EP0623402B1 - Process for extrusion of metal and extrusion press - Google Patents

Description

The subject of the invention is a method of spinning a metal billet in a spinning press according to the preamble of claim 1 and also covers a spinning press according to the preamble of claim 5 or 7, suitable for placing work of said process.

It is known that, in order to produce bars, wires or other metal profiles, particularly of non-ferrous metal, an metal billet is generally extruded in a spinning press comprising, in general, a container limiting a tubular housing centered on a spinning axis closed at its ends by two closing pieces and in which is placed a billet of metal to be spun, one of said pieces being provided with a die. The assembly is placed in a frame made up of two fixed crosspieces kept apart from one another by tie rods. One of the closing pieces is made up of a grain of the same diameter as the housing and placed at the end of a gland allowing its introduction into the housing under the action of a main spinning cylinder bearing on a fixed cross member, moving closer to the other closing part which bears on the other cross member. The metal compressed between the two closure parts is extruded through the die in the form of a profile of the same section.

In the so-called direct spinning process, the container is fixed and bears directly, with the closure part carrying the die, on one of the fixed crosspieces. The gland bearing the grain which constitutes the other closing part is actuated by the main spinning jack so as to make the grain penetrate into the container housing (see US-A-3649816 which corresponds to the preambles of claims 1 and 5) .

In the so-called reverse spinning process, the die is mounted on a grain of diameter equal to that of the container housing and placed at the end of a tubular gland bearing on one of the fixed crosspieces. The container is closed at its opposite end by a bottom and the assembly is mounted on a movable cross member actuated by the main extrusion cylinder, so that the housing threads on the grain by determining the extrusion by the die of the metal billet contained inside the housing , the extruded profile being removed by the tubular gland (see US-A-4989437 which forms the base of the preamble of claim 7).

The metal billets are produced from very long pieces in which pieces having a length slightly shorter than that of the container housing are cut. Each piece has, on the other hand, a cross section slightly smaller than that of the container housing so as to provide, between the internal face of said housing and the external face of each billet, a clearance necessary for the introduction of the billet into housing.

This is why, before the actual extrusion, a so-called precompression operation is carried out during which the billet, which begins to be crushed between the two closing parts approaching one another, swells slightly and is applied completely against the internal face of the container housing.

The air being in the clearance existing initially between the billet and the internal face of the housing is thus strongly compressed and must be evacuated, before spinning, by a so-called degassing operation.

Usually, in direct spinning presses, this degassing is carried out by controlling, after precompression, a slight recoil of the container with the gland to allow the container to come off the bottom carrying the die, allowing compressed air to escape into the housing . For this, auxiliary cylinders provided on the press are used for the operations isolated from the container and the return cylinders. of the main extrusion cylinder which normally is single acting.

These operations require hydraulic control reversals, by acting on pumps, valves or other members, with fairly long response times. This results in a real dead time which decreases the productivity of the press but which, until now, seemed inevitable because poor degassing can lead to defects, for example bubbles or blisters on the spun product and even risks of explosion during spinning.

The invention remedies these drawbacks by means of a new process which makes it possible to practically avoid the dead time which, until now, was necessary for degassing and, thus, to increase the productivity of the press. It is known, in fact, that the recent development of the technique leads to as continuous use as possible of the press while not neglecting any idle time, even of short duration.

The invention is intended more specifically for direct spinning presses, but can also find applications in reverse spinning presses.

The invention therefore applies, in general, to the spinning of a metal billet in a spinning press comprising a first and a second fixed sleepers spaced apart by a constant distance, a container provided with a tubular housing centered on a spinning axis and in which the billet is placed, said container bearing on the first fixed cross-member, two closure pieces at the two ends of the housing, respectively a first piece resting on said first fixed cross-member and a second piece, of section substantially equal to that of the housing, mounted at the end of an elongated gland bearing on the second fixed cross member and capable of penetrating by axial sliding inside the housing, a die centered on the spinning axis and mounted on one of said closing pieces, and means for controlling the bringing together of said closing pieces towards one another, by resting on one of said fixed crosspieces, for the spinning of the billet by extrusion in the die, the spinning operation being preceded by a phase of precompression of the billet between the two closure parts until its side wall is applied against the internal face of the housing.

The method according to the invention is characterized in that at least during the greater part of the precompression phase, the container is prevented from being applied to the first closure part while maintaining, between the latter and the end corresponding container, a small clearance for the progressive evacuation of the air contained in the housing during the precompression of the billet and until the complete application thereof on the internal face of the housing.

Preferably, to maintain said clearance, a spacer means is interposed between the container and the first cross member capable of exerting on the container a calibrated retaining force directed in the opposite direction to the direction of penetration of the second closure part. in the housing, the value of which is limited so that the spreading means yields under the pressure of the container, allowing the clearance to be removed and the piece prayer to be closed when the application of the billet on the wall of the housing is sufficient to secure the container with the billet.

