Five kinds of dry screw vacuum pump series are introduced
Dry screw vacuum pump consists of pump cover, pump body, disk, impeller, mechanical seal, motor and other components. Intake pipe exhaust pipe by installed on the pump cover of the suction hole on the disc and vent connected to the pump cavity, the eccentric shaft is installed in the pump body, impeller mounted on the shaft with the flat key, on the surface of the dry screw vacuum pump at both ends of the clearance between the pump body and disc pad to adjust, the disc on the impeller and the pump cover the gap between the disc and pad to adjust between the pump body, impeller clearance between two end face and the pump cover disc decided to gas in the pump cavity by the size of the loss from inlet to outlet flow and pressure. Dry screw vacuum pump seal using mechanical seal, mechanical seal installed between the impeller and pump body. The clearance between impeller and pump body is determined by mechanical seal. In the dry screw vacuum pump cover is installed with disk, disk with suction, vent and flexible exhaust valve, the role of flexible valve is when the gas pressure between the impeller blade to exhaust pressure, in the exhaust port before the gas discharge, reduce the power consumption due to gas pressure is too large, thereby reducing the rate of consumption.
Dry screw vacuum pumps of classification
Double circular lobes:
The double disk design is very similar to the current popular and widely used roots pump. In fact, some of the early dry pump design ideas were to superimpose roots pumps. This multi-stage design makes the gas path quite complex, and each stage requires a large flow of nitrogen to dilute and isolate. At the same time, in order to achieve a good vacuum degree, the gap of all levels has very strict requirements. Of course, the design of dry screw vacuum pump due to the increase of internal compression ratio makes its power consumption relatively low.
Three-leaf circular lobe type:
The three-bladed circular disk design works exactly the same as the two-bladed circular disk design, except that the gas is divided into three parts during the rotation cycle instead of two parts as in the two-bladed circular disk design. Three-lobe circular lobe design and double-lobe design have the same advantages and disadvantages. In order to further reduce power consumption, some manufacturers choose two dc motors in the transmission part, but this will also reduce torque and the ability to restart. As with the double circular lobe design, each stage of the three-bladed circular lobe design requires a large flow of nitrogen for dilution and isolation.
Combined type (roots + claw) :
The combined type (roots + claw) is designed to improve the pumping efficiency under lower pressure with roots, and to improve the pumping efficiency under higher pressure with claws. Its basic principle and gas path are exactly the same as the circular disk design described earlier. Some manufacturers have changed the second stage to a star design, so that the gas can be divided into five parts during the rotation, just as the three-circle splitter design can be divided into three parts. Similarly, in many processes, each stage of the combined design requires a large flow of nitrogen for dilution and isolation.
External compression screw type:
In the external compression screw design, a pair of equidistant screws is used. This reduces the internal compression to a small amount and makes the gas path short and simple. In this way, the gas stays in the pump body for a short time. Although this design has a relatively high power consumption due to the reduction of internal compression ratio, it shows high stability in many complex semiconductor processes. This single-stage design makes the nitrogen requirements very small and simple, which makes it very interchangeable in different processes. Many cleaning processes do not even use nitrogen. Related: dry screw vacuum pump use matters needing attention
Internal compression screw type:
The principles of internal compression screw design and external compression screw design are very similar except for the use of a pair of non-equidistance screws. The continuous reduction of the volume between the screw leads to its internal compression. This design reduces power consumption to the level of a multistage pump by generating internal compression. However, in many processes, this internal compression and multi-stage pump, easy to cause the physical and chemical changes of gas in the pump body and produce curing or liquefaction.
Although there are more and more kinds of dry screw vacuum pump, the mechanical vacuum pump, such as claw pump, is difficult to make the pumping speed, and the manufacturing difficulty is also large, high cost; There are also multi – blade series of roots pump, its disadvantages and claw pump similar. In this context, the dry screw vacuum pump has many advantages that its predecessor vacuum pump does not have, and these advantages ensure the advancement of dry screw vacuum pump and its advantages in application. At present, there are few reports on the rotor profile design of twin screw dry vacuum pump at home and abroad, mainly focusing on the improvement of screw vacuum pump performance prediction and supporting equipment, materials, processing methods and equipment, screw pump accessories, sealing conditions and so on.
At present, due to many countries on their own screw pump technology confidentiality and competition, and our country in the screw pump design there are still many specific details and technical problems have not been solved, in the screw pump design has not reached the world level. In the specific screw pump manufacturing, limited to China’s production equipment and processing conditions, China’s production of screw pump automation degree is not high, precision is not high, in some screw pump still can not be independently manufactured. Vacuum pumps are still mainly dependent on imports.
For all types of vacuum pumps, it is desirable to minimize the physical size of existing vacuum pumps. But this is inconsistent with the vacuum pump pumping rate. Because the pumping rate of vacuum pump is proportional to the volume of vacuum pump, small physical size means small volume. Of course, there is another factor that affects the vacuum pump pumping rate, that is, the speed of rotation.
In order to match the pumping rate of the small size vacuum pump with that of the large size vacuum pump, it is necessary to increase the rotation speed. To improve the speed of dry screw vacuum pump can be used to change the frequency of the power supply or change the transmission ratio of the gearbox. The former can provide a closed-loop control, but is prone to torque loss under large loads. Changing the gear box’s transmission ratio is an economical method, but it can only provide an uncontrollable single speed. The vacuum pump series with high rotating speed are more developed abroad.
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