EP0010510A1 - Improvement in methods and devices for the continuous hydrostatic extrusion of metals - Google Patents

Abstract

The invention relates to an improvement to methods and devices for continuous hydrostatic extrusion. In order to reduce the leakage of viscous fluid by the clearances between the rotor (3) and the stator (6) necessary for the operation of the apparatus, in the groove of the rotor, a driving fluid is used to advance the blank. viscosity higher than that of the fluid located in the isostatic chamber where the extrusion pressure prevails. The pumping power is, in fact, greatly reduced, and it is possible to avoid the use of expensive and fragile pressure multipliers. Application to the continuous hydrostatic extrusion of metals.

Description

The present invention relates to improvements to methods and devices for continuous hydrostatic extrusion.

We know, since the work of PW BRIDGMAN, that the ductility of many metals and alloys increases when an increasing pressure is applied to them and that we can deform them without fracture, and, in particular extrude them through a die, under very high pressures. These works were published, in particular, in the book "Large Plastic Flow and Fracture" published by Mc GRAW-HILL, New York, in 1952 and were the subject of the patent US 2,558,035.

However, all the attempts to implement the BRIDGMAN effect, with a view to extruding a blank of indefinite length, have come up against the complexity of the apparatus and have not so far resulted in industrial exploitation.

In its patents FR 2,310,813 and FR 2,373,339, the applicant has described a process and an apparatus opening the way to an industrial implementation of the hydrostatic extrusion of a blank of indefinite length. According to the first of these patents, the blank to be extruded is firstly formed to reveal two substantially parallel flat faces, then introduced into a channel formed by two coaxial members in relative motion, the movable member called "rotor ", carrying a groove of revolution deeper than wide, traced on its surface and comprising two substantially parallel lateral faces, the other member called" stator "forming with the bleed a channel closed by a lug secured to the fixed member and carrying , at least, a sector. The blank, surrounded on all sides by a viscous liquid, is driven towards the die by the forces developed in the fluid by the rotor, without there being direct contact, metal on metal, between the blank and the rotor walls, unlike what occurred in previous processes, such as that described in French patents 2,128,843 and 2,197,665.

According to the second of these patents, 2,373,339, which constitutes an improvement on the first, the blank to be extruded is applied to the walls or the bottom of the groove formed in the rotor, under the action of the viscous fluid, in such a way that said blank is driven by the rotor without sliding, towards an extrusion chamber from which it is spontaneously extruded through a die.

The viscous fluid is brought above the product to be extruded, at the extrusion pressure in the vicinity of the die and at lower pressures at one or more points located between the inlet of the product and "the die. the pressure of the viscous fluid above the product is such that the adhesion of the two generators of the product in contact with the sides of the trapezoidal groove is sufficient to ensure the entrainment of the product by metal-metal contact, without sliding relative to the rotor.

In this device, we have, in addition, arranged the die out of the groove, which allows it to be made more accessible and to be dimensioned more widely. From the outlet of the groove to the die, the product passes through a chamber formed in the stator where the extrusion pressure prevails, called the isostatic chamber.

Although these methods and the implementation device work quite satisfactorily, a certain number of drawbacks have appeared, in particular with regard to the pumping power of the viscous liquid. Indeed, the working pressure can reach 1600 MPa and the average leakage rate of the viscous fluid is of the order of 25 to 30 milliliters per second. Given the efficiency, this corresponds to a pumping power which is in the range of 50 to 100 kilowatts. In addition, under this high pressure, the pressure multipliers with large flow rates are subjected to very hard work and the entire apparatus requires relatively large and expensive maintenance.

The object of the present invention is an improvement of the process and of the hydrostatic extrusion device which have just been described.

