GB2372958A

GB2372958A - Mould assemblies

Info

Publication number: GB2372958A
Application number: GB0105458A
Authority: GB
Inventors: John Barrie Turner
Original assignee: Ceram Research Ltd
Current assignee: Ceram Research Ltd
Priority date: 2001-03-06
Filing date: 2001-03-06
Publication date: 2002-09-11
Anticipated expiration: 2021-03-06
Also published as: GB0105458D0; GB2372958B

Abstract

A slip casting mould assembly 10, comprising an inner lining 12 defining a moulding cavity 14. The inner lining 12 is mounted in an impermeable outer lining 16 with a fluid connecting arrangement between the inner and outer linings 12, 16. The fluid connecting arrangement comprising pipework 22 leading to an annular chamber 24, to allow pressurised slip to be supplied to the outside of the inner lining 12. The pipework also leads to a chamber 26. The inner lining 12 may be made aluminium expoxy resin composite and the outer lining 16 may be made of aluminium. The mould may be a three part mould (figures 3/4 - not shown). A mould assembly usable with solid cast-type moulding, where the solid material fills the interior of the mould, may be provided (figure 5).

Description

Mould Assemblies This invention concerns improvements in or relating to mould assemblies usable in forming shaped ceramic items, and particularly but not exclusively such assemblies usable in one of pressure slip casting or plastic pressing.

In pressure slip casting, slip which comprises a suspension of clay and perhaps other materials in a liquid which is generally water, is applied under pressure into a permeable mould such that the liquid in the slip is urged into the mould leaving the suspended solid within the mould to build up a layer of cast solid material. Conventionally the moulds used in this process have been made by moulding a porous plastic, but this material can distort under pressure and seam quality can be unsatisfactory. Other materials have been proposed for use as moulds, but difficulties are often encountered with other materials in obtaining good quality moulding and/or subsequent release from the moulds.

In plastic pressing soft clay is pressed between two profiled permeable moulds, which are conventionally formed of special plaster. This material however tends to only have a relatively short working life and can cause disposal problems. During pressing a significant amount of water comes out of the soft clay.

According to the present invention there is provided a mould assembly usable in forming shaped ceramic items, the assembly comprising a permeable inner lining defining a moulding cavity, a substantially impermeable outer lining surrounding the inner lining, and a fluid connecting arrangement comprising pipework leading into the assembly through the outer lining to one or more chambers in communication with an outer surface of the inner lining.

The chamber or chambers are preferably in communication with a significant proportion of the outer surface of the inner lining, and may be in communication with greater than 50% of said surface, and desirably within the order of at least 75% of said surface.

Means for urging fluid into the fluid connecting arrangement to provide mould release, may be provided. The inner lining is preferably made of a machinable material. The inner lining may be made of a metal resin composite, which may comprise a powdered metal which may be aluminium, and may also comprise an epoxy resin.

Alternatively, the lining may comprise a sintered material and desirably a sintered metal.

The inner lining is preferably less than 50 mm thick, and desirably less than 25 mm thick. The inner lining may be made of a number of parts. The outer lining may be made of a number of parts.

The chamber or chambers are preferably relatively shallow, and may have a depth of around 15% of the thickness of the inner lining. The chamber or chambers preferably have a depth of less than 5mm, and desirably less than 3mm.

The mould assembly may be usable in pressure slip casting.

The mould assembly may be usable in plastic pressing.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which : Fig. 1 is a diagrammatic cross sectional side view through a first mould assembly according to the invention; Fig. 2 is a diagrammatic plan view of the assembly of Fig. 1; Figs. 3 and 4 are similar views respectively to Figs. 1 and 2 of a second assembly according to the invention; and Fig. 5 is a similar view to Fig. 1 of a third assembly according to the invention.

Figs. 1 and 2 show a first mould assembly 10 comprising an inner lining 12 defining a moulding cavity 14. The inner lining 12 is made of a permeable aluminium epoxy resin composite which can be machined to a required profile.

The inner lining 12 is mounted in an impermeable aluminium outer lining 16 comprising an annular member 18 and a base plate 20. A fluid connecting arrangement is provided comprising pipework 22 leading from outside of the assembly 10 to an annular chamber 24 formed as a recess in the annular member 18, and a circular chamber 26 formed by a recess in the base plate 20, both chambers 24,26 abutting the outside of the lining 12. Two pipes 28 extend into opposite sides of the annular chamber 24, whilst a single pipe 30 extends downwardly and laterally from the cylindrical chamber 26.

In use the assembly 10 would be pressed against a closure member or against similar such assemblies in a bank of moulds, and slip would be supplied under pressure into the moulding cavity 14. Liquid from the slip would be forced into the inner lining 12 and into the chambers 24,26. At the same time solid material would be formed on the inside of the inner lining 12.

Once moulding had been completed, pressure would be released from the slip and excess slip would be drained from the cavity 14. Compressed air would then be introduced into the mould cavity 14 to force out excess water from the cast piece and firming up the cast piece. The air pressure would then be released from the cavity 14. Air would then be blown through the pipes 28,30 causing release of the moulded piece from the moulding surface of the inner lining 12. The liquid in the inner lining 12 and also the chambers 24,26 means that the moulded piece is actually floated off the inner lining 12 rather than blown off.

