Removable core for the production of tubular structures from fibre reinforced materials

Claim 1

A removable core for use in the production of a tubular structure from a fibre reinforced resin material, said core comprising a body composed of a foam material which softens or collapses under the action of heat sufficient to cure the resin material but is hard and cross-sectionally dimensionally stable under less heat than that, and a plastic tube of heat-shrinkable material surrounding said body of foam material and heat-shrunk thereonto under heat less than that required for curing the resin material so as to closely embrace said body without deforming the same and to constitute therefor a coating which imparts to the core enhanced rigidity, dimensional stability, and a smooth outer surface, said tube being adapted to undergo further shrinkage during the application of heat to a tubular structure build up on said core sufficient to cure the resin material of said tubular structure, thereby to exert on the concomitantly softened foam material of said body compressive forces sufficient to decrease the cross-sectional dimensions of said body and enable removal of the core from said tubular structure.