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Shanghai Nuoyou Valve Industry-How to make the valve more wear-resistant and more durable?
1. Increase material hardness
The research structure shows that the abrasive wear but the ratio of sterilized metal hardness Hm to abrasive hardness Ha.
When Hm / Ha ＞ 0.8, the amount of metal wear decreases rapidly. When Hm / Ha = 1.25-1.3, the amount of wear is already very small. It can be seen that to reduce abrasive wear, the hardness Hm of the metal material should be 1.25-1.3 times the hardness of the abrasive Ha, that is, Hm = (1.25-1.3) Ha. This data can be used as a judgement of low wear rate.
The amount of wear is divided into three regions corresponding to the relative hardness. However, at present, the sealing surfaces of the valve disc and the valve seat used in alumina plants in China are overlaid with hard alloy, but the hardness value is lower than the abrasive hardness, that is, the hardness of the valve disc and the valve seat is less than 0.8. Working in high wear areas, the valve life is very short.
2. Surface treatment
Using various surface treatment processes, changing the surface characteristics of the valve disc and valve seat is an important method to improve abrasive wear. In addition, improving the surface finish of the material flow surface can reduce the abrasive wear of the surface abrasion, and can also delay scaling.
In addition to the abrasive wear of the valve disc and valve seat, it is also accompanied by erosion and wear.
When the conveyed slurry is in contact with the valve flap and valve seat, the local pressure is lower than the evaporation pressure, which will cause air bubbles to form; the gas dissolved in the liquid also precipitates to form air bubbles. When these air bubbles flow through the high pressure area, the pressure exceeds the air bubbles When it is under pressure, it will burst, which will cause a great impact and high temperature in an instant. Due to the repeated formation and destruction of air bubbles, the surface of the valve flap and valve seat will be fatigued and abraded, and pits and cavities will be generated. This is cavitation wear.
The small liquid droplets rush to the surface of the valve disc and the valve seat at a high speed (1000m / s), which causes a high stress on the surface. When the yield strength of the material is exceeded, a single impact will often cause plastic deformation. Even if the stress is small, repeated impact will cause pitting. The wear caused by the fluid beam impacting the valve disc and the seat surface is erosion wear. In addition, the liquid contains hard particles, and the fluid beam impacts the valve disc. The valve seat also causes erosion and wear.
The way to prevent or slow erosion and erosion is still to increase the hardness of the material.
After years of development of valve technology, the valve's abrasion resistance has been fundamentally improved. It has been able to adapt to complex and severe working conditions, but the service life cannot be maintained for a long time. Therefore, the valve's abrasion resistance and service life are improved. It is also a big problem.