The improved method relates to the continuous hydrostatic extrusion of a first object, called a blank, of indefinite length, into a second object of equally indefinite length, but of different cross section, in which the blank, surrounded by a substantial quantity of '' a viscous fluid, is introduced into a groove, cut in a drive rotor and facing a stator forming a cover, applied to the rotor, directly receiving, by an introduction means, the viscous fluid called motor fluid, in which is generated by a progressive penetration of a step of the cover into the groove, a progressive pressure growth of the entry point, at ambient pressure up to the isostatic chamber where the extrusion pressure prevails, thus ensuring at all points sufficient adhesion for the movement of the rotor to drive said blank with negligible sliding upstream, at ambient pressure downstream, at the entrance to the isostatic chamber from which it escapes by hydrostatic extrusion through, at least, a die orifice. It is characterized in that the working fluid located in the groove has a viscosity greater than that of the fluid located in the vicinity of the die, which allows greater clearance between the rotor and the stator, without increasing the leakage rate. In addition, the fact that the working fluid, initially introduced under low or zero pressure, is brought under the high pressure necessary under the effect of the rotation of the rotor, makes it possible to eliminate the costly and relatively fragile pressure multipliers.

Each viscous fluid (the driving fluid contained in the bleeding and the fluid located in the vicinity of the die) can be chosen from solid, liquid, liquefied, pasty, pulverulent substances, having a flowability under the conditions of temperature and pressure prevailing in the bleeding and in the isostatic chamber. In this way, the choice is extremely wide. Among the substances suitable for the implementation of the invention, there may be mentioned fatty acid salts (such as oleates, sebacates, palmitates, stearates), and, in particular, calcium stearate, mineral powders or organic, for example powders in granules of polyvinyl chloride, polyolefins, polytetrafluorocarbon etc ...

With regard to the fluid located in the isostatic chamber, it can be given a viscosity lower than that of the working fluid located in the groove, by several means, either by heating the isostatic chamber, either by cooling the groove, or by introducing in the isostatic chamber a fluid having, by its nature, a viscosity lower than that of the working fluid located in the groove. This fluid can be a liquid, such as a liquid hydrocarbon, but also a gas liquefied under the pressure prevailing in the isostatic chamber: for example butane, propane, carbon dioxide.

Furthermore, since the implementation of the process is linked to the viscosity of the fluids used and the viscosity itself being dependent, under a given pressure, on the temperature, it is important to be able to maintain the temperature of the fluid (s), as well in the bleeding only in the isostatic chamber at a suitable value, that is to say heating to reduce the viscosity, or cooling to eliminate the heat given off by the extrusion process and increase the viscosity of the fluid (s).

• - le fluide moteur est introduit dans la saignée par, au moins, un orifice pratiqué dans le stator, par un dispositif de type connu ;
• - l'excès éventuel de fluide moteur peut être évacué par, au moins, l'un des orifices pratiqués dans le stator ;
• - le fluide moteur s'échappant de l'appareil par les différentes fuites indispensables à son fonctionnement peut être récupéré et réintroduit dans le circuit générateur de haute pression ;
• - grâce à la présence d'un stator composé de deux éléments identiques, on peut extruder simultanément deux ébauches ;
• - grâce à la présence d'un rotor comportant, au moins, deux saignées coiffées d'un couvercle en au moins deux éléments, faisant chacun fonction de stator, on peut extruder simultanément au moins deux ébau ches ;
• - l'ébauche peut être constituée de plusieurs éléments distincts introduits conjointement dans la saignée du rotor et fortement pressés ensemble lors de leur passage dans la filière d'extrusion.

Various ancillary provisions facilitate the implementation of the pro _- die:

• - the working fluid is introduced into the groove through, at least, an orifice made in the stator, by a device of known type;
• - the possible excess of working fluid can be evacuated by, at least, one of the orifices made in the stator;
• - the working fluid escaping from the device through the various leaks essential for its operation can be recovered and reintroduced into the high pressure generator circuit;
• - Thanks to the presence of a stator made up of two identical elements, it is possible to simultaneously extrude two blanks;
• - Thanks to the presence of a rotor comprising, at least, two grooves capped with a cover made of at least two elements, each acting as a stator, it is possible to simultaneously extrude at least two blanks;
• - The blank may consist of several separate elements introduced jointly into the groove of the rotor and strongly pressed together during their passage through the extrusion die.

