Method for making fiber reinforced plastic tubing

Abstract

Fiber reinforced plastic tubing is formed by an innermost layer of braided strands that include longitudinal stud fill strands within the braid, a second layer of longitudinal strands, and a third layer of braided strands, all thoroughly encased in a monolithic mass of plastic matrix material that is not, itself, divided into layers. The tube is fabricated on a continuous basis by winding two sets of strands in opposite directions on a mandrel and braiding the two sets with each other and with stud fill strands that prevent that first layer of braid from stretching longitudinally and thereby tightening immovably on the mandrel. The strands are braided dry but are wetted with liquid plastic matrix material as the braid is compacted on the mandrel. A fourth set of strands is wetted by liquid plastic matrix material and guided to lie longitudinally along and evenly spaced about the wetted first braid, and fifth and sixth set of strands are braided dry around the fourth set and compacted and wetted to press against the fourth set and to press the fourth set against the first setted braid. No curing is done until after the latter compacting and wetting. The multi-layer tubing is pulled along the mandrel by alternately-operating gripping devices in which a soft tube sealed into a rigid shell is expanded inwardly by fluid pressure between the shell and the soft tube, thereby forcing the soft tube to grip the tubing around the entire circumference of the tubing.