RU2296638C1 - Electrically welded straight-seam tube production method - Google Patents

Abstract

FIELD: plastic working of metals, possibly manufacture of electrically welded straight-seam tubes.

SUBSTANCE: method comprises steps of bending tube blank according to two radiuses; monotonously bending central portion of blank by means of decreasing radius of shaped gages from value (20 - 30)Rw till Rw; bending peripheral portions of blank till radius Rw; increasing bending radius of central portion in respective stand till value (1.45 - 4.25)Rw in zone of transition of open gage to closed gage; providing identical shaping effort in all working stands due to design and size of roll grooved passes and determining such effort according to formula : P_i ^Ф =(σ _i x Δε_i x S_m x B_i x L_i ^in.def.)/(K_Ф x m_i) for open gages and P_i ^Ф =( σ_i ⁿ x Δε_i x S_m x B_i x L^in.def.  ) /( K_Ф x m_i ) +B_i ^k x Δε_i x S_m for closed gages where P_i ^Ф - shaping effort for i-stand, N; σ_i ⁿ -stress in outer surface of strip determined from stress diagram, MPa; S_m - blank thickness, mm; B_i - blank width being in contact with rolls, mm; L_i ^in.def. - length of non-contact deformation zone in i-gage, mm; K_Ф - coefficient equal to 1 - 3; m_i - width of i-gage, mm; B_i ^k - complete perimeter of blank in closed i-stand, mm; Δε_i - bending deformation value in i-stand determined as deformations difference between i-gage and (i-1)-gage while taking into account value Δε_i= ε_i -(! - β)ε_i-1 where β - unspringing factor.

EFFECT: possibility for achieving identification of shaping efforts in all working stands due to calibration and determining dimensions of grooved rolls.

16 dwg, 7 tbl, 1 ex

Description

The invention relates to the field of metal forming and can be used in the manufacture of welded longitudinal pipes.

A method of manufacturing welded pipes during continuous molding of a billet in successively installed horizontal drive stands and vertical idle stands is traditional in the technological sequence of operations.

There is a known method for the production of welded pipes, in which the molding is carried out according to a two-radial folding scheme, while the peripheral sections of the tube stock are formed with a smaller and often constant forming radius from the first to the last stand and the value of this radius is close to the radius of the tube stock in the welding unit [Y. M .Matveev, Ya.L. VATkin, Tool calibration of pipe mills. M.: Metallurgy, 1970, 480 p.].

This method has been widely introduced into production at various plants specializing in the production of longitudinal welded pipes. However, it has a number of significant drawbacks that do not allow us to recommend it as a technical solution with practical parameters for implementation in production. There is no specific methodology for calculating the radius of curvature of the workpiece for the stands of the molding mill, which led to the development of many specific factory methods, which often contradict each other. The second significant drawback of this method is the lack of any recommendations for setting up the working stands according to geometric and power parameters. All this reduces the practical value of the method and obliges shop workers to conduct additional research and calculations.

Another well-known method for the production of longitudinally welded pipes, adopted for the prototype, which includes bending the billet according to a two-radial folding scheme, in which the peripheral sections of the billet are bent in profiled calibers of working stands with a radius less than or equal to the radius of the central section along the entire length of the molding mill, and the central section of the billet is bent monotonically decreasing radius of profiled calibers from the value of (20-30) R _{weld. node} to R _{weld. node} . [V.N.Danchenko, A.P. Kolikov, B.A. Romantsev, S.V. Samusev. Pipe production technology. M .: Intermetengineering, 2002, 562 p.].

