GB781925A - Improvements in or relating to methods of making hollow bodies from fibrous materialand heat-hardenable resin - Google Patents

Abstract

781,925. Moulding hollow fibre-resin articles. BRISTOL AIRCRAFT, Ltd. Sept. 9, 1955 [Sept. 23, 1954], No. 27577/54. Class 87(2). A method of making a tubular body comprises (i) covering a former with an impervious membrane, (ii) placing on the membrane a coating of fibrous material impregnated with thermosetting resin, (iii) placing the coated former in a mould and sealing the membrane to the mould so as to enclose a space between it and the mould containing the resin-impregnated fibrous material, (iv) evacuating the space so as to lift the material from the former and apply it to the internal mould surface, (v) placing the coated mould in a closed vessel, (vi) increasing the presence and temperature in the vessel to cure the resin while maintaining evacuation of the space between the membrane and the mould (vii) removing the mould from the vessel and removing the moulded article from the mould. The fibre is preferably asbestos felt and the resin a water soluble phenol-formaldehyde resin. Since it takes longer to place the coating on the former than it does to cure the resin two or more formers may be used with each mould. The mould and former may be recessed to receive extra layers of material for local thickening. The internal surface of the twopart mould 14, 15, Fig. 5, is shaped to give steps in the wall of the moulded article, Fig. 6, and is recessed at 22, Fig. 4, to thicken the wall where fittings are to pass through, and has a block 78 to form a recess in the face of the moulded article. The mould halves are flanged and the flanges have outer grooves 27 for rubber sealing strips and inner grooves 23, stopping short of the ends, connected through holes 26 with piping 25 which may be connected to a vacuum pump. The flanges 16 of one mould half have tapped holes 30 for screws which bear on the flanges of the other mould half, to assist in opening the mould. The former comprises three sheet metal sections 35, Fig. 3, with bentin edges, each section subtending an angle rather less than 120‹, which are bolted through interposed glass fibre and resin L-sectioned stiffeners 39, to end discs 36. Gaps 43 between the sections enable the former to be contracted when the discs 36 are removed or the sections moved inwards are allowed by slots in the discs. Steps are formed inside the moulding by glass fibre and resin rings 35 placed as shown in Fig. 6. The former has trunnions and can be rotated in a suitable support for convenience in applying fibrous-resin coating. The membrane is conveniently an open-ended tubular polyvinyl chloride bag 54, Fig. 6, into which the former is slipped and on which the layers of resinimpregnated asbestos felt are laid, slightly overlapping and tacked to one another by local heating so they do not fall off as the former is rotated. After coating the inside of the mould with a release agent, e.g. zinc stearate or silicone, pre-cut felt 57 is placed in