US3827845A

US3827845A - Presses

Info

Publication number: US3827845A
Application number: US00336077A
Authority: US
Inventors: R Matthews
Original assignee: African Explosives and Chemical Industries Ltd
Current assignee: African Explosives and Chemical Industries Ltd
Priority date: 1972-03-29
Filing date: 1973-02-26
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: AU5256673A; CA962119A; AU458529B2; DE2315029A1; AT323561B; BE797548A; GB1369775A; ZM4273A1; CH566864A5; IT977539B; ZA722167B; FR2178043B1; FR2178043A1

Abstract

This invention relates to press heads and is concerned with such press heads for use in compacting particulate material into self supporting or substantially self supporting articles. The invention is particularly, but not exclusively, concerned with such press heads for use in the manufacture of elements in the explosives industry as detonator charges and time delay elements.

Description

lJnited States Patent [191 Matthews Aug. 6, 1974 [54] PRESSES 2,627,086 2/1953 Hallenbeck 425/346 X 2,667,679 2/1954 Jackman 425/346 [751 Invent Rm Arthur Matthews 3,379,120 4/1968 Fogle 425/346 Johannesburg, South Africa [73] Assignee: AE & CI Limited, Johannesburg,

Transvaal, South Africa Filed: Feb. 26, 1973 Appl. No.: 336,077

Foreign Application Priority Data Mar. 29, 1972 South Africa 72/2167 US. Cl 425/346, 425/344, 425/406, 425/412, 425/443 Int. Cl. B29c 3/00 Field of Search 425/344, 406, 419, 346, 425/412, 443, 53, 100

References Cited UNITED STATES PATENTS 7/1940 Lassman 425/443 X Primary Examiner-R0bert L. Spicer, Jr. Attorney, Agent, or Firm-Cushman, Darby & Cushman [57] ABSTRACT This invention relates to press heads and is concerned with such press heads for use in compacting particulate material into self supporting or substantially self supporting articles. The invention is particularly, but not exclusively, concerned with such press heads for use in the manufacture of elements in the explosives industry as detonator charges and time delay elements.

23 Claims, 7 Drawing Figures 5/ 4 m'nimmm PMENTEB A118 1974 saw 2 BF 2 QMSB QQ PRESSES According to one aspect of the invention there is provided a press head comprising a hollow body member, a plurality of parallel bores in the body and all being connectable to a source of pressure, a plurality of parallel piston members slidable respectively within the .bores, a plurality of plungers associated respectively with the pistons in such a manner that there is a pressure transferring relationship between the pistons and their associated plungers, the plungers projecting from the body so that they may be introduced into dies to compress particulate material therein, there being provided a connection to drain between the ends of each bore and a sealing means to prevent pressure fluid passing beyond the drain connection, the sealing means comprising an impervious hollow member which is sealed to the body and which surrounds the associated plunger at least at the drain connection and a skirt sealed to the piston and extending beyond the hollow inember so that any pressure fluid passing the piston will pass directly into the drain connection and will be prevented by the sealing means from coming into contact with the plunger.

Each plunger may be integral with the piston but preferably the piston and plunger are formed separately and are preferably located in butting relationship. The preferred butting relationship is for the piston to have a conical recess on its underside and for the plunger to have a pointed upper end of smaller cone angle than the recess.

Each plunger may be a one piece element preferably having an enlarged upper portion and a lower portion of smaller cross section but it may be formed in two parts which are preferably in butting relationship. The lower parts in both these arrangements are the parts which are adapted to engage the particulate material.

There is preferably provided a chamber into which all the bores open and which constitutes the drain connection. The skirt on each piston may preferably contact the base of the chamber to limit the movement of the piston. This lower edge is preferably provided with fluid escape openings, preferably by being castellated, to allow any fluid entering the space between the skirt and the impervious. hollow member to escape from this space.

According to another aspect of the invention there is provided a press incorporating a press head as set out above.

