A while back, a German company that provides gas contacted Easy-Laser GmbH to participate in the troubleshooting of a machine that showed high vibrations levels. The machine was a geared compressor supplying nitrogen gas for the process. As part of the investigation, the compressor owner asked us to provide thermal compensation values for the alignment.
We got access to the report from the last shaft alignment job, where we could see that thermal compensation was applied.
Our plan for this investigation was to start by checking the shaft alignment status in cold conditions when the machine was standing still, in a non-operating state. And the results from this shaft alignment check revealed that the machines were misaligned more than twice the amount of the specified thermal compensation value in the vertical position.
We then installed laser sensors on the motor and the compressor to perform what is called a dynamic measurement (this is done using special brackets (see illustration below) and the alignment program EasyTrend).
We started the compressor and began to measure its dynamic movements. First, we performed a dynamic measurement until the machines reached operating temperature. Then we turned the machines off and performed shaft alignment verification in hot condition. Afterward, we mounted the sensors back on the machines again and measured the movement from hot to cold conditions.
We basically performed 4 measurements:
- Shaft alignment verification in Cold condition.
- Dynamic measurement from Cold to Running.
- Shaft alignment in Hot condition.
- Dynamic measurement from Hot to Cold condition.
The results:
The shaft alignment made during Cold condition revealed that thermal compensation values had been inserted into the alignment protocol, but they were more than doubled! A wrong interpretation of the compensation values or other mistakes must have occurred when the machines were aligned in the past.
The dynamic measurement from Cold to Running conditions revealed that the compressor movement in the vertical position, due to thermal expansion, was exactly the same as the specified thermal compensation value provided by the compressor owner. But, since that value was doubled, the compressor was heavily misaligned in the vertical direction. To our surprise, we found out that the compressor moved 1,3 mm in the horizontal position, which nobody expected. Horizontal misalignment of 1,3 mm is very severe.
The dynamic measurement from Hot to Cold conditions confirmed the values and direction of the movement while the compressor was cooling down.
Conclusion:
Do not assume that the calculated value for thermal compensation is correct and the machines are compensated for it correctly. Instead, measure your machines, check the alignment conditions, and verify.
Watch our Shaft Alignment Know-How: Thermal Growth video to learn the importance of accounting for thermal growth on rotating equipment!
Thank you Roman Megela with Easy-Laser for sharing this informative article with us!
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Alignment by Diana Pereda