FR2553012A1 - Method for controlling the lubrication conditions of a mandrel of a pilgrim step rolling mill (pilger mill) and device for implementing this method - Google Patents

Abstract

The method and the device according to the invention relate to the cold rolling of tubes using a pilgrim step rolling mill (pilger mill). The method consists in improving the cooling of the rolling surface 20 of the mandrel 19 by introducing a highly pressurised fluid into the annular space between the mandrel and the tube 21 during rolling. Passage means 23, 31 make it possible to ensure the arrival and the departure of the fluid through the mandrel and sealing means 26, 29 make it possible to control the course of the fluid. The method applies in particular to the rolling of tubes with large cross-sections, for example made from steel, with high reduction rates.

Description

PROCESS FOR CONTROLLING THE LUBRICATION CONDITIONS OF THE MANDREL OF A LEII.NOIR WITH NO PILGRIM AND DEVICE FOR CARRYING OUT THIS PROCESS.

The process which is the subject of the invention relates to the control of the temperature and lubrication conditions which prevail in the working area of a cold-pilgrim tube rolling mill.

 I1 is known that the very significant deformation that the tube undergoes during its rolling between the mandrel and the grooves of the cylinders of a rolling mill of this type causes a very significant heating of this tube which is transmitted to the mandrel. In order to limit this overheating, it is known to spray the tube externally by means of a lubricant which at the same time plays the role of cooling fluid.

 Generally, the tube is also lubricated inside. In known manner, this lubrication can be carried out for example by a soaking operation, in an oil tank, prior to rolling, or by i-trodllction of a lubricant inside the tube in the space between that -ci and the chuck rod upstream of the chuck. In fact, the lubricant introduced inside the tube has the essential purpose of creating a film on the surface thereof which allows the tube to slide without seizing on the mandrel during its deformation. Such means of lubrication and control of the rolling temperature are suitable for pilgrim rolling mills commonly used to reduce tubes of relatively small section.

On the other hand, it is known that, when it is desired to increase the production rates or to use such rolling mills to carry out large reductions or / and to work tubes of large section, serious difficulties are encountered. Indeed even a relatively intense sprinkling carried out on the external surface of the tubes during rolling does not prevent a very significant heating of these tubes in the zone which is in direct contact with the mandrel. This is in particular the case of tubes made of metals or alloys of low thermal conductivity such as steels. Under such conditions there is a rise in temperature of the mandrel, in its zone of contact with the tube which can be a cause of destruction of the lubricating film which covers the internal surface of the latter and of seizure of the tube on the mandrel. go
a 3sister a deterioration of the surface of the mandrel by cracking of said surface.

We therefore sought in order to improve the rolling conditions and / or to avoid deterioration of the mandrel the possibility, on the one hand of lowering the temperature of the nandrin to avoid the decomposition of the lubricants used, and on the other hand part to improve the lubrication conditions of the inner surface of the tube in the rolling zone.

The process for controlling the temperature and lubrication conditions of the mandrel of a cold pilgrim step rolling mill which is the subject of the invention applies to pilgrim step rolling mills equipped with a rolling mandrel. This rolling mandrel is preferably fixed removably by its upstream end to one of the two ends of a connecting piece, the other end being fixed to a nanorin carrier rod.

However, it is conceivable to use for the implementation of the invention a nonobloc assembly, not removable, constituted by the rolling man proper, and its connecting piece, which is then directly fixed to the downstream end of the chuck rod. The diameter of the bearing surface of revolution of this rolling mandrel decreases from downstream and is advantageously conical over most of its length. The process according to the invention consists in introducing a fluid under high pressure into the annular space between the mandrel and the tube during rolling upstream of the rolling range and downstream of a first annular sealing means, arranged around the connecting piece, which ensures the sealing between the tube and this part, so as to force the fluid to flow in the downstream direction between the mandrel and the tube.

Preferably a second annular sealing means also ensures a tight connection between the mandrel and the tube downstream of the rolling range so as to prevent the fluid from escaping downstream and to force it to return towards the upstream, through a passage formed in the mandrel so as to join a fluid departure area.