In a particularly advantageous way, to perfect the degassing, a hydraulic pressure is relieved for a short time and at the end of the precompression phase in the spinning control means, which determines a slight decline in the billet with the container and the reopening of the first closure part under the action of said spacing means, with instantaneous creation of a clearance allowing the escape of residual air.

The invention also covers a spinning press suitable for implementing the method of the invention as defined in claim 5 or 7.

In a preferred embodiment, said retaining means consist of at least two jacks arranged on either side of the spinning axis and bearing on one side on the first cross member and on the other on the corresponding end of the container.

Advantageously, the retaining jacks are associated with means for releasing the pressure when the latter exceeds a limit value.

However, the invention will be better understood from the following description of a particular embodiment of a direct spinning press, given by way of example and shown in the attached drawing.

In the single Figure, there is shown schematically, in longitudinal section, a spinning press comprising two fixed crosspieces 1, 11, spaced from one another by a constant distance maintained by tie rods 12, and between which is mounted sliding a movable cross member 2 carrying a container 3 in which is formed a cylindrical housing 4 centered on a spinning axis 10.

The container 3 can move axially with the movable cross member 2 under the action of auxiliary jacks 21 bearing on the fixed cross member 11. The container 3 can thus be applied against a part 13 forming a closure bottom of the corresponding end 41 of housing 4, on which is mounted a die 14 centered on the spinning axis 10.

On the opposite face 32 of the container 3, the end 42 of the housing 4 is closed by a thrust grain 5 mounted at the end of an elongated gland SI attached to the piston 52 of a main spinning cylinder whose body 53 is formed in the fixed cross member 11.

All these provisions are conventional and may, moreover, be subject to variants, or specific provisions allowing certain operations to be carried out.

First of all, a metal billet 6, of diameter slightly smaller than that of the housing 4, is placed inside the latter and the container is advanced by the auxiliary jacks 21 towards the die-holding part 13 which closes the 'corresponding end 41 of the housing 4. The gland 51 is pushed by the main jack 52 or else under the action of auxiliary jacks not shown, so that the thrust grain 5, which has a roughly identical cross section, to that of the housing 4, enters the corresponding end 42 thereof, and bears against the corresponding face of the billet 6 which is supported, itself on the bottom.

Before the actual spinning, a simple precompression is carried out by advancing the grain 5 under the action of the main cylinder 52. The billet 6 inflates and comes to be applied by its external face 61 against the internal face 43 housing 4.

Generally, during this operation, the container 3 is applied, by its front face 31, against the closure bottom 13 and the air contained in the existing set, originally, between the billet 6 and the housing 4, is compressed by the swelling of the billet 6.

This is why, after the precompression phase, this compressed air must be evacuated. So far, this degassing operation was carried out by retraction of the container and of the mobile crossmember 2 under the action of the auxiliary jacks 21.

Such an operation, which requires a certain time, is avoided by virtue of the arrangements according to the invention. In fact, during the precompression phase, the container 43 is prevented from applying by its face 31 against the die holder part 13 by means of jacks 7, 7 ′ which are interposed between the fixed cross member 1 and the container 3 or the movable cross member 2. Thus, in the example shown, two jacks 7, 7 ′ are used, the body 71 of which is fixed to the fixed cross member 1 and the rod 72 of which comes to bear against the movable cross member 2.

The length of the rods 72 is determined so that, in the extended position of the jacks 7, 7 ′, there is a slight clearance (e) between the front face 31 of the container 3 and the corresponding face 15 of the die holder part. 13.

The operation of the improved press is as follows:

After having loaded the billet 6 into the housing 4 of the container 3, by well known means, the movable cross member 2 is advanced by means of the auxiliary jacks 21 until it comes to bear on the jacks 7, 7 'which are in the fully extended position. In this position, the front face 31 of the container is therefore at a short distance (e) from the die holder part 13.

The grain 5 is then advanced under the action of the main cylinder 52 and the billet 6 is applied, by its front face 60, against the die holder bottom 13 and then begins to inflate. The air contained between the internal face 43 of the housing 4 and the external face 61 of the billet escapes progressively through the clearance (e) as the billet 6 swells.

From a certain pressure of application of the grain 5 against the billet 6, the external face 61 of the latter is completely applied against the internal face 43 of the housing 4. As a result, the container 3 becomes integral, by friction with the billet 6 and therefore tends to be, too, driven axially forward by the grain 5 but it is retained, in this movement, by the cylinders 7, 7 '. The play (e) is thus maintained during most of the precompression phase.

