On the reduced section of thin-walled tee, angle and cruciform profiles after local buckling. Development of methods for calculating the deformation-speed modes of hot reduction with the tension of pipes of increased accuracy
UDC 621.774.3
STUDY OF THE DYNAMICS OF CHANGES IN THE PIPE WALL THICKNESS DURING REDUCTION
K.Yu. Yakovleva, B.V. Barichko, V.N. Kuznetsov
The results of an experimental study of the dynamics of changes in the wall thickness of pipes during rolling, drawing in monolithic and roller dies are presented. It is shown that with an increase in the degree of deformation, a more intense increase in the thickness of the pipe wall is observed in the processes of rolling and drawing in roller dies, which makes their use promising.
Keywords: cold-formed pipes, thick-walled pipes, pipe drawing, pipe wall thickness, pipe inner surface quality.
The existing technology for the manufacture of cold-formed thick-walled pipes of small diameter from corrosion-resistant steels provides for the use of cold rolling processes on cold rolling mills and subsequent mandrelless drawing in monolithic dies. It is known that the production of pipes of small diameter by cold rolling is associated with a number of difficulties due to a decrease in the rigidity of the "rod-mandrel" system. Therefore, to obtain such pipes, a drawing process is used, mainly without a mandrel. The nature of the change in the pipe wall thickness during mandrelless drawing is determined by the ratio of wall thickness S and outer diameter D, and the absolute value of the change does not exceed 0.05-0.08 mm. In this case, wall thickening is observed at the ratio S/D< 0,165-0,20 в зависимости от наружного диаметра заготовки . Для данных соотношений размеров S/D коэффициент вытяжки д при волочении труб из коррозионно-стойкой стали не превышает значения 1,30 , что предопределяет многоцикличность известной технологии и требует привлечения новых способов деформации.
The aim of the work is a comparative experimental study of the dynamics of changes in the wall thickness of pipes in the processes of reduction by rolling, drawing in a monolithic and roller die.
Cold-formed pipes were used as blanks: 12.0x2.0 mm (S/D = 0.176), 10.0x2.10 mm (S/D = 0.216) from steel 08Kh14MF; dimensions 8.0x1.0 mm (S / D = 0.127) from steel 08X18H10T. All pipes were annealed.
Drawing in monolithic dies was carried out on a chain drawing bench with a force of 30 kN. For roller drawing, we used a die with offset pairs of rollers BP-2/2.180. Drawing in a roller die was carried out using an oval-circle gauge system. Pipe reduction by rolling was carried out according to the “oval-oval” calibration scheme in a two-roll stand with rolls 110 mm in diameter.
At each stage of deformation, samples were taken (5 pcs. for each variant of the study) to measure the outer diameter, wall thickness, and roughness of the inner surface. Measurement of the geometric dimensions and surface roughness of the pipes was performed using an electronic caliper TTTC-TT. electronic point micrometer, profilometer Surftest SJ-201. All tools and devices have passed the necessary metrological verification.
The parameters of cold deformation of pipes are given in the table.
On fig. 1 shows graphs of the dependence of the relative increase in wall thickness on the degree of deformation e.
Analysis of the graphs in fig. 1 shows that during rolling and drawing in a roller die, in comparison with the process of drawing in a monolithic die, a more intense change in the pipe wall thickness is observed. This, according to the authors, is due to the difference in the scheme of the stress state of the metal: during rolling and roller drawing, the tensile stresses in the deformation zone are smaller. The location of the wall thickness change curve during roller drawing is lower than the wall thickness change curve during rolling due to slightly higher tensile stresses during roller drawing due to the axial application of the deformation force.
The extremum of the function of the change in wall thickness as a function of the degree of deformation or relative reduction along the outer diameter observed during rolling corresponds to the value S/D = 0.30. By analogy with hot reduction by rolling, where a decrease in wall thickness is observed at S/D > 0.35, it can be assumed that cold reduction by rolling is characterized by a decrease in wall thickness at a ratio of S/D > 0.30.
