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AMCA International Technical Seminar 2009 Equipment Vibration Presented by: Bill Howarth, Illinois Blower Inc.
The Air Movement and Control Association International (AMCA), has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to the RCEPP. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by NCEES or RCEPP.
Learning Objectives • • • Describe the distinction between balance and vibration Know the levels of balance quality Know the levels of installed vibration Understand the importance of an adequate foundation Recognize symptoms and causes of problems Know how to avoid vibration problems
Equipment Vibration Presented by Bill Howarth Hartzell Fan, Inc.
ANSI / AMCA 204 -96 Balance Quality and Vibration Levels for Fans • Balance • Vibration
BALANCE Balance • Synonymous with Unbalance. A physical property results in centrifugal force being applied to the fan impeller. • Measured as the product of unbalance mass and distance from axis of rotation (oz-in).
UNBALANCE EXAMPLE: Center of Mass Shaft Axis of Rotation Fan Impeller • ROTOR WEIGHT = 300 LBS • RADIAL SEPARATION OF CENTER OF MASS FROM AXIS OF ROTATION=0. 0052 INCHES • UNBALANCE =300 LBS * 16 OZ/LB *0. 0052 IN. =25 OZ-IN.
UNBALANCE A. Particulate builds up uniformly on the rotor. Sticky-wet particulate in gas stream Scrubber B. A piece of particulate flies off. C. Center of mass shifts so that it no longer coincides with the axis of rotation. Fan
UNBALANCE Dead spot 250 F at top of housing 250 F 120 F at bottom of housing Top of shaft = 188 F Bottom of shaft = 187 F Fan wheel weight = 8500 lbs. Differential Expansion: (188 - 187 ) * (6. 5 E-6 in/in- F) * (200 in) = 0. 0013 in Shaft Bows Upward! = Displacement from axis of rotation = 0. 36” Then Unbalance = (8500)*(16)*( ) = 49, 000 oz-in 200. 0013 200. 0000
UNBALANCE Ro ta t io n Dust accumulation inside hollow airfoil blade.
Ro ta t io n UNBALANCE Buildup of dust on the backside of backward curves blades.
UNBALANCE Hub Shaft Setscrews initially hold hub tightly in position on the shaft. Setscrew tips are corroded or worn by fretting over time. This allows the hub and entire fan wheel to be displaced relative to the axis of rotation causing unbalance. Interference fit eliminates the possibility of the hub being displaced relative to the shaft in most systems.
EFFECT OF TEMPERATURE CHANGE Fan impeller initially operating at 70 F. Process gas temperature increases rapidly. Fan impeller and hub heat up more quickly than the shaft. Weld Integral hub and shaft for very rapid temperature change applications. Example: Conclusion: Shaft dia. = 3. 9375 in. • Initial interference fit should Hub average temp = 215 F be in excess of 0. 002 inches to Shaft average temp =80 F allow for thermal expansion plus an allowance for hub Then hub growth relative to shaft: expansion due to centrifugal (3. 9375) * (80) * (6. 5 E-6) = 0. 002 in. force. Fan impeller weight = 250 lbs. . (250 lbs. x 16 oz/lb. x 0. 002 inches) Resulting unbalance = 8. 0 oz-inches
ANSI / AMCA 204, TABLE 4 -1
ANSI / AMCA 204, TABLE 5 -1
ANSI / AMCA 204, APPENDIX C. 2
VIBRATION Vibration • The alternating mechanical motion of an elastic system, components of which are amplitude, frequency and phase. • In general practice vibration values are reported as: • Displacement - mils • Velocity - inches/second • Acceleration - peak g’s
VIBRATION VELOCITY 1780 RPM Uper = 12. 72 oz-in Maximum Vibration (in free space) =2. 5 mm/sec (or 0. 10 in. sec)
VIBRATION Small Diameter, Light Rotor Vibratio n Pickup Massive Bearing Housing High Stiffness Pedestal Note that the bearing housing is considerably lower than the expected vibration of the rotor in free space.
SLEEVE BEARING Shaft (rotating) Bearing Housing Proximity Probe measures shaft surface movement relative to the bearing housing. Bearing Liner (static) Oil Film supports shaft
EFFECT OF STRUCTURE Mass Fan Mass Cyclic Forces Fan operating speed = 1180 RPM Structural Steel acts as a spring Fn = 1200 cyc/min Flagpole acts as a spring Fn = 30 cyc/min Foundation Circus Flagpole Acrobat
SOLID FOUNDATION Vibratio n (in/sec) Normal Fn = 1680 cyc/min Operating speed (F) 0. 10 in/sec 1180 Speed (RPM) Fn >1. 4 * F
STRUCTURAL STEEL MOUNTING Normal Fn = 1200 cyc/min Vibratio n (in/sec) Operating speed (F) 0. 70 in/sec 1180 Speed (RPM)
FLEXIBLE MOUNT Expansion Joint Inlet Duct Structural Steel Platform Discharge Duct Rigid Sub-Base (Often concrete filled) Spring Isolation with static deflection of 1. 0 inches Fn = 187. 7/1. 5 =187. 7 cyc/min
ANSI / AMCA 204, TABLE 6 -3
TRANSDUCER MOUNTING Vertical Axial Horizontal SWSI Centrifugal Fans
TRANSDUCER MOUNTING Vertical Axial Horizontal DWDI Centrifugal Fans
TRANSDUCER MOUNTING Vertica l Axial Horizontal Vertical Axial Fans
VIBRATION SPECTRUM 0. 20 Velocity (In. /sec. ) Filter Out Filter In 0. 15 0. 10 0. 05 0. 00 0 500 1000 1500 Speed (RPM) 2000 2500
ANSI / AMCA 204, TABLE 6 -4