Analysis of Causes of Vacuum Pump Corrosion

Causes of Corrosion of Vacuum Pumps 1. Effect of Material The material selected under this condition is unreasonable. The vacuum pump casing, sealing liquid disc, and pump cover are made of gray cast iron. Cast iron facilitates the casting of complex structural components, but the strength of cast iron is low and corrosion resistance is poor. Due to the small amount of HCI gas contained in the medium handled by this pump, the working fluid is weakly acidic. The graphite in the gray cast iron is distributed in a network, forming a highly efficient primary battery in a weak acid solution. Iron undergoes a reaction that loses electrons, ie, an oxidation reaction, iron is an anode, and Fe→Fe2++2e. graphite is a reduction reaction. 2H++2e→H2, graphite is the cathode, this reaction easily makes the gray cast iron graphitized, resulting in selective corrosion, iron is dissolved, and the remaining graphite, pores and rust layer make up the porous loose material, making iron The specific gravity is reduced, the strength and mechanical properties are reduced, but the dimensions are not changed significantly and it is very dangerous. This is the main reason for the corrosion of the pump.

2. The shadow of cavitation is the metal component in the liquid. Because the vapor bubble forms and bursts rapidly on its surface, it causes the destruction of the hole features, which is called cavitation. Cavitation often occurs on metal surfaces where rapid flow and pressure alternate rapidly. When the pump works normally, in the inhalation phase, the liquid ring gradually moves away from the wheel Yi to form a negative pressure. The pumping medium sucks the person in the axial direction. When the pressure is lower than the vapor pressure of the liquid, bubbles are formed rapidly. In the discharging stage, bubbles are formed. Rapid pressure rupture, the resulting shock wave is like a "water hammer" effect, enough to damage the metal surface, the exposed metal surface is further corroded by the media, re-formation of the protective film. This process is repeated repeatedly, and finally a sponge pit is formed. Cavitation is the result of the interaction between the mechanical and corrosion factors. The cavitation of the pump's seal fluid is caused by cavitation.

3. Influence of Impact Corrosion The high flow rate of the medium has the function of mechanical wear, especially when the working medium contains solid particles, the wear is more serious. When the liquid ring in the pump shell flows at a high speed, the surface passivation film is broken, the corrosion product is quickly removed, a new passivation film is generated, and it is quickly removed and repeated, and the pump shell is impacted and worn. The pump dries the catalyst dust. During the nitrogen backflushing, powder particles are sucked into the flow passage, making the erosion phenomenon worse. At the root surface of the impeller, the working fluid is forced to scatter out. When the fluid suddenly changes direction, the fluid directly hits the metal surface of the pump casing and causes more serious corrosion than other parts, causing the pump casing to erode out of the annular shape. Erosion ditch, its thin as a piece of paper.

4. Influence of system load When the catalyst is dry, the system needs to backflush nitrogen, and because the supply system has leakage, the operating system of the vacuum pump is not stable and the operation load is large. The vacuum pump is in such a state of unstable and high-load operation for a long time, which intensifies the erosion of the vacuum pump, accelerates the damage of the vacuum pump, and shortens the service life of the pump.

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