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