This method has the following disadvantages. The methodology for calculating the forming radii by working stands does not take into account the necessary technical parameters, in particular, there is minimal information on the determination of contact areas and the technology for the interaction of the driven shaped tool and the workpiece in these areas. By this technique, there is always an uneven distribution of the molding force among the horizontal drive stands of the molding mill. In more loaded stands (most often 1 and 2), due to the greater molding forces perceived by the shafts with the profile rolls placed on them, through bearings, through pillows and other parts of the assemblies and mechanisms located in the molding stand, the force is transmitted to the bed, as a result of which uneven wear, abrasion, breakage and failure of bearings, flange joints, wedge locks, etc., which in turn affects the increase in downtime, decrease in unit performance, even if it is not a disaster wear and tear, and normative. Parts with uneven wear reduce durability, efficiency, and product quality.

In addition, the uneven wear of the deforming nodes in a separate section violates the stability of the shape change over the length of this section and is the cause of the formation of certain defects. Further, the pipe billet with existing defects is transferred to the following sections of the forming, and its defective sections make it difficult to produce high-quality products, since along with molding to the specified geometric parameters of this section, it is necessary to eliminate the defects obtained in the previous section, and this is not always possible due to limited technical capabilities of the roll tool.

In the proposed method for the production of longitudinally welded pipes, the bending of the peripheral sections of the workpiece in the first open gauges of full coverage and in all closed gauges of the mill is performed until the radius of the welding unit (R _{welded node} ) is obtained, and the radius of molding of the peripheral section is increased at the transition from open to closed gauges to the radius of the molding of the Central section in the appropriate stand to the value of (1.45-4.25) R _{weld. node} , while the values of the effort of forming for all working stands provide identical loads due to the design and size of the profiled roll calibers, and the force of forming is determined by the formula:

- для открытых калибров и

- for open calibers and

- для закрытых калибров,

- for closed gauges,

- усилие формоизменения в i-той клети;

- напряжение на наружной поверхности полосы в i-той клети, определяемое из диаграммы истинных напряжений [МПа]; S_m - толщина заготовки, [мм]; B_i - ширина заготовки, находящаяся в контакте с валками, [мм];

- длина неконтактной зоны деформации в I-том калибре, определяется по специальной методике, [мм]; К_ф - коэффициент схемы формовки; m_i - ширина i-того калибра, [мм];

- полный периметр заготовки в i закрытой клети; ε_i - величина деформации гиба в i-той клети, определяется как разность деформаций в i-том и в (i-1)-м калибре с учетом распружинивания: Δε_i=ε_i-(1-β)ε_i-1 Where

- force of forming in the i-th stand;

- stress on the outer surface of the strip in the i-th stand, determined from the diagram of true stresses [MPa]; S _m - the thickness of the workpiece, [mm]; B _i - the width of the workpiece in contact with the rolls, [mm];

- the length of the non-contact zone of deformation in the 1st caliber, is determined by a special technique, [mm]; To _f - the coefficient of the molding circuit; m _i is the width of the i-th caliber, [mm];

- the full perimeter of the workpiece in i closed stand; ε _i - the amount of bending deformation in the i-th stand, is defined as the difference of deformations in the i-th and in the (i-1) th caliber, taking into account the springing: Δε _i = ε _i - (1-β) ε _i-1

where β is the coefficient of springing.

When determining the efforts of forming, the following important technological factors were taken into account: change in the curvature of the stands taking into account springing, folding form (calibration), the extent of the zone outside contact deformation in roll calibers, and the physicomechanical properties of the tube billet.

The objective of the invention is to stabilize the operation of the equipment, improving the quality of the pipes, which is achieved by identifying the efforts of shaping for all working stands due to the development of calibration and determination of the overall dimensions of the profiled rolls.

The shafts of the upper and lower profile rolls must provide the bearing capacity of the node, i.e. normal operation of profiled rolls placed on the shaft, its bearings, etc. In the drive horizontal molding stands, the shafts of the upper and lower profile rolls forming the caliber have the same configuration, dimensions, materials from which they are made, bearing bearings that are located in pillows that are height-adjustable in the opening of the stand frame. Rotation from the electric motor through the gear stand by means of 2 spindles is transmitted to the shafts, through a key connection to the profile roll. Having a similar design, dimensions, stress concentrators (keyways, fillets, grooves, drilling, physical and mechanical characteristics) under identical loads, loading schemes will have equal elastic deformations, stiffness, bearing capacity, equal wear, endurance and durability.

