Contaminated lubricant is one of the leading causes of bearing damage and often a major factor in the premature end of bearing life. When a bearing operates in an environment that is clean, it should only fail from eventual, natural fatigue but when the system becomes contaminated, it can significantly shorten bearing life.
Lubricant can become contaminated with foreign particles from many possible sources. Even small amounts of dust, dirt or debris can contaminate the oil film enough to increase the wear on a bearing and impact the operation of the machine. In terms of the contaminant parameters, any increase in the size, concentration, and hardness will influence bearing wear. However, if the lubricant is not further contaminated, the rate of wear will diminish, as the foreign particles will be cut down and passed through the system during operation.
It’s important to remember that an increase in the viscosity of the lubricant would cut down bearing wear for any contamination level.
Water is particularly detrimental and even water based fluids like water glycol can cause contamination. As little as 1% water in oil can negatively impact bearing life. Without proper bearing seals, moisture can enter the system, causing corrosion and even hydrogen embrittlement on existing micro-cracks. If micro-cracks, brought about by repeated elastic deformation stress cycles, are left to propagate to an unacceptable size, it creates more opportunity for moisture to enter the system and continue the negative cycle.
So, for optimum reliability, make sure that your bearing lubricant is kept clean because even the finest lubricant on the market won’t save a bearing unless it's free from contaminants.