The extension part of the shaft head of the transmission shaft passes through the dynamic seal at the pump cover. The seal here is very important. If the seal is not strict, the leakage will seriously affect the pumping performance of the vacuum pump. Therefore, special attention must be paid to it. At present, there are many kinds of sealing measures, the most common are mechanical seal, asbestos disk root seal, leather bowl seal and anti-helical seal.
(1) Mechanical seals have many configurations. The double-end friction ring mechanical seals are widely used. The mechanical seals are reliable in operation, low in power consumption and high in allowable linear speed, but the structure is complex and the manufacturing cost is high.
(2) The power consumption of this kind of seal is slightly higher, but it is simple in structure and easy to replace. Generally, spare parts are often attached to the bowl seal when it is out of the factory. The lubrication of leather bowl is vacuum pump oil or MoS2 dry oil. The material of leather bowl is butadiene-eye rubber. Its linear speed is allowed to be below 12 m/s, temperature is below 120 C. When using fluorine rubber, the linear speed can be up to 30 m/s and temperature can be up to 250 C.
(3) The sealing structure of asbestos disk root seal is very simple, low cost and easy to replace, but it needs cooling and lubrication. Otherwise, the high temperature generated by friction heating will cause shaft burnout. In order not to damage the shaft, the shaft protection sleeve should be installed at this place. In order to reduce friction, the surface hardness and smoothness of the axle protective sleeve are required to be very high. The surface of the axle protective sleeve is often treated by quenching or carburizing quenching and then polished.
(4) The transmission shaft of Roots vacuum pump with anti-helical sealing structure can also be sealed by anti-helical sealing through the sealing of the pump cover. Reverse spiral seal is to use the sleeve with thread on the outer diameter to rotate along the axis, like a screw pump, to play a sealing role.
Reverse screw seal is short for screw seal. The screw seal is fixed on the axis by the axial tightening force of the round nut. It rotates along the axis and keeps a certain radial clearance between the screw seal and the end cover. The general clearance is 0.10-0.25 mm. When the shaft rotates, the screw seal pushes back the oil like a screw pump.
After use, the reverse spiral seal has the following characteristics:
1) To ensure the lubrication of bearings, when the shaft rotates, the screw seal works like a screw, and the oil is continuously sent to the bearings to ensure the lubrication of bearings;
2) Not limited by the speed of the pump shaft, the higher the speed, the greater the sealing pressure, especially at high speed, can play a sealing effect to ensure that there is no oil in the pump;
3) When the screw seal rotates at the same time with the shaft, there is a certain radial clearance between the screw seal and the stationary parts, which has no friction loss, reduces power consumption, fewer heating, long service life, no vibration and noise, and high reliability.
4) Low precision requirement and easy fabrication;
5) Cast iron is generally used as material, so the cost is low.
6) The sealing structure can only show its sealing effect when the shaft reaches a certain speed, but it will not work at rest. Therefore, it is inappropriate to use this method when sealing is also required in the static state. However, there is no adverse effect on Roots vacuum pump, mainly because after the shutdown of Roots vacuum pump, there is no requirement for the static seal between the pump chamber and the front and back cover, but only when the pump starts to operate, there is no requirement for the seal. Especially Roots vacuum pump with high-speed operation, dynamic sealing performance is very good.
Fast-Pumping-Speed-Doublele-Stage-Rotary-Vane-Vacuum-Pump
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