Welding Options For Molded Parts

Select the right welding system when joining rotationally molded parts. Edited by Jean M. Hoffman The Injectiweld system is said to be the only welding unit to make a permanent repair on rotomolded parts. Its heated aluminum tip, molten welding rod, and piston injection give the right temperature and pressure needed to make a weld that approaches 100% of the physical properties the part. The molecules of the parent material and that of the welding rod mix thoroughly. The welder also helps eliminate oxidation in the weld that reduces quality. It's often to a designer's advantage to make a rotationally or rotomolded part as simple as possible, then customize it with additional fittings, baffles, flanges, and various attachments using a variety of welding operations. A specialized welding system called Injectiweld also seals and permanently repairs imperfections such as blow-bys and voids. But not all plastics are weldable, including all thermosets. Welding thermoplastics is best done with a single-resin system. In other words, welded parts should be of the same material. Welds made with different plastics may have poor strength compared to part material. But there are a number of compatible resins systems that bond. They include: • High-density polyethylene (HDPE) to linear low-density polyethylene (LLDPE). • Acrylonitrile butadiene styrene (ABS) to polycarbonate (PC). • Polyvinyl chloride (PVC) to ABS. Conversely, HDPE doesn't weld to either polypropylene (PP) or ultrahigh-molecularweight PE (UHMPE). And cross-linked materials, which are in some respects similar to thermoset plastics, don't easily weld to HDPE either. First, the welding area must be clean. Surface oxidation and other contaminants such as grease, dust, and damaged material all must be removed. Surface preparation can be as simple as scraping a thin layer off the area to be welded. Second, no matter what kind of welding unit is in use there