Multilayer mould apparatus and method

Plastic article or earthenware shaping or treating: apparatus – Female mold including tamping means or means utilizing mold... – Means to vibrate shaping surface

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249 78, 249 79, B29C 3302

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active

059890088

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



FIELD OF THE INVENTION

The present invention relates to a mould apparatus for moulding materials such as thermoplastics and the like, and a method for moulding. The present invention is applicable to rotational moulding, injection moulding and other moulding processes.


BRIEF DESCRIPTION OF THE INVENTION

Moulding is a process for producing articles usually made of synthetic materials, such as plastics materials. Conventionally, the process uses a mould made out of sheet metal or some metal or alloy which is typically cast, fabricated, electroplated or metal sprayed. The most common form of moulds are cast aluminum and sheet metal. Plastics material granules or powder of thermoformed material are placed in the mould, or alternatively a thermoset plastics material in liquid form may be placed in the mould.
In rotational moulding the mould is rotated biaxially. Whilst rotating, the mould is placed in an oven and heated to approximately 200.degree. C. When the plastics material is coated onto the mould surface and consolidated, the mould is then removed from the oven and cooled, usually by air and water sprays. When the plastics material has solidified in the mould and has cooled enough to maintain its shape, it is removed from the mould. Similarly, moulds produced by other methods are heated and cooled in a similar manner.
However, the above method has several disadvantages. Firstly, the energy required to maintain a temperature of 200.degree. C. in the oven is considerable when compared with the temperature required to, melt the plastics material. Further, typically the mould is of considerable size and therefore much of the energy is absorbed by the mould, with comparatively little being transferred to the plastics material.
Further, forming a mould from sheet metal is typically not possible when the object to be moulded has compound curves.
Further, during the moulding process, small air bubbles may form and be trapped in the moulded material during the melt phase cycle. To remove the air bubbles it is necessary to increase the temperature and extend the time of the heating cycle. This requires more energy and time.
In addressing the disadvantages of conventional moulds, moulding apparatus formed of plastics material have been introduced.
U.S. Pat. No. 5,094,607 describes a mould for moulding thermoplastics material. The mould is constructed of a thermoset plastics material which has a heat distortion point greater than the thermoplastic material and, incorporates heat conductive modifiers in the thermoset plastics material. The heat conductive modifiers act to increase heat transfer when the mould is heated in a heating chamber or conventional oven.
U.S. Pat. No. 4,980,112 discloses a method for rotational moulding using a thermoset plastic mould as described in U.S. Pat. No. 5,0946,07.
The known prior art discloses thermoset plastic moulds which are typically heated by conventional means so that the mould is heated to fuse the thermoplastic material contained therein against an inner surface of the mould. To compensate for heating at lower temperatures and a low rate of heat transfer from the mould to the thermoplastic material heat conductive modifiers have been incorporated within the mould.
The present invention seeks to provide a mould apparatus which alleviates at least some of the problems of the prior art.


SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a mould apparatus for moulding materials characterised in that it includes a first layer of mould material, second layer disposed contiguous to the first layer, the second layer containing heating means such that in use the heating means heats the second layer so as to transfer heat to the first layer.
In accordance with a second aspect of the present invention there is provided a method of manufacturing a moulding apparatus charcterised in that it includes forming a pattern, applying a first layer of mould material to the pattern, applying a second layer contain

REFERENCES:
patent: 2979773 (1961-04-01), Bolstad
patent: 3387333 (1968-06-01), Irvine et al.
patent: 4563145 (1986-01-01), De Meij
patent: 4964943 (1990-10-01), Kruger et al.
patent: 5064597 (1991-11-01), Kim
patent: 5094607 (1992-03-01), Masters
patent: 5176839 (1993-01-01), Kim
patent: 5260014 (1993-11-01), Holton et al.
Patent Abstracts of Japan, vol. 12, No. 1 (M-656), Jan. 6, 1988, and JP62-167014, Jul. 1987.
Abstract of Japanese Application No. 63-84593 of Kouichirou Uezono, JP1-255510, Oct. 1989.
Abstract of Japanese Application No. 63-240360 of Hiroyasu Ogawa, JP2-88204, Mar. 1990.

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