 mm, z z 17 = 0.441, S 16 \u003d 3.151 mm. On this, we stop the calculation of z p i, because the condition z z14 >z total is fulfilled.

The calculated wall thickness values ​​for the mill stands are given in Table. 2.20.

To determine the number of revolutions of the rolls, it is necessary to know the rolling diameters of the rolls. To determine the rolling diameters, you can use the formulas given in:

, (2)

where D in i is the diameter of the roll at the top;

.

If a , then the calculation of the rolling diameter of the rolls should be carried out according to equation (1), if this condition is not met, then (2) should be used.

The value characterizes the position of the neutral line in the case when it is taken parallel (in plan) to the rolling axis. From the condition of force balance in the deformation zone for such an arrangement of slip zones

,

Given the input rolling speed V in =1.0 m/s, we calculated the number of revolutions of the rolls of the first stand

rpm

Turnovers in the remaining stands were found by the formula:

.

The results of calculating the speed mode are given in Table 3.3.

Table 3.3 - Results of calculating the speed limit

Stand number	S, mm	Dcat, mm	n, rpm
1	3,223	228,26	84,824
2	3,251	246,184	92,917
3	3,252	243,973	99,446
4	3,258	251,308	103,482
5	3,255	256,536	106,61
6	3,255	256,832	112,618
7	3,255	260,901	117,272
8	3,255	264,804	122,283
9	3,254	268,486	127,671
10	3,254	272,004	133,378
11	3,254	275,339	139,48
12	3,253	278,504	146,046
13	3,253	281,536	153,015
14	3,252	284,382	160,487
15	3,252	287,105	168,405
16	3,251	289,69	176,93
17	3,250	292,131	185,998
18	3,250	292,049	197,469
19	3,192	293,011	204,24
20	3,193	292,912	207,322
21	3,21	292,36	208,121
22	3,15	292,36	209
23	3,22	292,36	209
24	3,228	292,36	209

According to Table 3.3. a graph of changes in the revolutions of the rolls was built (Fig. 3.4.).

Roll speed

3.5 Power parameters of rolling

A distinctive feature of the reduction process in comparison with other types of longitudinal rolling is the presence of significant interstand tensions. The presence of tension has a significant effect on the power parameters of rolling - the pressure of the metal on the rolls and the rolling moments.

The force of the metal on the roll P is the geometric sum of the vertical R in and horizontal R g components:

The vertical component of the metal force on the rolls is determined by the formula:

,

where p is the average specific pressure of the metal on the roll; l is the length of the deformation zone; d is the gauge diameter; a is the number of rolls in the stand.

The horizontal component Р g is equal to the difference between the forces of the front and rear tensions:

where z p, z z are the coefficients of the front and rear plastic tensions; F p, F c - cross-sectional area of ​​the front and rear ends of the pipe; s S is the deformation resistance.

To determine the average specific pressures, it is recommended to use the formula of V.P. Anisiforova:

.

The rolling moment (total per stand) is determined by the formula:

.

The deformation resistance is determined by the formula:

,

where Т – rolling temperature, °С; H is the intensity of shear strain rates, 1/s; e - relative reduction; K 1, K 2, K 3, K 4, K 5 are empirical coefficients, for steel 10: K 1 = 0.885, K 2 = 7.79, K 3 = 0.134, K 4 = 0.164, K 5 = (–2 ,eight).

The strain rate intensity is determined by the formula

where L is the degree of shear deformation:

t is the deformation time:

The angular velocity of the roll is found by the formula:

,

Power is found by the formula:

In table. 3.4. the results of the calculation of the power parameters of rolling according to the above formulas are given.

Table 3.4 - Power parameters of rolling

Stand number	s S , MPa	p, kN / m 2	P, kN	M, kNm	N, kW
1	116,78	10,27	16,95	-1,91	-16,93
2	154,39	9,07	25,19	2,39	23,31
3	162,94	9,1	21,55	2,95	30,75
4	169,48	9,69	22,70	3,53	38,27
5	167,92	9,77	20,06	2,99	33,37
6	169,48	9,84	19,06	3,35	39,54
7	171,12	10,47	18,79	3,51	43,11
8	173,01	11,15	18,59	3,68	47,23
9	175,05	11,89	18,39	3,86	51,58
10	176,70	12,64	18,13	4,02	56,08
11	178,62	13,47	17,90	4,18	61,04
12	180,83	14,36	17,71	4,35	66,51
13	182,69	15,29	17,48	4,51	72,32
14	184,91	16,31	17,26	4,67	78,54
15	186,77	17,36	16,83	4,77	84,14
16	189,19	18,53	16,65	4,94	91,57
17	191,31	19,75	16,59	5,14	100,16
18	193,57	22,04	18,61	6,46	133,68
19	194,32	26,13	15,56	4,27	91,34
20	161,13	24,09	11,22	2,55	55,41
21	134,59	22,69	8,16	1,18	33,06
22	175,14	15,45	7,43	0,87	25,42
23	180,00	-	-	-	-
24	180,00	-	-	-	-

