The structure and features of oil seals
May 11, 2022
In terms of structural design, since the oil seals currently widely used are directly interfering with the rotating shaft to achieve dynamic sealing, they have very strict requirements on the eccentricity, dimensional deviation, out-of-roundness and surface roughness of the rotating shaft. Require:
1) The eccentricity of the shaft and the size of the eccentricity directly affect the distribution of the contact force of the oil seal lip, which is usually required to be within 0.3mm (the shaft diameter is 50-80mm, and the oil seal linear speed is 10-15m/s). However, in many cases The following is difficult to do. For example, the assembly technical requirements for the oil seal of the main reducer of the drive axle: the eccentricity between the center line of the input flange and the center line of the oil seal seat hole is less than 0.1mm.
2) Dimensional deviation of the shaft: Only by correctly selecting the dimensional deviation of the shaft can a good sealing effect be obtained. A shaft that is too large will increase the lip contact load, while a shaft that is too small will cause insufficient sealing pressure on the lip contact surface. Too much pressure can promote premature seal failure, while too little contact can cause leakage.
3) Shaft out-of-roundness: The out-of-roundness of the shaft is likely to cause the elastomer sealing lip to deform or lose its elasticity according to the irregular movement of the shaft, thereby causing fatigue damage.
4) The surface roughness of the shaft is generally specified as Ra1.6~3.2um. The surface is too smooth, which is not conducive to the formation and maintenance of the oil film. The dry friction of the sealing ring is easy to burn and cause leakage; if it is too rough, the friction and wear will increase, which will also cause oil seals. Early failure.
In terms of installation and use: before installation, a little grease must be applied to the lip of the oil seal. Since the lip of the oil seal has an interference relative to the shaft, attention must be paid to and prevent such as twisting and extrusion of the sealing lip during installation. When the shaft end is not tapered, rounded and threaded, more attention should be paid, otherwise the lip will be easily scratched and the sealing effect will be affected.
The existing oil seal is more sensitive to the damage of the shaft surface, and even a slight damage may have a great impact on its sealing effect and working life, and even lead to leakage directly.
The structure and advantages of the new oil seal: The main feature of the new oil seal is that it is made of PTFE material, and the oil seal realizes a dynamic seal between its lip and the outside. Its advantages are:
1. The PTFE oil seal can adapt to the relatively large eccentricity of the rotating shaft (usually only required to be about 0.5mm) and the large-scale dimensional deviation of the shaft, and has better axial and radial buffer performance.
2. The surface roughness of the PTFE oil seal is generally required to be within 0.2-04, and it is not sensitive to slight damage to the shaft surface, which improves the reliability of the oil seal.
3. The PTFE oil seal enables the oil seal to be firmly installed on the shaft. If grease is applied to the rubber surface before installation, the installation will become easier.
