The consequences of positional change due to thermal growth in machinery as it pertains to shaft alignment are well documented. Methods for determining these changes and compensating for them are not only essential to the reliability of machines but can prevent catastrophic failure. It is therefore of great importance that these methods be carried out as carefully as possible—minimizing human error as much as possible to ensure effective results.

One often-overlooked consideration when performing shaft alignment measurement is the temperature and thermal stability of the very components used for these measurements. Brackets, lasers, sensors—all components that are susceptible to thermal growth. Changes in the intensity of sunlight, large shifts in ambient temperature during the job, and performing measurements too soon after bringing the components out to the machine can all lead to lack of repeatability and improper shaft alignment corrections.

XT Components snow cold thermal growth
Photo credit: Brian Franks with JetTech Mechanical LLC.

XT Components sun hot thermal growth


You can minimize the effects of these conditions in various ways:

  1. Always allow a suitable amount of time for the alignment system to acclimate to the environment in which you will be performing the measurements. For example, if the equipment is moved from a warm office or truck to a cold environment and measurement is begun immediately without giving the temperature of its components enough time to stabilize, performing the shaft alignment will be a bit like trying to hit a moving target. The brackets and/or laser and sensor housing will still be physically changing in dimensions until stabilization has occurred.
  2. If sunlight conditions are unstable where you are working try to keep the alignment components shielded from the sun. Direct sunlight striking the laser housing of a shaft alignment system can have an adverse effect on the reliability of the readings during a measurement.
  3. Keep portable heaters and air conditioning units away from the area. It is natural to want to work in a comfortable environment, but the unstable air currents caused by heaters or a/c’s can wreak havoc on measurement repeatability.
  4. And one more: if a heat source is intense causing heatwaves in the path of the laser beam, thereby distorting or refracting the laser beam and affecting your repeatability, a simple fan to blow air through that area can help to stabilize conditions or provide a uniformly turbulent atmosphere for the laser to travel through, allowing its true position to be accurately averaged.

Observing these principles while performing shaft alignment readings will allow you to achieve more stable and reliable results and thus help you to #keepitrunning.

For more information, check out our Shaft Alignment Know-How: Thermal Growth and learn the importance of accounting for thermal growth on rotating equipment.

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, by Oliver Gibbs CRL