RU2006310C1 - Method for production of electric-welded pipes and machine therefor - Google Patents

Abstract

FIELD: metal pressure shaping. SUBSTANCE: method for production of electric-welded pipes includes joining of individual rolls into continuous strip; flexing of the latter with tensioning in driverless multiple roll bending and tensioning device; drawing the strip through the latter by pulling device; forming of the strip into skelp; welding of skelp edges; sizing of skelp into a finished pipe. The new feature is that maximal strip curvature value by its bending around the bending rolls is determined as a function of the processed strip thickness, minimal strip thickness from the machine assortment, minimum and maximum allowable bending deformation values for the outer layer, and is calculated from a mathematical dependence. Machine for production of steel pipes includes successively installed device for joining the rolls into continuous strip, bending and tensioning device, pulling and forming device, welding unit, and sizing assembly. The bending and tensioning device is provided with K sets of bending rolls of different diameters; the roll diameters for the L-th set are determined from a mathematical dependence. Furthermore, the bending rolls in the bending and tensioning device are enveloped by the strip in pairs, with changing of the strip curvature sign between the said pairs only. EFFECT: increased pipe welding machine output; increased quality of the pipes produced; decreased metal consumption by pipe production. 3 cl, 3 dwg, 1 tbl

Description

 The invention relates to the processing of metals by pressure and can be used in the manufacture of welded pipes of small and medium diameters.

 A known method of rolling a continuous strip in the manufacture of welded pipes, including the docking of the rolls into a continuous strip, rolling-calibration of the strip, molding of the tube stock, welding and calibration of the pipe. The method makes it possible to reduce the crescent shape of the initial strip and, consequently, the molding defects associated with it by controlling the magnitude of the reduction in strip thickness during the rolling-calibration process. In addition, due to rolling with compression of 5 - 10%, metal savings of up to 50 kg / t are achieved when pipes are delivered by theoretical weight.

 The disadvantage of this method is that due to the uneven width of the wear of the rolls, leading to increased compression of the edge sections, the quality of the weld is sharply reduced.

 A known method of manufacturing welded pipes, which includes welding individual rolls into a continuous strip, its alternating plastic bending in the vertical plane and bending in the horizontal plane, forming the strip into a pipe billet and welding its edges [1].

 Alternating bending of the strip is carried out by rollers with flanges of the bending and tensioning device (GNU), the axes of which are located in the same horizontal plane, with simultaneous stretching of the strip, which is provided by the braking effect of the GNU and the pulling force of the forming mill. As a result, the strip is elongated by reducing its thickness. Due to the fact that, in the first place, shorter longitudinal fibers are lengthened, and also under the influence of flanges, the sickle shape of the treated strip is reduced.

 A well-known mill for the production of electric welded pipes, containing sequentially installed device for docking rolls in a continuous strip, non-driven stand with cylindrical upper and lower rolls, tension units containing cylindrical non-driven rollers located at the inlet and outlet of the non-driven stand, forming stands and welding unit. The upper roll of the non-driven stand and the rollers of the tensioning devices are made with beads [1].

 Five-fold bending and bending of the strip in a vertical plane (alternating bending) is carried out in the rollers of the tension units and rolls of the non-drive stand. As a result of this bending, the strip receives an elongation of about 2%. When passing through the cage, the continuous strip is crimped by a value of the order of 0.2 - 0.5%. In the presence of the original rib curvature, it is corrected by bending the strip in the horizontal plane in the flanges of the tension unit rollers and the closed stand gauge.

 The aim of the invention is to increase the productivity of the pipe-welding unit, the quality of the manufactured pipes and reduce the metal consumption for their production by eliminating the longitudinal thickness variation and crescent shape of the continuous strip - billet.

