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The steps and techniques of pretreatment of thermal spray surface are briefly described

Author: langfeng Time: 2017-09-22

The steps and techniques of pretreatment of thermal spray surface are briefly described
Thermal pretreatment of the surface pretreatment is generally divided into surface pre-processing, surface cleaning and surface roughening (or activation) three steps to carry out.
1 surface pre-processing
Its purpose: First, the workpiece surface is suitable for coating deposition, increase the bonding area; the second is conducive to overcome the shrinkage of the coating stress. Some parts of the workpiece for the corresponding pre-processing to disperse the local stress coating to increase the coating's shear capacity. Commonly used methods are rounded and prefabricated troughs. Workpiece surface roughing thread is also one of the commonly used methods, especially in the spraying of large parts commonly used to increase the thread to increase the bonding area. Turning thread should pay attention to two problems, the first is the thread cross section to be suitable for spraying, rectangular section or semi-circular section is not conducive to the combination of coating. In addition, the thread should not be too deep, otherwise the spray will be too thick, the cost increases. You can also "knurled" the coated surface or combine the turning threads and knurling.
2 surface cleaning
Often used solvent cleaning, lye cleaning and heating degreasing and other methods to remove the surface of oil, to maintain cleanliness. Commonly used cleaning solvents are: gasoline, acetone, carbon tetrachloride and trichlorohexene. Large-scale repair workpieces often use lye cleaning. Alkaline is usually formulated with sodium hydroxide or sodium carbonate, which is a relatively inexpensive method.
3 sand blasting roughening treatment
Blasting can make the clean surface to form a uniform and uneven rough surface, in order to facilitate the mechanical combination of the coating. Driving clean grit with clean compressed air on the surface of the workpiece can produce compressive stress on the surface of the substrate, remove the surface oxide film, so that part of the surface metal lattice distortion, is conducive to the physical combination of the coating. Substrate metal in the sandblasting can be clean, rough and high activity of the surface. This is an important preprocessing method.
Sandblasting commonly used abrasive is: white corundum (pure alumina), corundum (alumina + iron oxide), silica sand and so on. White corundum sand hardness is high, broken rate is low, sandblasting effect is good. Corundum is also a commonly used abrasive, affordable, high hardness of silica sand but the broken rate is also high, chilled iron sand or grit can also be used to sandblasting, sand must be clean, so as not to secondary pollution of the surface, the size of the sand should be specific Shape to choose. In the sandblasting operation should pay attention to sandblasting distance and angle, the distance is generally selected in the range of 100 ~ 300mm, for thin-walled parts and flexible workpieces should pay special attention to not strong sandblasting. Sandblasting should avoid vertical blasting, angle control in 45 ° ~ 70 °. On the surface hardness of low materials, such as copper, aluminum, zinc and other soft, good ductility of the metal, with particular attention to sandblasting distance and angle control, otherwise it will make more sand debris embedded in the substrate. After blasting the surface has a high activity in the atmosphere easily oxidized, should be properly protected, and as soon as possible spraying, generally not more than 4h.
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