Screws are a common fastener and are widely used in machinery, appliances, and buildings. The general material is metal or plastic and has a cylindrical shape. Grooves with irregularities on the surface are called threads.
Due to the different units of measurement, the representation of various threads is not the same. For example, the M16-2X60 represents a metric thread. His specific meaning is to indicate that the nominal diameter of the screw is 16mm, the pitch is 2mm, and the length is 60mm. Another example: 1/4-20X3/4 means the inch thread, and his specific meaning is the nominal diameter of the screw. 1/4 inch (one inch = 25.4 MM), 20 teeth on one inch, 3/4 inch length. In addition, to express American screws, UNC and UNF are usually added after the English screws, so as to distinguish between American coarse teeth and American fine teeth.
Surface treatment of screws
First, the type of surface treatment:
Surface treatment is the process of forming a cover layer on the surface of a workpiece by a certain method. The purpose of the surface treatment is to give the appearance of the surface of the product and the effect of corrosion protection. The surface treatment methods are all attributed to the following methods:
1. Electroplating: The parts to be electroplated are immersed in an aqueous solution containing a metal compound to be deposited, and current is passed through the bath to precipitate and deposit the plated metal on the parts. General plating is galvanized, copper, nickel, chromium, copper-nickel alloys, etc.
Sometimes boiled black (blue), phosphatized, etc. are also included.
2. Hot-dip galvanizing: This is accomplished by immersing the carbon steel parts in a bath of dissolved zinc at a temperature of approximately 510°C. As a result, the iron-zinc alloy on the surface of the steel gradually becomes passivated zinc on the outer surface of the product. Hot dip aluminum plating is a similar process.
3. Mechanical plating: Impact the surface of the product by coating metal particles and cold-weld the coating to the surface of the product.