The motor bearing seal is a crucial component in many motor bearings. During the operation of the motor bearing, poor contact at the seal lip may result in heating of the motor bearing. This article provides a brief overview of this topic.
When designing the motor bearing seal, the contact force between the seal lip and the sealed surface is taken into account. The heat caused by the sliding friction that usually occurs at this part is controlled within a certain range and does not become a primary heat source for the motor bearing.
If the heat source of the bearing heating is found to be related to the seal, then it is necessary to conduct a corresponding check on the seal.
The investigation of these causes includes checks on the selection of seals and the installation of seals.
Firstly, the inspection of seal selection: The primary function of a seal for bearings is protection, preventing the leakage of lubrication, and so on. There are non-contact seals and contact seals. The stronger the contact between the seal lip and the contact surface, the better the sealing effect.
Correspondingly, the friction and heat generated by contact force and relative motion are greater. Conversely, the weaker the contact, the poorer the sealing effect, and the friction and heat produced due to contact force and relative motion are less. The choice and application of seals often involve balancing heat generation and sealing effectiveness.
Generally, the seals used in bearing applications include contact and non-contact seals. Non-contact seals ensure the sealing effect through lip design. Since there is no contact force, almost no heat is generated due to lip contact.
Light contact seals offer better sealing effects than non-contact seals. However, because the seal lip will have contact and relative friction with the sealed parts, some heat will be generated when the bearing is running.
Therefore, if the bearing temperature is significantly affected by the seal during motor operation, consider reducing the selection of seals with smaller contact forces while ensuring sealing effect to decrease the heat generation from the seal lip.
Overall, it involves the replacement of light contact seals with dust covers (non-contact seals), the substitution of heavy contact seals with light contact seals, or the adoption of special seal structures.
When the bearing seal heats up, it is also necessary to check whether there is undue friction or interference in the corresponding parts of the seal.
During normal operation, a bearing seal only experiences friction at the lip area against the sealed surface (non-contact seals should not experience friction at this point). Consequently, for non-contact seals, if signs of friction or interference are detected, the seal should be inspected for improper friction with surrounding components.
This friction may be due to component dimensions or improper handling during installation or disassembly.
In the case of contact seals, seals will experience some wear after extended operation; however, this wear should be slow, limited, and evenly distributed. If severe wear occurs over a short period, resulting in significant heat due to friction, engineers must apply their knowledge of seal selection for inspection and adjustment.
Additionally, seals typically have certain speed requirements even under reasonable contact pressure. Excessive speeds can cause excessive wear and heat in the seals. Normally, the linear speed of the lip contact surface should not exceed 15 meters per second.
If the friction marks observed on the seal lip are uneven, this may indicate an uneven foundation between the lip and the sealed surface.
Therefore, it is necessary to inspect the shaft’s relevant dimensions and check the concentricity and co-axiality during installation. Localized wear on the seal does not only cause excessive localized heat but can also lead to poor local sealing, raising the possibility of grease leakage or contamination ingress.
Of course, if there are obvious problems like deformations in the seal itself that cause excessive contact pressure and subsequent heat generation, corrections are also required. However, this issue is typically quite noticeable, and most engineers can identify and address it accordingly.