RU2040988C1 - Method of making welded straight-seam tubes - Google Patents

Abstract

FIELD: metal pressure forming. SUBSTANCE: method, providing lowered twisting of longitudinal butt of a tubular blank, comprises steps of lateral bending of an initial crescent-like blank, having concave and convex edges, along shaping transitions in rolls; twisting the blank at least in first intertransition zone around the concave edge with simultaneous applying to it a cross compression effort at a side of its convex edge in such a way, that a value of twisting deformation is no more, than an elastic deformation value of a material of the blank. EFFECT: enhanced quality of straight-seam welded tubes due to lowered twisting of their longitudinal butt upon making process. 1 cl, 9 dwg, 3 tbl

Description

 The invention relates to the processing of metals by pressure of sheet material using rolls of a special form and is intended for use in ferrous metallurgy, metal-consuming industries and construction in the manufacture of longitudinal welded pipes.

 In the production of longitudinal welded pipes, the initial rolled billet is used, according to the standards GOST 19903-74 "Hot-rolled sheet steel" and GOST 19904-74 "Cold-rolled sheet steel". The crescent shape of such steel supplied in rolls should not exceed 10 mm over a length of 3 m. When forming welded pipes from the sickle-shaped initial billet, they are twisted relative to the longitudinal axis, which makes it impossible to weld the edges with a seam and results in defective pipes due to poor quality weld. The quality of the pipes is further deteriorated when using loose strips, the edges of which often have burrs formed when the rolls are dissolved.

 A known method of manufacturing welded longitudinal pipes in roll molding calibers of horizontal and vertical design, according to which the operation of gradual bending of a strip along an arc of a circle of variable radius along transitions is applied, until the edges come into contact with their subsequent welding.

 A significant disadvantage of the analogue is that its use in the manufacture of welded straight-line pipes from sickle-shaped initial billets does not provide the proper quality of the pipe billets due to the non-parallelism of their edges and twisting of the longitudinal joint of the edges of the pipe billets relative to the axis of the welding gauge. This, in turn, makes it impossible to high-quality welding of the strip edges with a straight seam. This drawback is due to the absence of such a scheme of the deformed state of the strip metal, which would contribute not only to compensating for the lack of shape of the initial billet, but also to eliminating its crescent shape in the process of forming longitudinal pipes.

 There is also known a method of manufacturing an electric-welded straight-seam pipe, according to which, in order to improve the quality of the weld by eliminating the twisting of the tube billet, it is formed into an oval shape with a slot located symmetrically with respect to the vertical axis of the billet. The workpiece is formed with unequal perimeters of the parts of the workpiece, separated by the horizontal axis of the cross section of the workpiece, is also formed in the form of a profile asymmetric with respect to the horizontal axis of its section. Due to the asymmetry of the workpiece being formed relative to the horizontal and vertical axes, some prevention of the workpiece torsion, alignment of the longitudinal seam is possible, however, the crescent shape of the initial strip billet is not eliminated, which sharply reduces the quality of the weld of the finished pipe.

 Closest to the technical essence of the invention is the prototype method of continuous strip forming into a tube stock, selected according to which, in order to improve the quality of the pipe weld by preventing the longitudinal joint of the edges of the tube stock from twisting relative to the axis of the welding gauge simultaneously with the transverse bending of the strip in the stands of the molding mill a tension adjustable over the width of the strip is applied to the tube stock, and after the bending operation, additional resistance is created by the force tension by expanding the more extended edge of the strip.

 The disadvantage of the prototype is that its use in the manufacture of welded straight-seam pipes from sickle-shaped billets does not provide the proper quality of pipe billets due to the non-parallelism of their edges and twisting of the longitudinal joint of the edges of the pipe billets relative to the axis of the welding gauge, which makes it impossible to high-quality welding of the strip edges with a straight seam.

 The task of obtaining high-quality straight-seam pipes when using calibration of pipes with two radii is especially difficult (the extreme sections are of a small radius equal to the radius of the pipe and constant in all calibers, and the central section, constructed with a radius constant in this stand and gradually decreasing from stand to stand). Using this calibration, it is extremely difficult to prevent the longitudinal curvature of the workpiece.

 The invention is aimed at solving the problem of reducing the twisting of the longitudinal joint of a pipe billet during its bending along the transitions in the manufacture of welded longitudinal seam pipes from the original sickle-shaped strip.

 To solve the problem in a method for manufacturing longitudinal welded pipes, including transverse bending along forming transitions in the rolls of the original sickle-shaped workpiece with convex and concave edges, the workpiece is twisted around a concave edge at least in the first transitional section with the simultaneous application of a transverse compressive force of its side of the convex edge . The magnitude of the twisting strain does not exceed the amount of elastic deformation of the workpiece material.

