GB2128120A

GB2128120A - Expanding skew rolling mill

Info

Publication number: GB2128120A
Application number: GB08326233A
Authority: GB
Inventors: Karl-Heinz Brensing; Rolf Kummerling; Manfred Bellmann; Walter Knauf
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1982-10-01
Filing date: 1983-09-30
Publication date: 1984-04-26
Also published as: IT8323096A0; DE3236893A1; IT8323096A1; FR2533843A1; GB8326233D0; FR2533843B1; IT1166978B

Abstract

The invention relates to expanding skew rolling mills in which working rolls (2,3) arranged around a mandrel (4) and inclined to two perpendicular axes containing the mandrel axis to roll a hollow pipe (1) over the mandrel (4). According to the invention, the working rolls (2,3) have hyperbolic working surfaces (10) which cooperate with the tapered section (11) of the mandrel (4) to define a convergent roll gap through which the pipe (1) is driven. After the tapered section (11), the mandrel is formed with a further tapered section (12) in which the taper reduces. This region allows for equalization of the pipe material, and normally defines a non-convergent roll gap. <IMAGE>

Description

SPECIFICATION Expanding skew rolling mill The invention relates to expanding skew rolling mills, and particularly to the calibration of the working rolls and mandrel thereof.

The manufacturers of seamless pipes of large diameter, over 300 mm, requires very costly plant.

Owing to rapid cooling and the amortization of the capital expenditure on plant of this type, products of unsatisfactory quality are sometimes produced. A solution offered to this problem is to produce pipes of smaller dimensions in the usual manner, and progressively minimize the diameter using an expanding roller mill. The expenditure for tools in expanding rolling mills (working rolls and mandrels) is however, also considerable.

The present invention is an expanding skew rolling mill in which the working surfaces of the rolls are hyperbolic and matched to the contours of the mandrel to achieve a desired expansion of a workpiece. According to the invention such a mill has a plurality of rolls with hyperbolic working surfaces, arranged around a rolling axis, the axis of each roll being inclined to two perpendicular planes containing the rolling axis; and a mandrel located at the rolling axis, the mandrel having a first intake section, a second linear tapered section, and a third section in which the taper reduces the respective sections being axially contiguous in the direction of rolling, wherein the inclination of the rolls to the rolling axis is such that juxtaposed areas of the working surfaces of each roll and the second section of the mandrel define a convergant roll gap in which the mean diameter of an hollow workpiece being milled increases with a corresponding reduction in its wall thickness.

The inclination of the rolls to the rolls of the rolling axis is preferably such that juxtaposed areas of the working surface of each roll and the third section of the mandrel defines a non-convergant roll gap. The inclination may also be such that the line of contact between the outer surface of an hollow workpiece being milled and the working surface of each roll is substantially linear over the axial length of the second section ofthe mandrel in a plane containing the rolling axis. The angle of twist of the rolls; i.e. the angle defined by the projection of the axis of each roll onto a plane containing the rolling axis is normally in the range 2 to 35 , preferably about 15 .

Mills according to the invention can be made adaptable to provide various amounts of expansion with workpieces of different initial diameters by having the mandrel interchangeable with others in which the taper on the second section and/or the axial length thereof is different. By also rendering the inclination of the rolls adjustable, the aforesaid roll gap characteristic can be maintained in conjunction with a variety of different mandrels. The rolls can thus be given a contour such that they are suitable for the manufacture of a whole diameter series of large pipes and cooperate with mandrels which differ in length. Suitable roll contours can be readily designed. Expansions of approximately 20 to 100 mm have ben achieved with a single set of rolls.

Only the mandrel was changed to accommodate the different initial and finished dimensions.

Unexpectedly, rounding or equalizing of the pipe, necessary following the expansion, can take place as the workpiece passes over the end section of the mandrel. This, to some extent at least, obviates the need to include an additional treatment step; this qualitative improvement of the pipe is usually accomplished by means of a special skew-rolling mill or reeler.

An embodiment if the invention will now be described by way of example and with reference to the accompanying drawings wherein Figure lisa longitudinal section of an expanding rolling mill of the invention in the plane of the rolling axis thereof; and Figure 2 is a longitudinal section of one of the working rolls shown in Figure 1 on a plane containing the axis thereof.

In Figure 1 two inclined rolls 2 and 3 of an expanding rolling mill are shown on opposite sides of a mandrel 4 arranged therebetween on the mandrel rod 5, and a pipe 1, which is to be rolled.

The pipe or rolling axis 6 and the projections 7,8 of the roll axes on the plane of the drawing are also shown.

