October 27, 2011
Aligning Machines Mounted on Chocks
By Brad Case
“Our large machines use adjustable chocks, instead of shims for correcting the vertical alignment; can we use the VibrAlign Verti-Zontal compound move with our Fixturlaser XA when correcting the misalignment?”
Adjustable chocks are typically found on large machines such as the engine-compressor sets used in the gas compression industry. The chocks are used in place of shims at the equipment feet and require the alignment technician to perform the vertical adjustment “live”.
The Verti-Zontal process is modified slightly by taking the three alignment measurements from top to bottom (12 o’clock, 3 o’clock and 6 o’clock, for example) vs. side to side (9 o’clock, 12 o’clock and 3 o’clock) as when aligning a “shimmed” machine. After the results are analyzed press the shim icon as you normally would and note the feet position. This is the vertical position of the movable machine at the feet BEFORE the hold down bolts are loosened. Then press the live adjustment icon.
Since the 3rd alignment measurement was taken in the vertical plane, the live screen now shows the vertical view. After the hold down bolts are loosened note, if any, the change in the foot values as you will need to compensate the “live” vertical adjustment by this amount. (Remember the true vertical position of the movable machine is with the hold down bolts tight).
Perform the vertical adjustment, per the adjustable chock manufacturer’s recommended procedure, until the vertical alignment meets tolerance. Leave the hold down bolts loose or slightly snug.
Rotate the shafts to a horizontal plane following the same direction of rotation the alignment measurements were taken in. The XA’s screen will automatically change to the horizontal view. Correct the horizontal misalignment then tighten the hold bolts in a cross torque pattern in three passes. Then re-measure.
If further minor adjustments are required to meet the vertical and/or horizontal tolerances, do so accordingly; however, remember the sensors need to be in the plane you are correcting as both the vertical and horizontal corrections are done live with adjustable chocks. Once the alignment meets tolerance document it by saving.