Churn in grease lubrication

Churn is the mechanical agitation of grease caused when a lubricated component moves through, rolls through, or repeatedly works the grease.

In bearings, excessive churning occurs when there is too much grease, too high a speed, or both. The moving elements repeatedly push the grease around the bearing instead of allowing it to settle and redistribute naturally.

Why does churn matter?

Churning can generate:

• Heat — mechanical energy is converted into heat as the grease is displaced.
• Higher friction and torque — the bearing has to work harder to move through the grease.
• Grease degradation — elevated temperature and mechanical working can accelerate oil separation and oxidation.
• Reduced bearing life — excessive temperature and friction can negatively affect the bearing and lubricant.

This is why more grease is not necessarily better. The correct grease quantity and lubrication interval depend on factors such as bearing size, speed, load, temperature, grease type and operating conditions.

Churning vs. normal grease movement

Some grease movement is necessary and normal. After relubrication, excess grease may be displaced from the rolling elements into free space within the bearing housing. Problems arise when there is insufficient free space or excessive grease quantity, preventing the grease from moving away from the rolling elements.

Lubrication Reliability perspective

From a Lubrication Reliability™ perspective, grease quantity should be calculated, controlled and applied consistently rather than based on the assumption that a fuller bearing is better.