Since one of the factors determining the nature of the change in wall thickness is the ratio of tensile and radial stresses, which in turn depends on the parameters
Pass No. Pipe dimensions, mm S,/D, Si/Sc Di/Do є
Reduction by rolling (pipes made of steel grade 08X14MF)
О 9.98 2.157 О.216 1.О 1.О 1.О О
1 9.52 2.23O 0.234 1.034 0.954 1 .30 80.04
2 8.1O 2.35O O.29O 1.O89 O.812 1.249 O.2O
Z 7.01 2.324 O.332 1.077 O.7O2 1.549 O.35
Reduction by rolling (pipes made of steel grade 08X18H10T)
О 8,О6 1,О2О О,127 1,О 1,О 1,О О
1 7.OZ 1.13O O.161 1.1O8 O.872 1.O77 O.O7
2 6.17 1.225 0.199 1.201 0.766 1.185 0.16
C 5.21 1.310 0.251 1.284 0.646 1.406 0.29
Reducing by drawing in a roller die (pipes made of steel grade 08X14MF)
О 12.ОО 2.11 О.176 1.О 1.О 1.О О
1 10.98 2.20 0.200 1.043 0.915 1.080 0.07
2 1O.O8 2.27 O.225 1.O76 O.84O 1.178 O.15
Z 9.O1 2.3O O.2O1 1.O9O O.751 1.352 O.26
Reducing by drawing in a monolithic die (pipes made of steel grade 08X14MF)
О 12.ОО 2.11О О.176 1.О 1.О 1.О О
1 1O.97 2.135 0.195 1.O12 O.914 1.1O6 O.1O
2 9.98 2.157 O.216 1.O22 O.832 1.118 O.19
C 8.97 2.160 0.241 1.024 0.748 1.147 0.30
Di, Si are, respectively, the outer diameter and wall thickness of the pipe in the i-th passage.
Rice. 1. Dependence of the relative increase in pipe wall thickness on the degree of deformation
ra S/D, it is important to study the influence of the S/D ratio on the position of the extremum of the function of changing the pipe wall thickness in the process of reduction. According to the data of the work, at smaller S/D ratios, the maximum value of the pipe wall thickness is observed at large deformations. This fact was studied on the example of the process of reduction by rolling pipes with dimensions of 8.0x1.0 mm (S/D = 0.127) of steel 08Kh18N10T in comparison with the data on rolling pipes with dimensions of 10.0x2.10 mm (S/D = 0.216) of steel 08Kh14MF. The measurement results are shown in fig. 2.
The critical degree of deformation at which the maximum value of the wall thickness was observed during pipe rolling with the ratio
S/D = 0.216 was 0.23. When rolling pipes made of steel 08Kh18N10T, the extremum of the increase in wall thickness was not reached, since the ratio of pipe dimensions S/D, even at the maximum degree of deformation, did not exceed 0.3. An important circumstance is that the dynamics of the increase in wall thickness during the reduction of pipes by rolling is inversely related to the ratio of the dimensions S/D of the original pipe, which is demonstrated by the graphs shown in Fig. 2, a.
Analysis of curves in fig. 2b also shows that the change in the S/D ratio during the rolling of pipes made of steel grade 08Kh18N10T and pipes made of steel grade 08Kh14MF has a similar qualitative character.
S0/A)=0.127 (08X18H10T)
S0/00=0.216 (08X14MF)
Degree of deformation, b
VA=0;216 (08X14MF)
(So/Da=0A21 08X18H10T) _
Degree of deformation, є
Rice. Fig. 2. Changes in wall thickness (a) and S/D ratio (b) depending on the degree of deformation during rolling of pipes with different initial S/D ratios
Rice. 3. Addiction relative magnitude roughness of the inner surface of pipes on the degree of deformation
In the process of reduction different ways the roughness of the inner surface of the pipes was also evaluated by the arithmetic mean deviation of the microroughness height Ra. On fig. Figure 3 shows the graphs of the dependence of the relative value of the parameter Ra on the degree of deformation when pipes are reduced by rolling and drawing in monolithic dies
woolness of the inner surface of the pipes in the i-th passage and on the original pipe).
