EP0329567B1 - Method for extruding metal, particularly aluminium and extruding press for carrying out this method - Google Patents

Abstract

The subject of the invention is a method and an installation for extruding metal using the reverse method, in which a billet (5), placed in the housing (21) of a container (2), is compressed between a base (3) and an extruding block (4), each billet (5) to be extruded comprising, in the crude state, an outer layer capable of containing surface defects. <??>Billets (5) are extruded in the crude state without prior removal of the outer layer, leaving, between the periphery of the block (4) and the inner face of the housing (21), sufficient play in order to form, along the said inner face, an outer shell of a thickness which is at least equal to that of the outer layer to be removed, the next procedure being scraping of the housing (21) by means of a scraping block (7) whose periphery is separated from the inner face of the housing (21) by a play which is less than the thickness of the outer shell but sufficient for the outer shell to be removed over only a part of its thickness. <IMAGE>

Description

The subject of the invention is a metal spinning process by the reverse method, applicable especially to the spinning of aluminum and its alloys and also covers an improved spinning press for carrying out the process.

In such a method described, for example, in document US-A-3563079, a metal billet is placed in a housing formed inside a container and closed, on one side, by a bottom and by the 'other, by a grain carrying a die and placed at the end of a rod called gland and capable of threading inside the housing so as to carry out the extrusion of metal by the die, forming a bar which is discharged through an opening in the axis of the gland.

As it cannot be avoided that there is a slight clearance between the die carrying the grain and the internal face of the housing, there is formed, along the latter a thin metal film which must be removed because it contains impurities, in particular remnants of non-extruded metal and lubricant. This is why one periodically scrapes the housing by means of a grain of the same diameter which is threaded into the housing (US-A-3,563,079).

We know that, during the metal spinning by the reverse method, we find substantially in the spun product, from the outside to the inside, the different layers of the extruded billet. In particular, the outer layer of the billet appears, after spinning, on the surface of the spun products.

However, the surface of the metal billets to be spun from the foundries may present, in particular in the case of aluminum, surface defects such as casting skin, segregation of alloying or addition elements, cold recovery etc .... These defects can be encountered over a certain thickness from the external face of the billet which can be, for example, of the order of 2 mm.

Up to now, it has been estimated that before introducing the billet to be spun into the container, it was necessary to remove the external layer capable of encompassing surface defects.

In a first known method, this elimination is carried out by peeling on a lathe. This process is effective but obviously increases production costs and requires turning facilities for the preparation of billets. In another method, the outer layer is removed by scalping by passing the billet over blades which plan the outer face to the desired thickness. This process is faster than peeling but it must be carried out hot by means of a special device placed either between the billet heating furnace and the spinning press or directly on the press.

These two methods make it possible to obtain a good surface quality of the billets but have certain drawbacks. First of all, the thickness of metal to be removed must take into account the geometric tolerances on the diameter, the surface roughness, the thickness of the external layer having structural defects and the precision of the preparation device and it as a result, it is necessary to remove a relatively large thickness, up to 10 mm, which results in a large percentage of waste before loading into the press. However, the loss on ignition during the remelting of filming waste is very significant.

The invention remedies these drawbacks by means of a method making it possible to eliminate the preliminary treatment for eliminating the outer layer and therefore to simplify the installation which must no longer include additional devices provided for this purpose.

In general, the invention applies to a method of spinning metal by the reverse method, by extrusion through a die of a metal billet placed in a housing formed inside a container and closed on one side by a bottom and on the other by a grain carrying the die and mounted at the end of a fixed stuffer pierced with an axial orifice and capable of being threaded inside the housing by movement of the container and its bottom under the action of a main spinning cylinder, so as to produce, by extruding the metal in the die, the spinning of a bar , discharged through the ascending orifice (42) of the gland (40) process in which, during spinning, a clearance is left between the periphery of the die-holder grain and the internal face of the housing so as to form a jacket along said internal face and one then proceeds to a scraping of the housing.

