DE102018207908A1 - Stretch reduction mill with improved diameter and wall thickness tolerance - Google Patents

Abstract

Stretch-reducing mill (1) for producing seamless tubes (R), which has a plurality of rolling stands (10) arranged one behind the other in a conveying direction (F) of the tubes (R), each having three rollers (11) arranged at an angular distance of 120 °, the rolling stands ( 10) are subdivided into at least two groups (A, B) each having at least two rolling stands (10), the rolls (11) of adjacent rolling stands (10) within a group (A, B) being interlocked relative to one another by an intra-group angle α, and the rollers (11) of the rolling stands (10) of adjacent groups (A, B) are interlocked relative to one another by a group angle α which is smaller than the group-internal angle α.

Description

Technical area

The invention relates to a stretch reducing mill for the production of seamless tubes, which has a plurality of rolling stands arranged one behind the other in a conveying direction of the tubes, each having three rollers arranged at an angular distance of 120 °.

Background of the invention

In the production of seamless pipes, draft-reducing and / or sizing mills are used which have a plurality of rolling mills arranged one behind the other in the conveying direction of the pipe. The rolling stands usually have three rollers, which are arranged at an angular distance of 120 ° symmetrically around the tube.

It is known to arrange adjacent rolling stands relative to each other by 60 ° entangled, so that sections of the pipe to be rolled are rolled alternately in the caliber base and the jump in the caliber of the rolls. That's how it describes WO 2017/068533 A1 a rolling mill having a first section having a plurality of stands and adapted for rolling via a mandrel inserted into the pipe, and a second section having a plurality of stands and arranged for rolling without a mandrel. The rolling stands each have three rollers. The axes of rotation of the rolls of adjacent rolling stands are each tilted by 180 °, as in the 1A and 1B of the WO 2017/068533 A1 is shown. This corresponds to an entanglement around the above 60 °.

Especially in thick-walled pipes in conjunction with large diameter reductions due to the uneven distribution of velocity between the base of the caliber and the change in the caliber of the rolls in the stretch-reducing mill, an uneven formation of the interior of the pipe occurs. It forms a polygonal inner cross-section perpendicular to the tube axis. This phenomenon is also referred to as "inner polygon formation". If the rolling mill acts as a pullout mill, aggravating temperature differences from the previous pulping aggregate are added, which also give rise to different forming conditions between the base of the caliber and the leap in the caliber. This superimposes the inner polygon formation of the subsequent aggregate and can thus enhance the effect. Inner polygon formation is particularly pronounced when both the stretch aggregate and the pullout mill are three-roll construction. A four-roller construction as an alternative is usually out of the question due to the limited installation space for the roller bearings and the associated low absorption capacity of the forming forces.

Presentation of the invention

An object of the invention is to improve the rolling quality of a stretch-reducing mill for the production of seamless tubes, in particular to even out the rolled wall thicknesses.

The object is achieved with a stretch-reducing mill with the features of claim 1. Advantageous developments follow from the subclaims, the following description of the invention and the description of preferred embodiments.

The stretch-reducing mill according to the invention serves to produce seamless tubes, preferably of a metal material. The "stretch-reducing mill" is to be understood here as a generic term for rolling mills, which cause both a reduction of the outer diameter of the tube and a reduction of the inner diameter, whereby an elongation of the tube is effected. For this reason, the stretch reducing mill is preferably a mandrelless rolling mill. Depending on the set rolling speeds, the wall thickness of the tube can be increased or reduced to some extent. The stretch-reducing mill has a plurality of rolling mills arranged one behind the other in the conveying direction of the tubes, each having three rollers arranged at an angular distance of 120 °. The rollers are thus arranged symmetrically around the tube to exert a rolling force on the outer circumference of the tube from three sides. The rolling stands are subdivided into at least two groups, each with at least two rolling stands, wherein the rolls of adjacent rolling stands within a group are interlocked relative to one another by a group-internal angle. Further, the rolls of stands of adjacent groups are interlocked relative to each other by a group angle smaller than the intra-group angle.

The terms "entanglement" or "offset" encompass a relative rotation of adjacent rolling stands (analogous to groups) - more precisely, their rolls - around said group-internal angle (analogous to group angle). However, since the rolls are arranged symmetrically about the pipe at an angular interval of 120 °, a condition corresponding to a rotation by a certain angle can be obtained by rotating at one or more other angles. For example, a 60 ° tilt is achieved by tilting by 180 °. For this reason, the terms "entanglement" or "skew" are used herein to denote a twist both at and around this angle to denote all equivalent angles. The twisting can be done with respect to the rolling direction both clockwise and counterclockwise.