According to Table. 3.4 graphs of changes in the power parameters of rolling along the mill stands are plotted (Fig. 3.5., 3.6., 3.7.).

Change in average specific pressure

Changing the force of the metal on the roll

Changing the rolling moment

3.6 Study of the effect of transient speed reduction modes on the value of the longitudinal difference in wall thickness of the end sections of finished pipes

3.6.1 Description of the calculation algorithm

The study was carried out in order to obtain data on the effect of transient speed reduction modes on the value of the longitudinal difference in wall thickness of the end sections of finished pipes.

Determination of interstand tension coefficient from known roll revolutions, i.e. dependence Zn i =f(n i /n i -1) was carried out according to the method of solving the so-called inverse problem proposed by G.I. Gulyaev, in order to obtain the dependence of the wall thickness on the revolutions of the rolls.

The essence of the technique is as follows.

The steady process of pipe reduction can be described by a system of equations reflecting the observance of the law of constancy of second volumes and the balance of forces in the deformation zone:

(3.1.)

In turn, as is well known,

Dcat i =j(Zз i , Zп i , А i),

m i =y(Zз i , Zп i , B i),

where A i and B i are values ​​that do not depend on tension, n i is the number of revolutions in the i-th stand,  i is the drawing ratio in the i-th stand, Dcat i is the rolling diameter of the roll in the i-th stand, Zп i , Zz i - front and rear plastic tension coefficients.

Given that Zз i = Zп i -1, the system of equations (3.1.) can be written in general form as follows:

(3.2.)

We solve the system of equations (3.2.) with respect to the front and back coefficients of plastic tension by the method of successive approximations.

Taking Zz1 = 0, we set the value Zp1 and from the first equation of the system (3.2.) we determine Zp 2 by iteration, then from the second equation - Zp 3, etc. Given the value Zp 1, you can find a solution in which Zp n = 0 .

Knowing the coefficients of the front and rear plastic tension, we determine the wall thickness after each stand using the formula:

(3.3.)

where A is the coefficient determined by the formula:

;

;

z i - average (equivalent) coefficient of plastic tension

.

3.6.2 Study results

Using the results of calculations of the tool calibration (p. 3.3.) and the speed setting of the mill (roll speeds) with the steady reduction process (p. 3.4.) in the MathCAD 2001 Professional software environment, the solution of the system (3.2.) and expressions (3.3.) with the purpose of determining the change in wall thickness.

It is possible to reduce the length of the thickened ends by increasing the coefficient of plastic tension by changing the revolutions of the rolls during rolling of the end sections of the pipe.

At present, a control system for the high-speed mode of continuous mandrelless rolling has been created at the TPA-80 reduction mill. This system allows you to dynamically adjust the roll speed of the PPC stands during the rolling of the end sections of the pipes according to a given linear relationship. This regulation of the roll speed during the rolling of the end sections of the pipes is called the “velocity wedge”. Turnovers of the rolls during rolling of the end sections of the pipe are calculated by the formula:

, (3.4.)

where n i is the speed of the rolls in the i-th stand at steady state, K i is the coefficient of reduction of the speed of the rolls in %, i is the number of the stand.

The dependence of the roll speed reduction coefficient in a given stand on the stand number is linear

K i \u003d (Fig. 3.8.).

Dependence of the reduction factor of rolls in a stand on the stand number.

The initial data for using this control mode are:

The number of stands in which the speed setting is changed is limited by the length of the thickened ends (3…6);

The magnitude of the reduction in the speed of the rolls in the first stand of the mill is limited by the possibility of an electric drive (0.5 ... 15%).

In this work, to study the effect of the speed setting of the RRS on the end longitudinal wall thickness, it was assumed that the change in speed setting when reducing the front and rear ends of the pipes is carried out in the first 6 stands. The study was carried out by changing the speed of rotation of the rolls in the first stands of the mill in relation to the steady rolling process (variation of the slope of the straight line in Fig. 3.8).