According to a further aspect of the invention there is provided an article formed from particulate material compressed in a press as set out above.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings.

In the drawings:

FIG. 1 is an elevation, partially in section, of a press head of the invention.

FIG. 2 is a detail of a modified plunger. FIG. 3 is a diagrammatic representation of a press to which the press head of FIG. 1 is applied, and FIGS. 4a, 4b, 5 and 6 show the operation of compacting the particulate material into dies.

Referring now to FIGS. 1 and 3 there is shown a press head 10 which is bolted to the fixed upper platen 12 of an hydraulic press 14. The lower platen 16 of the press 14 is mounted for movement by an hydraulic ram 18 and normally carries a spoon assembly 20 (see FIGS. 4, 5 and 6) in which dies or sleeves 82 are mounted.

The press head 10 comprises a main body 24 that is formed in three

parts

26, 28 and 30 which are bolted and sealed together. The middle part 28 has a number of parallel bores 32 formed therein. The upper part 26 has an enlarged recess 34 in its lower face. This recess forms a main hydraulic chamber and all the bores 32 communicate with this chamber 34. The lower part 30 has a recess 36 in its upper face. This recess forms a drain chamber and all the bores 32 open into the drain chamber 36. The bores 32 have continuation portions 37 of slightly smaller cross section in the lower part 30 below the drain chamber 36.

Slidably received within each bore 32 is a hollow piston 38 that has a relatively large nominal clearance in the bore 32 which clearance is slightly more than one percent of the bore diameter. The piston 38 has an elongated skirt 40 for the purpose which will be described. The lower edge of the skirt 40 will normally engage the base 43 of the drain chamber 36, when the piston 38 is in its lowermost position and this lower edge of the skirt 40 is castellated at 42. The underside of the piston 38 has formed therein a concentric conical recess 44 which has a fairly large cone angle.

A plunger 46 is associated with each piston 38. Each plunger 46 has an upper portion 48 of larger cross section than its lower portion 50. The two

portions

48 and 50 are connected by a frusto-conical portion 52. The upper portion 48 has a conically pointed end 49 having a smaller cone angle than the recess 44. The lower portions 50 pass respectively through openings 54 in a carrying plate 56 secured to the lower head part 30 and registering openings 58 in a movable stripper plate 60.

The openings 54 each have a greater diameter than the plunger portions 50 that pass through them so that they, the openings 54, provide neither lateral support nor substantial frictional contact with these portions 50. The upper ends of the openings 54 are provided with conical inlets 61 of the same cone angle as the portions 52 and being adapted to act as seats for these portrons.

The openings 58 provide guides for the plunger portions 50. At their upper ends, the openings 58 have conical lead in portions 62 for the plunger ends.

The stripper plate 60 is carried by a number of hollow rods 63 which pass through the carrying plate 56 and are prevented from moving through the plate by flanges 64. The rods 63 are slidable on guide rods 66 and biassed downwardly by compression springs 68.

An oil barrier tube 70 is fitted in fluid tight manner in each bore continuation portion 37. Each oil barrier tube 70 surrounds its associated plunger 46 with clearance and extends up the skirt 40 of the piston 38 to define an elongated passage therewith. Indeed the upper ends of the tube 70 are close to the underside of the piston when the latter is in its lowermost position.

The drain chamber 36 is connected via a conduit 72, which is air vented, to the oil sump.

The main hydraulic chamber 34 is connected to a source of pressure and one side of a cylinder (not shown) arranged in parallel therewith. In the cylinder is a control piston the stroke of which is adjustable. When the pistons 38 are lifted, as will be described, the hydraulic fluid displaced by them moves the control piston upwardly until it is prevented from carrying out further movement. Pressure in the main hydraulic chamber 34 will then build up to the control pressure.

