You may have encountered that the bearings are running well, but from time to time, grease may seep out of the sealing ring, and if there is a lot of leakage, oil may be everywhere. There are many possible reasons for oil leakage, and this article attempts to list some of them for reference when diagnosing.
First of all, what we want to say is that the scope of this article is only for the normal operation of bearings, and we will not discuss the grease leakage caused by deformation and damage of ball bearings, retainers, or sealing problems.
The first possible reason is that there is too much oil filling. Usually, the filling amount of bearing grease is between 1/3 and 1/2, but it also depends on the type of bearing and speed coefficient. Usually, we choose bearings according to the manufacturer's filling amount (except for special requirements), and there won't be any problems. Excessive filling of grease often occurs during bearing maintenance, when maintenance personnel want to add more grease for a longer service life. This can cause grease leakage, but as the grease continues to decrease, once it reaches a normal state, the leakage usually stops.
The second reason is that there is a pressure difference between the inside and outside of the bearing. The reasons for this pressure difference are also diverse. For example, internal gas expansion caused by high temperature, blockage of exhaust and oil discharge channels, strong convection of air on the bearing seat, or vacuum adsorption effect caused by high-speed rotation of oil seals/inner rings too close to a plane. These all need to be considered during the design process.
The third one is high temperature. In addition to the pressure difference mentioned earlier, high temperature can also cause oil and grease to soften with increasing temperature. The softer or more fluid the lubricating grease, the greater the tendency for leakage. The working temperature of bearings is affected by environmental temperature, air flow rate, load, speed, and operating time. These need to be considered when analyzing.
The fourth factor is the influence of external dynamic loads. When external vibrations and impact loads are transmitted to the bearing, the sealing lip and sealing ring may experience instantaneous separation, especially when the bearing is operating under internal thermal pressure. This separation provides an opportunity for oil to overflow. In addition, when there is feed motion or tilting force applied to the bearings, alternating deformation of the lubricating grease may occur, leading to thixotropic flow of the grease and causing leakage.
The above are four possible factors that can cause bearing grease leakage. We hope everyone can analyze the problem and find it helpful!

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