EP3793755B1 - Stretch-reducing mill having improved diameter tolerance and wall thickness tolerance - Google Patents

Description

technical field

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

Background of the Invention

In the production of seamless tubes, stretch-reducing and/or sizing mills are used, which have several rolling stands arranged one behind the other in the conveying direction of the tube. The roll stands usually have three rolls which are arranged symmetrically around the tube at an angular spacing of 120°.

It is known to arrange adjacent roll stands offset by 60° relative to one another, so that sections of the tube to be rolled are rolled alternately in the base of the pass and by the pass of the rolls. That's how she describes it WO 2017/068533 A1 a rolling mill with a first section, which has several roll stands and is set up for rolling over a mandrel inserted into the tube, and a second section, which has several roll stands and is set up for rolling without a mandrel. The roll stands each have three rolls. The axes of rotation of the rolls of adjacent roll stands are each tilted by 180 °, as in the Figures 1A and 1B the WO 2017/068533 A1 is shown. This corresponds to an entanglement of the 60° mentioned above.

Especially with thick-walled tubes in connection with large reductions in diameter, there is an uneven formation of the inside of the tube in the stretch-reducing mill due to the uneven speed distribution between the bottom pass and the pass step of the rolls. A polygonal internal cross-section is formed perpendicular to the pipe axis. This phenomenon is also referred to as "internal polygon formation". If the rolling mill functions as a pull-out mill, temperature differences from the preceding stretching unit, which also cause different forming conditions between the bottom of the pass and the top of the pass, make matters worse. This overlays the interior polygon formation of the subsequent aggregate and can thus enhance the effect. The internal polygon formation is particularly pronounced when both the stretching unit and the pull-out mill are designed as three-rollers. A four-roller design as an alternative is usually out of the question due to the limited installation space for the roller bearings and the associated low capacity to absorb the forming forces.

The JP 2013 230500A , which forms the basis for the preamble of claim 1, describes a stretch-reducing mill with several roll stands, each comprising three rolls at an angular spacing of 120°. Stretch-reducing mills of similar structure also go from the CN 101773937A , CN 101823076A , JP 2002 066609 A and JP 2001 129603 A out.

Presentation of the invention

One object of the invention is to improve the rolling quality of a stretch-reducing mill for the production of seamless tubes, in particular to make the rolled wall thicknesses more uniform.

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

The stretch-reducing mill according to the invention serves to produce seamless tubes, preferably made of a metal material. The "stretch-reducing mill" is to be understood herein as a generic term for rolling mills which bring about both a reduction in the outside diameter of the tube and a reduction in the inside diameter, thereby causing the tube to elongate. For this reason, the stretch reducing mill is preferably a mandrelless mill. Depending on the set roller speeds, the wall thickness of the tube can also be increased or decreased to a certain extent. The stretch-reducing mill has several roll stands arranged one behind the other in the conveying direction of the tubes, each with three rolls arranged at an angular distance of 120°. The rollers are thus arranged symmetrically around the pipe to exert a rolling force on the outer circumference of the pipe from three sides. The roll stands are divided into at least two groups, each with at least two roll stands, the rolls of adjacent roll stands within a group being offset relative to one another by an angle within the group. Further, the rolls of roll stands of adjacent groups are skewed relative to each other by a group angle smaller than the intra-group angle.

The terms "interlacing" or "set" include a relative twisting of adjacent roll stands (similar to groups)—more precisely, their rolls—by the specified group-internal angle (similar to group angles). However, because the rollers are symmetrically spaced 120° around the tube, a condition that corresponds to twisting through a certain angle can also be achieved by rotating through one or more other angles. For example, a twist of 60° can also be achieved by tilting by 180°. For this reason, the terms "twist" or "twist" about an angle are used herein to denote a twist through that angle as well as through any equivalent angle. The twist can be either clockwise or counterclockwise with respect to the rolling direction.

According to the invention, the roll stands are crossed in a group-related manner by a group angle that is smaller than the group-internal angle. Due to such a twist, the inner polygon formation of one group is superimposed with an inner polygon formation of the following group inclined by the group angle. In this way the approximation to a circular internal cross-section of the tube is improved. A further technical effect is that the angular displacement of the rollers in groups improves the temperature equalization in the tube if there is a temperature gradient along the radial direction of the tube. Both effects contribute to the equalization of the rolled wall thicknesses and thus to an improvement in the rolling quality when rolling seamless tubes.

