Expansion of working area of ​​diffusion pump

【Abstract】 This paper introduces the exploration of expanding the work area of ​​the high pressure section of the traditional diffusion pump by developing a diffusion booster pump. It introduces in detail the various types of data of the pumping capacity debugging obtained during the development of the diffusion booster pump, and attempts to explore and grasp Various factors that affect the pumping capacity of the diffusion booster pump are needed to meet the need of increasing the pumping capacity. I. Introduction Oil diffusion pump is widely used in various types of gases can be effectively aspirated, but also has the advantages of low cost, no vibration and noise, easy to use and maintain, but its work area, especially the high pressure section Suction range, but subject to a great deal of limitations. The problem is that some of the large amount of deaeration of the vacuum coating equipment such as magnetron sputtering coating machine, winding vacuum coating machine, etc., especially the latter, the working vacuum often lO-1Pa range, and sustained a large amount of deflation . Therefore, the vacuum system vacuum pump matching requirements of the main suction pump in the 10-2 ~ 10-1Pa range to have a larger pumping speed, and the ultimate vacuum to be better than lO-3Pa. The traditional oil diffusion pump generally maintains a maximum pumping speed within a half-magnitude range of 10-3 ~ 10-2Pa, and its constant pumping speed range of the pumping speed curve generally extends to about 7 × 10-2Pa To be worse). If the inlet pressure exceeds the critical range, it will lead to the destruction of oil vapor jet, pumping speed curve began to decay sharply. While the oil booster pump in l0-1 ~ 10Pa about two and a half orders of magnitude with an effective pumping speed, but lO-2Pa range pumping speed is too poor, more lacking is the ultimate vacuum only lO-2Pa level. This makes the design of coating machine vacuum system in the vacuum pump matching, how to take into account the degree of vacuum and pumping efficiency rather hesitated. Obviously, this problem is not to solve the problem of diffusion pump or oil booster pump alone can only try to take into account their respective advantages in terms of vacuum and exhaust volume is therefore also proposed in the original diffusion pump Based on the expansion of its suction range of the idea of ​​its main means is based on the diffusion pump suction characteristics as a starting point, with reference to diffusion pumps and oil booster pump performance and structural characteristics of each to enhance its high-pressure pumping speed, extending extended exhaust Curve. The improvement of the pump we call diffusion booster pump.In recent years we have developed and used in large-scale coating equipment for large-diameter amplification pump (KZ series) are Ф600, Ф630, Ф800 three, in the performance tuning Get more useful data, but also accumulated some experience. Second, the design concept of the expansion pump The so-called expansion of high-pressure pumping speed, in practice, is two goals: Do not drop the pumping speed of the high-pressure section sharply to zero, forming a descending pumping speed curve; 2 Minimize the falling slope of this curve. Analysis of its characteristics, based on the original diffusion pump modified, consider three aspects: 1. Improve the nozzle structure. To remove the high-pressure section of the large amount of gas, the traditional diffusion pump nozzle structure is clearly not competent. In addition to changing the throat area of ​​each nozzle, expansion rate and other parameters to meet the boiler pressure to improve the variable, but also the original straight-shaped jet nozzle to Laval nozzle and the expansion of the tube with the match (see Figure 1) Produce a strong positive shock, greatly enhance the gas port at the portability; 2. Increase the heating power. The purpose of increasing power is to increase the pressure of the boiler so that at the same expansion rate, there is a higher oil vapor pressure at the exit of the nozzles at all levels to form a stronger oil vapor jet. For pump fluid. The replacement of pump fluid is attempting to greatly increase the saturated vapor pressure of the oil vapor in the boiler at the same heating temperature but the current restriction is still limited due to the fact that the alternatives are only booster pump oil and ordinary diffusion pump oil. Saturated vapor pressure is too high, the ultimate vacuum is limited, even if the effect of fractional distillation is not good, can not enter the 10-3Pa. The latter vacuum is high, but the high temperature vapor pressure is too low, the boiler pressure is not ideal, high pressure section Speed ​​to be subject to great losses. The ideal is saturated vapor pressure at room temperature than diffusion pump oil an order of magnitude higher, but the high temperature oil vapor pressure multi-directional oil booster pump oil move closer, both types of pump oil characteristics of oil. Such products abroad to have some options, the domestic is expected to spread pump oil manufacturers early development and introduction of new products. Regardless of the pumping mechanism or the specific structure of the pump, the expansion pump is equipped with a diffusion-based diffusion pump and a viscous carrier-based oil booster pump. In its wider working range, two different sections of the pumping speed curve can characterize this characteristic. As shown in Figure 2, regardless of the amplification pump or diffusion pump, the pumping speed curve can be basically divided into two areas: 4 × 10-2Pa as the cut-off point, the left for the low pressure section, the right for the high pressure section can be seen from the figure, The pumping speed in the two areas showed a completely different trend. Low-pressure section pumping speed curve range of 10-3 ~ 4 × 10-2Pa, within this range of oil vapor jet at all levels fully expanded, the vapor pressure is relatively low, and has the appropriate thickness, all levels of jet continuous and stable pumping. Being sucked gas can be in the largest pumping area that is, a surface circulation, the full diffusion into the oil vapor jet, which is carried by the removal. Corresponding