Why is balancing important?
Force (F) generated by unbalance can be calculated from formula:
F(Kg)= 0 .001 x(gmm)x(RPM/ 1000 )
2
r
F(Kg)= 0 .001 x(w x r)x(RPM/ 1000 )
2
where w = Unbalance weight in grams
r = Radius in millimetres
Effects of Unbalance
Reduced component life.
Bearings, seals, windings, rotor bars, foundations, supports.
Impaired clearancs / tolerances.
Component displacement, Reactive misalighment.
Resonance.
Flexing of critical speed rotors.
Excessive vibration and noise
Health / safety considerations
Poor product quality.
Diagnosing Unbalance
Vibration frequency equals rotor speed.
Vibration predominantly RADIAL in direction.
Stable vibration phase measurement.
Vibration phase shifts in direct proportion to measurement
direction.
Causes of unbalance
Rotor not mass centred geometrically
Machining / casting inaccuracioes.
Fitting / assembly tolerance inaccuracies.
Uneven mass distribution
Windings / commutator segments.
Blow holes / inclusions in castings.
Component mismatch.
Keys / keyways.
Causes of unbalance
Service effects
Thermal dimensional changes:
Stress relieving.
Uneven thermal growth.
Thermal displacement / loosening of components.
Displacement / settling of components:
Windings Impellers Fan side plates.
Deposit build-up / Erosion / corrosion.
Rotor flexibility
Forced whip.
critical speed deflection.
Induced by other forces
Aerodynamic.
Hydraulic.
Electrical.
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SPINDLE BALANCIN