In accordance with the invention, raw foundry billets are used, without prior elimination of the external layer and the first clearance left between the periphery of the spinning grain and the internal face of the housing is determined so that the jacket has a sufficient thickness to encompass all the surface defects of the rough billet and the housing is scraped, after spinning, by means of a scraping grain whose periphery is separated from the internal face of the housing by a second clearance less than the thickness of the liner but sufficient for it to be simply planed over only part of its thickness and there remains, after scraping, a metal film of regular thickness covering the entire internal face of the housing, the new billet then being loaded into the container while remaining perfectly centered on the axis of the housing so that said film is not likely to be damaged during during loading.

This first clearance left between the periphery of the die holder die and the internal face of the housing is determined as a function of the diameter of the billet and can be between 1.5 mm and 4 mm approximately depending on the diameter. The second clearance left between the periphery of the scraping grain and the face internal of the housing can be between 0.1 and 0.25 mm approximately.

It is particularly advantageous that, during loading into the container of the billet, the latter is kept perfectly centered on the axis of the housing so that the film left during the previous spinning is not likely to be damaged during loading.

To this end, according to a known method on the other hand, the billet is first placed exactly in the spinning axis and pinched between the die holder grain and the closure bottom, the container then being slid on the billet.

The invention also covers a press for carrying out the method and which, being intended for spinning by the reverse method, comprises a fixed stuffer pierced with an axial orifice and over which the housing of a container is threaded in which the billet to be spun has been placed, the latter being compressed between the closure bottom of the container and a die-holder grain placed at the end of the gland, so that it is formed during spinning, along the internal face of the housing, a jacket encompassing the surface defects of the billet. The press further comprises a means for cleaning the housing after the spinning comprising a scraping grain of the jacket capable of being threaded into the housing after the spinning.

According to the invention, given that raw foundry billets are used, without prior elimination of the external layer, the first clearance left between the periphery of the spinning grain and the internal face of the housing is determined so that the jacket has a thickness sufficient to encompass all the surface defects of the rough billet and the scraping grain has a diameter slightly smaller than that of the internal face of the housing so that it exists, between the periphery of said scraping grain and the internal face of the housing, a clearance less than the thickness of the jacket so that the latter is scraped inwards and over only part of its thickness, leaving behind, after scraping, a metal film of regular thickness and covering the whole of the internal face of the housing.

Preferably, the scraping grain is mounted on a second gland capable of being placed in the spinning axis and of being threaded into the housing of the container by axial displacement in a direction of scraping and withdrawn in the opposite direction. According to another essential characteristic of the invention, the scraping grain is coupled to the second gland so as to remain fixed at the end of the latter as well in the direction of scraping as in the direction of withdrawal and it has a variable diameter so that the clearance left between the periphery of said scraping grain and the internal face of the housing is smaller in the direction of scraping than in the direction of withdrawal.

To this end, the scraper grain preferably comprises a support body fixed to the end of the scraper plug and carrying on the side opposite to said scraper, a scraper segment in the form of an elastic ring cut by a slot centered in a radial plane and limited by two plane faces opening inwards towards V and between which engages an expansion wedge provided with bearing faces of corresponding inclination and slidingly mounted transversely on the support body, the latter being associated with means for controlling a transverse displacement of the corner towards the outside to determine the widening of the slot and the increase in the diameter of the scraper segment.

Advantageously, the scraper segment is provided, on its periphery, with a cutting edge for planing the jacket and it rests, via a smooth face perpendicular to the axis of the gland, on a smooth face corresponding formed at the end of the support body opposite the gland. In addition, the scraper segment is secured in axial displacement with said support body by a retaining flange in the form of a U-shaped ring comprising two wings respectively engaging corresponding circular grooves formed on the segment and on the body of support, said flange being cut by a slot at the segment slot.

In a preferred embodiment, the means for controlling the transverse movement of the expansion wedge comprise an operating rod slidably mounted axially inside the support body and on which is formed a cam comprising a plane face inclined relative to the axis of the support body and cooperating with a flat face of corresponding inclination formed on the expansion corner so as to control the transverse movement of the latter towards the outside by axial movement of the operating rod.

