GB2093384A

GB2093384A - Pilger rolling of tubes

Info

Publication number: GB2093384A
Application number: GB8205358A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1981-02-24
Filing date: 1982-02-23
Publication date: 1982-09-02
Also published as: CS245769B2; IT1140130B; ATA28582A; GB2093384B; DD202251A5; MX156528A; DE3107824A1; JPS57139410A; AT387732B; IT8125548A0; FR2500338A1; NL8105194A; FR2500338B1; DE3107824C2; KR830008746A

Abstract

A tube is rolled by means of grooved rolls supported in a reciprocable rolling stand movable backward and forward with respect to an axially fixed conical mandrel supporting the workpiece. To optimize the efficiency of the method, the total rolling work is distributed such that a major portion thereof is produced on the forward stroke and a minor portion on the backward stroke of the roll stand. Rotary indexing of the tube takes place at both the feed- and delivery dead centres, and may be from 20 DEG to 40 DEG at each centre. <IMAGE>

Description

SPECIFICATION Method for the rolling of tubes This invention relates to a method for the rolling of tubes of the type in which two calibrated rolls, arranged opposite each other and supported in a roll stand, are moved backwards and forwards on a tubular rolling material, which is arranged on an axially fixed conical mandrel. In such methods the rotatably driven rolls have working passes tapering on their circumferential surfaces and adapted to the shape of the conical mandrel, which roll out the rolling material on the mandrel, the rolls at the ends of the working passes releasing the rolling material in both dead centres of the rolling stand path for the purpose of producing the thrust and for rotation.

In a known method for the rolling of tubes the tubular material which is to be worked on an axially fixed conical mandrel is extended by means of calibrated rolls, moved backwards and forwards, supported in a roll stand. At the feed dead centre (dead centre on the feed side of the rolling material of the roll stand path), the tubular material is released from the ring rolls, enabling the thrust of the tubular material and the rotation of the tubular material about a particular required angle of rotation, to be carried out.

In the above method the thrust of the rolling material is produced at the feed dead centre; i.e., before the forward stroke of the roll stand. The necessary rotation of the rolling material - the angle of rotation lies in the range of 500 to 700 takes place in this rolling method also at the feed dead centre of the roll stand.

Since in this method the effective rolling work is performed practically on the forward stroke of the roll stand, this method has been termed "cold pilger method". On the backward stroke of the roll stand no rolling work was performed.

In a method disclosed in German Patent Specification No. 1 6 02 036, the thrust of the rolling material is produced 1 00% or for the most part at the delivery dead centre of the roll stand path; i.e., before commencement of the backward stroke, and to rotate the rolling material approximately 600 both at the feed dead centre and also at the delivery dead centre of the roll stand thrust. This specification also proposes that more expedient and more favourable deformation of the rolling material is achieved if the rolling takes place on the backward stroke. This proposal is disadvantageous for the following reasons:- When rolling on the backward stroke with large thrusts produced at the delivery dead centre, the rolling material must run in the opposite direction to the working rolls.In this way very great axial reaction pressure forces occur on the rolling mandrel, on the mandrel rod with mandrel support and on the feed slide. Since these axial reaction pressure forces must be coped with efficiently by the cold rolling mill, and a specific load limit cannot be exceeded, the size of the thrust which can be produced at the delivery dead centre is also therefore iimited. Thus, only relatively small thrusts can be applied at the delivery dead centre.

Consequently this proposal does not bring any improvements in comparison with the known cold pilger methods. The proposal was made without there being available, at that time, practical experience or theoretical basic knowledge of rolling technique with regard to the proposed rolling technique.

In is also proposed in German Specification No. 16 02 036, in addition to the single thrust generation at the delivery dead centre to carry out thrust generation at the feed dead centre, This does not bring any substantial increase in the total thrust (main thrust at the delivery dead centre and additional thrust and the feed dead centre), since through the additional thrust generation at the feed dead centre with the switching stroke necessary through this at the feed dead centre, as a result of the now shortened working pass length and the related increase in the rolling pressure forces, the axial reaction pressure forces on the backward stroke are increased. The size of permissible thrust in the delivery dead centre must again be reduced to such an extent that the proposal does not produce any increase in efficiency in comparison with the practised cold pilger rolling method.

