US3559271A

US3559271A - Hydrostatic extrusion of powder

Info

Publication number: US3559271A
Application number: US739487A
Authority: US
Inventors: Jan Nilsson
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1967-06-26
Filing date: 1968-06-24
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02
Also published as: GB1221879A; FR1569530A; JPS5132564B1; SE377434B; DE1758540B1

Abstract

RODS OR WIRE ARE PRODUCED FROM POWDER BY FORMING A BILLET COMPACTED TO GREAT DENSITY AND PROVIDED ON ITS SURFACE WITH A TEMPORARY, LIQUID-TIGHT BARRIER OF NONMETALLIC YIELDING MATERIAL. THE BILLET IS ENCLOSED IN A PRESSURE CHAMBER LOCATED ABOVE A DIE, WITHIN WHICH CHAMBER A LIQUID CAN BE COMPRESSED. THE COLD BILLET IS FORMED BY HYDROSTATIC EXTRUSION TO A CROSS SECTION DETERMINED BY THE NOZZLE OF THE DIE AFTER WHICH THE TEMPORARY BARRIER IS REMOVED. THE DEFORMATION IS CARRIED OUT UNDER SUCH PRESSURE AS TO PRODUCE A SUFFICIENT INCREASE IN TEMPERATURE TO SINTER THE POWDER.

Description

Feb. Z, 1971 .1. NlLssoN HYDROSTATIC EXTRUSION OF POWDER Filed June 24, 1968 du W V l Il //r, yA

INVENTOR. JAN Nl LS SON BY 3,559,271 HYDRSTA'HC EXTRUSON 0F POWDER Jan Nilsson, Robertsfors, Sweden, assigner to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed June 24, 1968, Ser. No. 739,487 Claims priority, application Sweden, .lune 26, 1967, 9,071 67 Int. Cl. B22f 3/24 U.S. CL :E9-420.5 13 Claims ABSTRACT F DISCLOSURE BACKGROUND OF THE INVENTION (l) Field of the invention The present invention relates to a method of producing rods or wire by means of hydrostatic extrusion, using powder as starting material.

(2) The prior art Many hard and brittle alloys which are difficult to machine or not malleable (can be mechanically deformed only with difficulty) consist of metals which, in unalloyed state, are individually soft and ductile. If components of such alloys are manufactured from powder mixtures by means of compression, and afterwards sintered so that an alloy is obtained or the constituents are bound together to give the finished component the desired properties, the components only need to be trimmed after they have become difcult to machine. When manufacturing components from powder it is extremely diicult to make them so compact that shrinkage during the sintering is so slight and uniform that the desired tolerance can be maintained or that the material is sufficiently dense so that its properties can be fully exploited. Particularly in the manufacture of long rod-shaped components, it has been diieult to obtain high and uniform density so that during sintering or compacting the alternations in dimension along the length of the rod are uniform and so negligible that the desired tolerance can be maintained.

Rods have also been produced by extruding powder with the addition of a binder through the die. With previously known methods the addition of a binder has been necessary for the compression to take place under reasonable pressure and so that the powder is held together during further treatment. The density of the powder is deteriorated due to this addition. The binder is removed before sintering or disappears partly or completely during the sintering and thus gives rise to spaces between the powder particles or to shrinkage of the body resulting in poor mechanical properties and diiiculty in maintaining small tolerance.

Hot extrusion of powder is also known. The high ternperature, often above 1,000 C., causes considerable strain on the tools, however. As with most other hot plastic machining methods, it is difficult to maintain small tolerance and satisfactory surface finish.

Patented Feb. 2, 1971 SUMMARY oF THE INVENTION ICC According to the invention tubes, rods or wire are manufactured by means of hydrostatic extrusion of a billet consisting of powder of a single material or a mixture of powders of different materials to provide the desired cornposition. No binder is added. Usually metal powder is used, but certain oxide powder mixtures of metal and oxide powder or metal powder with oxide coating may also be used.

