Principle and prevention of water ring vacuum pump for brick and tile enterprises
In the process of sintering brick mud, in order to popularize the molding performance, uniform density and green body strength of the mud, so that some low-plasticity inferior raw material medicines are not fully utilized, so that ordinary mud can produce thin-walled, high-strength hollow bricks. We usually adopt a vacuum pump to continue the vacuum degassing of the mud to make the gas content outside the mud meet the production requirements to lose the decent body.
There are many types of vacuum pumps adopted by brick and tile enterprises. Water ring vacuum pumps are a rare matching facility for vacuum evacuators. The vacuum pump runs under high vacuum, especially in winter. As the operating water temperature rises, the vaporization pressure of water also increases. At the suction end of the vacuum pump, the air bubbles in the water ring quickly condense and cause the air bubbles to burst. This is the mechanism of cavitation generated by the vacuum pump. The cavitation of the vacuum pump has no relationship with the vacuum degree of the vacuum pump and the operating water temperature, and has no indirect relationship with the progress of the vacuum line and the compression ratio. Under such operating conditions, any vacuum pump will cause cavitation, so no matter how the vacuum pump is structured and how large the compression ratio is, it will form an opposite vacuum on the suction side of the vacuum pump, and the tube will cause cavitation.
When working on the vacuum pump, try to operate in the high-efficiency zone as much as possible, that is, in the sea area with critical vacuum or critical exhaust pressure; prevent operation near the maximum vacuum or maximum exhaust pressure. Running in this area not only has extremely low efficiency, but also has a well-balanced operation, which is prone to vibration and noise. As for the vacuum pump with higher vacuum, the cavitation scene will also be generated when it is operated in this sea area. The obvious mark to produce this scene is the noise and vibration in the pump. Cavitation will cause the whole body of the pump body, impeller, etc. to be damaged, resulting in helpless operation of the pump. Bai Wen elaborated the principle and prevention of water ring vacuum pump cavitation. 1.Cavitation generation principle
Cavitation is caused by the vaporization of liquids. Liquid molecules escape the liquid name and become the inside of gas molecules, which is called "gasification". The level of liquid gasification has nothing to do with the pressure and heat. The gas dissolved in the liquid will also be released when the pressure and heat change, forming a cavitation. When the external pressure of the liquid province rises and is lower than the saturated vapor pressure of the liquid at the heat, bubbles or cavities are formed in all sea areas; while the central bubble where the pressure rises is suddenly crushed by the pressure everywhere, the liquid flow is caused by elasticity. The extremely high progress squeezed the core of the bubble, causing a hydraulic charge to the facility. The generation of such microbubbles, their collapse, and the physical and chemical effects on the nominal flow are called cavitation. When the bubbles generated during cavitation are fixed to low pressure, their volume decreases and disillusionment occurs. This phenomenon of bubbles missing in the liquid due to pressure rise is called cavitation collapse.
During the operation of the vacuum pump, if the entire water area of the vacuum pump flows (usually somewhere after the impeller blade inlet) for that reason, when the relative pressure of the pumped liquid rises to the pressure of the liquid vaporization under the subsequent heat, the liquid will At this point, gasification ends, and a large number of vapors form bubbles. When the liquid containing a large number of bubbles passes through the low-pressure area in the impeller, the low-pressure liquid around the bubbles causes the bubbles to expand sharply and rupture. At the same time as the bubble condensed and broken, the liquid particle fills the cavity with a high progress. At this time, a strong water hammer effect is generated, and the non-metallic name is hit with a high charge rate. The charge force reaches hundreds of thousands. At atmospheric pressure, the efficiency of the charge array reaches tens of thousands of times per second, and the wall thickness will be penetrated when it is significant.
In the vacuum pump, the cavitation inside the vacuum pump is the cavitation in the vacuum pump. After the cavitation of the vacuum pump, unless it has a damaging effect on the over-current components, it will also generate noise and vibration and cause the performance of the pump to increase. When it is significant, it will cause the liquid in the pump to stop and prevent abnormal operations.
The cavitation damage of the water ring pump is at the place where the bubble is generated and ruptured. The pitting scene appears in the name of non-metals, and a major honeycomb failure will occur. Then the air pump impeller has a large residual stress at the cavitation site, which will also lead to stress release and cracks. Due to the sudden burst of bubbles in the low-pressure area during the cavitation of the pump, and the noise and vibration generated by the strong water hammer, you can hear the sound of cracking like a bursting bean. At that time, the above-mentioned air bubbles burst in the non-metallic name, and the non-metallic name will be hit by successively strong water, and pits will appear, and the non-metallic grains will loosen and peel off into honeycomb shapes and even perforations. In addition to mechanical effects, cavitation damage is accompanied by many simple functions such as electrolysis and chemical erosion. The theoretical destruction motivation shows that the cavitation damage site of the pump overcurrent element is the center of the missing bubble. Vacuum pumps need to use liquid as the working medium. Each liquid has a corresponding saturated vapor pressure under a certain heat. When the relative pressure drawn into the sea area is near the saturated vapor pressure of the liquid, the liquid is near the evaporation state. At that time, a large number of air bubbles will be generated in the name of the working fluid inhaled in the sea area, because the working fluid vapor generated by the liquid in the working chamber will spread across the entire working chamber, and the suction power of the pump will increase. When the pressure in the sea area reaches the saturated vapor pressure of the working fluid, it can be felt that the working chamber is completely filled with the working fluid vapor. At this time, the external suction power of the pump is close to zero, and the cavitation scene of the pump is also the most significant at this time.
The working fluid was water. The higher the water temperature, the more the pumping performance of the pump increased. The water temperature of the water ring vacuum pump does not need to have a large performance, and the performance curve of the water ring vacuum pump is measured at a water temperature of 15 ° C. Therefore, the theoretical selection of the water ring vacuum pump continues to modify the pumping rate of the water ring vacuum pump. 2.Clearing steps and prevention of water ring vacuum pump cavitation scene
Short-time operation of water ring vacuum pump in cavitation state will cause the pump noise and vibration to increase, and even cause damage to the pump. Therefore, the water ring vacuum pump should be operated to prevent the water ring vacuum pump from operating in cavitation state.
(1) Increase the heat of water
Because the temperature of the icing water of the vacuum pump rises, it will cause a significant increase in the extraction power. The heat of the vacuum pump seal water must be lower than the saturation heat corresponding to the exhaust pressure. Otherwise, the vacuum will be improved and the vacuum pump impeller will be damaged by cavitation. . Thus increasing the heat of the water achieves the motivation to prevent cavitation.
(2) Popularize the correctness of selection and make the vacuum pump run in the insurance sea area
In the selection phase, the vacuum pump suction pressure and the heat of the water should be selected to avoid the pressure scale that the vacuum pump easily generates cavitation, that is, to prevent the vacuum pump from operating in the sea area with critical vacuum or critical exhaust pressure. produce.