Due to the small size of DIN 603 bolts, irregular shapes and some threading, there are some obvious defects in hot dip galvanizing.
- It is difficult to screw the screw after plating. After the hot dip galvanizing, the residual zinc remains in the thread and is not easily removed, and the thickness of the zinc layer is uneven, which affects the fitting of the screw. It is stipulated in GB/T13912-1992 “Technical Requirements for Hot Dip Galvanizing Layer of Metal Covered Steel Products” and GB/T2314-1997 “General Technical Requirements for Electric Power Fittings”; the external thread of fasteners shall be in accordance with GB196 before hot dip plating. Standards are specified for machining or tanning, while internal threads can be machined before or after hot dip coating. However, in practical applications, customers often require galvanized layers for both internal and external threads. Therefore, various measures have been taken to solve the problem of hot dip galvanizing of threaded fittings. Such as the backlash after the screwing of the screw; reserved a large fit clearance; centrifugation and other methods. The backlash easily destroys the plating of the threaded part and even exposes the steel substrate, causing the fastener to rust. Deliberately over-range to increase the nut diameter or reserve clearance, it is easy to reduce the mating strength, which is not allowed for high-strength fit.
2, hot dip galvanizing operation temperature is high, will reduce the mechanical strength of high strength DIN 603 bolts. The strength of some threads of 8.8 bolts after hot dip galvanizing is lower than the standard requirements; the strength of bolts above 9.8 after hot dip galvanizing is basically unable to meet the requirements.
- The working environment is poor and the pollution is serious. The hot dip galvanizing process of fasteners is carried out at high temperature. The solvent drying and the zinc to be plated will cause strong irritating hydrogen gas when it is immersed in the pool; the zinc pool is exposed to high temperature for a long time, and zinc is generated on the surface of the zinc pool. Vapor, the atmosphere of the entire working environment is bad.
Although there are many defects in hot-dip galvanizing of fasteners, the thickness of the hot-dip galvanized coating, the bonding strength is good, and the long-term rot effect is good. It has always been respected in the power, communications, and transportation sectors.