James,
Excellent note. Thank you.
Jim
-----Original Message-----
From: James <James@LWSD.com>
To: William M. Gilroy <wmgilroy@lucent.com>
Cc: mgs@autox.team.net <mgs@autox.team.net>
Date: Sunday, November 01, 1998 10:19 PM
Subject: Re: Painting parts
>A technique for removing rust is etching with Phosphoric Acid. Phosphoric
>Acid has a unique property of dissolving iron oxide quickly while etching
>iron very slowly. This means that you can leave metal in Phosphoric Acid
>for much longer than necessary with very little damage. The acid will
>attack bare metal slowly and will start the process of hydrogen
>embrittlement, so use the minimum etch time that removes all rust.
>
>Another unique advantage of Phosphoric Acid is that it leaves a fine
>coating of iron phosphate behind. Iron phosphate prevents rust. However,
>the iron phosphate coating is not very thick and not durable. Some
>additional protection is still required.
>
>Phosphoric Acid etch will leave a hard, bright metal finish. This is
>because it will etch the surface slightly, exposing new, bare metal. Often
>this is desirable. It leaves an attractive surface and a surface ready to
>paint. A common product which contains Phosphoric Acid is Naval Jelly.
>
>Auto body shops treat metal with acid metal wash, a solution of Phosphoric
>Acid and alcohol, before painting. This removes waxes and oils, removes
>slight amounts of rust that form between sand blasting and painting, and
>leaves a thin protective coat of iron phosphate. One commercial solution
>for this is DuPont Quick-Prep. Sherwin Williams has a similar product
>called Metal Prep.
>
>One more technique for removing rust is Electrolytic Rust Removal. Rust can
>be electrically etched off of iron or steel in a bath of mild alkali, such
>as Sodium Carbonate (swimming pool supply stores. Ask for product to raise
>water pH). Connect the rusty part to the negative terminal of a 12V battery
>or battery charger and a scrap piece of steel or iron to the positive
>terminal. Use one tablespoon of Sodium Carbonate per gallon of water. This
>technique has many advantages. First, the alkaline solution is much safer
>than some of the acids mentioned above. It is still a chemical, so rubber
>gloves and splash goggles are recommended. Another advantage of
>electrolytic rust removal is that it will have no effect on good metal, so
>you can leave the work in the bath for a long time and not damage the
>metal. There is no risk of hydrogen embrittlement nor of etching unrusted
>metal.
>
>Electrolytic rust removal will leave a black oxide surface, which is the
>result of a process that doesn't remove any good metal at all. The only
>thing removed is loose rust and embedded oxygen. If your goal is to keep as
>much of the original metal behind, this is the best technique.
>
>After removing ALL of the rust, I prep and spray immediately with a
>zinc-based primer, followed by a regular red primer, followed by the final
>color. Allow plenty of time (days, not hours) in between coats, or you'll
>be dealing with soft paint while you're trying to re-assemble parts. Powder
>coating, of course, is nice if you really want to go whole hog.
>
>- James Einolf
>'74 MGB (almost finished replacing the rear brakes that rusted solid and
>were *disconnected* by the DPO - without telling me when I bought it, of
>course....)
>
>>I was wondering what is the best way to prepare and paint parts.
>>Over the next couple of weeks I will be redoing my front suspension.
>>While I have it apart I would like to paint the A-arms, kinpins,
>>radiator shroud, etc. All of the following would address both
>>painting with an air compressor and without an air compressor. Currently
>>I don't have one but I will be buying one in the next couple of months.
>>
>>1. What is the best way to prepare the surface?
>>2. What type of primer and paint?
>>3. What is the most durable?
>>4. Should special paint be used for higher temp. items such as
>> radiator shrouds, coolant overflow containers, etc.
>>
>>I was just going to clean off all of the grease, remove the loose paint
>>and rust with a wire brush, and spray it with a can for rust-o-lem (sp?)
>>black. Am I missing anything? My main concern is that I spend time
>>doing this and then the paint chips or peels off in a short period of
time.
>>Any advice?
>>
>>Thanks,
>>
>>Bill Gilroy
>>77 Midget
>>wmgilroy@lucent.com
>
>
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