As a result of modeling the processes of filling the RRS stands and exiting the pipe from the pipe mill, we obtained the dependences of the wall thickness of the front and rear ends of the pipes on the magnitude of the change in the speed of rotation of the rolls in the first stands of the mill, which are shown in Fig. 3.9. and Fig.3.10. for pipes measuring 33.7x3.2 mm. Most optimal value The “velocity wedge” in terms of minimizing the length of the end trim and “hitting” the wall thickness in the tolerance field of DIN 1629 (wall thickness tolerance ± 12.5%) is K 1 =10-12%.

On fig. 3.11. and fig. 3.12. the dependences of the lengths of the front and rear thickened ends of the finished pipes are given when using the “velocity wedge” (K 1 =10%), obtained as a result of modeling transients. From the above dependences, the following conclusion can be drawn: the use of a “velocity wedge” gives a noticeable effect only when rolling pipes with a diameter of less than 60 mm and a wall thickness of less than 5 mm, and with a larger diameter and wall thickness of the pipe, the wall thinning necessary to achieve the requirements of the standard does not occur.

On fig. 3.13., 3.14., 3.15., the dependences of the lengths of the front thickened end on the outer diameter of the finished pipes are given for wall thicknesses equal to 3.5, 4.0, 5.0 mm, at different values ​​of the “velocity wedge” (we took the coefficient of speed reduction rolls K 1 equal to 5%, 10%, 15%).

The dependence of the wall thickness of the front end of the pipe on the value

“speed wedge” for size 33.7x3.2 mm

Dependence of the wall thickness of the rear end of the pipe on the value of the “velocity wedge” for the size 33.7x3.2 mm

The dependence of the length of the front thickened end of the pipe on D and S (at K 1 \u003d 10%)

The dependence of the length of the rear thickened end of the pipe on D and S (at K 1 \u003d 10%)

Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S=3.5 mm) at different values ​​of the “velocity wedge”.

Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S=4.0 mm) at different values ​​of the “velocity wedge”

Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S=5.0 mm) at different values ​​of the “velocity wedge”.

From the above graphs, it can be seen that the greatest effect in terms of reducing the end thickness difference of finished pipes is given by the dynamic control of the RPC rolls within K 1 =10...15%. Insufficiently intense change in the “velocity wedge” (K 1 =5%) does not allow thinning the wall thickness of the end sections of the pipe.

Also, when rolling pipes with a wall thicker than 5 mm, the tension arising from the action of the “velocity wedge” is unable to thin the wall due to the insufficient pulling capacity of the rolls. When rolling pipes with a diameter of more than 60 mm, the elongation ratio in the reduction mill is small, therefore, the thickening of the ends practically does not occur, therefore, the use of a “velocity wedge” is impractical.

The analysis of the above graphs showed that the use of the “velocity wedge” on the reduction mill TPA-80 of JSC “KresTrubZavod” makes it possible to reduce the length of the front thickened end by 30%, the rear thickened end by 25%.

As the calculations of Mochalov D.A. For more efficient use of the “velocity wedge” for further reduction of the end trim, it is necessary to ensure the operation of the first stands in the braking mode with almost full use of the power capabilities of the rolls by using a more complex nonlinear dependence of the roll speed reduction coefficient in a given stand on the stand number. It is necessary to create a scientifically based methodology for determining the optimal function K i =f(i).

The development of such an algorithm for the optimal control of the RRS can serve as a goal for the further development of the UZS-R into a full-fledged APCS TPA-80. As the experience of using such process control systems shows, the regulation of the number of revolutions of the rolls during the rolling of the end sections of the pipes, according to the Mannesmann company (the package of applied programs CARTA), allows to reduce the size of the end cutting of the pipes by more than 50%, due to the automatic control system for the process of reducing the pipes, which includes includes both a mill control subsystem and a measuring subsystem, as well as a subsystem for calculating the optimal reduction mode and real-time process control.

4. FEASIBILITY STUDY OF THE PROJECT

4.1 The essence of the planned activity

In this project, it is proposed to introduce the optimal speed mode of rolling on a stretch-reduction mill. Due to this measure, it is planned to reduce the consumption coefficient of the metal, and due to the reduction in the length of cut thickened ends of finished pipes, an increase in production volumes by 80 tons per month on average is expected.

Capital investments required for the implementation of this project are 0 rubles.

Financing of the project can be carried out under the item "current repairs", cost estimates. The project can be completed within one day.

