Handbook of Shaft Alignment Part 3 pdf

. Gravitational force . V-belt or chain tension . Shaft misalignment . Some types of hydraulic or aerodynamic loads Dynamic loads on shafts and bearings are caused by some of the following sources (not a complete list by any means): . Out of balance condition (i.e., the center of mass is not coincident with the centerline of rotation) . Eccentric rotor components or bent shafts (another form of unbalance) . Damaged antifriction bearings . Intermittent, period rubs . Gear tooth contact . Pump or compressor impeller blades passing by a stationary object . Electromagnetic forces Simply stated, vibration is motion. Vibratory motion in machinery is caused by forces that change their direction. For example, a rotor that is out of balance and is not 0.5 0.4 0.3 0.2 0.1 0 0 6000 12000 18000 2000 3000 Peak velocity in in/s DIDstrb P2-MIA Motor Inboard Axial Frequency in cpm Before alignment After alignment DIDstrb P2-MIA Motor Inboard Axial 0.5 0.4 0.3 0.2 0.1 0 0 6000 12000 18000 2000 3000 Frequency in cpm DIDstrb P2-POA Pump Outboard Axial DIDstrb P2-POA Pump Outboard Axial 0.5 0.4 0.3 0.2 0.1 0 0.5 0.4 0.3 0.2 0.1 0 0 6000 12000 18000 2000 3000 0 6000 12000 18000 2000 3000 Frequency in cpm Frequency in cpm 3556. 7191. FIGURE 2.33 Before and after axial vibration data on motor and pump. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 70 6.10.2006 5:21pm 70 Shaft Alignment Handbook, Third Edition rotating, does not vibrate. As soon as the imbalanced rotor begins to spin, it also begins to vibrate. This occurs because the ‘‘heavy spot’’ is changing its position, causing the (centrifugal) force to change its direction. The rotor=bearing=support system, being elastic, consequentially begins to flex or move as these alternating forces begin to act on the machine. Another detectable vibration pattern exists in gears and is commonly referred to as gear mesh. Gear mesh can be detected as forces increase or subside as each tooth comes in contact with another. Other types of mechanical or electrical problems that can be detected through vibration analysis can be traced back to the fact that forces are somehow changing their direction. On the other hand, when two or more shafts are connected together by some flexible or rigid element where the centerlines of each machine are not collinear, the forces transferred from shaft to shaft are acting in one direction only. These forces do not change their direction, as an imbalance condition does. If a motor shaft is higher than a pump shaft by 50 mils, the motor shaft is trying to pull the pump shaft upward to come in line with the motor shaft position. Conversely, the pump shaft is trying to pull the motor shaft downward to come in line with the pump shaft position. The misalignment forces will begin to bend the shafts, not flutter them around like the tail of a fish. Static forces caused by misalignment act in one direction only, which is quite different than the dynamic forces that generate vibration. Under this pretense, how could misalignment ever cause vibration to occur? If anything, misalignment should diminish the capacity for motion to occur in a rotor=bearing=support system. 2.2.10 KNOWN VIBRATION SPECTRAL SIGNATURES OF MISALIGNED FLEXIBLE COUPLINGS Despite the fact that shaft misalignment may decrease the amount of vibration in rotating machinery, vibration can and does occur due to this condition. As previously mentioned, it has been observed that the vibration spectral pattern of misaligned rotating machinery will frequently be different depending on the type of flexible coupling connecting the two shaft together. Figure 2.34 through Figure 2.39 show vibration patterns that have been observed on misaligned rotating machinery with different types of flexible couplings. Notice that the vibration peaks are occurring at running speed (1X) or multiples of running speed (2X, 3X, 4X, etc.). 2.2.11 VIBRATION CHARACTERISTICS OF MISALIGNED MACHINERY SUPPORTED IN SLIDING TYPE BEARINGS The vibration spectral patterns in Figure 2.34 through Figure 2.39 were seen on rotating machinery supported in rolling element type bearings. Frequently a different pattern emerges on machinery supported in sliding type bearings as shown in Figure 2.40. 