Why does vacuum corrode how to solve vacuum pump corrosion?

Corrosion analysis of vacuum pump 1. Influence of material The material selected under this condition is unreasonable. The material of the pump casing, the sealing liquid disc and the pump cover of the vacuum pump are all gray cast iron. Cast iron facilitates the casting of complex structural parts, but cast iron has low strength and poor corrosion resistance. Since the medium treated by the pump contains a small amount of HCI gas, the working fluid is weakly acidic. The graphite in the gray cast iron is distributed in a network, forming a high-efficiency primary battery in a weak acid solution. What is carried out by iron is the reaction of losing electrons, that is, the oxidation reaction, iron is the anode, and Feâ†’Fe2++2e. The reduction reaction is carried out on the graphite. 2H++2eâ†’H2, graphite is the cathode. This reaction makes it easy to graphitize the gray cast iron, produce selective corrosion, iron is dissolved, and the remaining graphite, pores and rust layer form porous loose material, making iron The specific gravity is reduced, the strength and mechanical properties are reduced, but the external dimensions are not significantly changed, which is very dangerous, which is the main reason for the corrosion of the pump.

2, the impact of cavitation Metal components in the liquid, due to the rapid formation and collapse of vapor bubbles on its surface, resulting in the destruction of the characteristics of the hole, known as cavitation. Cavitation often occurs on metal surfaces where high velocity fluids and pressures alternate rapidly. When the pump is working normally, in the inhalation phase, the liquid ring gradually moves away from the wheel, forming a negative pressure, and the pumping medium is sucked in the axial direction. When the pressure is lower than the vapor pressure of the liquid, bubbles are rapidly formed, and in the discharge stage, the bubble When the pressure is rapidly ruptured, the shock wave generated is like a "water hammer", which is enough to damage the metal surface, and the exposed metal surface is further corroded by the medium to form a protective film. This process is repeated repeatedly, and finally a sponge-like etch pit is formed. Cavitation is the result of the interaction between mechanical and corrosive factors. The sealing fluid of the pump is caused by cavitation.

3, the impact of impact corrosion The high flow rate of the medium has the effect of mechanical wear, especially when the working medium contains solid particles, the wear is more serious. When the liquid ring in the pump casing flows at a high speed, the surface passivation film is broken, the corrosion product is quickly removed, a new passivation film is generated, and the film is quickly removed, and the impact and wear on the pump casing are repeated. The pump dries the catalyst dust. When the nitrogen is blown back, the powder particles are sucked into the flow passage, which makes the erosion phenomenon worse. At the root surface of the impeller, the working fluid is forced to scatter. When the fluid suddenly changes direction, the fluid directly impacts the metal surface of the pump casing, causing more serious corrosion than other parts, causing the pump casing root to erode the annular shape. The gully is thin as a piece of paper.

4. Influence of system load When the catalyst is dry, the system needs to blow back nitrogen, and the supply system has leakage, which makes the operating system of the vacuum pump unstable and the running load is large. The vacuum pump has been in such an unstable and high-load operation for a long time, which has aggravated the erosion of the vacuum pump, accelerated the damage of the vacuum pump, and shortened the service life of the pump.