Guide to machine faults and how to get to root cause

06-28-2019 | Vibration
The Fluke 805 Vibration Meter is a reliable device offering a four-level severity scale to assess the urgency of machine faults.

The number of possible mechanical machine faults is nearly endless. However, up to 90 percent of the time, machine faults fall into one of four main categories: misalignment, imbalance, looseness, or bearing wear. As the old saying goes, “when you hear hoofbeats, think of horses—not zebras.” While rare machine faults do occur, they are just that—rare. Your resources are best allocated to learning to identify the most common types of machine faults.

Misalignment: The axes of rotation of two shafts are not collinear when the machine is running under normal operating conditions. This leads to excessive vibration and increases the wear of components including bearings and seals.

Imbalance: A heavy spot on the shaft causes forces in all radial directions that lead to excessive vibration and increase the wear of components including bearings and seals.

Looseness: The shaft, foundation, or a component has become loose, which causes forces that lead to excessive vibration and increase the wear of components including bearings and seals.

Bearing wear: Bearings will wear from excessive loads, other machine faults, poor lubrication or installation, etc. If not corrected, the bearings will eventually fail.

Root cause analysis is a method of determining how an issue occurred in the first place. Using root cause analysis can help you identify where a problem began and what caused it. Performing a root cause analysis is similar to retracing your steps. From there, you can take your knowledge about what happened and why to find ways to prevent it from happening again.

First, identify the boundaries of the problem. Where did it begin and where did it end? What are the variables, and what are the constants? What, if anything, changed to make the problem possible? Depending on the situation, it may be easier to trace a failure back to the event that set it in motion, or it may be easier to consider multiple possible catalysts and chart a path forward from each of those toward the failure.

An example of root cause analysis is when teams replace bearings and seals without looking for the root cause. The root cause could be misalignment, shaft imbalance, or looseness. Teams that find and fix the root cause find that they don’t need to keep fixing the symptom.

Failure mode and effects analysis, or FMEA, is an exhaustive look into the causes and effects of failure. It’s best used for more complex situations.

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