2.2.12 USING INFRARED THERMOGRAPHY TO DETECT MISALIGNMENT A very interesting study was performed by two maintenance technicians from a bottling company in 1991. The test was conducted by coupling a 10 hp motor to a 7200 W electric generator. A specific flexible coupling was installed between the motor and the generator; the unit was then accurately aligned and then started up. Vibration, ultrasound, and thermal Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 71 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 71 imaging data was then collected after 10 min run time. The unit was then shutdown, 10 mils of shims were placed under all 4 ft of the motor, the drive system started back up and the data was collected again. This was repeated several times with an additional 10 mils of shims installed under the motor feet each time. After the motor and generator drive was misaligned 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ Motor driven ANSI pump J. Lorenc horizontal misalignment at 90 mils IB & OB Jaw coupling Various vibration responses to misalignment Motor driven generator test D. Nower horizontal and angular misalignment at 15 mils/in. FIGURE 2.34 Observed vibration patterns on misaligned jaw-type couplings. (Courtesy of Lovejoy, Downers Grove, IL. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 72 6.10.2006 5:21pm 72 Shaft Alignment Handbook, Third Edition Motor driven ANSI pump J. Lorenc horizontal misalignment at 30 mils IB & OB Gear coupling Various vibration responses to misalignment Gas/power turbine driven compressor J. Piotrowski horizontal misali g nment at 65 mils IB & OB 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ FIGURE 2.35 Observed vibration patterns on misaligned gear type couplings. (Courtesy of Rexmord Coupling Group, Milwaukee, WI. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 73 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 73 Motor driven ANSI pump S. Chancey vertical misalignment 50 mils at IB & 75 mils at OB J. Lorenc horizontal misalignment at 90 mils IB & OB Metal ribbon coupling Various vibration responses to misalignment Motor driven generator test D. Nower horizontal misalignment at 50 mils IB & OB Motor driven centrifugal pump J. Piotrowski horizontal misalignment at 36 mils IB & OB 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ FIGURE 2.36 Observed vibration patterns on misaligned metal ribbon-type couplings. (Courtesy of Rexmord Coupling Group, Milwaukee, IL. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 74 6.10.2006 5:21pm 74 Shaft Alignment Handbook, Third Edition 30–40 mils, the flexible coupling being tested was removed, a different flexible coupling design was then installed, the shims were removed from the motor to get back to near perfect alignment, and the process was repeated. Figure 2.41 through Figure 2.46 show the results of the six different flexible couplings that were tested. Notice that as the misalignment increased, so too did the temperature of the coupling or of the flexing element. The increase in temperature is somewhat linear as illustrated in the temperature graphs with each coupling tested. Disappoint- ingly, however, the vibration and ultrasound data was never published with the infrared data. In addition, there must be a word of caution here because it is very tempting to make generalizations from this data. Not every flexible or rigid coupling will increase in temperature when subjected to misalignment conditions. The flexible couplings used in this test were mechanically flexible couplings (the chain and metal ribbon types) or elasto- meric types. In mechanically flexible couplings the heat is generated as the metal grid slides back and forth across the tooth slots in the coupling hubs or as the chain rollers slide across the sprocket teeth as the coupling elements attempt to accept the misalignment condition. In the elastomeric couplings, the elastomer is heated through some sliding friction but pri- marily by shear and compression forces as these coupling elements attempt to accept their misalignment conditions. What would have happened if a flexible disk or diaphragm type coupling was also tested? Flexible disk or diaphragm couplings accept misalignment conditions by elastically bending the two disk packs or diaphragms and virtually no heat will be generated by the flexure of metal disks as these types of couplings attempt to accommodate any misalignment conditions. 