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Metal Spinning Products Hot - Dip Galvanized In Surface Treatment

Shaoxing Huida Metal Factory | Updated: Sep 25, 2017

metal spinning products Hot - dip galvanized in surface treatment
Hardware is widely used in mechanical parts is no doubt. The galvanizing process is generally used in the production of galvanized zinc. metal spinning products The advantages of electroplating zinc:
(1) uniform coating, bright, passivation can get a variety of colors, decorative effect is good.
(2) low cost, simple operation. At the same time, metal plating products are also defective, such as easy to produce hydrogen embrittlement, especially high strength (≥827MPa) metal metal business products are more sensitive to hydrogen embrittlement, hydrogen is not completely caused by metal metal textile products connection failure (metal spinning products cracking, sudden fracture and so on). Plating thin, galvanized layer thickness is generally less than 10μm can not meet the requirements of outdoor corrosion.
(3) serious environmental pollution. Accounting for more than 60% of the total plating capacity, when the metal spinning products for indoor or other environment is not bad closed system, the electro-galvanized is preferred. However, the outdoor is not the case.
Hot-dip galvanized (or simply hot-dip galvanized) is a method of plating a metal metal business to a liquid metal zinc or its alloy with a lower melting point.
The use of flux method is hot - dip galvanized. The cleaned steel sheet is immersed in the plating pan before its surface forms a layer of flux to prevent oxidation and further removal of the surface residue. When the plating layer is heated and evaporated, the fresh steel surface is brought into direct contact with the molten metal, and the wetting, dissolving, chemical reaction and diffusion are formed. The γ phase, the δ1 phase and the ζ phase alloy layer are sequentially formed on the steel surface Molten metal zinc, after cooling to form η-phase zinc coating. The content of zinc in each alloy increases gradually from 77% to 99.97%. In modern hot-dip galvanizing production, a small amount of aluminum is usually added to the molten zinc solution to increase the adhesion of the galvanized layer. At this time, the main phase in the alloy layer is Fe2Al5, and the number of δ1 phase and ζ phase is small. There is no brittle γ phase.
Hot dip galvanized layer is a cheap and good corrosion resistance of the plating layer. Because of the electrochemical properties of zinc, it has a "sacrificial" protective effect on the steel matrix; and the corrosion product (basic zinc carbonate) of the zinc layer in the atmosphere is relatively dense, well attached and insoluble in water, and has some protection to the zinc layer effect. So hot-dip galvanizing is widely used to protect steel and its parts from atmospheric corrosion, especially for standard parts, metal spinning products of mass production.
It is generally believed that when the hot dip galvanized, the formation of galvanized layer is as follows: zinc melt into the matrix iron - iron and zinc reaction to produce iron - zinc alloy - in the iron - zinc alloy layer to form a pure zinc layer, galvanized layer formation of the basic The principle is high temperature metallurgical reaction. For hot - dip galvanizing is usually used to help the plating method (also known as solvent method), plating method of hot - dip plating process is divided into two kinds of wet and dry. Wet process to get the coating adhesion is not good, rarely used. The dry process allows a wide range of options for plating, with good coating quality. Therefore, the structural parts, metal spinning products, hardware hot dip galvanized general use dry method.
Hot-dip galvanized with metal bath products has the following characteristics: ⑴ thick coating can be obtained, good corrosion resistance. ⑵ coating adhesion is good, after plating can be appropriate molding, welding and painting processing.
As the metal spinning products smaller size, irregular shape, and some also need to match the thread, so hot dip galvanized there are some obvious defects.
(1) Difficulty after threading. Hot dip galvanized after the residual zinc stick in the thread is not easy to remove clean, and the thickness of the zinc layer is not uniform, affecting the cooperation with the threaded parts. In GB / T13912-1992 "metal cladding steel products hot dip galvanized layer technical requirements", GB / T2314-1997 "general technical requirements for power fittings"; metal spinning products of the external thread should be hot before plating GB196 standard processing or rolling, and the internal thread can be hot before plating or after processing. However, in practical applications, customers often require both inside and outside the thread galvanized layer, so people use a variety of measures to solve the problem of hot-dip galvanized with hot parts. Such as the screw after the back of the plating; set aside a larger gap; centrifugal rejection and other methods. Back attack is easy to damage the threaded part of the coating, and even exposed steel matrix, resulting in metal spinning products rust. Intentional oversize to increase the nut diameter or reserve the clearance, it is easy to reduce the fit strength, for high strength with this is not allowed. China is currently a mechanical centrifugal rejection to the more than zinc. In addition, people from the hot-dip galvanizing process itself to consider, adjust the hot-dip temperature and dip plating time to improve the quality of the coating, there is no fundamental solution to the problem.
(2) hot dip galvanizing operation temperature is high, will reduce the high strength metal spinning products mechanical strength. 8.8 grade bolts by hot-dip galvanized part of the thread strength is lower than the standard requirements; 9.8 above the bolts by hot dip galvanized after the strength is basically unable to meet the requirements.