Several Types Of Fastener Surface Treatment

The fastener is a very basic and important part, which is widely used in many fields, and the surface treatment of the fastener is also a very significant issue. As a professional fastener manufacturer, Xinchi Fastener Company would like to share several types of fastener surface treatments, hoping to be helpful.

Electro galvanizing

Electro galvanizing is the most commonly used coating for commercial fasteners. It is cheaper and has a better appearance. It can be black or army green. However, the corrosion resistance of the electro-galvanizing coating is not so good, and its corrosion resistance is the lowest among zinc plating (coating) layers. Under normal circumstances, electro galvanizing neutral salt spray test is within 72 hours. There is also a special sealer, which makes the neutral salt spray test of galvanizing reach more than 200 hours, but the price is more expensive, which is 5~8 times the general galvanizing.

It is easy to produce hydrogen embrittlement during the process of electro-galvanizing, so a galvanized finish is generally not used for bolts above grade 10.9. Although dehydrogenation can be done by oven after plating, it must be done before passivation after plating because the passivation film will be destroyed above 60℃. In this case, the maneuverability is poor and the processing cost is high. In reality, the general production plant will not actively dehydrogenate unless mandated by a specific customer.

Electrogalvanized fasteners have poor torque-preload consistency and are unstable, so they are generally not used to connect important parts. In order to improve the consistency of torque-preload, the method of coating lubricating material after plating can also be used.

Black oxide finish

Blackening + oiling is a popular coating for industrial fasteners because it is the cheapest and looks good until the oil runs out. Since blackening has little protection against rust, it will rust quickly without oil. Even if there is oil, the neutral salt spray test of blackened fasteners can only reach 3~5 hours.

Blackened fasteners also have poor torque-preload consistency. If needed, we can grease the inner threads before screwing the fasteners.

Cadmium (electro)plating

Cadmium coatings have good corrosion resistance, especially in the oceanic atmosphere, and their corrosion resistance is better than that of other surface treatments. The waste liquid produced in the process of cadmium plating is expensive to deal with. The cost of cadmium plating is high, and its price is about 15~20 times that of galvanizing. Therefore, cadmium plating is not used in the general industry. It is only used in some specific environments, such as fasteners for oil drilling platforms and Maritime aircraft.

Chromium plating

Chromium coating is very stable in the atmosphere and does not easy to discolor and lose luster, as well as high hardness and wear resistance. Chrome plating on fasteners is generally used for decorative purposes. Chrome plating is rarely used in industries where corrosion protection is required because good chrome plating fasteners are as expensive as stainless steel. Only when stainless steel is not strong enough, chrome-plated fasteners are used instead.

To prevent corrosion, copper and nickel should be plated before chrome plating. Chromium plating can withstand temperatures as high as 1,200 degrees Fahrenheit (650 degrees Celsius). But it also has the same problem of hydrogen embrittlement as electro-galvanizing.

Silver and nickel plating

The silver coating can not only prevent corrosion but also be used as a solid lubricant for fasteners. For cost reasons, nuts may be silver plated, but bolts are not, and sometimes small bolts are also silver plated. Therefore, silver is used in fasteners that work at high temperatures because of its high-temperature resistance and lubrication properties, to prevent bolts and nuts from being bitten by oxidation.

Fastener nickel plating is mainly used for both anti-corrosion, and good electrical conductivity, such as vehicle battery terminals.

Zinc impregnation

Zincizing is zinc powder solid metallurgical thermal diffusion coating. Its uniformity is good, and thread and blind holes can obtain a uniform layer. The coating thickness is 10~110μm, and the error can be controlled within 10%. The binding strength and anti-corrosion properties of zincizing and matrix are the best in zinc coating (electro galvanizing, hot dipping zinc, dacrosol). Its processing process is pollution-free and the most environmentally friendly.

Dacromet

Dacromet does not have hydrogen embrittlement problems and has good torque-preload consistency. Without considering the environmental concerns of hexavalent chromium, it is actually most suitable for high-strength fasteners with high corrosion protection requirements.

Anji Xinchi Fastening Piece Co., Ltd is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.