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Stainless steel is a wonderful material, providing a strong, attractive, waterproof and “stainless” finish to many different types of products, such as appliances, hand-rails, tanks, etc. But stainless does not always remain rust-free, and it often needs cleaning, especially outdoors or in environments around food, pharmaceuticals or other chemicals. At the same time, when preparing stainless steel for fabrication or finishing, it’s essential to ensure the surface is clean. There are fundamental differences in these two ways of cleaning stainless steel.
Cleaning Stainless Appliances
When cleaning the surface of stainless steel appliances, vent hoods or tanks, start with the simplest solutions first. Water, a drop of dish soap, and a microfiber cloth applied with elbow grease can accomplish a lot. Be sure to dry off any leftover water to prevent streaking. To shine the finish, rub a cloth containing a couple drops of mineral oil in line with the metal grain. If the surface shows cloudy oxidation or rust, use a non-toxic, non-acidic product such as Flitz Polish to remove the oxidation. For heavier stains, grease, mold or rust, use a commercial stainless steel cleaner that contains a degreaser.
Metal Surface PreparationIn the process of making a stainless steel product, oxide scale can form on the steel as a result of hot rolling, thermal treatments, welding, and brazing. Lubricants and coolants may be applied to the stainless during cutting and forming operations and bits of metal from cutting tools may become embedded in the surface. Shop dirt, fingerprints, and grime may accumulate on the stainless during handling and storage, and even protective paper or plastic sheets may permanently adhere to the surface over time. All these contaminants must be removed in the surface preparation process before welding, priming, painting, electro-static painting, and powder coating stainless steel.
Is Stainless Steel Really Stainless?Stainless steel contains at least 10 percent chromium, which is a highly reactive metal. The chromium on the surface of a piece of stainless oxidizes (rusts) quickly in the presence of oxygen or water molecules in the atmosphere. These oxidized chromium molecules form a very thin, tight film, called a passivation layer that acts as a barrier against the surrounding air, preventing any further oxidation of the steel.
But when this protective film is broken up in the process of manufacturing, a heavy scale can form on the surface. This scale could cause a welding or adhesion failure, and it is removed by “pickling,” or applying a combination of acids to the surface. Typically nitric acid is part of the solution, because it encourages the passivation layer to form. Another method for removing scale from stainless steel is sandblasting.
Certain types of welding can create a light scale or a heat tint discoloration on the surface. Any type of screw holes or other attachment points that create a break in the passivation film leave the stainless susceptible to rust.
Applying a pickling solution or metal degreaser to remove oil, grease, scale and rust should be followed by a protective coating to prevent further rust and leave a brighter surface finish.
Industrial Metal Supply carries cleaners, polishers, and degreasers for stainless steel and a range of ferrous and non-ferrous metals.