two shafts alignment
two shafts alignment
(OP)

I have a forced fan that has two equipment as driver, a electric motor (start-up) and a steam turbine (permanent). I want to know which equipment is better to set as stationary for shaft aligning? What is the best procedure? For example set fan as stationary and align turbine and motor based on it?





RE: two shafts alignment
Johnny Pellin
RE: two shafts alignment
Is this alignment quest as a result of some vibration analysis?
I'd think first about how movable each of the 3 component is.
I'm guessing the turbine and it's piping etc is not easily repositioned.
I'm guessing the motor is the easiest to move, and the fan with flexible duct connections relatively easy as well.
However, there is risk of any of the components becoming "bolt bound" when moving .
Or, even being bolt bound right now.
I insist on getting thermal growth compensation values for each component from the manufacturer(s). Turbines often experience 3 dimensional thermal growth.
*** I'd check the as-is alignment for the entire train before making any moves.
Starting at an end component, then aligning the middle component to it, will very likely result in the third component requiring impossibly large adjustments.
Whereas considering the entire train at once may find a relatively simple compromise alignment achieved by tweaking all 3 slightly.
RE: two shafts alignment
Johnny Pellin
RE: two shafts alignment
RE: two shafts alignment
Yes, the thermal growth info is required, at least as a starting point.
Is the fan large enough to have been designed as a one-off?
There may be a bunch of O&M manuals for the plant, with a section about the fan from the time of the original purchase.
I'd look for basic alignment procedures in there, including thermal growth information.
Like, "set the motor 0.005 inch low".
RE: two shafts alignment
An additional concern occurs for induced draft fans of this type. If the fan box is foot mounted and independent of the bearing pedestals, the vertical movement of the fan box must be accommodated. This does not affect the coupling alignment if the bearing pedestals are independent, outside of the fan box and cold supports. Instead, the vertical growth of the foot mounted fan box requires adjustment of the fan wheel inlet cone clearance. It can also create problems with the shaft seals where the shaft passes out of the fan box. In the fan I was describing above, the original clearance between the fan box and the shaft was not adequate and the fan box grew up into the bottom of the shaft at the seal locations. We had a hard shaft rub resulting in a failure. And, keep in mind, this is a shaft that is over 16 feet long and 12 inches in diameter at the seals.
Johnny Pellin
RE: two shafts alignment
Some extreme, and not-so-extreme examples here -
http://www.vibration.org/Presentation/Feb%202007/O...
Again, Is this alignment quest as a result of some vibration analysis?
RE: two shafts alignment
The above coupling statement isn't always, true. While it definitely needs to be considered, we have done numerous non-lubricated couplings that are designed to handle that type of axial growth. The key is what speed and torque you require. As well as how long it takes for the system to get up to operating temperature.
When it comes to couplings we are always here to help.
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