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Surface treatment of valves(2)

This article mainly introduces the other three methods of valve surface treatment.

3. Thermal Spraying

Definition and Principle: Thermal spraying is to heat metal or non-metal powder to a molten or semi-molten state by a heat source, and then spray it onto the valve surface with the help of a high-speed airflow to form a layer of coating with specific properties. Commonly used heat sources are flame, electric arc, plasma arc and so on. Thermal spraying through the high temperature heat source will be coated with molten material sprayed to the valve surface, forming a metallurgical bonding layer. Zirconia ceramic coating prepared by plasma spraying, the porosity can be controlled at 3% or less, in the waste incineration power generation of high temperature flue gas pipeline, the use of this coating of the valve, the surface temperature is reduced by 50 ℃, the life of the scour resistance is extended by 4 times.

The tungsten carbide coating prepared by supersonic flame spraying (HVOF) technology has a hardness of up to HV1300, and its service life has been increased from 3 months to 18 months when applied to high-pressure throttle valves used in shale gas extraction.

Coating materials and properties

Metal coatings: such as sprayed zinc, aluminum and other metal coatings with good corrosion resistance and electrical conductivity. Zinc coating in the atmospheric environment can form a dense zinc oxide protective film, the valve substrate to play a cathodic protection; aluminum coating has a high temperature resistance and oxidation resistance, in some high temperature environment can effectively protect the valve.

Ceramic Coating: Ceramic material has the advantages of high hardness, good wear resistance, high temperature resistance and chemical stability. Spraying ceramic coating can significantly improve the valve's wear resistance, corrosion resistance and high temperature performance. For example, in some powder transportation pipeline, the valve is susceptible to wear and tear of particulate materials, spraying ceramic coating of the valve can effectively resist wear and tear, to ensure that the sealing and service life of the valve.

4. Coating

Definition and principle: Coating is a method of coating the surface of the valve with paint to form a protective film through drying, curing and other processes. The film-forming substances in the coating form a continuous film on the surface of the valve, playing the role of isolation, protection and decoration.

Types and characteristics of coatings

Anti-corrosion coatings: Anti-corrosion coatings with epoxy resin, polyurethane, etc. as the main film-forming substances have good corrosion resistance, adhesion and mechanical properties. They can form a tough protective film on the surface of the valve and effectively resist the erosion of corrosive media such as acid, alkali and salt. For example, in the piping system of some sewage treatment plants, the valves are usually coated with epoxy resin anti-corrosion coatings to prevent corrosion of the valves by harmful substances in sewage.

High-temperature resistant coatings: These coatings use organosilicon and other high-temperature resistant materials as film-forming substances, which can maintain stable performance in high-temperature environments and prevent valve surface oxidation and deformation. In the piping system of some high-temperature furnaces and kilns, valves coated with high-temperature-resistant coatings can work normally under long-term high-temperature working conditions and extend the service life of the valves.

On the other hand, different color coatings can be used to distinguish different functions of pipes and valves for easy installation, maintenance and management. At the same time, some coatings with special functions, such as fire-resistant coatings, can also improve the safety of valves in emergencies such as fire.

5.Nitriding treatment

Definition and principle: Nitriding treatment is a heat treatment process in which nitrogen atoms are infiltrated into the surface of the valve to form a layer of nitriding layer with high hardness, good abrasion resistance and strong corrosion resistance. Under certain temperature and medium conditions, nitrogen atoms and metal elements in the valve material to form nitrides, thereby changing the organizational structure and properties of the valve surface.

Improved performance after treatment: After nitriding treatment, the hardness of the valve surface is greatly increased, generally up to HV900 - 1200, much higher than the hardness of ordinary steel. This makes the valves have good abrasion resistance and scuffing resistance, and can withstand higher pressures and harsher working conditions.

At the same time, the nitride layer also has good corrosion resistance, can effectively prevent the valve in some corrosive media corrosion failure. Application example: In the aerospace field of hydraulic systems, valves need to maintain good performance under high pressure and high frequency operating conditions. Nitriding treatment of the valve to meet these requirements, its high hardness and wear resistance can ensure that the valve in the frequent opening and closing process is not easy to wear, good corrosion resistance can adapt to the long-term role of hydraulic oil and other media, to ensure the reliability and stability of the valve to protect the safe operation of aerospace equipment.