From the side of the lower roll cushion to the lower cross member and from the upper cushion (pressure screw), the vertical forces equal to 1/2 of the maximum molding force act on the upper cross of the bed of the working stand. The horizontal forces acting on the bed at the time of the capture of metal by the rolls can be ignored, in comparison with vertical efforts, their value is insignificant, less by an order of magnitude.

In the condition that the molding efforts are identified in all the stands of the forming mill, equal elastic deformations of the stands and cross members of the stands of all stands are achieved, and the setup and reconfiguration time is reduced. With uneven vertical loads in more loaded stands and greater deformations of the racks, a pillow clamp is possible, which does not allow to adjust the position of the lower profile roll relative to the upper one both in the vertical and axial directions. When identifying efforts and equality of deformation of the bed, the conditions for monitoring slotted gaps between the uprights and pillows, between the upper and lower profile rolls are improved.

The traditional factory two-radius folding scheme includes a constant curvature of the peripheral sections from the first to the last drive molding stand. Such a scheme simplifies both the methodology for calculating the technical parameters of the tool and the process of manufacturing and operating a two-roll tool. However, a deeper comparative analysis of such a scheme reveals a number of significant drawbacks.

The calculated data showed that the values of the molding force in open and closed stands are significantly different (in closed stands - much less).

The studies showed that it is possible to increase the force of forming in closed gauges to the specified values of the molding force due to the reduction of the molded workpiece and due to this to ensure strict alignment of the process and fix the specified angle of convergence of the edges, which is necessary for high-quality flashing of the edges at given process speeds and the formation of a given weld structure.

Calibration and overall dimensions of the tool determine the geometric parameters of the contact interaction of the profiled tool and the workpiece. The magnitude of specific pressures and the nature of their distribution over the contact zone depend on the contact area (width and length). These values also determine the value of the total effort of forming in the i-th stand.

The width of the contact zone is determined by the calibration scheme and the condition of contact interaction in the ith caliber.

The invention is illustrated by drawings.

Figure 1-3 shows a contact diagram of the tool and the workpiece.

Figure 1 - in open gauges full coverage; figure 2 - in open gauges incomplete coverage; figure 3 - in closed calibers.

Figure 4 presents a diagram of changes in the molding coefficient depending on the calibration of the working tool and the paths of forming.

Figure 5 shows a graph of the change in curvature, constructed according to the factory calibration.

In FIG. 6-13 shows a roll tool for TESA 42-168 of the Volgorechensk pipe plant, respectively: 6, 8, 11 - upper rolls; 7, 9, 12 - lower rolls; figure 10, 13 - side rolls.

On Fig presents a graph of the distribution of curvature for the modernized calibration.

On Fig is a graph of the distribution of the total efforts of forming on the stands for the factory set of technological tools.

On Fig shows a graph of the distribution of the total efforts of forming on the stands for the proposed production method.

Consider typical cases for a two-radius folding scheme. As part of such a calibration, the most common are three contact circuits (Figs. 1, 2, 3).

Figure 1 presents a diagram of the full contact of the tool 1, 2 and the workpiece 3, which is implemented in the first open gauges, when the contact with the profiled roll tool is provided over the entire width of the workpiece and from the outside and from the inside. In this case, the distributed load q is uniformly applied on the outer and inner surfaces of the tube stock, providing bending (molding) to the specified parameters.