Normal commercial powder of copper, aluminium, iron, or the like having a particle size under 150g (under mesh) can be used. According to the method the powder is shaped into a billet and compacted to great density and provided on its surface with a temporary, liquid-tight barrier of non-metallic, tenacious material, after which the billet is shaped into a bar or tube by means of hydrostatic extrusion in equipment comprising a pressure chamber, a die inserted in this chamber with a nozzle to give the billet the desired cross-section, a pressure medium enclosed in the pressure chamber and a pressure-generator to generate the pressure necessary in the pressure chamber for the extrusion. After the extiusion the temporary barrier is removed which, during the extrusion process, prevents the pressure medium from penetrating into the pores of the billet.

The temporary barrier suitably consists of a plastic material having a hardness of at least 60 Shore A. With this or greater hardness the plastic has such resistance that it is not pressed into the pores between the powder particles of the billet. Plasticized PVC (polyvinyl chloride) is an extremely suitable material. The plastic layer forming the barrier can be applied by bringing the heated billet into contact with a powder or grains of the plastic and afterwards possibly inserting it in a furnace and treating it there so that the plastic layer obtains the desired density and hardness. It is also possible to apply the plastic by dipping the billet in a melt or solution of the plastic or by spraying molten plastic or plastic dissolved in a solvent onto the billet. Before extrusion the billet should be compacted, for example by means of hydrostatic compacting, to a density which is at least 60% of the theoretically possible density, that is the density of a solid billet of the same material.

For the compressed rods to obtain a crack-free surface it is necessary to use pressure above a certain minimum value. To a certain extent this pressure depends on the material. Usually the more brittle the material is the higher will be the required extrusion pressure. The required extrusion pressure can be obtained in most cases by making the extrusion ratio suiciently great. This :is normally designated R and is the ratio between the crosssection Ao of the billet and the cross-section A of the extruded product. Thus RzAo/A. with a small extrusion ratio a crack-free product can be obtained under compression with a counter-pressure on the output side of the die. Compression with a counter-pressure may be necessary when extruding brittle materials or when, for some other reason, it is desirable or necessary to operate with low extrusion ratio. The counter-pressure demands correspondingly higher pressure in the pressure chamber and greatly complicates the equipment. Higher counter-pressure than 4,0005,000 bar is hardly possible. With counter-pressures of this magnitude R 3 is desirable if a crack-free product is to be obtained. With R 6 it is usually possible to obtain a crackfree product without using counter-pressure during the extrusion. With very high extrusion ratio a temperature increase due to deformation is obtained of such magnitude that the powder is sintered while it is being pressed out through the die. When aluminium powder is being extruded an extrusion ratio R 60 is required for sintering. If the extrusion takes place under counter-pressure the nozzle on the output side is connected to a pressure chamber in which a constant counter-pressure can be maintained with the help of control means for the purpose.

The method enables products to be manufactured from powder which have greater density than is possible with previously known methods. The density involves more intimate contact between the powder particles, which enables the body to be more easily sintered. Similarly, the good particle contact involves less alteration in dimension during sintering and produces a nal product with better mechanical properties.

The powder used may consist of several substances, each of which is plastically formable. Upon extrusion a rod is formed in which the constituents, during the subsequent sintering, form those alloys which give the material the desired properties. In many cases it is possible to utilize the constituent alloying substances better and thus produce the desired properties in the finished product while using less of the alloying substances which usually constitute the most expensive particle components in the powder mixture.

Another advantage which is gained by the method according to the invention is that rods can be produced having desired dimensions and small tolerance from material which in the form of a nished alloy cannot be plastically machined and therefore cannot be given the desired dimension yby rolling or forging. On the other hand a powder mixture having the same composition can be shaped by extrusion to rods, assuming that at least a certain proportion of the constituents are individually ductile. Examples of the above-mentioned alloys are:

Iron-aluminium with high Al content Iron-nickel-cobalt with high Ni and Co content.

