RU2751408C1 - Reducing and stretching rolling mill with improved tolerance of diameter and wall thickness - Google Patents

Abstract

FIELD: pipe production.

SUBSTANCE: invention relates to a reduction-stretching rolling mill for the manufacture of seamless pipes. The mill contains a set of rolling stands, which are arranged one after another in the direction of the pipe feed and each of which has three rolls located at an angular distance of 120°. The rolling stands are divided into at least two groups, each of which contains at least two rolling stands. The rolls of the neighboring rolling stands in the group are crossed relative to each other by an intra-group angle, and the rolls of the rolling stands of the neighboring groups are crossed relative to each other by a group angle that is less than the intra-group angle.

EFFECT: ensured uniformity of the rolled pipe wall thicknesses.

9 cl, 3 dwg

Description

FIELD OF TECHNOLOGY

The invention relates to a reduction-stretching mill for the production of seamless pipes, comprising a plurality of rolling stands, which are located one behind the other in the direction of pipe feeding and each of which has three rolls located at an angular distance of 120 °.

LEVEL OF TECHNOLOGY

In the manufacture of seamless pipes, tension-reducing and / or sizing rolling mills are used, containing a plurality of rolling stands arranged one after the other in the direction of pipe feeding. The rolling stands usually contain three rolls symmetrically located around the tube at an angular distance of 120 °.

It is known to arrange adjacent rolling stands with crossing at an angle of 60 ° to each other, so that sections of the rolled tube are alternately rolled with the bottom of the groove and the projection of the groove of the rolls. Thus, WO 2017/068533 A1 describes a rolling mill with a first section containing a plurality of rolling stands and capable of rolling on a mandrel inserted into the tube, and a second section containing a plurality of rolling stands and capable of rolling without a mandrel. Each rolling stand has three rolls. The roll axes of adjacent milling rolls are deflected by 180 ° as shown in FIG. 1A and 1B WO 2017/068533 A1. This corresponds to a crossover of the above 60 °.

Especially in the case of thick-walled pipes, in combination with large reductions in diameter in tension reduction mills, due to the uneven distribution of speed between the bottom of the groove and the projection of the groove of the rolls, an uneven formation of the pipe bore occurs. An inner cross-section in the form of a polygon is formed perpendicular to the pipe axis. This phenomenon is also called "inner polygon formation". If the rolling mill functions as a mandrel extractor, this is complicated by temperature differences compared to the previous stretching mill, which also cause different plastic deformation conditions between the groove bottom and the groove protrusion. This is superimposed on the formation of the inner polygon in the subsequent mill and thus can enhance this effect. The formation of the inner polygon is especially pronounced when both the stretching mill and the mandrel extractor are of a three-roll design. The four-roll design is most often not used as an alternative due to the limited space for installing the roll supports and the associated low ability to absorb plastic deformation forces.

DISCLOSURE OF THE INVENTION

The object of the invention is to improve the quality of rolling on a stretch-reducing mill for the production of seamless pipes, in particular to ensure the uniformity of the rolled wall thicknesses.

This problem is solved thanks to a tension-reducing rolling mill with the features of paragraph 1 of the claims. Preferred improved embodiments follow from the dependent claims, the following description of the invention and the description of preferred embodiments.

The inventive stretching rolling mill is designed for the production of seamless pipes, preferably from a metal material. In the present description, the term "stretching mill" is to be understood as a generic term for rolling mills that cause both a decrease in the outer diameter of the pipe and a decrease in the inner diameter, which causes elongation of the pipe. For this reason, the stretching rolling mill is preferably a straightening mill. Depending on the set rotation speed of the rolls, it is also possible to increase or decrease the pipe wall thickness within a certain range. The stretch-reducing mill contains a plurality of rolling stands, which are arranged one behind the other in the pipe feed direction and each of which has three rolls spaced at an angular distance of 120 °. Thus, the rolls are arranged symmetrically around the pipe so as to apply a rolling force on three sides to the outer periphery of the pipe. The rolling stands are divided into at least two groups, each of which contains at least two rolling stands, and the rolls of adjacent rolling stands in the group are crossed relative to each other by an intragroup angle. In addition, the rolls of the rolling stands of adjacent groups are crossed relative to each other by a group angle, which is less than the intra-group angle.