, где N $\genfrac{}{}{0ex}{}{\text{мак}}{\text{изг}}$ ^с - максимальная кривизна полосы;

и

- соответственно минимально и максимально допустимые деформации изгиба наружного слоя; h - толщина обрабатываемой полосы; h_мин - минимальная толщина полосы в сортаменте агрегата; при этом в выражении для степени используют его целую часть, а после сварки кромок производят калибровку в готовую трубу.
Предлагаемый способ осуществляется с помощью агрегата, содержащего последовательно установленные устройство для стыковки рулонов в непрерывную полосу, гибочно-натяжное, тянущее и формовочное устройства, а также сварочный узел.This is achieved by the fact that in the method for the production of electric-welded pipes, including the joining of individual rolls into a continuous strip, its alternating plastic bending with tension in a continuous multi-roller bending and tensioning device, pulling the strip through it with a pulling device, forming the strip into a tube billet and welding its edges, according to the method, the value of the maximum curvature of the strip during its alternating bending is set as a function of the thickness of the processed strip, the minimum thickness of the strip from the assortment of the unit, minimum and maximum allowable bending deformations of the outer layer and is determined by the formula: N $\genfrac{}{}{0ex}{}{\text{poppy}}{\text{outcast}}$ ^c =

where N $\genfrac{}{}{0ex}{}{\text{poppy}}{\text{outcast}}$ ^c is the maximum curvature of the strip;

and

- respectively, the minimum and maximum allowable bending deformation of the outer layer; h is the thickness of the processed strip; h _min - the minimum thickness of the strip in the assortment of the unit; at the same time, in the expression for the degree, its integer part is used, and after welding the edges, they are calibrated into the finished pipe.
The proposed method is carried out using an assembly containing sequentially installed device for docking rolls into a continuous strip, a bending-tensioning, pulling and forming device, as well as a welding unit.

+1 , а диаметр роликов i-ого комплекта определяют по выражению:
d₁=

, i = 1, . . . , K, где d_i - диаметр роликов i-ого комплекта; h_макс - максимальная толщина полосы в сортаменте агрегата. При этом в гибочно-натяжном устройстве гибочные ролики меньших диаметров установлены с возможностью попарного изгибания полосой с изменением знака кривизны полосы только между парами. Агрегат снабжен калибровочным узлом, установленным за сварочным.The bending and tensioning device is made in the form of K-sets of bending rollers of various diameters, where K =

+1, and the diameter of the rollers of the i-th set is determined by the expression:
d ₁ =

, i = 1,. . . , K, where d _i is the diameter of the rollers of the i-th set; h _max - the maximum thickness of the strip in the assortment of the unit. Moreover, in the bending and tensioning device, bending rollers of smaller diameters are installed with the possibility of pairwise bending by a strip with a change in the sign of strip curvature only between pairs. The unit is equipped with a calibration unit installed behind the welding unit.

 The invention consists in the following.

The process of alternating bending with tension, carried out by bending a strip of rollers of a bending-tensioning device, allows to achieve elongation of the strip, and due to this reduction, its crescent and longitudinal thickness variation. Moreover, the greatest impact on the main process parameters, such as the maximum possible elongation of the strip in the GNU ε _max , the tension force in the strip T _max and the force on the rollers P _max , is exerted by the bending strain of the outer layer of the strip
_mfd ε = 2hN, (1) where h - the thickness of the strip; N is its maximum curvature on the GNU bending roller.

до

, интервал толщин полос от h_мин до h_максразбивают на подынтервалы [h_мин; h₁] , [h₁; h₂] , . . . , [h_k-1; h_макс] . Полосы из каждого i-ого подынтервала по толщине подвергаются знакопеременному изгибу с фиксированной величиной максимальной кривизны Ni, которая определяется следующим образом.In order to ensure the deformation of the strip of any thickness from the assortment of the aggregate within the rational range of bending deformations from

before

, the interval of thicknesses of the strips from h _min to h _{max is} divided into subintervals [h _min ; h ₁ ], [h ₁ ; h ₂ ],. . . , [h _k-1 ; h _max ]. The stripes from each i-th subinterval in thickness are subjected to alternating bending with a fixed value of the maximum curvature Ni, which is determined as follows.

