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How to Weld Polyurethane

Polyurethane was first developed in Germany during WWII as a synthetic replacement for rubber, and was patented by Dr. Otto Bayer in 1937. Polyurethane is commonly used to make tires, shoes, insulation, bumpers, spandex and catheters. All polyurethanes are based on the reaction of organic isocyanates with compounds that contain a hydroxyl group. The two groups of polyurethanes are thermoset (PUR, RIM or RRIM) and thermoplastic (TPU) and this difference affects the way that each one can be welded. Both are common as automotive pieces, especially bumpers.

Instructions

Welding Thermoset Polyurethane

1

Identify which type of plastic you have by heating the plastic welder to max and touching it to the back of the piece of plastic. If it is thermoset polyurethane, it will smoke and discolor and once cool it will still be sticky. Thermoplastic polyurethane will not smoke and discolor and once cool it will not be sticky. If the plastic is thermoplastic polyurethane, proceed to Section 2 for welding directions.

2

Align the broken pieces together with clamps or aluminum body tape. Apply the tape on the finish side of the piece. With a teardrop bit on the air die grinder, grind a V-groove along the complete break halfway through the break.

3

Turn the airless plastic welder to the lowest setting for R1 repair rod and allow it to heat up. Insert the rod through the welding shoe. Hold the shoe off of the base plastic and allow the melting plastic fill the V-groove. The process is more akin to brazing or soldering than welding. Fill only about 2 inches of the V-groove at a time and let it cool.

4

After completing the V-groove on the back side of the piece, remove the aluminum tape from the finish side and make a V-groove halfway through from the finish side. Sand the slick finish off with the die grinder and a Rolex sanding pad.

5

Fill the V-groove from the front as directed above. Sand the fill flush with the Rolex pad. The part is now ready for finish work and painting.

Welding Thermoplastic Polyurethane

6

Align the broken pieces together with clamps or aluminum body tape. Apply the tape on the finish side of the piece. With a teardrop bit on the air die grinder, grind a V-groove along the complete break halfway through the break.

7

Turn the airless plastic welder to the setting for TPU repair rod and allow it to heat up. Insert the rod through the welding shoe. Lay the shoe on the surface of the base plastic and allow the melting plastic rod to fill the V-groove. Fill only about 2 inches of the V-groove at a time and before it has time to cool go over the area with the welder to make sure the base material and rod are melted and blended together. Continue this process until the whole break line is filled and welded.

8

Remove the aluminum tape from the finish side and make a v-groove halfway through from the finish side after completing the backside of the piece. Sand the slick finish off with the die grinder and a Rolex sanding pad.

9

Fill the V-groove from the front as directed above. Sand the fill flush with the Rolex pad. The part is now ready for finish work and painting.

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