GB2075392A

GB2075392A - Drawing tubes

Info

Publication number: GB2075392A
Application number: GB8110221A
Authority: GB
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1980-05-10
Filing date: 1981-04-01
Publication date: 1981-11-18
Also published as: AU6946081A; JPS579524A; DE3018052A1; DE3018052C2; GB2075392B

Abstract

Drawing apparatus comprising a drawing drum rotatable about a vertical axis and a drawing die (2) mounted on a universal joint and being movable upwards with each turn of drawn tube wound on the drum by a distance comparable with the tube diameter of the drawn tube includes a roller straightening tool (3) provided in line with and upstream of the drawing die (2). In use, during upward movement of the drawing unit, the unit is aligned and fixed at the pitch angle of the turns drawn on to the drawing drum. After the uppermost turn has reached the rim of the drum the unit is aligned and fixed in respect of a point of aim offset by the amount of the radius of the tube running out. <IMAGE>

Description

SPECIFICATION Apparatus and method for drawing tubes The invention relates to an apparatus of the type suitable for use in drawing tubes and comprising a drawing drum which can be driven to rotate about a vertical axis and which applies the requisite drawing force, and a drawing die mounted on a universal joint; the tube end guided through the drawing die (in use) being engaged by drawing tongs and the requisite number of turns of drawn tube being wound on to the drawing drum as a result of rotation of this drum; the drawing die being moved upwards with each turn by a distance comparable with the tube diameter of the drawn tube; and, after application of (a) pressure roller(s), the drawing tongs releasing the tube end, upon the turns reaching the rim at the upper end of the drawing drum.

Apparatus of this type is known from U.S.

Patent Specification 3,496,751. The tube end which is guided through a die mounted on a universal joint is engaged by a gripper and wound on to a vertically disposed drawing drum, and the drawing die, which is mounted so as to be freely rotatable, is transported slowly upwards in the direction of the axis of the drawing drum, until the uppermost turn encounters the rim of the drawing drum. At this moment, pressure rollers are brought up to the drawing drum and the drawing tongs sever the tube end. The drawing force is now transmitted by friction only. An equivalent amount of tube to the amount of tube running on to the drawing drum is conveyed into a basket-like container placed underneath the drawing drum.

The tube to be drawn is similarly extracted from a basket-like container, into which it has been inserted in coils. The tube enters the drawing means in a curved attitude, and consequently from changing directions, because it runs out of the basket-like container laterally. The drawing means would adjust itself to the different directions,.but is simultaneously aligned, by the drawing force applied by the drawing drum, in the direction of the point of aim of the tube on the drawing drum.

Thus, as a result of the forces which act upon it, the drawing die is set in a middle position which guarantees neither a perpendicular entry into the die nor a perpendicular exit from the die. The varying resistances during the delivery of the tube from the basket result in indentations in the tube with which are associated sharply alternating directions of entry into the drawing means, and which, to that extent, lead to non-uniform wall thickness in the tube.

Theoretical considerations and practical tests have indicated that insignificantly non-uniform wall thicknesses can be achieved only if, under all circumstances, the tube enters the drawing die at right angles and leaves it at right angles, during the entire drawing process.

It is an object of the present invention, therefore, to provide a tube drawing apparatus of the type first mentioned herein which makes it possible for a tube to enter the drawing die at right angles and leave the drawing die at right angles, during the entire drawing process, and, therefore, to produce a tube which has a virtually uniform wall thickness over its entire cross-section.

According to the present invention, an apparatus of the type first mentioned herein is characterised in that a roller straightening tool is provided in line with and upstream of the drawing die, and in that the drawing unit comprising the said tool and die is, in use, during its upward movement, aligned and fixed at the pitch angle of the turns drawn on to the drawing drum, and, after the uppermost turn has reached the rim of the drum, aligned and fixed in respect of a point of aim offset by the amount of the radius of the tube running out. The requirement for entry into the drawing die at right angles is met by the provision of the roller straightening tool, which is arranged, together with the die, in a drawing unit mounted on a universal joint.However, in an apparatus according to the invention, the universal joint mounting does not serve, as in the known apparatus, to ensure that the drawing unit can adjust itself to the direction of the tube, but serves instead to enable the drawing unit to be adapted for use with different tube diameters. During the actual drawing operation, the drawing unit is aligned, as indicated above, with a point of aim offset by the amount of the radius of the tube running out. Particularly with tubes which have small diameters or thin walls, the drawing forces could be insufficient to align the drawing unit, so that the forces which act on the die from the entry side of the die would change the direction of the drawing die constantly. However, an improvement in quality can be noted even in the case of relatively large tube dimensions.

According to a preferred feature of the invention, it is provided that, at a distance from the point of rotation of the drawing unit, a horizontally adjustable cylinder and a vertically adjustable hydraulic cylinder engage on the drawing unit, these hydraulic cylinders each pressing the drawing unit, in the position desired at any given time, against a respective stop. The stop, and consequently the orientation of the drawing unit, are fixed for each tube dimension.

An especially useful adaptation to the different tube diameters can be achieved if, as is particularly preferred, the stops are vertically and laterally adjustable, for example by means of a screw thread adjustment device.

In addition to the apparatus, the invention includes a tube drawing method wherein the tube to be drawn is passed through the straightening tool and drawing die, and wound on to the drawing drum, of an apparatus as just described, under the conditions indicated.

