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Repair a Tear to the Edge of a Bumper Cover with a Nitrogen Plastic Welder
This video will show you how to repair a tear to the edge of a bumper. We recommend that you practice this on a scrap bumper. Just cut it with some tin snips and follow along with the video.
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.
Now it's time to apply your skills to repairing an actual tear to the edge of the bumper. Again, we recommend that you practice this on a scrap bumper. Just cut it with some tin snips.
Clean the bumper with soap and water first and let it dry. Then use plastic cleaner to remove any oil-based contamination. Spray a heavy wet coat then wipe dry with a clean paper towel. Using a die grinder or Dremel tool, rough up the backside of the plastic. Just grind it flat. Remove any paint overspray on the back side and get down to some clean, raw plastic. Use some of our heat resistant aluminum tape on the front side to hold the tear together. This also keeps the melted welding rod from pushing through the crack as you make your weld.
For maximum strength, we are going to use the wide ribbon on the back side. Preheat the bumper and the end of the rod. After about 10 seconds, touch the rod down, get it folded over, and start pushing the rod down so it folds toward the torch. Control your speed so the rod and bumper are both pre-melted before the pressure exerted by the rod fuses them together. With a wide ribbon, you will need to move the hot nitrogen flow in an oval motion to melt the ribbon all the way across. Note the puddle of plastic in front of the ribbon as you make your pass. Continue to weld all the way to the edge. When you get to the end, lay the rod down flat and focus the heat on the back of the ribbon until it turns clear. You can nip off the ribbon with the torch's nozzle.
While the ribbon is still hot, let's go back and smooth out the edges with the airless welder. First, go back over the edges of the ribbon with the hot nitrogen gas and heat them back up again. See how the natural rod gets translucent when it gets to the melting point. Then, lay the hot airless welder tip on it and smooth the edges out. This is not necessary for strength, only for cosmetics. Let the weld cool a bit.
Now we're going to put a tee across the edge with a narrow ribbon to reinforce it. Most of the time this will not be necessary, but it's a good idea for maximum strength in a high-stress area. Use a die grinder to remove overspray and rough up the plastic along the edge for about two inches on either side of the tear. Start by blowing the hot nitrogen gas on the bumper about an inch and a half from the tear. Notice how the plastic starts to turn glossy as the surface melts. Lower the rod down and preheat the end of it at the same time. You'll need to heat for about 10 seconds. Touch the rod to the bumper. When it sticks, apply pressure and fold the rod forward slightly so that the first quarter-inch of welding rod sticks to the surface. Keep the torch at a 45 degree angle and focus the heat where the rod and bumper come together. You want to pre-melt the top surface of the bumper in front of the rod and also pre-melt the bottom surface of the rod before it comes down to meet the bumper. Once you get it going, you should have a small puddle of melted plastic in front of the rod. Continue your weld straight across the other welding rod. When you get to the end, fold the rod forward, focus the heat on the top of the ribbon until it turns clear, then nip it off with the nozzle. Smooth the edges out again with the airless welder, and we'll be done with the backside.
On the front side, we will grind a v-groove so that there's still some rod there when we sand it flat. You can use either the one-eighth inch round rod or the narrow ribbon. The round rod is easier to weld and sand, but the narrow ribbon will give us a stronger repair. We'll use the narrow ribbon this time. Grind a v-groove about the width of the ribbon and about as deep as its thickness. Start the weld away from the edge. Pre-melt the bumper and the end of the rod for a few seconds, touch the rod down, get it folded toward the torch, and keep the hot nitrogen gas focused on the area where the rod and bumper come together. Apply a steady downward pressure as you make your pass to fuse the rod and bumper together. Continue the weld all the way to the edge of the bumper. When you get to the end, fold the rod forward, focus the heat on the top of the ribbon, then nip the rod off with the welder nozzle.
On the front side, it's best to smooth out the welding rod to make it easier to sand. Again, focus the hot nitrogen on the welding rod, start to turn it clear, then use your airless welder to smooth the rod. It's best to use a light touch and don't let the airless tip dig into the plastic. As always, practice makes perfect.
After letting the welding rod cool completely, sand it with 80 grit in a DA sander. The polypropylene rod will feather out nicely on the bumper, indicating a strong bond. After the weld is completely cool, test your weld strength. Often you have to fold the bumper completely in half to get a tear started. If the strength of the weld isn't what you expected, keep practicing on the scrap bumper until you can't tear your weld.