US3082477A

US3082477A - Plunger dies

Info

Publication number: US3082477A
Application number: US67730A
Authority: US
Inventors: Jan F H Custers; Henry B Dyer; Bernard W Senior; Peter T Wedepohl
Original assignee: Adamant Laboratories Pty Ltd
Current assignee: Adamant Laboratories Pty Ltd
Priority date: 1959-11-10
Filing date: 1960-11-07
Publication date: 1963-03-26
Anticipated expiration: 1980-03-26
Also published as: SE300810B; CH372286A; GB924840A; BE596902A; NL124995C

Description

March 26 1963 J. F. H. cusTl-:Rs ETAL 3,082,477

PLUNGER DIES Filed NOV. '7, 1960 3,982,477 PLUNGER BEES .lan F. H. Custers, Henry E. Dyer, Bernard W. Senior, and Peter T. Wedepohl, all ci .Iohannesburg Transvaal, Republic of South Africa, assignors to Adamant Laberatories (Proprietary) Limited, .lohannesburg Transvaal, Repubiic ci South Africa Filed Nov. 7, 1960, Ser. No. 67,73@ Claims priority', appiication Republic of South Africa Nov. it?, i959 Claims. (Cl. .iS-16.5)

This invention relates to the production of a die capable of exerting pressures on material enclosed within its pressure chamber of the order of say 50,000 atmospheres and above. While 4it is not excluded that the die be used to compress the material in the cold, the purpose for which the die of the invention has been evolved is to compress the charge and heat it to elevated temperature simultaneously, so that the object of the invention is also to provide a die which can successfully be applied to this end.

The production of dies which are capable of imposing on the material charged into them high pressures of the order of 50,000 .atmospheres and above presents no great technical difficulties. Indeed, in laboratory equipment dies have been made in which pressures -above 70,000 atmospheres have been achieved. Similarly, there is no diiiiculty in bringing material to elevated temperature, say up to 1800 C. and this can readily be achieved while the material is kept under moderate pressure. Where, however, grave difficulties do arise is when material is to be heated to temperatures of this order and simultaneously maintained under high pressure of the order of say 70,000 atmospheres.

The kind of die to which the invention relates is that in which a plunger is caused to enter the chamber to compress the charge against an anvi-l which is rigid or is a second plunger.

The limitation of this kind of die is the compressive strength of the plunger itself since the opposed axial forces upon it tend to spread it laterally, or in the case of a brittle hard metal plunger, to cause plunger breakage. According to the inventoon, the die has a body deiining a pressure chamber, at least one plunger movable to enter the chamber to compress a charge within it, and supporting means for that part of the plunger protruding from the die consisting in a collar surrounding that protruding part, located to be compressed between the body of the die and the platen of the press containing the die, and make of a material that undergoes plastic deformation at the pressure to be applied to the die. The material is characterized by having mechanical strength properties such that it is capable of exerting a sustained inward quasi-hydrostatic pressure on the plunger periphery of the order of thousands of atmospheres.

If the material be a metal it is desirable that its yield shear strength be of the order of l() kilogrammes per square millimetre or greater; that its percentage elongation at tensile failure be of the order of 10% or more; and that it be characterized by the ability to increase its yield shear strength by work-hardening as plastic deformation proceeds.

If the material be non-metallic it is desirable that it have a high internal friction and low yield shear strength, so that it may resist the tendency to extrude readily when compressed and so relieve the inward quasi-hydrostatic pressure generated.

It is not necessary that these mechanical properties of the collar material obtain at room temperature for the collar may be heated to a temperature within a limited ata. i

3,032,477, Patented Mar. 26, i953 temperature range where the desired mechanical properties obtain. f

The shape of the plunger may vary widely. It is desirable .although not essential that the outer face of the plunger in contact with the anvil be of greater area than the inner face in contact with the charge, so tha-t the unit applied stress on the upper face is less than that developed in the lower face.

The radial inward support pressure may or may not be uniform over the peripheral surface of the plunger. It is desirable that this support pressure be relatively high where the plunger enters the pressure chamber.

If part of the plunger encased in the collar have a cross-sectional area which increases toward the outer face, it may be, depending upon the rate of increase` of area with distance from the inner face of the plunger, that the supporting stress, due to the collar, on the periphery of the plunger at or near the inner plunger face may be insufficiently enhanced as the plunger is forced through the coliar to enter the pressure chamber, because of the wedging action of lthe tapered plunger building up a maximum stress at or near the outer collar face which is transmited via lateral shear stresses to the inner collar face.

Where this effect is undesirable due to plunger configuration the collar may be so designed as to include a body of material of low yield shear and low compressive strength which while reducing the iniluance of the lateral shear stresses due to wedging described above, acts as a pressure transmitting medium.