The improved device, which is also an object of the invention, and which allows the continuous hydrostatic extrusion of a first object known as a blank, of indefinite length, into a second object of equally indefinite length, but of different section, comprises two cooperating coaxial members, one mobile said rotor carrying, traced on its surface, a groove of revolution receiving the blank to be extruded, the other fixed, said stator, forming a first sector of the groove containing the blank and the fluid motor, a cover that is substantially leaktight with respect to said fluid, the stator also comprising, in a second sector of the groove, located downstream from the previous one, a relief known as a lug completely obstructing the cross-section of the groove and exactly adjusted to it ci, to make it sufficiently tight vis-à-vis the working fluid, the stator comprising a means for feeding the bleeding in working fluid, as well as an orifice located opposite the first sector of the bleeding, in the vicinity of the seco nd sector and opening, by an elongated conduit crossing the stator, in an isostatic chamber communicating towards the exterior through at least one die orifice, the means for supplying motive fluid, generating in the first sector of the groove a pressure gradient from the entry point, at ambient pressure up to the entry of the conduit opening into the isostatic chamber where the extrusion pressure prevails. It is characterized in that it includes means for regulating the temperature of each fluid. It is also characterized in that the isostatic chamber is provided with a closable orifice which can be connected to a means of injection, under pressure, of a fluid with a viscosity lower than that of the working fluid. ,

By source of simplification, we designate by the term "fluid" any liquid or liquified substance, pasty or pulverulent or even solid, having under the conditions of temperature and pressure prevailing in the device a flowability.

• The figures and examples which follow will make it possible to specify the implementation of the invention.
• Figures 1 and 2 show two profiles of the groove in which the blank is entrained.
• Figure 3 shows the die through which the blank is extruded.
• Figure 4 shows the general arrangement of the extrusion device according to the invention.
• Figure 5 shows schematically the evolution of the pressure in the bleeding. .

. The blank (1) is arranged in the trapezoidal section groove (2) formed in the rotor (3). In this case, the blank rests on the sides of the groove, but it is driven without sliding, that is to say without metal-to-metal friction. The fluid pressure is generated by the spiral step (4) of the stator, as in patent FR 2,310,813. However, it is also possible to adopt a groove (5) with parallel faces (FIG. 2), in which the blank is entirely surrounded by the working fluid, without contact between the blank and the walls of the groove.

The stator (6) may include one or more pluriears (7) locally connecting the groove of the rotor to a radial duct (8). It is thus possible to adjust the pressure in the corresponding zone of the groove by injecting through the orifice or orifices (7) a supplement of working fluid, or, on the contrary, by allowing the escape of a surplus.

It has been discovered that the working fluid can no longer necessarily be a "fluid" in the conventional sense of the term, but any substance li--; solid, liquified, pasty or pulverulent, or even solid, possessing, under the conditions of temperature and pressure prevailing in the bleeding and in the extrusion chamber, a flowability. In particular, it has been discovered that a certain number of powders, and in particular the fatty acid salts, possessed, under the pressures used, of the order of several thousand bars, a flowability which allows their use. both as a hydrostatic pressure transmitting agent and as a driving agent for the blank to be extruded, but, because of their very high "viscosity", as far as we can speak of viscosity in the case of a substance which is not really fluid, the leak rate at the various operating clearances is extremely low. As the power of the pumping unit is equal (to the nearest yield) to the product of the leakage rate by the pressure, it follows that the power required is lowered considerably compared to that which is necessary in the case of a fluid. conventional viscous, such as natural or synthetic oils.

Likewise, powders or granules of polyvinyl chloride, of polyolefins (polyethylene), polytetrafluorocarbon, are suitable for the implementation of the invention.

However, it is sometimes difficult to reconcile in the same fluid the different characteristics required by sealing, on the one hand, (low leakage rate) and by extrusion on the other hand (ability of the fluid to lubricate the Faculty).

It is then possible to use either the same fluid in two different states, or two different fluids, for example a stearate powder as the driving fluid and a product with lower viscosity in the isostatic chamber (9) in the vicinity of the die ( 10) injected, for example, through the orifice (11). This fluid can be any liquid hydrocarbon, natural or synthetic oils, or even simple petroleum (also called kerosene).

