Several surface treatment methods for screws

Several surface treatment methods for screws

Screws are a type of fasteners that are used for fastening connections and are widely used. It is used in a wide range of industries, including screen, energy, electronics, electrical appliances, machinery, and other industries. There are standard parts and non-standard parts. The surface treatment of screw fasteners is the process of forming a covering layer on the surface of the workpiece through a certain method. The surface of the product is beautiful and the effect of anti-corrosion.

1. Put the screw to be blackened in the sodium hydroxide and sodium nitrite oxidant in the solution tank (145±5°C) to heat and oxidize, so that a layer of magnetic ferric oxide film is formed on the surface of the metal screw. The thickness is generally 0.6-0.8μm, and it is black or blue-black.

2. Phosphating is a process in which chemical and electrochemical reactions form a phosphate chemical conversion film. The formed phosphate conversion film is called a phosphating film. The main purpose of phosphating is to provide protection to the base metal and prevent the metal from being corroded to a certain extent.

3. Hot-dip galvanizing is to immerse the rust-removed screws in a zinc solution melted at a high temperature of about 600°C so that the surface of the steel member is attached with a zinc layer. The thickness of the zinc layer is not less than 65 μm for thin plates below 5 mm, and not less than 86 μm for thick plates of 5 mm and above. to achieve the purpose of anti-corrosion.

4. Dacromet is the transliteration and abbreviation of DACROMET, referred to as Dacromet. It is named zinc chromium coating in China. It is a new type of anti-corrosion coating with zinc powder, aluminum powder, chromic acid, and deionized water as the main components. Suitable for high-strength fasteners with high corrosion protection requirements.

5. Electrogalvanizing: also known as cold galvanizing, is the process of forming a uniform, dense, and well-bonded metal or alloy deposition layer on the surface of the workpiece by electrolysis. Electro galvanizing is a commonly used coating for fasteners. It is cheaper and looks better, and it can be black or army green. However, its anti-corrosion performance is average. Generally, the neutral salt spray test of electro-galvanizing is within 72 hours, and special sealants are also used to make the neutral salt spray test more than 200 hours, but the price is expensive, which is 5-8 times of general galvanizing.