The term "crossing" includes the relative rotation of adjacent rolling stands (similarly - groups), more precisely, their rolls, at a specified intragroup angle (similarly - group angle). However, since the rolls are arranged symmetrically around the pipe at an angular distance of 120 °, the position corresponding to a rotation through a certain angle can also be achieved by rotation through one or a plurality of other angles. Thus, for example, a 60 ° cross is achieved also by a 180 ° tilt. For this reason, in the present description, the term "crossing" at an angle is used to mean rotation through both the specified angle and all equivalent angles. Rotation relative to the rolling direction can be performed both clockwise and counterclockwise.

According to the invention, the rolling stands are crossed by a group angle belonging to the group, which is smaller than the intra-group angle. Due to this crossing, the formation of the inner polygon of the next group, inclined by the group angle, is superimposed on the formation of the inner polygon of one group. Thus, the approximation to the circular inner cross-section of the pipe is improved. Another technical effect is that due to the group angular crossing of the rolls, the temperature equalization in the pipe is improved, since there is a temperature gradient along the radial direction of the pipe. Both effects contribute to an equalization of the rolled wall thicknesses and, therefore, to an improvement in the rolling quality when rolling seamless pipes.

Preferably, the intra-group angle is 60 °, whereby the pipe sections are rolled alternately with the groove bottom or the groove protrusion. This improves the formation of the wall thickness within the group.

Preferably, the group angle is 60 ° / n, where n is an integer greater than 1, i.e. n = 2, 3, 4 ... ,. Preferably the group angle is 30 °. Due to this crossing, the formation of the inner polygon of the next second group, inclined by 30 °, is superimposed on the formation of the inner polygon of the first group. An inner dodecagon is formed, the deviations of which in the range from the maximum wall thickness to the minimum wall thickness are significantly less in comparison with the hexagon.

It should be noted that the number of rolls per caliber can in principle differ from three, in particular, four rolls per caliber can be used, although in practice this is rather an exception. In the case of four rolls per gauge, the intra-group angle is preferably 45 ° and the group angle is preferably 45 ° / n, where n is an integer greater than 1, i.e. n = 2, 3, 4 ... ,.

Preferably, the rolls of rolling stands belonging to one group have a groove shape other than a round shape. In this way, material can be prevented from entering the nip between the rolls, as a result of which the surface of the rolled material could be damaged.

Preferably, at least one neutral rolling stand is provided between the two groups (when viewed in the direction of pipe feed), comprising three rolls spaced at an angular distance of 120 °, the shape of the groove of which counteracts the torque acting on the pipe. Thus, the neutral rolling stand is designed to prevent the tube from turning between two adjacent groups. The reason for the possible rotation of the pipe is that, in particular in the case of non-circular gauges, a torque can be exerted on the pipe about its own axis if a group-related crossing is used. To counteract this tendency to twist, preferably at least one neutral rolling stand is located between adjacent groups. A neutral rolling stand can differ, for example, in that its groove shape has a smaller deviation from the round shape than the corresponding deviation in other stands, and / or the reduction in diameter is reduced compared to other stands. Preferably, the rolls of one or a plurality of neutral rolling stands have a round or nearly round groove shape.

One or, respectively, a plurality of neutral rolling stands preferably do not form an independent group (s), moreover, they are preferably wholly or at least partly a constituent part of the structure of the groups defined above, for example a group in the feed direction of the upstream ... Since not all neutral rolling stands related to the transition between the two groups are part of the upstream group, the remaining neutral rolling stands are structurally preferable to the downstream group. This avoids a special constructive solution.