Two embodiments of dies according to the invention Y are illustrated .as FIGURES l and 2, in the accompanying drawings, both views being sections. FIGURE 3 is a sectional view of a suitable heating means.

yIn FIGURE 1 is shown a die in which the inclusion of :a body of material of low shear strength with the collar is desirable. In this figure the `body 10 of the die is a ring deining a pressure chamber 12. The faces of the ring are dished at 14. The ring 10 may be made of a refractory metal-bonded carbide characterized by a very high tensile strength and .a high compressive strength. As an example the material of the ring may be a medium grained tungsten carbide bonded with about 10% of cobalt.

The ring 10 as shown is supported by three high

tensile steel rings

16, 18, and 20 which have been shrunk or force-tted together.

Two plungers 22 have noses 24 that enter the chamber 12. The parts 26 protruding from the chamber are of greater diameter than the noses.

Surrounding the parts 26 are collars 28 of steel, which may be stainless steel, which have annular grooves 30 that are open to the peripheral surfaces of the plungers. Each groove 30 is iilled with la material 32 having low shear strength and negligible compressibility, such as lead. The inner faces 34 of the collars adjacent to the ring are formed to complement or nearly to complement the dishing of the ring 10.

In use, the pressure chamber 12. is lled with charge material and the charge die is placed between anvils 36 atached to the platens of -a press.

The outer faces 38 of the plungers 22 must be exactly complementary to the inner faces 40 of the anvils 36; this avoids high local stresses where the area of contact is less than the total `area ot plunger face 38. To achieve this axact complementary condition a thin layer of metal may be introduced between the faces 38 `and the anvil face fill.

As load is applied the plunger is forced to enter the pressure chamber and the collars, being confined between the anvils and :the die ring are compressed and eventually plastically deformed. A compressive stress is induced in the filling 32 which is transmitted as a quasi-hydrostatic pressure to the peripheral surfaces 26 of the plungers protruding from the die faces.,

The part of each plunger that enters the pressure chamber 12 is obviously :smaller in diameter than the diameter of the chamber, to permit its inward movement. There are therefore annular extrusion gaps 62 through which the material being compressed 4may escape. 'The width of each gap is Vso regulated that the internal friction of the material l eing compressed, together with the pressure developed in the filling 32 is sufficient to prevent appreciable extrusion and consequent loss of pressure. The sealing of the gaps can more eiiciently be realized by inserting into the pressure chamber 12 a body 44 of material, such as pyrophyllite, having high internal friction and deformable at the pressures involved.

The material of thebody 44 will extr'ude only to a lmited extent into the annular gaps, being restrained by its own internal friction and the pressure within the lead. The plungers may be so designed -as to taper toward their inner face. By this means the areas of -the annular gaps are reduced as Vthe plunger-s move inwardly into the pressure chamber and higher internal pressures are generated.

The body 44 has a central cavity 46 that accommodates the charge.

In FIGURE 2, the die ring l is the same .as in FIG- URE l, and is supported, again as in FIGURE l, by hightensi-le steel rings 1j6, 18 and 20. The plungers 48 are bosses that may ormay not be inter-gral with, and project from, anvils 50' that are supported by high-tensile rings 52.

The faces 54 .of the anvils flanking the plungers 48 are conical tor conoidal to Vconform with or nearly to conform with the dishing of the ring 10. Between the faces 54 and the ring 10= and sunrounding the protruding portion 56 of each plunger, is a dished collarV SS of steel; for instance a medium alloy die steel `in the softened condition giving an ultimate 4tensile strength of 55 tons in 2 and an elongation ofY 20%V may be used. There may be linings 60 of materials, such as lead, *between the collars 58 and the plunger-s 56.

The collars, being confined between the anvils and the die ring, are compressed and' eventually plastically deformed. Friction between the collars and the faces of the anvils and the die ring resists the tendency to spread and there is set up an inwardly directed quasi-hydrostatic force, which is applied to the protruding parts 56 of the plungers and constitutes a radial support thatrincreases substantially the pressure which the plungers will withstand across their lateral faces.

'Friction between the collars and the anvils and the die ring may be increased by coating the contact surfaces with jewellers rouge or another similar high friction material.

As in the case illust-rated in FIGURE l there is an annular gap l62 -between the peripheral surface of the entrant plunger and the pressure chamber wall. Extrusion of the material being compressed is restrained by friction and the sealing effect of the collars. The width of'each gap 62 is so arranged that extrusion is contained within -acceptable'limits As in the previous case, the seal-ing of the gaps can more eiciently be realized by inserting into the pressure chamber 12V a hollow -body 64 of materia-l, such as pyrophyllite having high internal lfriction and deformable at the pressures involved. The plungers may be so ydesigned as to taper toward their inner faces. By this means lthe area ofthe annular gaps 62 `are reduced as the plungers move inwardly into the pressure chamber and higher internal pressures are generated.

