Oftentimes, when we think of alignment and lubrication, we always think of them as separate entities that do not have bearing on each other.

In truth, the two are actually intertwined. Last month, we conducted an extensive webinar on precision alignment. Now, let’s explore how shaft alignment relates to lubrication and see how they affect one another.

In lubrication, Stribeck’s equation states that the increase of dynamic film thickness happens when there is an increase in viscosity and speed. But, a decrease happens when there is an increase in the load. Design engineers apply this concept to ensure that machines will have a good lifespan and durability.

Load and Bearing Life

Victor Wowk illustrated in his book entitled, “Machinery Vibration: Alignment”, the relationship of load and component life as shown below:

Source: Machinery Lubrication

However, there are cases where a piece of equipment tends to be more or less tolerant of misalignment. This depends on the bearing type and coupling type. But there are some exemptions, of course, where some equipment are observed to be more or less tolerant of misalignment which is determined by their bearing type and coupling type.

Researchers measured that an axial misalignment of about 0.8 degree can double the effective load and reduce the hydrodynamic lubricating film thickness by 75 percent. If this happens, there will be a higher risk of bearing wipe and scoring happening especially when there are abrasive particles that are embedded unto the surface of a soft bearing. When misalignment occurs, there will be a reduction in the effective clearance of the machine. In many instances, the lubricant's film is completely gone that surface-to-surface contact is inevitable. When two surfaces are in contact with each other this leads to two-body abrasion. This is common in components that have one surface that is made of a harder material than the other. In instances where the two surfaces are made of the same strong material such as steel and the load is sufficient, misalignment can lead to the formation of adhesive wear. Lubricants that are formulated with extreme-pressure (EP) or anti-scuff additives may be protected from adhesive wear to a certain extent, however, a bad case of misalignment is simply too great for additives to combat.

But let us say, the film is still there, however, if the film is greatly reduced due to misalignment, excessive component wear can still happen. This type of wear is in the form of contact fatigue and three-body abrasion. Contact fatigue is often situated in the gear teeth at the pitch line and rolling element bearings due to the high concentration of load that is transformed across a small area. Meanwhile, three-body abrasion occurs in the presence of abrasive wear.

Source: machinerylubrication.com