Is there any set guide lines when you should allow for thermal growth during alignment .What would the differance between the Driver and Driven have to be to consider aligning with thermal growth in mind .Any comments would be greatly appreicated.Thanking you in advance.Keith

Materials for example: Steel = 6.3 x 10^-6 while SS = ~9 x 10^-6.

Product: propane compressors are hot on one end and cold on the other or a hot oil pump is ~700F while the motor is ~140F? Or turbine driving something cold.

Distance: what's the center heigth difference? Are the legs cooled? What are the delta's along the leg - a consideration?

Hi Keith

A good printable form for thermal growth calculation can be found on Tim Duntons website:
http://www.unitechinc.com/pdf/A113Thermal_Growth_Calculation_Form.pdf

Regards Brad

Brad,

The referenced form is fine to calculate the thermal growth/rise at each foot. For large critical machines it may be necessary to evaluate both sides of the machine, since temperatures may not be uniform. A scaled sketch of the machine feet and coupling center can be used to compute the net offset and angle at the coupling center.

Walt

Keith, if you have machines that run really hot as in Sam's examples, then it's a good idea to be pretty thorough in calculating expected thermal growth. And if possible, it's good to do a hot alignment check (lasers make this pretty easy -- just mark your bracket positions on the shaft when you do the initial alignment and save the 'distance' measurements (also, do NOT break down the brackets). If the guards can be left off, you can throw the brackets on and do a hot alignment check in probably less than 5 minutes (assuming the shafts/environment is not too hot for the laser). This can be done with indicators as well, but a laser is easier I think (if it will work).

In general, if there have been no problems with a machine (bearings, seals, couplings) then thermal growth is likely not a problem. If you are doing routine realignment after a teardown not related to bearings/seals/couplings, then I wouldn't sweat the thermal growth too much. Let the machine's history be your guide.

On the other hand, using an infrared thermometer and a measuring tape, it's pretty easy to do a quick temperature profile on most machines if they are running. Any thermal compensation is usually better than none.

Thermal growth should always be considered. Once calculated across all the feet of the machine, then it can be determined whether to correct for the growth. The determination is dependent on your alignment tolerances. If the growth takes you out of tolerance, then you should correct for it. It should be remembered that coupling manufacturers sell couplings, they do not consider bearing or seal clearances when they tell you how much misalignment a coupling can handle. With a 0.002" tolerance, I have found many machines that we never considered thermal growth on actually end up way out of tolerance when up to operating temp.

As for hot alignment checks, that doesn't happen here anymore. By the time we can shut down a machined, isolate it, pull the power, lock it out, and try test the switch, the machine is damn near cold!!

Happy Holidays,

Gary B
general all around flunky

Word of caution here: an acorss the coupling check must be done in the few minutes Rusty mentioned or null. And is the least desirable method but better than nothing maybe. I've done it using an indicator reverse setup in less than three minutes.

With laser you can do the initial alignment and record. Then place the lasers or mount them on the driver's bearing housing and driven's bearing housing - note, this can only be done on small rigid machines. NEVER PEDESTAL
BEARINGS OR LARGE MACHINES - else huge errors can occur.

General best accepted on a very high precentage of machines is the Essinger bars or acculign system of hot alignment. As about as good as it gets and your in-house millwrights can perform this type of setup and readings. You can also incorporate it into your PdM program by taking 'hot' data every quarter of semi-annual or with changes in the weather. You can also monitor axial movements and piping. It is very affordable.

We can go on to optical alignment but it requires expert personnel with a lot of expense. But, it is a very good method in the hands of qualified personnel..........and qualified personnel only.