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    Fastener use Damian-based pieces of machinery there is no doubt. Electro-galvanized fasteners commonly used in production roll plating process. Electro-galvanized fasteners advantages: (1) coating evenly bright, passivation is given to a variety of colors, decorative effect is good. (2), low cost, easy to operate. At the same time, electro-galvanized fasteners, there are some shortcomings, such as easy to produce hydrogen embrittlement, especially high-intensity (≥ 827MPa) Fasteners more sensitive to the hydrogen embrittlement, hydrogen does not completely drive to connect cause fastener failure (fasteners cracking, such phenomena as the sudden fracture). Thin coating, electro-galvanized layer thickness generally less than 10μm can not meet the requirements of outdoor corrosion. (3) The serious environmental pollution. Of the total volume of over 60% of plating, when the fasteners used in indoor or other enclosed environment is not bad system, electro-galvanized is preferred. However, the outside is not. Hot-dip galvanized (or referred to as hot-dip galvanizing) is to be immersed in fastener plating a low melting point liquid metal zinc or their alloys for plating method. Hot-dip galvanized fasteners to use more flux method. Purified pan-plated steel parts prior to immersion, the surface layer before the formation of a layer of flux to prevent oxidation and to further remove surface residues. Dip, when the evaporation heat flux levels, so that the fresh steel surface in direct contact with the molten metal occurs infiltration, dissolution, chemical reaction, diffusion, the surface of the steel in order to form γ-phase, δ1 phase and ζ-phase alloy layer and attach to a layer of molten zinc, after cooled to form η-phase zinc coating. Each phase alloys of zinc content from 77 to 99.97% increase gradually. The modern hot-dip galvanized steel production, usually in the molten zinc to add a small amount of liquid aluminum in order to enhance the adhesion of zinc layer. At this point in the main phase alloy layer for Fe2Al5, while the δ1 phase and a small number of ζ phase. Brittleness of the γ phase does not exist. Hot-dip galvanized layer is a low cost and corrosion resistance of the coated layer. As the electrochemical properties of zinc, its steel substrate has a ""sacrifice"" the protective effect; while zinc layer in the atmosphere of the corrosion products (basic zinc carbonate) to compare dense, good adhesion and does not dissolve in water, there are certain degree of protection to the zinc coating effect. Therefore, hot-dip galvanized steel has been widely used to protect against atmospheric corrosion of steel and the workpiece, in particular, suitable for standard parts, fasteners of the high-volume production. Generally considered hot-dip galvanizing, the zinc coating formation process is as follows: infiltration of molten zinc-iron matrix - the reaction of iron and zinc iron - zinc alloy - iron - zinc alloy layer formed on pure zinc coating, galvanized layer to form a basic principle is that high-temperature metallurgical reactions. Right hardware, hot-dip galvanized fasteners are usually used fluxing agent method (also known as solvent), hot-dip process fluxing agent method is divided into two kinds of wet and dry. Get wet process coating adhesion is not good, now seldom used. Dry process allows for fluxing agent with a wider range of options, coating quality. Therefore, the structural parts, fasteners, hardware parts generally used in hot-dip galvanized dry. Hot-dip galvanized fasteners with the following features: ⑴ get thick coating, good corrosion resistance. ⑵ coating adhesion is good, plating can be an appropriate post-forming, welding and painting and other processing. As the fastener small size, irregular shape, and some also need to screw with, so there are hot-dip galvanized some obvious flaws. (1) screw thread together after plating difficult. Zinc hot-dip galvanized after I stick remain in the thread is not easy to remove clean, and the uneven thickness of zinc coating, affecting the parts with the screw. In the GB/T13912-1992 ""metal coating layer of hot-dip galvanized steel products technical requirements"", GB/T2314-1997 ""Electric Power Fitting General technical requirements"" in the regulations; the external thread fasteners should be hot-dip pre-standard by GB196 provides processing or rolling system, but within a thread can be hot-dip before or after processing. However, in practical applications often require that customers have a zinc coating inside and outside the thread, so people are using a variety of measures to address the thread with pieces of hot-dip galvanizing issue. Such as the screw parts of the back attack after plating; reserve with a larger gap; centrifugal methods such rejection. Back to the attack could easily undermine the threaded part of the coating, even the bare steel substrate, resulting in corroded fasteners. Deliberately to increase the scope of super-nuts with the clearance aperture or reserved, it is easy to reduce with the intensity, for high-strength tie in with this is not allowed. China currently to more than mechanical centrifugal rejection of zinc as a universal. In addition, people from the hot-dip galvanizing process itself is considered to adjust the temperature and the hot-dip-dip time to improve the coating quality, they are not fundamentally solve the problem. (2) hot-dip galvanizing operation temperatures are high, will lower the mechanical strength of high strength fasteners. 8.8 The hot-dip galvanized bolt thread the latter part of the strength of sub-standard requirements; 9.8 or more bolts through the strength of hot-dip galvanized after basically can not meet the requirements. (3) The working environment is poor, pollution is serious. Fasteners hot-dip galvanizing process is carried out at high temperatures, solvents, drying and the workpiece to be coated zinc dipping into the pool will be a strong irritant of the recorded precipitation of hydrogen; zinc pool in a long time at high temperatures, zinc pool surface of zinc vapor , the whole atmosphere of poor working environment. Currently, many private companies still use coal-fired furnace for hot-dip galvanized reflective production and emissions to the atmosphere contains a large number of So2, CO2, CO and dust of smoke, resulting in serious air pollution. Hot-dip galvanized fasteners Although there are a variety of flaws, but as hot-dip galvanized coating thickness, combined with high strength, long-term effects of good rot. Electricity, communications, transportation department has been praised. If JB/T8177-1999 ""insulator layer of hot-dip galvanized metal attachment general technical conditions"" in the right of hot-dip zinc insulated terminals made detailed requirements, DL/T764-2002 ""Electric transmission line tower and a fastening cold upsetting hot-dip galvanized bolt and nut ""and right parts of hot-dip galvanized layer of thread made detailed provisions. As China's electric power, transport large-scale development will promote the development of fasteners hot-dip zinc; Therefore, development of automated centrifugal rejection equipment, improving fastener hot-dip galvanizing process, improve the quality of fasteners hot-dip galvanized coating is very important to .