• La figure 1 représente schématiquement , en vue de dessus , une presse de filage classique fonctionnant par la méthode inverse.
• La figure 2 représente, en 1/2 coupe partielle, une billette à l'état brut;
• La figure 3 représente, en 1/2 coupe partielle, une billette chargée dans le conteneur et après tassage;
• Les figures 4 à 11 représentent schématiquement les différentes étapes du filage d'une billette avec râclage du conteneur .
• La figure 12 est une vue en coupe axiale du grain de râclage représenté en position expansée dans la demi-vue supérieure et en position rétreinte dans la demi-vue inférieure .
• La figure 13 est une vue en coupe transversale selon la ligne A-A de la figure 10 .
• La figure 14 est une vue de dessus du grain de râclage avec coupes partielles.

However, the invention will be better understood from the following description of a particular embodiment, given by way of example and shown in the accompanying drawings.

• Figure 1 shows schematically, in top view, a conventional spinning press operating by the reverse method.
• Figure 2 shows, in 1/2 partial section, a billet in the raw state;
• Figure 3 shows, in 1/2 partial section, a billet loaded in the container and after tamping;
• Figures 4 to 11 schematically represent the different stages of spinning a billet with scraping of the container.
• Figure 12 is an axial sectional view of the scraper grain shown in the expanded position in the upper half-view and in the constricted position in the lower half-view.
• FIG. 13 is a cross-sectional view along the line AA in FIG. 10.
• Figure 14 is a top view of the scraping grain with partial sections.

In Figure 1, there is shown, by way of simple example, the essential members of a spinning press by the reverse method which comprises a bed base 11 and a fixed cross member 12 connected together by columns 13 and between which are mounted sliding, parallel to the spinning direction, a container 2 and a movable cross member 30 actuated by a main spinning jack 14 bearing on the fixed cross member 12. Auxiliary jacks 15 and 16 make it possible to maneuver the movable cross member 30 and a cross member respectively 20 carrying the container 2 without actuating the main cylinder 14.

The container 2 is pierced with a cylindrical housing 21 centered on a spinning axis 10 and capable of being closed at one end by a bottom 3 carried by the movable cross member 30.

On the bed base 11 is supported a gland 40 consisting of a tubular column carrying at its free end a spinning grain 4 carrying a die 41. The latter opens onto a bore 42 formed in the axis of the gland 40 and extended by a discharge orifice 17 passing through the bed base 11. The assembly is centered on the axis of the housing 21 which constitutes the spinning axis 10.

We know the principle of reverse spinning. A billet 5 of metal to be spun is placed inside the housing 21 of the container 2 closed on one side by the bottom 3 carried by the movable cross member 30. When the main cylinder 14 pushes the movable cross member 30 towards the bed base 11 by driving the container, the billet 5 is compressed between the container bottom 3 and the die 41 carried by the spinning grain 4 on which s progressively threads the housing 21 of the container driven by the movable cross member 30. This results in an extrusion of the metal from the billet 5 which forms a profile discharged through the aligned orifices 42 and 17.

The reverse spinning process is well known and has been the subject of numerous improvements.

In particular, in the embodiment shown in Figure 1, the press is provided with a shear 23 slidably mounted along the rear face of the container 2 and adjustable stops 61 for limiting the advancement of the container. In addition, the spinning gland 40 is associated with a second gland 70 offset laterally and carrying a scraping grain 7; the two pluggers are fixed on a support 6 slidingly mounted on the internal face of the bed base 11 and actuated by a jack 62 making it possible to place one or the other of the two pluggers 40 and 70 in the spinning axis 10.

Usually, at the end of the spinning, there remains along the internal face of the housing 21, a thin metal jacket having passed between said internal face and the periphery of the spinning grain 4 and connected to the metal base remaining between the grain of wiring 4 and container bottom 3.

After shearing the base, the container 2 is moved back, the second gland 70 is placed in the spinning axis and the container is again advanced. The scraping grain 7, which has a diameter equal to that of the housing 21 is threaded into the latter by pushing back the metal jacket so as to clean the internal face of the housing 21.

The invention uses such arrangements but by adapting them in a way which makes it possible to use for the spinning of raw billets.

In Figure 2 there is shown, in 1/2 partial section and on an enlarged scale, a billet 5 in the raw state. This latter has on its periphery surface defects which can be encountered on an outer layer 54 of thickness (a). On the other hand, the side wall 55 of the billet is not perfectly smooth or straight. Therefore, to remove all of these defects, by peeling or scalping, it is necessary to reduce the diameter of the billet 5 to a thickness (b).

