The Steep Price of Shaft Misalignment

Proper shaft alignment is really a matter of cost avoidance.

When shafts are optimally aligned, energy consumption and unplanned downtime decrease, while equipment lifespan and efficiency ramp up.

“Shaft misalignment is responsible for up to 50% of all costs related to rotating machinery breakdowns […]

When shafts or belts on rotating equipment are misaligned, the risk of costly, unplanned machine downtime rises dramatically. Misalignment also damages seals and couplings. Lubrication problems often can be traced to seals that have been compromised by shaft or belt misalignment. Simply replacing a seal will not stop future seal failure and associated loss of lubricant — only correcting the misalignment will solve the problem.

Failure to align the shafts or belts properly will increase the amount of stress on the units, resulting in a range of potential problems that ultimately can seriously impact a company’s bottom line:

→ Increased friction, resulting in excessive wear, excessive energy consumption, and the possibility of premature breakdown of equipment

→ Excessive wear on bearings and seals, leading to premature failure

→ Premature shaft and coupling failure

→ Excessive seal lubricant leakage

→ Failure of coupling and foundation bolts

→ Increased vibration and noise”

(The Importance of Shaft Alignment)

Or, put another way:

“When two pieces of rotating equipment are connected through a shaft coupling, every effort should be made to minimize coupling and shaft misalignment. Proper alignment will reduce bearing, shaft and coupling failures, bearing and coupling temperature, vibration, and energy consumption. In addition, good alignment will extend equipment life between planned maintenance intervals.

When considering how precise the alignment needs to be, consider alignment limitations of all the system components, not just the coupling. A flexible coupling is no excuse for excessive misalignment.”

(Coupling Alignment Fundamentals)

So, what does shaft alignment and misalignment look like?

There are three types of misalignment. Here’s an overview of each from the US Department of Energy, Advanced Manufacturing Office.

1. Angular misalignment occurs when the motor is set at an angle to the driven equipment. If the centerlines of the motor and the driven equipment shafts were to be extended, they would cross each other, rather than superimpose or run along a common centerline. The "gap" or difference in slope of the motor shaft when compared with the slope of the stationary machine shaft can have horizontal misalignment, vertical misalignment, or both. Angular misalignment, in particular can cause severe damage to the driven equipment and the motor.

2. Parallel misalignment occurs when the two shaft centerlines are parallel, but not in the same line. There are two planes of parallel misalignment as shafts may be offset horizontally (displaced to the left or right), vertically (positioned at different elevations), or both.

3. Combination misalignment occurs when the motor shaft suffers from angular misalignment in addition to parallel misalignment.

Looking to avoid misalignment and its heavy costs?