Slide 1

Vibration Any motion which repeats itself after an interval of time is called vibration.

Vibration is simply the motion of a machine part back and forth from its position of rest.

Balancing By Three Point Method Method of Balancing by Three Point MethodFix the

Thumb Rule for Trial Wt

Why Importance of Vibration ?

All Rotating parts , machines vibrate.Machines Vibrate because of imperfections when imperfection is more, it becomes a defect.Different defects produce vibrations of different characteristicsVibration Parameters to measured .

DisplacementVelocityAccelerationFrequencyPhase

Parameter Description Unit of measurement Displacement Total distance of movement of the part MicronsVelocityThe velocity with which part is moving changes continuously mm/secAccelerationRate of change of velocity withg respect to timeMm/sec2FrequencyNo of cycles of the movement for given periodHzPhase Phas anglle is the position of vibrating part at a given instant.Angle deg.

Vibration Measurement locations on Overhang Rotor.

BALANCING OF ROTOR AT WORKS

Balancing of Shaft at works

Alignment

Parallel Misalignment

Angular Misalignment

Combination of both Parallel and angular Misalignment.

Good Alignment

Dynamic Unbalance

Sources of Vibration contd.Aerodynamic VibrationAerodynamic vibration, also referred to as aerodynamicpulsation, is one cause of fan-system vibration. It occurs when a fan operates to the left of its peak static pressure point. The vibration frequency, when checked with instruments, is at a frequency other than the wheel rotation speed.

Mechanical Vibration Mechanical vibration is the most common type of fan Vibration.It is caused by unbalanced wheels or other rotating fan components. Its negative impact is increased with loose fasteners and poor structural support.

Electrical Vibration

Aerodynamic Vibration

Three Axis of MeasurementBalance Quality Grade G 6.3 or G 2.5 of ANSI S2.19-1975._____Fan unit dropped during shipment bent shaft or bearing damage_____Loose anchor bolts, bearing bolts, or motor bolts_____Foundation structure is not adequate_____Fan is not shimmed and grouted properly_____Material build-up on impeller_____Fan wheel set-screws are loose_____Inlet orifice rubbing fan wheel_____Wear on wheel or bearings_____Duct work binding fan housing, or duct work not properly separated from fan housing with flexibleinlet or discharge connections._____Aerodynamic pulsation caused by system design._____Fan out of balance It is common for assembled units to require trim balancing to reduce vibrationlevels after installation. Qualified balance personnel should be made available at start-up forpossible trim balancing of equipment._____Improper alignment of coupling couplings have been aligned at the factory, however provisionsshould be made at start-up to check coupling alignment after shipment and installation._____Improper alignment of V-belt drive Sheaves have been aligned at the factory, however provisionsshould be made at start-up to check alignment after shipment and installation._____Improper V-belt tension V-belt tension should be checked at start-up, and after the first few hoursof rotation._____Improper wheel rotation insure that motor is wired for correct wheel rotation as indicated byrotation arrow on equipment._____Shaft has been bent or distorted during high temperature shutdown._____Defective motor_____Resonant frequencies of structural mounting supports_____Defective bearings or moisture in bearings Request a copy of Fan bearing failure checklistCHECK LIST FOR EXCESSIVE VIBRATION Balancing as a Correction Tool Minimize noise Increase bearing life Decrease operating stresses Consume less energy Improve product quality Decrease operator fatigue Eliminate fatigue of support structures Satisfy customers.Benefits of Balancing Processes of BalancingDetectionAnalysisCorrectionInstruments used for Vibration Analysis1.IRD 3082.IRD 3503.IRD 8804.FFT analyser

Vibration Standards Salient FeaturesVDI 2056/1964 [5,6]It is a German standard developed on the basis of Rathboness [3]work. It is intended for use with overall level measuring equipment,which allows only these components of the signal within thefrequency range 10 Hz to 1000 Hz to pass.BS 4675[7],ISO 2372 [8,9],ISO/IS3945 [6]These standards are identical to VDI 2056.Indian Standard 4729[5]These are applicable to rotating electrical machines with powerranging from 0.15 kW to over 1000 kW.In all the above standards measurements are expected to have been carried out by seismictransducers [5] on the bearing caps or structures of the rotating machinesIRD Mechanalysis[4,6]The standard is laid on the peak to peak velocity in mm/sec for allcategories of machines and does not give standards that canencompass the entire range of speeds and loads.ISO 3945 [5]It is based on ISO 2372 and defines the rules for evaluating thevibration performance of large prime movers and other largemachines.CANADIANGovernmentSpecification. [8,10]Canadian government specification [5,7] covers frequency range of10 Hz to 10kHz but here the standards are defined for gas turbines,pumps, electric motors and so on.