In FIG. 3, the billet 5 is shown after tamping in the housing 21 of the container 2. As will be seen, the method according to the invention makes it possible to reduce the diameter of the billet 5 only over a thickness (a ′ ) substantially equal to the thickness (a) of the outer layer 55 which may include defects.

The operation of the various members for implementing the invention is shown in detail, on an enlarged scale, in FIGS. 4 to 11 which show the different stages of the process.

In these figures, only the members shown between the bed base 11 and the movable cross member 30 are shown.

Figure 4 shows the introduction into the container 2, of a new billet 5 which, as indicated, is used in the raw state. In a particularly advantageous manner for the implementation of the invention, a known process known as pinching the billet is used for this purpose. The loading operation begins after the container has been cleaned, that is to say after the container 2 has been threaded onto the gland 70 carrying the scraping grain 7. The movable cross member 30 has been moved away from the container by a greater distance to the length of the billet and a new billet 5 was brought into the spinning axis by a loading shovel 53 which positions the billet 5 between the scraping grain 7 and the bottom of container 3 so that it is exactly centered on the spinning axis 10. By controlling the approximation of the movable cross member 30, the billet 5 is clamped between the bottom of the container 3 and the scraping grain 7, in the position shown in FIG. 4. The loading shovel 53 can then be removed without the billet risk of moving, then backing the container 2 towards the movable cross member 30 by means of its operating jacks 16 so that the housing 21 of the container slides onto the billet 5. This introduction can be done easily and without the billet comes into contact with the wall 21 of the housing since it is kept centered and clamped between the grain 7 and the bottom of the container 3.

At the end of this movement, the container 2 ′ shown in dashed lines in FIG. 4, is applied to stops 31 of the movable cross member 30. The billet 5 is then completely threaded into the housing 21.

As shown in FIG. 5, packing of the billet is then carried out inside the housing 21 by applying significant pressure to the movable cross member 30. The billet 5, compressed between the bottom 3 and the scraping grain 7 decreases slightly in length while its diameter increases and its peripheral surface is applied strongly against the internal face 22 of the housing 21.

We can then move back the movable cross member 30 with the container 2 to release the scraping grain 7, then control, by means of the jack 62, a translation of the support 6 which comes to put in the spinning axis 10 the tubular gland 40, in the position shown in FIG. 6. Normally, the die and the spinning grain used during the previous spinning were removed with the base and a new spinning grain must be mounted on the gland 40.

To this end, a new spinning grain 4 is placed opposite the gland 40 by means of a loading member. 43 then a new advance is commanded towards the bed base 11 of the movable cross member 30 which drives the container 2 and the spinning grain 4. The latter is applied on one side to the billet 5 and is threaded from the another on a suitable support provided at the end of the gland 40.

The spinning can then begin, the billet 5 being compressed between the bottom of the container 3 and the grain 4 which carries the die 41. FIG. 7 represents the spinning in progress and it is seen in particular how the extrusion is formed. profiled bar 50 which is discharged through the axial orifice 41 of the gland 40.

According to an essential feature of the invention, the die-holder grain 4 is given an outside diameter (D1) much smaller than that (D2) of the internal face 22 of the housing 21. In this way, it is formed along this last a metal liner 51 whose thickness is particularly large and corresponds substantially to the clearance (C) left between the periphery of the grain 4 and the internal face (22) of the housing 21. In practice, this clearance (C) is calculated from so that the thickness (a ′) of the jacket 51 thus formed is at least equal to the thickness (a) of the outer layer (54) of the billet (5) capable of encompassing surface defects. This thickness (a) which must be eliminated can be between 1 and 4 mm depending on the diameter of the billet.

