Spraying coating process should be adopted in the following cases:
1) The hardness of the coating is HV130-350, the thickness of the coating is from 0.3 to several millimeters, and the surface roughness is Ra10-25 μ m. The surface roughness of the coating after grinding can reach Ra0.8-0.4 μ m. Such as the bearing parts of various shafts.
2) It is required to be resistant to cavitation and water erosion, and the roughness after machining shall not exceed Ra0.4 μ M surface, such as imported automobile crankshaft, train crankshaft, marine crankshaft, etc.
3) The material is copper alloy, aluminum or aluminum alloy and other non-ferrous metals, which need to restore the size or improve the surface wear resistance.
4) Copper based powder or aluminum powder is the best choice for spraying on non-ferrous metal workpieces such as copper alloy, aluminum or aluminum alloy.
5) When used in corrosive medium, the coating is required to be dense without pores. According to the working environment, working temperature, medium concentration and composition of the workpiece, the plastic, ceramic or corrosion-resistant metal that can meet the service conditions shall be selected. After spraying, the coating shall be sealed with appropriate sealing agent.
6) Bonding strength of spraying layer and substrate: the tensile bonding strength of traditional flame spraying layer is generally 20-30N / mm2. ZK8032 powder multi-function high-speed flame spraying gun newly developed and produced by Shaanxi Zhongke Surface Engineering Co., Ltd. is used to spray aluminum clad nickel composite coating on the surface of nodular cast iron after sand blasting, and the shear bonding strength of the coating can reach 63.7N/mm2; Although the bonding strength of the spray coating is not as high as that of the spray welding coating, it is enough to meet the needs of repairing the parts with lubricating metal friction and failure resistance; For Dongfanghong 75 tractor, it is only 5.5N/mm2, which is far lower than the shear strength of the coating.
7) Wear resistance of spray coating: take the spray coating of automobile crankshaft as an example, the sprayed main journal has higher wear resistance than the new crankshaft. Our company once sprayed the Hino automobile crankshaft made in Japan, and the wear amount of the repaired main journal is 0.022-0.03mm after overhaul, while the wear amount of the main journal without spray coating is 0.2-0.25mm, which is almost ten times different, From this example, it can be shown that the spray coating has good wear resistance, even in the case of engine oil shortage, it can still keep running for several hours without burning the Bush and holding the shaft.
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