Preferably, the intragroup angle is 60°, whereby portions of the tube are alternately rolled at the bottom or at the top of the gauge. This improves the wall thickness characteristics within the group.

Preferably the group angle is 60°/n, where n is an integer greater than 1, i.e. n=2,3,4.... The group angle is preferably 30°. By such a twist, the interior polygon formation of a first group is superimposed with an interior polygon formation inclined by 30° of a subsequent second group. A dodecahedron-shaped inner polygon is generated, the deviations between a maximum wall thickness and a minimum wall thickness of which are significantly reduced compared to a hexagonal polygon.

It should be pointed out that the number of rolls per caliber can in principle deviate from "three", in particular four rolls per caliber are possible, even if this is rather the exception in practice. In the case of four rolls per caliber, the intragroup 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....

The rolls of the group-related roll stands preferably have a caliber shape that deviates from the circular shape. This way you can prevent material from entering the gap between the rolls, which could damage the surface of the rolled stock.

According to the invention, at least one neutral roll stand is provided between two groups (seen in the conveying direction of the pipe), 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 rolling stand thus serves to avoid twisting of the tube between two adjacent groups. The reason for any twisting of the barrel is that, particularly in the case of non-circular calibers, a torsional moment can act on the barrel about its own axis when a group-related set 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 roll stand is characterized in that its caliber shape has a smaller deviation from the circular shape than that of the other stands. In addition, the reduction in diameter relative to the other stands can be reduced. Preferably, the rolls of the one or more neutral roll stands have a circular or approximately circular caliber shape.

The one or more neutral roll stands preferably do not form an independent group(s), rather they are preferably completely or at least partially a structural component of the groups defined above, for example the group located upstream in the conveying direction. Unless all of the neutral roll stands belonging to the transition between two groups are part of the upstream group, the remaining neutral roll stands preferably belong to the downstream group structurally. In this way, a special structural solution can be avoided.

The size of the groups, ie the number of roll stands in each group, can be made dependent on the dimension to be rolled. How to find preferably about 35% to 70% of the total diameter reduction occurs in the first group and the remaining diameter reduction occurs in the second group. The reason for this distribution is that the inner polygon formation gradually builds up and there is therefore a risk of overcompensation. In other words, in the case of an unfavorable distribution, the optimal compensation is not behind the last roll stand, but on an inside roll stand.

Preferably, the stretch-reducing mill is an extracting mill. A drawing mill is a rolling mill that is located downstream of a stretch rolling mill with a mandrel in order to pull the tube rolled out over the mandrel from the mandrel. Extracting rolling mills are increasingly being designed in such a way that, in addition to simply separating the tube from the mandrel, they also cause the tube to be relatively strongly deformed. At this stage of the process, the pipe has a comparatively strong temperature gradient from the outside (cold) to the inside (warm). If the pull-out mill is designed as a stretch-reducing mill, the inhomogeneous temperature distribution in the tube can have a particularly disadvantageous effect on the rolling result. For this reason, a group-related set is particularly suitable for a stretch-reducing rolling mill.

Further advantages and features of the present invention are evident from the following description of preferred exemplary embodiments. The features described there can be implemented on their own or in combination with one or more of the features set out above, insofar as the features do not contradict one another. The following description of the preferred embodiments is made with reference to the accompanying drawings.

Brief description of the figures

• The figure 1 Fig. 12 is a schematic view of a clustered stand stretch reduction mill.
• The figure 2 shows a roll stand in three-roll design.
• The figure 3 shows a schematic of a group setting of roll stands.

Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. Elements that are the same, similar or have the same effect are provided with identical reference symbols in the figures, and a repeated description of these elements is sometimes dispensed with in order to avoid redundancies.

The figure 1 is a schematic view of a stretch-reducing mill 1. The stretch-reducing mill 1 has a plurality of roll stands 10, fifteen in this case by way of example. The roll stands 10 can preferably be controlled individually. In particular, the speeds of rollers 11 (cf. figure 2 ) of the roll stands 10 individually adjustable.