Figure 2 - the second diagram characterizes the caliber of incomplete coverage or contact. Such gauges include, first of all, open gauges located in the composition of the molding mill in front of the closed stand section. A characteristic feature of this caliber is that the upper roll 1 is quite narrow and contacts the inner surface of the workpiece 3 at a limited width, which decreases with increasing angle of the workpiece molding. The lower 2 and side rolls 4 are in contact with the outer surface of the tubular billet, as shown in figure 2, while the distributed load q is applied to the contact sections of a certain width of the billet.

Figure 3 - the third diagram, typical for closed gauges with a split washer 5. In such calibers, the contact of the workpiece 3 with the upper 1 and lower 2 and side 4 rolls occurs only on its outer surface and the ends of the pipe workpiece and the distributed load q is applied only to parts of the outer surface.

The developed technique allows you to take into account many important technological factors:

- numerous types of calibrations of the technological tool;

- dimensions of profile rolls that determine the size of the caliber, type of caliber (full coverage, incomplete, closed, etc.);

- mechanical characteristics of the material of the tubular billet, affecting the magnitude of the stress-strain state.

Horizontal rolls, the radius of curvature of which in the molding mill is gradually decreasing, fold the tape into a tube stock with specified geometric parameters, and edger stands prevent the tube stock from springing up and increase bending deformation. Studies of the contact interaction process showed the need to take into account the efforts not only directly in the contact zone of the local deformation zone, but also in non-contact. The length of the non-contact zone was determined as:

where the length of the contact zone is determined taking into account the springing, because the magnitude of the vertical force in the first place, as studies have shown, is influenced by the amount of deformation of the workpiece in the i-th gauge, taking into account the influence of the non-contact zone of the source and the spring zone, which is reflected in the formula.

One of the important factors affecting the magnitude of the vertical efforts of forming, is the coefficient of the molding scheme, which is taken into account in the calculations and varies in the range K _f = 1-3.

In modern production of welded pipes, a wide range of various types of calibrations is used. The existing classification of calibrations used in practice determines the purpose of each type, combines and describes the types of possible transitions of geometric sections along the stands. This classification is quite common and includes five types of calibrations [Machines and assemblies of pipe production: Textbook for Universities / A.P. Kolikov, V.P. Romanenko, S.V. Samusev, etc. - M .: "MISiS", 1998 . - 536 p.].

The values of the coefficients of the molding scheme are determined depending on the calibrations of the technological tool used in practice: for the first type of calibration, Fig. 4, made with one radius R with a central angle φ-K _f = 1; for the second type of double-radius calibration, the coefficient of the molding scheme is 2. For more complex oval vertical calibration schemes, the coefficient of the molding scheme is 3. There are combinations of types of calibrations along the routes from the first to the second type - route 6, from the second to the fourth type - route 7, from the first to the fourth type - route 8. In the reverse order from the fourth to the second type of calibration - route 9.

The components of the longitudinal and transverse plastic deformation of the tubular billet during continuous shaping determine the amount of force required for its implementation. But in a roll gauge rotating from an external drive, a certain priority list of technical factors affects this value both in one local roll gauge and in individual sections of the mill containing several roll gauges.

It is impossible to equalize the molding force in the basic (factory set) open gauges without modernizing the calibration in this section. It is possible to equalize the values of the shaping force for the working stands of open gauges with allowance for geometric deformation factors that determine the geometric parameters and conditions of contact interaction (the value of the contact area between the profiled roll tool and the workpiece). Selecting these parameters according to the developed methodology, it is possible to determine the calibration and overall dimensions of the rolls, ensuring equality of the molding force in the stands.

In stands with a closed caliber profile, the equality of vertical forces is hampered by the fact that the change in the curvature of the profiles and the value of transverse deformations in these stands are insignificant compared with the same parameters in the open gauge section. This is explained by the fact that the main deformation of the bend is carried out in the area of open calibers, and the profile is formed and compliance with the alignment of the process in the area of closed calibers. Accordingly, the values of vertical forces in traditional schemes are always greater in the area of open calibers. To equalize the values of these values is possible only with a change in the deformation pattern of molding in the closed gauge section.

