First, we summarized several common causes of oil leakage:
1) Assembly reasons
① Deformation of the oil seal after pressing due to tooling issues during press-fitting;
② Damage to the lip during assembly due to contact with threads or splines;
③ Excessive pressing force due to low surface roughness of the oil seal seat, leading to spring failure or lip inversion.
2) Seal structure reasons
Failure of the oil seal spring due to material and manufacturing problems. Spring failure manifests as: the spring being too tight or too loose. When too loose, the spring pressure is insufficient to achieve a sealing effect; when too tight, the spring pressure is too high, leading to improper fit between the oil seal and the rotating shaft, causing abnormal wear of the oil seal and ultimately oil leakage.
3) Working medium reasons
The working medium is the oil. The selection of oil seal material should consider its compatibility with the oil. Poor compatibility between the two can lead to swelling, hardening, softening, or cracking of the lip, ultimately resulting in oil leakage.
4) Lip wear reasons
① Cleanliness issues: Accumulation of casting sand, machining chips, oil impurities, etc., at the oil seal lip area, causing abnormal wear during operation;
② Misalignment between the oil seal seat and the rotating shaft, leading to uneven wear after oil seal installation and abnormal lip wear;
③ Poor lubrication with lithium-based grease at the oil seal lip, resulting in dry friction and abnormal wear.
5) Shaft reasons
① Unreasonable surface roughness and hardness of the rotating shaft. The automotive industry generally uses a surface roughness of no less than 0.8, and the mating surface with the oil seal is typically high-frequency hardened to a hardness of no less than HRC55;
② Defects on the surface of the rotating shaft, such as corrosion, scratches, directional machining marks, etc.