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As the flange nut size is small, irregular shape, and some also need to thread, so hot-dip galvanizing there are some obvious shortcomings.
Flange nuts are still defective and difficult to thread after threading. After hot-dip galvanized zinc residue left in the thread is not easy to remove clean, and zinc layer thickness is not uniform, affecting the cooperation of the threaded parts. GB / T139121992 "metal coated steel products, hot-dip galvanized layer of technical requirements", GB / T23141997 "general technical requirements for electrical fittings" in the provisions; fasteners of the external thread should be hot dip.
1, after the difficulty of threading screw. After hot-dip galvanized zinc residue left in the thread is not easy to remove clean, and zinc layer thickness is not uniform, affecting the cooperation of the threaded parts. In the GB / T13912-1992 "coated steel products, hot-dip galvanized steel sheet technical requirements", GB / T2314-1997
"General technical requirements for electric power fittings" in the provisions; fastener external screw should be hot-dip galvanized before GB196 standard processing or rolling, and the internal thread can be hot-dip galvanized before or after processing. But in practice, customers often require internal and external threads are galvanized layer, so people use more
Measures to solve the hot-dip galvanized screw with the problem. Such as screw pieces of the back after the plating; set aside a large gap; centrifugal rejection and other methods. Back to attack easily damaged part of the thread coating, and even bare steel matrix, resulting in corrosion fasteners. Intentionally oversize the nuts or increase the aperture
With the gap, it is easy to reduce the matching strength, with the high-intensity which is not allowed.
2, hot-dip galvanizing operation temperature is high, will reduce the high strength flange nut mechanical strength. 8.8 bolts after hot-dip galvanized part of the thread after the strength of less than the standard requirements; 9.8 bolts above the hot-dip galvanized after the basic strength can not meet the requirements.
3, the work environment is poor, serious pollution. Fasteners hot dip galvanizing process is carried out at high temperatures, solvent drying and to be plated workpiece dip zinc into the pool will precipitate a strong irritant of hydrogen gas recording; zinc pool for a long time at high temperatures, the zinc pool surface zinc Steam, resulting in an unusually embarrassing atmosphere.