The invention will be explained in more detail with reference to the accompanying drawings in which Fig. 1 is a diagrammatic side view, mostly in section, of the drawing unit of an apparatus according to the invention, Figure 2 is a corresponding top view, and Figure 3 is a graph showing certain tubedrawing results, explained below.

A copper tube 1 which runs out of a basket-like container (not shown) is, as described in U.S.

Patent Specification 3,496,751, drawn through a die 2 and coiled on to a drawing drum, not shown.

Before it enters the die 2, the copper tube 1 is guided through a set of straightening rollers 3 and a lead-in ring 4. The die 2, ring 4 and rollers 3 are mounted on a carriage to provide a drawing unit 5, which is hinged on a universal joint 6. As in the case of the above-mentioned U.S. Patent Specification, the unit 5 can be moved vertically at the start of the drawing process. In contrast to the case of the above-mentioned U.S. Patent Specification, however, the unit 5 cannot pivot freely, but is fixed in a predetermined position.

There serve for this purpose hydraulic cylinders 7 and 8 which align the unit 5 in a vertical and horizontal direction, and press it against respective stops 9 and 10, which can be adjusted vertically and laterally rnspectively. A further hydraulic cylinder 11 is provided to open the set of straightening rollers 3 for introducing the leading end of the tube 1. An adjusting lever 12 permits an adjustment to suit the relevant tube diameter, or the desired straightening effect. In any case, the set of straightening rollers 3 guarantees a perpendicular entry of the tube 1 into the die 2.

Irrespective of the direction from which the tube 1 enters, it is preliminarily straightened, and is supplied to the die 2 centrally and at right angles.

It is important that the die 2 and rollers 3 should be connected to one another in a fixed relationship in a movable unit, since otherwise one could not satisfy the principle of an entry at right angles even by means of a straightening mechanism.

Two phases are to be distinguished when the tube 1 leaves the die 2 at right angles. During an entry phase, the direction of the drawing unit 5 must be inclined at a certain angle in a vertical direction. This angle corresponds to the pitch angle of the turns of the tube on the drawing drum. The drawing unit 5 is set in this inclined position by means of the hydraulic cylinder 7 and the stop 9. When the tube 1 has reached the rim of the drum, the hydraulic cylinder 7 is reversed to bring the drawing unit 5 into exact alignment with the contact point at the rim and holds the drawing unit 5 fast again. The desired condition of an exit at right angles is, in this way, guaranteed perfectly in both phases.

The hydraulic cylinder 10 and the stop 8 are provided to enable one to adjust the drawing unit 5, in the event of a change in the diameter of the tube 1 to be drawn.

Figure 3 is a graph in which are plotted, on the abscissa, the non-uniformity of the wall thickness of the tube (as a percentage), and, on the ordinate, the proportion of measurements (as a percentage).

Here, the broken line relates to tubes processed by means of a conventional drawing appliance. In the case of the conventional drawing appliance, the maximum percentage of measurements occurs at a non-uniformity of the tube wall thickness of 13 to 14%, whereas the unbroken line (drawing appliance according to the invention) shows a maximum percentage of measurements at a not uniformity of the tube wall thickness of 4 to 5%.

It is of particular advantage, when the tube diameter is changed and after the die has been replaced, if a programme control system can be employed to carry out automatically all such process sequences as the setting of the straightening tool to suit the diameter of the incoming tube, the adjusting of the drawing unit laterally to the new point of aim, the setting of the angle of the drawing unit when it is raised, and the reversal when the drawing drum rim is reached.

Claims

1. Apparatus suitable for use in drawing tubes and comprising a drawing drum which can be driven to rotate about a vertical axis and which applies the requisite drawing force, and a drawing die mounted on a universal joint; the tube end guided through the drawing die (in use) being grasped by drawing tongs, and the requisite number of turns of drawn tube being wound on to the drawing drum as a result of the rotation of this drum; the drawing die being moved upwards with each turn by a distance comparable with the tube diameter of the drawn tube; and, after application of (a) pressure roller(s), the drawing tongs releasing the tube end, upon the turns reaching the rim at the upper end of the drawing drum; characterised in that a roller straightening tool (3) is provided in line with and upstream of the drawing die (2), and in that the drawing unit (5) comprising the tool (3) and die (2) is, in use, during its upward movement, aligned and fixed at the pitch angle of the turns drawn on to the drawing drum, and, after the uppermost turn has reached the rim of the drum, aligned and fixed in respect of a point of aim offset by the amount of the radius of the tube running out.

2. Apparatus according to claim 1, characterised in that, at a distance from the point of rotation of the drawing unit (5), a horizontally adjustable cylinder (8) and vertically adjustable hydraulic cylinder (7) engage on the drawing unit (5), these hydraulic cylinders each pressing the drawing unit (5), in the position desired at any given time, against a respective stop (10, 9).

3. Apparatus according to claim 2, characterised in that the stops (9, 10) are vertically and laterally adjustable.

4. Apparatus according to claim 1, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

5. A tube drawing method wherein the tube to be drawn is passed through the straightening tool and drawing die, and wound on to the drawing drum, of an apparatus as claimed in claim 1, 2 or 3 under the conditions indicated therein.

6. A method according to claim 5, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

7. Drawn tubing obtained by a method according to claim 5 or 6, or by means of an apparatus according to claim 1, 2, 3 or 4.