pumping speed curve at its maximum value showed a more constant state, a slightly curved horizontal line, which is the basic characteristics of the diffusion pump. The pumping speed curve of the high-pressure section ranges from 4 × 10-2 to 10-1Pa, and the inlet pressure in this range increases continuously. When the pressure is close to 10-1Pa, the pressure of the gas to be drawn is similar to or even higher than the oil vapor pressure at the exit of the first-stage diffusion nozzle. First grade steam jet expansion degree decreases, and finally even compressed. It is not possible to form a steam jet which can effectively evacuate and "seal" the back flow of the evacuated gas. Was pumping gas reflux increased. Pumping rate began to decline. Similarly, with the import pressure continues to rise, a similar situation in the second and third nozzles have emerged. Based on this, 4 × 10-2Pa inflection point after the pumping speed curve is a falling line. Comparing the pumping speed curve of the amplification pump and the diffusion pump, the pumping speed curve of the diffusion pump is more stable in the low pressure section, while the expansion pump is somewhat similar to the oil booster pump, the pumping speed starts to climb from a lower position, Until 10-2Pa after the diffusion pump, expansion pump, the nozzle exit of the oil vapor jet density is much larger than the diffusion pump, the gas molecules are diffused into the oil vapor jet and the probability of being extracted is lower, and in the more Low pressure at the gas molecules were pumping back the number of small, no advantage of the expansion pump at all, so the pumping speed is lower than the diffusion pump. In the high-pressure section, the result changes in the opposite direction, the inlet pressure gradually increased, not to 10-1Pa, diffusion pump pumping speed has dropped significantly, the amplification pump is more "defensive." In addition to the pumping speed curve, Figure 2 also shows the pump and the diffusion pump pump exhaust curve, with the exception that the pump with the inlet pressure increases while the amount of linear increase in pumping, to 10-1Pa stabilized. 2 × 10-1Pa, then the emergence of the amount of pumping jumped. Pumping curve, the pump in the high-pressure section of the pumping performance is shown more clearly. Third, the development of pumping speed pumping test developed KZ-600 amplification pump, pumping speed for some of the factors that have made a series of pumping speed performance tuning, the paper briefly described as follows: 1. Diffusion pump throat area on the suction rate can be seen from Figure 3, the first-order diffusion nozzle structure parameters only have a significant impact on low-pressure section pumping speed: the same jet angle, the same expansion rate, different throat area conditions , The curve in the low-pressure section of the gap significantly, pumping speed (5 ~ 6 × 10-2Pa Department) at a difference of more than 30%. After the gradual convergence, to 2 × 10-1Pa after tended to be consistent, this section depends mainly on pumping speed nozzle two and three Laval nozzle parameters, consistent with the original design ideas. Test shows that a throat area should not be less than 9cm2. 2. Effect of Pumping Fluid Type on Pumping Rate Pumping fluid with high saturated vapor pressure at high temperature provides higher boiler pressure at relatively low power (without significantly increasing oil temperature and avoiding pump cracking) Steam jet intensity, which in the high-pressure section to improve pumping speed is extremely beneficial. KZ-600 pump with booster pump oil and diffusion pump oil (KS-3) were made pumping speed test. Import pressure is greater than 3 × 10-2Pa, the two began to show different trends, the greater the import pressure, the more obvious advantages of booster pump oil. Booster pump oil has a much better pumping performance than diffusion pump oil at high pressure, but it is still decided to use diffusion pump oil as the pump pump fluid for better vacuum. This also shows us from another perspective: If you can develop between the two (saturated vapor pressure at room temperature below the booster pump oil, high temperature pump fluid diffusion pump oil) oil. Should be more able to become a pump pump fluid optimization. 3. Impact of water-cooled cap on the pumping speed Figure 5 tests show that, coupled with the water-cooled oil cap, pumping speed low pressure section increases, but no significant changes in the high pressure section. This is due to the addition of water-cooled oil cap, although the exhaust area slightly reduced, but the effective oil retaining effect so that a large number of reflux steam is trapped, played a part of the role of pumping condensable gases, which pumping In the high pressure section, compared with the total amount of gas being exhausted, the ratio of the amount of gas is small, the effect of the above analysis is not significant, so the pumping speed curve tends to be consistent. Such as the oil cap with a lower temperature cooling medium, in the low cell condensate pumping gas phase higher working gas, the effect will be better. 4. Effect of Different Heating Power on Pumping Speed ​​The working area of ​​the expansion pump is wide, so the best heating power curve is also different in each section. In the low pressure section, after the heating power exceeds the optimum power, the vapor flow density increases, but the diffusion coefficient of the gas to be drawn decreases and the pumping speed decreases. However, after the high-pressure section increases power, the intensity of the oil vapor stream increases, the capability of carrying the gas to be drawn is enhanced, the pumping speed increases unabated, and the curve drops slowly. Figure 6 shows the different power pumping speed contrast, 10-2Pa area in addition to 18.5kW, other power pumping speed is basically the same. The 10-1Pa area, neatly arranged clearly shows that with increasing power pumping speed slowed down the decline (slope reduction). Fourth, the structural characteristics of the expansion pump Different from the proliferation of pump performance characteristics of the expansion pump of course has its own

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