GB2144360A

GB2144360A - Production of hollow bodies

Info

Publication number: GB2144360A
Application number: GB08419597A
Authority: GB
Inventors: Peter Odenthal; Werner Wintergerst
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1983-08-02
Filing date: 1984-08-01
Publication date: 1985-03-06
Also published as: JPS6056407A; GB8419597D0; FR2550114A1; IT1174638B; DE3328269A1; IT8422213A0

Abstract

Hollow bodies (3) are manufactured from round ingots (6) by piercing with a mandrel (4), typically between skew rolling mill rolls (1,2). Prior to piercing, a depression (7) is formed in the end of the ingot where the mandrel (4) emerges at the end of the piercing process. As a result, the creation of burrs and/or other protuberances at the runout end of the hollow body is substantially reduced or eliminated. A depression may also be formed at the mandrel entry end of the ingot (6). The depression may be formed by a twist drill, a spinning tool, or flashing off with an electric carbon arc. <IMAGE>

Description

SPECIFICATION Method for the production of a hollow body The present invention relates to the manufacture of hollow bodies from round ingots using a piercing mandrel. More particularly it relates to the preparation of the ingot for the manufacturing process. A typical such process comprises skew rolling with the piercing mandrel held between the rolls.

It is known in the manufacture of hollow bodies from round steel ingots using a piercing mandrel and skew rolling to form a depression in the front face of the ingot. The ingot is introduced into the rolling mill, and the mandrel enters into the ingot through the front face with the depression. It is important that the depression is arranged centrally to the ingot cylindrical surface and that it is formed such that the piercing mandrel hits the ingot mate riai with its tip as late as possible. Under these conditions the depression fulfill its purpose of centering the piercing mandrel.

In the manufacture of hollow bodies it is not only the central application of the piercing mandrel which is important; it is also desirable that the piercing mandrel emerges from the hollow body without leaving a burr. In known processes protuberances of material frorn the front face of the hollow body result at the end of the piercing process.

The ring-shaped, dish-shaped or tongue-shaped thin-walled protuberances so formed often have little connection with the hollow body, and can break off from the hollow body either during skew-rolling itself or in a subsequent working process. This constitutes a risk to machinery operators, and the broken pieces can also damage plant equipment and partially or fully finished products.

We have found that the creation of burrs andor other protuberances at the end of an hollow body from which the mandrel emerges in processes of the above type can be reduced and sometimes eliminated by the formation of a substantially central depression in the corresponding end of the round ingot prior to piercing with the mandrel.

Such a depression may be formed using a twist drill or spinning tool, but preferably by means of flashing off with an electric carbon arc. After flashing off, the depression may be blown out using an oxygen-containing gas such as air or oxygen-enriched air to remove molten material and smooth and spread the base. In this stage some combustion can also be desirable. The depression finned according to the invention is preferably of frustoconical shape, and most preferably widens conically towards its base.

According to the invention the above flashing off technique may also be used to form a depression at the mandrel entry end of an ingot.

The shape of a depression formed according to the invention can be especially selected for a particular piercing process to reliably reduce or eliminate burrs and/or protuberances as aforesaid. So that undulations of material are not pressed out in front of the piercing mandrel, the depression is preferably of a depth which is all the greater, the greater the mean bore diameter of the depression.

It is not important here that the undulation of material is urged radially without a shoulder into the wall thickness of the hollow body; it may also result in a rolling lap inside the hollow body and of course pinpointed at the end shortly before the emergence of the piercing mandrel from the hollow body. Such rolling laps pressed against the hollow body do not cool down so quickly and therefore do not embrittle. They do not snap off during transportation or during further processing of the hollow body. Depending on the further processing, the ends of the hollow body are separated immediately in any case, whereby the rolling lap is also eliminated.

It is not desirable for the run out of the piercing mandrel to be conducted such that the undulation of material is sheared as a ring of material in the hollow body and perhaps remains still firmly attached to the piercing mandrel. This can lead to considerable disturbances in the revolving and cooling of the mandrel. Such a situation occurs principally when the depression is not present at the emergence of the piercing mandrel or is of too small a depth. in the case of large mean diameters and smail depths of depression, however, the result is chiefly hroken off, protruding burr rings, as a.e likewise undesirable.

The depressions for the mandrel emergence side are advantageously produced in the cycle of piercing on the skew rolling mill and as noted above, preferably through flashing off with an electric carbon arc. In this way, a depression may be produced in approximately 10 seconds, and only one device to produce the depression is required for the skew rolling mill train. Technologically, the production of the depression through flashing off by carbon arc is advantageous, when a round continuous casting is used for skew rolling, which is blazed off to the length at which it is to be used.

