Plastic article or earthenware shaping or treating: apparatus – Preform reshaping or resizing means: or vulcanizing means... – By fluid pressure actuated flexible diaphragm
Patent
1995-01-16
1998-06-23
Davis, Robert
Plastic article or earthenware shaping or treating: apparatus
Preform reshaping or resizing means: or vulcanizing means...
By fluid pressure actuated flexible diaphragm
156285, 156382, 264316, 264571, 4254051, B29C 7044
Patent
active
057702438
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus useful in the production of composite products by the vacuum bagging system and in particular relates to an improved seal therefor.
2. Description of Related Art
Vacuum bagging is the term used to describe a method of producing pressure and vacuum on various resin filled, carbon, glass, synthetic material and metal laminates known as composites while curing and consolidation takes place, usually by means of heating in a pressurised autoclave or oven or hydraulic press. The method may be used in the production of various composite parts useful in the aircraft and motor industries as well as for the production of things such as printed circuit boards for the electronic industry.
EP-A-0175510 describes an apparatus of the type described which comprises a stretchable membrane or vacuum bag held within a rigid framework which is hollow and forms a vacuum manifold supplying vacuum to a seal affixed to the membrane and carried on the framework by one or more passages communicating with a cavity, the resilient seal defined in the cavity within which vacuum can be drawn when the framework and membrane are placed on a mould base. This system has been found to be very effective and the double seal arrangement defining a cavity within which vacuum can be drawn is much more secure than single seal arrangements since the cavity is considerably larger than the cavity adjacent to a single seal and thus a greater clamping effect can be obtained than with any single seal arrangement giving much more security to the vacuum bag.
However, the membrane in the system of the above mentioned European patent publication is subject to maximum stress adjacent to the inner seal and this is the most common point of failure when a vacuum bag apparatus becomes worn. The present invention seeks to provide a sealing arrangement improved in this respect. WO87/05557 discloses an apparatus comprising a stretchable membrane with rigid sections attached to a rigid hold down frame. The frame carries outer and inner sections defining a vacuum cavity and the inner seal is attached to the membrane.
SUMMARY OF THE INVENTION
According to the present invention there is provided an apparatus for forming composite articles which comprises a stretchable or pre-shaped membrane (12) adapted to be placed on a mould and a rigid framework (10) carrying an outer seal (14a), there being an inner seal (18a) attached to the membrane and located between the membrane and the inner side of the rigid framework (10) defining a vacuum cavity (22), the membrane being attached to the seal at the lower-most point thereof characterised in that the seals are substantially square in section and have cut-out sections (36, 40) to enhance resilience, and in that the outer seal has an outwardly directed downwardly extending curtain portion (38) to form an initial loose seal with a mould base.
In the apparatus of the invention the membrane is attached to the bottom of the seal rather than the top as in the above mentioned European patent publication. This ensures that the membrane lies flat against the mould base and the point of stress referred to above is eliminated.
Moreover, where desirable as discussed more fully hereinafter, the seal may be affixed to the membrane only, and not to the vacuum manifold (in contrast to WO87/05557). That is, the outer seal will be fixed to the vacuum manifold but the inner seal need be fixed only to the membrane, and the cavity between them is defined when the two are assembled. This has the advantage that a number of membranes of different pre-shaped sizes may be provided with a single manifold thus allowing stacks of composites of different sizes and configuration to be moulded without requiring a separate seal and manifold assembly for each one, the manifold being constant and only the membrane changing. This reduces both expense and storage problems associated with the membrane and manifold assemblies. The membranes can, of course, be folded and
REFERENCES:
patent: 4216047 (1980-08-01), Hilliard et al.
patent: 4323413 (1982-04-01), Trempe
patent: 4886442 (1989-12-01), McCowin et al.
patent: 5433165 (1995-07-01), McGuiness et al.
Davis Robert
Launchfirm Ltd.
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