Polycarbonate Hot Air/Nitrogen Welding

Repairing plastic on our old snowmobiles.  That seems to be an issue that we all face and there seems to be some misinformation out there as to the reparability of Polycarbonate. 

Polycarbonate is VERY repairable.  You can use the welding technique (hot air or airless).   You can also use adhesives.  Adhesives will be another day.

I am using hot air because for large repairs as it is the better way to go, and polycarbonate is a bit harder to weld with a airless since the base material needs to be heated properly for the rod to properly mix in and weld.

Polycarbonate is only one type of plastic that was used, and this page will only be for Polycarbonate.  Ski-Doo, Skiroule, Rupp, Arctic Cat were just some of the snowmobile manufacturers that used Polycarbonate.  Polycarbonate when used on snowmobile hoods is a plastic (not fiberglass) that is colored all the way through.  Smooth on both sides.  Polycarbonate can be a "blend" of other plastics.  You need to test your rod if welding a unknown plastic.

Some plastics are thermoset such as urethane and cannot be truly welded.  Fiberglass/SMC can not be welded. 

For more information on welding and repairing, feel free to check out this companies website.  Urethane Supply.  They have a large library of videos if you are a video type person.

I have done a couple of practice repairs to hone my skills on Ski-Doo hoods.  Which I will document here.  These hoods were junk so play time was fun!

Replacing a piece

Many times there is a fractured area or a hole that replacing would be a good repair.  That is what this is simulating.  I took a piece of Ski-Doo hood, (donated by Goose)  Cut a piece out and welded it back in.  This could easily be done from a donor hood that was damaged in another area.

The piece with the replacement section fit in.  I used 3m aluminum tape on the back side.  This is used a lot in plastic welding and should be part of your tool box if you decide to do this.  I then took some paint sticks and vice grips to hold the piece in place.  You could also tack weld it first.  In hind sight, I will do that in the future. I obtained some yellow polycarbonate welding rod!  This was not a easy find, but I did find some.  I will offer this for sale by the foot along with some red rod. 

I then welded the "back side" using the yellow polycarbonate welding rod shown in the above picture.  I then ground it somewhat smooth because I think most of us would do that. 

You could finish it off if you really wanted to.  Finishing the repair off may weaken the weld slightly.

A note on cleaning the plastic before starting.  I used carb cleaner here because I think most of you sled heads have that lying around.  I wasn't happy with how it softened the plastic though.  I will recommend using a proper plastic cleaning product.  I am going to recommend DuPont 2319S.  The reason?  Some plastic cleaners will soften Polycarbonate like the carburetor cleaner did.  In fact the DuPont 2320S is not recommended for Polycarbonate.

You then want to sand before welding and groove out the break for your welding material.  I used a die grinder with a carbide bit for this.

I then took a hammer to the repair.  I did break it, but I am extremely pleased with the outcome.  First, I had only welded one side.  This means the weld did not have full strength.  Second, I actually broke the material around the weld also.  In real life, the hood would have been damaged before the weld would have given.  (this photo shows the back side weld being repaired already).  I threw my phone in there so you could see the size of the hammer!

While not optimum, a one sided repair may be desirable if painting and refinishing is not needed or desired.  Sometimes we just want to make the part structurally useable again.

The front side before welding.  A little more care could have created a better looking repair if a front side repair was not desired.

Prepping the front side for welding.  Notice that you can see the back side welding material all the way around. 

Now for the front side.  I tried something here a little different.  What if we make our own plastic rod out of a scrap piece of polycarbonate?  The color would be correct, the repair would somewhat be camouflaged of refinishing was not desired.  While it worked, it did not work as well as I would have liked.  The polycarbonate rod is the better way to go.  Notice the black around the weld?  That black ring is filled with impurities from the plastic rod that was created from the donor hood material.  I fear the weld would be weakened by the impurities.  This is the reason for using Nitrogen versus oxygen for the welding also.  Less impurities in the weld leads to a stronger weld.  While I am not saying I won't use this method sometimes, I am going to keep that in the back of my mind.

I think the finished product would make for a strong repair.  It could easily be cosmetically repaired with some proper plastic material.  If this were a real job, there would be a couple of areas I would have run a little more rod into.  My rod that I created from junk donor material should have been a little bigger it turns out.  But overall, I am happy with this repair.

Lets repair a Crack in a Polycarbonate Hood

I don't have a step by step here, but I think with the above demonstration and the picture provide, you can get a good idea.

This is a crack in a Ski-Doo Polycarbonate hood.  A fairly substantial crack, about 12 inches long.  I opened up the crack with the die grinder and carbide bit, then laid in some clear polycarbonate welding rod.  This was only a one sided repair as it is only for demonstration purposes only.  Even with that said, I think it would hold up rather well, but a two side would be better.  This repair would be fairly easy to do a cosmetic repair to.