In the rotation proposed in German Specification No. 1 6 02 036, of the rolling material about the angle of rotation indicated for the rolling material, mandrel with mandrel rod and feed and delivery chuck of approximately 600 both in the feed dead centre and in the delivery dead centre of the roll stand path, 9 considerable switching stroke is necessary also for the rotation in the delivery dead centre. In comparison with the cold pilger method, in which thrust and rotation takes place in the feed dead centre, this switching stroke of the working pass length and hence of the rolling work length is lost.Since basically the extent of thrust is simply proportional to the working pass length, a substantial shortening of the working pass length means a substantial reduction in the extent of thrust, so that in this proposal a reduction in efficiency would even occur in comparison with the previously practised cold pilger method.

The present invention seeks to provide a method for the rolling of tubes of the type described above, while achieving an optimal increase in efficiency in comparison with the cold pilger method through substantial increase in the total rolling work in the cold rolling of tubes. and hence a corresponding increase in the output of the rolling mill.

In a method according to the invention two calibrated rolls, arranged opposite each other and supported in a roll stand, are reciprocated on a tubular workpiece mounted on an axially fixed conical mandrel, the rotatably driven rolls having working passes tapering on their circumferential surfaces and adapted to the shape of the conical mandrel, to roll out the workpiece on the mandrel.

The rolls release the rolling material at both the feed and delivery dead centres of the roll stand cycle for the purpose of producing the thrust and for rotation. A major portion of the total rolling work performed on the workpiece is produced on the forward stroke of the roll stand and a minor portion of the total rolling work is produced on the backward stroke, and the workpiece is partially rotated at each of the feed and delivery dead centres.

In preferred methods of the invention the total rotation of the workpiece in each cycle of the roll stand is 50 to 70%, the rotation at each of the feed dead centre and the delivery dead centre being in the range 200 to 400.

It has been shown in rolling tests carried out, that with a thrust generation taking place exclusively in the delivery dead centre the total rolling work is distributed approximately half onto the following backward stroke of the roll stand and on the forward stroke of the roll stand following that.In the method of the invention, in which the major portion of the rolling work of the rolling material takes place on the forward stroke and the smaller portion on the backward stroke, there is optimal increase in efficiency in comparison with the cold pilger method, since both the forward stroke and the backward stroke are loaded with so much rolling work, that the elements of the cold rolling mill, in particular the thrust-and rotation mechanism, mandrel support and roll stand with the calibrated rolls are no more highly loaded than those of an equivalent cold pilger rolling mill with the cold pilger rolling method, and hence do not have to be altered.In the proposed method the smaller portion of the total rolling work assumes an extent which represents appreciable rolling work on the backward stroke, which therefore permits a substantial increase in the total thrust rate in comparison with the cold pilger method.

This appreciable extent of the smaller portion of the total rolling work on the backward stroke is possible because of the angles of rotation adopted according to the invention for the workpiece at the feed and delivery dead centres. With small angles of rotation, on rolling on the backward stroke the axial reaction pressure forces on the mandrel, mandrel rod, mandrel support and feed slide, are substantially smaller than in the known angle of rotation of approximately 500 to 700 both at the feed- and at the delivery dead centre. The rolling of the spread occurring on rolling in the roll gap is distributed, with the presence of the small angle of rotation at the feed- and delivery dead centres of approximately 200 to 400, onto the next forward stroke and onto the next backward stroke.

Consequently, there is a substantial reduction of the axial reaction pressure forces.

The rolling method according to the invention also produces an improvement in tube tolerances, a reduction in the differences of the tangential and longitudinal inner stresses of the cold-rolled tubes and a substantial lengthening of the service life of the rolling tools.

