| One of the main failure mode of the ball valve is that it’s sealing surface is damaged by wear. And it’s a good method to use surface treatment process on sealing surface of ball valve to improve it’s hardness and wear resistance, which can not only reduce costs but also obtain good use effect. At present, valve enterprises in Wen Zhou always focus their attentions on the wear resistance of the sample, ignoring the effect of the ball valve’ s working environment. At the same time, neither method nor equipment is absent to them, which are helpful to evaluate the strengthening effect of different surface treatment technology to ball valve. Therefore this paper gives a comparative study on the different physical properties of the nitriding, high velocity oxygen fuel spraying of WC(HVOF WC), spray welding Ni60 and spray welding Ni60+PVD. And a machine used to test service life of ball valve is also designed, which can simulate actual working conditions of ball valve, and is intent to research the effects of different surface treatment on ball valve wear resistance.Due to its own process, the nitriding’s strengthening layer is the thinnest, while the other three kinds of process can form thicker ones. HVOF WC has the largest void ratio, and secondary remelting makes that both spray welding Ni60 and spray welding Ni60+PVD ’s void ratio is as half as HVOF WC’s. All of these four kinds of process can satisfy the production requirements on the geometric roundness. Among them, nitriding’s hardness is closed to HVOF WC, both of which are higher than spray welding Ni60, but lower than spray welding Ni60+PVD composite process. And then the composite process’ s hardness is pure spray welding Ni60’s two times. Considering thermal shock resistance, spray welding Ni60+PVD composite process is obviously better than that of pure spray welding Ni60 but slightly below the nitriding process, and at the same time HVOF WC is the worst one. The substrate of stainless steel is infiltrated with N element in the nitriding process, which lead to chromium depletion causing the decrease of the corrosion resistance. However, there is no such a problem in other three kinds process, whose corrosion resistance are better than the nitriding process. Through integrated into account, it is reasonable thatspray welding Ni60+PVD composite process has the best comprehensive physical properties.In this paper, a ball valve life test device composed of 6 parts including execution system, gas pressurization system, piping system, valve actuator, valve pinch device and electric control system was designed, which could be used to simulate the ball valve actual working conditions. And according to enterprise’s own conditions, this device can be simplified to decrease the cost, too.This ball valve life test device was used to detect the four surfacetreatment technology’s strengthen effect on the ball valve sealing surface. During low pressure life test(0.6MPa), the ball valve of spray welding Ni60 had the shortest service life, whose hardness was also the lowest. During high pressure life test(5MPa), the service life of the HVOF WC ball valve was little shorter than that of spray welding Ni60+PVD composite process, and both of them were longer than the rest. And considering HVOF WC’s large void ratio and bad thermal shock resistance, it had reason to believe that composite process was the best, which hadn’t the same problem of HVOF WC. Then a high temperature life testing was determined on composite process which had the best strengthen effect, and the results showed that there was no saltation in operation torque curve with experimental temperature 200℃and 400℃, and ball valves worked well in hydrostatic test without leakage before and after high temperature test. So it was proved that the composite process was an effective surface treatment, which could effectively improve the ball valve abrasion resistance.In this paper, the research on physical properties of the 4 kinds of surface treatment technologyand the design of ball valve life test device provide great application value and important reference for enterprises to choose the appropriate ball valve sealing surface strengthening technology to prolong the service life of ball valve. |
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