To ensure the required amount of additional molding effort in closed gauges, it is proposed to use the cold reduction process in closed gauges, which will improve the quality of forming the workpiece profile due to precise contact over the entire width, ensure alignment of the forming process, a given angle of convergence of the edges and, most importantly, the identity of the values vertical molding efforts for all stands of the molding mill. To do this, it is necessary to propose a methodology for calculating the value of the value of additional reduction for closed gauges, and it is proposed to determine these values as follows:

- дополнительное усилие редуцирования в i-клети, [н]; S_m - толщина заготовки, [мм];

- ширина заготовки после редуцирования в i-клети, [мм], Δε_i - величина деформации гиба в i-той клети, определяется как разность деформаций в i-том и в (i-1)-м калибре с учетом распружинивания: Δε_i=ε_i-(1-β)ε_i-1 Where

- additional reduction force in the i-stand, [n]; S _m - the thickness of the workpiece, [mm];

- the width of the workpiece after reduction in the i-stand, [mm], Δε _i is the amount of bending deformation in the i-th stand, is defined as the difference in deformations in the i-th and in the (i-1) -th gauge, taking into account the springing: Δε _i = ε _i - (1-β) ε _i-1

where β is the coefficient of springing.

The values of the radii of curvature at the transition section of open calibers were selected in the specified range of values (1.45-4.25) R _{wel. node} , while the forming radii gradually decrease from a larger range to a smaller one. The extreme values of the range are established experimentally, the research results are presented in table No. 1.

Concrete example

Strip forming was carried out in the eight-stand molding mill TESA 42-168 at the Volgorechensky pipe plant using technological tools with factory calibration. The existing factory calibration of the technological tool for a pipe with a diameter of 159 × 10 mm is given in table No. 2

Table number 2 1st crate 2nd crate 3rd crate 4th crate 5th crate 6th crate 7th crate 8th crate Central radius mm 0 516.5 227.5 154.0 116 98.6 84.8 155.2 Central angle, degrees 0 39.9 89.9 119.9 159.9 94.9 49.9 5.8 Peripheral radius, mm 80.1 80.1 80.1 80.1 80.1 80.1 80.1 80.1 Peripheral angle, degrees 50,0 fifty 49.9 49.9 49.9 one hundred 139.9 175.0 Split washer, mm 0 0 0 0 0 113.3 45.4 13,4

а центрального участка - зависимостью

A graph of the distribution of curvature for the peripheral and central sections of the tube stock is shown in FIG. On the graph, the change in the curvature of the peripheral region is represented by the dependence

and in the central section - by addiction

The roll tool for TESA 42-168 of the Volgorechensk Pipe Plant is shown in Figs. lower rolls; roll diameters along the bottom and flanges for the upper and lower rolls, respectively; widths of the upper and lower rolls.

The dimensions of the factory technological tool for calibration according to table No. 2 are presented in table No. 3.

The roll tool for TESA 42-168 is shown in FIGS. 6-13 with overall dimensions, where φ are the molding angles for the central and peripheral sections of the upper, lower and side rolls, respectively; forming radii R - of the central and peripheral sections of the upper, lower and side rolls; D - diameters on the bottom and flanges for the upper, lower and side rolls. Fig.6, Fig.7 - the upper and lower rolls of an open two-radius caliber full coverage. Fig. 8 is the upper one, Fig. 9 is the lower one, and Fig. 10 is the side roll of an open two-radius caliber of incomplete coverage. FIG. 11 - upper, FIG. 12 - lower, Fig - side rolls of closed caliber.

The data for calculating the vertical efforts of forming on the working stands of the molding mill according to tables No. 2 and No. 3 are presented in table No. 4.

