RU2241557C1 - Tube cold rolling method and cold rolling mill for performing the same - Google Patents

Abstract

FIELD: equipment for making seamless cold rolled elongated tubes.

SUBSTANCE: method comprises steps of batch feeding of blank to deformation zone formed by means of two pairs of rolls; deforming first portion of tube by means of first and second pairs of rolls performing reciprocation motion relative to fixed mandrel; calibrating tube wall by thickness before deforming it between second pair of rolls at deformation degree 5 -15 % and calibration factor 2.0 - 2.5; rotating blank before forward stroke and before reverse stroke of rolling stand. Tube cold rolling mill includes housing, stand with rolling rolls having in necking portions gear wheels, stationary racks engaged with gear wheels, mechanism for reciprocation motion of stand, rotating and feeding apparatus. Stand with rolling rolls is provided with additional pair of rolls that may be shifted out of engagement; deformation zone is formed by two pairs of rolls with possibility of deforming blank onto cone mandrel along which are arranged: zones for reducing by diameter, zones for reducing wall by thickness, calibration zone and overlap zone in which metal is deformed by means of two pairs of rolls. It allows to calibrate tube wall in portion of overlapping reducing zones, and it is possible to make tubes of two sizes from blank of one size.

EFFECT: enhanced quality of rolled tubes due to lowered difference of wall thickness values.

2 cl, 3 dwg, 3 tbl

Description

The invention relates to equipment for the production of seamless cold-rolled long pipes.

It is known that rolling on roll type mills is carried out by work rolls, which on cold pipe rolling mills (CPT) consist of so-called "gauges" and "roll axes". The stream, cut around the circumference of the caliber, has a semicircle with side outlets in the meridional plane of the roll. In its simplest form, the broadening of the stream is a truncated cone with a constant inclination of the generatrix. The crest of the stream in this case will have a curve shape close to the Archimedean spiral. This calibration of the crest of the stream is called conical. Perhaps such a construction of the ridge profile, in which its sweep is a broken line, and the working cone consists of several conical and one cylindrical section (the so-called multi-link conical calibration of the ridge of the stream). An analysis of the methods for cold rolling pipes and conical calibrations of streams of cold rolling mill mills shows that these methods and their corresponding calibrations do not satisfy the correct construction and flow of the rolling process.

Irrational use of the plastic properties of the wrought metal causes peak loads in individual parts of the stream, including finishing ones. The introduction of multi-link calibrations made it possible to significantly improve the conditions of metal deformation and increase the service life of a rolling tool [Teterin P.K. Theory of periodic rolling. - M .: Metallurgy, 1978. - 256 p .; Shevakin Yu.F., Gleiberg A.Z. Pipe production - M .: Metallurgy, 1968. - 440 p .; Koff Z.A., Soloveichik P.M., Aleshin., Grinshpun M.I. Cold rolling pipes. - Sverdlovsk: State. NTI literature on ferrous and non-ferrous metallurgy, 1962. - 462 p.].

However, the main drawback of the known methods and conical calibrations is not eliminated - the irrational use of the power of the cold rolling mill.

The closest to the claimed solution for the purpose, technical nature and the achieved result when using is a method of cold rolling of pipes, comprising a batch feed of the workpiece into the deformation zone formed by two pairs of rolls, and deformation of the filed portion sequentially by the first and second pairs of rolls during their reciprocating movement on a fixed mandrel [see description of author St. USSR No. 1409358, M.cl. In 21 In 21/00, from 01/07/86], in which, in order to increase productivity before deformation of the second pair of rolls, the workpiece is ovalized with an ovalization coefficient of 1.05-1.12 and with a fractional ratio of 2-2.5.

A well-known cold rolling mill pipe containing a working stand, placed in the cage body two pairs of stream rolls mounted coaxially, and a drive for moving the stand [see description of author St. No. 1785757, M.C. At 21 At 21/00, from 08.01.91]. Compared to the known ones, the mill allows improving the quality of rolled pipes and reducing the time of the mill reconfiguration from one route to another.

However, equipping the mill with an additional pair of rolls does not allow solving a number of problems associated with the difference in the pipes both in length and in diameter. This is especially noticeable with low quality workpieces.

Closest to the claimed solution is also a cold pipe rolling mill containing a bed, a crate with work rolls having gear wheels on the necks, stationary rails interacting with the wheels, the cage reciprocating movement mechanism, and a rotary-feeding device [see description of author St. No. 1419768, M. cl. In 21 In 21/00, from 12.26.86], in which the work rolls can be rotated by means of a worm gear, including stationary racks with worm thread and gears.