In a modified arrangement shown in FIG. 2, the plunger 46a is formed in two separate parts namely an upper larger diameter part 48a having a conical upper end 49a which is similar to the end 49 and a lower smaller diameter part 50a. The lower end 74 of the part 48a is enlarged and forms a slidable guide in the oil barrier tube 70. This end 74 engages an enlarged head 76 on the lower part 50a. This head 76 prevents the lower part 50a from escaping through the carrying plate 56a. In this arrangement the openings 54a in the carrying plate 560 are plain cylinders.

In use, the spoon assembly 20 which (as shown in FIGS. 4 to 6) comprises a base plate 78, an apertured plate 80 for receiving the element sleeves 82 and the cover plate 84 which rests on the sleeves 82 are placed on the platen 16 with the sleeves 82 in position and with the particulate material in the sleeves 82. Pressure fluid is now supplied to the ram 18 which lifts the platen l6 and the spoon assembly 20 until the cover plate 84 engages the stripper plate 60 and lifts the latter. The lower ends of the plungers 46 now pass through the openings 58 (the lead-ins to which are omitted in FIGS. 4 to 6) in the stripper plate 60 and then through openings in the cover plate 84 until these ends engage the particulate material in the sleeves. The plungers are now lifted until their conical ends 49 engage in the conical recesses 44 on the underside of the pistons (or in the case of the FIG. 2 arrangement, the lower parts 50a engage the upper parts 48a and lift these until their upper ends engage in the recesses on the underside of the pistons). Further upward movement of the ram 18 causes the pistons 38 to be lifted, displacing hydraulic fluid into the main hydraulic chamber 34 and from there to the control cylinder lifting the control piston. When the control piston has come to the end of its strike the pressure in the chamber 34 rises until the pressure applied to the particulate material is such that the material is compressed to the desired amount (see FIG. 4b). Once the due pressure is detected in the hydraulic chamber circuit, the pressure supply to the ram is interrupted to hold the ram stationary for a predetermined period of time after which the pressure supply will be reversed and the ram will be lowered to its starting position and the spoon assembly 20 may be removed and be replaced by a freshly charged spoon assembly.

The press is arranged so that there will be a small clearance 86 when the spoon assembly carries sleeves 82a for the manufacture of the delay elements of the maximum size (as seen in FIG. 4). This means that where smaller elements are being made the clearance will be very substantial as seen in FIG. 5, and consequently the ram will have to make a fairly long movement without doing any useful work. We have found therefore that packings 88 can be provided which will lift the spoon assembly off the platen so that there will be substantially the same clearance between the upper face of the cover plate 84 and stripper plate for all sizes of elements.

We have found that the arrangement above described provides a number of substantial advantages. Because of the large clearance between the pistons 38 and the bores 32 there is minimal friction between the pistons 38 and the bores. The fluid which leaks through between the pistons 30 and the bores finds its way into the drain chamber 36 from whence it passes to the sump. Further in FIG. 1 arrangement the only place where the plunger is subject to frictional force is the openings 58. Thus the plungers will all apply the same pressure on the particulate material so that these are all compressed at the same pressure. In the FIG. 2 arrangement there is a little more friction on the plunger 46a namely at the end 74 of the upper part 48a but this does not have a substantial retarding effect and therefore in this arrangement too the particulate material is compressed to substantially the same degree in all the elements.

Further because of the provision of the oil barrier tube extending up the skirt of the piston, no hydraulic fluid will contact the plunger 46 and therefore the possibility of the hydraulic fluid contacting and contaminating the particulate material is virtually eliminated. Because the lower edges of the skirt 40 are castellated at 42, should only oil tend to move between the skirt 40 and the barrier tube there will be no pressure build up here and the oil will escape through the castellations.

The press head can be used on a conventional press with the minimum of modifications.

The apparatus can be used for compacting any particulate material, for example, in the pharmaceutical industry where it is essential that the material is not contaminated. However its main use is for compacting elements in the explosives industry such as the charge of detonators and time delay elements and for inserting delay elements into detonators. The invention is not limited to the precise constructional details hereinbefore described and illustrated in the drawings.