 In this case, the task is solved by creating between two bends of the workpiece such a deformation state of the metal, in which, after the next bending, the sickle shape of the workpiece is reduced or completely compensated.

 Performing at least at the first transition junction twisting the workpiece around a concave edge and simultaneously applying a transverse compressive force from the convex edge side provides conditions for partial or final straightening (reduction of the crescent shape) of the workpiece. In this case, the set value of twisting deformation, not exceeding the amount of elastic deformation of the workpiece material, is necessary to prevent the loss of stability of the edges.

 This is ensured by the complex stress-strain state of the metal arising from the action of torsion forces, transverse compression and longitudinal tension. If the one-time creation of the specified stress-strain state before one forming transition does not compensate for the crescent, then it is repeated before the next and so on transition.

 Thus, a new technical result is ensured: the creation of a stress-strain state before bending the workpiece in which, after bending, the crescent decreases or is completely compensated.

 In the manufacture of a tube billet from a crescent-shaped initial strip, twisting of its contact edges relative to the longitudinal axis usually occurs, due to the asymmetry of the metal distribution over the strip cross-section with a symmetrical application of molding forces.

 To obtain a tube billet of the required quality, it is sufficient, in principle, to provide a symmetrical arrangement of the strip (along its entire length) with respect to the axis of molding. In the prototype method, this is achieved by twisting the tube stock in two opposite directions directly in the process of forming pipe bending.

 However, in this case, the curled tube billet is pinched by the forming rolls and the rib dressing of the bent tube billet becomes ineffective, especially when the crescent exceeds 2 mm per 1 m of the length of the initial billet.

 The most appropriate method to prevent twisting of the longitudinal seam of the tube stock is to bend it from an almost flat (not sickle-shaped) initial strip. The elimination of the crescent for this is carried out in time intervals between the forming flexible by vertical displacement of vertical non-driven rolls.

In this case, the force P is applied vertically by a non-drive roller from the side of the convex edge. At the same time, the workpiece is affected (in addition to the forming bending forces) by the tangential torsional force P ₁ , compressing the radial (transverse) force P ₂ , aimed at eliminating the crescent shape and the longitudinal tensile axial force P ₃ , caused by the cross-brace tension of the strip and the torsional force P ₁ . Such an effect of efforts when forming the initial strip creates a “torsion-tension” condition for deformation that is more effective in influencing the elimination of sickle shape in comparison with the known “bending-tension” condition for straightening smooth bands. But the first of them more accurately straightens and prevents the appearance of the crescent of the original strip between the forming transitions, which more effectively aligns the straightness and quality of the longitudinal welds of welded pipes. Moreover, the joint use of bending-tensioning and twisting-tensioning systems allows to obtain high-quality longitudinal pipes from the original strips with a sickle-shaped variable in length.

.Thus, when molding according to two-radius or single-radius calibrations of welded straight-line-seam pipes with a small wall thickness (S ≅ 4 mm) according to the proposed method, initial strips with widely varying specific crescent shape (0.3.1.4) x can be used

.

 According to this method, forces are applied to the convex and concave edges of the workpiece, providing a torsional-tension condition, and when crescent is eliminated, an additional bending-tension effect is used to prevent tearing and the appearance of corrugations at the edges. This is ensured by the self-regulating effect of the created stress-strain state of the metal when editing the sickle-shaped strip, carried out by the action of twisting, bending and tensile forces.

 According to the information available to the applicant in the known solutions there are no signs similar to those that distinguish the claimed technical solution from the prototype, which allows us to conclude that it meets the criterion of "inventive step".

< 1, достаточно прикладывать к деформируемой полосе скручивающее усилие в одном межклетьевом промежутке, а при

> 1, необходимо, как правило, выполнять скручивание и перед другими переходами.When using the original bands with a crescent not exceeding the permissible deviations

<1, it is sufficient to apply a torsional force to the deformable strip in one inter-stand space, and when

> 1, it is necessary, as a rule, to perform twisting before other transitions.