Such cut surfaces can be hardened in places and run slightly vertically or perpendicuiar to the longitudinal axis of the ingot. Other means for the production of depressions are less reliable.

The invention will now be described by way of example and with reference to the accompanying schematic drawings wherein: Figure 1 shows the rolling process; Figures 2-4 show various depressions on the front face; and Figure 5 shows an apparatus for forming a depression in the end of a steel ingot.

In Figure 1 a solid round steel ingot is rolled out into a hollow body 3 by the skew rolling mill rolls 1 and 2, which are driven in the same direction of rotation. To form the perforation a mandrel 4 is arranged between the rolls, which mandrel is held in a support by the mandrel rod 5. In the position shown, the round steel ingot 6 is almost completely reformed into the hollow body. The mandrel 4 enters with its flattened tip into the depression 7, which is applied on the end of the round steel ingot at the runout side. On conclusion of the rolling process, the completely rolled out hollow body 3 is situated on the mandrel rod 5.

The conveying direction of the workpiece during rolling is therefore from left to right in the figure.

Figures 2 to 4 show the round steel ingot 6 in the position as it passes through the rolling mill.

This means that the front face 8 is that through which the mandrel emerges from the resulting hol low body. This front face is provided with differently formed depressions 7a,b and c.

The depression 7a may be produced through boring with a twist drill on the cold round steel ingot. The depression 7b may be produced on the al ready heated round steel ingot by a spinning tool.

The depression 7c is able to be produced with its tapered expansion for example on the cold ingot by melting on as shown in Figure 5.

Figure 5 shows apparatus for the production of a depression on the front face 8 of the round steel ingot 6. For this purpose, the round steel ingot is mounted horizontally in cold state. It may also be mounted rotating about its longitudinal axis. A car bon electrode 9 is held in a sliding carriage 10 op posite the front face of the ingot. The sliding carriage 10, in turn, is slidably arranged on a machine base 11. The movement in accordance with arrow 12 brings about the flashing off process, i.e.

the sliding carriage 10 is firstly driven so far up to the front face 8 of the round steel ingot 6 that the arc 13 can be ignited. The sliding carriage is then driven back, so that an arc is drawn. In the course of flashing off and the increase in depth of the depression in the surface 8, the sliding carriage is again driven toward the right in the drawing, in the direction towards the round steel ingot.

In the sliding carriage 10 a clamping device is available for the carbon electrode 9, in which the carbon electrode may be pushed in accordance with the arrow 14. The supply of electric current likewise takes place via the sliding carriage 10. This, and similarly the collec tion of the consumption of the carbon arc are not shown.

Claims

1. The formation of a substantially central depression at the end of a round ingot from which an hollow body is to be produced using a piercing mandrel, which end is that from which the mandrel will emerge in such production.

2. The formation of Claim 1 by means of flashing off with an electric carbon arc.

3. The formation of Claim 2 including the step of biowing out the depression using an oxygencontaining gas.

4. The formation of Claim 2 wherein the gas is one of air and oxygen-enriched air.

5. The formation of any preceding Claim wherein the depression is substantially frusto-conical.

6. The formation of Claim 1 by means of a twist drill.

7. The formation of Claim 1 by means of a spinning tool.

8. The formation of a substantially central depression at the end of a round ingot substantially as described herein with reference to the accompanying drawings.

9. A round ingot intended for the manufacture of an hollow body using a piercing mandrel having a substantially central depression formed in one end thereof, which end is that from which the mandrel will emerge in the manufacturing process.

10. A steel ingot according to Claim 9.

11. A round ingot substantially as described herein with reference to the accompanying drawings.

12. A method of manufacturing an hollow body from a round solid ingot which method comprises forming a depression substantially centrally at one end of the ingot; and piercing the ingot by forcing a mandrel therethrough from the other end.

13. A method according to Claim 12 wherein the hollow body is produced by skew rolling with the piercing mandrel held between the rolls.

14. A method according to Claim 12 or Claim 13 wherein the depression is formed by flashing off with an electric carbon arc.

15. A method according to Claim 14 including the step of blowing out the depression using an oxygen-containing gas.

16. A method according to Claim 15 wherein the gas is one of air and oxygen-enriched air.

17. A method according to any of Claims 12 to 16 wherein the depression formed is substantially frusto-conical with its narrower end at said end of the ingot.

18. A method according to Claim 12 or Claim 13 wherein the depression is formed using a twist drill.

19. A method according to Claim 12 or Claim 13 wherein the depression is formed using a spinning tool.

20. A method of manufacturing an hollow body substantially as described herein with reference to the accompanying drawings.