4.2 Calculation of the cost of production

Calculation of the cost price of 1t. products at the existing standards for trimming the thickened ends of pipes are given in table. 4.1.

Calculation for the project is given in table. 4.2. Since the result of the implementation of the project is not an increase in output, the recalculation of the cost values ​​for the processing stage in the design calculation is not carried out. The profitability of the project is to reduce the cost by reducing trimming waste. Trimming is reduced due to a decrease in the consumption coefficient of the metal.

4.3 Calculation of design indicators

The calculation of the project indicators is based on the costing shown in Table. 4.2.

Savings from cost reduction per year:

Eg \u003d (C 0 -C p) * V pr \u003d (12200.509-12091.127) * 110123.01 \u003d 12045475.08r.

Reported profit:

Pr 0 \u003d (P-C 0) * V from \u003d (19600-12200.509) * 109123.01 \u003d 807454730.39r.

Project profit:

Pr p \u003d (P-C p) * V pr \u003d (19600-12091.127) * 110123.01 \u003d 826899696.5r.

The increase in profit will be:

Pr \u003d Pr p - Pr 0 \u003d 826899696.5-807454730.39 \u003d 19444966.11r.

Product profitability was:

Profitability of products for the project:

The cash flow for the report and for the project are presented in Table 4.3. and 4.4., respectively.

Table 4.1 - Calculation of the cost of 1 ton of rolled products in the shop T-3 JSC "KresTrubZavod"

No. p / p	Cost item	Quantity	Price 1 ton	Sum
1	2	3	4	5
I	Given in the redistribution: 1. Billet, t/t; 2. Waste, t/t: trimming substandard;
I I	Transfer costs 2. Energy costs: power electric power, kW/h steam for production, Gcal technical water, tm 3 compressed air, tm 3 recycled water, tm 3 industrial wastewater, tm 3 3. Auxiliary materials 7. Replacement equipment 10. Overhaul 11. Work of transport shops 12. Other shop expenses Total conversion costs
W	Factory overhead

Table 4.2 - Project costing of 1 ton of rolled products

No. p / p	Cost item	Quantity	Price 1 ton	Sum
I	Given in the redistribution: 1. Billet, t/t; 2. Waste, t/t: trimming substandard; Total specified in the redistribution minus waste and scrap
P	Transfer costs 1. Process fuel (natural gas), here 2. Energy costs: power electric power, kW/h steam for production, Gcal technical water, tm 3 compressed air, tm 3 recycled water, tm 3 industrial wastewater, tm 3 3. Auxiliary materials 4. Basic salary of production workers 5. Additional salary of production workers 6. Deductions for social needs 7. Replacement equipment 8. Maintenance and maintenance of fixed assets 9. Depreciation of fixed assets 10. Overhaul 11. Work of transport shops 12. Other shop expenses Total conversion costs
W	Factory overhead Total production cost
IV	non-manufacturing expenses Total full cost

Improvement of the technological process will affect the technical and economic performance of the enterprise as follows: the profitability of production will increase by 1.45%, savings from cost reduction will amount to 12 million rubles. per year, which will lead to an increase in profits.

Table 4.3 - Reported cash flow

cash flows	Of the year
	1	2	3	4	5
A. Cash flow:
- Volume of production, tons
- Product price, rub.
total inflow
B. Cash outflow:
-Operating costs
-Income tax	193789135,29
Total outflow:	1521432951,34	1521432951,34	1521432951,34	1521432951,34	1521432951,34
Net cash flow (A-B)
Coeff. Inversions	0,8	0,64	0,512	0,41	0,328
E=0.25
	493902383,46	889024290,22	1205121815,64	1457999835,97	1457999835,97

Table 4.4 - Cash flow for the project

cash flows	Of the year
	1	2	3	4	5
A. Cash flow:
- Volume of production, tons
- Product price, rub.
- Sales proceeds, rub.
total inflow
B. Cash outflow:
-Operating costs
-Income tax
Total outflow:	1526220795,63	1526220795,63	1526220795,63	1526220795,63	1526220795,63
Net cash flow (A-B)	632190135,03	632190135,03	632190135,03
Coeff. Inversions	0,8	0,64	0,512	0,41	0,328
E=0.25
Discounted flow (A-B)*C inv
Cumulative Cash Flow NPV

The financial profile of the project is shown in Figure 4.1. According to the graphs shown in fig. 4.1. the cumulative NPV of the project exceeds the planned figure, which indicates the unconditional profitability of the project. The cumulative NPV calculated for the implemented project is a positive value from the first year, since the project did not require capital investments.

