Method for making thermoplastic composite pressure vessels

Abstract

A process of making a composite vessel with superior mechanical and aesthetic characteristics includes the steps of: A) preforming a composite thermoplastic shell (e.g., by winding a commingled roving of fiberglass and a thermoplastic material onto a thermoplastic liner) having an opening for access to the interior; B) placing the shell (which may optionally be preheated) into a mold (which itself may optionally be preheated); C) introducing an inflatable bag containing a heater into the shell through the opening; D) heating the inflatable bag to a temperature which is sufficient to render the shell fluid while pressurizing the interior of the inflatable bag; E) continuing step D) until the shell forms against the interior walls of the mold; F) allowing the formed composite vessel to cool; G) removing the inflatable bag; and H) removing the formed composite vessel from the mold. Prior to step C), an insert having an opening may be juxtaposed in alignment with the opening in the shell such that, during step C), the inflatable bag is inserted through the opening in the insert. If desired for the intended purpose of the composite vessel, a portion of the exterior surface of the insert may be threaded such that threads are formed in the opening of the shell whereby the insert can be unscrewed leaving a threaded port into the vessel.