powder coating

[Gavin]

Hi, I am looking at having a frame powder coated. Does anyone know the best way to fill in the small rust indents before getting a bare frame powder coated? or to put the question in another form. is there "fill" product that is compatible with the powder coating process?

Look forward to some answers. Thanks,

Gavin.

[duTch]

 Gav, Might be best talking to the powder coated too...?

[morris]

As Dutch is saying, your powder coater should be able to answer that but I don't think there exists a "filler" compatible with powder coating. The process needs a perfectly clean surface for the powder to "stick" prior to the heating. It also needs a temperature of about 200°C for the powder to "melt" and form a uniform coating.
I have had the plunger's frame powder coated, but in hindsight I wouldn't do it again. I didn't notice, but my frame was sprayed with filler, then sanded back and (badly) painted. The sandblasting before the powder coating brought out all the rust pits again. With the good quality paints you have today, I should have just sanded it back again and then got it professionally sprayed with a good quality two pack.
Luckily the rust pits are in less visible places so I'm not bothered to much, but...

[Brian]

Maybe I can help here, powder coating is what I do for a living. I've only been working at it for a few months
but the guy I work for has been doing it for 15 years.

To try and answer some of the questions, there is a two part filler that can be used but we have not found it
very good so dont use it. It has the tendency to "gas out" which means it emits gases as it cooks and ruins the
finish over the top of it. You can weld up holes or use brazing but nothing that will melt under 200° C. We cook
at 180° C.

Like all things the people doing the powder coating vary in skill and interest so the quality of the finish varies.

First the item must be totally free of oils or contaminants, it then must be sandblasted to leave bare metal.
A good operater will then sand down the part and apply a zinchromate undercoat and bake it and then sand it again
before the top coat.

I have been using powder coating on my bike frames and parts for about 12 or more years and if its applied
correctly it is far superior to two pack or any other paint as far as durability and if applied correctly the
finish is as good as two pack.

Unfortunately a lot of operaters that dont do the job properly have put some people off the process. Incidentaly
powder coating and two pack are not as different as most think, powder is a polymer and two pack is poly urethane.
The main difference is how the stuff is suspended and applied and dried.

Generally I get frames and engine plates and any "solid" parts powder coated but paint tinware

[Gavin]

Thanks guys. I have found the replies above very useful. Given that my frame is savagely pitted in a few obvious places I will fill it and use 2 pac to paint it. Some other parts (Front Forks, hubs etc) are fine for a powder coat finish.

[bsa-bill]

the guy that did my last frame got a large gap filled with braze before powder coating, he made a nice job of the frame but did emphasize not to use anything other than just wax on the frame as the powder coated surface is softer than paint and not suitable for abrasive type polish ( Tcut and such), not a problem as the powder coat does not seem to fade at all.
Don't know if this applies to all powder coating, probably differing grades? - comment Brian

[Brian]

I'm not sure what your guy is thinking Bill but he's got his wires crossed. Powder coating is harder than paint, thats why its used in industries worldwide for all sorts of stuff like guards and railings etc.

Having said that though it has to be remembered that no finish is indestructable, any finish of any kind can be damaged/scratched if subjected to normal wear and tear.

You can cut and polish powder coating the same as paint but it is best not to use cutting type polishes, as your man said just use waxes or any non abrasive type of polish. Black is a particularly bad colour for showing up scratches, once you have polished it it looses that smooth gleam that is has "off the gun". This applies to all finishes.

All finishes have their good and bad points so some are better suited to some applications than others. Personally I use powder coating on solid parts like frames and engine plates, lower fork legs and guard stays, anything that is going to get a lot of weather and general knocking around. I use two pack on tinware as usually it has to have fillers under the finish plus like tool boxes they have transfers that have to be clear coated over.

You also have to remember that any modern finish will be far superior to the original finish, we have all seen bikes that gleam in the sunlight, they didnt look like that when they were new.

[bsa-bill]

what you said Brian  is probably what he meant, one thing that does powder coating no good at all is gasket remover DAMUIK (probably quite obvious but you know - act first think later)

[Greybeard]

...we have all seen bikes that gleam in the sunlight, they didnt look like that when they were new.

A chap in a pub yard recently commented on my bike: "There's something wrong with that bike". "Oh?", say I, slightly irritated. He replies; "The paintwork wouldn't have been that good when it was new!"
The chap asked me what my machine was worth. I said maybe £6k. He then offered to buy it.

