Why does a bad oil seal cause oil leakage in the equipment?

Oil seal is the customary name for general seals, which simply means the seal of lubricating oil. The sealing problem of equipment has always been an important factor that troubles normal operation and safety. Today, let's make a summary and focus on the most common oil seals.

The sealing mechanism of oil seals involves two factors. One is the sealing of the cavity, which is mainly the positioning of the outer edge of the oil seal (static component) in the cavity; the other is the dynamic sealing of the sealing lip in contact with the surface of the rotating shaft, which is the most important function of the oil seal.

There are many types of oil seals. Among all forms of oil seals, skeleton spring rubber oil seals are the most commonly used.

The oil seal is to contact the rotating shaft with a certain pressure through its extremely narrow sealing contact surface (less than 0.5mm) of the lip, and to achieve sealing under the action of liquid lubrication. As an elastomer seal, the cross-sectional shape of the oil seal and the clamping spring make the lip have better tracking and compensation performance to the shaft, so that a good sealing effect can be obtained with a smaller lip radial force.

Next, we will use a company's split oil seal as an example to explain the installation process:

Step 1: First, use the oil seal spring surface facing the medium, then pull the oil seal split port open and put it on the shaft, and the pull-open angle is the minimum value that can pass through the shaft.

Step 2: Insert the exposed skeleton at one end of the oil seal into the groove at the other end, and then press the oil seal against the seat hole with the split port facing up.

Step 3: Knock the oil seal counterclockwise from the split port of the oil seal. Note that only half of the oil seal height is inserted into the seat hole, and the last installation position should be the split port joint.

Step 4: Use the same method again to knock all the remaining height of the oil seal into the seat hole, and the speed should be uniform, and finally ensure that the outer end face of the oil seal is flush with the end face of the cavity.

We have summarized several common causes of oil leakage:

1) Assembly reasons

① Due to the reasons of press-fitting tooling, the oil seal is deformed after press-fitting;

② During the assembly process, the oil seal passes through the thread or spline, causing scratches on the lip;

③ Due to the low roughness of the oil seal position and the excessive press-fitting force, the spring fails or the lip flips.

2) Skeleton reasons

Due to the material and manufacturing problems of the oil seal spring, its performance fails. The form of spring failure is: the spring is too tight or too loose. When it is too loose, the spring compression force is small and the sealing effect cannot be achieved. When it is too tight, the spring compression force is large, and the oil seal and the rotating shaft are improperly matched, resulting in abnormal wear of the oil seal and eventually oil leakage.

3) Working medium reasons

The working medium is oil. The selection of oil seal materials should take into account its compatibility with oil. Poor compatibility between the two will cause lip swelling, hardening, softening, cracking, etc., and eventually oil leakage.

4) Causes of lip wear

① Cleanliness problem: casting sand, machining iron filings, oil impurities, etc., accumulate in large quantities at the oil seal lip, causing abnormal wear during operation;

② The custom oil seal is not coaxial with the rotating shaft, and the oil seal is worn eccentrically after press-fitting, causing abnormal wear on the lip;

③ Poor lubrication of the lithium-based grease at the oil seal lip will cause dry friction, leading to abnormal wear.

5) Causes of the shaft

① The surface roughness and hardness of the rotating shaft are unreasonable. The automotive industry currently generally uses a roughness of not less than 0.8, and the parts that match the oil seal will use high-frequency quenching, with a hardness of not less than HRC55;

② There are defects on the rotating shaft surface, such as corrosion, scratches, directional knife marks, etc.