Bonding polypropylene?

[sauluk]

Seems a lot of bits on bikes are made out of polypropylene (PP) which is, I've read, a difficult plastic to bond as it is resistant to a lot of adhesives / solvents.

My question is whether Araldite will work? more specifically the slow cure precision one, not rapid set.

[rictus01]

Hmmmmmm, I suppose it's worth a try, if it's all you've got, I generally use this stuff (http://www.shop4glue.com/universal-bond-adhesive-glue-pack-for-all-plastic-repairs-ptfe-polyethylene-polypropylene-silicone-150-p.asp), in th crack and if needed plastic weld the back.

Cheers Mark.

[sauluk]

Thing is, if it's not going to work I'm not going to risk it. One of the headlight lugs has snapped so if it wont glue I have to order a whole headlight... at quite some expense...

[rictus01]

As said I use the two part stuff I linked to, that works most of the time, but if you'll have to order a new one, no harm trying is there ?

[Specialone]

You can buy PP specific two part adhesive, when I used to use it in my last job I got it from rs components www.rswww.com.

Depends what you expect from glue, structual stuff I would buy as above, if it's just cosmetic stuff that wont be subject to any stress then araldite will be fine IMO .

[sauluk]

It holds the headlights in place so I'd say structural. I might just pick up some new ones to be on the safe side but have just tested some araldite on 2 pieces of PP and will let it go off overnight...

[yorkie_chris]

Plastic weld it

[Sally]

Have managed to do this on my old SV using industrial strength glue.

[sauluk]

Plastic weld it

I test ran another bit of PP with araldite, flexed it a bit this morning and it snapped, not strong enough.

I don't have a plastic welder and they look pricey, more expensive than just getting a new headlight.

Think I'll just bite the bullet and sell mine on eBay to someone with the gear to fix it.

[yorkie_chris]

£5 for a cheap soldering iron, less than a decent bottle of glue ;)

[sauluk]

Will a cheap one do though? Do you not need a specific temperature?

[yorkie_chris]

Depends how good a joint you need, headlights probably aren't massively stressed if there are a few mounting points.
You could also try solvent welding.

Or actually I know a guy who's a wizard at it, does body panels up here as a bit of a sideline. Could post your lamp?

[GagginForraPint]

There are adhesives that will do it I did a search for "bond polypropelene" for example 3M Scotchweld 4693H, link below for amazon at £15.99

http://www.google.co.uk/url?sa=t&source=web&cd=4&ved=0CC8QFjAD&url=http%3A%2F%2Fwww.amazon.co.uk%2F3M-Scotch-Weld-4693H-Polyethylene-Polypropylene%2Fdp%2FB002G3M9S0&ei=q4A8TYzsAo6AhQf4tb2wCg&usg=AFQjCNHIo8VQct_0FFMUPcFb3tiWP1PDpA

[sauluk]

Problem is that stuff is elastomeric so will be flexible. Might have better shear strength but I don't want to be cutting corners. I've put in an offer for new ones but if I don't get em I'll plastic weld them.

Thanks again org, always got answers.

[mikerj]

Can you not make a 'mechanical' repair with e.g. a steel bracket and some fasteners?

[sauluk]

Not much clearance around the lug. Thought about reinforcing it with a paperclip or the like but am after some new ones now which I'll hopefully get.

[embee]

Just as an aside, whenever I've really had to try to fix something similar I try to use a loop of lock-wire through some holes to give it mechanical strength. You can either drill or sometimes use heated wire to melt a hole. Lock-wire is stainless and nice and flexible, paper clips are usually rather stiff for this sort of trick, thin copper wire can be used. Then build up with Araldite around it if there's space.

Polythene and polypropylene can be tricky to get a successful bond, as you all know. The wire can give the epoxy something to get hold of.