Tell-tale Signs of Faults in Mechanical Equipment
Misalignment
- High amplitudes at 1X, 2X, and sometimes 3X
- Typically 180 degree (+/- 30) across coupling on shaft
- Axial for angular
- Radial for parallel - Cocked bearing - twisting motion
- 180 degree (+/- 30) top-to-bottom or side-to-side
Unbalance
- High amplitudes at 1X
- Typically 90 degree (+/- 40) from horizontal to vertical
- Phase differences left and right positions should be stable, otherwise other issues
- Looseness
- Misalignment - Other faults need to be corrected before ever starting to correct balance
- Side to side phase to determine unbalance type
- 0 degrees indicates force (static) unbalance
- 180 degrees indicates couple unbalance
Resonance
- High amplitudes at 1X and other low orders of running speed
- 0 degree phase change on stationary points on machine
- 180 degree phase change indicates parts that are moving in opposite directions at running speed
- Varying machine speed at resonance
- 180 degree change when moving from below resonance to above resonance
- 90 degree change at resonance
- Slight machine speed change results in large phase shifts
Eccentric Belt Pulley
- High 1X at running speed of pulley
- Phase difference of 0 or 180 degrees on horizontal and vertical readings (versus expected 90)
- Straight line motion in line with belts
Mechanical Looseness
- High amplitudes at multiples of 1X
- Sometimes multiples of 0.5X; e.g., 1.5X, 2.5X, etc.
- Fluctuating phase readings
- Around bearing at 30-degree intervals will be significantly different
Soft Foot - High amplitude peak at 1X
- 90 to 180 degree phase shift on machine foot to base
- Also difference in phase reading on other feet