'I'he body 'has a central cavity 66 that accommodates the charge.

The charge may be electrically heated while it is under pressure by, -for instance, lining the cavity ofthe body 64 with a conductive tube 70 that is insulated electrically from the charge by an inner tube 68. Current is fed to the tube along a path comprising a

plunger

22 or 48, a conductive pad 72, also insulated electrically from the charge by a `disc 74, a second conductive pad 76 insulated electrically from the charge by a disc 77, and the second plunger or a rigid anvil `if only one plunger is being used.

Alternatively, the heating element may be a conductive rod, or Wire, embedded in the charge and electrically insulated from it. The conducting rod or wire may be of graphite. However, the charge itself, if an electrical conductor, may be used as a heating element.

In order to insulate the plungers from the body 10 of the die, an insulating layer, such as an annular ring 78 of mica, is interposed between the inner face of at least one collar and the appropriate die ring face. 'It is useful to coat the mica with a high friction material such as jewellers rouge.

Using thedie of the invention pressures of at least the order vof 70,000 atmospheres may be generated within the pressure chamber.

We claim:

1. In combination, a press and a die, between the platens of the press, having a body defining a pressure chamber, the body being dished on opposite faces, two opposed plungers movable to enter the pressure chamber rto compress a charge within it between them and supporting means for that part ofreach plunger that protrudes from the body, cach of such supporting means consisting in a collar surrounding lthat protruding part and substantially complemental to the dishing of the body, located to `be compressed between the body and a platen and made of a material that undergoes plastic deformation at the pressure to be applied to the die as well as being capable of exerting a sustained inward quasi-hydrostatic pressure on the plunger periphery 2. VThe subject matter of claim 1 in which the part of the plunger that enters the pressure chamber is diametrally less `than the protruding part.

3. The subject matter of claim 1 in which the collar is metallic. Y

4. T he subject matter of claim 3 in which the collar is of high-tensile steel.

V5. The subject matter of claim 1 in which each collar has an annular groove directed towards the plunger and in which the groove is iilled with a soiid'material having low shear strength and insignificant compressibility.

6. The subject matter of claim 5 in which the filler material is lead.

7. The subject matter of claim 1 in which the radially inner part of the collar is of low shear strength and insignificant compressibility.

8. The subject matter of claim 7 in which the radially inner part of the collar is of lead.

9. The subject matter of claim l including body of material within the pressure chamber hollowed to receive charge material and characterized by high internal frictional and the ability toundergo plastic deformation at the pressure to be applied to the die.

10. The subject matter of claim l in which the nose of each plunger is substantially cylindrical.

References Cited in the tile of this patent UNITED STATES PATENTS 2,554,499 Poulter c May 29, 19,51 2,938,998 Wilson May 31, 1960 2,941,241 Strong June 21, 1960 2,941,243 Bundy lune 2l, 1960 2,941,244 Wentorf lune 21, 1960 2,941,246 Bundy lune 21, i196() 2,941,252 Bovenkerk .Tune 2l, 1960 2,947,034 li/'eutorfY Aug. 2, 1960 '2,947,609 Strong Aug. 2, 1960

Claims

1. IN COMBINATION, A PRESS AND A DIE, BETWEEN THE PLATENS OF THE PRESS, HAVING A BODY DEFINING A PRESSURE CHAMBER, THE BODY BEING DISHED ON OPPOSITE FACES, TWO OPPOSED PLUNGERS MOVABLE TO ENTER THE PRESSURE CHAMBER TO COMPRESS A CHARGE WITHIN IT BETWEEN THEM AND SUPPORTING MEANS FOR THAT PART OF EACH PLUNGER THAT PROTRUDES FROM THE BODY, EACH OF SUCH SUPPORTING MEANS CONSISTING IN A COLLAR SURROUNDING THAT PROTRUDING PART AND SUBSTANTIALLY COMPLEMENTAL TO THE DISHING OF THE BODY, LOCATED TO BE COMPRESSED BETWEEN THE BODY AND A PLATEN AND MADE OF A MATERIAL THAT UNDERGOES PLASTIC DEFORMATION AT THE PRESSURE TO BE APPLIED TO THE DIE AS WELL AS BEING CAPABLE OF EXERTING A SUSTAINED INWARD QUASI-HYDROSTATIC PRESSURE ON THE PLUNGER PERIPHERY.