Analysis of curves in fig. 3 shows that in both cases (rolling, drawing) an increase in the degree of deformation during reduction leads to an increase in the Ra parameter, that is, it worsens the quality of the inner surface of the pipes. The dynamics of change (increase) in the roughness parameter with an increase in the degree of deformation in the case of
ducting of pipes by rolling in two-roll calibers significantly (about two times) exceeds the same indicator in the process of drawing in monolithic dies.
It should also be noted that the dynamics of changes in the roughness parameter of the inner surface is consistent with the above description of the dynamics of changes in wall thickness for the considered reduction methods.
Based on the research results, the following conclusions can be drawn:
1. The dynamics of changes in pipe wall thickness for the considered cold reduction methods is the same - intense thickening with an increase in the degree of deformation, subsequent slowdown in the increase in wall thickness with the achievement of a certain maximum value at a certain ratio of pipe dimensions S / D and a subsequent decrease in the increase in wall thickness.
2. The dynamics of changes in pipe wall thickness is inversely related to the ratio of the original pipe dimensions S/D.
3. The greatest dynamics of the increase in wall thickness is observed in the processes of rolling and drawing in roller dies.
4. An increase in the degree of deformation during reduction by rolling and drawing in monolithic dies leads to a deterioration in the state of the inner surface of the pipes, while the increase in the roughness parameter Ra during rolling occurs more intensively than during drawing. Taking into account the conclusions drawn and the nature of the change in the wall thickness during deformation, it can be argued that for drawing pipes in roller dies,
The change in the Ra parameter will be less intense than for rolling, and more intense in comparison with monolithic drawing.
The information obtained about the regularities of the cold reduction process will be useful in designing routes for the manufacture of cold-formed pipes from corrosion-resistant steels. At the same time, the use of the drawing process in roller dies is promising for increasing the thickness of the pipe wall and reducing the number of passes.
Literature
1. Bisk, M.B. cold deformation steel pipes. In 2 hours, Part 1: Preparation for deformation and drawing / M.B. Bisk, I.A. Grekhov, V.B. Slavin. -Sverdlovsk: Mid-Ural. book. publishing house, 1976. - 232 p.
2. Savin, G.A. Pipe drawing / G.A. Savin. -M: Metallurgy, 1993. - 336 p.
3. Shveikin, V.V. Technology of cold rolling and reduction of pipes: textbook. allowance / V.V. Shveikin. - Sverdlovsk: Publishing House of UPI im. CM. Kirova, 1983. - 100 p.
4. Technology and equipment for pipe production /V.Ya. Osadchiy, A.S. Vavilin, V.G. Zimovets and others; ed. V.Ya. Osadchy. - M.: Intermet Engineering, 2007. - 560 p.
5. Barichko, B.V. Fundamentals of OMD technological processes: lecture notes / B.V. Barichko, F.S. Dubinsky, V.I. Krainov. - Chelyabinsk: Publishing House of SUSU, 2008. - 131 p.
6. Potapov, I.N. Theory of pipe production: textbook. for universities / I.N. Potapov, A.P. Kolikov, V.M. Druyan. - M.: Metallurgy, 1991. - 424 p.