 It is particularly advantageous, in order to promote the passage of the fluid between the mandrel seat and the tube during rolling, to advance the tube twice during each rolling cycle, that is to say in the vicinity of each of the two upstream and downstream dead spots.

The arrival of the fluid under high pressure is preferably carried out from the inside of the mandrel holder rod and the departure of this fluid is preferably carried out also in the annular space between the mandrel holder rod and tube.

This departure can also be carried out from the inside of the portemandrin rod by adapting the necessary pipes.

The fluid used must have lubricating properties.

It can be a fluid based on hydrocarbon compounds or any other fluid capable of playing the role of lubricant. This fluid advantageously has good heat transfer properties.

The invention also relates to a device for introducing fluid between the rolling mandrel of a rolling mill with cold pilgrim steps and a tube during rolling; it comprises a first annular sealing means arranged around the workpiece. connection forming a sliding seal between the mandrel and the tube, and a first passage means arranged inside the connection piece, the inlet of which is located at the upstream end of the connection piece or in its immediate vicinity in the connection zone with the mandrel holder rod is in communication with a pressurized fluid inlet disposed inside the mandrel holder rod the outlet of this first passage means is in communication with the annular space included between the mandrel and the tube upstream of the rolling surface and downstream of the first sealing means.

Advantageously, a second annular sealing means forming a sliding seal between the mandrel and the tube is arranged around the mandrel, downstream of the rolling surface, and a second passage means is provided inside the mandrel and the connecting piece, the entry end of this second passage means is in communication with the annular space comprised between the mandrel and the tube, downstream of the rolling range, and upstream of the second means of sealing. The other end of this passage means is in communication with a fluid departure zone in the vicinity of the upstream end of the connecting piece.

Preferably, the communication between the second passage means and the fluid departure zone is carried out in the annular space comprised between the connecting piece and the tube upstream of the first annular sealing means. This communication can also be carried out at the connection between the upstream end of the connecting piece and the mandrel holder rod, inside this rod by adapting the necessary pipes. The fluid injection pressure is advantageously between 10 and 50 bars.

The description and the figures below show in a nonlimiting manner various embodiments of the method and of the device according to the invention.

Figure 1 shows in section a known embodiment of a mandrel for rolling down with pilgrim's steps
Figure 2 shows in section a first embodiment of a mandrel according to the invention.

Figure 3 shows in section a second embodiment of a mandrel according to the invention.

We see in Figure 1 a mandrel (1) fixed to the end of a mandrel holder rod (2) of tubular shape by means of a connecting piece (5). A tube (3) is shown during rolling on the conical surface (4) of the mandrel, and therefore in intimate contact with it. On the other hand, an annular space is formed between the connecting piece and the tube and there is also a slight clearance between the mandrel and the rod in the downstream part of the latter.

The internal lubrication of the tube is carried out by an inlet of pressurized oil which is carried out from the inside of the mandrel holder rod at (7), crosses the passage (8) produced inside the connecting piece. and opens into the annular space (9) upstream of the rolling surface (4).

During operation, the internal lubricant which opens into the annular space escapes mainly upstream, flowing in the space between the mandrel holder rod and the tube to be laminated.

A small fraction permeates the internal wall of the tube and allows it to slide over the bearing surface of the mandrel (4) during rolling.

On the other hand, the quantity of lubricant thus entrained downstream is much too low to cool the mandrel significantly.

as a result, in cases where large section tubes are rolled with high reduction rates, the temperature of the mandrel becomes such that the lubricants lose their effectiveness, which is a cause of seizure.

FIG. 2 shows a first embodiment of a mandrel according to the invention making it possible to implement the method also according to the invention.

We see a mandrel (10) with a tapered rolling surface (11) placed inside a tube (12) during rolling and connected to a hollow mandrel holder rod (13) by means of a piece of removable link P1.

