Is it possible to plastic weld a bumper with a heat gun?

Question

I have a 1500 watt heat gun with 12 settings from another project (the Wagner 3500, if anybody is curious.)

I have an acquaintance that managed to crack their bumper, and I was hoping that I could fix it for them, as I felt bad for them under the circumstances. The goal was to use plastic welding, but I don't want to buy an $300 tool to do it.

So: Is it possible to do the plastic with a heat gun? Would I need a special attachment? Would I need any other tools, like a roller?

(I already have/have access to the other tools required for this job.)

Answer 1

The problem with plastic welding with a heat gun is the concentration of heat, I think you allude to this in your post.

When/if you can concentrate a heat gun's output on a small area and concentrate the heat you can get the level of heat that's required to melt the crack along a 'bead'.

The tip that's required will often back up the heat in the gun and fry it. I've done it a bunch of times.

The tip that you want allows excess back pressure from building up with a bleed off port before the tip.

The rectangular hole allows for any back pressure to be released thereby preventing the gun from overheating and melting itself. These tips have varying sizes of bleed off and of course the most effective tips are the ones with smallest bleed off area and highest chance of cooking the gun. The more heat is concentrated from the tip the higher the chance it will be effective at melting the crack you want to plastic weld.

Answer 2

You can buy a specific heat gun for plastic welding for about $50. I would try the gun you have using plastic welding rod from Harbor Freight ($5.99). The rod package comes with a variety of materials for different plastics. You can experiment with just the rod to see at what temperature setting it melts. You may want to sand off the paint in the damaged area to prevent it from burning off and potentially ruining the repair.

Answer 3

The alternative to hot air is a soldering gun style plastic welder. Mine has variable temp and a special flat spreader tip with a 1/8" passage through it. The plastic welding rod is fed through the passage right into the melting plastic under the tip. There is also a bigger spreader with no feed passage. It is made by Polyvance, formerly Urethane supply. The current model 7 is 200 watts.

I have not yet tried hot air welding but I have read that that it is best for plastics over 1/16" thick. I have not done a bumper but I have repaired a splash guard under the engine and it was pretty thick. You must either match the original plastic to get a bond or they have a great product called Fiberfix. It does not chemically fuse but acts like a thermal glue; think hot melt glue on steroids.

To make it work even better you can cut a piece of stainless screen and embed it into the Fiberfix patch. The Fiberfix comes in flat sticks that do not feed through the regular tip. You use the spreader tip instead.

A soldering gun like the Weller (with a spreader tip) might work too. There are more types of plastic than are in the Harbor Freight kit. There are tests where you heat a scrap of plastic and from how it burns or doesn't burn and the color of the smoke and the odor and the texture of the melted plastic you can identify what you are trying to repair. Also, many plastics are marked with the recycle symbol with a number inside the triangle.The number identifies the plastic. Sometimes the type of plastic is also listed under the triangle. Number decoding info is on line.