Yakovleva Ksenia Yuryevna, junior researcher, Russian Research Institute of the Pipe Industry (Chelyabinsk); [email protected]
Barichko Boris Vladimirovich, Deputy Head of the Seamless Pipe Department, Russian Research Institute of the Pipe Industry (Chelyabinsk); [email protected]
Kuznetsov Vladimir Nikolaevich, head of the cold deformation laboratory of the central plant laboratory, Sinarsky Pipe Plant OJSC (Kamensk-Uralsky); [email protected]
Bulletin of the South Ural State University
Series "Metallurgy" ___________2014, vol. 14, no. 1, pp. 101-105
STUDY OF DYNAMIC CHANGES OF THE PIPE WALL THICKNESS IN THE REDUCTION PROCESS
K.Yu. Yakovleva, The Russian Research Institute of the Tube and Pipe Industries (RosNITI), Chelyabinsk, Russian Federation, [email protected],
B.V. Barichko, The Russian Research Institute of the Tube and Pipe Industries (RosNITI), Chelyabinsk, Russian Federation, [email protected],
V.N. Kuznetsov, JSC "Sinarsky Pipe Plant", Kamensk-Uralsky, Russian Federation, [email protected]
The results of the experimental study of dynamic changes for the pipe wall thickness during rolling, drawing both in single-piece and roller dies are described. The results show that with the deformation increasing the faster growth of the pipe wall thiknness is observed in rolling and drawing with the roller dies. The conclusion can be drawn that the usage of roller dies is the most promising one.
Keywords: cold-formed pipes, thick-wall pipes, pipe drawing, pipe wall thickness, quality of the inner surface of pipe.
1. Bisk M.B., Grekhov I.A., Slavin V.B. Kholodnaya deformatsiya stal "nykh trub. Podgotovka k deformatsii i volochenie. Sverdlovsk, Middle Ural Book Publ., 1976, vol. 1. 232 p.
2 Savin G.A. Volochenie tube. Moscow, Metallurgiya Publ., 1993. 336 p.
3. Shveykin V.V. Tekhnologiya kholodnoy prokatki i redutsirovaniya trub. Sverdlovsk, Ural Polytechn. Inst. Publ., 1983. 100 p.
4. Osadchiy V.Ya., Vavilin A.S., Zimovets V.G. et al. Tekhnologiya i obrudovanie trubnogo proizvodstva. Osadchiy V.Ya. (Ed.). Moscow, Intermet Engineering Publ., 2007. 560 p.
5. Barichko B.V., Dubinskiy F.S., Kraynov V.I. Osnovy tekhnologicheskikh protsessov OMD. Chelyabinsk Univ. Publ., 2008. 131 p.
6. Potapov I.N., Kolikov A.P., Druyan V.M. Teoriya trubnogo proizvodstva. Moscow, Metallurgiya Publ., 1991. 424 p.
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 tubes made of 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 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 company, 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. Samples shall be cut along either end of the pipe by a method that does not cause changes in 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 is insulated heat-insulating material. For oven maintenance and maintenance 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, burned with the help of burners of the GR type (radiation burner low pressure) installed on the vault. 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, °С | 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);
Rising temperature flue gases before 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 stand | 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 intended for transporting the draft pipe through the induction heating installation, rolling on the reduction mill, cooling and further transporting it to the cold cutting section.
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 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 pipe cooling 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 shop, 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. The technical characteristics of the straightening machine RVV 320x8 are 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 mandrels 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. Continuity of the technological process, automation of all transport operations, large length of rolled pipes provide high productivity, good quality of pipes in terms of 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 for further development of the continuous rolling method 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 by 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 Automation was possible only for simpler and less efficient tasks, while requiring significant time and money 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 compared to 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 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 in the process. 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 change in speed takes place on stand No. 1, the minimum - on stand No. 10. Photo relays are used as sensors for the position of the ends of the pipe in the mill, which give commands to change the 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 resistance to deformation 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 pair 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 diameter of the cutter D f and its displacement relative to the plane of the axes of the rolls (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 Speed calculation
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 - ztotal, 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, Zp 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 when rolling 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 angle of inclination 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. dependences of the lengths of the front and rear thickened ends of the finished pipes are given 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 effective application“velocity wedge” to further reduce 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 due to the use of a more complex non-linear 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 automated process control systems shows, the regulation of the number of revolutions of the rolls during the rolling of the end sections of pipes, according to the Mannesmann company (CARTA application software package), makes it possible to reduce the size of the end cut of pipes by more than 50%, due to the system automatic control pipe reduction process, which includes both mill control subsystems 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. 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 |
|||
| 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
1. Anuryev V.I. "Handbook of the designer-machine builder" in 3 volumes, volume 1 - M. "Engineering" 1980 - 728 p.
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.
