Plant & Works Engineering
Misaligned shafts in rotating machinery
Published:  15 November, 2007

The answer to this month's trouble shooting teaser is provided by Phil Burge, marketing manager for SKF (U.K.).



I understand that misaligned shafts in rotating machinery can cause bearings and other parts to fail but what"s the most effective method of checking shaft alignment?



Up to 50% of mechanical breakdowns in rotating machinery are estimated to be the result of misalignment of one type or another. Incorrect alignment can put excess strain on components, leading to increased friction and vibration levels, greater wear on bearings and shafts, and an increase in energy consumption.

Traditional alignment methods, such as using a straight edge or piano wire, although still in common use, can struggle to produce the positional accuracy required by much of today’s precision machinery. More accurate methods such as dial indicators may give the required result, but they are generally time consuming and can require a specialist operator.

The latest generation of laser-based alignment systems can provide a simple and accurate solution, providing a three-step process for correcting alignment: measurement, alignment and documentation. The first step is to measure the machinery’s actual alignment status to determine the degree of misalignment, if any. The machine is then re-aligned if necessary, both horizontally and vertically, and the entire process is documented for reporting and analysis.

For larger, more complex systems, where it is crucial that a series of machines are correctly lined up with each other, starting at one end and working through machine by machine can be time consuming and makes the assumption that the first machine is the 'stationary’ one in the train, with which all the others are aligned. Laser alignment tools are now available that take measurements at every coupling in the train to determine which is the ‘stationary’ machine before work begins. The laser system is then used to align the rest of the train with that machine.