2.2.13 POWER LOSS DUE TO SHAFT MISALIGNMENT It has been widely publicized that shaft misalignment will cause the driver to work harder and therefore take more energy or power to run the drive system. However, a study conducted by the University of Tennessee in 1997 where both 50 and 60 hp motors were purposely misaligned to dynamometers using four different types of couplings and subjecting each coupling to 15 misalignment conditions came to the following conclusions: ‘‘The results of these tests show no significant correlation between misalignment and changes in efficiency when the tested couplings were operated within the manufacturer’s recommended range. Power consumption and power output remained constant regardless of the alignment condition.’’ 2.2.14 THE MOST EFFECTIVE WAY TO DETERMINE IF MISALIGNMENT EXISTS After years of study, one invariable conclusion can be made. Misalignment disguises itself very well on the operating rotating machinery. There are no easy or inexpensive ways to determine if rotating machinery is misaligned while it is running. The most effective way to determine if a misalignment condition exists is to shut the drive system down, safety tag and lock out the machinery, remove the coupling guard, and employ one of the alignment measurement methods described in Chapter 7 to see if a misalignment condition is present. Even if the alignment looks good when you do an off-line check, running misalignment may occur. So it is suggested that you also review Chapter 9, which discusses off-line to running machinery movement. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 75 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 75 Motor driven BFW pump Motor driven demonstrator J. Piotrowski horizontal misalignment at 80 mils IB & OB Flexible disk-type coupling Various vibration responses to misalignment Motor driven motor experimental test D. Dewell parallel at 96 mils Motor driven generator test D. Nower horizontal and angular misalignment at 75 mils high 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ FIGURE 2.37 Observed vibration patterns on misaligned flexible disk-type couplings. (Courtesy of Thomas Rexnord, Warren, PA. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 76 6.10.2006 5:21pm 76 Shaft Alignment Handbook, Third Edition Motor driven ANSI pump J. Lorenc horizontal misalignment at 90 mils IB & OB J. Piotrowski horizontal misalignment at 80 mils IB & OB Rubber tire-type coupling Various vibration responses to misalignment Motor driven generator test D. Nower horizontal and angular misalignment at 75 mils high 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ FIGURE 2.38 Observed vibration patterns on misaligned flexible disk-type couplings. (Courtesy of Dodge-Reliance Electric, Cleveland, OH. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 77 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 77 Motor driven pump—Motor IB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB Motor driven pump—Pump IB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB Motor driven pump—Motor OB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB TB Woods-type coupling various vibration responses to misalignment 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ 1ϫ 2ϫ 3ϫ 4ϫ 5ϫ 6ϫ 7ϫ 8ϫ 9ϫ 10ϫ FIGURE 2.39 Observed vibration patterns on misaligned flexible disk-type couplings. (Courtesy of T. B. Woods and Sons, Chambersburg, PA. With permission.) (continued ) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 78 6.10.2006 5:21pm 78 Shaft Alignment Handbook, Third Edition Sliding type bearing Force Proximity probes Shaft When the signals from two proximity probes are combined together in a two channel oscilloscope or vibration analyzer, the orbital motion of the shaft can be observed (called a Lissajous pattern). A typical shaft orbit in a sliding type bearing with no external forces applied to the shaft is shown to the right. Even if a pure imbalance condition existed causing an even radial force, the orbital pattern would be elliptical due to the different horizontal and vertical stiffnesses of the machine case. If a downward force from shaft misalignment is now applied to the rotor/bearing system, the elliptical orbit begins to “flatten out”. The static misalignment force is limiting the amount of shaft movement in the vertical direction. If the force from misalignment increase the orbit continues to flatten and distort. As the force begins to steadily increase, the orbit begins to take a pickle shape. When the force is great enough, the orbit changes shape to a figure “8”, hence a 2ϫ running speed vibration component appears. FIGURE 2.40 Observed vibration orbital patterns on rotors supported in sliding type bearings. