Molecular pump is a common equipment for obtaining high vacuum and ultra-high vacuum. There is a high-speed rotating rotor inside the molecular pump, and the bearing supporting the smooth rotation of the rotor bears a large load. Correct use and timely maintenance are of great significance to the normal operation of the molecular pump bearing and even the entire molecular pump.
1) Try to avoid frequent start and stop
When the molecular pump is working at a constant speed, the rotor blades are only affected by centrifugal force; and when accelerating and decelerating, the blades are also subjected to a force in the tangential direction of rotation, which is equivalent to bending the blades. It is obvious that bending the blade contributes more to its fatigue life.
In addition, the molecular pump has a large power during acceleration, and the internal heating is relatively serious. Frequent start and stop (the interval between two starts <30 minutes) will cause heat accumulation, make the temperature inside the molecular pump too high, and aggravate bearing wear.
2) Select appropriate cooling according to process conditions
Our vacuum pump pumping speed covers 300L/s ~ 3600 L/s, of which the 300L/s small pump only has air cooling; the 600-1600L/s molecular pump has two cooling methods, air cooling and water cooling; 2000-3600L/s large Water cooling is recommended for the pump.
No matter which cooling method is adopted, the ambient temperature of the molecular pump should be kept between 5-35 degrees Celsius. When water cooling is adopted, treated soft water should be used, and the temperature and flow of the cooling water should also meet the requirements of the instructions.
3) Neutral sliding is not advisable
When the molecular pump is working, the speed is very high (tens of thousands of revolutions per minute). During the acceleration and deceleration process, it is inevitable to pass through some dangerous resonance frequencies. Running at these resonance frequencies for a long time will increase the bearing load and increase the failure of the molecular pump. risks of. When the pump is stopped naturally under vacuum (neutral sliding), due to the small air resistance under vacuum, the rotor of the molecular pump will take tens of minutes or even hours to completely stop, and the time of running at the resonance frequency will also be relatively long.
It is generally recommended that when the molecular pump is stopped, manually or through a special charging valve, fill air/nitrogen through the charging port to increase the rotor resistance to make it stop quickly; when manually charging, pay attention to controlling the charging speed, so that the shutdown time is equal to the start time of the molecular pump. (It varies according to the size of the pump, generally 3-10 minutes).
4) Pay attention to monitoring the backing pump
Molecular pump is a kind of high vacuum pump, it can work normally only with a suitable and good performance backing pump. Our two-stage rotary vane pump 2XZ series or EVP/EVP-PB series dry scroll pump are usually used as backing pump. In addition to selecting the recommended backing pump when selecting the model, attention should also be paid to monitoring the pressure of the exhaust port of the molecular pump when using it, so as to avoid excessively high exhaust pressure of the molecular pump due to the performance degradation of the backing pump, resulting in overload Large, the pump temperature is too high.