The Contact Surfaces Of The Valve Ball And Valve Seat Are Matched In Terms Of Hardness.

Metal sliding contact surfaces need to have a certain hardness difference; otherwise, seizing can easily occur. In practical applications, the hardness difference between the valve ball and the valve seat is generally 5–10 HRC. This hardness difference allows the ball valve to have a good service life. Due to the complex machining and high machining cost of the ball, to protect the ball from damage and wear, the hardness of the ball surface is generally chosen to be higher than that of the valve seat surface.

Hardness matching of the contact surfaces of the valve ball and valve seat

There are two widely used hardness combinations for the contact surfaces of the valve ball and valve seat:

① Valve ball surface hardness 55HRC, valve seat surface hardness 45HRC. The valve ball surface can be coated with Stelite 20 alloy using supersonic spraying, and the valve seat surface can be overlaid with Stelite 12 alloy. This hardness combination is the most widely used hardness combination for metal-sealed ball valves and can meet the normal wear requirements of metal hard-seal ball valves; ② Valve ball surface hardness 68HRC, valve seat surface hardness 58HRC. The valve ball surface can be coated with tungsten carbide using supersonic spraying, and the valve seat surface can be overlaid with Stelite 20 alloy using supersonic spraying. This hardness combination is widely used in the coal chemical industry and has high wear resistance and service life.

In foreign countries, valve balls and seats with the same surface hardness are used. Both the valve ball and seat surfaces are coated with tungsten carbide using supersonic spraying, resulting in a surface hardness greater than 72 HRC. Even under ultra-high hardness conditions, the contact surfaces of the valve ball and seat are not prone to seizing.