According to the invention, the rolling stands are interlocked group-wise, to a group angle which is smaller than the intra-group angle. By such a restriction, the Innenpolygonbildung a group is superimposed with an inclined by the group angle Innenpolygonbildung the following group. In this way, the approach to a circular inner cross section of the tube is improved. Another technical effect is that by the groupwise angular displacement of the rollers, the temperature compensation in the pipe, if a temperature gradient along the radial direction of the tube is present, is improved. Both effects contribute to the homogenization of the rolled wall thicknesses and thus to the improvement of the rolling quality when rolling seamless pipes.

Preferably, the intra-group angle is 60 °, whereby portions of the tube are rolled alternately in the caliber base or by the caliber jump. As a result, the wall thickness characteristic is improved within the group.

Preferably, the group angle is 60 ° / n, where n is an integer greater than 1, i. n = 2, 3, 4 ..., is. Preferably, the group angle is 30 °. By such a restriction, the Innenpolygonbildung a first group is superimposed with a 30 ° inclined Innenpolygonbildung a subsequent second group. A dodecahedron-shaped inner polygon is produced whose deviations between a maximum wall thickness and a minimum wall thickness are significantly reduced compared to a hexagonal polygon.

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

The rolls of the group-related rolling stands preferably have a caliber shape deviating from the circular shape. In this way, it is possible to prevent material from entering the nip between the rolls, which could damage the surface of the rolling stock.

Preferably, between two groups (viewed in the conveying direction of the tube) at least one neutral rolling mill is provided, each with three rollers arranged at an angular distance of 120 °, the caliber shape of which counteracts a torsional moment acting on the pipe. The neutral mill stand thus serves to avoid twisting of the pipe between two adjacent groups. The reason for a possible twisting of the tube is that, in particular in the case of non-circular caliber, a torsion moment can act on the tube about its own axis if a group-related setting is applied. In order to counteract such a tendency to torsion, at least one neutral roll stand is preferably connected between adjacent groups. A neutral rolling mill may be characterized, for example, by the fact that its caliber shape has a smaller deviation from the circular shape than that of the other stands and / or the decrease in diameter relative to the other stands. Preferably, the rolls of the one or more neutral rolling stands have a circular or approximately circular caliber shape.

The one or more neutral rolling mills preferably do not form a separate group (s), but rather are preferably completely or at least partially structural components of the groups defined above, such as the upstream group in each case. Unless all of the neutral rolling stands belonging to the transition between two groups are part of the upstream group, the remaining neutral rolling stands are structurally preferred to the downstream group. In this way, a special construction solution can be avoided.

The size of the groups, i. the number of rolling stands in the respective group can be made dependent on the dimension to be rolled. Thus, preferably about 35% to 70% of the total diameter reduction in the first group and the remaining diameter reduction in the second group occur. The reason for this distribution is that the inner polygon formation gradually builds up and thus there is a risk of overcompensation. In other words, in the case of an unfavorable distribution, the optimum compensation does not lie behind the last roll stand, but on an inner roll stand.

Preferably, the stretch reducing mill is a pullout mill. As Ausziehwalzwerk a rolling mill is referred to, which is downstream of a drafting mill with mandrel to deduct the rolled over the mandrel tube from the mandrel. Ausziehwalzwerke be increasingly designed so that they at the same time cause a relatively strong deformation of the tube in addition to the mere separation of the tube from the mandrel. The tube has a comparatively strong temperature gradient from the outside (cold) in this process stage inside (warm) up. Thus, if the Ausziehwalzer is designed as a stretch-reducing mill, the inhomogeneous temperature distribution in the pipe can have a particularly adverse effect on the rolling result. For this reason, a group-related setting is particularly suitable for a drawing-out mill designed as a stretch-reducing mill.

Further advantages and features of the present invention will be apparent from the following description of preferred embodiments. The features described therein may be implemented alone or in combination with one or more of the features set forth above insofar as the features do not conflict. The following description of the preferred embodiments will be made with reference to the accompanying drawings.

list of figures

• The 1 Fig. 11 is a schematic view of a stretch reducing mill with grouped rolling stands.
• The 2 shows a roll stand in three-roll design.
• The 3 schematically shows a group-wise setting of rolling stands.

Detailed description of preferred embodiments

In the following, preferred embodiments will be described with reference to the figures. In this case, identical, similar or equivalent elements in the figures are provided with identical reference numerals, and a repetitive description of these elements is partially omitted in order to avoid redundancies.

The 1 is a schematic view of a stretch-reducing mill 1 , The stretch-reducing mill 1 has several, here by way of example fifteen, rolling stands 10 on. The rolling stands 10 are preferably individually controllable. In particular, the speeds of rollers 11 (see. 2 ) of the rolling stands 10 individually adjustable.

