Roots vacuum pump is a rotary volumetric vacuum pump. Its structure is evolved from a Roots blower. First appearing in Germany in 1944, it was used as a mechanical booster pump to accommodate vacuum melting systems with large pumping speeds in the 10-1000 Pa pressure range.
According to Roots vacuum pump working pressure range is divided into straight row of atmospheric vacuum Roots pump; vacuum Roots pump (mechanical booster pump) and high vacuum multistage Roots pump. The largest amount of domestic vacuum Roots pump. Roots vacuum pump compared with other oil-sealed vacuum pump has the following characteristics:
(1) a larger pumping speed in a wide range of pressure;
(2) The rotor has a good geometric symmetry, so the vibration is small, stable operation. Between the rotor and the rotor and the shell are gaps, without lubrication, friction loss is small, can greatly reduce the drive power, enabling high speed;
(3) The pump chamber without oil seal and lubrication, can reduce the oil vapor on the vacuum system pollution;
(4) pump chamber without compression, no exhaust valve. The utility model has the advantages of simple structure and compact structure, and is insensitive to the dust and water vapor in the gas being drawn;
(5) Compression ratio is low, the hydrogen extraction effect is poor;
(6) the rotor surface is more complex shape of the curve cylinder, processing and inspection more difficult. Roots vacuum pump in recent years at home and abroad to get faster development. In smelting, petrochemicals, electrician, electronics and other industries have been widely used.
Sweaters are knitted by machine or by hand. The history of Sweater knitting is very long. Human beings used leaves and animal skins to cover their bodies in primitive life, and later learned to use knitting techniques, so sweaters were produced. With the evolution of civilization and the invention of technology, there are more and more types of sweaters, with better and better quality. The function of sweaters is generally to keep warm, but with the progress of mankind, people began to pursue the beauty of sweaters.
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