What are the applications of supersonic spraying and arc spraying on boilers?

Boiler is a special type of enclosed thermal facility. It is not only directly washed away by flames and smoke, but also has a higher pressure than atmospheric pressure. Therefore, the safe operation of boiler equipment is directly related to national property and personal safety. Strengthening boiler maintenance is one of the important links to ensure the safe and economical operation of boilers.

In China, coal-fired power plant boilers and industrial boilers are dominant. In 1998, the share of electricity produced from coal in China was about 75%. With the increasing attention to global resource and environmental pollution issues, although the share of renewable energy sources such as natural gas and nuclear energy in power production and manufacturing will increase year by year, it is expected that coal's share as a power source in China will exceed 50% until 2050.

Supersonic spraying is the process of using a heat source to heat, melt or soften the sprayed material, relying on the power of the heat source itself or external compressed airflow to atomize the molten droplets or push the molten particles into the jet particle beam, and spraying them onto the surface of the substrate at a corresponding speed to produce a coating.

During the entire spraying process or after the coating is produced, the metal substrate and coating are heated to melt the coating on the surface of the substrate and diffuse or melt with the substrate, resulting in a spray coating that is metallurgically combined with the substrate. This is also one of the methods of thermal spraying, called thermal spray welding (hereinafter referred to as spray welding).

Corrosion starts from the surface, wear occurs on the surface, and fatigue is significantly accelerated due to surface damage. As an important branch of surface engineering technology, thermal spraying technology is an inevitable choice for technological development in the field of boiler protection.

At present, supersonic spraying and arc spraying technologies are widely used in the field of boiler protection in coal-fired power plants in China. Supersonic spraying technology is a method of creating a high-pressure flame by burning combustion supporting gas and combustion gas in a combustion chamber, and then injecting a high-speed flame stream through a specially designed nozzle, which heats and accelerates the powder material fed into it and sprays it onto the surface of the substrate to produce a coating. Can be used with liquid fuels such as propane, propylene, hydrogen, acetylene, diesel, or kerosene.

The coating prepared by supersonic spraying technology is particularly dense, with high bonding strength (up to 70 MPa or more) and extremely low porosity (around 1% to 3%). NiCr-Cr3C2 is a powder material commonly used for the protection of boiler tube walls in power plants using supersonic flame spraying technology. The coating prepared from it has a microhardness of around 1400HV and excellent wear resistance to abrasive particles. At present, the application of boiler protection in domestic power plants is becoming increasingly widespread.