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Powdercoat on mating faces?


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Will there be any issues if mating faces such as the diff flange or the stub axle flanges are powdercoated? The coating is around 100Microns. Or do the faces need to be masked so they are free from the powder coat and then treated in another way?

I'm talking about axle cases and swivel housings here mainly. Don't need to be told the powdercoat will damage, as paint will do the same ;)

Thanks in advance :)

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Yep, clean... otherwise bolted up components may move microscopically and over time crush the coating, making the bolts no longer be up to torque spec, and therefore come undone -not what I would want for a swivel housing :)

Well that's my theory on it. :)

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yeah clear faces. Mask or whip off before fitting. Dimensionally I can't think of anything where it would hurt, I can't think of anything where a preload or anything is set relying on mating faces and/or gaskets of correct thicknesses. There is the issue of the coating compressing or failing and the fixings working loose as a result. Joints of importance on the winches I build are not painted

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I zinc plated my axle casings and suspension arms at the time, but it isn't that durable and they are now fairly rusty. If I had to do it again, I would galvanize them. without masking anything, maybe only the arms in the bores were the bushes fit. its the only thing that lasts in that environment. lets face it, a couple of strikes from a rock and it will go rusty in no time.

Daan

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Yep, clean... otherwise bolted up components may move microscopically and over time crush the coating, making the bolts no longer be up to torque spec, and therefore come undone -not what I would want for a swivel housing :)

Well that's my theory on it. :)

I thought that might be the case.... However bashing out the thread just before the end of lunch meant I didn't write it :P.

Powder coating is "A COATING" it will chip n peel off leaving a unclean unlevel mating surface (you tart),

better to passivate which is embeeded into the metal (and no so tartish so you won't like it as much)

so it does chip or peel of

:P

Nige

The plating is also a coating Nige, its only on the surface. In the places on the axles that will get abuse, the zinc wouldn't stand up to it either. Powder coating done properly will not peel.

I zinc plated my axle casings and suspension arms at the time, but it isn't that durable and they are now fairly rusty. If I had to do it again, I would galvanize them. without masking anything, maybe only the arms in the bores were the bushes fit. its the only thing that lasts in that environment. lets face it, a couple of strikes from a rock and it will go rusty in no time.

Daan

I'd sort of ruled out galvanising due to the heating and quenching it would endure. I thought that it might effect the axle cases as there are lots of different thicknesses/pressings/castings.

By now I think we all know Ross is after a tart's machine, shiny and only ever in 'extreme' conditions when on an RTI ramp at a show :P;)

:banned::P She'll be a beauty, but she will be used and abused.

You can get a special type of masking tape for use before powder coat

I am aware, but thanks Lewis :). I was thinking that if its all covered then its a few things less for them to mask.

So, masking the faces will be the best option.

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I wouldn't trust the powder coater to do the masking - do it yourself.

I appreciate that you're well read up Ross, and have confidence in the companies you have spoken to, but listen to the advice of your fellow forumeers, learn from their experiences so you don't have to spend YOUR hard earned learning their lessons again :)

I am yet to see a decent powder coating which does not chip, and subsequently flake off.

I work for a defence contractor, we make stuff for the military, we buy the best there is and pay through the nose to get it, and you cannot get powder coat to last in the conditions you expect the underside of an off road vehicle to see

If you are dead set on powder coat then get it passivated first - it provides a texture that powder adheres well to - and also provides that second degree of corrosion protection so when your powder coat inevitably chips and lets water get behind it your components aren't just bare steel

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Hope it doesn't seem like I'm trying to be difficult here :P.

Powdercoating is 100microns total, so 4x the electroplate/passivation spec I was given by Simon R.

I assume the masking will have to be done by them as it will be after the blast prep?

The reputation of powdercoat is a bit harsh I think. My first four bumper is powdercoated and I think 3rd hand, it's taken a beating and hasn't peeled on the few places it's been damaged. There is a lot of **** Powdercoating out there!

Powdercoating will chip, as will any paint or other coating. Talking to the chap, the blast prep needed to get proper adhesion will remove any electroplating. (Plating and then powdercoat was my plan for all the brackets/links/etc). The powdercoat does not stick well to the passivate surface, it's not rough enough. And anywhere that's hit hard enough to remove the Powdercoat would take any electroplate off too.

If you're allowed to say Lewis, what does last?

I'm only exploring the powdercoat from this particular place as I've seen their work first hand. The original wrex racing tray back cage was done by them and that had a battering and hadn't broken through in most places and where it had come through, not peeled. The other one is a friends bumper.

