Surface treatment of screws

Screw fasteners generally use surface treatment processes to meet customer requirements in order to meet product needs. Some involve changes in the surface treatment of hardware screws, while others involve changes in screw performance. So, what material is suitable for what surface treatment, and what type of surface treatment can achieve rust prevention performance? Let's briefly introduce the surface treatment processes of commonly used screw fasteners and their respective characteristics.

1. Environmentally friendly nickel. Generally, it refers to products plated with nickel or zinc nickel alloys that do not contain restricted harmful substances. To achieve environmentally friendly nickel (compliant with ROHS standards), it is simple. After plating, hexavalent chromium passivation cannot be used (of course, the other five types in ROHS cannot be included). The problem that needs to be solved is discoloration resistance. Unlike anti rust nickel, anti rust nickel is mainly characterized by rust prevention. The surface treatment of anti rust nickel adds a layer of anti rust oil, which has a certain anti rust effect. Generally, it can pass the salt spray test for 48 hours, while environmentally friendly nickel cannot pass the salt spray test because it does not have anti rust effect. Materials suitable for surface treatment of environmentally friendly nickel and rust resistant nickel include carbon steel and copper.

2. Environmentally friendly black zinc, which can pass the salt spray test for 48 hours, is suitable for materials such as copper, iron, and stainless steel. It is worth noting that the surface of stainless steel screws coated with environmentally friendly black zinc may occasionally peel off, but a large number of stainless steel screw products coated with environmentally friendly black zinc can avoid such situations.

3. Using chemical or electrochemical methods, a colored film or interference film is formed on the surface of a metal. The film is very thin, and sometimes the interference film itself has almost no color. When the metal and the film surface reflect light, the light waves cancel each other out, forming various colors. As the thickness of the film gradually decreases, the color tone changes accordingly, generally from yellow, red, blue to green, until the color of the film itself is displayed If the thickness of the film is uneven, it will produce rainbow or speckled colors. The surface of screw fasteners coated with colored zinc can pass the salt spray test for 96 hours and is suitable for carbon steel materials.

4. Dacromet, Dacromet surface treatment can be plated in three colors: black, silver gray, and silver white The biggest feature of Dacromet surface treatment is its good rust prevention performance. Dacromet screws can pass 500 hours of salt spray testing without red rust and 72 hours without white rust, but materials suitable for Dacromet surface treatment include carbon steel and stainless steel.

5. Tin plating, high-temperature tin (260 plating for 2 minutes, high-temperature welding). If the customer does not have specific requirements, ordinary tin surface treatment is generally done. The material suitable for tin plating is iron.