Dent filling then powder coating

[bobg]

Picked up a decent Pete Matthews frame last week, stripped it ready for shot blasting and powder coating when I noticed a couple of small dents. In the past when I've taken frames to a mate in my local Nissan dealer, I've filled any dents with resin/hardener etc and its been no problem.. until the garage closed...
I asked my local powder coater if I could collect the frame after shot blasting so that I could fill the dents and return it for the final powdercoating/ lacquering. He said that the filler would fall out during the powdercoating process. Can anybody elaborate please. I didnt think there was a high temp baking process involved and he wasnt keen to elaborate?? It seems hardly worth refinishing and leaving the dents...

ta

 

[numbnuts]

I don't know what the temperature is but it is quite high as it has to melt the powder any filler would burn, the only way it could be done is to fill it with brazing rod not something you could do at home not unless you have the full kit

 

[bobg]

I don't know what the temperature is but it is quite high as it has to melt the powder any filler would burn, the only way it could be done is to fill it with brazing rod not something you could do at home not unless you have the full kit

Thanks Numb, I should have spent more time googling before posting this. The temp to cure the powdercoating will indeed melt all fillers although there is mention of High Temp Lab Weld on various sites but I can't find it available in the UK. Think I'll just have to find another tame car body sprayer for this one. I'm too mean to spend Argos prices when its only a resale job.

 

[tyred]

I suppose lead loading is a possibility but again, the temp used to powder coat could very well melt the solder. You would need to check that out first.

 

[jethro10]

I work for an aluminium manufacturer and we have a powder coating plant (Sorry, not suitable for bike frames!)

Car filler resin / hardner is fine to use. I tend to use two part epoxy glue like Araldite - Works fine also

both have a melting point way above what Powder cures at.

I've seem 100's of jobs as "foreigners" on all sorts of old crap filled with Epoxy glue and coming out fine.
I've even seen folk use it structurally on things like window box brackets etc.

Jeff

 

[swee'pea99]

FWIW I powder coated (or rather had powder coated) a frame with a couple of small dents in it and you really wouldn't notice them unless you knew they were there.

 

[bobg]

I work for an aluminium manufacturer and we have a powder coating plant (Sorry, not suitable for bike frames!)

Car filler resin / hardner is fine to use. I tend to use two part epoxy glue like Araldite - Works fine also

both have a melting point way above what Powder cures at.

I've seem 100's of jobs as "foreigners" on all sorts of old crap filled with Epoxy glue and coming out fine.
I've even seen folk use it structurally on things like window box brackets etc.

Jeff

Thanks Jeff, thats excellent news, It'll widen my choice of frames to restore no end. I've turned down some really nice stuff because of the presumed powder coating over filler issue.

It's amazingly resilient given the flexing of tubing!! My fixie which uses a 1954 Claud Butler New Allrounder frame had some dings repaired with epoxy filler and finishing putty, it was sprayed with two pack so melting points were not an issue but it's used all the time and there's no sign of cracking on the repaired areas even after about 3 years.

 

[bobg]

A bit more info in case anyone else encounters this problem. Just been to visit a couple of powder coaters .

One said he has yet to discover a filler that will withstand the 200-220 degrees necessary to finish a powder coat. He said that they tend to shrink.

Another said a customer filled gouges on his aluminium car wheels with "chemical metal" a loctite product and the job was perfect. His oven operated at 220 degrees... the tech data for this product says " stable to 160 degrees" ??

research continues

 

[Matt C]

i had a trials bike drame with dents in, PC guy said the same bout fillers so took mine to a alloy welder who filled it with alloy weld then ground and polished it back flush with the frame. Then had it PCand looks bang on.

 

[deanbmx]

I used chemical metal when refurbishing some alloy wheels. they were fine with the powdercoat process.

 

[bobg]

Final conclusion - Chemical Metal used to fill dents of less than 2mm tends to crack during the baking process of powder coating. More than that depth seems ok but dont forget to abrade the surface prior to filling. This info based on 10 filled dents of various depths in Reynolds 531 tubing and presuming a baking time of approx 20 minutes at 200 degrees, which appears to be about average. Not that anybody gives a damn except me ...

 

[jethro10]

Final conclusion - Chemical Metal used to fill dents of less than 2mm tends to crack during the baking process of powder coating. More than that depth seems ok but dont forget to abrade the surface prior to filling. This info based on 10 filled dents of various depths in Reynolds 531 tubing and presuming a baking time of approx 20 minutes at 200 degrees, which appears to be about average. Not that anybody gives a damn except me ...

Glad your sorted.
I suspect most products are conservative on their rating "just in case"
Like I said, Araldite works fine here.
Yes, 200 degrees is quite normal, some of our powders are 220 - mostly metallics I think.

J

 

[bobg]

Just for the sake of personal satisfaction, I tried a brazing torch ( well actually a plumbers blowtorch ) - max temp 1370 c and a couple of general purpose flux coated brazing rods, cleaned the surface of a dent, filled the dent and filed it down. Quite pleased with the result but you need to get the tube "red" hot, May even try something more ambitious next...