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# Hot Alignment

## Hot Alignment

(OP)
Measure the distance from the shaft centerline down to the base of the feet. Take a surface temperature of the foot/case every inch or two along that distance and do the math. A known temperature distribution over a known distance of a known material provides a known growth.
Can someone please elaborate above statement?

### RE: Hot Alignment

Where's the part you don't understand?

Have you made the suggested measurements, so we might have a real data set to examine?

Basically, the statement suggests doing a piecewise approximation of a thermal gradient, which is likely to be continuous. But you can get close enough for most purposes by dividing the part as suggested, putting imaginary latitude planes between the temperature measurement targets, and assuming that the entire 'lamination' corresponding to a particular temperature is at that temperature.

The statement doesn't address the issue of expansion along the shaft axis, which should be addressed, but separately.

Mike Halloran
Pembroke Pines, FL, USA

### RE: Hot Alignment

It is common practice in our plant to cold align hot machines using an offset based on the sort of temperature measurements you are describing. With the machine in normal operation, we would measure the temperatures along the supports. Based on the dimensions, the temperatures and the known coefficient of thermal expansion of the material, we would estimate the thermal growth from ambient temperature. Then, when the machine was down and cold (ambient), we would perform the alignment with the offsets based on that calculated growth. If our estimates were accurate, the machine would grow into alignment when it runs and this would be verified with vibration data from continuous or portable vibration systems. This method avoids the need to shut the machine down and attempt a quick alignment in hot condition. We have had very good results using this method.

Johnny Pellin

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