Dispersion-tempered products with extremely good properties can also be manufactured with advantage according to the method. Particles of hard material, for example certain oxides, are then mixed into the powder or are included in specially treated powder where the surface of the powder particles is coated with an oxide. During the extrusion process the separate particles are greatly deformed and the hard substances broken down to very small particles which are also very evenly distributed in the iinished rod. This means that the content of dispersion-tempered substances can be kept low since it is the free path between particles of the additional material which determines the properties of the product. With a low content of additional material its negative effect will be negligible. It is thus possible according to the method to manufacture aluminium conductors having great mechanical strength but approximately the same Conducting capacity as conductors of pure aluminium. If a billet is extruded having a content of 0.5% A1203 it is possible to obtain a final product with an ultimate tensile strength ab=26, proof stress ay2=24 and elongation measured on a length of 5X the diameter S5=l0%. It is also possible to manufacture aluminium products having a high content of A1203 which can be used in temperatures up to 400 C.

Products of this type have previously been extremely diicult to manufacture and consequently very expensive. A Swiss product is sold under the name SAP-aluminium. Material for gas turbine pistons having great mechanical strength at high temperatures, based on nickel with ThO2 as the dispersion-tempered material seems also possible to manufacture according to this method.

The shape of the extrusion nozzle is important for the quality of the surface of the extruded rod. The nozzle should have a conical entrance part the acute angle of which should be greater than 25 and less than 90 depending on the material of the billet to be extruded. For most materials an acute angle of around 45 is suitable. The Calibrating part of the nozzle below ythe entrance cone should have a certain minimum length if the best result is to be obtained. A length of approximately l mm. has been found suitable and sufficient for materials extruded so far.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in the following with reference to the accompanying drawing which shows schematically a pressure means for carrying out tne method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS- In the drawing 1 designates a high pressure chamber, extrusion chamber, formed by a steel cylinder 2 which is strongly pre-stressed with the help of a surrounding tape or a wire sheath 3, an extrusion nozzle 4 and a piston 5. The piston 5 is connected to a piston l6 in a cylinder 7 with a lid `8 through which the piston 5 passes. The lid 8 is attached to the cylinder 7 by bolts 9. 10 is a yoke which supports the cylinder 7 and absorbs pressure from it during the extrusion. The cylinder rests on a table 11 which is joined to the yoke by means of columns, not shown in the drawing. The nozzle 4 is arranged in a holder 12 sunk into the table 11. Below the extrusion nozzle 4 is a counter-pressure chamber 13 consisting of a tube'14 which is connected to the holder 12 and attached to the table 11 by means of flanges 15 and 'bolts 16. At its lower end the tube is closed by a lid 17 which is easily removed, for example by a bayonet catch, so that the extruded rods can be removed from the counter-pressure chamber 13. The pressure chamber 13 is connected for pressure control by means of the channel 18 to a cylinder 19 with a piston 20 which is in turn connected to a piston 21 in a cylinder 22. The lid 23 is attached to the cylinder 22 by means of bolts 24. In the lid 23 are channels 25 and a valve seat 26 against which a valve body 27 is pressed by the spring -28, the tension of which can be regulated by the screw 29 so that the desired counter-pressure can be obtained in the chamber 13. Through the channel 30 and conduits, not shown, the cylinder 22 is connected to a pressure source so that between pressure operations the plstons 20 and 21 can be moved to approximately the position shown in the drawing. 31 is a billet to be extruded and 32 a rod which has left the pressure nozzle 4 and reached the counter-pressure chamber 13. The cylinder 7 is connected by the

channels

33 and 34 to a pressure source for operating the piston 6, The space is, by means of the channel 41 and the -pipe fittings, not shown in the drawing, in connection with a collecting container for hydraulic Huid, 35, 36, 37, 38 and 39 are seals between construction elements in the hydraulic system.

