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Nitrogen Plastic Welding: Bumper Flange Repair
Many bumpers have a flange at the edge where the bumper snaps into a bracket on the fender. Because the flange is thin and 90 degrees to the bumper face, it's hard to repair with two part adhesives. One of Polyvance's nitrogen plastic welders can be used to repair this type of damage.
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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.
Many bumpers have a flange at the edge where the bumper snaps into a bracket on the fender. Because the flange is thin and ninety degrees to the bumper face, it's hard to repair with two-part adhesives. The nitrogen welding system can be used to repair this type of damage.
First, clean the area with soap and water, then use a plastic cleaning solution like our Super Clean or Eco-Clean. Spray a wet coat on the surface and wipe dry with a clean paper towel. On this tab, we will weld the outer surface first to keep an eye on alignment of the flange on the bumper. Use one or two layers of our 6485 two-inch aluminum tape on the backside of the bumper to keep the flange in location as you do your weld.
Using our 6125 carbide burr and a straight die grinder, grind a deep v-groove into the plastic flange. Be careful not to cut into the bumper face. The v groove cuts into the backside of the bumper face and down most of the way through the flange. When you reach the end, wrap the v-groove around so you can lock the weld into the solid surface around the edge for extra strength. Deburr the v-groove when finished.
For repairs in tight areas like this, use our one-eighth inch diameter. Since this is a polypropylene bumper, we're using the R02-01 welding rod. Preheat the bumper and the end of the welding rod, touch it down, then start rolling the welding rod toward the torch as it gets to the right temperature. For repairs on thin areas like this, the nitrogen flow is turned way down, to about 7 liters per minute. Notice how the torch is focusing most of the heat on the rod instead of the bumper. This is because the bumper is so thin in this area, especially where it's been v-grooved. You want to melt the surface of the bumper, but you don't want to overheat the base material. It will take you some practice to know how much heat to put into the bumper while you're welding. Practice on a scrap bumper first. When you get to the end, continue to wrap the weld around the edge and into the v-groove you ground into the bumper there. This puts a continuous piece of welding rod around the end for extra strength. Here, we are doing a short second pass at the end to fill up the v-groove and to provide extra strength.
While the rod is still hot, reheat with the hot nitrogen gas then smooth the weld with a hot airless welder tip. Lay the airless welder tip flat on the surface and move it slowly to smooth the surface. Blowing hot nitrogen on the surface will keep the temperature up and prevent the welder tip from smoking. Let the top cool a bit before you smooth the weld at the edge. You don't want to heat everything up at the same time, because it's more likely something will move around on you. Let the top get some strength first, then smooth around the end.
Let the weld cool. You can accelerate the process by blowing on it with shop air. Once the weld cools to the touch, you can peel the aluminum tape off the back. Use the 6125 carbide burr again to grind the plastic on the back side. Remove any paint overspray, because the welding rod will not stick to paint. Grind into the corner, but be careful not to go too deeply. You should see some of the welding rod from the other side at the bottom of the v-groove.
Using the 1/8 inch round polypropylene rod, weld the back side of the flange using hot nitrogen gas. Again, turn the air flow down very low to about 7 liters per minute. The angle of the torch should focus more heat on the rod than on the plastic. Maintain a slow pace, making sure the surface of the bumper is melted as you make your pass. When you get to the end, make sure you get into the tight corner to lock the welding rod into the wheel arch flange. This is always a good strategy for increasing the strength of a flange repair.
To make sure that the weld is flat enough not to interfere with the mounting bracket, use the airless welder tip again to smooth the weld on the backside. Use the hot nitrogen gas to speed the process and to keep the tip from smoking. Lay the welder tip flat on the surface and move slowly for best results. Allow the weld to cool completely. Sand it with 80 grit in a DA sander to flatten the flange on top. Be careful not to sand off any body lines or features along the edge that will increase the gap between the bumper and fender. With proper care and practice, these repairs can be done without touching the paint on the face of the bumper, which will reduce refinish time and prevent paint matching problems.