For the metal hard sealing ball valve
, wear resistance and sealing performance still need improvement.
Hardening treatment of ball and valve seat surface:
The special ball valve
is mainly used in the operation condition of high temperature, high pressure and the medium containing solid particles. Therefore, this kind of ball valve must adopt the metal hard sealing. Normal ball valve is made from carbon steel, stainless steel or dual phase steel and other metal materials. These metal material themselves do not have abrasion resistance, so it is necessary to spray a coating on the seal surface. After spraying coating made of tungsten carbide, tungsten carbide cobalt chromium, nickel base alloy, chromium carbide, etc., the hardness of sealing surface can reach HRC60 ~ HRC70.
In addition, the adhesion strength of the coating material and substrate material should be very good, otherwise the coating may fall off after it is used for a period of time. Through improving the technology of spraying, wear resistant powder layer and substrate material can gain higher adhesion strength and higher density, thus the ball valve
will have better wear resistance and corrosion resistance, so as to ensure the service life.
For special ball valve, the sealing performance is directly related to its service life, especially in the working condition of high differential pressure. If there was some leakage of the valve, the leakage parts is easy to be scoured by high-speed flow medium, resulting in more leakage and final failure of the valve. The sealing between ball and valve seat, valve seat and valve body is crucial. The sealing materials usually is graphite, which has a wider range of compression force. At the same time, the spring plays a very important role. Like coal, coal slurry transportation, don’t let slurry particles flow into the sealing area of seat and cover, otherwise that will cause hardening of graphite, reducing sealing effect. If the impurities get stuck in the spring, the spring can’t perform effective scalability and provide necessary pre-tightening force, thus that will affect the sealing performance. Now various parameters of ball valve (such as temperature, pressure, etc.) is higher and higher, for example, those ball valve applied to coal chemical industry can reach class 900 lb, temperature 300 ℃ ~ 400 ℃. Under this kind of condition of high temperature and high pressure, the gaskets and sealing performance of packing area are usually requested to have excellent quality.
The main technical difficulties of hard sealed ball valve are in wear-resisting, service life, sealing, torque control and other several aspects. Wear-resisting is embodied in sealing surface, bearings, etc. of ball valve seat. In addition to the spraying process, other aspects such as material selection of different parts, wear-resistance of bearing of hard sealing ball valves are also expected to conform to strict requirement.