The sealing surface is the most critical face of the valve. The quality of the sealing surface directly affects the service life of the valve. The material of the sealing surface is also an important factor to ensure the sealing surface quality. Therefore, the choice of valve sealing surface material should consider the following factors: ①corrosion-resistant. "Corrosion" is the sealing surface under the action of the medium, the surface is destroyed. If the surface is damaged by this, the sealing can not be guaranteed, therefore, the sealing surface material must be resistant to corrosion. The corrosion resistance of a material depends largely on the material and its chemical stability. ② anti-scratch. "Scratch" is the relative movement of the sealing surface, the material due to friction caused damage. This damage will inevitably lead to the destruction of the sealing surface, therefore, the sealing surface material must have good abrasion resistance, especially gate valve. Scratch resistance of materials is often determined by the material's internal properties. ③ erosion-resistant. "Erosion" is the process of the sealing surface being damaged when the medium flows at high speed through the sealing surface. This destruction in the high temperature and high pressure steam medium used in the throttle, the relief valve is more obvious, a great impact on the sealing damage, therefore, erosion-resistant sealing material is also an important one of the requirements. ④ should have a certain degree of hardness, and in the provisions of the working temperature of a great decline in the hardness. ⑤ sealing surface and the main body of the linear expansion coefficient should be similar, which seals the structure of the ring is more important to avoid the high temperature prone to additional stress and cause looseness. ⑥ use in high temperature conditions, there should be sufficient resistance to oxidation, thermal fatigue and thermal cycling and other issues. In the current circumstances, to find a full meet the above requirements of the sealing surface material is difficult to achieve, only according to different valves and uses, focusing on meeting certain requirements. For example, the valves used in high-speed media should pay special attention to the erosion-resistant requirements of the sealing surface; and when the medium contains solid impurities, the sealing surface material with higher hardness should be selected.
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