In the cold pilgering of copper tubes with thrust and rotation at the feed dead centre with frequently required large ingot weights (over 400 to 500 kg), in the latter portion of each ingot at the end of the working pass great retardation forces occur in the rolling material, through which there is the risk that the workpiece will make undesired movements in the delivery direction. To avoid this, it was to some extent necessary to reduce the working speed of the rolling mill in the latter region of each ingot, which meant a reduction in output.

If the rolling method according to the invention is used in the rolling of copper tubes with corresponding large ingot weights, then the retardation forces on rolling are substantially reduced, so that a reduction in the working speed of the cold-rolling mill is no longer essential.

In the preferred method according to the invention, with the small angles of rotation of approximately 200 to 400 and with the stated distribution of the total rolling work on forwardand backward thrust, the force for the thrust generation (the mandrel release force) is substantially reduced. As a result of the small mandrel release forces and the small reaction pressure forces, the cold-rolling mill runs substantially more quietly than in the application of the known cold pilger rolling method. The noise level in the cold-rolling mill with the rolling method according to the invention is thus substantially reduced.

The rolling method of the invention has particular advantage when adopted in a cold pilger rolling mill with ring grooved rolls, in which a device is provided, by means of which the angle of rotation (total roll-off angle) of the ring groove rolls used, in relation to the pitch diameter of the roll axis pinion, during each forward or backward stroke is greater than 3300. This means that the switching stroke for thrust and/or rotation of the workpiece at the delivery dead centre in the groove opening of the ring rolls and thereby on thrust or rotation at the delivery dead centre the working pass length of the ring rolls is not adversely affected.

Further, cold-rolling mills of this type, as described for example in published German Patent Application No. P 23 29 526.3, have a mechanical rotation device to produce the rotation of the workpiece, in which the necessary switching time is proportional to the size of the angle of rotation to be produced.

In the application of the method according to the invention in a cold-rolling mill of the above type, the following advantages are produced: Since the preferred angle of rotation at the feed dead centre is only approximately 200 to 400 in comparison with the size of angle of rotation of 50 to 700 in the cold-pilger method, the switching time at the feed dead centre can also be reduced by approximately half. This produces an over proportional shortening of the switching stroke at the feed dead centre and consequently the length of working pass can be correspondingly lengthened (approximately 1 5 to 20%), without the roll diameter of the ring rolls, as was used in conventional long stroke cold pilger rolling mills, being altered.This results in a particularly large long stroke, with the aid of which a corresponding increase in the total thrust; i.e., the total rolling work of the rolling material on each backward and forward movement of the roll stand, is made possible.

Since the preferred angle of rotation at the delivery dead centre in the rolling method of the invention is approximately 20C to 40 , the necessary extension of the roll stand stroke in a cold-rolling mill, which uses the method, in comparison with the roll stand stroke which the cold pilger method used on the long-stroke cold pilger rolling mill (e.g. according to published German Application No. 23 29 526) is only approximately 5 to 10%. Thus the mechanical main drive of a cold rolling mill must only be strengthened to a small extent to use the method according to the invention, resulting in a minimal increase in the weight of the total cold rolling mill.

On the other hand, an overall increase in efficiency of approximately 40 to 50% is produced in comparison with the output capacity of the known pilger rolling mill.

Claims

1. A method for the rolling of tubes, in which two calibrated rolls, arranged opposite each other and supported in a roll stand, are reciprocated on a tubular workpiece mounted on an axially fixed conical mandrel, the rotatably driven rolls having working passes tapering on their circumferential surfaces and adapted to the shape of the conical mandrel, to roll out the workpiece on the mandrel, and in which the rolls release the rolling material at both the feed and delivery dead centres of the roll stand cycle for the purpose of producing the thrust and for rotation, wherein a major portion of the total rolling work performed on the workpiece is produced on the forward stroke of the roll stand and a minor portion of the total rolling work is produced on the backward stroke, and the workpiece is partially rotated at each of the feed and delivery dead centres.

2. A method according to Claim 1 wherein the total rotation of the workpiece in each cycle of the roll stand is 50 to 70%, the rotation at each of the feed dead centre and the delivery dead centre being in the range 20C to 40 .

3. A method for the rolling of tubes according to Claim 1 and substantially as herein described.