As, moreover, the viscosity of a substance decreases, under a given pressure, when the temperature rises, it may be advantageous to provide the extrusion device with known means for bringing the temperature of the fluid, locally or in its together at a suitable value. This is how we can either heat the isostatic chamber or cool the groove (and possibly the blank), so that the fluid located in the groove has a viscosity higher than that of the fluid located in the chamber. isostatic, in accordance with the invention. If the viscous fluid is calcium stearate, it is possible, for example, to heat the isostatic chamber in the vicinity of or above its melting point which is 180 ° C. One can, incidentally, cool the die which generally tends to heat up by the very process of extrusion. Likewise, in some cases, it may be advantageous to preheat the blank to increase its deformability. In the case where a different fluid than the one in the groove is injected into the isostatic chamber, in the vicinity of the die, it is necessary to use a small pressure multiplier, but it should be noted that this multiplier works at high pressure under a low flow rate, because there is no other leakage at this level than the thin film of fluid entrained by the extruded product and which is used to lubricate the die and this leakage is very low.

EXAMPLE 1

In a device in accordance with that of FIGS. 2 and 4, a copper blank 10 millimeters in diameter was introduced, driven at a speed of 0.50 meters per second. The working fluid is calcium stearate powder. Was injected, in addition, into the isostatic chamber through the orifice (11), in the vicinity of the die (16) of petroleum (kerosene) under a pressure of 1500 MPa.

The active part of the rotor, shown diagrammatically in Figure 5 by the thickened part of the outer circle, has a length of 2.5 meters and the groove has a section of 80 x 10 mm at the entrance, gradually decreasing, according to the diagram in figure 5, up to 20 x 10 at the inlet of the channel (12), leading to the die, the outlet diameter of which is 2 mm, this arrangement ensuring the pressure gradient along the groove up to the chamber isostatic.

The powder is injected through the orifice (13) under a low or zero pressure which increases up to approximately 1500 MPz at the inlet of the canai (12), The blank advances with the rotor because the adhesion force of the blank in the powder is greater than the reverse push, which would tend to

roll it back, exerted on it by the pressure of 1500 MPa. It is estimated that the adhesion force of the powder on the walls of the groove is, on average, greater than 200 newtons per cm 2 of contact surface. The force exerted by the powder to advance the blank is therefore greater than 3.14 x 1 x 250 x 200 = 15.7 10 ⁴ N.

The force exerted by the extrusion pressure and opposing the advance of the blank is: 1.5.10 ⁹ Pa x 0.785.10 ^-4 m2 = 11.8.10 ⁴ N.

× 100 = 33%). Le fond de la saignée peut alors avoir une forme quelconque, ainsi d'ailleurs que le produit à extruder, à la seule condition qu'il puisse être logé dans la saignée (5).The comparison of these two results shows that the driving of the blank by the powder, in the absence of direct metal-metal contact of the blank on the walls and / or the bottom of the groove, is carried out with a largely sufficient safety factor (

× 100 = 33%). The bottom of the groove can then have any shape, as well as the product to be extruded, on the only condition that it can be accommodated in the groove (5).

EXAMPLE 2:

The operation was carried out under conditions identical to those of Example 1, but the orifice (11) was closed and the area of the isostatic chamber was heated so as to bring its temperature to 180 ° C., corresponding to the point starting liquefaction of calcium stearate.

An extrusion of a 2 mm wire was obtained without difficulty and without jamming of the die.

Other types of powders, in particular, the fatty acid salts can be used as "viscous fluid" under conditions comparable to those which have just been described.