where, p is the number of the current iteration; vt is the total speed of metal sliding over the tool surface; vn is the normal speed of metal movement; wn is the normal speed of the tool; st - friction stress;
- Yield stress as a function of the parameters of the deformable metal, at a given point; - Medium voltage; - Intensity of strain rate; x0 - strain rate of all-round compression; Kt - penalty factor for the speed of metal sliding over the tool (specified by the iteration method) Kn - penalty factor for metal penetration into the tool; m - conditional viscosity of the metal, refined by the method of hydrodynamic approximations; - tension tension or backwater during rolling; Fn is the cross-sectional area of the end of the pipe to which tension or support is applied.
The calculation of the deformation-speed mode includes the distribution of the state of deformations along the stands along the diameter, the required value of the coefficient of plastic tension according to the state Ztot, the calculation of the drawing coefficients, roll diameters of the rolls and the rotational speed of the main drive motors, taking into account the features of its design.
For the first stands of the mill, including the first stand that rolls, and for the last ones placed after the last stand, rolls, the coefficients of plastic tension in them Zav.i are less than the required Ztot. Due to such a distribution of the plastic tension coefficients over all stands of the mill, the calculated wall thickness at the exit from it is greater than necessary along the reduction route. In order to compensate for the insufficient pulling capacity of the rolls of the stands located in the first and after the last stands that are rolled, iterative calculation is necessary to find such a value Ztot that the calculated and specified wall thicknesses at the exit from the state are the same. The greater the value of the required total coefficient of plastic tension according to the state Ztotal, the greater the error in its determination without iterative calculation.
After the iterative calculations have calculated the coefficients of the front and rear plastic tension, the thickness of the pipe wall at the inlet and outlet of the deformation cells along the stands of the reduction mill, we finally determine the position of the first and last stands that are rolled.
Of course, rolling the diameter is determined through the central angle qk.p. between the vertical axis of symmetry of the roll groove and the line drawn from the center of the pass, coincides with the rolling axis to a point on the surface of the pass groove, where the neutral line of the deformation zone is located on its surface, is conventionally located parallel to the rolling axis. The value of the angle qk.p., first of all, depends on the value of the coefficient of the rear Zset. and front Zper. tension, as well as the coefficient
hoods.
Determination of rolling diameter by the value of the angle qk.p. usually performed for a caliber, has the shape of a circle with a center in the rolling axis and a diameter equal to the average diameter of the caliber Dav.
The largest errors in determining the value of the rolling diameter without taking into account the actual geometric dimensions of the pass will be for the case when the rolling conditions determine its position either at the bottom or at the groove flange. The more the real shape of the caliber differs from the circle accepted in the calculations, the more significant this error will be.
The maximum possible range of change of the actual value of the diameter rolls the caliber is a roll cut. The greater the number of rolls forms a caliber, the greater the relative error in determining the rolling diameter without taking into account the actual geometric dimensions of the caliber.
With an increase in the partial reduction of the pipe diameter in the caliber, the difference between its shape and the round one grows. Thus, with an increase in the reduction of the pipe diameter from 1 to 10%, the relative error in determining the value of the rolling diameter without taking into account the actual geometric dimensions of the caliber increases from 0.7 to 6.3% for a two-roller, 7.1% for a three-roller and 7.4% - for a chotirio-roll "rolling" stand when, according to the kinematic conditions of rolling, rolling the diameter located along the bottom of the caliber.
Simultaneous increase in the same