EP0010510B1 - Improvement in methods and devices for the continuous hydrostatic extrusion of metals - Google Patents

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 work "Large Plastic Flow and Fracture" published by McGRAW-HILL, New York, in 1952, and one is the subject of the patent US 2,558,035.

However, all attempts to implement the BRIDGMAN effect, with a view to extruding a blank of indefinite length, have come up against the complexity of the equipment 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 for industrial implementation of hydrostatic extrusion of a blank of indefinite length.

According to the first of these patents, the blank to be extruded is first of all shaped to reveal two substantially parallel flat faces, then introduced into a channel formed by two coaxial members in rotary motion, the mobile 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 known as a "stator" forming with the bleed a channel closed by a lug secured to the fixed member and carrying, at less, 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 happened 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 distribution 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 slipping. 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 problem therefore arose of reducing the leakage rate of the working fluid to a strict minimum while maintaining adequate lubrication of the die by means of a sufficient leakage rate.

The object of the present invention is an improvement of the process and of the hydrostatic extrusion device which have just been described, and which makes it possible to have a very low leakage flow rate in the groove, and to ensure the lubrication of the die at the passage of the blank.

The improved process 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 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 known as the driving fluid, in which is generated by a progressive penetration of a step of the cover into the groove, a progressively increasing pressure from the entry point, at ambient pressure to the isostatic chamber where the extrusion pressure prevails, thus ensuring adhesion at all points sufficient for the movement of the rotor to cause said blank with a negligible slip from upstream, at ambient pressure to downstream, at the entrance to the isostatic chamber from where e It escapes by hydrostatic extrusion through at least one die orifice, the viscosity of the working fluid located in the groove being greater than that of the fluid located in the vicinity of the die. According to the in vention the working fluid is an alkaline or alkaline-earth salt of a fatty acid chosen from oleic, sebacic, stearic and palmitic acids, 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, can be 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.

The driving fluid contained in the bleeding and the fluid located in the vicinity of the die may be originally in a solid, liquid, liquefied, pasty or pulverulent state, having a flowability under the conditions of temperature and pressure. reigning in the bleeding and in the isostatic chamber. As the fatty acid salt, in particular, calcium stearate is chosen.

As regards the fluid located in the isostatic chamber, it can be given a viscosity lower than that of the working fluid located in the groove, or, if it is the same substance, by bringing it to a higher temperature by heating the isostatic chamber or cooling the bleeding, either by choosing a fluid different from the working fluid and having, by nature, a viscosity at equal temperature, lower than that of the working fluid located in the bleeding. 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, either that it is heated to decrease the viscosity, or that it is cooled to remove 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 ébauches;
• 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.

Different ancillary provisions facilitate the implementation of the process:

• - the working fluid is introduced into the groove through at least one 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 so-called lug relief completely obstructing the 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 passing through the stator, in an isostatic chamber communicating towards the outside through at least one die orifice, the means of supply of working fluid, generating in the first sector of the bleeding a pressure gradient from the entry point, at ambient pressure to the entry of the conduit opening into the isostatic chamber where the extrusion pressure prevails. It is characterized in that the driving fluid consists of an alkaline or alkaline earth salt of a fatty acid chosen from oleic, sebacic, stearic and palmitic acids. In addition, it may include means for regulating the temperature of each fluid. It is also characterized in that the isostatic chamber can be provided with a closable orifice which can be connected to a pressure injection means, of a fluid with a viscosity lower than that of the working fluid.

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 cross-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 have one or more orifices (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 an excess.

It has been discovered that the working fluid could no longer necessarily be a "fluid" in the conventional sense of the term, but a liquid, liquefied, pasty or pulverulent, or even solid substance, having under the conditions of temperature and pressure prevailing in the bleeding. and in the extrusion chamber, a flowability. The fatty acid salts, characterized in the claim have, under the pressures used, of the order of several thousand bars, a flowability which allows their use both as an agent for transmitting hydrostatic pressure. and as a driving agent of 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 flow rate of leakage 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.

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 retains 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.

To inject into the isostatic chamber, in the vicinity of the die, a fluid different from that which is in the bleeding, a small pressure multiplier is used. However, it should be noted that this multiplier works at high pressure under a low flow rate, because there is at this level no other leak than the thin film of fluid entrained by the extruded product and which is used to lubricate the die and this leak is very weak.

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 FIG. 5 by the thickened part of the outer circle, has a length of 2.5 meters and the groove has a section of 80 × 10 mm at the entrance, gradually decreasing, according to the diagram in FIG. 5 , up to 20x10 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 isostatic chamber.

The powder is injected through the orifice (13) under a low or zero pressure which increases up to approximately 1500 MPa at the inlet of the channel (12).

The preform advances with the rotor because the adhesion force of the preform in the powder is greater than the reverse thrust, which would tend to make it move 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 effort exerted by the powder to advance the blank is therefore greater than 3.14 × 250 × 200 = 15.7. 104N.