The thickness (a ′) of the jacket will therefore be determined in this interval as a function of the diameter of the billet and it can be seen that it can be much less than the thickness (b) of metal which had to be removed in the usual processes and which could go up to 10 mm. In fact, in the known methods, this removal is carried out before the introduction of the billet into the housing and it is therefore necessary to take into account not only the depth (a) up to which surface defects can be found but also surface defects and defects of straightness of the billet. In the method according to the invention, on the contrary, a billet in the raw state is introduced into the housing 21 and of which, consequently, the external face (55) can not not be smooth or straight but this does not have any disadvantages since thanks to the pinching technique, the billet 5 is perfectly centered during its introduction into the container 2 and that the packing carried out then makes it possible to apply the periphery exactly of the billet on the internal face 22 of the housing 21. Therefore, as can be seen in FIG. 3, the external layer 55 to be eliminated in turn becomes rectilinear and its thickness (a ′) depends only on the importance of the surface defects and the thickness of a metal film 52 which will be discussed later. This is a first advantage of the invention.

The jacket 51 thus formed along the housing, however, has a thickness much greater than that which is usually formed and it follows that the annular section of metal between the periphery of the grain 4 and the housing 21 approaches and can even exceed the section of the bar extruded by the die 41. One might then fear that the metal is preferably extruded from the periphery. We will see that another characteristic of the invention, set out below, makes it possible to avoid this drawback.

At the end of the spinning, there remains between the die holder 4 and the bottom 3 a metal base 56 which is connected in its central part to the extruded bar 50 and on the periphery to the jacket 51. According to a known process, after moving the movable cross member and the bottom 3 back, the container 2 is advanced to adjustable stops 61 whose advancement is determined, as shown in FIG. 8, so that, when the container 2 comes into abutment, its rear side is aligned with the front side of the die 4 which protrudes before only the base 56. A shears 23 is then moved along the rear face of the container which cuts the base 56 by separating it from the bar 50 and the liner 51. The base 56 and the bar 50 are then removed and it does not remains more in the housing 21 than the thick jacket 51.

As indicated in FIG. 9, the stops 61 are then moved back and the container 2 is advanced so as to release the spinning grain 4 which can be removed by means of a recovery shovel 24.

The spinning gland 40 being thus freed from the grain it was carrying, there is no risk of damaging the thick jacket 51 by advancing the container 2 again to come into the position of FIG. 10 in which the removal of spinning grain 4.

By translating the support 6, the scraper grain 7 mounted on the second gland 70 is then brought into the spinning axis 10.

The scraping grain 7 which will be described in detail below has the particularity of being coupled to its gland 70 and also of being expandable so as to present in the direction of scraping a larger diameter than in the direction of withdrawal. In the scraping position, the diameter of the grain 7 is indeed slightly smaller than the diameter of the housing 21 so that there is between the periphery of the grain 7 and the internal face of the housing 21 a clearance (d) which can be understood, for example, between 0.1 and 0.25 mm depending on the case.

This clearance (d) is therefore greater than the simple sliding clearance which is usually left between the scraping grain and the internal face of the housing and that is normally sought to reduce to a minimum so that the scraping grain performs a complete cleaning of the housing. In the invention, on the contrary, the scraping grain 7 does not completely push the jacket 51 out of the housing but only planes its internal part leaving a metal film 52 along the internal face 22 of the housing, the thickness of which therefore corresponds substantially to the second clearance (d) left between the scraping grain and the side wall of the housing. This clearance (d) will be determined in particular taking into account the nature of the metal so that the film thus left does not risk tearing at the time of scraping and on the contrary entirely covers the side wall of the housing 21.

At the end of the scraping, the container 2 is therefore completely threaded on the gland 70 in the position shown in FIG. 4 and the cycle can be resumed by bringing a new billet 5 between the scraping grain 7 and the bottom of container 3.

Thanks to the use of the pinching technique for loading the billet, it is perfectly centered on the spinning axis. In addition, while exerting on the billet 5 the clamping pressure necessary to maintain it, it is possible, by means described below, to control a reduction in the diameter of the scraping grain 7 when the container is moved back after the scraping so that the removal of the scraping grain 7 does not risk damaging the film 52 left along the side wall of the housing. In addition, the scraping grain 7 is coupled to its gland 70 which allows it to be kept exactly in the axis of the housing both in the scraping direction and in the withdrawal direction. Therefore, the grain is not likely to rest on the bottom of the housing 21 and the film 52 formed during scraping has a perfectly regular thickness.