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My experience of powder costing (rock sliders plus swing away carrier) is that all flaked and peeled and all seemed to experience increased corrosion under the flaked and peeling bits. Would not buy anything powder coated again. The cause of the poor experience I suspect is that they did not allow enough baking time to pre heat the metal before applying the coating and because all of the sections had differing thicknesses they all cooled at different rates so the coating did not uniformly stick to the metal. Hence there were small bubbled sections under the coating which grew. Attracted water and rusted

The solution (not armchair critic no experience of doing the job) is to get the part sand blasted first to get a rough surface, then passivate coat, so the rough surface remains (did this for my bulkhead although I think they used a tannin type chemical instead of passivate) then topcoat with powdercoat

Remember I no nothing but in my opinion the problem seems to be people trying to powdercoat smooth steel or very lightly pitted steel. As the process above adds quite a bit of time plus cost to the process but if you do the preparation my experience is you always get a quality outcome

What substantiates this is it proved to be a right PIA to get the coating off the welded joints of the wheel carrier when I sand blasted it to bear metal but the other areas came off with little effort

With regards to mated surfaces i would not do them but hence tape them as best as possible at sand blast stage with masking tape (so they remain smooth plus easy to scrape) and then use a standley knife scraper (cheap plastic window scraper with insert blades so you've always got a sharp one) to cut away any excess powdercoat the got on the flanged surfaces

Rob

Sorry for the long post

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I'd sort of ruled out galvanising due to the heating and quenching it would endure. I thought that it might effect the axle cases as there are lots of different thicknesses/pressings/castings.

I dont think a 6mm axle casing will notice galvanising. if anything it will stress relieve it. you can get the best powdercoat you like, but in the end your axle cases will look exactly like they do now.

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Ross if I had the money I would have the ibex axles galvanized.

I agree with others that powder coating will stay put no better than paint I've no doubt there is good and bad. I'm also sure yours will be the best it can be and look lovely the point is it will flake off eventually as will paint. Zinc passivate or galv only come off with wear.

You pay your money and take your choice paint/powder coat will be good, work well and look nice. Passivate/galv will be better and last a lot longer but not look as nice. Passivate tends to get surface rust after a while and may be better with a paint coating on top.

So back to your original question bare mating surface is the way to go but remember this will give you a bare edge for the rust to start from.

Mike

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Thanks for the thoughts Rob, don't apologise for the long post! As with all coatings of any type, the better the prep, the better the job.

Daan, I wasn't worried so much about the temperature.... as you say it will probably stress relieve it. I'm more worried about the quenching/quick cooling the galv stuff gets normally. That said I'm now leaning back towards galvanising, following that up with powdercoat.

Since I spoke to Nige a while back and he suggested zinc passivating the axles I've discounted it as its going to wear to bear metal just as easily as paint. and as for leaving them bare after the zinc, they're not going to stay looking good. It didn't take long for my X-Brake to discolour.

The bare edge was my old worry with powdercoating them. Thinking back to the orignal question in relation to galvanising, I can't see the zinc compressing in the same way that paint or powder would. Am I right in thinking that?

Hammerite? :banned: I'd be better off painting them with liquid rust!

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There is powdercoat and then there is powder coat. Even with the best application of the appropriate product it will chip on an axle housing but it shouldnt peel off. As a somewhat random piece of information the most durable finish I came across was AkzoNobel zinc rich epoxy under coat powder followed by a polyester powder. Even then the pre treatment had a huge effect on durability (salt spray test). The parts were not blasted as it is not practical for production quantities (and it takes off zinc but powder coating over zinc is another story). Parts went through multiple degrease tanks followed by an acid wash and then a phosphate conversion process, which does key the surface somewhat.

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There is powdercoat and then there is powder coat. Even with the best application of the appropriate product it will chip on an axle housing but it shouldnt peel off. As a somewhat random piece of information the most durable finish I came across was AkzoNobel zinc rich epoxy under coat powder followed by a polyester powder. Even then the pre treatment had a huge effect on durability (salt spray test). The parts were not blasted as it is not practical for production quantities (and it takes off zinc but powder coating over zinc is another story). Parts went through multiple degrease tanks followed by an acid wash and then a phosphate conversion process, which does key the surface somewhat.

This would explain the amount of peeling stuff out there! Is the undercoat you mention a powder type? If it is then it could be the stuff that was mentioned to me the other day.

Powdercoating over zinc info would be great if you have any?

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Yes it is a bit strange the polyester overepoxy compared to composites. It was a couple of years ago when I was doing this but the epoxy powder was applied then did one loop of the oven and went straight through the polyester booth then two more loops of the oven. Im guessing this may work because the epoxy isnt fully cured when the polyester is applied. For my application the polyester was required for uv resistance.

Zinc.... the application I was involved with was mass production so the only economical process was the same as I outlined for steel but with a weaker acid and less time in the acid tank, this was for welded parts made from electroplated tube, in my opinion it took too much zinc of for it to be worth while, especially with Chinese quality control and production targets/bonuses. For one off work degreasing and a light blast with wallnut shell or similar would be the go. It goes get a bit more interesting though as the zinc ages, I think there are 3 stages, new zinc needs some form of mechanical keying, I cant remember the second stage but old zinc only requires the white oxide removed which can be done with a scrubbing brush, obviously these all need degreasing as well.

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