Using the method described above, it was possible to increase the degree of one-time deformations per pass by reducing the hardening of the metal and increasing the ductility before deformation in the second pair of rolls. This has reduced the number of cold redistribution cycles in the production of pipes with related operations.

The use of the cold pipe rolling mill described above has improved the quality of rolled products and the reliability of the mill, but basically reduced its overall dimensions.

However, if there is a longitudinal difference in the workpiece, it is largely preserved during further processing. It is not possible to exclude the longitudinal difference, since it is due to the technology of rolling billets at hot rolling mills, on which pipes with thickenings at the ends reaching 30-40% of the nominal pipe wall thickness are obtained. Only the difference in the interval of not more than ± 7 ... 8% indicates a good quality of the finished pipe.

In addition, the deformation zones known in modern world practice at the KhPT mills allow the production of pipes of the same product range, which is determined by the gauges installed on the mill. For pipes of a different assortment, it is necessary to use other calibers, which is extremely uneconomical. Since calibers are an expensive tool, the costs of their manufacture and installation significantly affect the cost of the finished product.

Therefore, the purpose of the proposed technical solution is to improve the quality of the finished product by reducing the difference in the pipes, as well as reducing its cost by reducing the cost of equipment of the mill in terms of manufacturing and transshipment of rolls. It is known that transshipment of rolls due to the replacement of calibers takes up to 10-20% of the working time fund, which negatively affects the productivity of the HPT mill as a whole and the cost of the finished product.

This goal is achieved by the fact that in the known method of cold rolling pipes, including a batch feed of the workpiece into the deformation zone formed by two pairs of rolls, and the deformation of the fed portion sequentially by the first and second pairs of rolls during their reciprocating movement relative to the stationary mandrel, according to the invention, the calibration the wall thickness is carried out before deformation by a second pair of rolls with a degree of deformation of 5-15% (μ) and a calibration coefficient of 2.0-2.5 (δ), while the workpiece is rotated as Ed forward stroke, and before the reverse rolls.

This goal is also achieved by the fact that in the known cold rolling mill of pipes containing a bed, a crate with work rolls having gear wheels on the necks, stationary rails interacting with the wheels, a cage reciprocating mechanism, a rotary-feeding device according to the invention the work rolls additionally contains a second pair of rolls having a gear wheel on the neck, interacting with an additional rack made with the possibility of its disengagement, and the deformation zone, formed by two pairs of rolls, made with the possibility of deformation of the workpiece on a conical mandrel along which there are reduction zones in diameter, compression along the pipe wall thickness and diameter, a calibration zone and an overlap zone on which the metal is deformed by both pairs of rolls, while the parameters of the metal deformation zones on the mandrel are set and executed on the basis of a set of equalities in which the taper of the calibrating sections of the input pair of rolls and mandrel is made in accordance with the equality

where tgγ _k is a parameter characterizing the taper of the calibrating part of the stream;

tgα is a parameter characterizing the taper of the mandrel, the distance between the pairs of rolls is made in accordance with the equality

taking into account the equalities

where Lx is the stroke length of the rolls (or stand stroke), mm;

lп - the length of the overlap of the crimp zones of the first and second pairs of rolls, mm;

A is the distance between the centers of the pairs of rolls, mm;

l _k1 - the length of the calibration zone of the first pair of rolls, calibrating the thickness of the pipe wall, mm;

m is the supply of the workpiece for the double course of the mill, mm;

M ₁ - drawing coefficient, or taking into account the following equalities

where l _p2 is the length of the reduction zone of the second pair of rolls, mm;

M _p2 is the drawing coefficient in the reduction zone of the second pair of rolls, and the cross section of the streams of the calibrating zone of the first pair of rolls is made in accordance with the following equality

where B is the width of the stream, mm, D is the diameter of the stream, mm of the calibrating zone of the first pair of rolls.

The numerical values of the coefficients indicated in the equalities are established as a result of experimental studies and practical application. As a result of the studies, it was found that only when choosing the parameters of the method and the linear dimensions of the device in the indicated ranges, it is possible to ensure high quality of pipes from the point of view of the difference in pipe thickness and diameter.

It has been experimentally established and confirmed by practice that when the length of the calibrating section is 2.0-2.5, the length of the linear displacement of the metal per rolling cycle is enough to obtain good pipe quality with a double turn of the workpiece (before the forward and backward movement of the stand). If you perform only one turn, then this indicator should be greater.

The proposed technical solutions allow, without decreasing the total sweep length of the grooves of calibers of both roll pairs, which determines the productivity of the HPT mill, to position the pipe calibration section on the overlap area of the crimp zones of both roll pairs, which allows for a correctly selected feed (m) to reduce the difference by 3-7 times when rolling with two pairs of rolls.

