oil free scroll vacuum pump technology and application

Vortex technology has been patented since the 20th century. However, due to the limitation of technical level at that time, the vortex could not be produced, and the vortex was forgotten. In 1973, the scroll mechanism was lifted up again and the first model mechanism was made, which made the practical application of this technology possible. The potential and huge advantages of scroll mechanism, such as high reliability, stable operation, extremely low noise, energy saving and so on, immediately attracted the attention and urgent demand of the refrigerator industry. It was favored by industry leaders and quickly put into industrial application. Scroll compressor technology and products lead the wave of scroll technology application in the world, and drive the technical progress and product upgrading of many industries such as refrigerator and air conditioner.

Now the scroll technology has been extended from the initial application in the compressor industry to the vacuum pump manufacturing industry, realizing the practicality of the vortex clean vacuum acquisition technology with no oil, more stable operation, lower noise and more energy saving. By using the concept and principle of vortex, a series of single-stage and double-stage oil-free scroll vacuum pumps have been manufactured, which have no pollution to vacuum equipment and environment, and have better pumping speed, life and energy consumption than ordinary oil pumps. In the early 1990s, the world’s first scroll vacuum pump was put into the market, and the scroll technology was widely used as a new type of vacuum acquisition technology in the world.

Clean vacuum environment has always been the ideal vacuum environment pursued by scientists and enterprises. Since the vacuum environment can be created, people have tried to use different means to achieve the effect of clean vacuum. Up to now, clean vacuum acquisition equipment has developed to condensate pump, husai pump, claw pump, scroll pump and diaphragm pump and other products.

Compared with other oil-free vacuum pumps, the oil-free scroll vacuum pumps have the following characteristics:

① No oil, no friction – there is no oil in the vacuum chamber, no contact, no wear, no dust pollution, clean vacuum can be obtained;

② Large pumping capacity – double scroll plate with the same diameter compared with single-stage pump, the pumping volume is 2 times, saving energy;

③ High pumping efficiency: with 3-4 pumping units, the pressure difference is small; the air and vacuum are sealed by O-ring, with low leakage;

④ . non contact, good balance, low torque influence, low noise and low vibration;

⑤ The structure is simple and compact. Under the same size, the motion radius is small and the operation is stable;

⑥ Convenient, low maintenance cost;

⑦ . air cooling without water cooling.

Oil free scroll vacuum pump application industry:

① Semiconductor industry – film preparation equipment, semiconductor device packaging equipment;

② Scientific instrument industry — synchrotron radiation beam line, electron microscope, analysis and testing instrument;

③ Mechanical equipment industry – material preparation equipment, vacuum detection, material purification equipment;

④ Chemical industry;

⑤ Medical equipment – dental instruments, dialysis machines, biological products and drug preparation;

⑥ Packaging industry – food, medicine, biological products and other packaging equipment.

The oil-free scroll vacuum pump is mainly composed of five parts：

① The dynamic and static scroll plates are attached to the base;

② . crankshaft;

③ . gasket;

④ Anti rotation mechanism;

⑤ . motor.

The scroll plate of oil-free scroll vacuum pump is a kind of scroll disk structure formed by one or several involute spirals connected with a plane at one end. A static scroll plate and a moving scroll plate are cross assembled together, and the anti rotation mechanism guarantees 180 between them. In this way, a pair of scroll disk pairs formed the basic pumping mechanism of oil-free scroll vacuum pump. The static scroll plate and the moving scroll plate contact each other on several straight lines (i.e. several points on the cross-section vortex line) to form several pairs of crescent cavities. The moving scroll plate moves around the center of the scroll body driven by the crankshaft, so that the contact point between the static scroll and the moving scroll moves along the scroll surface, realizing the suction, compression and exhaust.

