What is molecular pump：
Molecular pump is a kind of vacuum pump which uses high-speed rotating rotor to transfer momentum to gas molecule, so as to obtain directional speed, and then compressed and driven to the exhaust port for the front stage pumping.
Molecular pump classification:
1. The traction molecular pump gas molecules collide with the high-speed rotor to obtain momentum, which is driven to the pump outlet.
2. the turbo molecular pump can be pumped by high-speed rotating blades and stationary blades. Such pumps usually work in molecular flow.
3. Compound molecular pump is a kind of compound molecular vacuum pump which is composed of two kinds of molecular pumps: turbine pump and traction pump.
|High vacuum flange||mm||150CF||160ISO-K||200CF||200ISO-K||250CF||250ISO-K||400 ISO-K|
|Fore pipe flange||mm||40 KF||40 KF||50 KF||100 ISO-K|
|Fore pump speed||L/s||4-8||8-15||15||30-70|
|Cooling method||/||Air / water||Air / water||Air / water||water|
|Mounting position||/||Vertical ±5°||Vertical ±5°||Vertical ±5°||Vertical±5°|
Molecular pump structure features:
Compound molecular pump is a series combination of turbine molecular pump and traction molecular pump, which combines the advantages of the two pumps in one. Pump in a wide range of pressure ((10-6-1Pa) has a large pumping speed and high compression ratio, greatly improving the pump outlet pressure. A composite molecular pump with aerostatic bearings and dynamic seals produced by Alcatle, France, can be completely oil-free and can be exhausted directly into the atmosphere without the use of a front-stage pump.
Molecular pump working conditions:
(1) the rotor speed reaches 20000r/min, so the startup time of molecular pump is longer.
(2) gas is in the state of molecular flow, so it needs to be equipped with a front stage pump. The rotary pump is usually used as the front stage pump.
Molecular pump classification:
There are many forms of compound molecular pump, according to the structure, there are two main types: one is the turbine blade and disk traction pump series combination; the other is the turbine blade and cylinder traction pump series combination. Turbine stage is mainly used to improve the pump speed, generally used to improve the speed of the blade shape, Series in the l0 stage. The traction stage is mainly used to increase the compression ratio of the pump and increase the outlet pressure of the pump.
Disc type traction stage is a flat disk plane according to a certain law out of a number of profiles grooves, and then a number of discs connected in series to form, profiles have Archimedes spiral, logarithmic spiral, arc line, etc. The gas molecule is "dragged" by a high-speed rotating disc in order to make the gas molecule flow from inside to outside and from outside to inside reciprocating along the groove.
Cylindrical traction stage is a cylindrical rotor or stator on the cylindrical surface of a certain section of the groove, such as rectangular, circular arc, triangular and other shapes of multi-head spiral groove. Because the groove of the profile of the simple traction pump is open on the outer surface of the rotor cylinder or the inner surface of the pump, it can make full use of the higher linear velocity of the cylinder to transfer the momentum of the gas molecules and improve the pumping effect of the pump. In the design and manufacture, the spiral groove channel and the angle between the direction of pumping (spiral angle) can be changed to achieve a better pumping effect.
Molecular pump design points:
In the design of compound molecular pump, it is necessary to deal with the matching and connection between turbine stage and traction stage. Because the turbine stage has a large pumping area and a large pumping speed, and the traction stage groove has a small pumping area, at the junction of the two structures, the flow pattern of the gas molecules compressed by the turbine blades suddenly changes, resulting in the movement of the gas molecules from orderly to disorderly at the junction, to make the reflux increase, and the pumping capacity decreases. . Therefore, in order to improve the pumping performance of the pump, a transition stage structure should be added at the transition between the turbine stage and the traction stage.
With the continuous improvement of the composite molecular pump, its application field is more and more extensive. In some pumping systems, it can replace the diffusion pump, shorten the pumping time of the system, and obtain clean vacuum environment without oil pollution.