The size of the groups, i.e. the number of rolling stands in the respective group can be set depending on the rolling size. Thus, preferably from about 35% to 70% of the total diameter reduction occurs in the first group, and the rest of the diameter reduction occurs in the second group. The reason for this distribution is that the formation of the inner polygon occurs gradually and thus there is a danger of overcompensation. In other words, if the distribution is unfavorable, the optimal compensation is not located behind the last rolling stand, but in the inner rolling stand.

Preferably, the stretch reduction mill is a mandrel extractor. A mandrel extractor is a rolling mill located after a stretching mill with a mandrel for removing the pipe rolled along the mandrel from the mandrel. In addition, the mandrel extractors are designed so that, in addition to simply separating the tube from the mandrel, they simultaneously produce a relatively strong plastic deformation of the tube. At this stage of the process, the pipe has a relatively strong temperature gradient from the outside (cold pipe) to the inside (warm pipe). Thus, if the mandrel extractor is designed as a tension reduction mill, the non-uniform temperature distribution in the tube can particularly adversely affect the rolling result. For this reason, the group-related crossover is particularly suitable for a mandrel extractor designed as a tension reduction mill.

Additional advantages and features of the present invention will become apparent from the following description of preferred embodiments. The features described therein can be implemented separately or in combination with one or more of the above features, if the specified features do not contradict each other. Preferred embodiments are described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a tension reducing mill with grouped rolling stands.

FIG. 2 shows a rolling stand of a three-high structure.

FIG. 3 schematically shows a group crossing of rolling stands.

CARRYING OUT THE INVENTION

Preferred embodiments are described below using the drawings. In this case, the same, similar or identically functioning elements are designated in the drawings with identical reference symbols and, in order to avoid redundancy, a detailed description of these elements is partially omitted.

FIG. 1 is a schematic view of a stretch reduction mill 1. The stretch reduction mill 1 comprises a plurality, in this case fifteen, rolling stands 10. The rolling stands 10 are preferably configured to control each stand individually. In particular, the rotational speed of the rolls 11 (see FIG. 2) of the rolling stands 10 can be adjusted individually.

The rolling stands 10, preferably computerized, are controlled by the control device 2. If necessary, the control device 2 takes over the control of the additional components of the stretching mill 1. It should be noted that the term “control device” covers both central and decentralized structures for control of the tension-reducing mill 1. Accordingly, the control device 2 should not be located at the "location" of the tension-reducing mill 1 or be a part of it. In addition, control tasks, data processing stages, etc. can be distributed across various computing devices, which are then collectively encompassed by the term "control device". In addition, the communication of the control device 2 with the controlled components can be carried out both physically by means of a cable, and without wires.

For rolling the tube R, said tube passes through the stretch-reducing mill 1 in the feed direction F. Before entering the tension-reducing mill 1, the tube R on the inlet side has a wall thickness d1. When leaving the last rolling stand 10, the tube R has a wall thickness d2 and a reduced diameter. The wall thickness d2 is not necessarily reduced as compared to the wall thickness d1, moreover, depending on the rotational speed of the rolls, it may be less than, equal to or even greater than the original wall thickness d1.

The wall thickness d1 on the inlet side and / or, respectively, the wall thickness d2 on the outlet side can be measured by means of one or a plurality of wall thickness measuring instruments (not shown). In addition, additional process parameters can be measured or otherwise determined, for example, pipe speed R on the inlet and / or outlet side, weight of the pipe R on the inlet and / or outlet side, etc. The process parameters determined in this case can be transmitted to the control device 2 for controlling the rolling process.

FIG. 2 shows a rolling stand 10, 10 'with three rolls 11 arranged symmetrically at an angular distance of 120 ° around the tube R. According to this embodiment, the rolls 11 of each rolling stand have an arcuate cross-section of the rolling surface, i.e. round caliber shape. The 13 gauge bottom is the center of the rolled surface, when viewed in cross-section of FIG. 2 and in the axial direction of the corresponding roll 11. Both outer ends of the rolled surface - also when viewed in cross-section of FIG. 2 and in the axial direction of the corresponding roll 11 are called a projection 14 gauge. The 13 gauge bottom and the 14 gauge protrusion are characteristic positions of the rolled surface.

