Precautions for Leakage Prevention of Rotary Sealing Device

1. The influence of the seal surface state on the leakage
In order to explain completely a sealed surface, there must be five parameters: roughness, flatness, wave degree, knife mark state and discontinuous state. All these parameters will affect the sealing performance, among them, the influence of roughness, knife mark state and discontinuous state is the most significant.

Roughness refers to the difference of surface micro peak, micro valley and peak valley value caused by material cutting. Rough seal surface the seal makes it easy to wear and increase the leakage. On the contrary, if the roughness is too small, the minimum oil film thickness that is needed in movement is difficult to form on the surface, so that the seal is in dry friction or semi dry friction, and the seal performance is unstable and the leakage will increase.

The state of tool marks refers to the direction of tool processing traces, which are unidirectional, multi-directional, radial and circumferential, all of which depend on the processing method. The most commonly used turning methods for machining rotating shaft parts are circular knives, which are beneficial to the improvement of sealing performance. If the machined surface cannot form circular knife marks, it is necessary to improve the surface roughness in order to achieve the same sealing performance.

2.  Thermal deformation of sealed clearance
The deformation of the sealing surface caused by the axial temperature gradient is that when the temperature of the outer diameter is low, the rise ring expands in the radial direction to conical. When the low temperature is located in the inner diameter, the rise ring cones inward along the radial direction.

There are several heat sources in the ring type rotary seal device, which strongly affect the distribution of the radial temperature along the ring. In addition to the friction heat of the friction pair, there are other heat sources, such as the heat of the working medium, the heat of the rotating shaft, and the heat of the eddy motion of the working medium. The radial temperature gradient mainly depends on the heat source, thermal conductivity and heat transfer coefficient, followed by the type and viscosity of the working medium. The existence of radial temperature gradient changed the initial parallel clearance shape of the sealing surface.

3.  Cleanliness of the working medium
If the wear powder or external dust of the sealing device enters the working medium during the operation, the working medium will become worse, forming the oil mud and solid impurities, causing the scratch of the seal lip and sealing surface, destroying the surface friction state, causing the sharp wear of the seal and increasing the leakage.