GB1127761A - Improvements in the production of castings from mouldable materials - Google Patents

Abstract

1,127,761. Moulding concrete or plaster panels. 4D RESEARCH & DEVELOPMENT CO. Ltd. 6 Oct., 1965 [10 July, 1964; 27 Nov., 1964], Nos. 28607/64 and 48350/64. Heading B5A. [Also in Division E1] Concrete or plaster mouldings of an improved surface finish, e.g. large concrete panels, with an exterior smooth, textured or patterned concrete surface and a plaster interior surface, or panels with two smooth plaster surfaces and which may be provided with reinforcement or cored with insulating material such as polystyrene, wood wool or foamed concrete, are produced by casting in a preferably vibrated mould in contact with a membrane 4, e.g. of rubber or plastics, which is extendable and flexible at atmospheric temperatures and which is drawn into the mould form by a vacuum source 7, which vacuum is released after the material has set, and may be replaced by a higher than atmospheric pressure, to facilitate release from the mould. The mould sides are preferably hinged to the base and a panel may be produced by using a pair of open-topped moulds (Figs. 5 to 7, not shown), the bases (1) whereof are pivoted into the vertical closed position and vibrated after each mould has been filled. Additional moulding material may be added between each mould. Hooked lifting rods may be incorporated into the panel. The inner mould surfaces are preferably permeable to air and water, e.g. of wood, and the exterior mould surfaces impermeable, e.g. of varnished wood, and the membrane 4 may vary from completely impermeable to a high degree of permeability, e.g. interconnected cell foamed latex or, with an impermeable mould, the surface of the membrane 4 adjacent the mould may be permeable or roughened to facilitate the application of vacuum. Retarder additives, e.g. sugar solution, may be introduced into the membrane to produce a roughened concrete surface finish upon subsequent brushing. A template may be arranged between the mould base and the membrane 4. The membrane 4 is preferably sealed to the mould base 1 between a pair of air inflated tubes (13) (Fig. 8, not shown) and is retained around a similar pair of tubes by a third inflated tube (15) (Fig. 9, not shown) when used for more than one adjacent mould. The membrane 4 may be allowed to remain on the moulding during the curing period and to effect protection during storage and transport. The membrane employed is preferably extendable from 1000% upwards and capable of being drawn into the mould under negative pressure of 2 to 28 inches of mercury.