Reader Question: Does This Plastic Welder Work?
By Chuck Cage
TM reader LJDobie writes: “I restore 80s and 90s autos, and something like this plastic welder from Harbor Freight sounds like it’d be great for fixing borken door clips or similar things, or even patching up the fenders on my ATV. Have any of you used it? Do you know exactly how it works?”
The last time I did any “plastic welding” it was with one of those kiddie construction kits that included a “welding gun” that spun plastic rods quickly to generate heat. Wow — that sounds really dangerous now that I say it to you, though at the time it made perfect sense.
So have you used one of these “real” plastic welders? Let us know about it in comments.
Plastic Welding Kit [Harbor Freight]
July 31st, 2007 at 3:26 pm
I have one, it kinda works. It is very hard to get the plastic to the proper melting point and not burning it at the same time. The plastic ends up getting brittle. I originally bought to fix a fuel pump on a grand cherokee i had years ago, the weld leaked like crazy so I went back to ol reliable JB Weld
All in all I wouldn’t recommend it, I only use it as a heat gun anymore.
July 31st, 2007 at 8:32 pm
When I was into downhill skiing (maaaaany moons ago) there was a way to repair the botom of a ski if you happened to hit a rock or something solid enough to gouge it. I believe they were called Ptex sticks, one would burn or heat them up to liquify them and then drop / drip the liquid plastic into the gouge. The hard part was trying to NOT burn oneself in the process!
August 1st, 2007 at 7:24 am
Yes, these do work. Check out “Getting Started in Welding Plastics”, Glenn Vandiver, Home Shop Machinist, May/June 2004, pages 44-51 for some hints. A big hint is to pick up a “router speed control,” often on sale for $12.50, regular $25 from Harbor Freight, so as to be able to regulate the heat while maintaining a reasonable air volume. Otherwise, the only way to regulate the heat is by varying the air flow, which is not optimal or fun.
The “trick” seems to be to get the temperature just right. There are some big differences between metal welding and plastic welding. Thermoplastics are poor heat conductors, so the filler rod may not even thoroughly melt–in even a good weld, the rod can look unchanged, though the material on either side of the weld should look melted. There is a narrow range of viable temperatures too–just a bit too much heat at one point can char or burn the plastic. In general, plastic welding is not about having the materials flow together as a liquid, but fuse together in a “plastic” state. A proper joint can be up to 90% as strong as the original material. In general, most any joint type normally done in metal welding is possible with plastic welding.
See also Kamweld.com website, especially their article “Plastic Welding Using Kamweld’s Durable Welders” (see under “Resources”).
*NEVER* let the air pressure drop to zero–there is no protection built-in, and the welder will catch fire. When you are done using it, just let the remaining air in your compressor tank flow through (or if you have a Big Tank, until everything is cool).
August 1st, 2007 at 7:26 am
Take a look at the alternative units sold by Urethane Supply Company.
They market an all inclusive (airless welder and different welding rods) as a package. Their Mini-Weld #6 (replaces the older model 5 which is still being sold - out there) has a temperature controller connected to an 80 watt “soldering iron type handle” that has special-purpose tips. Not as cheap as Harbor Freight - but shop around for prices in the $140-150 range.
August 1st, 2007 at 8:07 am
Good information so far. I just wanted to make sure it was more special that a regual soldering gun that melts plastic rods. I had tried melting plastics back together in the past using heat (read butane lighter) but the repair rarely ever holds. I may drop some cash and try this out myself. The router speed control makes sense. I wondered what the air regulator was for on here… Seems kind of dangerous to blow the air out onto molten plastic. But I have a 60 gal 6hp air compressor… Guess I was thinking big..
August 2nd, 2007 at 8:13 pm
You’re all missing an important part! You don’t hook up to an air compressor, you get a bottle of argon, an inert shielding gas, and run that through the welder at 3~4psi. It heats the work and filler rod while shielding them from the air (oxygen) so they won’t burn. My local HF had small gas cylinders on the same shelf as this welder.
August 21st, 2007 at 10:05 am
how much are the argon cylinders?
August 26th, 2007 at 8:09 pm
I’ve repaired two plastic radiators with this welder. I decided to give it a try after pricing a new Mazda Protege radiator… It’s not cheap. With the price of a Harbor Freight plastic welder at $40 what was there to lose? I had a dime sized hole to repair in the protege upper tank and a 5″ long crack along a seam on the Jeep upper tank. I managed to repair both radiators with the Harbor Freight kit, saving around $400 total. The repairs have held up to this day, and seem to be just as strong as the surrounding material.
I have owned two of these tools. The first one caught on fire in my driveway after I forgot to turn on the airflow from my compressor after plugging in the unit. These things put out a LOT of smoke when they combust!
March 18th, 2008 at 11:35 am
I have use a tool like that - not exactly the same, but similar. The most important thing to remember is that (as somebody else said) plastic is generally not a good thermoconductor, so plastic welding can be tricky to do well.
February 4th, 2009 at 5:53 pm
I have 2 one is airless and one is hot air.I prefer the airless best I feel that I have more control over the plastic.Check out the urethane supply company model 6 welder.
April 8th, 2009 at 11:33 am
Hey Jerry have you used the model 6.