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Repairing plastic bike parts by welding




Q. I have a PP plastic part of my bike, which is cracked. The part is made of PP (polypropylene) and I want to weld it back together. What is the best tool to use: A hot air gun or a soldering iron? I purchased some PP welding rods, but the plastic part deforms quicker then the welding rods melts. How to make a strong weld?

Thanks,

Andreas K [last name deleted for privacy by Editor]
hobbyist - Denpasar, Bali, Indonesia
2004


A. Hi, Andreas.

I don't think it can be done with a soldering iron, Andreas, but there are airless plastic welders [affil links]. More traditionally, a hot air welder [affil links] is used, but we're talking about a specialized tool into which you feed the PP welding rod, not a hair dryer. The manufacturer of the hot air welder should include operating instructions, but if they are too brief, books like Plastics and Composites Welding Handbook [affil link on Amazon] are available. Good luck with it!

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004



"How to Repair plastic Bodywork"

on AbeBooks

or Amazon

(affil links)

A. Andreas,

What Ted says is true.

You won't, you can't make a repair with a soldering iron.

Welding guns, thermoplastic variety of course, are available with various tips ... the normal being a tip where you preheat the rod and the material and at the same time you are simultaneously forcing the rod into the material. Then there's the so-called speed tip where you normally use coil material and this preheats the rod. Not recommended in your case. Not as strong as hand welding, either. OK for long runs. Plastic welding, good plastic welding, is an ART!

In the USA there's a company called LARAMY which sell little how-to-do-it-booklets ... along with their welding guns. Get one if you can.

Lastly, maybe your PP is a natural colour, maybe it has been U.V. attacked in which case it will be brittle and easily stress crack. Hopefully not because then you sure ain't got a hope in Hades of fixing it.

freeman newton portrait
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

2004




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