September 17, 2012
Machine Train Shaft Alignment-To Move or Not to Move
By Brian Shanovich
It is always the question with machine train shaft alignments: what needs to be moved? The best way to approach a multiple machine set shaft alignment project is to know where everything is and where everything needs to be.
This particular auxiliary generator set has 10 pieces of rotating equipment to align. An induction motor in the middle with five pieces going to the north and four pieces going to the south, all rotating at 1800 rpm
This assessment is tackled by measuring the alignment condition from the induction motor to the first piece north. After this is measured, then the remaining pieces going north will be measured by using the Machine Train program. With the Fixturlaser XA Pro, we can make the machine template with machine names and dimensions and store it in the XA’s memory before the shaft alignment conditions are assessed. When the alignment assessment is needed, just recall the saved fie from memory and measure the rotational centerlines from machine to machine.
The induction motor to delivery bridle top generator alignment is clearly within the 1800 rpm tolerances of 0.7 mils/inch angularity and 4.0 mils offset.
As for the remaining pieces of equipment, the results again meet the correct shaft alignment tolerances.
Now the south generator set needs to be assessed. Remember the induction motor has a shaft that connects to both the north and south stands. After measuring across four couplings, the results are a bit more interesting. The XA Pro has a default “Best Fit” solution that is displayed after the measurements are completed. There are two machines out of alignment (designated by orange values), both Stand 1 and Stand 2 Front Screw Down Generators. The best fit solution has the Stand 2 Front Screw Down Generator with the least amount of correction (shimming less than 90 mils). Let’s not forget that the induction motor is also coupled with the north generator set and that is completely within tolerance. If the induction motor is moved, the north generator set will be out of alignment. The best solution (not necessarily the ‘best fit’) is to select the induction motor by touching the lock over the induction motor and now the assessment can be done to see if there is enough movement both vertically and horizontally to meet the alignment specifications.
As seen in the report below, if the induction motor is now the “fixed” machine, the vertical and horizontal values are recalculated to show the corrections needed in this scenario. The farther away from the fixed machine, the more the correction. The horizontal adjustment will be easily met with a correction at the back foot of Stand 2 Rear Screw Down Generator (far right) of 114 mils. The vertical correction could be more dubious; but, there were over 500 mils of shims at both of the Stand 2 Front and Rear Generators and over 300 mils of shims for both of the Stand 1 Front and Rear Generators.
In conclusion, a machine train alignment can be completed with much less frustration if the proper tools are utilized. It is always better to see where you are before you start moving equipment around–plan your work then work your plan.