Page 178 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

tions. In any alignment process, this is accomplished by aligning
the machine opposite the hot readings.
When using this method to offset the equipment to compen-
sate for thermal growth, be sure to record the temperature of all
equipment during the alignment process. This will assure the
most accurate final alignment. After any alignment process, be
sure to measure and record the final vibration amplitudes and
record them on the alignment form for future reference.

Example 9-2
The machine in Example 9-1 has known thermal growth for
both the stationary machine and the adjustable machine. The out-
board foot of the stationary machine grows vertically 3.5 mils and
the inboard foot grows 2 mils. The D distance is measured at 12
inches and the E distance at 56 inches. The adjustable machine will
grow 1 mil at the inboard foot and shrink 2 mils at its outboard
foot. Determine what corrections need to be made to perfectly
misalign the machines to assure proper alignment when at oper-
ating temperatures. What should be the final indicator readings?

Step 1. The first step is to lay out a graph of the equipment and
determine the thermal growth effects. The hot centerlines for both
machines will be plotted to determine their final positions.
The basic graph layout is illustrated in Figure 9-7. Note again
that all distances are measured from the stem of the stationary
indicator.

Step 2. Next, the hot position of each foot is located and the
centerlines for the hot alignment are drawn.
In this example, the stationary machine hot centerline crosses
the inboard foot of the adjustable machine at plus 1 (+1) mil and
the outboard foot at zero. The hot centerline of the adjustable
machine also is at plus one mil at the inboard foot and minus two
(–2) mils at the outboard foot. Both machines will grow to the
same point on the adjustable machine inboard foot, and thus no
correction is required. Since the adjustable machine hot centerline