EP0623402A1 - Process for extrusion of metal and extrusion press - Google Patents

Abstract

The subject of the invention is an extrusion process for extruding a metal billet (6) placed in a container (3) delimiting a housing (4) for the billet (6), the housing being closed at one end by a back piece (plate) (13) and at the other end by a dummy block (bearing plate) (5), in which process, before carrying out the extrusion, the billet (6) is precompressed in order to press the latter against the internal face (43) of the housing (4). In accordance with the invention, at the start of the precompression phase, a small clearance (e) is maintained between the closure back piece (13) and the corresponding end (31) of the container (3), preventing the container (3) from moving closer to the back piece (13) during the precompression in order to allow removal, via the clearance (e) thus maintained, of the air contained between the billet (6) and the internal face (43) of the housing (4), during the expansion of the billet (6) and the said clearance (e) is then left to close up by advancing the container (3) thus rendered integral with the billet (6). The invention applies more especially to direct extrusion, but may also be of interest in the case of reverse extrusion. <IMAGE>

Description

The subject of the invention is a process for spinning a metal billet in a spinning press and also covers an improved spinning press for implementing the 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 parts 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 housing of the container.

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.

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, letting the compressed air 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 short.

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 container provided with a tubular housing centered on a spinning axis and in which the billet is placed, a first crosspiece on which the container is supported during spinning, two closure pieces at the two ends of the housing, respectively a bottom carried by a first crosspiece on which the container is supported and a thrust grain, of section substantially equal to that of housing, mounted at the end of a gland and capable of penetrating axially inside the housing, a die centered on the spinning axis and mounted on one of said closing parts, and means for controlling the approximation of these towards each other, by resting on a second crosspiece, for the spinning of the billet by extrusion in the die, the spinning operation being preceded a phase of precompression of the billet between the grain and the bottom to apply the external force against the wall of the housing.

According to the invention, at least during most of the precompression phase, the container is prevented from being applied to the bottom by maintaining, between the latter and the corresponding end of the container, a small clearance allowing the progressive evacuation of the air contained in the housing during the precompression of the billet and until the complete application thereof on the wall of the housing.

Preferably, to maintain said clearance, there is interposed, between the container and the first cross member, a spacing means capable of exerting on the container a calibrated retaining force directed in the opposite direction to the direction of penetration of the grain in the housing and 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 bottom 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 bottom under the action of said spacing means, with instantaneous creation of a clearance allowing the escape of residual air.

The invention also covers an improved spinning press for implementing the method comprising means for retaining the container interposed between the first cross member and the corresponding end of the container and extending over a distance sufficient to allow it to remain, between said end of the container and the closure bottom, sufficient play to allow the evacuation of the air contained between the billet and the internal face of the housing.

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, 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 51 fixed on 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 refined, 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 which are interposed between the fixed cross member 1 and the container 3 or the cross member mobile 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 mobile 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 in 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 '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).

Of course, the invention is not limited to the details of the embodiment which has just been described, and which could be the subject of variants for the implementation of the method according to the invention.

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. 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 mobile crossmember which carries a bottom closing the container and bears on it to push it towards the fixed crossmember 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 (7)

Method for spinning a metal billet in a spinning press comprising two fixed crosspieces (1, 11) spaced by a constant distance, a container (3) provided with a tubular housing (4) centered on a spinning axis (10) and in which the billet (6) is placed, said container (3) bearing, during spinning, on a first crosspiece (1), two parts (13, 5) for closing the two ends of the housing (4 ), respectively a bottom (13) carried by said first crosspiece (1) for supporting the container (3), and a thrust grain (5), of section substantially equal to that of the housing (4) mounted at the end an elongated gland (51) and capable of penetrating by axial sliding inside the housing (4), a die (14) centered on the spinning axis (10) and mounted on one of said closure parts (13, 5), and means (51, 52) for controlling the bringing together of said closure parts (13, 5) towards one another, by resting on a sec transverse wave (11), for the spinning of the billet (6) by extrusion in the die (14), the spinning operation being preceded by a phase of precompression of the billet (6) between the grain (5) and the bottom (13) until its side wall (61) is applied against the internal face (43) of the housing (4), characterized in that at least during most of the decompression phase, it prevents the container to be applied on the bottom while maintaining, between the latter and the corresponding end of the container, a small clearance allowing the progressive evacuation of the air contained in the housing during the precompression of the billet and up to 'to the full application thereof on the wall of the housing. Spinning method according to claim 1, characterized in that the play (e) is maintained, between the container (3) and the bottom (13) by interposing, between the front face (31) of the container (3) and the first crosspiece (1) carrying the bottom (13), a spacing means (7) capable to exert on the container (3) a calibrated retaining force directed in the opposite direction to the direction of penetration of the grain (5) in the housing (4) and whose value is limited so that said spacing means (7) yields under the pressure applied by the container (3) secured to the billet (6) while allowing the container (3) to advance and the bottom (13) to close when said pressure exceeds a taring limit value. Method according to claim 2, characterized in that the taring limit value of the retaining force (7, 7 ') corresponds to a pressure applied to the billet (6) from which the metal would tend to pass through the clearance (e) between the closure bottom (13) and the container (3). Method according to one of the preceding claims, characterized in that, after the application of the container (3) on the bottom (13), the hydraulic pressure is reduced for a short time in the means (52) spinning control, which determines a slight retreat of the billet (6) with the container (3) and the reopening of the bottom (13) under the action of said spacing means (7, 7 '), with instant creation of a clearance allowing the escape of the air possibly remaining inside the container (3) when the bottom (13) is closed. Press for spinning a metal billet comprising two crosspieces (1, 11) kept spaced from each other by a constant distance, a container (3) provided with a tubular housing (4) centered on a spinning axis (10) and in which is placed the spinning billet (6), said container (3) bearing on a first crosspiece (1), during spinning, two parts (13, 5) for closing the two ends of the housing (4), respectively a bottom (13) carried by the first crosspiece (1) for supporting the container (3) and a grain (5), of section substantially equal to that of the housing, mounted at the end of an elongated gland (51) and capable of penetrating by axial sliding inside the housing (4), a die (14) centered on the spinning axis (10) and mounted on one of said closing pieces (13), and means (52) for controlling the bringing together of said closing pieces (13, 5) towards each other bearing on a second crosspiece (11) for the spinning of the billet (6) by the die (14), characterized in that it comprises means (7) for retaining the container interposed between the first crosspiece (1 ) and the corresponding end (31) of the container (3) and extending over a distance sufficient to allow to remain, between the corresponding end e (41) of the housing (4) and the closure bottom (13), a clearance (e) sufficient to allow the evacuation of the air contained between the billet (6) and the internal face (43) of the housing ( 4) during the inflation of the billet (6) at the start of the bringing together of said closure parts (13, 5) towards each other. Spinning press according to claim 5, characterized in that the retaining means consist of at least two hydraulic cylinders (7, 7 ') arranged on either side of the spinning axis (10) and comprising each a body (7, 7 ') and a rod (72, 72') bearing, respectively, on the first crosspiece (1), and, on the corresponding end (31) of the container (3). Spinning press according to claim 6, characterized in that the retaining jacks (7, 7 ') are associated with means (73) for releasing the pressure in the chamber (71) of each cylinder (7, 7 ') when the latter exceeds a limit value.

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