Claims (19)

1. A method of continuous hydrostatic extrusion of a first object, called a blank, of indefinite length, into a second object, of equally indefinite length, but of different section, in which the blank surrounded by a substantial quantity of a viscous fluid is introduced into a cut cut in a rotor directly receiving by a means of introduction the driving fluid generating, by a progressive penetration of the cover in the cut, a progressively increasing pressure from the point of entry at ambient pressure up to the isostatic chamber where the extrusion pressure prevails and ensuring sufficient adhesion for the movement of the rotor to drive said blank with negligible sliding from upstream at ambient pressure to downstream, at the entrance to the chamber isostatic from which it escapes by hydrostatic extrusion through at least one die orifice, characterized in that the viscous fluid located in the groove has a higher viscosity to that of the fluid located in the vicinity of the die. 2. Hydrostatic extrusion method according to claim 1, characterized in that each fluid is chosen from solid, liquid, liquefied, pasty, pulverulent substances having a flowability under the temperature and pressure conditions prevailing in the bleeding and in the isostatic chamber. 3. A method of continuous hydrostatic extrusion according to claim 1 or 2, characterized in that the working fluid is a fatty acid salt. 4. A method of continuous hydrostatic extrusion according to claim 1, 2 or 3, characterized in that the working fluid is an alkaline or alkaline earth salt of a fatty acid chosen from oleic, sebacic, stearic, palmitic acids . 5. A continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that the fluid located in the isostatic chamber is brought to a temperature higher than that of the working fluid located in the groove. 6. Continuous hydrostatic extrusion method according to any one. of the preceding claims, characterized in that a fluid whose viscosity is lower than that of the working fluid located in the groove is injected into the isostatic chamber. 7. A continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that the temperature of the working fluid located in the groove is regulated. 8. A method of continuous hydrostatic extrusion according to any one of the preceding claims, characterized in that the temperature of the fluid located in the isostatic chamber is regulated. 9. A continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that the working fluid is introduced into the groove by, at least, an orifice made in the stator. 10. A method of continuous hydrostatic extrusion according to any one of the preceding claims, characterized in that the possible excess of working fluid can be evacuated by at least one of the orifices made in the stator. 11. A continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that the working fluid escaping from the device by the various leaks essential for its operation, is recovered and reintroduced into the circuit. 12. A continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that the blank is preheated, to increase its ability to deform. 13. Continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that, thanks to the presence of a stator composed of two identical elements, two blanks are simultaneously extruded. 14. Continuous hydrostatic extrusion method according to any one of the preceding claims, characterized in that, thanks to the presence of a rotor comprising at least two grooves, capped with a cover in at least two elements, each acting as a stator, at least two blanks are extruded simultaneously. 15. A method of continuous hydrostatic extrusion according to any one of the preceding claims, characterized in that the blank consists of several distinct elements introduced jointly into the groove of the rotor and strongly pressed together, during their passage through the die. extrusion. 16. Continuous hydrostatic extrusion device for a first object known as a blank, of indefinite length, into a second object of equally indefinite length, but of different section, in which two coaxial members cooperating, one mobile, known as a bearing rotor, traced on its surface, a groove of revolution receiving the blank to be extruded, the other fixed said stator, forming a first sector of the groove containing the blank and a working fluid, a cover substantially sealed with respect to said fluid , the stator also comprising in a second sector of the groove, located downstream of the previous one, a relief known as a lug, completely obstructing the cross-section of the groove and exactly adjusted to it to make it sufficiently tight vis-à-vis the viscous fluid, the stator comprising a means for supplying the bleeding with working fluid, as well as an orifice located opposite the first sector of the bleeding, in the vicinity of the second sector and emerging, by an elongated conduit passing through the st ator, in an isostatic chamber communicating outwardly through at least one die orifice, the means for supplying motive fluid generating in the first sector of the bleeding a pressure gradient from the point of entry, at the ambient pressure, up to the entry of the conduit opening into the isostatic chamber where the extrusion pressure prevails, characterized in that it comprises means for regulating the temperature of each fluid ... 17. Continuous hydrostatic extrusion device according to claim 16, characterized in that the isostatic chamber is provided with a closable orifice placed in the vicinity of the die. 18. Continuous hydrostatic extrusion device according to claim 17, characterized in that the closable orifice is connected to a means for injecting pressurized fluid. 19. Continuous hydrostatic extrusion device according to any one of claims 16, 17 or 18, characterized in that it comperte a means of preheating the blank.

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