Balancing Causes Of Unbalance l l l l

Balancing

Causes Of Unbalance l l l l Uneven distribution of mass of rotor. Dirt accumulation on fan rotors. Rotor eccentricity Roller deflection, especially in paper machines Machining errors Uneven erosion and corrosion of pump impellers Missing balance weights

Effects Of Unbalance l l l High vibration due to centrifugal force. Excessive load on bearings. Premature bearing failure High noise Unbalance to be corrected after correcting all other inaccuracies.

Types Of Unbalance l Static Unbalance l Couple Unbalance l Overhang Rotor Unbalance

Static Unbalance Detection: Highest horizontal vibration l Amplitude increases as square of speed. l Dominant frequency at 1 x rpm l Horizontal to vertical phase difference 900 on the same bearing housing l

Correction Can be corrected by one balance weight

Couple Unbalance Detection: • High horizontal & some times axial vibration • Dominant frequency at 1 x RPM • 1800 phase difference between both bearings horizontal as well as vertical direction.

Unbalance Signature

Correction It requires two plane balancing

Overhung Rotor Unbalance Detection: • High horizontal & axial vibration • Dominant frequency at 1 x RPM • Axial readings will be in phase but radial phase readings might be unsteady.

Correction Overhung rotors might be having both static and couple unbalance and each of which requires correction.

Types of Balancing Procedure 1. Three point method or 4 run method 2. Phase Method

Three point Method

Three point method – Polar plotting Trail weight Mt= Vibration without trail weight Vo= Vibration with trail weight at 0° V 1= Vibration with trail weight at 120° V 2= Vibration with trail weight at 240° V 3= Mt*Vo/Vt=Mb Mb in grams

Balancing with phase information Reference point Phase is a measure of relative time difference between two sine waves