The roll stands 10 are controlled via a control device 2, preferably computer-based. If necessary, the control device 2 assumes the control of further components of the stretch-reducing mill 1. It should be pointed out that the term "control device" includes both centralized and decentralized structures for controlling the stretch-reducing mill 1. Accordingly, the control device 2 does not have to be located at the "site" of the stretch-reducing mill 1 or be part of the same. In addition, control tasks, data processing steps, etc. can be distributed to different computing devices, which then come under the name "control device" in their entirety. Furthermore, the communication of Controller 2 done with the components to be controlled both physically via cable and wirelessly.

To roll a tube R, it runs in a conveying direction F through the stretch-reducing mill 1. Before it enters the stretch-reducing mill 1, the tube R has a wall thickness d1 on the inlet side. Upon exiting the last roll stand 10, the tube R has a wall thickness d2 and a reduced diameter. The wall thickness d2 is not necessarily reduced compared to the wall thickness d1; rather, depending on the roll speed, it can be smaller, but also greater than the initial wall thickness d1.

The inlet-side and/or outlet-side wall thickness d1 or d2 can be measured using one or more wall thickness gauges (not shown). In addition, other process parameters can be measured or otherwise determined, for example the inlet and/or outlet speed of the tube R, the inlet and/or outlet weight of the tube R, etc. The determined process parameters can be transmitted to the control device 2 to control the rolling process.

The figure 2 1 shows a roll stand 10, 10' with three rolls 11 which are arranged symmetrically around the tube R at an angular spacing of 120°. According to this exemplary embodiment, the rollers 11 each have a circular arc-shaped cross section of the roller surface, ie a round caliber shape. As caliber base 13, the center of the rolling surface is referred to in cross section figure 2 and seen in the axial direction of the corresponding roller 11. The two outer ends of the rolling surface - also in cross section figure 2 and seen in the axial direction of the corresponding roll 11 - are referred to as gauge jump 14. The caliber base 13 and the caliber jump 14 are characteristic positions of the rolling surface.

The caliber shape preferably deviates from a perfect arc of a circle. The reason for the deviation from the circular shape is that in this way it can be prevented that material enters the gap between adjacent rolls 11--more precisely, between the caliber jumps 14 of adjacent rolls 11. It is achieved by local caliber reduction and local caliber increase that deviations in the pipe diameter are compensated.

Coming back to the figure 1 the roll stands 10 are divided into two groups A and B, each having seven roll stands 10. The groups A, B are disjoint, ie they are arranged sequentially one after the other and do not overlap or interpenetrate. Within a group A, B, the rolls 11 of the roll stands 10 according to the present exemplary embodiment are offset against one another by an angle α _I within the group of 60° or approximately 60°, so that the tube sections are rolled alternately in the base of the pass 13 or from the pass 14. The number of roll stands 10 per group A, B is dimensioned in such a way that the formation of the inner polygon is minimized. The number of roll stands 10 per group A, B is at least two, it is preferably in the range from 2 to 8. The number of roll stands 10 can vary from group A to group B.

The groups A, B--more precisely, the rolls 11 of the roll stands 10 of two, preferably adjacent groups A, B--are crossed relative to one another by an angle which is referred to herein as the group angle α _G . Preferably, α _G is equal to or about 30°. Due to such a twist, the inner polygon formation of a group A is superimposed with an inner polygon formation of the following group B inclined by α _G . To a certain extent, an internal dodecahedron is produced whose deviations between a maximum wall thickness and a minimum wall thickness are significantly reduced compared to an internal hexagon. The inner geometry of the tube R is thus approximated to an ideal round.

The group-related twisting or setting outlined above is shown schematically in figure 3 out. The roll stands 10 of groups A, B are shown schematically therein. Within a group A, B, the roll stands 10 or their rolls 11 (without reference numbers in the figure 3 ) alternately rotated and tilted by 180°, whereby the above-described twisting of 60° is achieved. A rotation of 90° was made between groups A and B, resulting in an entanglement of 30°. Of course, the two types of entanglement can also be achieved directly by rotation about the group angle α _G and the group-internal angle α _I . The one in the figure 3 However, the variant shown has design advantages, particularly when coupling the rollers 11 to the drives (not shown). More precisely, when using roll stands 10 with three rolls 11 each, the twist of 60° results, for example, by tilting the roll stands 10 by 180°. In this way, the drives can be arranged on the usual plug-in side and opposite the plug-in side in the case of internal power distribution. This simplifies the installation and maintenance of the drives, since the coupling can take place directly when the scaffolding is pushed in.

