Recent arrivals to the cleaning arsenal, such as poly and flap wheels that mount on small angle grinders and small, inexpensive pneumatic scrapers and needle scalers, can make a huge difference in your cleaning practices and results.
I hope that you find the material that is presented here useful. That was my intent.
BASIC METAL CLEANING CONSIDERATIONS
Whatever great project plans you have, if the metal on which they are based is corroded or otherwise contaminated, your plans will founder sooner rather than later. Although some factors in metal projects cannot be controlled, the surface condition of metal is largely within the range of what you can make go your way for most purposes.
I am not talking about “laboratory or metallurgically clean” here. I am describing the level of cleanliness necessary for successful painting, welding, brazing, soldering, plating, and more. If you think that there must be exceptions to the necessity for clean metal as the basis for some projects and purposes, you are probably right. Cast-iron boat anchors come readily to mind.
Is achieving clean metal easy to do? Yes and no. It depends on your facilities, your skills, your judgment, and the size and nature of what you are trying to clean. Let’s survey some of the possibilities.
The first consideration is the size of your object. Obviously, cleaning the metal in a piece of jewelry is very different from cleaning an auto body, which is very different from cleaning an airplane or ocean liner. In this book I stick with the jewelry-to-car size range and leave the likes of ocean liners, airplanes, and boxcars to the specialists in those fields.
This 1930s fender provides a good example of the enemy: dirty, rusted metal. A band of metal with some paint on it is visible through the middle of the photo, with superficial rust coming through the paint. The top and bottom of the photo show flaking and deep, pitting rust.
The size of an item often determines what cleaning processes can and cannot be used. For example, immersion in chemical cleaners, use of electrolytic “dip tank” processes, or car factory “pickling baths” and “e-coat” painting are practical up to the automobile end of the size range. However, ultrasonic cleaning, another liquid process, is limited to smaller parts because the cost of the equipment for this process increases radically with tank size.
Small parts such as this sheet-metal cover are usually much easier to clean than larger parts. Abrasive blasting, wire brushing, and chemical treatment and dipping are among the obvious ways to deal with them.
With medium-size items you may have fewer cleaning options than with very small items. After you remove grease and grime with solvent (to avoid contaminating the equipment during the next step), a trusty stationary electric wire brush wheel gives you a good start for removing rust and paint.
Large parts and panels such as this 1940s hood offer even fewer cleaning options. Dipping in chemicals is usually impractical. Even with handheld power equipment, wire brushing tends to be too slow and less than fully effective.
Disc sanding is an obvious choice for cleaning this hood. It’s reasonably fast and, if done carefully, avoids damage to the metal. This is how body panels were traditionally stripped of paint and surface rust.
Abrasive blasting with the appropriate media is another way to clean large panels, such as this hood. A lot of air and a well-isolated location are needed, too, along with considerable skill to avoid warping the sheet metal.
Small, delicate items such as this hood shutter thermostat must be handled very carefully to avoid damage. Ultrasonic cleaning works well for this part, but ultrasonic tank systems that can hold larger parts are very expensive.
Some cleaning jobs benefit greatly from automation. The cylinder heads shown here were oven baked for 20 minutes at 400 degrees F, bombarded with steel shot (that was generated airlessly), tumbled in the device shown here to remove the shot, and then jet washed to remove any remaining contamination. The system efficiency is outstanding.
Metals corrode in different ways. A badly corroded aluminum alloy step plate is shown on the left. At center is a piece of copper that is polished on its left side and in various stages of corrosion on its right side. The steel bumper cover on the right exhibits common red rust.
No doubt about it. This bronze emblem is very delicate. It needs special attention to get its surface down to clean metal so that its recesses can be painted and its raised sections polished. Soda blasting, shown here, is ideal to accomplish an initial, gentle cleaning.
Here’s a metal-cleaning nightmare. Nothing delicate about it! This incredibly rusted cap screw should be scrapped and replaced. As rugged as it was, no amount of cleaning can return it to structural integrity. Sometimes cleaning isn’t enough. It is important to know when that’s the case.
Quantity is also an issue in choosing a cleaning process. I once had a contract to clean and refinish several thousand 1-inch-diameter upholstery tacks that had cast, embossed, brass heads. I determined experimentally that I could clean and refinish these items with motor-driven wire brush wheels, composition wheels, and conventional buffing equipment and compounds. This whole manual process used about five minutes of labor per tack. However, that result, 12 tacks per person/hour, was unacceptable. It would have made my bid for the job non-competitively high. Hand finishing worked fine for a dozen tacks, or even a hundred, but not for a few thousand.
Ultimately, I settled on a combination of tumbling and vibratory cleaning, followed by light hand buffing.