When a new billet to be spun is introduced into the housing thus covered with a metal film 52 and the packing is carried out, this operation realizes a real welding of the lateral face 55 of the billet 5 with the film 52 and we found that, during the spinning, the presence of this film 52 which adheres perfectly, on one side on the internal face 22 of the housing 21 and on the other on the side face 55 of the billet 5, achieves a real seal by opposing the preferential spinning, by the peripheral clearance (c), which could occur when the passage section of the die is of the same order as the annular section left by the clearance (c). In addition, because the film 52 has a constant thickness in all directions, it achieves perfect centering of the billet and therefore of the flow of metal in the bar or the spun tube.

To achieve the expansion and the shrinking of the scraping grain 7, it is advantageous to carry out the latter as shown in FIGS. 12 to 14 which, however, are given only by way of non-limiting example, other embodiments can obviously be imagined to obtain the same result.

In Figure 12, there is shown in longitudinal section the scraper grain in its two positions, respectively in the expanded position on the upper half-cut and in the necked position on the lower half-cut. Similarly, Figure 13 which is a cross-sectional view along the line AA of Figure 12, and Figure 14 which is a top view, show the grain 7 in the expanded position on the lower part and in the position of shrunk on the upper part.

As seen in Figure 12, the scraping grain consists essentially of a segment 7 mounted at the end of a tubular body 71 having, on the side of the gland 70, a threaded bore 72 engages on a corresponding thread 72 ′ of the gland 70.

The segment 7 is constituted by an elastic ring cut by a slot 73 centered in a radial plane P₁ passing through the axis of the gland and limited by two plane faces 74, 74 ′ inclined symmetrically with respect to the plane P₁ so as to open inward V.

Furthermore, the scraper segment 7 is provided, on the side opposite the gland 70, with a cutting edge 75 and is supported, by means of a smooth face 76, on the end of the support body 71 with which it is secured in axial displacement by a retaining flange 77 with a U-section comprising two wings respectively engaging in corresponding circular grooves 78, 78 ′ formed respectively on the segment 7 and on the support body 71 and the depth of which is determined so as to leave a radial clearance which allows a slight variation in diameter of segment 7. The retaining flange 77 is advantageously made in two parts placed on either side of the plane P and the ends 77 ′ of which are separated by a free space at the level of the slot 73 of the segment 7.

The variation in diameter of segment 7 is controlled by an expansion wedge 8 which is interposed between the two end faces 74, 74 ′ of the scraper segment 7 on which it is supported by faces 81, 81 ′ likewise tilt. In this way, a radial displacement towards the outside or towards the inside of the wedge 8 determines the expansion or, respectively, the narrowing of the segment 7.

To this end, the corner 8 is provided towards the inside with a flat face 82 inclined with respect to the axis 10 of the gland and cooperating with a face 90 of the same inclination formed on a cam 9 on which the corner 8 is applied. inwards due to the elasticity of segment 7 and the V-shaped inclination towards faces 74, 74 ′.

The cam 9 is fixed to a control part 91 provided with an enlarged part 92 which can slide axially in a bore 93 formed in the support body 71, along a guide ring 94 ensuring a smooth sliding. The cam 9 is placed in a longitudinal groove 95 formed in the enlarged part 92 and limited by two flat faces 96, 96 ′ along which side faces 85, 85 ′ can slide radially guiding the expansion wedge 8.

The control piece 91 is threaded and fixed on an operating rod 97 slidably mounted in an axial bore 79 of the gland 70 and connected to the rod of a jack 98 housed in the support 61.

In this way, as can be seen in longitudinal section in FIG. 12 and in cross section in FIG. 13, the axial displacement of the control piece 91 under the action of the jack 98 determines, by means of the wedge 8, the expansion or constriction of the scraper segment 7, the external profile of the expansion wedge 8 being determined so as to ensure the continuity of the two branches of the scraper segment 7 in the expansion position 8. Similarly, in the expansion position, the end faces of the corner 8, of the segment 7 and of the operating part 91 are placed in the same plane P₂ perpendicular to the axis 10 so as to constitute a smooth face 86 for the packing of the billet.

