- Buyer's Guide
I am a shaft alignment trainer. My insight on the real state of industrial alignment practices comes from many hours spent making alignment checks and corrections on process equipment. Here are some of my observations:
Most of the attention to precision alignment has centered on large, process-critical machines.
Most maintenance departments have been downsized and spend much of their human capital addressing unscheduled maintenance.
Most of the unscheduled maintenance activity is on small equipment such as ANSI pumps and mixers.
Most plants have very few people capable of achieving precision alignment.
There are even fewer people who really understand shaft alignment.
Most tradesmen are smart and can learn alignment in one or two days.
Shaft alignment of direct coupled machines can be done quickly without sacrificing precision.
Small, rotating machines are often badly aligned. I see terrible things: piles of coupling debris, spare coupling parts in the mechanical room, packing and seals leaking profusely, and misalignment so severe that it can be seen with the naked eye. No doubt, large machines are important, but they are rarely severely misaligned. Huge payback can result from aligning the many small machines that often fail catastrophically. How big can the payback be? A corn processor in the Midwest with a population of around 800 pumps used to repair two to three pumps every day. After focusing on small pump alignment, the site now repairs one to two per month and is saving more than 4,000 maintenance hours per year. That is equivalent to adding two people to the maintenance staff.
Figure 1. Dimensions are entered.WHY ALIGNMENT?
Every shaft rotates around an axis that forms a straight line. If two shaft rotational axes are positioned so that they are collinear when the machines are at operating temperatures and conditions, the forces at the power planes will be minimal. As a result, bearing and seal life is lengthened.
You can accomplish precision alignment in one or two moves virtually every time. Multiple alignment correction moves frustrate tradesmen and waste time. But, perform pre-alignment steps prior to using precision tools or your alignment corrections will be unpredictable. The box on Page 36 shows five simple steps that eliminate most unnecessary corrective moves.
Figure 2. The measurement -12.4 shows the need to add .012 inches to the front feet; +9.7 means remove .010 inches from the rear feet.MEASURE MISALIGNMENT
Rotate the shafts from 60 to 180 degrees to determine the vertical and horizontal position of the two rotational axes at the sensors. The laser system calculates the misalignment at the coupling (where the forces are generated) to determine the alignment quality. In this case, color guidance indicates that the alignment tolerances aren't satisfied. The laser also computes the vertical and horizontal positions at the machine feet because that is where adjustments can be made.
Figure 3. Measure the misalignment.
Conventional wisdom in shaft alignment is to completely solve the vertical misalignment first. Horizontal corrections are only undertaken after vertical tolerances are satisfied. What dismays many is that after making horizontal adjustments, the vertical tolerances are no longer satisfied. Therefore, after time has been spent to make a precise vertical alignment and after the horizontal alignment is made, the vertical will again require readjustment. This is because vertical misalignment affects the horizontal alignment and vice versa.
A NEW APPROACH
A compound move is a process where both the vertical and horizontal alignment is made from one set of alignment data. After measuring the misalignment, the vertical shim adjustment is performed.
Before rechecking the vertical outcome and before the bolts are retightened, also make the horizontal alignment (Figures 4-5). Live correction data gives the operator feedback on the correction. Color guidance indicates when tolerances are satisfied.
Only then, after both vertical and horizontal corrections are made, should you retake the alignment data. By making compound vertical and horizontal corrections, you minimize the "cross effect". The first compound move should get you very close to tolerance in both planes. Consequently, repeating the procedure with a second compound move will result in a precise alignment virtually every time.
KEYS TO SUCCESS
Here is my advice to you:
Figure 6. Final alignment data.
Figure 7. The document is saved.
David Zdrojewski is the founder and CEO of VibrAlign Inc., an educational resource and distributor of vibration analysis equipment. To learn more, call 804-379-2250 or visit www.vibralign.com.