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Flange nuts still have defects

Update:27-01-2021
Summary:

Due to the small size of flange nuts, irregular shapes, […]

Due to the small size of flange nuts, irregular shapes, and some require threaded fit, hot-dip galvanizing has some obvious defects
1. It is difficult to screw the threads after plating. After hot-dip galvanizing, the remaining zinc sticks in the threads and is not easy to remove, and the thickness of the zinc layer is uneven, which affects the fit of the threaded parts. In GB/T13912-1992 "Technical Requirements for Hot-dip Galvanized Coating of Metal Covered Steel Products", GB/T2314-1997
It is stipulated in the "General Technical Requirements for Electric Power Fittings"; the external thread of the fastener should be processed or rolled according to the GB196 standard before hot-dip plating, and the internal thread can be processed before or after the hot-dip plating. However, in actual applications, customers often require galvanized layers for both internal and external threads, so people use more
Measures to solve the problem of hot dip galvanizing of threaded fittings. Such as the back tapping of the threaded parts after plating; reserve a larger matching gap; centrifugal throwing and other methods. Back-attack easily damages the coating of the threaded part, or even exposes the steel matrix, causing the fastener to rust. Intentionally enlarge the nut aperture or reserve over the range
The fit gap can easily reduce the fit strength, which is not allowed for high-strength fits.
2. The high operating temperature of hot-dip galvanizing will reduce the mechanical strength of high-strength flange nuts. The strength of some threads of 8.8 grade bolts after hot dip galvanizing is lower than the standard requirement; the strength of bolts above 9.8 grade 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 dipped into the bath, strong and irritating hydrogen gas will be precipitated; the zinc bath will be at high temperature for a long time, and the surface of the zinc bath will produce zinc Steam, the atmosphere of the entire working environment
bad.
Although there are many defects in hot-dip galvanizing of fasteners, hot-dip galvanizing has a thick coating, good bonding strength and long-term corrosion effect. It has always been respected in the power, communications, and transportation sectors.

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