This tendency for the container 3 to move forward depends on the friction between the latter and the billet 6 and, consequently, on the thrust applied thereto by the grain 5.

However, the metal, thus compressed, should not have a tendency to escape through the peripheral play (e). This is why, the pressure in the chamber 71 of each cylinder 7 (7 ′) is calibrated so as to resist the advancement of the container only up to a certain limit of the pressure applied to the billet, from which the metal could seep into the game (e). From this limit, the friction between the billet 6 and the internal face 43 of the housing 4 is such that the container 3 is sufficiently secured to the grain 5 to repel the jacks 7, 7 ′ which yield under the applied thrust, allowing the advancement of the container 3 until its front face 31 comes to bear against the corresponding face 15 of the die holder part 13 by completely closing the end 41 of the housing 4.

The actual spinning operation could then begin.

However, it is feared that the closure of the container took place before the complete evacuation of the air and that a certain residual quantity of air exists still between the billet and the housing. This is why, to perfect the degassing, it is possible, for safety, to control, for a short time, an expansion of the hydraulic pressure in the chamber 54 of the cylinder 52. As the pressure of the cylinder 52 is applied to the container 3 by 1 'intermediate the billet 6, this hydraulic expansion in the chamber 54 allows the jacks 7, 7' which had remained under pressure, to slightly push the container 3 and the grain 5 with the gland 51. It appears again, between the face before 31 of the container 3 and the die holder part 13, a slight clearance through which may escape, possibly, the highly compressed residual air which could have remained inside the housing.

It therefore appears that most of the degassing was carried out gradually, during the time necessary for the inevitable phase of precompression, that is to say in masked time.

As for the second degassing step which, moreover, may not always be essential, it is carried out automatically and almost instantaneously under the action of the jacks 7, 7 ′ maintained in pressure as soon as a trigger is ordered in the main cylinder 54. This is an essential advantage compared to the arrangements used until now, in which the air was allowed to compress in the container during the decompression phase, the degassing being carried out then by controlling the recoil of the container by means of the auxiliary cylinders 21 or else the return cylinders of the main cylinder (not shown in the Figure). Such recoil requires different hydraulic maneuvers which are eliminated in the process according to the invention, which makes it possible to improve productivity by avoiding the corresponding dead time.

The invention can also be implemented by a very simple device, which comprises only two jacks 7, 7 'supplied by a hydraulic circuit 74 under a limited pressure, for example, by a calibrated valve 73 whose adjustment can be determined taking into account the characteristics of the press, the nature of the metal and the pressure from which it could escape through the clearance (e) left between the container (3) and the die holder (13).

In addition, if the invention is particularly applicable to the case of a direct spinning press of the type just described. It could, however, also find an interest in the case of a reverse spinning press as defined in claim 7. Similar means could then be used for the implementation of the same process.

In fact, in a reverse spinning press, the container is mobile and slides onto the gland which is fixed and carries, at its end, a grain on which the die is mounted and which penetrates into the front end of the housing. In this case, the main spinning actuator actuates a movable cross member which carries a bottom for closing the container and bears on it to push it towards the fixed cross member carrying the gland, the spun product being discharged through an orifice provided in the axis of the gland.

The container retaining jacks would then be placed on the movable cross member to rest on the rear face of the container and prevent the application of the latter against the movable cross member, leaving a clearance between the container and the closure bottom. the gradual evacuation of the air as precompression and until the pressure of application of the billet against the internal face of the housing is such that the container is sufficiently integral with the latter so that the retaining jacks yield while letting the play close.

The reference signs, inserted after the technical characteristics mentioned in the claims, have the sole purpose of facilitating the understanding of the latter and in no way limit their scope.

Claims (9)

