Post on 21-Feb-2017
VIBRATION ANALYSIS FOR CBMBASIC CONCEPTS – UNIT 2
BY DIBYENDU DE
VIBRATION MONITORING
Degrees of Freedom?
Degrees of Freedom determines the direction in which we measure vibration
Measurement direction - Horizontal, Vertical, Axial.
MEASUREMENT DIRECTION - HORIZONTAL, VERTICAL, AXIAL.
Horizontal Vertical
AxialInstrument
CONCEPT OF PHASE - 1
Masses C and D are in sync or are in-step
That is they move together
Hence the masses are vibrating in phase
CONCEPT OF PHASE – 2
While Mass X is now at the upper limit
Mass Y is at the neutral position and moving downwards towards the lower limit
Hence Masses X & Y are moving 90 degrees out of phase
CONCEPT OF PHASE – 3
While Mass A is now at the upper limit
Mass B is at the lower limit
Hence Masses A & B are moving 180 degrees out of phase
UNITS OF VIBRATION
Displacement in Microns or Mils
1mil = 1/1000 inch
Velocity in mm/sec or
inch/sec
Acceleration in meter/sec^2 or ‘g’
Frequency in CPM or Hz
Hz x 60 = CPM
Vibration
EnergyMass, Stiffness, Space
Natural Frequency Motion
Time
Strain
Kinetic
Force
Overall
Time wave form
Orbit
Signatures
Envelope
Cepstrum
Faults = Unbalance, Misalignment, Bearings, Product defect etc
frequency
Low
Medium
High
d
v
a
Spike Energy
Patterns
VIBRATION - CAR ANALOGY
Low FrequencyLong period (T)High displacementAverage VelocityLow Acceleration
Medium FrequencyMedium period (T)Average displacementAverage VelocityAverage Acceleration
High FrequencyShort period (T)Low displacementAverage VelocityHigh Acceleration
VIBRATION
Displacement:Sensitive to lowfrequencies.Good guide for imbalance,& other low frequency faults.
Velocity:Has average sensitivity throughout the frequency range.Reasonably sensitive to imbalance, misalignment, looseness androlling element bearing damage.
Acceleration:Sensitive to high frequencies.Good for rolling element bearing damage.
EXERCISE – CHOOSE APPROPRIATE PARAMETER
• Anti friction Bearings – velocity and acceleration
• Gears
• Journal Bearings
• Bush Bearings
• Pump casing
• VFD shaft
• Thrust bearing
• Pipes and fluid flows
EXERCISE – CHOOSE APPROPRIATE PARAMETER & DIRECTION
• Motor
• Pump
• Cooling Tower Fan
• On steel and concrete structures
• Foundations
• Slow speed anti-friction bearing
• Vibrating Screen
• Steam Turbines
EXERCISE - FAILURE MODES – PARAMETER?
Pitting of anti-friction bearings
Wear out and/or clearances of journal bearings
Lubrication starvation
Unbalance, misalignment, looseness
Screw wear out and shear of extruders
Leakage of mechanical seals
Gear teeth sheared from root
Cavitation
Cracks in shafts
Cracks in structures
EXERCISE – THINK OVER THE QUESTIONS
• Which is the weakest bearing?
• Which direction is the weakest?
• What might be the failure modes?
• What would be the parameters?
• What is the most important direction
• What would be the most important technique?
• What would define the health of the machine? FAN
BEARING
6320
BEARING
NU320
BEARING
NU219
BEARING 6219 & NU219
BLOWER ASSEMBLY
THANK YOU FOR COMPLETING UNIT 2 CONTACT: FOR FACILITATED TRAINING
DIBYENDU DE, EMAIL ID: DDE337@GMAIL.COM