GB1015758A - Centrifugal casting - Google Patents

Abstract

Foam plastics material is rotationally cast in a mould by centrifugal force of 10-500G, at least part of the foaming occurring during the action of the centrifugal force. The mould may be positioned eccentrically to give uneven wall thickness. Suitable materials, mixed with blowing agents if necessary, include polythene, polyvinyl chloride, polystyrene, nylon, synthetic and natural rubbers, epoxy resins, phenolic resins and polyurethanes. A hollow cylindrical mould may be rotated vertically, horizontally or in inclined position and the mould may be annular to determine the inner diameter of the article. The foaming ingredients may be introduced into the mould by a spraying nozzle to give a single jet, a multiple jet or a cone spray and may be withdrawn along the axis of the mould at a controlled speed. The mould may be cardboard and may remain in the composite paper/foamed plastic pipe or tube so formed. The cardboard mould is made by helically winding paper ribbons on a rotating mandrel, the ribbons either overlapping or abutting, in the latter case the butts being covered by a further ply of paper of equal width. Up to 20 plies may be superimposed in this manner. The foam preparation is fed into the tube through the mandrel. An external tubular sheath may give initial support to the formed tube. The tubes may be shaped by passing them through annular tubes or dies concentric and rotating with the mould, quasiquadratic, hexagonal and oval shapes being mentioned. Heat may assist the shaping. Polyurethane foams produced by the interaction of organic polyisocyanates with hydroxyl group containing polymers, e.g. polyesters, polyesteramides and polyethers, modified, e.g. by water, to produce blown cellular materials, are preferred.