Static molds – Including means within surface to confine heat exchange medium – Mold part of particular material
Reexamination Certificate
1999-07-21
2001-07-10
Derrington, James (Department: 1731)
Static molds
Including means within surface to confine heat exchange medium
Mold part of particular material
C249S081000, C249S134000, C264S086000, C264S087000, C264S084000, C264S085000
Reexamination Certificate
active
06257546
ABSTRACT:
This application is a national stage application, according to Chapter II of the Patent Cooperation Treaty. This application claims the priority date of U.K. Patent Application No. 9606447.2 filed on Mar. 27, 1996.
This invention concerns improvements in or relating to slip casting, and particularly but not exclusively a method of slip casting, a mould usable in slip casting, and also a synthetic mould.
In slip casting, slip which comprises a suspension of clay and perhaps other materials in a fluid such as water, is supplied into a permeable mould such that the fluid in the slip is drawn into the mould leaving the suspended solid within the mould to build up a layer of cast solid material. Moulds can be of the open cast type where the layer of solid material is provided around the inner surface of the mould, or of the solid cast type where the solid material fills the interior of the mould. Conventionally the moulds have been made of plaster of paris which draws water thereinto by virtue of capillary forces between the needles of the material, and also by cation exchange. Considerable disadvantages can be encountered with plaster of paris moulds in that they only have a relatively short working life and can cause disposal problems. It is usual to have a “bank” comprising a plurality of moulds all connected to a single source of slip. Inconsistencies often occur between the moulds due to different chemical conditions in the moulds and/or different rates of wear thereby reducing product quality.
According to the present invention there is provided a method of slip casting, the method comprising supplying slip into a sealingly closed mould and applying reduced pressure to the mould so as to draw fluid from the slip into the mould to cause casting.
The mould is preferably connected to a supply of slip during casting. The reduced pressure is preferably applied to the mould prior to the supply of slip thereto.
The reduced pressure may be applied by sucking through the mould. The reduced pressure is preferably applied substantially uniformly throughout the walls of the mould. The reduced pressure may be applied by sucking fluid through a sealed pipe which extends around the mould and connects with a plurality of porous branch pipes spaced throughout the mould.
The mould is preferably heated during casting, and desirably to a temperature in the order of 40° C. The mould may be heated by passing a heated fluid through piping in the walls of the mould.
A plurality of moulds are preferably provided, and the maoulds may be connected to a single supply of slip, heated fluid and/or a single means for sucking fluid, which means may comprise a vacuum pump.
The mould preferably comprises a plurality of parts which are sealingly connectable together prior to casting.
After casting the cast piece is preferably held on a one or more of the mould parts by sucking fluid through only said one or more parts, and desirably also blowing fluid through some or all of the other parts to remove the cast piece therefrom. Following removal from said one or more other parts the cast piece may be located on a former and fluid blown through the said one or more parts to remove the cast piece therefrom.
The mould may be drained of slip prior to removal of the cast piece from the mould.
Following removal of the cast piece from the mould, fluid and desirably air is preferably blown through the mould to purge same.
The slip is preferably supplied into a plastics material mould.
The invention also provides a mould usable in slip casting, the mould comprising a plurality of parts sealingly connectable together to provide a closed permeable mould which is impervious to fluids outside of the mould.
An impermeable coating may be provided on the outside of the mould, and the coating may be formed of wax.
The mould may comprise means for supply reduced pressure within the walls of said mould, and said means may comprise a network of tubing extending within the walls and connectable to a source of reduced pressure.
The network of tubing may comprise a sealed tube extending around the mould with a plurality of porous tubes extending from the sealed tube. The porous tubes may extend between spaced locations on the sealed tube.
The mould preferably comprises heating means, and the heating means preferably extend substantially throughout the walls of the mould.
The heating means may comprise a pipe connectable to a source of heated fluid.
Alternatively, the heating means may comprise a heating element.
The mould preferably comprises an inlet connectable to a supply of slip.
The mould may be made of a plastics material and desirably a water fillable polyester.
The plastics material preferably has the following constitutents, and desirably in the following proportions:
Weight (%)
Acrylic resin
0-10
Polyester resin
0-40
Water containing surfactant
0.1-4
Initiator/Catalyst
1-2
Water
4-40
Acrylic Powder
30-60
The acrylic resin preferably comprises a mix of polymethylmethacrylate in methylmethacrylate monomer. The polyester resin preferably comprises isophalic unsaturated polyester resin. The initiator/catalyst preferably comprises dibenzoyl peroxide. The acrylic powder preferably comprises methacrylate polymer.
The mould is preferably made by mixing the acrylic resin and powder with the polyester resin, subsequently adding the water containing surfactant to form an emulsion, adding the initiator/catalyst and pouring the mixture into a case mould.
Any heating means and/or network of tubing are preferably located in the case mould before the mixture is poured thereinto.
The mould is preferably purged with compressed air prior to use.
The pore size of the mould material is preferably 2-15 microns, and desirably 2-5 microns.
The invention still further provides a synthetic mould according to any of the previous six paragraphs.
The mould may be used in plastic forming of clay or other processes.
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Patent Abstracts of Japan, vol. 015, No. 267 (M-1133), Jul. 8, 1991 & JP 03 090302 A (Tokai Rubber Ind Ltd.), Apr. 16, 1991.
Patent Abstracts of Japan, vol. 014, No. 144; (M-0951), Mar. 19, 1990 & JP 02 009604 A (Katsunobu Ito), Jan. 12, 1990.
Deakin Robert Norman
Watson Andrew
Adams, Schwartz & Evans P.A.
British Ceramic Research Limited
Derrington James
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