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 79 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 79 [...]... validation, Journal of Sound and Vibration (1994b), 176(5), 681–691 Xu, M., Zatezalo, J.M., and Marangoni, R.D., Reducing power loss through shaft alignment, P=PM Technology, October 19 93 Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 88 6.10.2006 5:21pm Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page 89 29.9.2006 5:53pm 3 Foundations,... insert following page 32 2.) Section view of a typical rigid foundation Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page 98 29.9.2006 5:53pm 98 Shaft Alignment Handbook, Third Edition Reinforcement rods should be spaced no more than 12 in apart, using a minimum rod size of 1=2 in (12.7 mm) The concrete should be rated at a compressive strength of 4000 psi for 28 d Once... FIGURE 3. 15 Solid metal baseplate bonded to a concrete floor or pad Concrete bonding glue Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page 102 102 29.9.2006 5:53pm Shaft Alignment Handbook, Third Edition 2 Possibility of anchor bolts pulling out, loosening, or breaking if proper precautions are not taken during the installation of the anchor bolts 3 Possibility of baseplate... provides good bonding 3 Can be flipped upside down and grout poured into the cavity before final installation FIGURE 3. 3 Frame supporting a belt drive fan Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page 93 29.9.2006 5:53pm Foundations, Baseplates, Installation, and Piping Strain FIGURE 3. 4 Cast baseplate FIGURE 3. 5 Fabricated baseplate FIGURE 3. 6 Weak structural steel... coupling running under good alignment conditions, (c) an infrared image of the coupling running with the worst misalignment condition (d) temperature of coupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute, Shelburne, VT.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 83 6.10.2006 5:21pm 83 Detecting Misalignment on Rotating... etc 3 Minimize the height of the centerline of rotation from the baseplate 4 Rotating equipment that will experience large amounts of thermal or dynamic movement from off-line to running conditions should be spaced far enough apart to insure that the maximum allowable misalignment tolerance is not exceeded when the shafts Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page... Alignment Handbook, Third Edition DK 432 2_C0 03 Final Proof page 92 29.9.2006 5:53pm 92 Shaft Alignment Handbook, Third Edition FIGURE 3. 2 Spring isolated inertia block with motor and pump foundation design, Figure 3. 2 shows a typica inertial block (aka floating) design, and Figure 3. 3 shows a typical frame design 3. 2.1 BASEPLATES Baseplates are typically either cast or fabricated as shown in Figure 3. 4 and... image of the coupling running under good alignment conditions, (c) an infrared image of the coupling running with the worst misalignment condition (d) temperature of coupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute, Shelburne, VT.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 85 6.10.2006 5:21pm 85 Detecting Misalignment... misalignment and unbalance, Part I: Theoretical model and analysis, Journal of Sound and Vibration (1994a), 176(5), 6 63 679 Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 87 6.10.2006 5:21pm Detecting Misalignment on Rotating Machinery 87 Xu, M and Marangoni, R.D., Vibration analysis of a motor—flexible coupling—rotor system subject to misalignment and unbalance, Part. .. VT.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 82 6.10.2006 5:21pm 82 (a) Shaft Alignment Handbook, Third Edition (b) Temperature (8F) 200 100 (d) 40 mils 30 mils 20 mils 10 mils 0 mils 0 Misalignment (c) FIGURE 2. 43 Observed temperature patterns on misaligned rubber insert type coupling (a) A photograph of the coupling, (b) an infrared image of the coupling running . With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 74 6.10.2006 5:21pm 74 Shaft Alignment Handbook, Third Edition 30 –40 mils, the flexible coupling. (Courtesy of Thomas Rexnord, Warren, PA. With permission.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 76 6.10.2006 5:21pm 76 Shaft Alignment Handbook, Third. VT.) Piotrowski / Shaft Alignment Handbook, Third Edition DK 432 2_C002 Final Proof page 80 6.10.2006 5:21pm 80 Shaft Alignment Handbook, Third Edition (a) (c) (d) (b) Temperature (8F) Misalignment 0 50 100 150 0