Of course, this embodiment of the scraping grain has only been described as a preferred example, other arrangements that can be used to produce an expanding grain coupled to its gland.

Similarly, to ensure the replacement of the spinning grain by the scraping grain, other arrangements could be employed than the mounting, moreover known, of the two pluggers on the same sliding support which has been described above to illustrate the 'invention.

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 (14)

1. A method of extrusion of metal by the inverse method, by extruding through a die (41) a metal billet (5) placed in a housing (21) which is arranged inside a container (2) and closed at one side by a bottom (3) and at the other by a block (4) which carries the die (41) and is mounted at the end of a rammer (40) pierced with an axial hole (42) and capable of being threaded inside the housing (21) by displacement of the container (2) and its bottom (2) under the action of a main wiredrawing jack (14) so as to produce by extruding the metal in the die (41) the extrusion of a bar (50) which is discharged through the axial hole (42) of the rammer (40), the method being one in which at the time of the extrusion a certain clearance (c) is left between the periphery of the bush (4) carrying the die and the inner face (22) of the housing (21) to form along the said inner face (22) a lining (51) and the housing (21) is then scraped , the said method being characterized by the fact that the billets employed are rough from the foundry without previous elimination of the outer layer and that the first clearance (c) left between the periphery of the extrusion block (4) and the inner face of the housing (21) is determined in such a way that the lining (51) has a thickness (a′) sufficient to embrace all of the surface defects of the rough billet and by the fact that the scraping of the housing (21) after extrusion is effected by means of a scraper block (7) the periphery of which is separated from the inner face (22) of the housing (21) by a second clearance (d) which is less than the thickness of the lining (51) but sufficient for the latter to be simply planed over only a portion of its thickness and that a skin (52) of metal of uniform thickness persists after scraping and covers the whole of the inner face (22) of the housing (21), the next billet (5) being then loaded into the container (2) by remaining perfectly centred on the axis (10) of the housing (21) so that there is no risk of the skin (52) becoming deteriorated during the loading.

2. A method of extrusion as in Claim 1, characterized by the fact that the first clearance (c) left between the periphery of the extrusion block (4) and the inner face (22) of the housing (21) is determined as a function of the diameter of the billet and lies between 1.5 and 4 mm.

3. A method of extrusion as in one of the Claims 1 or 2, characterized by the fact that the second clearance (d) left between the periphery of the scraper block (7) and the inner face (22) of the housing (21) lies between 0.1 and 0.25 mm.

4. A method of extrusion as in one of the preceding Claims, characterized by the fact that for loading it into the container (2) the billet (5) is first of all set exactly upon the axis of extrusion and pinched between the scraper block (7) and the closure bottom (3), the container (2) then being threaded over the billet (5) by sliding it axially.

5. A method of extrusion as in one of the preceding Claims, characterized by the fact that it is applied to the extrusion of aluminium and its alloys.

6. A press for the extrusion of metal by the inverse method, having a fixed rammer (40) pierced with a hole (42) centred on an axis of extrusion (10) and bearing at one end against a bearer (11) and carrying at the other end of it a die (41) mounted on an extrusion block (4), a container (2) in which a cylindrical housing (21) is arranged and centred upon the axis of extrusion (10) and at the side remote from the rammer (40) bears against a movable crossbar (30) carrying a head (3) for closure of the housing (21), means (53) of loading a metal billet (5) for extrusion into the housing (21) in the container (2) and at least one jack (14) for displacing the movable crossbar (30) and the container (2) towards the fixed rammer (40) in order by extrusion of the billet (5) in the die (41) to extrude a metal bar (50) which is discharged through the axial hole (42) of the rammer (40), and for scraping the housing (21) after the extrusion, means which comprise a scraper block (7) mounted on a rammer (70) and capable of being threaded into the housing (21), the extrusion block (4) having a diameter (D₁) less than that (D₂) of the inner face (22) of the housing (21) so as to leave a first clearance (c) which during the course of the extrusion enables a lining (51) to be formed along the inner face (22) of the housing (21), characterized by the fact that inasmuch as billets are employed which are rough from the foundry, without previous elimination of the outer layer, the first clearance (c) left is between the periphery of the extrusion block (4) and the inner face of the housing (21) is determined in such a way that the lining (51) has a thickness (a′) sufficient to embrace all of the surface defects of the rough billet and that the scraper block (7) has a diameter (D₃) slightly less than that (D₂) of the inner face (22) of the housing (21) so that between the periphery of the said scraper block (7) and the inner face (22) of the housing (21) there exists a second clearance (d) which is less than the first clearance (c) yet is sufficient for the lining (51) to be scraped towards the inside and only over a portion of its thickness whilst letting a skin of metal (52) persist after scraping, which is of uniform thickness and covers the whole of the inner face (22) of the housing (21).

