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The other side of plastic repair

Fix plastics without nitrogen
Friday, October 2, 2015 - 07:00
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When ABRN last talked with some of its most recent Top Shops winners, several mentioned they were introducing nitrogen welding gradually. They were giving their techs the opportunity to examine the technology before fully implementing it into their operations. Considering there is a slight learning curve and that nitrogen welding promises to offer a number of repair solutions that ordinarily might involve a new replacement part, this is the smart, expected strategy. Once these shops become comfortable with the technology, others are sure to follow. Indeed, that's always been the path for most new repair techniques in the collision industry.

For now, shops can turn to a number of other plastic repairs that can be conducted with airless welders and other tools they should already possess. Refer to the following instructions, provided by the Urethane Supply Company, to handle some of your most common plastic repairs.

Proper preparation

Virtually all collision repair tasks begin with cleaning the vehicle or part surface. Nowhere is this more important than plastic work, where the strength of the repair relies on a clean start.

Step 1: Begin by cleaning both sides of the repair area with hot water and soap designed for cleaning plastic.

Step 2: Dry with compressed air or a clean shop cloth

Step 3: Hard-to-remove contaminants such as wax or tar may still remain on the plastic. Thoroughly clean the area again with dedicated plastic cleaner.

Step 4: Using a clean, lint-free cloth, wipe the cleaner off while it is still wet. Be certain to wipe in one direction to avoid spreading any contaminants back over the clean area.

Examine the plastic for any sign of distortion. If there is, reshape the distortion with these steps:

Step 1: Heat the distortion with a heat gun. Note that the plastic must be heated all the way through.

Step 2: Maintain the heat gun on the area until the opposite side of the plastic is uncomfortable to the touch.

Step 3: Use a screwdriver handle or other blunt tool to force the plastic back into position.

Step 4: Use a damp cloth to cool the area. Stretched areas will shrink once the bumper cools.

Step 5: Once the distortion is reshaped and smooth, check your work by sanding it with 80 grit paper, which will help you identify any remaining low spots.

Step 6: Repeat the heating, reforming and cooling process to push out any remaining low spots.

Note that this process can be replaced with another for certain plastics. Thermoset polyurethanes (PUR and RIM) possess a “memory” characteristic that sometimes will allow them to return to their original position if they are held under a heat lamp or in a heated spray booth.

Any cuts or tears in the plastic also must be prepped. Use aluminum body tape on the back of the repair area to align the cosmetic surface. Aligning the outer surface helps minimize the amount of filler required to restore the exact profile of the part.

(Photo courtesy of the Urethane Supply Comapny) Clean plastics twice, frist with hot water and a specialty soap then with a plastic cleaner, to remove any wax and remaining contaminants. (Photo courtesy of the Urethane Supply Comapny) Use either a teardrop cutter bit or tapered burr to make a v-groove on the repair. (Photo courtesy of the Urethane Supply Comapny) The rod should come out of the bottom of the welder's shoe completely melted and clear.
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