Apparatus and method for manufacturing heat-shrinkable sleeve using

Abstract

Long lengths of a heat-shrinkable sleeve for use in splicing electrical cables and the like are manufactured by providing an elongated impermeable core having a smooth outer surface, extruding an elongated sleeve around and in contact with the core, the sleeve having a smooth inner surface conforming to the outer surface of the core, and effecting an initial expansion of a portion of the sleeve to a larger diameter in an expansion zone so that the sleeve separates from the core and leaves a space between the sleeve and core. A fluid is introduced into the space under pressure via a fitting at the downstream end of the sleeve while continuously advancing the sleeve and core through the expansion zone. To begin the process, a permeable core is used, and the sleeve is extruded around and in contact with the permeable core. A fluid is introduced under pressure from a fitting upstream or downstream of the expansion zone through the permeable core to the inside of the sleeve in the expansion zone, and the leading end of the impermeable core is welded to amd trailing end of the permeable core at a location upstream of the expansion zone. The sleeve has a composite structure comprising an inner compound and an outer compound, the inner and outer compounds having different characteristics. In a first crosshead, the inner compound an a thin layer of outer compound are applied, and the balance of the outer compound is applied around the sleeve in a second crosshead. Between the two crossheads, liquid nitrogen cools and stabilizes the inchoate sleeve.