. Отсюда N₁ =

. (2)
Поскольку все полосы из этого подынтервала толщин должны подвергаться изгибу с одинаковой максимальной кривизной N₁, а деформация изгиба наружного слоя не должна превышать

, то верхняя граница первого подынтеравала толщин h₁ определится из условия
ε_изг = 2h₁N₁ =

, откуда h₁ =

, или с учетом (2) h₁ =

. (3)
Рассуждая аналогично, для второго подинтервала толщин [h₁; h₂] получим
N₂ =

, h₂ =

, а для i-ого интервала [h_i-1; h_i] N_i =

, h_i =

. (4)
Для определения в какой подынтервал по толщинам попадает полоса толщиной h, воспользуемся соотношением
h ≅

[h_i] или с учетом (4)
h ≅

h

Выполнив преобразования, получим
i ≥

, или с учетом того, что i является целым числом
i =

+ 1, (5) причем от дроби оставляем только целую часть числа.For a strip of thickness h _min (the minimum thickness from the first sub-interval [h _min ; h ₁ ]), the condition
ε _ex = 2h _min N ₁ =

. Hence N ₁ =

. (2)
Since all strips from this subinterval of thicknesses must be bent with the same maximum curvature N ₁ , and the bending strain of the outer layer should not exceed

, then the upper boundary of the first subinterval of thicknesses h _{1 is} determined from the condition
ε _ex = 2h ₁ N ₁ =

, whence h ₁ =

, or taking into account (2) h ₁ =

. (3)
Reasoning in the same way, for the second subinterval of thicknesses [h ₁ ; h ₂ ] get
N ₂ =

, h ₂ =

, and for the i-th interval [h _i-1 ; h _i ] N _i =

, h _i =

. (4)
To determine which subinterval for thicknesses a strip of thickness h falls in, we use the relation
h ≅

[h _i ] or in view of (4)
h ≅

h

Having completed the transformations, we obtain
i ≥

, or given that i is an integer
i =

+ 1, (5) whereby from the fraction we leave only the integer part of the number.

до

ее максимальная кривизна в ГНУ должна быть функцией от этих величин, толщина полосы h, а также минимальной толщины из сортамента h_мин и определяется выражением N $\genfrac{}{}{0ex}{}{\text{мак}}{\text{изг}}$ ^с=

. (6)
Обеспечить такую максимальную кривизну возможно применением в ГНУ К-комплектов гибочных роликов с диаметрами
d_i=

, i= 1, . . . K где K =

+ 1, (7)
h_макс - максимальная толщина полосы в сортаменте агрегата.Thus, in order for any strip from the mill gauge to undergo bending deformation in the range from

before

its maximum curvature in the GNU should be a function of these values, the thickness of the strip h, as well as the minimum thickness from the range h _min and is determined by the expression N $\genfrac{}{}{0ex}{}{\text{poppy}}{\text{outcast}}$ ^c =

. (6)
It is possible to provide such maximum curvature by using K-sets of bending rollers with diameters in GNU
d _i =

, i = 1,. . . K where K =

+ 1, (7)
h _max - the maximum thickness of the strip in the assortment of the unit.

;

] зависит, в первую очередь, от требований к качеству поверхности металла, его механических свойств, количества циклов знакопеременной деформации (роликов ГНУ).The rational interval of the process of alternating bending of the strip with tension in magnitude of the bending strain of the outer layer [

;

] depends primarily on the requirements for the surface quality of the metal, its mechanical properties, the number of cycles of alternating deformation (GNU rollers).

определяется из условия отсутствия приспособляемости металла к циклическому пластическому деформированию. При деформации изгиба меньшей некоторого порогового значения знакопеременный изгиб полосы с натяжением не приводит к пластическому удлинению полосы или его удлинение незначительно. Исследования показали, что для материалов, применяемых для производства электросварных труб (углеродистые и нержавеющие стали), таким порогом, а следовательно, и нижней границей рационального интервала для деформации изгиба наружного слоя полосы является значение

= 0,03.Lower bound of interval

is determined from the condition of the lack of adaptability of the metal to cyclic plastic deformation. When the bending strain is less than a certain threshold value, the alternating bending of the strip with tension does not lead to plastic elongation of the strip or its elongation slightly. Studies have shown that for materials used for the production of electric-welded pipes (carbon and stainless steels), this threshold, and therefore the lower limit of the rational interval for bending strain of the outer layer of the strip, is the value

= 0.03.

