Patent ID: 6676790
Filing Date: 2004-01-13
Classification: B29C,B29K,B29L,B65D

Abstract:
Process for the manufacturing of non-reinforced load carriers of thermoplastic material, the process comprising:a i) extruding work pieces in the shape of sheets and allowing the extruded work pieces to cool and post shrink uniformly after the extruding during and intermediate storing of at least a couple of hours; ii) extruding extended bar sections, the bar sections optionally having a rectangular or polygonal cross-section, and allowing the extruded bar sections to cool and post shrink uniformly after the extruding, during an intermediate storing of at least a couple of hours; whereupon, b i) forming an upper deck member by heating, followed by molding, two uniformly post shrunk work pieces in a first mold, the first mold comprising a first and a second mold half, which mold halves each comprise one shaping cavity, which shaping cavities together are a negative representation of an upper deck member of a load carrier whereby the mold halves are arranged so that an intermediate space is formed between them and that the cavities are facing each other, whereupon the two heated work pieces are placed in the intermediate space between the two cavities after which each work piece is under influence of vacuum and/or pressure whereupon the mold halves are pressed together while the thermoplastic material is still hot so that the two work pieces are welded with each other and form a hollow unit whereupon the thermoplastic material is allowed to cool somewhat before the mold is opened, the upper deck member is removed and the process can be repeated; ii) forming a lower deck member, by heating and then molding two further, also post shrunk, work pieces, which after heating is formed in a second mold comprising a first and a second mold half, which mold halves each comprises one shaping cavity, which two cavities together is a negative representation of a lower deck member of a load carrier, whereby the two heated work pieces are placed, molded, welded and removed in the same manner as the forming of the upper deck member; and optionally, iii) forming a skid by heating and then forming two extended bar sections in a third mold comprising a first and a second mold half comprising a first and a second mold half, which mold halves each comprise one shaping cavity, which two cavities together is a negative representation of a skid of a load carrier, whereby the two heated bar sections are placed, molded, welded and removed in the same manner as the manufacturing of the deck members; whereupon, c) the upper deck member and the lower deck member are allowed to cool and post shrink uniformly, after being removed from the respective molds during an intermediate storing of at least a couple of hours; whereupon, d) heating a number of joining surfaces on a lower side of upper deck member, on upper and lower sides of the lower deck member and on an upper side of two or three bar sections or alternatively two or three skids, which, in one or more steps, are heated by means of infrared heating, laser or by being pressed against a heated weld core, whereby the different parts, in one or more steps, are pressed together so that the thermoplastic material in the lower joining surfaces of the upper deck member and on the upper and lower joining surfaces of the lower deck member as well as the joining surfaces of the bar sections or the skids form weld or melt joints, whereafter the thermoplastic material in the joining surfaces is allowed to cool and solidify at least partly before the pressing is discontinued, whereby a joined, non-reinforced load carrier of thermoplastic material is achieved; and optionally e) coating predetermined surfaces on the load carrier with a friction enhancing material by flame or corona treating the surface to be coated after the extrusion of the work pieces or extended bar section, respectively, or after the joining whereupon the surface is spray coated with the friction enhancing material.