I cannot attest to durability or actual quality produced by Prijon, but I have studied the actual process and it holds a couple advantages over the rotomolding. 1. stronger plastic - the blowmolding process can use a crosslinked polyethylene which has many more bonds between molecules than linear polyethylene. I also find the polyethylene boats to be a little stiffer and less likely to deform. 2. less plastic used - the extruding portion of the blow molder allows the amount of plastic to be varied along the length of the boat. There is more plastic extruded in the center where the boat is wider and receives higher stress. This allows for a much more uniform hull thickness. The rotomolding process is very imprecise and much more plastic than is actually needed must be loaded into the mold to ensure the minimum hull thickness. For those of you not familiar with the process, I will try and describe it. Imagine a two piece vertical mold, above it sits the extruder. Below all of this is the compressor and injector. The plastic is loaded into a hopper above the extruder and heated until is is pliable enough to be extruded and so that the crosslink bonds will form. This plastic is pressed down through an adjustable nozzle that creates a hollow tube of plastic. The nozzle varies the thickness of the wall of this tube according to preset values. Once a tube the length of the boat is ready, the mold is closed over the tube. Air or other gas is injected that forces the plastic against the surface of the mold until it cools and can be removed. There may be a couple discrepancies from my description to the actual physical process used by Prijon. I have only studied it as a student of Engineering from descriptions, schematics and information from other engineers. I personally don't own any plastic boats at this time, but if the only deciding factor for me was roto- or blowmolded, I would choose blowmolded. Daniel ************************ Daniel Key UW ACMS dtheman_at_u.washington.edu ************************ *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Wed Jun 14 2000 - 23:16:48 PDT
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