Characteristics of thermal spraying technology and knowledge sharing of coating function classification[2]

       Fourth, the formation and evaluation of the coating

  After the spraying material is sprayed by a spraying equipment with a certain form of heat source, its flight time is only a few thousandths of a second or less before reaching the surface of the substrate to be sprayed. In such a short period of time, it is heated, melted or semi-melted to form small and scattered droplets, which rush to the surface of the substrate and are hit into flat stacked small pieces, and the previously generated flat pieces are covered by the later ones. , And soon formed a coating layer made of many flat stacks, that is, sprayed layer. The higher the temperature of the heat source, the greater the impact velocity of the droplets, and the denser the coating formed. Coating performance is related to many factors.

Five, coating function

  When a certain engineering problem is raised, the working condition of the part (usually the working surface of the equipment or facility) on which the workpiece to be constructed is sprayed should be clarified first, and the coating function is the main factor in determining the spraying process and materials. Basis, but also consider whether it is economically permissible.

  The coating can be divided into:

  1. Wear-resistant coating. Including anti-adhesive wear, surface fatigue wear coating and erosion resistant coating. In some cases, there are anti-low temperature (<538oC) wear and high temperature (538～843oC) wear coatings.

  2. Heat-resistant and anti-oxidation coating. This kind of coating includes high temperature process (including oxidizing atmosphere, corrosive gas, erosion and thermal barrier above 843oC) and molten metal process (including molten zinc, molten aluminum, molten iron and steel, molten copper). Coating.

  3. Anti-air and immersion corrosion coating. Atmospheric corrosion includes corrosion caused by industrial atmosphere, salt atmosphere, field atmosphere, etc.; immersion corrosion includes corrosion caused by drinking fresh water, non-drinking fresh water, hot fresh water, salt water, chemical and food processing.

  4. Conductivity and resistance coating. This kind of coating is used for conductivity, resistance and shielding.

  5. Restore size coating. This kind of coating is used for iron-based (cuttable and groundable carbon steel and corrosion-resistant steel) and non-ferrous metal (nickel, diamond, copper, aluminum, titanium and their alloys) products.

  6. Gap control coating for mechanical parts. This kind of coating can be ground.

  7. Chemical resistant coating. Chemical corrosion includes corrosion of various acids, alkalis, salts, various inorganic substances and various organic chemical media.

  Among the above-mentioned coating functions, the ones that are closely related to metallurgical industry production are wear-resistant coatings, heat-resistant and oxidation-resistant coatings, and chemical corrosion-resistant coatings.