[muskrat]

G'day Brian.
I thought powder coating used a + - process in that the part was + charged and the powder was - charged so it stuck to the part and then heated. So any filler would have to be conductive eg brass, lead wipe, solder.
Don't they chrome plastic by first giving it a coat of carbon to take the charge for the chrome to adhere to?
Cheers

[Brian]

Sort of Musky, the item being coated is earthed so negative. The powder is positive charged so the powder "sticks" to the item. There are all sorts of things that come into play and thats where the skill of the operator comes into it, I'm still learning.
Some items like aluminium are better conductors than say normal steel so you dont have to put the powder on quite so heavy.
Another thing that happens is whats called Faridays cage, a electric phenonemen that causes the powder to go around the item and not adhere to it. I have to say its a lot more complex than I ever thought.

Any filler does have to be conductive but the main problem is heat, it has to be able to withstand 200° C without melting or emitting gases etc. Solder or lead melts way below that temperature.

Some metals like alloy castings are difficult as they emit impurities when heated, we usually cook them first to hopefully purge them but even then sometimes it all goes wrong. You cant coat over the top of any old paints, you can re coat powder coating but its not easy and sometimes there are problems. You can coat over electro plating and anodising.

[BSA_54A10]

G'day Brian.
I thought powder coating used a + - process in that the part was + charged and the powder was - charged so it stuck to the part and then heated. So any filler would have to be conductive eg brass, lead wipe, solder.
Don't they chrome plastic by first giving it a coat of carbon to take the charge for the chrome to adhere to?
Cheers

Close but no cigar.
You coat most plastics with an organo-tin solvent which dissolves into the surface of thermo setting plastics.
a process we invented at Raynors which Spalvens sold off to Mitsubishi after he did an asset strip for land development.

[BSA_54A10]

Sort of Musky, the item being coated is earthed so negative. The powder is positive charged so the powder "sticks" to the item. There are all sorts of things that come into play and thats where the skill of the operator comes into it, I'm still learning.
Some items like aluminium are better conductors than say normal steel so you dont have to put the powder on quite so heavy.
Another thing that happens is whats called Faridays cage, a electric phenonemen that causes the powder to go around the item and not adhere to it. I have to say its a lot more complex than I ever thought.

Any filler does have to be conductive but the main problem is heat, it has to be able to withstand 200° C without melting or emitting gases etc. Solder or lead melts way below that temperature.

Some metals like alloy castings are difficult as they emit impurities when heated, we usually cook them first to hopefully purge them but even then sometimes it all goes wrong. You cant coat over the top of any old paints, you can re coat powder coating but its not easy and sometimes there are problems. You can coat over electro plating and anodising.

When you get deeper into it you will find "Powder coating" is about as general as "painting"
The original powders were basically glazes that formed semi metallic glasses when fused with the oxide layer on the metal which originally was aluminium. Th next cab off the rank was an iron glaze and the bath tub renovation industry was born.
These coatings were hard, and polishable but it was not easy.
Then we went into the second generation which were resins & polly amides.
these chemically bonded to the oxide layer on the surface rather than fusing and creating a new compound.
These are tough but not as hard as the vitreous finishes.
finally we have the strait plastics which basically are sublimation dyes same as on your T-shirts.
they are soft and rely on full encapsulation. These are the ones that lift off when cut.

[bonny]

Powder coating is popular on motorcycle projects for a few reasons imho. 1. Convenience, You can strip a bike down to a bare frame, bundle the frame, cycle parts etc into the boot of the car and drop it all off at the local blasters/powder coaters. Pop back a few days or a  week later and pick it all up and job done. So no paint stripping, wire brushing, having paint overspray all over the shed , parts hanging out of bits of wire all over the place.
 
2. Its relatively cheap, good quality paint is expensive and the new 2k paint is dangerous to your health.

But for me i'll never use powder coating again, a few years ago i had my triumph frame and cycle parts grit blasted and powder coated by a place everyone was raving about. "Its so tough", "You'll never need to have it done again". But despite the job being only a few years old , the rust is working away merrily under this fabled super tough powder coat and its falling off in chunks. This means i'll have to strip the machine again and do the job PROPERLY this time. 
My A10 was up on the bench being rebuilt having been powder coated by the same place, it never seen the road since i bought it, and already the rust was having a field day under this crap.           

[terryg]

One of my machines has, I'm pretty sure, a lot of powder coated parts on it.  While they look really good (it does not get much use) I have chosen to go down the home-spray route with the current restoration.  That has meant an air-fed mask, a bigger compressor to run both it and the gun and other sensible PPE.  The principal reason for the choice was to keep everything under my own control and perhaps also to have some flexibility in both prepping and the timing of finishing operations.

I'm no expert sprayer but I think I'm improving.  The results I get are mine and there's no-one else to blame.  However, if it's wrong I can relatively quickly have another go at getting it right.  All of which I like.

Horses for courses, I suppose.