Landracing Forum
Tech Information => Technical Discussion => Topic started by: hotschue on February 26, 2011, 06:59:20 PM
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Can someone share their experience re: the effect salt has on a powdercoated chassis with regard to longevity and finish...thanks
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A lot of people do it; but, it is not recommended because cracks and problems can develop under the surface and not be detected.
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and you can't weld stuff on without a major hassle. Just paint it and clean it well
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My experience has been the powder coat is hard but brittle. Salt water gets under it and causes corrosion, as mentioned previously. My standard finish is primer topped with paint. Yesterday a bridge engineer gave me some advice at work. We have coastal bridges and salt s a problem. He said to use an "etch" zinc chromate primer for steel exposed to salt water. I do not know what that is.
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Because rust is an electro chemical process , isn't the zinc in the paint acting as a sacrificial anode .
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Living at the coast I use "etching" zinc chroma. as the base primer. When it is applied the primer etches the bare metal with microscopic "pits" to give the primer solids a firm grip and the zinc helps to short circuit the electrochem. process. I then use a "gray etching" primer prior to finish primer and top coat. This is not used on the body but frame and suspension componets. Airplanes, metal boats and the like use zinc chroma. as the base primer for corrosion protection. it is typically light green in color.
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Thanks for the replies....guess I know what I'm going to do. In the rush to make Aug.'10 didn't have time to prep chassis properly. Have now disassembled car, time to blast and sand chassis....let the "painting" begin. Have to admit powdercoat would have been the easy way out. Thanks all!
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My experience has been the powder coat is hard but brittle. Salt water gets under it and causes corrosion, as mentioned previously. My standard finish is primer topped with paint. Yesterday a bridge engineer gave me some advice at work. We have coastal bridges and salt s a problem. He said to use an "etch" zinc chromate primer for steel exposed to salt water. I do not know what that is.
We used that when painting Galvinized towers to get paint to stick.
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I agree that paint is a better choice for a frame. Powder coating is difficult to remove for repairs and could mask cracks.
As far as salt water getting under the coating, that is a sign of a poor powder coat job. All OEM automotive wheel are powder coated. The company I worked for produced 15 million wheels a year. Test wheels were exposed to excessive ultraviolet, hot salt spray, and other tests for months at a time. The wheels were cut to test adherence. Some wheels were scratched an then tested. Powder coating works.
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Zinc chromate primer is the light green you see inside surfaces of airplanes and also used on outside of airplanes under the topcoat. The main active corrosion preventative is the chromate. Chromate is also used on fasteners over zinc plating. It is what gives the very light blue appearance in a box of new hardware, or yellow/gold color. Zinc chromate is a good primer for almost anything to get good adhesion and corrosion resistance, but not for a filler primer. That is not what it is intended to be used for.
I agree on powder coating being able to hide cracks and also is difficult to remove for any welding. It is very good for corrosion resistance if applied correctly as stated.
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On the frames I have looked at, powder coating seems to offer better coverage than sprayed paint.
It was in every little nook and cranny, in order to get the same coverage with paint I think it would have to be dipped.
Don
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From a weldor/fabricator point of view I hope that no repairs or modifications are ever needed to the frame. It's ugly to work near and the fumes are baaaaad. Part of the problem is the material is applied to the frame with heat and when it's remelted during the welding process it can run just about anywhere. If it's applied correctly it can be very difficult to remove successfully, even with blasting, and that definitely doesn't contribute to the structural integrity of the weld.
Pete
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Go look at a 1990ish Toyota with tube bumpers and let me know how powder holds up in a tough environment
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I had a conversation with a powder coater a couple of months ago. He said the coating is pretty much paint with out the thinners/reducers.
I questioned whether on nice tubing, no rust, do you bead blast to give a tooth?
He said no, just a scuff pad. He pre-bakes bare parts and chassis at 400* to clean and degrease. Then applies the material to the cool part and goes into the oven again to melt the material.
So what you get is a plastic like coating that is made from the basic componants as paint.
I also asked why a primer is not needed and he had no good answer for that, just that it's not necessary.
We did find out that brake cleaner dissolves the coating. And that if scuffed, you can compound and get the shine back.
I wouldn't powder coat a chassis that was gonna get altered and updated every year.
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Don't use brake cleaner where you're going to weld. The heat of the weld causes the formation of phosgene gas. Even a very small dose can cause serious nerve damage or even kill you.
Pete
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Let me second the "DO NOT allow brake cleaner around welding" comment. I welded a small piece for my new streamliner that had been cleaned with brake cleaner, dried by compressed air & had sat untouched for a while. I thought it was safe to weld but the small residue unknowingly trapped in the joint created the gas, I breathed a very small amount & my racing plans abruptly ended for last year. The hospital bills & other expenses may keep the liner in the garage again this season. Now you ECTA guys know why we never returned with the SCREAMLINER.
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I have run in to the dreaded fumes but only with certain brands of brake clean. CRC brand in the red can delivered the worst fumes. All others I have used have no affect or put off gas during welding of cleaned parts. You guys must be real sick or old to have it shut you down for so long. Even with just a whiff? Or did you just keep breathing it. If so I dont know how you did it. Shits nasty as hell but never got sick from it.
Brian.
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There was a series of posts about how "Brewdude" the chopper builder almost killed himself after welding a part cleaned with brake cleaner. Don't take any chances. Rubbing alcohol is what I use for weld area cleaning after reading about Brew. It works almost as good as brake cleaner and it is safe.
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Acetone works really well for cleaning any traces of oil before tig welding and it doesn't give off any fumes as it evaporates almost instantly.
There are certain brands of brake clean that don't give off the phosgene gas but if you're foolish enough to take the risk then be prepared for the consequences. I too survived a couple of doses with no consequences, but that doesn't mean I'd get away with it again. Why take the chance? Too many have been seriously injured.
Pete
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There was a series of posts about how "Brewdude" the chopper builder almost killed himself after welding a part cleaned with brake cleaner. Don't take any chances. Rubbing alcohol is what I use for weld area cleaning after reading about Brew. It works almost as good as brake cleaner and it is safe.
Yeah, Steve Garn aka Brewdude is actually messed up for life from that deal.