Grease is composed of base oil, thickener, and additives. Its performance and physical properties vary depending on its composition and manufacturing method, thus affecting the grease's lifespan. The main influencing factors include: viscosity, penetration, shear stability, thermal stability, oxidation stability, oil separation, and fluidity. In practical applications, it is also closely related to the type of rolling bearing and the amount of grease filled.

　　In bearing applications, the selection of grease is crucial. Grease inevitably ages and fails during use, but if the chosen grease allows the bearing to meet its expected lifespan, it can be considered reliable to a certain extent. If the grease fails prematurely, the failure mechanism needs to be analyzed and optimized.

　　As shown in the figure, the causes of grease aging include energy, reactants, and reaction promoters. These factors cause aging through different mechanisms, which is important in grease usage.

　　Through the above analysis of the causes of grease aging, we can also obtain the key elements for ensuring lubrication lifespan:

No.1 Operating Conditions

　　Operating conditions are affected by temperature, speed, and load (presence or absence of vibration, impact load, etc.), with temperature having the greatest impact. As the temperature rises, i.e., heat increases, the thickener and base oil oxidize. Due to oxidation, the network structure of the thickener is destroyed, causing grease leakage and base oil evaporation and decomposition, thus affecting the grease's lifespan.

Using simulation software, setting the bearing operating temperatures to 100℃ and 120℃ respectively, under the same operating conditions and grease parameters, as the temperature rises, the bearing's lifespan gradually decreases, as shown in Figure 2. This means the grease reaches the end of its lubricating life prematurely.

No.2 Environment

　　The environment and air (ozone, nitrogen oxides, corrosive gases, humidity, dust and other impurities) also affect the grease lifespan. These environmental factors accelerate the oxidation and aging of the grease, thus shortening its lifespan. Figure 3 shows grease aging and deterioration due to rust corrosion of the bearing, meaning the grease will inevitably fail to meet the expected lifespan requirements.

No.3 Grease Composition and Properties

　　Our company attaches great importance to the impact of grease performance on bearing lifespan and has conducted numerous comparative tests of different greases under the same operating conditions. In 2023, grease comparison tests accounted for 20% of the total number of experiments. Figure 4 shows the condition of two greases after operating at 120℃ for 1000 hours. The grease on the left shows slight yellowing and base oil separation but still maintains good lubricating performance. The grease on the right is completely black, showing significant aging, indicating that it is nearing the end of its lubricating life.

Source: Grease Information Platform