A first passage means (14) puts in communication an inlet for pressurized lubricating fluid which takes place at (15) with the annular space (16) comprised between the connecting piece and the tube upstream of the rolling surface (11). This annular space is closed upstream by a first annular sealing means. In the case of the figure, this sealing means is an annular lip seal (17) arranged in a groove (18) formed around the connecting piece; the lip of this seal is oriented so as to resist the pressure of the fluid contained in the annular space (16) while allowing the tube (12) to slide from upstream to downstream.

In the area where this joint is located, there is no significant heating of the tube and the connecting piece since the deformation takes place downstream. Thanks to this seal, the fluid can only flow downstream between the tube and the mandrel.

Such flow is favored each time the tube is moved downstream, the mandrel remaining fixed which takes place at least once per rolling cycle. The tube is then detached from the mandrel; thanks to the taper thereof, a relatively large fluid flow can be achieved between the mandrel and the tube, provided that the supply pressure is sufficient.

The lubricating fluid thus comes into contact with the zone which has just been heated by the deformation of the tube and its cooling action is therefore particularly effective although very brief. In fact, as soon as the rolling phase begins, the passage of the fluid between the tube and the mandrel is interrupted again.

In order to increase the quantity of fluid which passes between tube and mandrel, the tube can advantageously be subjected to two advances per rolling cycle, one in the vicinity of the upstream dead center and the other in the vicinity of the downstream dead center.

This can further reduce the surface temperature of the chuck reach.

For example, a lubricant similar to that which is usually used is used as the cooling fluid. Thanks to the reduction in the operating temperature and also to the frequent renewal of the film of lubricating fluid which covers the internal surface of the tube, it is possible to prevent the tube from jamming on the mandrel, even in the case of significant reductions made on large section tubes.

It can be seen that in the case of FIG. 2, the fluid after passage in the interval between the mandrel and the tube flows downstream and must therefore be collected at the downstream end of the tube in progress or after rolling, which has practical drawbacks for the use of this technique.

FIG. 3 shows a second embodiment of a mandrel according to the invention which makes it possible to avoid the flow of the fluid downstream.

The mandrel (19) with a tapered rolling surface (20) placed inside a tube (21) during rolling is connected to a hollow rod holder rod (22) by a connecting piece P2 as in the case of Figure 2 I1 similarly comprises a first passage means (23) communicating the arrival of pressurized lubricating fluid which takes place in (24) with the annular space (25) between the connecting piece and the tube and located upstream of the rolling surface (20). This annular space is closed on the upstream side by a first annular sealing means drilled by a lip seal (26) housed in a groove (27).

Downstream of the conical rolling surface (20) an annular space (28) drilled around a substantially cylindrical extension of the mandrel is limited downstream by a second sealing means constituted by an annular seal (99) placed in a throat (30). Given the relatively high temperature reached in this area, this seal (29) can be formed.

by one or more metallic seignants which scrape the internal surface of the
tube. A second passage means (31) which extends over almost the entire length of the mandrel and opens out through the radial channels (32) into the annular space (28) places this space in communication with the annular space (33) between the chuck rod and the tube upstream of the lip seal (26).

It can be seen that, in the case of this mandrel thus arranged, the pressurized fluid which is sent into the annular space (25) from the arrival zone and through the first passage means (23) flows downstream between the tube (21) and the tapered seat t20) of the mandrel to the annular space (28). Thanks to the second seal (29) the fluid returns upstream through the second passage means (31-3?) Until
the annular space (33).

Beyond the fluid flows upstream and can be easily collected and recycled. Such an arrangement makes it easier to operate the rolling mill. In the embodiments shown in Figures 2 and 3 the connecting pieces P1 and P2 are connected to the rolling mandrels t0) and (l9) by threaded ends R1 and R2.

The connector R2 is crossed by the passage means (31). As has been said above, it is possible to envisage making a single piece I> ek seems to be formed by the rolling mandrel and the connecting piece.

By way of example, a rolling steel tube of 114 mm outside diameter and 16 mm diameter is cold rolled on a pilgrim step rolling mill provided with a mandrel comprising a lubrication device in accordance with FIG. 3. thickness.