1. Process for extruding a metal billet in an extrusion press comprising a first fixed crosspiece (1) and a second fixed crosspiece (11) separated by a constant distance, a container (3) having a tubular housing (4) centered on an extrusion axis (10) and in which the billet (6) is placed, said container (3) bearing, during extrusion, on the first crosspiece (1), two pieces (13,5) for closing the two ends of the housing (4), respectively, a first piece (13) carried by said first fixed crosspiece (1) and a second piece (5) having a section substantially equal to those of the housing (4) provided at the end of an elongated rammer bearing on the second fixed cross-piece (11) and liable to enter by axial sliding inside the housing (4), a die centered on the extrusion axis (10) and which is mounted on one of said closing pieces (13,5) and control means (51,52) to move closer said closing pieces (13,5) one to another and which bear against one of said fixed crosspieces (1,11) for extruding the billet (6) in the die (14), the extrusion operation being preceded by a phase for precompressing the billet (6) between the two closing pieces (13,5) until application of the side wall (61) thereof against the internal face (43) of the housing (4),
   characterized in that at least during most of the precompression phase, the container (3) is prevented from pressing against one of the closing pieces (13) by providing a small clearance (e) between said latter and the corresponding end of the container (3), the small clearance (e) allowing the air contained in the housing (4) to be progressively expelled during precompression of the billet (6) and up to the time said billet is fully applied against the internal face (43) of the housing (4).
2. Extrusion process according to claim 1, characterized in that the clearance (e) is maintained between the container (3) and the first closing piece (13) by interposing a spacing device (7,7') between the corresponding face (31) of the container (3) and the crosspiece (1) on which it bears and which is able to exert a calibrated retaining force on the container (3) directed in the direction opposite to that in which the second closing piece (5) penetrates into the housing (4) and whose value is limited such that the said spacing means (7,7') yields under the pressure applied by the container (3) rigidly locked with the billet (6) and allowing the container (3) to advance and the first piece (13) to close when said retaining force exceeds a calibration limit value.
3. Process according to claim 2, characterized in that the calibration limit value of the retaining force corresponds to a pressure applied on the billet (6) from which the metal would tend to pass into the clearance (e) between the first closing piece (13) and the container (3).
4. Process according to one of the preceding claims, characterized in that after the container (3) has been applied to the first closing piece (13), the hydraulic pressure in the extrusion control means (52) is released for a brief moment, bringing about a slight withdrawal of the billet (6) with the container (3) and the reopening of the first piece (13) under the action of the said spacing means (7,7') with the instantaneous creation of a clearance allowing any air to escape which was trapped inside the container (3) at the time the first piece (13) was closed.
5. Press for extruding a metal billet comprising a first and a second fixed crosspieces (1,11) held apart from each other by a constant distance, a container (3) provided with a tubular housing (4) centered on an extrusion axis (10) and in which a billet (6) to be extruded is placed, said container (3) bearing, during extrusion, on the first crosspiece (1), two pieces (13,5) for closing the two ends of the housing (4) repectively, a bottom (13) carried by the first crosspiece (1) on which the container (3) bears, and a block (5) whose cross section is substantially identical to that of the housing, said block being mounted on the end of an extended rammer (51) bearing on the second fixed crosspiece (11) and able to penetrate into the housing (4) by an axial sliding movement, a die (14) centered on the extrusion axis (10) and which is mounted on the closing bottom (13), and means (52) which bear on the second crosspiece (11) to control the penetration of the pushing block (5) in the housing (4) in order to extrude the billet (6) through the die (14), characterized in that it comprises means (7,7') for spacing the container which are interposed between the first crosspiece (1) and the corresponding end (31) of the container (3) and extending over a sufficient distance to let a sufficient clearance (e) between the corresponding end (41) of the housing (4) and the closing bottom (13) to allow the air contained between the billet (6) and the inner face (43) of the housing (4) to be expelled when the billet (6) expands at the time the said closing pieces (13,5) start coming together.
6. The extruding press according to claim 5, characterized in that the spacing means are made up of at least two hydraulic jacks (7,7') arranged either side of the extrusion axis (10) and each comprising a body (7,7') and a rod (72,72') which bear, respectively, on the first crosspiece (1) and on the corresponding end (31) of the container (3).
7. Press for extruding a metal billet comprising a first and a second fixed crosspieces held apart from each other by a constant distance, a container provided with a tubular housing centered on an extrusion axis and in which a billet to be extruded is placed, said container bearing on a moveable crosspiece activated by an extrusion jack bearing on the first fixed crosspiece, two pieces for closing the two ends of the container housing, respectively a bottom carried by said moveable crosspiece and a block whose cross-section is substantially identical to that of the housing and bearing a die centered on the extrusion axis, said block being mounted on the end of an extended tubular rammer bearing on the second fixed crosspiece to which is pushed the moveable crosspiece bearing the container and the bottom thereof under the action of the extrusion jack with penetration of a the block by axial sliding inside the housing and extrusion of the billet by the die, characterized in that it comprises means for spacing the container which are interposed between the moveable crosspiece and the corresponding end of the container and extending over a sufficient distance to prevent the application of said latter against the moveable crosspiece to let a clearance between the container and the closing bottom to allow the air contained between the billet and the inner face of the housing to be expelled when the billet expands at the time the said closing pieces start coming together.
8. The extrusion press according to claim 7, characterized in that the spacing means are made up of at least two hydraulic jacks arranged either side of the extrusion axis and each comprising a body and a rod which bear respectively on the moveable crosspiece and on the corresponding end of the container.
9. The extrusion press according to one of claims 6 to 8, characterized in that the spacing jacks (7,7') are associated with means (73) for releasing the pressure in the chamber (71) of each jack (7,7') when said latter exceeds a limit value.

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