Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B17/00—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling
  • B21B17/08—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling with mandrel having one or more protrusions, i.e. only the mandrel plugs contact the rolled tube; Press-piercing mills
  • B21B17/12—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling with mandrel having one or more protrusions, i.e. only the mandrel plugs contact the rolled tube; Press-piercing mills in a discontinuous process, e.g. plug-rolling mills

Definitions

• the invention relates to a method for producing seamless tubes according to the plug rolling process in which a hollow block is expanded and stretched into a billet in at least two passes into a billet in a roll stand with a closed caliber in at least two passes, the billet after each pass is pulled off the bar against the rolling direction by means of a driving device and is rotated by 90 degrees about its longitudinal axis before the following stitch.
• Known rolling processes for the production of seamless steel pipes differ in longitudinal and cross rolling processes.
• longitudinal rolling process in contrast to the cross rolling process, an essentially round and closed caliber shape is required, which must be adapted to the desired pipe cross section.
• the present invention relates to a longitudinal rolling process with an internal tool, as is known under the name plug rolling process.
• Boot rolling mills originally consisted of a perforated cross-rolling mill, a stretch diagonal rolling mill, Stiefelscher plug rolling mill, and at least one smoothing mill in front of a downstream reduction mill as a finishing stage. Because there was a high temperature loss on the tube after the many process steps from the piercing to the reducing roller mill, the tubes were generally reheated to the reducing roller temperature in a specially designed oven after the smooth rolling.
• the original boot plug mill had rolls with several calibers cut next to each other. Later, single-caliber plug rolling mills were developed because the multi-caliber rolls caused inaccuracies in the rolled product due to the deflections.
• a hollow block is rolled out to form a slug over a fixed plug supported on a rod, preferably in two or three passes.
• the billet is pulled off the rod against the direction of rolling by a driving device and rotated 90 degrees to the next stitch.
• the plugs are changed after each stitch.
• Today plugs with a short working length are usually used, the diameter of which is larger than the inside diameter of the hollow block used.
• a method of operation is also known in which the hollow block is larger in inner diameter than the first plug diameter.
• the hollow blocks are expanded over the stopper, which results in more favorable gripping conditions for the rollers.
• the plugs with a short working length are economical and, thanks to the favorable gripping conditions, higher ones Achieve wall thickness reductions.
• the plug diameter of the second stitch is usually slightly larger than that of the first stitch, while the third plug can be the same size or larger than the second.
• the blanks lose considerable temperature due to the low rolling speeds and during the long rolling process, they are usually reheated before rolling out in dimension, reducing or stretch-reducing rolling mills, so that the plug rolling mill compared to others Rolling mills is very complex and uneconomical.
• the present invention achieves this aim by a method which is characterized in that, in the case of a plurality of successive stitches, at least one, preferably in the first stitch, in the region of the caliber base, by changing the pitch of the rollers Wall thickness is set, which takes into account the thin drawing of this wall area in the subsequent roll pass in the sense of a wall thickness of the finished rolled stopper that is uniform over the circumference.
• the proposal of the invention is based on the knowledge that the hollow block introduced into a longitudinal rolling mill after passing through the first rolling stand, that is to say in plug rolling mills after the first pass, with regard to its wall thickness with a correspondingly adapted decrease in wall thickness also in caliber jump compared to the hollow block wall thickness, although areas of the There were no caliber jumps on the plate with the rollers.
• the same phenomenon can also be observed in the second and further stitches until the stretching in the respective framework or stitch has reached a value close to 0.
• the invention thus proposes that the degree of thin drawing in the caliber jump of the subsequent stitch as an addition to the caliber base of the previous one Scaffolding or stab is slammed, with the aim of achieving a wall thickness profile that is uniform over the cross section.
• the rollers are opened by moving them apart to a distance that corresponds to the wall thickness to be set in the area of the caliber base. Since in single-caliber plug rolling mills all passes have to be rolled in one and the same calibration (unlike in the case of continuous longitudinal rolling processes, for example, a tube continuous line), you can get variation options of the caliber in plug rolling by setting the rolls differently for the different passes.
• the rollers can be opened by the amount of this addition before the first stitch. With three stitches, the rollers can also be opened before the second stitch.
• the wall thickness profile in the subsequent stitch in the caliber base of the previous stitch is set by appropriately designing the mathematically or empirically determined contour curve describing the caliber base. It was found that the wall thinning in the caliber jump does not necessarily take place over the entire freely deformed area with a constant decrease in wall thickness, but with a different decrease in wall thickness, depending on whether one looks at the exact center of the caliber jump or the adjacent zones. A round and precisely centric calibration would possibly lead to inaccurate wall thicknesses.
• the wall thickness itself is specified in the base of the caliber by a corresponding selection of the plug diameters. So if the wall in the base of the caliber is to receive an offer, that is Reduce the plug diameter of this stitch accordingly. However, this leads to a large number of finely graduated diameters with a correspondingly expensive storage of plugs.
• the plug rolling process takes on a new meaning and becomes competitive with other modern rolling processes.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
• Control Of Metal Rolling (AREA)
• Metal Rolling (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Citations (2)

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• 1992
  • 1992-04-16 DE DE4213276A patent/DE4213276C2/de not_active Expired - Fee Related
• 1993
  • 1993-03-12 DE DE59301525T patent/DE59301525D1/de not_active Expired - Fee Related
  • 1993-03-12 EP EP93250081A patent/EP0566223B1/fr not_active Expired - Lifetime
  • 1993-04-16 US US08/049,059 patent/US5412974A/en not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (2)

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