This arrangement has been found to provide good moulding with ready release of moulded pieces. Without the chambers around the inner lining one or both of these features would almost certainly not be present.

Figs. 3 and 4 show a similar assembly 32 but which is provided with a three-part mould. This comprises two half annular pieces 34 and a base part 36. An almost half annular chamber 38 is provided in each of the pieces 34, with the chamber 38 extending close to the edge of the pieces 34. Otherwise the assembly 32 is the same as the assembly 10. This assembly can be used in a similar manner to the assembly 10 but obviously requires an appropriate arrangement to clamp the mould pieces 34,36 together.

Fig. 5 shows a further assembly 40 which is similar to the assembly 32 except that the assembly 40 is usable with solid cast-type moulding, where the solid material fills the interior of the mould. Accordingly an internal mould piece 42 is provided which has a similar aluminium epoxy resin lining 44 provided with an internal annular chamber 46 and a shallow cylindrical chamber 48 at its lowermost part connected via pipework 50 through an aluminium body 52.

There is thus described pressure slip casting moulding assemblies of relatively simple construction but which permit materials to be used for the mould lining which otherwise would not operate satisfactorily. Materials as described can be machined and can thus readily be produced in required and if necessary complex shapes.

In the described examples an inner lining thickness of around 12 to 20 mm has generally been found to be optimum. It is important for a significant portion of the outside of the inner lining to locate against a chamber. Results achieved with mould assemblies as described above have been very good and in many instances it has not been necessary to carry out fettling (removal of mould lines) due to the quality of moulded pieces obtained. In general it is appropriate for the chambers to be relatively shallow, and in the above examples a depth of around 2mm has been used.

Whilst the above examples relate to pressure casting, the invention is also applicable to plastic pressing. A generally similar arrangement is provided with soft clay being pressed into shape in the mould cavity defined between two mould parts. After pressing the shaped piece is held on one part of the mould by reduced pressure and blown off the other part, with floating off occurring as a result of the chamber or chambers, as described above. The shaped piece is subsequently blown off said one piece in a similar manner, onto a carrier.

Various other modifications may be made without departing from the scope of the invention. For instance, the mould may take a different form, may have a different shape and/or number of components. Different materials may be used for the inner or outer lining of the mould. For example, other machinable materials such as sintered metal may be usable.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS 1. A mould assembly usable in forming shaped ceramic items, the assembly comprising a permeable inner lining defining a moulding cavity, a substantially impermeable outer lining surrounding the inner lining, and a fluid connecting arrangement comprising pipework leading into the assembly through the outer lining to one or more chambers in communication with an outer surface of the inner lining.
2. A mould assembly according to claim 1, in which the chamber or chambers are in communication with a significant proportion of the outer surface of the inner lining.
3. A mould assembly according to claim 2, in which the chamber or chambers are in communication with greater than 50% of said surface.
4. A mould according to claim 3, in which the chamber or chambers are in communication with at least 75% of said surface.
5. A mould assembly according to any of the preceding claims, in which means for urging fluid into the fluid connecting arrangement to provide mould release are provided.
6. A mould assembly according to any of the preceding claims, in which the inner lining is made of a machinable material.
7. A mould assembly according to claim 6, in which the inner lining is made of a metal resin composite.
8. A mould assembly according to claim 7, in which the metal resin composite comprises a powdered metal.
9. A mould assembly according to claim 8, in which the powdered metal is aluminium.
10. A mould assembly according to any of claims 7 to 9, in which the metal resin composite comprises an epoxy resin.
11. A mould assembly according to claim 6, in which the lining comprises a sintered material.
12. A mould assembly according to claim 11, in which the sintered material is a sintered metal.
13. A mould assembly according to any of the preceding claims, in which the inner lining is less than 50 mm thick.
14. A mould assembly according to claim 13, in which the inner lining is less than 25 mm thick.
15. A mould assembly according to any of the preceding claims, in which the inner lining is made of a number of parts.
16. A mould assembly according to any of the preceding claims, in which the outer lining is wade of a number of parts.
17. A mould assembly according to any of the preceding claims, in which the chamber or chambers are relatively shallow.
18. A mould assembly according to claim 17, in which the chamber or chambers have a depth of around 15% of the thickness of the inner lining.
19. A mould assembly according to claims 17 or 18, in which the chamber or chambers have a depth of less than 5mm.
20. A mould assembly according to claim 19, in which the chamber or chambers have a depth of less than 3mm.
21. A mould assembly according to any of the preceding claims, in which the mould assembly is usable in pressure slip casting.
22. A mould assembly according to any of the preceding claims, in which the mould assembly is usable in plastic pressing.
23. A mould assembly substantially as hereinbefore described and with reference to Figs. 3 and 4 of the accompanying drawings.
24. A mould assembly substantially as hereinbefore described and with reference to Figs. 1 and 2 of the accompanying drawings.
25. A mould assembly substantially as hereinbefore described and with reference to Fig. 5 of the accompanying drawings.
26. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.