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Parkerizing

Parkerizing (also called phosphating and phosphatizing) is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of an electrochemical phosphate conversion coating. Parkerizing is usually considered to be an improved zinc or manganese phosphating process, and not to be an improved iron phosphating process, although some use the term parkerizing as a generic term for applying phosphating (or phosphatizing) coatings that does include the iron phosphating process. Parkerizing is commonly used on firearms as a more effective alternative to bluing, which is another electrochemical conversion coating that was developed earlier. The Parkerizing process cannot be used on non-ferrous metals such as aluminum, brass, or copper. It similarly cannot be applied to steels containing a large amount of nickel, or on stainless steel. (See Passivation for protecting other metals.) Application The process involves submerging the metal part into a phosphoric acid solution whose key ingredient is often zinc or manganese, with varying additional amounts of nitrates and chlorates and copper. In one of the many processes that have been developed, the solution is heated to a temperature of 190-210 °F (88-99 °C) for a period ranging between 5 and 45 minutes. A stream of small bubbles is emitted from the metal part as the process takes place; when the bubbling stops, the process is complete. In addition to this particular processing temperature, there have also been various similar Parkerizing processes developed and patented that permit using either lower temperatures (for energy efficiency) or higher temperatures (for faster processing). Appearance and usage Zinc phosphating results in a non-reflective, light- to medium-gray finish. Manganese phosphating produces a medium- to dark-gray or black finish. Iron phosphating produces a black or dark gray finish similar to manganese phosphating. The grain size of the zinc phosphating is usually the smallest among the three processes, providing a more appealing cosmetic appearance in many applications. Many firearms that are Parkerized turn to a light greenish-gray color within a few years, as the coating ages, with the protective coating remaining intact. Cosmoline, especially, interacting with Parkerizing, can cause the highly-desired and attractive greenish-gray patina to develop on firearms that are stored in armories. Manganese and iron phosphating coatings are usually the thickest electrochemical conversion coatings, being thicker than electrochemical conversion coatings such as zinc phosphating and bluing. All of the electrochemical conversion coating finishes are not painted coatings, but chemically become part and parcel of the metal surface to which they are applied. As for all electrochemical conversion coatings, the Parkerized surface must be completely covered with a light coating of oil to maximize corrosion and wear resistance, primarily through reducing wetting action and galvanic action. A heavy oil coating is unnecessary and undesirable for achieving a positive grip on Parkerized metal parts. Alternatively, the Parkerized surface may be painted over with an epoxy or molybdenum finish for added wear resistance and self-lubricating properties.

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