A suitable lubricant is injected at (23) under a pressure of approximately
15 bars. This lubricant after circulation between mandrel and re tube
turns upstream through passage (32) and (31).

A laminated tube with an outside diameter of 76 mm and a thickness of 8 mm is obtained, produced at a rate of approximately 160 m / hour. It can be seen that the surface condition of the internal wall of the tube is excellent.

Many modifications can be made to the device and to the process which are the subject of the invention without departing from the field of the latter. One can in particular use mandrels of shape other than comic, provided that the section of their rolling range decreases from upstream to downstream; it is indeed necessary that at the time of the advance of the tube it comes off the mandrel. The sections of the first and second passage means must be determined, taking into account the fluid pressure on arrival to allow a sufficient flow of this fluid without, however, harming the mechanical pressure of the mandrel. A wide variety of coolants can be used in addition to the lubricants commonly used.

The fluids must combine the capacity for heat transfer and the capacity for lubrication under the conditions specific to rolling mills with pilgrim steps.

Claims (9)

10) Method of lubricating the mandrel of a rolling mill with cold pilgrim's step in which a rolling mandrel is used, the upstream end of which is extended by a connecting piece fixed to the mandrel holder rod, this mandrel having a bearing whose diameter decreases from upstream to downstream, characterized in that a fluid is injected under high pressure into the annular space between the connecting piece and the tube being rolled upstream of the rolling range and downstream of a first annular sealing means, which ensures a tight connection between the tube and the connecting piece, so as to force the fluid to flow in the downstream direction between the mandrel and the tube. 20) Method according to claim 1, characterized in that a second annular sealing means, which ensures a tight connection between the mandrel and the tube downstream of the rolling surface prevents the fluid from escaping downstream and the 'forces to return upstream, through a passage formed in the mandrel so as to join a fluid departure area. 30) Method according to claim 1 or 2, characterized in that the passage of the fluid is favored by carrying out a double advance of the tube at each rolling cycle in the vicinity of each of the upstream and downstream dead centers. 40) Method according to claims 1 or 3, characterized in that the arrival of the fluid under high pressure takes place from the inside of the mandrel holder rod and in that the departure of the fluid takes place in the interval ring between chuck rod and tube or inside the chuck rod. 50) Method according to claims 2 or 3, characterized in that the arrival of the fluid under high pressure is effected from the inside of the mandrel holder rod.  60) Method according to one of claims 1 to 5, characterized in that the cooling fluid is a lubricant based on hvdrocarbon compounds.  7) Method according to one of claims 1 to 6, characterized in that the mandrel and the connecting piece constitute a single piece. 80) Device for introducing fluid between the surface (11) of a rolling mandrel (10) of a rolling mill with cold pilgrim steps and a tube (12) during rolling, characterized in that it comprises a first annular sealing means (17) disposed around the connecting piece upstream of the rolling surface, forming a sliding seal between the connecting piece and the tube, and a first passage means (14) formed at the the interior of the connecting piece, the inlet of which, located at the upstream end of the mandrel, or in its immediate vicinity in the zone of connection with the mandrel holder rod, is in communication with a pressurized fluid inlet (15) disposed inside the mandrel holder rod (13), the outlet of this first passage means being in communication with the annular space (16) between the connecting piece and the tube upstream of the rolling surface and downstream of the first sealing means (17). 90) Device according to claim 8, characterized in that a second annular sealing means (29) is arranged around the mandrel downstream of the rolling surface so as to form a joint between the mandrel and the tube, and a second means passage (31), being arranged inside the mandrel, the inlet end (32) of which is in communication with the annular space (28) comprised between the mandrel and the tube downstream of the rolling surface (20) and upstream of the second sealing means, the other end being in communication with a fluid starting area (33) in the vicinity of the upstream end of the connecting piece (P2). 100) Device according to claim 9, characterized in that the communication with the starting area of the fluid is carried out in the annular space comprised between the connecting piece and the tube upstream of the first annular sealing means. 110) Device according to one of claims 8 to 10, characterized in that the mandrel and the connecting piece constitute a single piece.