7. An extrusion press as in Claim 6, characterized by the fact that the first clearance (c) between the extrusion block (4) and the inner face (22) of the housing (21) is determined as a function of the diameter of the billet over a range from about 1.5 to 4 mm.

8. An extrusion press as in one of the Claims 6 or 7, characterized by the fact that the second clearance (d) between the scraper block (7) and the inner face (22) of the housing (21) lies between 0.1 and 0.25 mm

9. An extrusion press as in Claim 6, in which the scraper bush (7) is mounted on a second rammer (70) capable of being placed on the axis of extrusion (10) and threaded into the housing (21) in the container (2) by axial displacement in one direction for scraping and withdraw in the opposite direction, characterized by the fact that the scraper block (7) is coupled to its rammer (70) so as to remain fixed to the end of the latter both in the direction for scraping and in the direction of withdrawal and that it has a diameter (D₃) which is able to vary so that the second clearance (d) between the periphery of the said scraper block (7) and the inner face (22) of the housing (21) is smaller in the direction for scraping than in the direction of withdrawal.

10. An extrusion press as in Claim 9, characterized by the fact that the scraper block (7) comprises a supporting body (71) which is fixed to the end of the scraper rammer (70) and carries at the opposite side from the said rammer a scraper segment (7′) in the form of an elastic ring through which is cut a gap (73) centred on a radial plane P₁ and bounded by two plane faces (74, 74′) opening in a V towards the inside, between which an expander wedge (8) engages which is equipped with bearing faces (81, 81′) of corresponding slope and is mounted to slide transversely across the supporting body (71), the latter being associated with means (9) of controlling the transverse displacement of the wedge (8) towards the outside in order to determine the widening of the gap (73) and the increase in diameter of the scraper segment (7′).

11. An extrusion press as in Claim 10, characterized by the fact that the scraper segment (7′) is equipped on its periphery with a cutting edge (75) for planing the lining (51) and bears by way of a smooth face perpendicular to the axis of the rammer (70) against a smooth face (76) arranged to correspond at the end of the supporting body remote from the rammer (70), the scraper segment (7′) being locked in axial displacement to the said supporting body (71) by a retainer clamp (77) in the form of a ring of a U-section which comprises two flanges engaging respectively in corresponding circular grooves (78) (78′) arranged on the segment (7′) and the supporting body (71) respectively, whilst the said clamp (77) comprises two ends (77′) face to face separated by a space to correspond with the gap (73) in the segment (7′).

12. An extrusion press as in Claim 11, characterized by the fact that the means of controlling the transverse displacement of the expander wedge (8) comprise a cam (9) which exhibits a plane face (90) inclined with respect to the axis (10) and cooperating with a plane face (82) of corresponding slope arranged on the expander wedge (8), the said cam (9) being fixed to a control member (91, 92) mounted to slide in an axial bore (93) in the supporting body (71) so as to control the transverse displacement of the latter towards the outside by axial displacement of the operator rod.

13. An extrusion press as in Claim 12, characterized by the fact that the expander wedge (8) is mounted to slide transversely in a slot (95) cut in a widened portion (92) of the control member (91) and bounded by two plane faces (96, 96′) parallel with the axis (10), which cooperate with corresponding lateral faces (85, 85′) on the expander wedge (8).

14. An extrusion press as in Claim 12, characterized by the fact that the control member (91, 92) is actuated by an operator rod (97) which is mounted to slide in an axial bore in the rammer (70) and connected to the rod of a jack (98) for controlling the axial sliding.

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