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Powder coating sheet metal

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mmkid
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PostPosted: Wed Apr 03, 2019 5:09 am    Post subject: Powder coating sheet metal Reply to specific post Reply with quote

Do guys have sheet metal sandblasted and powder coated?
I am by no means a painter. And I don?t wsnna wire wheel all
this stuff really. I?m not concerned about a few imperfections in
the metal that would look better if they were bondoed and
sanded. Or is sand blasting to extreme and could damage it?
Thanks. Just had a couple sets of 9 bolt rims sand blasted
and powder coated and having this done just seems like the
way to go.
 
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yakob
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PostPosted: Wed Apr 03, 2019 5:24 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

CVPost-mmkid wrote:
(quoted from post at 08:09:42 04/03/19) Do guys have sheet metal sandblasted and powder coated?
I am by no means a painter. And I don?t wsnna wire wheel all
this stuff really. I?m not concerned about a few imperfections in
the metal that would look better if they were bondoed and
sanded. Or is sand blasting to extreme and could damage it?
Thanks. Just had a couple sets of 9 bolt rims sand blasted
and powder coated and having this done just seems like the
way to go.


Sand blasting can damage sheet metal but that doesn't mean that it will. It has more to do with the technique and blasting material than anything.

You might want to see how the rims hold up over the next 5-10 years before you go all in on powder coating. I've read a lot of posts where guys coated wheels and were very happy like yourself but then once a scratch finally does happen, the coating just flakes back from there.
 
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North Maine
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PostPosted: Wed Apr 03, 2019 3:07 pm    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

CVPost-mmkid wrote:
(quoted from post at 09:09:42 04/03/19) Do guys have sheet metal sandblasted and powder coated?
I am by no means a painter. And I don?t wsnna wire wheel all
this stuff really. I?m not concerned about a few imperfections in
the metal that would look better if they were bondoed and
sanded. Or is sand blasting to extreme and could damage it?
Thanks. Just had a couple sets of 9 bolt rims sand blasted
and powder coated and having this done just seems like the
way to go.


Why not sand blast and then paint? That's what I'm doing to my 3020... I'm not a fan of wire wheeling, plus the mechanical adhesion that occurs with epoxy over a blasted surface can't be beat!
 
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showcrop
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PostPosted: Wed Apr 03, 2019 5:25 pm    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote


I have a number of things that are powder coated. The thrower on my baler, some parts of some tractors that I have repainted, my 22,400 tandem dual trailer and some others. The problem with it is if it is out in the weather and gets scratched, the rust spreads much faster under it than it does under paint. If you were to prime it first with paint it would last much better, but then you lose the advantage of powder coat.
 
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504
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PostPosted: Wed Apr 03, 2019 6:06 pm    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

I keep looking, but I just keep seeing huge pieces of power coat falling off,with rust 1/8 thick
going with it. Give me paint. FYI the powder coat company's here sand blast everything before they
coat.
 
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Stephen Newell
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PostPosted: Wed Apr 03, 2019 6:37 pm    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

Sand blasting or using a wire wheel would only help adhesion. The only thing that is different about powder coating is instead of spraying a liquid primer on the metal the metal is charged with static electricity and the polyester powder is sprayed on. Then the metal is put in an oven so the powder melted together and to the metal.
 
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North Maine
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PostPosted: Thu Apr 04, 2019 5:55 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

CVPost-Stephen Newell wrote:
(quoted from post at 22:37:45 04/03/19) Sand blasting or using a wire wheel would only help adhesion. The only thing that is different about powder coating is instead of spraying a liquid primer on the metal the metal is charged with static electricity and the polyester powder is sprayed on. Then the metal is put in an oven so the powder melted together and to the metal.


Yes that is the process, however that “only thing that is different” is a significant difference. Powder coating frequently suffers undercutting at a scratch or chip that leads to large scale coating failure. While this can also happen on a traditionally painted panel it is far less likely on a surface that has been blasted and epoxy primed before topcoating.
 
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yakob
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PostPosted: Thu Apr 04, 2019 6:43 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

North Maine wrote:
(quoted from post at 08:55:23 04/04/19)
CVPost-Stephen Newell wrote:
(quoted from post at 22:37:45 04/03/19) Sand blasting or using a wire wheel would only help adhesion. The only thing that is different about powder coating is instead of spraying a liquid primer on the metal the metal is charged with static electricity and the polyester powder is sprayed on. Then the metal is put in an oven so the powder melted together and to the metal.


Yes that is the process, however that “only thing that is different” is a significant difference. Powder coating frequently suffers undercutting at a scratch or chip that leads to large scale coating failure. While this can also happen on a traditionally painted panel it is far less likely on a surface that has been blasted and epoxy primed before topcoating.


