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Identifying plastic so I can weld a repair Answered

I am repairing a broken wheel on a old lawnmower for which spares are not available. The hub (holding the roller bearing) has broken away from the rim and tyre. I've managed to weld the two parts back together using the hot air gun on my rework station but some small pieces are missing and I'd like to replace these and reinforce the welds by adding material.

It is possible to buy rods of different plastics to carry out these repairs but I need a better understanding of the material I'm working with. It is an opaque white plastic with a greasy or soapy feel. It melts relatively easily (I used the heat gun at 180 degrees C) and bonds back to itself well. I suspect it is a polypropylene of some flavour - straight Polyprop, HDPE or LDPE.

I don't have scrap material to test without removing some from the wheel. Any thoughts on what it is likely to be and do I have to know exactly which it is or will the different materials bond with each other?


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2 years ago

Thanks Jack - that's a great and comprehensive flow chart that introduces a few helpful steps before setting samples on fire and observing the flame colours!

Jack A Lopez
Jack A Lopez

2 years ago

A while back I found a sort of flow-chart for identifying plastics, in PDF form, and I saved a copy of it, here:
The actual tests are simple, e.g. Does a soldering iron melt it? Does it float or sink in water? When it burns, what does the flame look like? When it burns, what odor does it make?
The most powerful of these tests is, of course, the smell test. However, I am not going to comment on the activity of inhaling vapors from burning plastics, except to say, maybe it is unhealthy. You know, try not to inhale too much, because it might be bad for you.