определяется из условия отсутствия растрескивания поверхности обрабатываемой полосы вследствие малоцикловой усталости. В соответствии с линейной гипотезой накопления повреждений при циклическом пластическом деформировании функция повреждений выражается в виде
П = N

, (8) где П - функция повреждения (П = 0 соответствует "идеальному" начальному состоянию, П = 1 соответствует появлению макротрещины); N - число циклов пластического деформирования; Δε- амплитуда пластической деформации, С и α- коэффициенты, зависящие от механических свойств металла.Upper bound of interval

is determined from the condition that there is no cracking of the surface of the processed strip due to low-cycle fatigue. In accordance with the linear hypothesis of damage accumulation during cyclic plastic deformation, the damage function is expressed as
P = N

, (8) where P is the damage function (P = 0 corresponds to the "ideal" initial state, P = 1 corresponds to the appearance of a macrocrack); N is the number of cycles of plastic deformation; Δε is the amplitude of plastic deformation, C and α are the coefficients depending on the mechanical properties of the metal.

, (9) где Ψ- абсолютная величина относительного сужения при разрыве.It has been found that for carbon and stainless steels
α = 0.5. . . 0.6, C = 0.5ln

, (9) where Ψ is the absolute value of the relative narrowing at break.

= 0,5С([П] /N)^α . (10)
В некоторых случаях (когда, например, не обеспечено прохождение поперечного сечения сварного шва через ГНУ без деформирования) величина

определяется из условия отсутствия разрывов поперечных стыков в гибочно-натяжном устройстве.If we take some allowable damage during alternating bending of the strip with tension [P], then with a known number of deformation cycles N

= 0.5C ([P] / N) ^α . (10)
In some cases (when, for example, the cross-section of the weld through GNU without deformation is not ensured), the value

is determined from the condition that there are no gaps in the transverse joints in the bending-tensioning device.

до

.The method is as follows. The strips rolled up into rolls are unwound, butt-welded into a continuous strip, which is sent to a bending-tensioning device. In GNU, the strip is subjected to alternating plastic bending in a vertical plane with a maximum curvature defined by expression (6). In this case, a set of bending rollers with diameters defined by expression (7) is used. In the GNU, the strip receives the necessary elongation ε, as a result of which the crescent and longitudinal thickness variations are eliminated. When the unit switches to a different thickness of the processed strip, another set of bending rollers is selected according to dependences (6) and (7). As a result, for any strip processed in GNU, the value of its maximum bending strain of the outer layer lies in the range from

before

.

 Through the GNU, the strip is pulled by a pulling device (for example, a rolling stand or a tension station).

 A strip without crescent and longitudinal thickness variations enters the molding mill, which favorably affects the molding of the tube billet and the welding of its edges. At the same time, the quality of manufactured pipes and the performance of TPPA are increased, and metal consumption is reduced.

 In FIG. 1 shows a bending and tensioning device with two sets of bending rollers; in FIG. 2 - GNU with movable roller blocks in the upper position; in FIG. 3 - the same in the lower position.

 The bending-tensioning device (Fig. 1) contains a frame 1, in which the stationary 2 and movable 3 roller blocks are placed. Both movable and fixed roller blocks contain one bending roller of large diameter 4 and 4 'and a pair of bending rollers of small diameter 5 and 5'. The axis of the rollers of one block are stationary relative to each other, and the axis of the bending rollers of small diameter 5 and 5 'of one block lie in one horizontal plane.

 In the initial position (Fig. 1), the vertices of the large bending rollers 4 of the fixed blocks 2 and the small bending rollers 5 'of the movable blocks 3 should be in the same horizontal plane. The possibility of vertical movement of the movable roller blocks 3 up should provide at least the axes of the bending rollers of small diameter 5 and 5 'in the same horizontal plane (Fig. 2), and down - the axes of all the bending rollers of large diameter 4 and 4' in the same horizontal plane (Fig. 3).

 In a bending-tensioning device, bending rollers of small diameters are bent around in pairs with a change in the sign of strip curvature only between pairs.

 The use of a pair of bending rollers, instead of single bending rollers of the same diameter, makes it possible to achieve a better coverage of the rollers by the strip due to a decrease in the gap between the rollers, to reduce the load on the side of the strip by one bending roller by about 2 times, to obtain an elongation of the strip on the pair of rollers 1.85 times greater than the elongation on one roller, while in accordance with (8) the damage increases only by 50%.