When carrying out the method with the help of the equipment shown in the drawing, the operation is as follows:

A billet 31 consisting of a powder of one or usually several materials, normally metals, is shaped and surrounded by a yielding, liquid-tight casing. It is then compacted in a pressure chamber by means of a hydrostatic pressure. After compacting, the casing is removed and one end of the billet is shaped to fit the nozzle or die 4. The billet is provided with a new, thin, liquid-tight casing, for example a layer of varnish. The billet is then inserted in the pressure chamber 1 and the punch 5 is pushed by the piston 6 into the cylinder 2 so that pressure is generated in the chamber 1 which, when it reaches a certain value, is able to deform the billet so that it is pressed or extruded through the nozzle 4 and a rod 32 is obtained. This has extremely high density and great accuracy of dimension. In this way very small and uniform shrinkage is obtained during the subsequent sintering and the need for final processing is minimal.

In the example shown the extrusion takes place under counter-pressure. The rod 32 which leaves the nozzle 4 is pressed or extruded into a chamber 13 in which a constant counter-pressure is maintained during the extrusion process. This pressure is maintained by a pressure-regulating means connected to the chamber 13 having a differential piston with the

pistons

20 and 21 and a control valve with a valve body 27 actuated by the spring 2S, which permits liquid to pass out of the cylinder 22 when the pressure has reached a certain predetermined value. When the extrusion process is complete the lid 17 is removed and the extruded billet taken out. The piston is returned to its upper position by supplying liquid to the space below the cylinder 6 in the cylinder 7 through the channel 33. The pistons 20` and 21 are returned to the position shown in the drawing by supplying liquid to the cylinder 22 through the channel 30. A new working cycle can then be commenced.

The invention is not limited to the above-described method. Several variations and modifications are possible within the scope of the following claims.

I claim:

1. Method of producing rods or wire of desired configuration from powder by hydrostatic extrusion, comprising the steps of:

(a) forming a billet from powder;

(b) compacting the billet to great density;

(c) applying a temporary, liquid-tight barrier of nonmetallic, yielding material directly upon the surface of the powder billet, said barrier preventing pressure medium from penetrating into the pores of the billet during hydrostatic extrusion;

(d) inserting the billet in a pressure chamber of an extrusion press, said pressure chamber having a die with an opening to shape a product and containing a pressure medium surrounding the billet;

(e) generating a pressure in said pressure medium sufficient to drive the billet through the die; and thereafter (f) removing the temporary barrier from the extruded billet.

2. Method according to claim 1, in which the temporary barrier consists essentially of a plastic layer with a hardness of at least 60r Shore A.

3. Method according to claim 2, in which the ternporary barrier consists essentially of plasticized PVC (polyvinyl chloride).

4. Method according to claim 1, in which the temporary barrier consists essentially of a plastic layer which is applied by bringing a heated billet into contact with powder or grains of plastic.

5. Method according to claim 1, in which the temporary barrier consists essentially of a plastic layer which is applied by dipping in a melt or in a plastic dissolved in a solvent.

6. Method according to claim 1, in which the ternporary barrier consists essentially of a layer of plastic material which is applied by spraying on a plastic or elastomeric material dissolved in a solvent.

7. Method according to claim 1, in which before the extrusion the billet is compacted to a density which is at least of the density of a solid billet of the same material.

8. Method according to claim 1, in which the ratio R between the cross-section of the billet and the crosssection of the extruded product is greater than 3:1.

9. Method according to claim 1, in which the hydrostatic extrusion takes place underV such high pressure that the deformation provides suicient temperature increase to sinter the powder.

10. Method according to claim 9, in which when extruding a billet of aluminium powder, the ratio is 60: 1.

11. Method according to claim 1, in which a powder consisting essentially of a mixture of substances which are individually plastically deformable, is formed by hydrostatic extrusion into a rod in which the constituents form alloys during subsequent sintering which give the rod material the desired properties.

12. Method according to claim 1, in which a powder of dispersion-tempering products is mixed into the metal powder.

13. Method according to claim l, in which a billet extruded through the nozzle is subjected to a counter-pressure in a chamber connected to the nozzle externally.

References Cited UNITED STATES PATENTS 3,076,916 2/ 1963 Koppius 29-420.5UX 3,344,507 10/1967 Green 29-420.5 3,390,985 7/1968 Croeni et al. 29420.5X 3,407,475 10/ 1968 Koppius L29- 420.5

JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S. Cl. X.R. 72-710