Preferably, the shape of the gauge deviates from a perfect circular arc. The reason for the deviation from the circular shape is that, in this way, material can be prevented from entering the nip between adjacent rolls 11, more precisely between the groove projections 14 of the adjacent rolls 11. Due to the local decrease in the caliber and the local increase in the caliber, compensation of the deviations of the pipe diameter is achieved. ...

As shown in said FIG. 1, the rolling stands 10 are divided into two groups A and B, each of which contains seven rolling stands 10. Groups A, B are divided, i.e. they are located sequentially one after the other and do not overlap or penetrate each other. According to this embodiment, within the group A, B, the rolls 11 of the rolling stands 10 are crossed relative to each other by an intra-group angle α _{I of} 60 ° or approximately 60 °, so that the pipe sections are alternately rolled with a 13 gauge bottom or a 14 gauge projection. In this case, the number of rolling stands 10 per group A, B is selected in such a way that the formation of the inner polyhedron is minimized. The number of rolling stands 10 per group A, B is at least two, preferably in the range from 2 to 8. The number of rolling stands 10 can vary from group A to group B.

Groups A, B, more precisely, the rolls 11 of the rolling stands 10 of two, preferably adjacent groups A, B, are crossed relative to each other by an angle denoted here as the group angle α _G. Preferably α _G is equal to or approximately equal to 30 °. Due to this crossing, the formation of the inner polygon of one group A is superimposed on the formation of the inner polygon of the next group B, inclined by the angle α _G. To a certain extent, an internal dodecagon is formed, the deviations of which in the range from the maximum wall thickness to the minimum wall thickness are significantly smaller compared to the internal hexagon. Thus, the internal geometry of the pipe R approaches the ideal circle.

The above-described group-related pivoting or crossing, respectively, is shown schematically in FIG. 3. This drawing schematically shows rolling stands 10 of groups A, B. Within group A, B rolling stands 10 or, respectively, their rolls 11 (not indicated in Fig. 3) are alternately rotated or, respectively, inclined by 180 °, as a result, the 60 ° crossover described above is achieved. A 90 ° turn was performed between groups A and B, resulting in a 30 ° overlap. Of course, both types of crossing can also be achieved directly by rotating through the group angle α _G and the intra-group angle α _I. However, the embodiment shown in FIG. 3 has constructive advantages, in particular when connecting the rolls 11 with drives (not shown). More specifically, when using rolling stands 10, each of which has three rolls 11, a crossover of 60 ° is obtained, for example by tilting the rolling stands 10 by 180 °. This allows the drives with internal power distribution to be located on the normal insertion side and opposite the insertion side. This simplifies the installation and maintenance of the drives, since the connection can take place directly when the stands are being pushed in.

The size of groups A, B, i.e. the number of rolling stands 10 in the corresponding group A, B can be set depending on the rolling size. Thus, preferably about 35% to 70% of the total diameter reduction occurs in the first group A, and the rest of the diameter reduction in the second group B. The reason for this distribution is that the formation of the inner polygon occurs gradually and, therefore, there is a risk of overcompensation ... In other words, with an unfavorable distribution, optimal compensation does not take place behind the last rolling stand 10, but in the inner rolling stand 10.

In addition, in FIG. 1 and 3 show a rolling stand 10 ', which is referred to herein as a "transition pass" or "neutral rolling stand". The neutral rolling stand 10 'is designed to prevent rotation of the pipe R between groups A and B. The reason for the possible rotation of the pipe is that in the case of non-circular plastic deformation, the pipe R can be subjected to a torque around its own axis if the group-related crossing α _{G is used.} ... To counteract this tendency to twist, preferably at least one neutral rolling stand 10 'is located between the groups A, B. Thus, the shape of the groove of the rolls 11 of the neutral rolling stand 10 'is set in such a way that the tendency to twist is counteracted. Preferably, the rolls 11 of the neutral rolling stand 10 'have a round or nearly circular groove shape as shown in FIG. 2.

