Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/26—Producing shaped prefabricated articles from the material by slip-casting, i.e. by casting a suspension or dispersion of the material in a liquid-absorbent or porous mould, the liquid being allowed to soak into or pass through the walls of the mould; Moulds therefor ; specially for manufacturing articles starting from a ceramic slip; Moulds therefor
  • B28B1/261—Moulds therefor
  • B28B1/262—Mould materials; Manufacture of moulds or parts thereof
  • B28B1/263—Plastics
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B7/00—Moulds; Cores; Mandrels
  • B28B7/34—Moulds, cores, or mandrels of special material, e.g. destructible materials
  • B28B7/346—Manufacture of moulds

Definitions

• This invention concerns improvements in or relating to a method of making moulds, and particularly but not exclusively moulds for use in the ceramic industry, and especially 'case moulds' .
• a "block” mould is produced in one or more parts by casting plaster of Paris against a model of the required shape.
• a "case” mould is then produced by casting either hard plaster, silicone rubber or epoxy resin against each of the block mould parts. Resin and silicone case moulds are generally more durable. They are, however more expensive to produce. (It is usual practice also to produce master block and case moulds at this stage).
• "Working" moulds are in turn cast against the case moulds and it is from these working moulds that the required shapes are produced by slip casting or plastic making.
• the working moulds are usually fabricated from plaster of Paris although some porous plastic alternatives have been developed for roller making and casting at elevated pressure.
• thermo-forming a case mould of the type hereinbefore described comprising heating a piece of thermo plastics material sheet to a softening point, placing said piece on a suitably shaped former and forming said piece to a required shape by thermo-forming.
• the piece is preferably shaped by differential pressure thermo-forming, and desirably by vacuum forming.
• the former is preferably a block mould of the type hereinbefore described.
• the former may approximate the required case mould profile.
• the thermo-formed sheet may subsequently be machined to give an acceptable working profile.
• thermoplastics material may be any of those conventionally used in thermo-forming methods, including acrylic plastic, ABS, polystyrene, PVC, polyolefins e.g. polypropylene, high density polyethylene.
• a backing material may be attached to an innerside of the shaped piece.
• the backing material may comprise any of a polymer concrete, hydraulic concrete or plaster of Paris.
• the polymer concrete may be made from sand or a light weight filler such as Fillite, bonded with an epoxy or polyester based resin. Glass fibre filler may be added to the polymer to further increase strength and toughness.
• thermoplastics material is preferably heated to its Vicat softening point.
• the present invention also provides a method of making a mould for producing ceramic articles, the method comprising forming a case mould by a method according to any of the preceding seven paragraphs, and casting a curable material against said case mould to produce a working mould against which a clay article may be cast.
• the block mould is preferably formed by casting a curable material against a slightly over sized model of the required shape
• the curable material is desirably plaster of Paris or a porous plastic body.
• a double cup handle shape case mould was formed using a plaster of Paris block mould with dimensions of approximately 160 x 100 mm.
• the permeability of the plaster was measured as 3.8 x 10 ⁇ 3 cm2/s per cm of water pressure.
• a 2 mm thick sheet of polypropylene was heated to between 140 and 160°C to its Vicat softening point, placed on the block mould, and formed into the required shape by producing a vacuum of 40-60 mbar on the opposite side of the block mould to the plastic sheet.
• the entire operation was completed in under 12 minutes, with 7 minutes heating time, 2 minutes forming time, and 2-3 minutes cooling time.
• the reproduction of surface features was at least as good as usually achieved using traditional techniques.
• the conventional plaster block mould used as the forming tool allows the air to escape from between the thermoplastics sheet and the tool during forming.
• the backing material comprises a polymer concrete of polyester based resin with a light weight filler such as Fillite and up to 2 percent chopped glass fibre as an additional filler to provide strength and toughness.
• This method of case mould manufacture has a number of advantages over the traditional method. For example there is a reduced labour requirement and no extra tooling is necessary. The process time involved is greatly reduced, as opposed to the time for the traditional method which in some cases can be 5-7 days. Cheaper raw materials are generally used. This simplified case mould production method allows new shapes to be developed more readily. There is a reduction in the toxic hazard present when silicone rubber or epoxy resin are used. Natural release of working moulds from the case mould will generally be obtained alleviating the need for release agents. There is no requirement for any finishing operations on the case moulds once formed. The case moulds formed in this manner may be used to make either plaster of Paris or synthetic plastic working moulds.
• thermoplastics materials such as acrylic plastic, ABS, polystyrene, PVC, or polyolefins e.g. high density polyethylene.
• a different backing material could be provided which may comprise a polyester based resin and sand could be used as a filler. Alternatively hydraulic concrete or plaster of Paris could be used as a backing material. In certain cases a backing layer may not be required.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Dispersion Chemistry (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

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Family Applications (1)

Country Status (2)

Cited By (2)

Citations (5)

• 1991
  • 1991-02-12 GB GB919102954A patent/GB9102954D0/en active Pending
• 1992
  • 1992-02-07 EP EP92301055A patent/EP0499420A1/de not_active Withdrawn

Patent Citations (5)

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