What are the effects of excessively high or low oil levels during forced lubrication of sliding bearings?

1. Effects of Low Oil Level

This is the most destructive situation, typically leading to bearing failure.

Oil Film Interruption (Core Risk):

In forced lubrication, although oil pressure is the primary supply, the oil groove or oil ring still needs to maintain a basic oil level to ensure pre-lubrication during startup and buffering in case of unexpected oil interruption. Low oil level can cause air to be drawn into the oil suction port (or oil ring), resulting in oil flow interruption or discontinuous oil film, leading to direct metal-to-metal contact between the rotor and the bearing.

Sharply Decreased Heat Dissipation:

Lubricating oil is the primary heat dissipation medium. When oil is insufficient, the heat generated by friction cannot be dissipated, causing the bearing temperature to spike within minutes, leading to softening and melting of the Babbitt metal.

Abnormal Oil Temperature Increase:

Due to the low oil volume, the limited lubricating oil will be rapidly heated during circulation, causing the return oil temperature to exceed the limit and accelerating oil oxidation.

2. Effects of High Oil Level

While a high oil level will not immediately cause mechanical damage, it will trigger a series of operational problems.

Oil Spill and Environmental Pollution (Most Common Consequences): When the rotor rotates at high speed, excessively high oil levels can cause splashing. If the oil retainer ring or seal cannot withstand this, lubricating oil will leak from the shaft extension or end cover gaps, resulting in waste, pollution of the motor foundation and environment, and potentially even seeping into the motor stator, causing insulation damage.

Increased Oil Temperature (Agitation Losses): Excessive immersion of rotating components (such as journals and oil slingers) in lubricating oil requires overcoming significant liquid agitation resistance. This not only increases the motor's mechanical losses (wasted work) but also converts all this energy into heat, leading to an abnormally high oil temperature.

Oil Deterioration: Vigorous agitation intensifies the mixing of lubricating oil with air, generating numerous bubbles (foam). The bursting of these bubbles accelerates oil oxidation and reduces its lubricating properties (increased compressibility).

Oil Ring Slippage (For Structures with Oil Slingers): If the oil level is too high, the oil ring may be immersed too deeply, resulting in excessive viscous resistance. This can cause the oil ring to not keep up with the rotor's rotation speed (slippage), thus compromising the oil-carrying effect.