A long time ago I did some alignment checking on a few turbine drive generators.
I recall each of the manuafacturer's specs included several thousandths of 3 dimensional compensation for where the gearbox shafts would be when running due to oil film plus gear forces. (plus some even larger thermal growth values for the hot turbine).

Anyway, what I'm looking for now is a sample of a gearbox spec calling for significant static adjustment for the running shaft position, just to gently prove a point here at work. An online link would be slick, but Google so far has let me down.

Thanks,

Dan T

Dan,

Many years ago I aligned a steam turbine generator with reduction gear. The gear manufacturer provided a diagram with all of the offset values. The gearbox hot alignment moved more than turbine and generator in both horizontal and vertical directions. I recall it was a Lufkin gearbox. I also worked on a GT with gearbox and generator. The gearbox was Swiss manufacture. A large gearbox (say 40 MW) can have 10 to 15-mils clearance in journal or tilt-pad bearings. Here are the important forces and thermal expansions:

Gearbox expansion:
Horizontal depends on temperature and key location
Vertical depends on temperature

Shaft position in bearing clearance:
Separation force in-line with shaft centers
Torque force (tangential with direction depending on shaft rotation)
Gravity (shaft/gear weight in vertical direction)

The final shaft position is a combination of the three position forces and two thermal expansions

Try contacting one or more large gearbox manufacturers.

Walt

I don't think our guys use that type of correction when aligning our machines with gearboxes. I know we use Permalign to compensate for thermal and piping effects, but that is based on housing position so I don't think it would show that effect (would it?).

I'd be interested to hear more about it as well. I'll check our vendor manuals on Monday to see if they say anything about it.

Permalign or other case expansion measurements doe not measure actual shaft position. This is a non-issue for gearboxes with antifriction bearings, but can be important for large gears with journal bearings that have substantial clearance.

Walt

Dan, you can go to the link http://www.philagear.com/pdf/HighSpeedGearDrives.pdf and download a copy of Philadelphia Gear's High Speed Service manual. Pages 22-24 cover exactly the discussion you are after. I've attached just this span of pages.

I worked for Philadelphia Gear Corp. for 18 years and I can attest to the fact that alignment of units with sleeve bearings was a frequent issue. Many people aligned to colinear shafts without taking into account where the shafts would move in the bearings due to load.

John

HighSpeedGearDrives.pdf (328 Kb, 30 downloads) alignment discussion from PGC High Speed Service Manual

John,

Thanks for the reference.

Walt

Thank you everyone