Due to the group-related crossing at the group angle α _G , as explained above, an improved approximation of the internal geometry of the pipe R to an ideal circular cross-section occurs.

Another technical effect is that due to the group-displaced 13-gauge bottom in the pipe R, in the event of a possible temperature gradient, the temperature equalization is improved. This effect takes place in particular when a non-uniform temperature distribution exists along the radial direction of the pipe R, as is the case, in particular, in the case of mandrels. Mandrels, usually located immediately after the mandrel stretch mill, are designed to separate the R pipe from the mandrel. At this stage of the process, the pipe R has a relatively strong temperature gradient from the outside (cold pipe) to the inside (warm pipe). If the mandrel extractor is made in the form of a tension-reducing rolling mill 1, i.e. In addition to separating the mandrel and the tube, it is simultaneously made with the possibility of severe plastic deformation of the tube R, inhomogeneous temperature distribution in the tube R can adversely affect the rolling result. For this reason, the group-related crossing according to the illustrated embodiments is particularly suitable for a mandrel extractor, in particular for a mandrel extractor in the form of a tension reducing mill 1.

Where applicable, all of the individual features shown in the exemplary embodiments may be combined with one another and / or interchanged without departing from the scope of the invention.

List of reference symbols

1 tension reduction mill

2 control device

10 rolling stand

10 'neutral rolling stand

11 roll

13 caliber bottom

14 gauge protrusion

A group of rolling stands

To the group of rolling stands

R pipe

F feed direction

d1 pipe thickness on the inlet side

d2 pipe thickness on the outlet side

α _I intragroup angle

α _G group angle

Claims (12)

1. Reduction and stretching mill (1) for the production of seamless pipes (R), containing a plurality of rolling stands (10), which are located one after the other in the feed direction (F) of the pipes (R) and each of which has three rolls (11 ) located at an angular distance of 120 °, in which rolling stands (10) are divided into at least two groups (A, B), each of which contains at least two rolling stands (10), rolls (11) of adjacent rolling stands (10) in group (A, B) are crossed relative to each other by the intragroup angle α _I , and the rolls (11) of the rolling stands (10) of adjacent groups (A, B) are crossed relative to each other by the group angle α _G , which is less than the intra-group angle α _I. 2. Stretching-reduction mill (1) according to claim 1, characterized in that the intragroup angle α _I is approximately 60 °. 3. Stretching rolling mill (1) according to claim 1 or 2, characterized in that the group angle α _G is 60 ° / n, where n is an integer greater than 1. 4. Stretching rolling mill (1) according to claim 3, characterized in that the group angle α _G is approximately 30 °. 5. Reduction and stretching rolling mill (1) according to any one of paragraphs. 1-4, characterized in that the rolls (11) of the rolling stands (10) of groups (A, B) have a groove shape that differs from a round shape. 6. Reduction and stretching rolling mill (1) according to any one of paragraphs. 1-5, characterized in that at least one neutral rolling stand (10 ') is provided between the two groups (A, B), containing three rolls (11) located at an angular distance of 120 °, the shape of the groove of which counteracts the torque, acting on the pipe (R). 7. Reduction and stretching mill (1) according to claim 6, characterized in that the shape of the roll groove (11) of the neutral rolling stand (10 ') has the shape of a circular segment. 8. Reduction and stretching rolling mill (1) according to any one of paragraphs. 1-7, characterized in that from 35% to 70% of the total reduction in the diameter of the pipe (R) is provided in the first group (A), and the rest of the reduction in diameter is in the second group (B). 9. Reduction and stretching rolling mill (1) according to any one of paragraphs. 1-8, characterized in that it is a mandrel extractor.

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