Plating Info

Zinc is the most popular of all commercial platings because it is relatively economical and offers good corrosion resistance in environments not subject to excessive moisture. A clear or blueish chromate finish is applied on top of the zinc to provide additional protection against white oxidation spots which can form due to moisture. Electroplating is the most common way of applying zinc coatings to fasteners. It is recommended by certain industry experts that case-hardened parts which are electro-plated should be baked after plating to minimize the risk of hydrogen embrittlement.

Yellow chromate offers a greater degree of protection from white corrosion than does clear chromate. Electroplating is the most common way of applying zinc coatings to fasteners.

The ASTM B633 standard was revised in 2007. One of the changes concerned the amount of time certain fasteners are baked to reduce the effects of hydrogen embrittlement. Prior to this revision, plated Grade-BD cap screws were required to be baked for at least 4 hours at a temperature of 190ºC to 220ºC. The new standard calls for these parts to be baked for at least 10 hours at 190ºC to 220ºC. All of the manufacturers we use for making Grade-BD cap screws meet this standard.

Black chromate offers a similar appearance to black oxide but with greater degree of protection that black oxide lacks. Electroplating is the most common way of applying zinc coatings to fasteners.

A wax lubricant is added to the zinc coatings of certain fasteners to improve the ease of assembly. This is the standard plating for trilobular thread rolling screws as well as two-way reversible center-lock nuts. Case-hardened parts are still recommended to be baked after plating.

Mechanically applying zinc to fasteners reduces the risk of hydrogen embrittlement forming within the parts. This minimizes the need for the precautionary practice of baking the parts soon after plating. A clear or bluish chromate finish is applied on top of the zinc to provide additional protection against white oxidation spots, which can form due to moisture. It is common for lock washers made from spring steel to be plated this way to avoid brittleness after baking.

This finish is identical to mechanical zinc but with a yellow chromate finish. This is the standard plating for high-alloy split lock washers and for tooth lock washers used with zinc yellow machine screws.

Socket cap screws can receive a zinc plating of 0.0002 inches thickness. A clear chromate finish is applied on top of the zinc to provide additional protection against white corrosion. The manufacturer must be notified prior to the thread rolling process that the parts are to be plated. The plated parts are then baked at 375ºF for 24 hours within one hour of plating then subjected to a 72-hour stress test.

Commercial zinc green is the finish applied to machine screws and thread-cutting screws that will be used a “grounding screws” in electrical applications.

Zinc/Nickel is selected to achieve the highest resistance to corrosion with the smallest thickness of protective coating. Typically, the nickel content of the alloy finish is 12-15%. The finish will withstand a minimum 1,000 hour Salt Spray test.

A three-layer coating consisting of (1) a metallic zinc layer, topped with a (2) chemical conversion film layer, which is finally covered by a (3) baked ceramic surface coating. The finished parts have a dull silver color and will withstand a minimum of 1,000 hour Salt Spray test.

Nickel has more of a silver color to it than zinc and has similar corrosion resistant characteristics. It is the standard finish of cap nuts, countersunk finishing washers, brass spacers and standoffs, as well as other parts to achieve a more decorative appearance.

Tin plating is sometimes used on parts in the food handling industry because it resists organic acid. It improves the lubricity of steel and offers a high degree of corrosion resistance.

Silver is an excellent conductor of electricity. Its benefits are both decorative and protective as it resists thread galling when mated parts are under extreme pressure or exposed to extreme heat.

Cadium plating results in a smoother surface and greater resistance to white oxidation spots than zinc plating. However, cadmium is a much more toxic metal than zinc, which makes the plating process more difficult and costly. The standard most commercial platers use when applying cadmium is a minimum thickness of .0002 inches. A supplemental wax coating is often added as a lubricant when cadmium is used on prevailing torque lock nuts.

Electroplated screws, which are case hardened, should be baked for a minimum of 4 hours within the temperature range of 375-450ºF no later than 4 hours after the plating operations. However, this process does not guarantee that hydrogen embrittlement will not still be present after baking or that it will not occur at a later date while in service. Specialized testing or a substitute part may be required, depending on the application. This heat treatment practice is recommended for tapping screws, drywall screws, SEMS screws, clinch nuts and clinch studs.

This process enhances stainless steel’s corrosion resistance. The fasteners are dipped in a solution, which removes surface imperfections and produces a slight film on the surface of the parts.

This is the standard finish for most drywall screws, particle board screws and retaining rings. It can have either a dull or bright appearance. No additional oil treatment is required.

The most common standard coating of black phosphate and oil is 1100mg per sq./ft., minimum. The oil serves as a rust inhibitor and a lubricant. Some fasteners with this plating are required to pass a salt-spray test, the duration and cost of which must be agreed upon between buyer and seller prior to the sale. Floorboard screws, frame bolts, Grade-GT locknuts and spring nuts are usually supplied with a black phosphate and oil finish.

This is a “conversion coating” which means it is formed by a chemical reaction with the metal to form an integral surface, as opposed to an “applied coating” like zinc which bonds to the metal. Black oxide on steel offers no corrosion resistance unless an oil or wax finish is applied as a rust inhibitor. Black oxide on stainless steel yields excellent corrosion protection due to the properties of the base metal. For more information about black oxide.

Chrome plating can be done in two ways: 1) A “hard chrome” finish deposits a thick layer of chrome on the part. This gives the fastener a very hard finish and superior wear resistance but does not offer much protection to corrosion; 2) A “nickel-chrome” finish is achieved by applying a flash of chrome on top of the nickel plating. This offers resistance to tarnishing and corrosion.