With the great development of electric power and transportation in our country, the development of hot-dip galvanizing of flange nuts will be promoted; therefore, automatic centrifugal throwing equipment is developed, the hot-dip galvanizing process of fasteners is improved, and the quality of hot-dip galvanizing coating of fasteners is improved. is very important.

Although there are many defects in hot-dip galvanizing of fasteners, due to the thick coating, good bonding strength and long-term corrosion effect of hot-dip galvanizing. It has always been respected in the electric power, communication and transportation sectors.

1. It is difficult to screw the thread after plating. After hot-dip galvanizing, the residual zinc sticking in the thread is not easy to remove, and the thickness of the zinc layer is uneven, which affects the fit of the threaded parts. The external thread of the fastener should be processed or rolled according to the GB196 standard before hot-dip coating, while the internal thread can be processed before or after hot-dip coating. However, in practical applications, customers often require both internal and external threads to have galvanized layers, so people adopt various measures to solve the problem of hot-dip galvanizing of threaded fittings. Such as the back-tapping of the threaded parts after plating; reserving a large matching gap; centrifugal throwing and other methods. Back-tapping can easily damage the coating of the threaded part, or even expose the steel matrix, causing the fasteners to rust. Deliberately increasing the diameter of the nut or reserving the fit gap can easily reduce the fit strength, which is not allowed for high-strength fit.

2. The high operating temperature of hot-dip galvanizing will reduce the mechanical strength of the high-strength flange nut. After hot-dip galvanizing of 8.8 grade bolts, the strength of some threads is lower than the standard requirement; the strength of bolts above 9.8 after hot-dip galvanizing basically cannot meet the requirements.

3. Poor working environment and serious pollution. The hot-dip galvanizing process of fasteners is carried out at high temperature. When the solvent is dried and the workpiece to be plated is galvanized into the pool, a strong irritating hydrogen gas will be precipitated; the zinc pool will be exposed to high temperature for a long time, and zinc will be produced on the surface of the zinc pool. Vapor, the atmosphere of the whole working environment is harsh.