The implementation of the invention is shown by the example of the production of pipes from carbon steels with a wall thickness from h _min = 1.5 mm to h _max = 3.5 mm on a pipe-welding unit 10-60.

 To ensure elongation of a strip of any thickness from the assortment of at least 2%, necessary to eliminate crescent and longitudinal thickness differences, a bending and tensioning device with seven bending blocks is installed in the line of the unit (Fig. 1).

= 0,03 определена из условия отсутствия приспособляемости полосы при знакопеременном изгибе с натяжением.Value

= 0.03 is determined from the condition of the lack of adaptability of the strip with alternating bending with tension.

= 0,5ln

0.4 в соответствии с (10)

= 0,5C([П] /N^α)=

0,06
Количество комплектов гибочных роликов и их диаметры определены из выражений (7)
K =

+1 =

+ 1 = 2
d₁=

=

= 50 (мм)
d₂=

=

×

= 100 (мм)
Сравнение величин максимальных удлинений для полос всего сортамента по предлагаемому способу и способу-прототипу приведено в таблице. При этом диаметры роликов по способу-прототипу выбраны равными 100 мм, поскольку только они удовлетворяют условию прочности для всего сортамента.For N = 3.5 (7 bending blocks) with an acceptable value of the damage function [P] = 0.3, coefficients depending on mechanical properties (for carbon steel)
α = 0.5
C = 0.5ln

= 0.5ln

0.4 in accordance with (10)

= 0.5C ([P] / N ^α ) =

0.06
The number of sets of bending rollers and their diameters are determined from the expressions (7)
K =

+1 =

+ 1 = 2
d ₁ =

=

= 50 (mm)
d ₂ =

=

×

= 100 (mm)
A comparison of the maximum elongations for the bands of the entire range of the proposed method and the prototype method are given in the table. In this case, the diameters of the rollers according to the prototype method are chosen equal to 100 mm, since only they satisfy the strength condition for the entire assortment.

 As can be seen from the table, in contrast to the prototype according to the proposed method, alternating bending with tension in the GNU provides the minimum 2% elongation of the strip for correction of the crescent and longitudinal thickness variations for the entire mill assortment.

 The application of the proposed method allows to increase the accuracy of the strip entering the molding mill and, thereby, increase the stability of the molding and welding processes, improve the quality of the finished pipes, reduce the expenditure coefficient of the metal during their manufacture, and increase the productivity of the pipe welding unit. (56) 1. USSR author's certificate N 1301516, cl. B 21 C 37/08, 1987.

Claims (3)

1. Method for the production of electric-welded pipes, including the docking of individual rolls into a continuous strip, its alternating plastic bending with tension in a non-driven multi-roller bending and tensioning device, pulling the strip through it with a pulling device, forming the strip into a pipe billet and welding its edges, characterized in that maximum curvature value N ^max _mfd strip as it is set in alternating bending function of the strip thickness, the minimum thickness of the strip gauge unit, and minimum Maximum Feed allowable bending deformation of the outer layer and is determined by the formula
N $\genfrac{}{}{0ex}{}{\text{max}}{\text{outcast}}$ =

where ε _bending ^min and ε _bending ^max - respectively, the minimum and maximum allowable bending deformation of the outer layer;
h is the thickness of the processed strip;
h _min - the minimum thickness of the strip in the assortment of the unit, while in the expression for the degree, the whole part is used, and after welding the edges, they are calibrated into the finished pipe. 2. An assembly for the production of electric-welded pipes, containing a sequentially installed device for docking rolls in a continuous strip, a bending-tensioning, pulling and forming device, as well as a welding unit, characterized in that it is equipped with a calibration unit installed behind the welding, and bending-tensioning the device is made in the form of K sets of bending rollers of various diameters, where K =

+1 and the diameters of the rollers of the i-th set are determined by the expression
d ₁ =

, i = 1,. . . . , k,
where h _max - the maximum thickness of the strip in the assortment of the unit.  3. The assembly according to claim 2, characterized in that in the bending-tensioning device, bending rollers of smaller diameters are installed with the possibility of pairwise bending around with a strip with a change in the sign of curvature only between pairs.

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