The control of the rolling stands 10 via a control device 2 , preferably computer-based. The control device 2 if necessary, controls the activation of additional components of the stretch-reducing mill 1 , It should be noted that the term "controller" includes both centralized and decentralized structures for controlling the draft-reducing mill 1 includes. The control device 2 does not have to be at the "location" of the stretch-reducing mill 1 be or form part of it. In addition, control tasks, data processing steps, etc. can be distributed to different computing devices, which then fall in their entirety under the name "controller". Furthermore, the communication of the control device 2 with the components to be controlled both physically via cable and wireless.

For rolling a pipe R this runs in a conveying direction F through the stretch-reducing mill 1 , Before entering the stretch-reducing mill 1 shows the tube R an inlet wall thickness d1 on. At the exit from the last rolling stand 10 shows the tube R a wall thickness d2 and a reduced diameter. The wall thickness d2 is not necessarily opposite the wall thickness d1 reduced, but it can depending on the roll speed smaller, but equal to greater than the initial wall thickness d1 his.

The inlet side and / or outlet side wall thickness d1 respectively. d2 can be measured by means of one or more wall thickness gauges (not shown). In addition, other process parameters may be measured or otherwise determined, such as the upstream and / or downstream speeds of the tube R , the inlet side and / or outlet side weight of the tube R etc. The determined process parameters can be used to control the rolling process to the control device 2 be transmitted.

The 2 shows a rolling stand 10 . 10 ' with three rollers 11 , which are symmetrical at an angular distance of 120 ° around the pipe R are arranged around. The rollers 11 each have according to this embodiment, a circular arc-shaped cross section of the rolling surface, ie a round caliber shape on. As caliber reason 13 the center of the rolling surface is referred to, in cross-section of 2 and in the axial direction of the corresponding roller 11 seen. The two outer ends of the rolling surface - also in cross section of 2 and in the axial direction of the corresponding roller 11 seen - are considered a leap in quality 14 designated. The caliber reason 13 and the caliber jump 14 are characteristic positions of the rolling surface.

Preferably, the caliber shape deviates from a perfect circular arc. The reason for the deviation from the circular shape is that in this way it can prevent material from entering the nip between adjacent rolls 11 - more precisely, between the caliber jumps 14 adjacent rolls 11 - entry. It is achieved by local caliber reduction and local caliber enlargement, that deviations of the pipe diameter are compensated.

Coming back to the 1 are the rolling stands 10 in two groups A and B divided, each with seven rolling stands 10 exhibit. The groups A . B are disjoint, ie they are arranged sequentially in succession and do not overlap or penetrate each other. Within a group A . B are the rollers 11 the rolling stands 10 according to the present embodiment by an intra-group angle α _I of 60 ° or about 60 ° against each other entangled, so that the pipe sections alternately each in the caliber base 13 or from the caliber jump 14 to be rolled. The number of rolling stands 10 per group A . B is here dimensioned so that the formation of the inner polygon is minimized. The number of rolling stands 10 per group A . B is at least two, it is preferably in the range of 2 to 8. The number of rolling stands 10 can from group A to group B vary.

The groups A . B - more precisely, the rollers 11 the rolling stands 10 two, preferably adjacent groups A . B are at an angle, here as a group angle α _G is referred to, interlocked. Preferably α _G equal to or about 30 °. By such a restriction, the inner polygon formation becomes a group A with one order α _G inclined internal polygon formation of the following group B superimposed. In a sense, an inner dodecahedron is produced whose deviations between a maximum wall thickness and a minimum wall thickness compared to a hexagon are significantly reduced. The internal geometry of the pipe R is thus approximated to an ideal round.

The above group-related rotation or tilt is schematically from the 3 out. Therein are the rolling stands 10 of the groups A . B shown schematically. Within a group A . B are the rolling stands 10 or their rollers 11 (without reference number in the 3 ) alternately rotated by 180 ° or tilted, whereby the above-described entanglement of 60 ° is achieved. Between the groups A and B a rotation of 90 ° was made, resulting in an entanglement of 30 °. Of course, the two types of entanglement can also directly by rotation about the group angle α _G and the intra-group angle α _I be achieved. The in the 3 However, variant shown has constructive advantages, especially in the coupling of the rollers 11 to the drives (not shown). Specifically, when using rolling stands 10 each with three rollers 11 For example, the 60 ° offset results from tipping the rolling stands 10 around 180 °. As a result, the drives can be arranged with an internal power distribution on the usual insertion side and opposite the insertion side. This simplifies the installation and maintenance of the drives, since the coupling can take place directly when the scaffolding is inserted.

