Analysis of the causes of the corrosion of the vacuum pump 1, the material effects In this case the material selected is unreasonable. Vacuum pump casing, sealing liquid disc, pump cover are made of gray cast iron. Cast iron castings facilitate the structure of complex parts, but the lower the strength of cast iron, corrosion resistance is poor. Due to the pump medium containing a small amount of HCI gas, the working fluid was weakly acidic. Graphite in gray cast iron is reticularly distributed, forming a highly efficient primary battery in weak acid solution. Iron is the electronic reaction to lose, that is, oxidation, iron is the anode, Fe → Fe2 ++ 2e. Graphite on the reduction reaction. 2H + + 2e → H2, graphite cathode, this reaction is very easy to graphite gray iron cast, resulting in selective erosion, iron is dissolved, and the remaining graphite, holes and rust layer composed of porous loose material, making the iron The proportion of reduced, lower strength and mechanical properties, but the external dimensions did not change significantly, very dangerous, which is the main reason for corrosion of the pump. 2, the impact of cavitation Metal components in the liquid, due to the rapid formation and collapse of steam bubbles on the surface, resulting in the destruction of the hole features, known as cavitation. Cavitation often appear in high-speed flow and rapid alternating pressure on the metal surface. During normal operation of the pump, during the suction phase, the liquid ring is gradually away from the wheel Yi to form a negative pressure, which sucks in the pumping medium axially. When the pressure is lower than the vapor pressure of the liquid, bubbles rapidly form. During the discharge phase, bubbles Rapid pressure rupture, the resulting shock wave as a "water hammer" effect, enough to make the metal surface damage, exposed metal surface by the media further corrosion, re-form the protective film. This process is repeated, and finally sponge-like pits are formed. Cavitation is the result of the interaction of both mechanical and corrosion factors. The cavitation pitting of the sealing liquid of the pump is caused by cavitation. 3, the impact of corrosion The high velocity of the medium with mechanical wear and tear, especially in the working medium containing solid particles, wear more serious. When the liquid ring in the pump casing flows at a high speed, the passivation film on the surface is broken and the corrosion products are rapidly removed to produce a new passivation film. The passivation film is rapidly removed and the pump cycle shocks. The pump is dry catalyst dust. Nitrogen backflush powder particles were sucked into the runner, making the erosion worse. In the impeller root surface, the working fluid is forced to diverge out, when the fluid suddenly change direction, due to direct impact of the fluid to the pump shell metal surface, resulting in more serious than other parts of the corrosion, causing the pump housing erosion of the annular root Erosion ditch, the site thin as paper. 4, the impact of system load When the catalyst is dry, the system needs to backflush nitrogen, but also because of the leakage of the supply system, making the operating system of the vacuum pump is not stable, running load. Long-term in this vacuum pump is not stable, high-load operation of the state, exacerbating the erosion of the vacuum pump to accelerate the damage to the vacuum pump and shorten the life of the pump.
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