3 looseness

Vibration Analysis Mechanical LOOSENESS : 

Vibration Analysis Mechanical LOOSENESS Not an exciting force Allows exciting frequencies already present to exhibit much higher amplitudes Loss or reduction in normal stiffness Caused by: loose mounting bolts deterioration of grouting cracked welds

Two Types Of Looseness : 

Two Types Of Looseness Looseness of Rotating Components Loose Rotors Bearings Loose on the Shaft or in Housing Excessive Sleeve Bearing Clearances Looseness of Support System Loose Mounting Bolts Grouting Deterioration Cracks Poor Support Frame Distortion

Mechanical Looseness (support system) : 

Mechanical Looseness (support system) Caused by structured weakness of machine feet, base plate or foundation; also by deteriorated grouting, loose Hold-Down bolts and distortion of the frame or base. Radial vibration high 1* RPM dominant 180 deg. Phase differences between mating surfaces which have looseness between them.

Mechanical Looseness (support system) cont…. : 

Mechanical Looseness (support system) cont…. Looseness produces 2X RPM Freq.

Slide 9: 

Mechanical Looseness (support system) cont….

Looseness Of Support System : 

Looseness Of Support System Identified by Highly directional radial vibration Bouncing Taking comparative phase readings across interfaces and look for amplitude variation Typically loose in vertical direction

Vibration AnalysisMechanical Looseness : 

Vibration AnalysisMechanical Looseness Caused by looseness in bearing housing bolt, rocking motion induced by differential length support legs, loose bearing or improper component fit problems are only of minor severity. Radial vibration high 2* RPM normally dominant. 0.5*. 1* and 3* RPM may also be present 180 deg. Phase difference between mating surfaces which have looseness between them

Vibration AnalysisMechanical Looseness : 

Vibration AnalysisMechanical Looseness Looseness due to Rocking Motion or Cracked Structure / Bearing Pedestal 2* RPM normally dominant. 0.5*, 1* and 3* RPM may also be present Amplitudes are somewhat erratic Nonlinear Time Wave Form Erratic phase readings

Looseness Of Rotating System : 

Bearing loose in housing Excessive Internal Bearing Clearances Bearing Liner Loose in its cap Loose Rotor Bearing Loose and turning on shaft Looseness Of Rotating System

Looseness Of Rotating System : 

Looseness Of Rotating System Rattling condition cause impacts due to excessive clearance in a rolling element or sleeve bearing Impacts cause multiple running speed harmonics to appear in the spectra Identified by: multiple harmonics unstable phase highly directional radial vibration

Looseness Of Rotating System : 

Looseness Of Rotating System Multiple running speed harmonics sometimes up to 10X or even 20XRPM are clearly present in the spectrum. Directional, maximum vibration is not either in Horizontal or vertical, but may be somewhere in between the two. If the amplitude of harmonics becomes significant this can also generate frequencies spaced at ½ times RPM or even some times at 1/3 times RPM In case of a loose rotor phase will vary from one start up to the next.

Typical Spectrum for Looseness of Rotating System : 

Typical Spectrum for Looseness of Rotating System

Typical Spectrum For Looseness of Rotating System : 

Typical Spectrum For Looseness of Rotating System

Typical looseness spectrum-Rolling element bearing : 

Typical looseness spectrum-Rolling element bearing

Typical looseness spectrum-Rolling element bearing : 

Typical looseness spectrum-Rolling element bearing

Notes : 

IIPM 20 Notes