The size of the groups A . B ie the number of rolling stands 10 in the respective group A . B , can be made dependent on the dimension to be rolled. Thus, preferably about 35% to 70% of the total diameter reduction in the first group A and the remaining diameter reduction in the second group B instead of. The reason for this distribution is that the inner polygon formation gradually builds up and thus there is a risk of overcompensation. In other words, with an unfavorable distribution, the optimum compensation is not behind the last stand 10 but on an internal rolling stand 10 ,

From the 1 and 4 also goes a rolling mill 10 ' referred to herein as a "transition caliber" or "neutral mill". The neutral rolling stand 10 ' serves to twist the tube R between the groups A and B to avoid. The cause of a possible twisting of the pipe R lies in the fact that in the case of a non-circular forming a torsional moment on the tube R can act on its own axis if a group-related set of α _G is applied. In order to counteract such a tendency to torsion, at least one neutral mill stand is preferably used 10 ' between the groups A . B connected. The caliber shape of the rolls 11 of the neutral rolling stand 10 ' is thus set so that the tendency to torsion is counteracted. Preferably, the rollers 11 of the neutral rolling stand 10 ' a circular or approximately circular caliber shape, as in the 2 shown.

Due to the group-related restriction around the group angle α _G finds, as explained above, an improved approach of the internal geometry of the tube R to an ideal circular cross section instead.

Another technical effect is that due to the groupwise offset caliber base 13 a temperature compensation at a possible temperature gradient in the pipe R is improved. This effect is particularly noticeable when along the radial direction of the tube R an inhomogeneous temperature distribution is present, as occurs in particular in the case of Ausziehwalzwerken. Extending mills, which are usually located immediately behind a drafting mill with a mandrel, serve to make the pipe R to separate from the thorn. The pipe R has a comparatively high temperature gradient from the outside (cold) to the inside (warm) at this stage of the process. If the pullout mill as stretch-reducing mill 1 is executed, ie in addition to the separation of Thorn and pipe R at the same time for a strong deformation of the pipe R is designed, the inhomogeneous temperature distribution in the pipe can R adversely affect the rolling result. A group-related Schränkung according to the embodiments set forth is for this reason for a Ausziehwalzwerk, in particular a stretch-reducing mill 1 executed Ausziehwalzwerk, particularly suitable.

Where applicable, all individual features set forth in the embodiments may be combined and / or interchanged without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1

stretch

2

control device

10

rolling mill

10 '

Neutral rolling stand

11

roller

13

groove base

14

caliber jump

A

Group of rolling stands

B

Group of rolling stands

R

pipe

F

conveying direction

d1

Inlet wall thickness of the pipe

d2

Outlet side wall thickness of the pipe

α _I

Group internal angle

α _G

group angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2017/068533 A1 [0003]

Claims (9)

Stretch-reducing mill (1) for producing seamless tubes (R), which has a plurality of rolling stands (10) arranged one after the other in a conveying direction (F) of the tubes (R), each having three rollers (11) arranged at an angular distance of 120 °, the rolling stands ( 10) are subdivided into at least two groups (A, B) each having at least two rolling stands (10), the rolls (11) of adjacent rolling stands (10) within a group (A, B) being interlocked relative to one another by an intra-group angle α _I , and the rollers (11) of the rolling stands (10) of adjacent groups (A, B) are interlocked relative to each other by a group angle α _G which is smaller than the intra-group angle α _I. Stretch reducing mill (1) after Claim 1 , characterized in that the intra-group angle α _{I is} about 60 °. Stretch reducing mill (1) after Claim 1 or 2 , characterized in that the group angle α _{G is} 60 ° / n, where n is an integer greater than 1. Stretch reducing mill (1) after Claim 3 , characterized in that the group angle α _{G is} about 30 °. Stretch- reducing mill (1) according to one of the preceding claims, characterized in that the rollers (11) of the rolling stands (10) of the groups (A, B) have a caliber shape deviating from the circular shape. Stretch- reducing mill (1) according to one of the preceding claims, characterized in that between two groups (A, B) at least one neutral rolling stand (10 ') is provided, each with three arranged at an angular distance of 120 ° rollers (11) whose caliber shape on counteracts the tube (R) acting torsional moment. Stretch reducing mill (1) after Claim 6 , characterized in that the caliber shape of the rollers (11) of the neutral roll stand (10 ') is circular segment-shaped. Stretch- reducing mill (1) according to one of the preceding claims, characterized in that 35% to 70% of the total diameter reduction of the tube (R) in the first group (A) and the remaining diameter reduction in the second group (B) takes place. Stretch-reducing mill (1) according to one of the preceding claims, characterized in that this is a Ausziehwalzwerk.

Images