You can try Naval Jelly, available in hardware stores, made for removing rust. When rust is very bad I end up sanding and painting a chassis. The best paint I've found is called stainless steel. It's made for touching up appliances.
Norm
:I have picked up an old Stewart Warner, mid-20s battery set, with a very rusty chassis. Any recommendations as to how to clean?
If you are willing to completely strip all parts from the chassis, the following method will hold up well for many years. This method can be used for all steel parts, including rusty hardware such as screws, nuts, washers, etc., and requires them to be completely submerged in phosphoric acid until all visible rust is removed.
A somewhat weak solution of phosphoric acid named Metal Prep is available in gallon jugs at automotive paint stores, and will serve your purpose well. It is meant to be mixed with water for auto body preparation, but you will be using it full strength. Any glass, wood, or plastic container of suitable size can be used for a vat.
Before dipping, clean all loose rust or scale from the chassis. Once in the solution, very light rust will immediately begin to disappear, but heavier rust will take longer. Maybe overnight or even longer. Phosphoric acid etches steel, so if the chassis is soaked for several days, the thickness of the metal may be measurably thinner. The temperature of the solution is a factor, so keep it at room temperature or higher. Heating is OK for faster results, but keep it well below the boiling point.
When removed from the solution, DO NOT FLUSH WITH WATER, and allow the chassis to dry. You will know it is completely dry when a white powder looking substance forms on the metal. This may take over night if the humidity is high. Some dark spots may be visible on the surface when dry. If present, this is rust in the deeper pits, but don’t worry about it if all scale was removed before hand.
Now, here is the important part. As long as this phosphorus coating on the surface remains dry, the chassis will never rust. A nice even coat of paint will keep moisture from this coating, so it makes an excellent primer. Prior to painting, lightly scrub the chassis with a scuff pad, just enough to remove the excess.
Use a high temperature engine and exhaust manifold paint rated at 1000 to 1200 degrees. I’ve tried high temperature paints rated at lower temperatures, but they did not give good results. This type of paint is available in spray bombs from automotive stores, but it must be cured at a high temperature. Without proper curing, your finished chassis will look exactly like what it was painted with. A cheap silver spray bomb.
Spray the chassis heavy enough for good solid coverage, but don’t try to build it up with several coats. After it has air dried, it should be safe enough to begin baking. I have had good results with a 500 degree oven, but a higher temperature would probably be better. I usually bake for a few hours, but less time would probably be good enough. The idea here is to make certain that all the solvents have been worked out of the finish, including any moisture that may remain from the phosphoric acid. You probably won’t see it when it happens, but when the temperature of your chassis gets high enough, the paint will flash to a brighter finish. After the solvents have worked out, the finish should be thin and hard as nails. A successful finish should appear more like a thin plating, rather than a layer of paint. Your results will vary depending on the condition of the metal to begin with, and also the brand of paint that you use.
::I have picked up an old Stewart Warner, mid-20s battery set, with a very rusty chassis. Any recommendations as to how to clean?
:
:If you are willing to completely strip all parts from the chassis, the following method will hold up well for many years. This method can be used for all steel parts, including rusty hardware such as screws, nuts, washers, etc., and requires them to be completely submerged in phosphoric acid until all visible rust is removed.
:
:A somewhat weak solution of phosphoric acid named Metal Prep is available in gallon jugs at automotive paint stores, and will serve your purpose well. It is meant to be mixed with water for auto body preparation, but you will be using it full strength. Any glass, wood, or plastic container of suitable size can be used for a vat.
:
:Before dipping, clean all loose rust or scale from the chassis. Once in the solution, very light rust will immediately begin to disappear, but heavier rust will take longer. Maybe overnight or even longer. Phosphoric acid etches steel, so if the chassis is soaked for several days, the thickness of the metal may be measurably thinner. The temperature of the solution is a factor, so keep it at room temperature or higher. Heating is OK for faster results, but keep it well below the boiling point.
:
:When removed from the solution, DO NOT FLUSH WITH WATER, and allow the chassis to dry. You will know it is completely dry when a white powder looking substance forms on the metal. This may take over night if the humidity is high. Some dark spots may be visible on the surface when dry. If present, this is rust in the deeper pits, but don’t worry about it if all scale was removed before hand.
:
:Now, here is the important part. As long as this phosphorus coating on the surface remains dry, the chassis will never rust. A nice even coat of paint will keep moisture from this coating, so it makes an excellent primer. Prior to painting, lightly scrub the chassis with a scuff pad, just enough to remove the excess.
:
:Use a high temperature engine and exhaust manifold paint rated at 1000 to 1200 degrees. I’ve tried high temperature paints rated at lower temperatures, but they did not give good results. This type of paint is available in spray bombs from automotive stores, but it must be cured at a high temperature. Without proper curing, your finished chassis will look exactly like what it was painted with. A cheap silver spray bomb.
:
:Spray the chassis heavy enough for good solid coverage, but don’t try to build it up with several coats. After it has air dried, it should be safe enough to begin baking. I have had good results with a 500 degree oven, but a higher temperature would probably be better. I usually bake for a few hours, but less time would probably be good enough. The idea here is to make certain that all the solvents have been worked out of the finish, including any moisture that may remain from the phosphoric acid. You probably won’t see it when it happens, but when the temperature of your chassis gets high enough, the paint will flash to a brighter finish. After the solvents have worked out, the finish should be thin and hard as nails. A successful finish should appear more like a thin plating, rather than a layer of paint. Your results will vary depending on the condition of the metal to begin with, and also the brand of paint that you use.
:
About the only experience I have had with self cleaning ovens in relation to radio repair, is melting the tar out of Atwater Kent power supplies. They are a life saver when that stinking stuff spills out in the bottom of the oven. The self cleaning feature will reduce it to a light gray dust, and the wife won’t even be able to smell it when she gets home.
Thomas
Back when I was restoring automobiles, I used phosphoric acid dips for body parts, and if large chrome parts such as bumpers were rusty, I had them dipped as well. This kept them free from rust until the chrome shop finally got around to plating them.
Generally speaking, I prefer chemical stripping over sandblasting, especially for steel sheet metal parts. I live in an area where the humidity is usually high, and have seen a very light rust color forming on the metal a few minutes behind my work. Then to, sandblasting peens the metal on the side that is being blasted, and if the metal is too light, it will warp. Glass bead blasting is usually safer on more delicate parts, but I have learned to stay away from all forms of blasting on thin sheet metal.
As for a chassis that was originally zinc plated, I never found a shop in my area that can duplicate this finish on automotive parts, so have not tried them since I began restoring radios. Dull nickel worked fair in some cases if it was not buffed. I have been told that silver zinc with a clear chromate dip may be what I am looking for, but I have never tried it and have no idea what it looks like. In reality, most of the radios that I have redone just haven’t been worth the expense of a plating shop. However, some of the radios that I have restored for contest display would have been worth it, had it been needed. Fortunately, my contest radios were usually manufactured before plated chassises were in use.