(1) где D/S показатель, характеризующий размеры трубы;
D и S соответственно диаметр и толщина стенки трубы, мм;
α_c В и gZ показатели, характеризующие величину смещения вертикального валка при кручении заготовки;
В ширина заготовки перед скручиванием, мм;
g удельная серповидность;
g 0,00 Δ,
Δ среповидность, мм;
Z очаг скручивания сгибаемой полосы (расстояние между смежными клетями с вертикальными и горизонтальными валками), мм.The method allows to reduce not only one-sided crescent, but also a variable along the length of the workpiece, which is achieved by shifting the rolls of the vertical stand in the first interstitial gap, first on one side, and in the next interstitial gap on the other side of the workpiece edge. In this case, the total twist angle of the workpiece α _c , ensuring the elimination of its crescent, is determined experimentally from the mathematical expression
α _c =

(1) where D / S is a measure of pipe dimensions;
D and S, respectively, the diameter and wall thickness of the pipe, mm;
α _c B and gZ are indicators characterizing the amount of displacement of the vertical roll during torsion of the workpiece;
In the width of the workpiece before twisting, mm;
g specific crescent;
g 0.00 Δ,
Δ strepovost, mm;
Z the center of twisting of the bent strip (the distance between adjacent stands with vertical and horizontal rolls), mm.

 The value of the total torsion angles necessary to eliminate the existing sickle shape Δ in the initial workpiece are given in Table 1.

The permissible one-time twist angle α _{g is} ensured during elastic deformation from the condition of preventing loss of stability of the edges, preventing their plastic deformation and the appearance of cracks.

(2)
τ_д=

(3) где М_кр и Р_кр крутящий момент и усилие скручивания.Permissible twists and shear stresses
α _d =

(2)
τ _d =

(3) where M _cr and P _cr torque and twisting force.

(5) При α_c≅ α _g серповидность устраняется разовым скручиванием заготовки в одном межклетьевом промежутке.P _cr P / cosα _g ; P _{compression channel} P˙sinα _g; P and P _SJ force moving the roller and the laterally-pressing the workpiece;
L center of twisting;
and 0.32 coefficient characterizing the moment of inertia Ik and the moment of resistance W _k when twisting;
G 8˙10 ³ , kg / mm ² modulus of elasticity;
B and S width before twisting and thickness of the workpiece. From expression (3)
P _{cr cr g g} S ² , (4) substitute in the formula (2)
α _d =

(5) When α _c ≅ α _g, crescentness is eliminated by single twisting of the workpiece in one inter-stand gap.

For α _c > α _g, elastic twisting is performed in more than one inter-stand gap (inter-transition section) in order to eliminate crescent shape and provide conditions for preventing loss of edge stability.

 Values of permissible tangential stresses of various steel grades are given in Table 2.

 The analysis of the proposed method for the manufacture of welded straight-line pipes indicates that the method is industrially applicable when used on a conventional pipe bending mill. A positive effect during the implementation of the invention will be obtained due to the possibilities of using sickle-shaped Δ (0.3-1.4) S strip blanks and obtaining high-quality longitudinal pipes from them by performing technological torsion in the intermediate transitions of the bent strips.

 Figure 1 shows a diagram of the implementation of the proposed method; figure 2 section aa in figure 1; figure 3 view along arrow B in figure 1; 4-7 diagrams of torsion stresses and deformation forces; on Fig diagram of the direction of compressive forces along the edge; Fig.9 is a diagram of the formation of the tube billet transitions.

со стороны выпуклой кромки 8, где φ₂ угол подгибки кромок. При этом усилие смещения Р вертикального валка 6 раскладывается на усилие скручивания Р₁, и радиального валка 6 раскладывается на усилие скручивания Р₁, и радиального перемещения Р₂. Величина деформации скручивания между отдельными переходами не превышает величину упругой деформации материала заготовки.According to this method, the manufacturing process of welded straight-seam pipes includes transverse bending along the forming transitions I-XIII in rolls 1-6 of the original shear billet 7 with convex 8 and concave 9 edges. Wherein at least the first portion mezhperehodnom between transitions I and III preform 7 twisting force F ₁ at an angle α in the direction F to a position 10 around the concave edges 9 with simultaneous application of a compressive force F _{compression channel}

from the side of the convex edge 8, where φ _{2 is the} angle of the hem edges. In this case, the displacement force P of the vertical roll 6 is decomposed into the twisting force P ₁ , and the radial roll 6 is decomposed into the twisting force P ₁ , and the radial displacement P ₂ . The magnitude of the twisting strain between the individual transitions does not exceed the magnitude of the elastic deformation of the workpiece material.

Forming with a flexible tube billet 11 was carried out relative to the axis of molding 10 by two-radius calibration with the bending radii R in the middle and r along the edges with bending angles φ ₁ and φ _2, respectively, at transitions I-XIII, then the edges are welded with a longitudinal seam 13. In this case, the transverse compressive force P _Compresses are applied within the elastic deformation until a symmetrical arrangement of the edges of the pipe billet 11 is obtained in the cross section XIII in the last forming transition 11. Elimination of the crescent shape Δ is carried out as a result of the action on the workpiece 7 transverse compressive and tensile _{compression channel} P ₃ P effort roll tension. The value of the total twist angle α _c is determined from the mathematical expression. The bending angle β along the length of the deformation zone L is determined depending on the displacement h of the vertical roll
tg β h / L (6).

