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 vibrationDescribe the distinction between balance and vibration Know the levels of balance qualityKnow the levels of balance quality Know the levels of installed vibrationKnow the levels of installed vibration Understand the importance of an adequate foundationUnderstand the importance of an adequate foundation Recognize symptoms and causes of problemsRecognize symptoms and causes of problems Know how to avoid vibration problemsKnow 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 BalanceBalance VibrationVibration
BALANCE Balance Synonymous with Unbalance. A physical property results in centrifugal force being applied to the fan impeller.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).Measured as the product of unbalance mass and distance from axis of rotation (oz-in).
Center of Mass Axis of Rotation Shaft Fan Impeller UNBALANCE EXAMPLE: 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. B. A piece of particulate flies off. C. Center of mass shifts so that it no longer coincides with the axis of rotation. Scrubber Sticky-wet particulate in gas stream Fan
UNBALANCE 200.0013 200.0000 = Displacement from axis of rotation = 0.36” Then Unbalance = (8500)*(16)*( ) = 49,000 oz-in Dead spot 250 F at top of housing 120 F at bottom of housing Top of shaft = 188 F Bottom of shaft = 187 F 250 F Fan wheel weight = 8500 lbs. Differential Expansion: (188 - 187 ) * (6.5E-6in/in- F) * (200 in) = 0.0013 in Shaft Bows Upward! 120 F
UNBALANCE Buildup of dust on the backside of backward curves blades. Rotation
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. Weld Fan impeller and hub heat up more quickly than the shaft. Integral hub and shaft for very rapid temperature change applications. Conclusion: Initial interference fit should be in excess of 0.002 inches to allow for thermal expansion plus an allowance for hub expansion due to centrifugal force. Example: Shaft dia. = 3.9375 in. Hub average temp = 215 F Shaft average temp =80 F Then hub growth relative to shaft: (3.9375) * (80) * (6.5E-6) = 0.002 in. Fan impeller weight = 250 lbs.. (250 lbs. x 16 oz/lb. x 0.002 inches) (250 lbs. x 16 oz/lb. x 0.002 inches) Resulting unbalance = 8.0 oz-inches
VIBRATION Vibration The alternating mechanical motion of an elastic system, components of which are amplitude, frequency and phase.The alternating mechanical motion of an elastic system, components of which are amplitude, frequency and phase. In general practice vibration values are reported as:In general practice vibration values are reported as: Displacement - milsDisplacement - mils Velocity - inches/secondVelocity - inches/second Acceleration - peak g’sAcceleration - peak g’s
VIBRATION VELOCITY 1780 RPM U per = 12.72 oz-in Maximum Vibration (in free space) =2.5 mm/sec (or 0.10 in.sec)
VIBRATION Note that the bearing housing is considerably lower than the expected vibration of the rotor in free space. Vibratio n Pickup High Stiffness Pedestal Massive Bearing Housing Small Diameter, Light Rotor
SLEEVE BEARING Proximity Probe measures shaft surface movement relative to the bearing housing. Shaft (rotating) Bearing Housing Bearing Liner (static) Oil Film supports shaft
EFFECT OF STRUCTURE Fan Mass Mass Circus Flagpole Acrobat Flagpole acts as a spring Fn = 30 cyc/min Cyclic Forces Structural Steel acts as a spring Fn = 1200 cyc/min Fan operating speed = 1180 RPM Foundation
SOLID FOUNDATION Normal Fn = 1680 cyc/min 0.10 in/sec 1180 Speed (RPM) Fn >1.4 * F Operating speed (F) Vibration(in/sec)