Introduction of ceramic rod spraying equipment and spraying process

1.Equipment

Ceramic rod spraying requires a specialized ceramic rod flame spray gun, which consists of a front gun body and a rear gun body. Oxygen and acetylene are mixed and burned in the front gun body, and then melting the ceramic rod. Compressed air will atomize the molten ceramic rod material into fine droplets and spray it onto the substrate, forming ceramic coating. The rear gun body is a set of bar feeding mechanism that uniformly feeds the ceramic rod into the flame at a certain speed. The gun can be operated by hand or fixed by a clamp, which is very light and flexible.

2.Brief process

(1) Pretreatment of the substrate surface: 

In order to make the coating have good bonding strength with the substrate, the surface of the sprayed substrate must be pretreated. The methods include purification treatment, solvent cleaning, alkali cleaning, ultrasonic cleaning, heat treatment and so on. Commonly used organic solvents are gasoline, alcohol, acetone, carbon tetrachloride, trichloroethylene and others.

(2)Roughening treatment: 

The surface of the purified substrate is subjected to sandblasting or others to form an uneven rough surface, thereby forming a good bonding force with the coating layer. The main methods of surface roughening treatment include sandblasting roughening, spraying self-bonding metal layer, and mechanical processing methods such as vehicle groove, embossing knurling, and planar groove. Now focus on the material spraying with the bonded metal underlayer, the most ideal one is the nickel-chromium alloy (rod), and the grade is 8020, which has good thermal shock resistance and high temperature oxidation resistance. The service temperature can reach 1200 ~ 1300 °C, which is the common bonding bottom layer of ceramic coating.

(3)Spraying process: 

Do ceramic spraying on the roughened substrate. The thickness of the ceramic coating can be controlled according to actual requirements. The optimum spray ceramic coating thickness is between 0.3mm and 1.0mm. For work pieces with complex shapes, they can be clamped to a fixture such as a lathe for ceramic spraying.

(4)Post-processing: 

If the surface of the work piece needs to be precisely matched, grinding processing will also be needed after spraying. If it is a corrosion-resistant part such as an acid-resistant pump casing, it also needs to be “sealed”. Since the sprayed ceramic layer has certain gap, of which the porosity is about 4% to 12%, and the pores communicate with each other and extend from the surface to the substrate. In order to protect the substrate from being penetrated and corroded through the pores by corrosive medium, it is necessary to seal the micropores. Commonly used sealants are phenolic resin, paraffin wax, crystalline paraffin, epoxy resin, polyamide, polyester, sodium silicate and so on.