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The length of the molecular chains has a strong influence on the weldability. Therefore, the different chain lengths should be as equal as possible in order to achieve homogeneous flowing properties. If there are very high molecular weights, as with PE 100 (an ultra high-molecular polyethylene- PE- HD -UHMW), the chain reaches such a length that the molecular chains in thermoplastic state cannot slide down anymore due to the many entanglements with … |
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(Image: Temperature) Polyethylene has a very wide thermoplastic range between about 280 °F and 570 °F (140 °C and 300 °C). However, experience shows that polyethylene has the best (long term-) strength in heating element butt welding at a welding temperature of 390 °F and 430 °F (200 °C to 220 °C). (Image: Condition range of polyethylene according to [SKZ] [Image: S&P GmbH]) (Image: Attention!) Lower or higher temperatures, respectively, have negative … |
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Why is the welding load important? The welding load serves to bring the plastified join partners into contact in such a way that the molecular chains are sufficiently mixed and that the semi-crystalline structures, which determine the strength of the polyethylene, can develop. The necessary welding load (specific jointing pressure) for polyethylene is determined by the formula presented below, and has to be converted for the corresponding welding surfaces (… |
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What is the consequence of inadequate joining pressure?
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What are some of the main causes of failure of the welding process? Sources of failure:
Thus, there must be a certain layer thickness of the residual cast after the welding procedure. It is assumed that the best strength values of the welding seam can be achieved with a melt displacement … |
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The image below presents the major causes of failure and their consequences if the required welding times are not followed. (Image: Influence of the welding times – sources of failure and consequences) |
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Nov 04, 2016 Below are shown the main factors that influence the welding quality:
(Image: Factors of influence on the welding quality) |
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Nov 04, 2016 The following preliminary tasks should be accomplished prior to starting the heating element butt welding process:
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Nov 04, 2016
(Image: Heating element butt welding device) (Image: Welding of the HD-PE long pipes into continuous pipes) (Image: Welding of the HD-PE long pipes into continuous pipes) |
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Nov 04, 2016 The joining areas are pressed against the heating element as long as the complete areas lie flat (coplanar) against the heating element. The alignment process is finished when the heights of beads have reached stipulated values along the whole perimeter or the whole top of the panel, respectively. The bead heights are indications that the joining areas lie evenly against the heating element. The adjusting pressure is maintained during the whole procedure. |
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