For example pressure equalising rings can be provided in the peripheries of the skirts of the pistons if desired.

I claim:

1. A press head comprising a hollow body member, a plurality of parallel bores in the body and all being connectable to a source of pressure, a plurality of parallel piston members slidable respectively within the bores, a plurality of plungers associated respectively with the pistons in such a manner that there is a pressure transferring relationship between the pistons and their associated plungers, the plungers projecting from the body so that they may be introduced into dies to compress particulate material therein, there being provided a connection to a drain between the ends of each bore and a sealing means to prevent pressure fluid passing beyond the drain connection, the sealing means comprising an impervious hollow member which is sealed to the body and which surrounds the associated plunger at least at the drain connection and a skirt sealed to the piston and extending beyond the hollow member so that any pressure fluid passing the piston will pass directly into the drain connection and will be prevented by the sealing means from coming into contact with the plunger.

2. A press head as claimed in claim 1 wherein each plunger is integral with the associated piston.

3. A press head as claimed in claim 1 wherein each plunger is separate from the associated piston.

4. A press head as claimed in claim 3 wherein the plunger is in butting connection with the piston.

5. A press head as claimed in claim 4 wherein the piston has a conical recess in its underside and the plunger has a conical end part that is received within the recess and engages in the recess.

6. A press head as claimed in claim 5 wherein the cone angle of the plunger end is less than the cone angle of the recess.

7. A press head as claimed in claim 1 further comprising a guide plate movable relative to the body member, the guide plate havingtherein a plurality of guide bores through which the ends of the plungers remote from the pistons respectively slidably pass.

8. A press head as claimed in claim 7 wherein the guide plate is adapted to engage die means and to be moved thereby relative to the body.

9. A press head as claimed in claim 7 wherein the guide plate is biassed away from the hollow body.

10. A press head as claimed in claim 7, wherein there is a conical lead-in to each guide bore.

11. A press head as claimed in claim 1 wherein each plunger comprises a portion of larger cross section adjacent the piston and a portion of smaller cross section located remote from the piston and adapted to engage and compact the particulate material.

12. A press head as claimed in claim 11 wherein the two portions are integral with one another.

13. A press head as claimed in claim 12 wherein the plunger has a tapered section connecting the two portions.

14. A press head as claimed in claim 13 further comprising means located between the body and the guide plate and having openings therein through which the plungers respectively pass and wherein each opening has a tapering seat which the tapered section of the associated plunger engages to limit movement of the plunger out of its bore.

15. A press head as claimed in claim 11 wherein the plunger sections are separate.

16. A press head as claimed in claim 15 wherein the plunger sections are arranged in butting relationship.

17. A press head as claimed in claim 16 further comprising means located between the body and the guide plate and having openings therein through which the smaller cross section portions of the plungers respectively pass and wherein the smaller cross section portion of each plunger has a projection to engage the said means to prevent the smaller cross section portion of the plunger passing through the said means.

18. A press head as claimed in claim 17 wherein the projection is a head of larger section than the associated opening.

19. A press head as claimed in claim 1 wherein the bores open into a chamber which is connectable via a conduit to a sump and which constitutes the drain connection.

20. A press head as claimed in claim 19 wherein the skirt on each piston is able to contact the base of the chamber to limit the movement of the piston.

21. A press head as claimed in claim 20 further comprising fluid escape openings in the edge of the skirt to enable fluid entering under the skirt to escape therefrom.

22. A press head as claimed in claim 1 wherein the hollow body member has a main hydraulic chamber into which all the bores open and which is connectable to a source of pressure fluid.

23. A press head as claimed in claim 22 wherein the main hydraulic chamber is connected to a cylinder containing a piston movement of which piston is limited to control the amount of movement of the pistons in the bores of the main body member.

Claims

7. A press head as claimed in claim 1 further comprising a guide plate movable relative to the body member, the guide plate having therein a plurality of guide bores through which the ends of the plungers remote from the pistons respectively slidably pass.