Project financial profile

The break-even point is calculated by the formula:

The break-even point characterizes the minimum volume of production at which losses end and the first profit appears.

In table. 4.5. data are presented for calculating variable and fixed costs.

According to the reporting data, the amount of variable costs per unit of production is Z lane = 11212.8 rubles, the amount of fixed costs per unit of production Z post = 987.7 rubles. The amount of fixed costs for the entire volume of output according to the report is 107780796.98 rubles.

According to the design data, the amount of variable costs Z lane \u003d 11103.5 rubles, the amount of fixed costs Z post \u003d 987.7 rubles. The amount of fixed costs for the entire volume of output according to the report is 108768496.98 rubles.

Table 4.5 - The share of fixed costs in the structure of planned and project costs

No. p / p	Cost item	Amount according to the plan, rub.	Project amount, rub.	The share of fixed costs in the structure of costs for redistribution, %
1	2	3	4	5
1	Transfer costs 1. Process fuel (natural gas), here 2. Energy costs: power electric power, kW/h steam for production, Gcal technical water, tm 3 compressed air, tm 3 recycled water, tm 3 industrial wastewater, tm 3 3. Auxiliary materials 4. Basic salary of production workers 5. Additional salary of production workers 6. Deductions for social needs 7. Replacement equipment 8. Current repair and maintenance of fixed assets 9. Depreciation of fixed assets 10. Overhaul 11. Work of transport shops 12. Other shop expenses Total conversion costs
2	Factory overhead Total production cost			100
3	non-manufacturing expenses Total full cost			100

The reported break-even point is:

TB from t.

The break-even point for the project is:

TV pr t.

In table. 4.6. the calculation of revenue and all types of costs for the production of sold products necessary to determine the break-even point was carried out. Schedules for calculating the break-even point for the report and for the project are shown in Figure 4.2. and Fig.4.3. respectively.

Table 4.6 - Data for calculating the break-even point

Calculation of the break-even point according to the report

Calculation of the break-even point for the project

Technical and economic indicators of the project are presented in Table. 4.7.

As a result, we can conclude that the measure proposed in the project will reduce the cost of a unit of manufactured products by 1.45% by reducing variable costs, which contributes to an increase in profit by 19.5 million rubles. with an annual production of 110,123.01 tons. The result of the project implementation is the growth of the cumulative net present value in comparison with the planned value in the period under review. Also a positive point is the reduction of the break-even threshold from 12.85 thousand tons to 12.8 thousand tons.

Table 4.7 - Technical and economic indicators of the project

No. p / p	Indicator	Report	Project	Deviation
				Absolute	%
1	Production volume: in kind, t in value terms, thousand rubles
2	The cost of fixed production assets, thousand rubles.	6775032	6775032	0	0
3	General costs (full cost): total issue, thousand rubles units of production, rub.
4	Product profitability, %	60,65	62,1	1,45	2,33
5	Net present value, NPV	1700,136
6	Total amount of investments, thousand rubles	0
7	Reference: break-even point T.B., t, the value of the discount rate F, GNI internal rate of return maximum cash outflow K, thousand rubles.

CONCLUSION

In this thesis project, a technology for the production of general-purpose pipes according to DIN 1629 was developed. The paper considers the possibility of reducing the length of thickened ends formed during rolling on a reduction mill by changing the speed settings of the mill during rolling of the end sections of the pipe using the capabilities of the UZS-R system. Calculations have shown that the reduction in the length of thickened ends can reach 50%.

Economic calculations have shown that the use of the proposed rolling modes will reduce the unit cost of production by 1.45%. This, while maintaining the existing production volumes, will make it possible to increase profits by 20 million rubles in the first year.

Bibliography

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2. Anuryev V.I. "Handbook of the designer-machine builder" in 3 volumes, volume 2 - M. "Engineering" 1980 - 559 p.

3. Anuryev V.I. "Handbook of the designer-machine builder" in 3 volumes, volume 3 - M. "Engineering" 1980 - 557 p.

4. Pavlov Ya.M. "Machine parts". - Leningrad "Engineering" 1968 - 450 p.

5. Vasiliev V.I. "Fundamentals of designing technological equipment of motor transport enterprises" textbook - Kurgan 1992 - 88 p.

6. Vasiliev V.I. "Fundamentals of designing technological equipment of motor transport enterprises" - Kurgan 1992 - 32 p.