For example, in the two-stage oil-free scroll vacuum pump, there are two directions corresponding to the static scroll, and one is located between the two scroll plates. The relative motion of the rotating and static scroll plates forms a crescent shaped true cavity with constant volume, which makes the gas inhaled and discharged from the exhaust port to complete the cycle of suction, compression and exhaust. Every rotation of the crankshaft, a new set of crescent cavities will be formed. Therefore, the suction, compression and exhaust cycles of the oil-free scroll vacuum pump are continuously repeated at a frequency of nearly 1500 rpm to contain and force the extracted gas.

As we all know, oil-free scroll vacuum pump has significant characteristics compared with ordinary oil vacuum pump.

The main advantages of oil-free scroll vacuum pump mainly include:

① It is easy to seal and reach a higher vacuum degree because there is no leakage channel directly connected to suction and exhaust chambers like mechanical pump;

② The rotating radius is small, the relative sliding speed of the rotor and stator scroll is only about 1 / 7 of that of the rotary vane vacuum pump, and the dynamic sealing between the dynamic and static scroll plates is relatively easy, which is beneficial to prolong the service life of the pump;

③ The compression process must be slow. There are two or three compression processes at the same time. The compression chamber is symmetrical relative to the crankshaft. In this way, the operation process of the pump is stable, the driving torque and gas impact fluctuation are small, and the noise and vibration of the pump are reduced.

In a word, the oil-free scroll vacuum pump has simple structure, high compression ratio, stable pumping speed in a wide pressure range, and wide working pressure range; the clearance between the dynamic and static scroll plates is small and the leakage is small. Because the volume change of the compression chamber is continuous, the driving torque change is small, the power change is small, the vibration noise is low, and the reliability is high. This is not available for other types of dry vacuum pumps.

The problems of oil leakage, noise, oil return pollution, high energy consumption and vibration of common vane oil pump have adverse effects on users, such as oil vapor pollution in biological products industry and semiconductor industry and oil return problem in process system. In the coating process of vacuum coating equipment, if the ordinary rotary vane mechanical vacuum pump is used as the front vacuum pump when the coating is under 20 ~ 40Pa vacuum condition, the coating process equipment will be polluted and the film quality will be affected. Compared with the pump used in semiconductor wafer manufacturing process, there is a significant gap in yield, and the discharged oil mist vapor also pollutes the environment. In the scientific instrument industry, especially in the analysis and testing instrument industry, the use of oil pump will cause adverse effects on the test results. The oil-free scroll vacuum pump used in the large synchrotron radiation beam line is also very obvious. In addition, the oil-free scroll vacuum pump eliminates the environmental pollution and trouble caused by the oil leakage of ordinary oil pump. The advantages and reliability of the oil-free scroll vacuum pump have been proved by the use of the existing users.

In order to prevent the oil return pollution of ordinary rotary vane oil vacuum pump to the vacuum system, it is necessary to add a cold trap to capture oil molecules in the pumping system, and regularly clean and remove oil during the operation of the system; Some need to change the vacuum pump oil regularly. The first part of the oil-free scroll vacuum pump needs to add a cold trap and other oil catching mechanisms, the second does not need to replace the vacuum pump oil, the third one has smaller vibration, more stable operation, the fourth is lower energy consumption, the fifth is lighter weight, and the sixth one breaks through the limitation of oil pump application range. These advantages make the oil-free scroll vacuum pump become the replacement product of ordinary vane oil vacuum pump.

The main components of the oil-free scroll vacuum pump are the scroll plate, the crankshaft and the sealing gasket. The pumping compression exhaust mechanism of the pump is that the suction cavity and compression cavity are formed according to the relative rotation of the dynamic and static scroll plates under the condition that the dynamic and static scroll plates do not contact each other. The extracted gas is discharged and the process of suction, compression and exhaust is completed continuously. In the case of heat exchange during the pumping process, the radial and axial clearance between the dynamic and static vortices should be reduced as far as possible, which can improve the pumping speed and the limiting vacuum degree. In view of the weakness of the structure of oil-free scroll vacuum pump, which is easy to accumulate moisture and impurities and easy to wear the bearing during operation, it is necessary to select the filling valve.