The size of the groups A, B, i.e. the number of roll 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 takes place in the first group A and the remaining diameter reduction in the second group B. The reason for this distribution is that the inner polygon formation gradually builds up and there is therefore a risk of overcompensation. In other words, in the case of an unfavorable distribution, the optimal compensation is not behind the last rolling stand 10, but on an inner rolling stand 10.

From the figures 1 and Figure 4 also shows a roll stand 10', referred to herein as a "transition pass" or "neutral roll stand". The neutral Roll stand 10' serves to prevent twisting of the tube R between sets A and B. The reason for any twisting of the tube R is that in the case of a non-circular deformation, a torsional moment can act on the tube R about its own axis if a group-related twist of α _G is applied. In order to counteract such a tendency to torsion, at least one neutral roll stand 10' is preferably connected between the groups A, B. The caliber shape of the rolls 11 of the neutral roll stand 10' is thus determined in such a way that the tendency to torsion is counteracted. Preferably, the rolls 11 of the neutral roll stand 10' have a circular or approximately circular caliber shape, as in FIG figure 2 shown.

Due to the group-related twisting around the group angle α _G , as explained above, the inner geometry of the pipe R comes closer to an ideal circular cross-section.

A further technical effect is that the caliber base 13 offset in groups improves temperature compensation in the event of any temperature gradient in the tube R. This effect comes into play particularly when there is an inhomogeneous temperature distribution along the radial direction of the tube R, as occurs in particular in the case of extracting rolling mills. Pull-out mills, which are normally located immediately after a mandrel-type stretch mill, serve to separate the tube R from the mandrel. At this stage of the process, the pipe R has a comparatively strong temperature gradient from the outside (cold) to the inside (warm). If the pull-out mill is designed as a stretch-reducing mill 1, ie, in addition to separating mandrel and tube R, it is also designed for strong deformation of tube R, the inhomogeneous temperature distribution in tube R can have an adverse effect on the rolling result. A group-related constraint according to the exemplary embodiments presented is for this reason it is particularly suitable for a drawing mill, in particular a drawing mill designed as a stretch-reducing mill 1 . As far as applicable, all individual features that are presented in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the invention defined by the claims.

Reference List

1

stretch reducing mill

2

control device

10

mill stand

10'

Neutral mill stand

11

roller

13

caliber reason

14

caliber leap

A

Group of rolling mills

B

Group of rolling mills

R

Pipe

f

conveying direction

d1

Upstream wall thickness of the tube

d2

Downstream wall thickness of the tube

αI

Intragroup angle

αG

group angle

Claims (6)

1. Stretch-reducing rolling mill (1) for producing seamless tubes (R), which comprises a plurality of roll stands (10), which are arranged in succession in a conveying direction (F) of the tubes (R), each with three rolls (11) arranged at an angular spacing of 120°, wherein the roll stands (10) are divided into at least two groups (A, B) each with at least two roll stands (10) and

   the rolls (11) of adjacent roll stands (10) within one group (A, B) are staggered relative to one another by a group-internal angle α_I,

   wherein

   the rolls (11) of the roll stands (10) of adjacent groups (A, B) are staggered relative to one another by a group-internal angle α_G, which is smaller than the group-internal angle α_I,

   characterised in that

   the rolls (11) of the roll stands (10) of the groups (A, B) have a pass shape differing from the circular shape and

   provided between two groups (A, B) is at least one neutral roll stand (10') with three respective rolls (11) which are arranged at an angular spacing of 120° and the pass shape of which has a smaller difference from the circularly round shape than that of the roll stands (10) of the groups (A, B).
2. Stretch-reducing rolling mill (1) according to claim 1, characterised in that the group-internal angle α_I is 60°.
3. Stretch-reducing rolling mill (1) according to claim 1 or 2, characterised in that the group angle α_G is 60°/n, wherein n is a whole number greater than 1.
4. Stretch-reducing rolling mill (1) according to claim 3, characterised in that the group angle α_G is 30°.
5. Stretch-reducing rolling mill (1) according to any one of the preceding claims, characterised in that the pass shape of the rolls (11) of the neutral roll stand (10') has the shape of a segment of a circle.
6. Stretch-reducing rolling mill (1) according to any one of the preceding claims, characterised in that this is a drawing rolling mill.

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