As can be seen from the presentation of the essence of the proposed solution, it differs from the prototype and, therefore, is new.

Solutions also have an inventive step. The basis of the invention is the task of improving the method of cold rolling of pipes, in which, due to calibration along the wall thickness before deformation, a second pair of rolls with a degree of deformation of 5-15% (μ) and a calibration coefficient of 2.0-2.5 (δ), with rotation of the workpiece both before the forward stroke and before the reverse stroke of the stand, the uniformity of the metal supply to the second pair of rolls is ensured, the overflow of the calibrating zone by the metal of the second pair of rolls is eliminated, and due to this, the pipe difference is significantly reduced.

The basis of the invention is also the task of improving the cold rolling mill of pipes, in which, due to the stand with work rolls with an additional pair of rolls having a gear wheel on the neck, interacting with an additional rack made with the possibility of disengaging it, performing a deformation zone formed by two pairs of rolls, with the possibility of deformation of the workpiece on a conical mandrel along which there are reduction zones in diameter, compression in the pipe wall thickness and diameter, and the calibration and the overlap zone, on which the metal is deformed by both pairs of rolls, setting and fulfilling the parameters of the metal deformation zones on the mandrel based on the above set of equalities, ensures the calibration of the pipe wall at the overlap of the crimp zones, the uniformity of the metal supply to the second pair of rolls increases, eliminating metal overfilling of the calibers of the second pair of rolls, and due to this, on the one hand, it is possible to obtain a finished product of higher quality, on the other hand Orons, the ability to receive with the help of a single focus of deformation of the pipe two standard sizes from one standard size of the workpiece.

The consequence of such possibilities of the proposed method and a rolling mill with a deformation zone carrying out this method is to reduce the number of gauge transshipments, reduce the number of calibers used, increase the productivity of the cold pipe rolling mill, reduce the cost of finished products by reducing the cost of refitting the HPT mill.

As noted above, a known method of cold rolling pipes and cold rolling mills with two rows of rolls.

However, the difference in the finished product obtained using known mills and methods remains significant, since it significantly depends on the difference in the blanks.

When rolling pipes in accordance with the proposed method in two pairs of rolls, subject to the conditions of a certain degree of deformation and calibration coefficient when turning the workpiece both before direct and reverse, the alternating deformation acts on the structure already formed during the preliminary deformation, ordering it, leads to the intensive development of relaxation processes, the consequence of which is a decrease in the hardening of the metal and, ultimately, an increase in one-time degrees of deformation, and hence loneliness.

Since the above technical results are already achieved to a large extent when processing in one pair of rolls, and processing in the second pair, using the achieved, increases them, in some cases it is possible to limit processing to only one pair of rolls, using the second pair of rolls mainly to obtain precision pipes.

The proposed method for cold rolling pipes and a mill for implementing this method are currently the only ones that allow obtaining precision tubes with a difference in the range of ± 2.0-3.0% from the workpiece with almost any difference. This circumstance makes it possible to use billet pipes obtained at hot rolling units for processing at HPT mills, including production waste of different thicknesses.

The proposed technical solutions fundamentally differ from the known ones in that they reduce the quality requirements for hot-rolled tubes-blanks used in the production of cold-rolled tubes, both along their perimeter and in length, since obtaining high-quality hot-rolled tubes is currently an insoluble problem.

The proposed solutions also provide the opportunity to obtain two sizes of pipes from the same size of the workpiece. The first size is obtained after deformation in the first pair of rolls, the second size is obtained after deformation in the second pair of rolls.

As noted above, the difference after processing in the second pair of rolls is reduced by 5-7 times.

Figure 1 - arrangement of zones of deformation of the metal on the mandrel.

Figure 2 - diagram of the rack-and-pinion drive rolls of the mill 2-row rolling.

Figure 3 is a cross section of the stream of the calibrating zone of the first pair of rolls.

The proposed method was implemented on the mill KhPT-32 and KhPT-55. A method including a batch feed of a workpiece into a deformation zone formed by two pairs of rolls, and deformation of the fed portion in series with the first and second pairs of rolls during their reciprocating movement on a stationary mandrel was carried out with the parameters shown in table 1.

The cold pipe rolling mill contains a bed, a cage with two pairs of work rolls 1 and 2 (Fig. 1) having gear wheels 3 and 4 (Fig. 2) on their necks, interacting with stationary rails 5 and 6 (Fig. 2), a mechanism reciprocating movement of the stand and rotary-feeding device. Rail 5 provides movement of the input pair of rolls, rail 6 - the output pair of rolls. Adjusting wedges of 7 rails of drives provide an opportunity of shutdown of the second pair of rolls.