Table No. 4. 1st crate 2nd crate 3rd crate 4th crate 5th crate 6th crate 7th crate 8th crate Radius at the edge of the tube stock (lower roll), mm 172.8 224.9 261.5 255.5 178.3 174.8 171.1 171.8 Caliber profile height (upper roll), mm 26.8 75.7 62.8 60.6 30.7 9.8 20,2 23.1 The maximum length of the contact of the edge with the lower roll, mm 25.1 47.2 63.6 61.3 26.8 24.5 22.0 21.9 The maximum length of the contact of the edge with the upper roll, mm 25.0 49.6 45.3 48.1 34.3 5.1 13.8 20.7 The area of contact with the lower roll, mm ² 905.6 4843.9 6873.8 5837.6 1197.1 936.7 711.2 698.7 The area of contact with the upper roll, mm ² 5967.7 9718.8 5881,2 5096,0 2240.1 41.2 288.2 620.3 The force of forming the lower roll, N 17404.3 14647.1 41,986.7 43,720.7 7338.9 4557,0 1909.0 365.8 Forming force of the upper roll, N 16877.5 14046.6 34374.0 35187.9 6719.0 4591.9 1909.0 365.8 The total force of forming in the stand, N 34282 28690 76236 78900 14060 9150 3800 720

In accordance with the obtained data of the total molding force, Fig. 15 shows the dependence: the distribution of the total value of the molding force over the stands of the molding mill for the basic (factory) set of the technological tool, where in the 1st stand the force is 34282 N, in the 2nd stand - 28690 N, in the 3rd stand - 76236 N, in the 4th stand - 78900 N, in the 5th stand - 14060 N, in the 6th stand - 9150 N, in the 7th stand - 3800 N and in 8 -th stand - 720 N.

On the basis of the developed method and the initial calibration tables, the dimensions of the tool, we make a change - the selection of the curvatures of the sections of the tube stock according to the method developed above to ensure an identical value of the vertical force of forming in the working stands.

To achieve this goal, the factory calibration of the tool was adjusted. The modernized calibration of the technological tool for a pipe with a diameter of 159 × 10 mm with a changed curvature in the corresponding sections of the gauges of the working stands is presented in table No. 5.

Table No. 5. 1st crate 2nd crate 3rd crate 4th crate 5th crate 6th crate 7th crate 8th crate Central radius mm 2000 516.5 301.6 240.3 116 98.6 84.8 80.1 Central angle, degrees 10 39.9 67.8 76.8 159.9 94.9 49.9 351 Peripheral radius, mm 80.1 80.1 80.1 80.1 80.1 80.1 80.1 80.1 Peripheral angle, degrees 50,0 fifty 49.9 49.9 49.9 one hundred 139.9 175 Split washer, mm 0 0 0 0 0 114.7 47.2 15.0

- изображено сплошной линией и характеризует постоянную кривизну в 1 и 2 открытых клетях и 6-7 закрытых клетях, кривизна периферийного участка в 3, 4 и 5 открытых клетях равна кривизне центрального участка трубной заготовки

в соответствующей клети до величины (1,45-4,25) R_{свар. узла}. Кривизна центрального участка трубной заготовки при непрерывной формовке монотонно возрастает от1 формовочной клети до значения кривизны в сварочном узле равной

The curvature distribution graph for the upgraded calibration is shown in FIG. The distribution of the curvature of the peripheral sections of the pipe billet

- is shown by a solid line and characterizes the constant curvature in 1 and 2 open stands and 6-7 closed stands, the curvature of the peripheral section in 3, 4 and 5 open stands is equal to the curvature of the central section of the pipe billet

in the appropriate stand to a value of (1.45-4.25) R _{weld. node} . The curvature of the central section of the tube billet during continuous molding monotonically increases from 1 molding stand to the curvature in the welding unit equal to

The dimensions of the technological tool for the modernized calibration according to table No. 5 are presented in table No. 6.

