Fasteners include bolts, screws, studs, nuts, tapping screws, wood screws, washers, rings, pins, rivets, connectors and assemblies and other categories, the surface of the galvanized requirements are two reasons: anti-corrosion and decoration, anti-corrosion. The use of the environment generally includes: indoor (such as home decoration, household appliances, etc.), outdoor (such as electricity, communications, warehouses, seaports, etc., including the rural atmosphere, industrial atmosphere, the sea atmosphere environment).
In recent years, the power, construction, transportation, warehousing and other fields of fasteners have put forward higher requirements: ⑴ longer service period, that is, 4 years of service to maintain the original appearance of fasteners, 6 years of service should ensure that manual tools are easy to disassemble, 10 years of service must ensure secure connection. ⑵ Environmental Friendly, July 1, 2006, the EU formally implement RoHS (Environmental protection Directives), the prohibition of electroplating in the CR6; China's green directives are also implemented on March 1, 2007, and should be said not to comply with environmental directives, containing harmful toxic products are not allowed to enter the market.
⑶ for automated assembly, such as automotive fasteners using robots or automated tool assembly, each assembly of the torque should be basically equivalent, the friction coefficient can not be too large, thread parts of the coating can not affect the coordination. Galvanized coating is a typical anode coating for steel fasteners, which plays an electrochemical protective effect on the matrix metal.
In addition, because it is relatively stable in the atmosphere, and low cost, so in the anti-corrosion of fasteners has been widely used. The traditional zinc plating process is galvanized, hot-dip galvanized, zinc, and has developed in the past 20 years: Mechanical galvanized, the technology of Rockwell coating.
In many zinc plating process, the anti-corrosion effect of galvanized coating is not related to the process itself, the corrosion resistance of the same service environment is determined by the thickness of the galvanized layer. Therefore, we choose the fastener surface galvanized treatment, should be based on two principles: the thickness and economy of galvanized coating.
The thickness of galvanized coating is determined mainly by the service environment, and the general indoor fasteners are both anti-corrosion and decorative. At present, the process of electroplating zinc as the first choice.
Outdoor fasteners due to the relatively poor service environment, galvanized to corrosion-oriented, can choose hot dip galvanized, zinc and mechanical zinc plating. However, the current domestic and foreign hot-dip galvanizing process for outdoor fasteners, mechanical zinc plating and zinc leaching is not widely promoted, which is related to the development level of China's manufacturing industry and relative industrial standards.
For example: for zinc-coated and mechanical galvanizing in China only the general technical specifications, and in related industries (such as traffic, electricity, communications, vehicles) of the technical specifications of the fastener hot-dip galvanized coating quality requirements and testing standards. Many defects in hot-dip galvanizing treatment during the process of fastener manufacture also promote the rapid development of mechanical galvanizing and zinc permeation.
Threaded fasteners selected mechanical galvanized, zinc, high efficiency, low cost, and good interchangeability; for high-strength bolts, will not produce hydrogen embrittlement, not because of heating to reduce the strength, so mechanical galvanized is the appropriate choice. such as the hot-dip galvanized layer of the chain of the surface of the tumor, the thickness is very uneven, using mechanical galvanized after the appearance of the coating has been significantly improved and easy to control the thickness of the coating.
Injection nails, cement nails type of elastic parts, coating thickness requirements are not thick (general ≤10μm), can not produce hydrogen embrittlement, nail tip site requires coating, coating appearance requirements smooth, bright, only mechanical galvanized to be competent. Therefore, in selecting the fastener galvanizing process, in addition to considering the thickness and economic principle, but also to achieve specific problems specific analysis, for the structure of fasteners and performance requirements to make the best choice.
Tin plating process solutions for complex shapes. (1) Strengthen solution maintenance. (2) Strengthen the treatment after plating. (3) sealed for safekeeping.
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