Along the conical mandrel are reduction zones of diameter l _p1 , l _p2 , compression of the pipe wall thickness l _o1 , l _o2 and diameter, calibration zone l _k1 , l _k2 and overlap zone lп, on which the metal is deformed by both pairs of rolls.

The cold pipe rolling mill operates as follows, implementing the proposed method. The workpiece, fixed in the rotation mechanism, is sent to the reduction zone L _p1 , in which the workpiece is crimped in diameter by the first pair of rolls. After the workpiece passes the wall compression zone l _o1, it enters the calibration zone l _k1 . In this way, pipes of the same size are obtained. Then the workpiece enters the reduction zone l _p2 (compression by diameter of the second pair of rolls) and then into the compression zone l _o2 of the wall by the second pair of rolls. Before the workpiece enters the zone l _p2, it passes through the zone ln, in which the metal of the workpiece is deformed by both pairs of rolls. The second pair of rolls is turned on using adjusting wedges 7, if necessary, to obtain large deformations and pipes with a minimum difference and receive pipes of a different size.

In accordance with the proposed solution, the mills KhPT-32 and KhPT-55 were modernized. The results of the modernization of the mills are shown in table 2.

The results of the application of the proposed method on cold rolling mills of pipes ХПТ-32 and ХПТ-55 are shown in table 3.

As can be seen from the presentation of the essence of the claimed solutions and the parameters of their specific embodiment, their implementation allowed us to reduce the difference between the pipes by 7-8 times and made it possible to obtain pipes of two sizes from one workpiece.

A direct consequence of improving the quality of the finished product at KhTP mills by reducing the pipe spacing with the proposed mill design is to expand the range of rolled pipes, reducing costs by reducing the cost of equipment of the mill, in particular the manufacture of additional pairs of rolls to obtain new pipe sizes, as well as by reducing the number of cold rolled cycles.

Claims (2)

1. A method of cold rolling pipes, including a batch feed of the workpiece into the deformation zone formed by two pairs of rolls, and deformation of the fed portion sequentially by the first and second pairs of rolls during their reciprocating movement relative to the stationary mandrel, characterized in that the wall thickness calibration is carried out before the deformation of the second pair of rolls with a degree of deformation of 5-15% (μ) and a calibration coefficient of 2.0-2.5 (δ), while the workpiece is rotated both before the forward stroke and before the roll reverse . 2. Cold pipe rolling mill, comprising a bed, a cage with work rolls having gear wheels on the necks, stationary rails interacting with the wheels, a cage reciprocating movement mechanism, a rotary-feeding device, characterized in that the cage with work rolls additionally contains a second a pair of rolls having a gear wheel on the neck interacting with an additional rack configured to disengage from it, and the deformation zone formed by two pairs of rolls is made with the possibility of deformation of the workpiece on a conical mandrel, along which there are reduction zones by diameter, compression by the pipe wall thickness and diameter, the calibration zone and the overlap zone on which the metal is deformed by both pairs of rolls, while the parameters of the metal deformation zones on the mandrel are set and made on the basis of set of equalities in which the taper of the calibrating sections of the input pair of rolls and mandrel is made in accordance with the equality tgγ _c / tgα = (1.1-1.2), (1) where tgγ _k is a parameter characterizing the taper of the calibrating part of the stream; tgα is a parameter characterizing the taper of the mandrel, the distance between the pairs of rolls is made in accordance with the equality L _x = A + l _p , (2) taking into account the equalities l _k1 = (0.6 ÷ 0.8) l _p , (3) l _k1 = δmM ₁ , (4) where L _x - the stroke length of the rolls (or stand travel), mm; l _p - the length of the overlap of the crimp zones of the first and second pairs of rolls, mm; A is the distance between the centers of the pairs of rolls, mm; l _k1 - the length of the calibration zone of the first pair of rolls, calibrating the thickness of the pipe wall, mm; m is the supply of the workpiece for the double course of the mill, mm; M ₁ - drawing coefficient, or taking into account the following equalities l _p = l _k1 + l _p2 , (5) l _p2 = (l, 8 ÷ 2.0) mM _p2 , (6) where l _p2 is the length of the reduction zone of the second pair of rolls, mm; M _p2 is the drawing coefficient in the reduction zone of the second pair of rolls, and the cross section of the streams of the calibrating zone of the first pair of rolls is made in accordance with the following equality B / D = 1.02-1.03, (7) where B is the width of the stream, mm; D is the diameter of the stream, mm.

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