The key problem in the design of roots vacuum pump

Roots vacuum pump is a rotary positive displacement vacuum pump, its structure is evolved from roots blower. First appeared in Germany in 1944, it was used as a mechanical booster pump to adapt to vacuum smelting system with high pumping speed in the range of 10-1000pa pressure. In the long-term practice, punnock felt that some key issues must be paid attention to in the design of roots vacuum pump to reflect good applicability and economy, so what are the key issues in the design of roots vacuum pump in Germany?
Compared with other oil-sealed mechanical pumps, roots vacuum pump has the following characteristics:
1. Large pumping speed within a wide range of pressure;
2. The rotor has good geometric symmetry, so the vibration is small and the operation is smooth. There are gaps between the rotor and between the rotor and the shell, no lubrication, small friction loss, can greatly reduce the driving power, so as to achieve a higher speed;
3. No oil seal and lubrication is needed in the pump chamber, which can reduce the pollution of oil vapor to the vacuum system;
4, no compression in the pump chamber, no exhaust valve. The structure is simple, compact and insensitive to dust and water vapor in the pumped gas.
About the roots vacuum pump design key questions, by the technical personnel to answer for you.
One, the key parts of roots pump is the rotor, and the key to the rotor is its shape line. The outer contour of the rotor cross section is the profile of the rotor. Pump work, the surface of the rotor does not contact, but the gap between the rotor to maintain a certain, so the rotor profile must be made into a conjugate curve. When selecting rotor profile in actual design, in addition to meeting the above motion requirements, the following conditions should be considered:
(1) the volume of the pump rotor utilization coefficient to as large as possible, that is, the volume of the rotor accounted for small
(2) the rotor should have good geometric symmetry to ensure smooth operation and good interchangeability
(3) ensure that the rotor has sufficient strength
(4) the rotor should be easy to process and obtain high accuracy
In order to control the clearance between the pump rotor and the pump shell, the axial and radial displacement of the bearing should be controlled within a certain range. In the design, the accuracy of the bearing should be correctly selected and the type of bearing suitable for the working conditions of the pump should be selected. Considering the influence of the rotor axial thermal expansion, the rotor shaft should have a movable end (generally the end of the gear) to allow the shaft to move axially due to the factors such as thermal expansion. The axial clearance between the rotor and the end face of the shaft can be larger. And the axial clearance between the shaft fixed end rotor and the end cover should be selected smaller.
Three, the requirements of the gear wear, smooth transmission, the clearance between the teeth should not be too large. The accuracy of gear is often selected 5~ 6 grade. In order to make the transmission smooth, low noise, commonly used helical gear. In order to make it convenient for gear assembly and rotor clearance adjustment, the gear with adjustable clearance structure can be selected and the connection between the gear and shaft is adopted.
The above is our company after years of practice experience of the roots pump should pay attention to some of the key problems in design, in fact, the applicable conditions of the roots vacuum pump is protean, design can also be varied, even under the working conditions of a unified, also can have different design, but design of applicability and economical efficiency has always been in the design of roots pump should be the pursuit of the goal.

Dry screw vacuum pump in silicon nitride process
Gas drainage station water ring vacuum pump
Roots-water ring vacuum pump set in butyl acrylate unit
Vacuum pump vacuum system for Vacuum coating machine