The data necessary for calculating the vertical force of forming on the working stands of the molding mill according to the developed method (tables No. 4 and No. 5) are presented in table No. 7 and in Fig.16. On Fig - presents the distribution of the total value of the molding efforts on the stands of the molding mill for the developed production method, where in the 1st stand the force is 28710 N, in the 2nd stand - 28820.7 N, in the 3rd stand - 29290 N , in the 4th stand - 29150 N, in the 5th stand - 29000 N, in the 6th stand - 28900 N, in the 7th stand - 28818 N and in the 8th stand - 28710 N; distribution of the total value of the molding force in the stands for the base (factory) set - dashed line; distribution of the total value of the molding force in the stands for the developed set in accordance with the proposed method for the production of pipes - solid line; additional values of molding force from reduction in working stands (additional value of molding force equal to 14000 N in the 3rd transitional stand between stands with open and closed gauges is achieved by modernized calibration and overall dimensions of profiled rolls; in the 6th stand - Δ ₆ = 19751 N, in the 7th stand - Δ ₇ = 25000 N, in the 8th stand - Δ ₈ = 27978 N).

Table number 7. 1st crate 2nd crate 3rd crate 4th crate 5th crate 6th crate 7th crate 8th crate Radius at the edge of the tube stock (lower roll), mm 172.8 224.9 247.1 251.0 178.3 174.8 171.1 171.8 The maximum length of the contact of the edge with the lower roll, mm 42.1 47.2 58.2 59.6 26.8 24.5 22.03 21.9 The maximum length of the contact of the edge with the upper roll, mm 35.0 49.6 37.7 35,4 34.3 5.1 13.8 20.71 The area of contact with the lower roll, mm ² 5123,4 4843.9 6260.6 6104.6 1197.1 936.8 711.2 698.7 The area of contact with the upper roll, mm ² 3867.8 9718.9 4724.7 3449.6 2240.1 41.27 288.2 620.3 The force of forming the lower roll, N 16776 14610.1 17600 17563.7 15150.8 4557,0 1909.0 365.9 Forming force of the upper roll, N 11934 14109.6 11690 11586.3 13849.5 4591.9 1909.0 365.8 Reduction Force - - - - - 19751 25000 27978 The total force of forming in the stand, N 28710 28820.7 29290 29150 29000 28900 28818 28710

Claims (1)

A method for the production of electric-welded straight-seam gas-and-oil-pipe pipes, comprising bending a pipe billet according to a two-radius folding scheme, in which the peripheral sections of the billet are bent in profiled gauges with a working stand with a radius less than or equal to the radius of the central section along the entire length of the molding mill, and the central section of the billet is bent with a monotonously decreasing radius of the profile calibers from the value of (20-30) R _{weld site} to R _{weld site} , characterized in that the bending of the peripheral sections of the workpiece in p The first open gauges of full coverage and in all closed gauges of the mill are produced until the radius of the welding unit is _obtained (R weld node), and at the transition from open to closed gauges, the radius of molding of the peripheral section is increased to the radius of molding of the central section in the corresponding stand to the value ( 1.45-4.25) R _{weld site} , while the values of the shape-changing force for all working stands are identical due to the design and size of the profiled roll calibers, and the shape-changing force is determined by the shape mule

- for open calibers and

- for closed gauges, Where

- the effort of forming in the i-th stand, [n];

- stress on the outer surface of the strip, determined from the diagram of true stresses, [MPa]; S _m - the thickness of the workpiece, [mm]; B _i - the width of the workpiece in contact with the rolls, [mm];

- the length of the non-contact zone of deformation in the ith caliber, [mm]; To _f - the coefficient of the molding circuit, equal to 1-3; m _i is the width of the i-th caliber, [mm];

- the full perimeter of the workpiece in the i-th closed stand, [mm]; Δε _i is the value of bending deformation in the i-th stand, is defined as the difference of deformations in the i-th and (i-1) -th gauges taking into account the springing: Δε _i = ε _i - (1-β) ε _i-1 , where β is the coefficient of springing.

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