Up Time Magazine- February/March 2008

with a simple 90 degree 0.150” deep notch. A small tapped hole in the center allowed a small filler piece to be clamped in the notch to vary the stiffness change due to the notch. Tests were run with the filler piece removed, partially and fully tightened. Figure 2 - SpectraQuest’s Machinery Fault Simulator (MFS) Time Waveform 4E+0 2E+0 0E+0 -2E+0 -4E+0 2.4 5 10 15 20 25 30 35 40 Time (s) 45 50 55 60 65 68 g Figure 4 - Time waveform of the start-up and cost-down test for “all bolts tight” condition. Spectrogram 247.2 220 200 180 -1.1E+2 -21.2 Experimental Results and Analysis All experimental data have been collected and analyzed by using SpectraQuest’s VibraQuest software package. Transient, Waterfall and Analysis tools of this software package were mainly used in this study. A. Cracked shaft simulated using Flange B. Notched shaft with V-shape crack 1.6” from the inboard bearing housing C. Notched shaft with V-shape crack 1” from the inboard bearing housing The changes of critical speeds for the intact and cracked shafts were studied in experiments A and B. The changes of 1X and 2X frequency responses for the intact and cracked shafts were investigated in experiments B and C. The running speeds were chosen to be 2000 rpm and 4000 rpm. The tests were conducted on the rotor MFS which is illustrated in Figure 2. Four accelerometers were mounted on the inboard and outboard bearing housings in the vertical and horizontal direction, respectively. The setup of experiment A is shown in Figure 3. Figure 3 shows the flange-simulated cracked shaft. It consists of two separable shafts joined at the mating flanges. The four (4) bolts compress Belleville washers which can be loosened or tightened in a pattern to create an unsymmetrical time varying stiffness and simulate the opening and closing of a transverse crack. The large disc next to the flanges provides gravity loading and a shaft bending moment. Tests were run with one, two and three bolts loosened. The setup for experiments B and C use a shaft Frequency (Hz) 160 140 120 100 80 60 40.9 40.9 Change of Critical Speeds The critical speed in start-up tests can be identified by using time-frequency spectrogram, time waveform, and a waterfall plot of the acceleration signals, shown in Figs. 4 through 6 respectively. In Fig. 5 the abscissa is time (second). The red spot where a cursor points represents the first critical. The cursor values indicates that the critical occurs at 21.7 second and 65.62 Hz. For Experiment A, the critical speeds for different cracked conditions on the shaft are listed in Table 1, where the ‘all bolts tight condition’ simulates no crack on the shaft, and ‘three-loose’ means the most seriously cracked condition. Figure 5 - Intensity plot of the stat-up in the ﬂangesimulated crack test. The critical speeds for differFigure 6 - Waterfall plot of the start-up and coast-down in ent cracked conditions on the ﬂange-simulated crack test the shaft in Experiment B are listed in Table 2. Intact means no crack on the shaft and “No-filler” represents the most Conditions All Bolts Tight One Bolt Loose Two Bolts Loose Three Bolts Loose Critical Speed (Hz) 65.62 65.00 64.37 64.37 Conditions Intact Filler Fully Tightened Filler Partially Tightened No Filler Critical Speed (Hz) 65.00 62.50 62.50 60.00 Figure 3 - Setup for experiment A www.uptimemagazine.com Table 1 - Change of the critical speed in Experiment A Table 2 - Change of the critical speed in Experiment B 79 http://www.uptimemagazine.com

Table of Contents Feed for the Digital Edition of Up Time Magazine- February/March 2008

Up Time Magazine- February/March 2008 Contents Upfront Upclose: Lessons Learned from the Walter Reed Story Information Technology: Parenting and Asset Performance Infrared: It's Alive! Lubrication: A Sense of Change Maintenance Management: PdM, Standardized Motor Testing: Being Well Connected Precision Maintenance: How to be Marketable Reliability: The Voyage of Wells Dairy Ultrasound: Two is Better Than One Vibration: Diagnosing a Cracked Shaft Upgrade: A Different Kind of Journey

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