Causes of damage and repair of water ring vacuum pump shaft

In the damage of the parts of the water ring vacuum pump, the damage of the shaft occupies a large proportion. Damage to pump shaft includes bending, crack and fracture.

The reason of the pump shaft bending is mostly due to the lack of stiffness of the sleeve, coupled with the large imbalance of the impeller, resulting in deformation during operation. The bending direction and size of the axis can be measured by the following methods:

Flat on the shaft bearing and two supporting points (can be a pump shaft center hole, it can also be a shaft neck) to contour, choose several isometric profile on shaft, the shaft rotating a circle with dial gauge measuring lift respectively four directions (i.e., turn 90 ° measuring once a week) on the radial runout, a record. According to this data, the bending values in four directions can be obtained, and the maximum bending direction and size can be found by the graphical method, so that the straightening can be carried out.

The fracture and fracture parts of the pump shaft often occur in places where local stress is concentrated, such as the edge of the keyway and the abrupt change of diameter. The cause of damage is often fatigue damage due to vibration.

If the pump shaft appears fatigue crack (soon to break the warning), it should be replaced in time. The temporary remedy is to reweld the crack if it needs to be continued due to the temporary impossibility of replacement due to objective factors. When using the pump shaft after rewelding, always pay attention to the change of the rewelding zone to avoid accidents.

In the use of the single-purpose water ring vacuum pump, the common failure is the breaking of the pump shaft (especially the pump with large air volume). Generally, the fracture surface is perpendicular to the axis line, which is very neat like a knife cutting. The whole section is mostly smooth and metallic luster, while a small part is rough. Obviously, this is the fracture characteristics caused by fatigue failure.

The main reason for the fatigue failure is that the pressure of gas in the pump chamber on the pump shaft is caused during the running of the pump shaft, which is also called radial force.

The fatigue damage of pump shaft is not only the fundamental reason of radial force in water ring vacuum pump, but also the important reason of unreasonable structure. Mainly include:

At present, the water ring type vacuum pump shaft and the impeller are all first-order dynamic coordination, and the type 0 sealing ring is not used in the keyway. When the liquid in the pump (especially when corrosive liquid is used as the liquid ring in chemical industry) will enter the shaft hole through the combination of clearance and keyway, corroding the shaft and the shaft hole of the impeller, greatly reducing the fatigue strength. The increase of the mating clearance after corrosion and wear (some of which are grinding into oval shaft holes) not only affects the performance, but also aggravates the vibration, leading to fatigue fracture.

General water ring vacuum pump shaft has not been heat treated, so the fatigue strength is low. In order to prevent the fracture, the pump shaft must be at least tempered and nitrogen seepage should be carried out where conditions permit.

When designing, avoid excessive cross – section mutation. The transition should be rounded without sharp corners. Surface finish should not be low, especially where the shaft is easy to break. During processing, the circular processing at the transition points of different axle diameters should ensure the quality, strictly according to the dimensions required by the drawings and the smoothness. The surface of the pump shaft and the transitional execution should not have knife marks, scratches, bruises and other defects.

The fatigue damage of pump shaft is very harmful to production. The solution is to check the fatigue strength of the pump shaft according to the radial force. When using corrosive gas and liquid ring, the pump shaft must be adjusted, and the quality must be guaranteed.