The force exerted by the extrusion pressure and opposing the advance of the draft is: 1.5. 10 ⁹ Pax0.785. 10 '"' m2 = 11.8. 10 ⁴ N.

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

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 of Beginning liquefaction of calcium stearate. There was obtained, without difficulty and without jamming of the die, the extrusion of a 2 mm wire.

Other types of powders of alkali or alkaline earth salts of fatty acids can be used as "viscous fluid" under conditions comparable to those which have just been described.

Claims (14)

1. A process for the continuous hydrostatic extrusion of a first object, referred to as a blank, of indefinite length, to form a second object, which is also of indefinite length but of different section, wherein the blank which is surrounded by a substantial amount of a viscous fluid is introduced into a groove cut in a rotor for directly receiving by an introduction means the drive fluid which, by the cover member progressively penetrating into the groove, produces a progressive increasing pressure from the entry point at ambient temperature to the isostatic chamber where the extrusion pressure obtains and which ensures sufficient adhesion for the movement of the rotor to entrain said blank with negligible slip from the upstream position at ambient pressure in a downstream direction to the entry of the isostatic chamber from which it escapes by hydrostatic extrusion through at least one die aperture, the viscosity of the fluid in the groove being higher than that of the fluid in the vicinity of the die, characterised in that the drive fluid is an alkaline or alkaline-earth salt of a fatty acid selected from oleic, sebacic, stearic and palmitic acids.

2. A continuous hydrostatic extrusion process according to claim 1 characterised in that a fluid other than that in the groove and having a viscosity lower than that of the drive fluid in the groove is injected into the isostatic chamber.

3. A continuous hydrostatic extrusion process according to claim 1 or claim 2 characterised in that the temperature of the drive fluid in the groove is regulated.

4. A continuous hydrostatic extrusion process according to any one of claims 1 to 3 characterised in that the temperature of the fluid in the isostatic chamber is regulated.

5. A continuous hydrostatic extrusion process according to any one of claims 1 to 4 characterised in that the drive fluid escaping from the apparatus by way of the different leaks due to the clearances which are essential for operation thereof is recovered and reintroduced into the circuit.

6. A continuous hydrostatic extrusion process according to any one of claims 1 to 5 characterised in that the blank is preheated to increase its aptitude to deformation.

7. A continuous hydrostatic extrusion process according to any one of claims 1 to 6 characterised in that the blank comprises a plurality of separate elements which are jointly introduced into the groove in the rotor and strongly pressed together when they pass through the extrusion die.

8. Apparatus for carrying out, in accordance with any one of claims 1 to 7, the process for the continuous hydrostatic extrusion of a first object, referred to as a blank, of indefinite length, to form a second object which is also of indefinite length but of different section, wherein two co-axial co-operating members, one being movable, referred to as a rotor which, at its surface, carries a groove therearound for receiving the blank to be extruded, the other being fixed and referred to as the stator, forming over a first sector of the groove containing the blank and a drive fluid, a cover member which is substantially sealed with respect to said fluid, the stator also being provided in a second sector of the groove which is disposed downstream of the first sector, with a projection referred to as a lug, which totally blocks the section of the groove and is precisely adapted thereto to make it sufficiently sealed with respect to the viscous fluid, the stator comprising a means for supplying the groove with drive fluid, and an orifice disposed facing the first sector of the groove, in the vicinity of the second sector, and communicating by way of an elongate conduit passing through the stator with an isostatic chamber which communicates with the exterior through at least one die aperture, the drive fluid supply means generating in the first sector of the groove a pressure gradient from the entry point at ambient temperature to the entry of the conduit communicating with the isostatic chamber where the extrusion pressure obtains, characterised in that said drive fluid is an alkaline or alkaline-earth salt of a fatty acid selected from oleic, sebacic, stearic and palmitic acids.

9. Apparatus according to claim 8 characterised in that it comprises means for regulating the temperature of the drive fluid.

10. Apparatus according to claim 9 characterised in that the stator comprises at least one orifice for introducing or discharging any excess of drive fluid in the groove.

11. Apparatus according to claim 9 or claim 10 characterised in that it comprises a stator formed by two identical elements, permitting simultaneous extrusion of two blanks.

12. Apparatus according to claim 9 or claim 10 characterised in that the rotor comprises at least two grooves capped by a cover member comprising at least two elements each acting as a stator, permitting the simultaneous extrusion of at least two blanks.

13. Apparatus according to any one of claims 9 to 12 characterised in that the isostatic chamber is provided with a closable orifice which is disposed in the vicinity of the die and connected to a means for injecting fluid under pressure, the viscosity of which is less than that of the drive fluid in the groove.

14. Apparatus according to any one of claims 8 to 13 characterised in that it comprises a means for preheating the blank.

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