The axes of the rolls 2,3 are inclined and twisted relative to the rolling axis 6 to thereby produce, with the same direction of rotation, a thrust onto the pipe to the left of the drawing as shown. The contour of the rolls is shown in Figure 2, in which the roll axis 7 is in the plane of the drawing. It consists of an intake taper or rounding 9 and a hyperbola-like or hyperbolic working surface 10. The other, possibly also several other, rolls are of the same construction. The axes of the rolls 2,3 are inclined to the rolling axis 6, to an extent corresponding to the shape of the working surfaces 10 and the taper of the mandrel 4, and the rate of advance required for pipe 1 through the wall. Figure 1 shows a relatively small angle between the roll and rolling axis.The angle of twist (in a plane perpendicular to that of the drawing is about 15 although, according to circumstances, different angles of twist may be used, normally in the range 2 to 35". By altering the angle of twist the ratio of longitudinal to circumferential speed over the length of contact of the roll is varied.

The hyperbolic working surface of the rolls 2 and 3 is dimensioned such that the spatial lines of contact between rolls 2,3 and rolling material 1 lie on a taper with an axis which coincides with the rolling axis 6.

Between the rolls it will result in an emergence from the assumed deformation taper. The mandrel 4 on the rod 5 is mounted for rotation about the longitudinal axis 6. The rod 5 is held in a support in a manner known perse, and is not shown in the drawing.

The mandrel 4, apart from rounding of edges, consists primarily of three sections; a first intake section, and second (11) and third (12) tapered sections without hyperbolic retraction. The second section 11, is operative in conjuction with the rolls 2,3 for the expansion of the hollow body 1. The extent of the expansion of the hollow body 1 is determined by the length of the taper 11. The third section 12 follows on from second section 11.

Section 12 has a smaller angle of taper than section 11, which further reduces along its axial lengths so that the pipe, sliding over it and releasing itself from the contact with the rolls, is equalized. The pipe 13 emerging from the expanding rolling mill is a finished pipe, which must undergo slight longitudinal rolling, if required, to true measurement. The rounding 14 of the mandrel 4 following the tapered section 12 in the direction of rolling can serve for further finishing, but is not of great significance in the rolling technique itself.

The axial extent of the second, tapered section 11 is cooordinated to the desired expansion, so that during rolling the mean diameter of the pipe 1 as it passes over section 11 increases as much as the wall thickness decreases. The third section 12 is of smaller axial length and has a smaller angle of taper at its junction with section 11, which reduces to a very small angle of taper at its other axial end. Thus, the overall cross-section of the pipe wall may remain the same before and after rolling and no axial extension or compression of the pipe 1 need take place.

Claims

1. An expanding skew rolling mill having a plurality of rolls with hyperbolic working surfaces arranged around a rolling axis, the axis of each roll being inclined to two perpendicular planes containing the rolling axes; and a mandrel located at the rolling axis, the mandrel having a first intake section, a second linear tapered section, and a third section in which the taper reduces, the respective sections being axially contiguous in the direction of rolling, wherein the inclination of the rolls to the rolling axis is such that juxtaposed areas of the working surface of each roll and the second section of the mandrel define a convergant roll gap in which the mean diameter of an hollow workpiece being milled increases with a corresponding reduction in its wall thickness.

2. A skew rolling mill according to Claim 1 wherein the inclination of the rolls to the rolling axis is such that the line of contact between the outer surface of an hollowworkpiece being milled and the working surface of each roll is substantially linear over the axial length of the second section of the mandrel in a plane containing the rolling axis.

3. A skew rolling mill according to Claim 1 or Claim 2 wherein the inclination of the rolls to the rolling axis is such that juxtaposed areas of the working surface of each roll an the third section of the mandrel defines a non-convergent roll gap.

4. A skew rolling mill according to any preceding Claim wherein the mandrel is interchangeable with others in which the axial length of the second section differs, and wherein the inclination of the rolls to the rolling axis is adustable to establish the aforesaid roll gap characteristics with any one of such other mandrels.

5. A skew rolling mill according to any preceding Claim wherein the projection of the axis of each roll onto a plane containing the rolling axis defines one angle with the rolling axis in the range 2 to 35".

6. A skew rolling mill according to Claim 5 wherein said angle is 15 .

7. A skew rolling mill according to any preceding Claim wherein two said rolls are arranged on diametrically opposed sides of the rolling axis.

8. An expanding skew rolling mill substantially as described herein with reference to the accompanying drawings.