Yeah, that "only thing that is different" followed by a list of differences made me giggle a bit.

I've heard of some powder coaters putting epoxy primer on before doing the powder. I don't know how the long term durability of this is...it would make sense that now there is a "protective" layer to keep rust from spreading, but at the same time is it OK for epoxy primer to be baked on that hot???
 
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North Maine
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PostPosted: Thu Apr 04, 2019 11:53 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote


most epoxies hit their "glass transition temperature" where they chemically start to breakdown around 140F though I know of some marine industry tank linings that are rated for 180F. Never anything as high as powder coat baking temps thought.
 
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yakob
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PostPosted: Thu Apr 04, 2019 11:55 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

North Maine wrote:
(quoted from post at 14:53:16 04/04/19)
most epoxies hit their "glass transition temperature" where they chemically start to breakdown around 140F though I know of some marine industry tank linings that are rated for 180F. Never anything as high as powder coat baking temps thought.


A quick google shows me one that is rated for 400F:

http://www.ppgaerospace.com/Products/Coatings-Removers-Cleaners/Commercial-Civil-Aviation/Specialty-Products/DeSoto%C2%AE-519X303-High-Temperature-Epoxy-Primer.aspx

Looks expensive Embarassed
 
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paintron
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PostPosted: Fri Apr 05, 2019 9:44 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

My current employer paints a lot of sheet metal, millions of pounds. Paint won't properly stick to most of it, with a few exceptions, without a pretreatment. Zinc phosphate is by far the best, many chrome based treatments also work or you could use a wash primer which is a treatment and primer in one.

Prime it next, usually a epoxy or urethane are good choices through their are others, then powder coat.
 
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yakob
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PostPosted: Fri Apr 05, 2019 9:50 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

CVPost-paintron wrote:
(quoted from post at 12:44:26 04/05/19) My current employer paints a lot of sheet metal, millions of pounds. Paint won't properly stick to most of it, with a few exceptions, without a pretreatment. Zinc phosphate is by far the best, many chrome based treatments also work or you could use a wash primer which is a treatment and primer in one.

Prime it next, usually a epoxy or urethane are good choices through their are others, then powder coat.


I'm going to have to bite on this one:

What on Earth is going on that they can't get paint/primer to stick without pretreatment?

In auto refinishing the only time a treatment is really mentioned is when we are trying to dissolve away rust that is in a stubborn place or where sandblasting isn't going to work, etc...

Epoxy gives you a mechanical bond. I'm assuming that in your industry blasting/sanding is not suitable for some reason?
 
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paintron
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PostPosted: Fri Apr 12, 2019 8:58 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

When us OEM guys get together, you would not believe the humour when we discuss the various shows on TV where cars motorcyles etc. painted are repainted. Mechanical adhesion is only on type of adhesion and not remotely as effective as chemical bonding.

Paint on it's own is porous and will not stop corrosion for any length of time. Fortunately I have had access to salt spray chambers in most of my previous and current position and have seen first hand how various treatments vs no treatment effect the finished product. .
 
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yakob
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PostPosted: Fri Apr 12, 2019 9:13 am    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

paintron wrote:
(quoted from post at 11:58:03 04/12/19) When us OEM guys get together, you would not believe the humour when we discuss the various shows on TV where cars motorcyles etc. painted are repainted. Mechanical adhesion is only on type of adhesion and not remotely as effective as chemical bonding.

Paint on it's own is porous and will not stop corrosion for any length of time. Fortunately I have had access to salt spray chambers in most of my previous and current position and have seen first hand how various treatments vs no treatment effect the finished product. .


So you are saying that epoxy has a chemical bond with pretreatments that have been applied and cured before moving to the epoxy? Sure, the treatment reacts chemically with the metal, but the next step is not another chemical bond.

Of course certain treatments will affect the finished product in certain ways, but it is not always relevant or necessary. If I'm painting a medicine cabinet then I can probably get by with Rustoleum for 100 years on it because it stays dry and out of UV light. Some of your "industrial" applications may need every last bit of help they can get for corrosion resistances, but a tractor (esp. a restoration)? Come on. Even the synthetic enamels and primers the equipment dealers sell aren't going to show you corrosion issues. The salt spray test simulates just that -- salt spray.

I'm not against the treatments totally. They are useful in a lot of cases. Mostly I'm interested them for the under-body and frame of a car. A blanket recommendation for them is adding extra cost, hassle, and room for error, especially for a typical DIY'er.
 
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David G
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PostPosted: Fri Apr 12, 2019 5:33 pm    Post subject: Re: Powder coating sheet metal Reply to specific post Reply with quote

I personally do not believe powder coating adheres as good as primer/paint, have seen two much peel off.
 
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