Don't let shafts be an afterthought

Nov. 1, 2010
Accurate alignment saves energy and costs.

Did you know that shaft misalignment accounts for nearly half of all expenses related to rotating machinery breakdowns? By accurately aligning the shafts of rotating machinery, many of these breakdowns — and their associated downtime — can be prevented.

Shaft misalignment

To function at its best, machinery needs to be aligned in both the horizontal and vertical planes. When incorrect alignment occurs, it is often due to parallel or angular misalignment, or more often, a combination of both. The consequences of improper shaft alignment are serious, including increased friction and therefore higher energy consumption, premature bearing and seal failure, and excessive lubricant leakage. Other negative results can include premature shaft and coupling failure, malfunction of coupling and foundation bolts, and increased noise and vibration levels. However, by properly aligning the shafts of rotating equipment (such as an electric motor coupled to a pump or fan), component wear and tear can be reduced and energy consumption minimized.

Alignment methods

The most common shaft alignment method is to do nothing at all: Many engineers and plant maintenance workers believe that flexible couplings and bearings can handle machine misalignment just fine. However, this approach often leads to equipment failure and excessive energy consumption.

Another approach is to use a straight edge. While this quick and easy method is an improvement over doing nothing, accuracy varies significantly between users and this simple tool offers zero guidance on how to correctly align shafts. Dial indicators are yet another method of bringing shafts into line with each other. While these indicators offer high accuracy, they tend to be time consuming to set up and require expertise and training to deliver consistent results. Another drawback is potential rod sag of the bars holding the indicators in place.

To address these and other issues, laser shaft alignment tools are another possibility. Although costs vary among manufacturers depending on complexity, laser-based tools are fairly easy to use, quick to set up, and provide highly accurate readings.

One such system from SKF USA Inc., Lansdale, Pa., includes a handheld tool with a mini-HMI screen showing corrections that need to be made. This third-generation laser product family includes TKSA 20 and TKSA 40 versions. Both models are easy to use and display realtime alignment values to confirm results of alignment corrections as they are made. No special training is required to use the devices. Among their features, the TKSA 20 integrates a quick-start guide and fast measuring unit positioning capabilities while the TKSA 40 is designed with built-in tolerance checking and a memory that enables results to be stored and shared. Using these tools can help reduce energy consumption and the potential for machinery failures typically encountered when shafts are misaligned. Their use can also contribute to reduced stress on mechanical components, enhanced equipment reliability, and extended machinery service life.

This month's handy tips courtesy of SKF USA Inc.,

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