Plastic repair GURUS since 1981
Repairing Urethane Bumper Covers with an Airless Plastic Welder
Urethane bumper covers are often discarded because of cracks and tears. Thermoset polyurethane was commonly used on domestic bumpers back in the 1980's and 90's. It's pretty much been replaced by polypropylene now, but you'll still see the old yellow plastic out there once in a while.
Polyvance was formed in 1981 as Urethane Supply Company to address the needs of bumper recyclers and to supply products to repair urethane bumper covers. Around that time, many people did not think urethane bumpers could be repaired. We proved they can be repaired.
Polyurethane is a thermoset plastic. In the molding process, two chemicals are mixed and injected into the mold. It forms a solid through a chemical reaction. The molecules form crosslinks throughout the solid like vulcanized rubber. Because of this thermoset polyurethane is not meltable. You will NOT be able to use the nitrogen welder on this type of plastic. You can repair it with the airless plastic welder. This will not provide a fusion weld. The urethane welding rod is used more like a hot melt glue.
You can use our Mini-Weld Model 7 or the integrated airless welder that is part of our nitrogen plastic welding systems to perform the repair. These two options are recommended because you need to be able to control the temperature of the welder.
How do you know if your bumper is thermoset polyurethane? Look at the back side of the bumper for the ID symbol. If you see “PUR” or “RIM” molded in, you know urethane. If you can't find the ID symbol, if the backside of the bumper is yellow like this Camaro, you know it's urethane. Yellow bumpers are always urethane, but not all urethane bumpers are yellow. Some Toyota and GM urethanes can be light or dark gray, so don't go by the color alone.
This article can help you determine if your plastic part is thermoset polyurethane or a thermoplastic.
Always wear proper safety gear while working!
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Note: This is a list of the Polyvance products that can be used to make this repair. This list does not include sanders, grinders, or other common tools you will need. If you have any questions, please don't hesitate to call technical support at 800-633-3047.
To keep the damage aligned while performing the repair, use aluminum body tape. Aluminum body tape is stiff and can withstand the heat from the repair process. Because thermoset urethane will not melt, you will need to grind a v-groove along the crack line. Use a rotary tool with a teardrop shaped cutting bit and grind about halfway through the plastic. Round off any sharp edges. This will help eliminate any stress risers that may compromise the integrity of the repair.
Set the temperature of the plastic welder to match the selected rod. While holding the welder's tip off of the surface, melt the rod into the v-groove. Don't overheat the base material. Simply melt the rod onto the surface. The repair on thermoset urethane is not a true fusion weld, but more like a brazing process. The urethane rod should maintain its clear appearance when melting without excessive smoke, discoloration, or bubbling.
Allow the repair to cool before you begin working on the opposite side. Peel off the tape that was used to keep the crack aligned. As you did on the opposite side, v-groove along the crack line with a rotary tool. Grind the area surrounding the crack line to expose more plastic and round off any sharp edges to eliminate stress risers. Apply melted rod into the crack and exposed plastic the same way that you did on the opposite side. To reduce the chance of the repair failing, continue applying melted rod all the way around the edge. Even though the repair is not a true fusion weld, it is still a very strong repair.