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AMCA International Technical Seminar 2009. Equipment Vibration Presented by: Bill Howarth, Illinois Blower Inc.
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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.
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 Learning Objectives
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: • 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. Center of Mass Shaft Axis of Rotation Fan Impeller
UNBALANCE A. Particulate builds up uniformly on the rotor. Sticky-wet particulate in gas stream Scrubber B. A piece of particulate flies off. Fan C. Center of mass shifts so that it no longer coincides with the axis of rotation.
UNBALANCE Dead spot 250F at top of housing 250F Top of shaft = 188F Bottom of shaft = 187F 120F Fan wheel weight = 8500 lbs. Differential Expansion: (188 - 187) * (6.5E-6in/in-F) * (200 in) = 0.0013 in Shaft Bows Upward! 120F at bottom of housing = Displacement from axis of rotation = 0.36” Then Unbalance = (8500)*(16)*() = 49,000 oz-in 200.0013 200.0000
UNBALANCE Dust accumulation inside hollow airfoil blade. Rotation
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.
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) Resulting unbalance = 8.0 oz-inches EFFECT OF TEMPERATURE CHANGE Fan impeller initially operating at 70 F. Process gas temperature increases rapidly. Weld Integral hub and shaft for very rapid temperature change applications. Fan impeller and hub heat up more quickly than the shaft.
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)
Small Diameter, Light Rotor Vibration Pickup Massive Bearing Housing High Stiffness Pedestal VIBRATION • Note that the bearing housing is considerably lower than the expected vibration of the rotor in free space.
SLEEVE BEARING Proximity Probe measures shaft surface movement relative to the bearing housing. Shaft (rotating) Bearing Liner (static) Bearing Housing Oil Film supports shaft
EFFECT OF STRUCTURE Mass Fan Mass Cyclic Forces Structural Steel acts as a spring Circus Flagpole cyc/min Fn = 1200 Fan operating Acrobat speed = 1180 RPM Flagpole acts as a spring cyc/min Fn = 30 Foundation
Normal Fn = 1680 cyc/min Operating speed (F) Vibration (in/sec) 0.10 in/sec 1180 Speed (RPM) Fn >1.4 * F SOLID FOUNDATION
Normal Fn = 1200 cyc/min Operating speed (F) 0.70 in/sec Vibration (in/sec) 1180 Speed (RPM) STRUCTURAL STEEL MOUNTING
FLEXIBLE MOUNT Expansion Joint Expansion Joint Discharge Duct Inlet 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 Structural Steel Platform
Vertical Axial Horizontal TRANSDUCER MOUNTING • SWSI Centrifugal Fans
Vertical Axial Horizontal TRANSDUCER MOUNTING • DWDI Centrifugal Fans
TRANSDUCER MOUNTING Vertical Axial Horizontal • Axial Fans Vertical
VIBRATION SPECTRUM 0.20 Filter Out Filter In 0.15 Velocity (In./sec.) 0.10 0.05 0.00 0 500 1000 1500 2000 2500 Speed (RPM)