Patent ID: 7833449

Claim:
A process of continuously forming from a thermoplastic material a hollow product having one or more external surfaces with a variable configuration, said process comprising: feeding continuously said thermoplastic material at a temperature above its glass transition temperature into a nip region formed between a pair of revolving belt molds mounted opposite each other and at which said material in the nip region is subjected to an elevated pressure in excess of 15,000 pounds per square inch, said thermoplastic material being fed through an open mouth of a mold member and said open mouth being contoured to match closely an overall general shape of the exterior of the product and positioned upstream and adjacent to the nip region, said nip region having a portion of an elongated mandrel element extending into and through the nip region with the thermoplastic material flowing from the open mouth into the nip region over and around the mandrel element as a single, generally tubular stream of melted thermoplastic material, said mandrel element having an exterior surface and said revolving belt molds having exterior surfaces, at least one of said exterior mold surfaces corresponding to the external surface on the hollow product with said variable configuration, maintaining said belt molds and mandrel element surfaces at a temperature below the glass transition temperature of the thermoplastic material, and contacting the said surfaces of said material in said nip region (i) to reduce to a temperature within or below the material's memory retention temperature range the material contacting said mold surfaces to form a solid skin on the external surfaces of the product, said variable surface configuration being formed in the skin on at least one external surface of the hollow product, and (ii) to reduce to a temperature within or below the material's memory retention temperature range the material contacting the mandrel element surface to form a solid skin defining a hollow interior section of the product, said skins enabling the product to be self-supporting.