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Sr. Member
Posts: 670
Reply with quote  #16 
Originally Posted by Big Al
It's been a few years since I last did a laser alignment, but there were a few critical machines that we would return to after running them up to temperature and carry out a hot alignment. Have all the thermal growth calculators made this practice redundant now?

We did this on boiler feed pumps, for initial alignment we keep the hot water running until reaches operation temperatures, and align with this temperatures witout termal growth considerations, LOTO doesnt take much time in my plant and coupling guard is easy to remove, our alignment system you only have to verify one distance (target to coupling center) everything takes than 30 minutes and ussually we dont make corrections, if needed some small shiming and horizontal corrections takes another half hour.

to be fair, we have not take any temperature change during measurements.

for vibration as long as it stays in tolerance is good enough for us.

Sr. Member
Posts: 1,918
Reply with quote  #17 
Yes I done that on a small food plant a hi pressure powder milk fan, small plant, minimal delay, laser is on as the fan rolled out... I was stupid setting the thing normal with motor slightly low and the fan get really hot and raised a lot so I actually got the famous 2x RPM vibration for once, a quick hot alignment and it run another 10 years, no 2x RPM. Now plant is sold and work with none milk milk stuff like soy or oats emulating milk or so.
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
Big Al

Sr. Member
Posts: 102
Reply with quote  #18 

These were Hoffman blowers (3000RPM). The switchroom was next door to the blower house so we could lock-out and remove the two guard bolts within 60 seconds. With two of us on the job, I'd say that we were achieving an initial sweep in less than 5 minutes. I appreciate that the temperature was dropping from the moment rotation stops, but felt it was still better than a cold alignment.

This was in a previous job with a different employer. I've been with my current employer over 17 years now, so you're asking me to dig deep in the memory bank. I don't remember if we ever did a before and after on the vibration signatures.

Posts: 35
Reply with quote  #19 
Hot running, SISW, overhung fans are typically manufactured by OEM's to separate the rotors pressure section of the housing thermal from the horizontal bearing base by a gap between them, sometimes insulated sometimes not. Often the two fan sections of this arrangement have their own individual base rail mounts but are shipped bolted together for convenience and sale to customers of a so-called ready to bolt down "assembled" unit. They are intended to be unbolted from each other  and thermal gap separated on site, doesn't always happen. Not doing that can put a thermal twist in the bearing base, effecting bearings, and cause multiple alignment complications

A few manufacturers maybe not knowing or caring dont do anything to mitigate this thermal potential and there is a significant thermal growth delta from one end of the bearing mounting area to the other. Again, can cause twisting. Not unsolvable alignment if one knows or can calculate the delta from the obvious, the cold vs hot temps of the bearing base ends. Once armed with that simple data it is easy to program cold alignment targets, more than just vertical parallel, into a laser device. 
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