 The inventive method can be carried out using a device containing a set of horizontal drive and vertical non-drive rolls.

So, for example, the manufacture of a welded pipe with a longitudinal weld with a diameter of D = 42.3 mm from mild steel St3 used an initial billet with a width of V _zag 128 mm (V 125 mm), a thickness of 3.2 mm with a specific crescent g 0.003 (Δ mm).

Pipe forming was carried out on a 2.4 x 60 250 pipe-welding unit with a span distance of 600 mm (L 300 mm). For forming the tube was applied dvuhradiusnaya calibration rolls in the forming plane of the first transition of the master I possessed crescent initial preform _zag width B of 128 mm symmetrically relative to the molding axis. The first predetermined transition is executed only hem edges at an angle φ ^of 45 °. Then, between adjacent transitions preform twisted around the concave edges 9 with simultaneous application of transverse compressive force F _with convex side edges 8, which was accomplished by vertical displacement of the vertical grooved roll 6 by an amount h.

 The total and permissible torsion angles of the sickle-shaped workpiece were determined by formulas (1) and (5).

5,5^°;
α_д=

10,1^°; т.е. при α_c < α_g серповидность заготовки (Δ 3,0 мм) устраняли путем ее скручивания в одном межклетьевом промежутке.α _c =

5.5 ^° ;
α _d =

10.1 ^° ; those. at α _c <α _{g, the} crescent shape of the preform (Δ 3.0 mm) was eliminated by twisting it in one inter-stand space.

 In rough transitions II-XII, the workpiece was bent in the transverse direction along a two-radius curve with an increase in the bending angle according to regime 90; 120; 150; 180; 210; 240; 270; 290; 310; 326; 344; 350; 360.

 Moreover, in all rough passages, it was bent in the transverse direction by two radii, of which the radius r of the extreme sections of the strip is equal to the radius of the formed pipe, and the central radius R is variable, decreasing from one molding stage to another until the edges come into contact and the pipe billet 11 and the thirteenth rough transition. The values of the radii and bending angles are given in table.3.

 According to the claimed method, there was no twisting with respect to the longitudinal axis on the finished pipe billet made of the original billet with a crescent Δ3.0 mm, and the edges were parallel.

 In the thirteenth technological transition, the edges of the strip were welded with a longitudinal seam 13 and a welded round pipe with a diameter of D 42.3 mm was obtained.

 When using the original workpiece with a relatively high sickle shape (Δ> S), the removal of the sickle shape sometimes has to be performed more than before one rough transition.

For example, in the manufacture of welded longitudinal pipes with a diameter of 42.3 mm, thickness 3.2 mm mild steel St10 another source has been used in _room preform width 128 mm (125 mm) having a specific sickle g 0,0045 (Δ 4, 5 mm). Forming and twisting of the workpiece was performed on the same mill.

8,2^°.The total and permissible torsion angles of the sickle-shaped workpiece had the following values
α _c =

8.2 ^° .

7,4^°, т.е. при α_c > α_g серповидность заготовки (Δ 4,5 мм) следует устранить за два приема в двух межпереходных промежутках первом и втором.α _d =

7.4 ^° , i.e. at α _c > α _{g, the} crescent shape of the workpiece (Δ 4.5 mm) should be eliminated in two steps in two transitional spaces of the first and second.

The twist angles were set equal to 4.1 ^about , compensating for the magnitude of the crescent at first to Δ 2.25 mm, then eliminating the crescent shape finally. The pipe was formed using the same calibration as in the previous example. The resulting pipe met all the specified requirements.

To compare the quality, a pilot billet for a round welded pipe with a diameter of D42.3 mm and a thickness S of 3.2 mm was made from a sickle-shaped initial billet with a width of B _zag 128 mm with a specific crescent g 0.003 according to the prototype method according to the mode: 60-90-120 -150-180-220-285-296-340-360. Moreover, in the penultimate transitions, the tube stock was twisted relative to the longitudinal axis, first in one direction, then in the other, within the limits of elastic deformation. At the finished tubular blank curling was observed, reaching 2-2.5 ^about 1 m length, which excluded the possibility of quality welding interlocking edges straight seam-welded pipe and reception.

Claims (1)

 METHOD FOR PRODUCING WELDED RECTANGULAR PIPES, including transverse bending along forming transitions in sickle-shaped rolls, characterized in that at least in the first transitional section the workpiece is twisted around a concave edge with a simultaneous application of transverse compressive force from the convex edge side, while the amount of twisting deformation is not exceeds the amount of elastic deformation of the workpiece material.

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