Mechanical Vibratuin- Mechanical Looseness Problem

1. MECHANICAL LOOSENESS
Gilang Sandy Firdaus (15/385231/TK/43893)
Hotjon Junadi Simanullang (15/385235/TK/43897)
Jumalin (15/385239/tk/43901)
Faris Yoga Andhika (15/385226/TK/43888)

2. Mechanical Looseness
• An improper fit between component parts. If we consider in rotating machine
the looseness causes machine can’t rotating perfectly. So the vibration will
be an amplifier that mean produce a loudly sound.
• When a component is loose, whatever forces are present will be able to move
the affected components much more easily. If there are a little or no forces
present, however, vibration may only increase a very small amount.

3. 1. Internal assembly looseness :
• This category of looseness could be between a bearing liner in its cap, a sleeve or
rolling element bearing, or an impeller on a shaft.
• It is normally caused by an improper fit between component parts, which will produce
many harmonics in the Fast Fourire Transformation (FFT) due to the nonlinear
response of the loose parts to the exciting forces from the rotor.

4. • Mechanical looseness is often highly
directional and may cause noticeably
different readings when they are taken
at 30° increments in the radial direction
all around the bearing housing.
• Also note that looseness will often cause
sub-harmonic multiples at exactly ½× or
_× rpm

5. •Structural Looseness Symptoms : High
radial vibration harmonics of 1x.
•Harmonics can stretch all the way across
the spectrum in cases of severe looseness
and can even generate half-harmonics in
extreme cases (1.5, 2.5, 3.5, etc.).

6. 2. Structure Looseness :
• This type of looseness is caused by structural
looseness or weaknesses in the machine’s
feet, baseplate or foundation. It can also be
caused by deteriorated grouting, loose hold-
down bolts at the base and distortion of the
frame or base.
• This weakness allows the machine to vibrate
more freely in the direction where the
weakness is greatest, therefore vibration at
turning speed will be elevated.

7. • Structural looseness will generate a strong
1X in the direction of greatest weakness –
unless there is impacting, in which case
there will also be harmonics.
To distinguish looseness :
• If 1X horizontal more than twice the
amplitude of 1X vertical, looseness is
suspected. If that amplitude ratio changes
when the machine speed is changed the
resonance should be suspected.

8. 3. Looseness between machine and base-plate :
• This problem is associated with loose pillow-
block bolts, cracks in the frame structure or
thebearing pedestal.
• Looses causes higher vibration than normal
so it can make the component wear quickly
and damaged. Below show the ilustration of
looseness between machine and base-plate

9. • The FFT of mechanical looseness
between machine and baseplate :

10. There are two types of mechanical looseness
1. Rotating looseness and non-rotating looseness
2. Structural looseness

11. Rotating Looseness and Non-Rotating Looseness
• Caused by excessive clearance between
rotating and stationary elements of
machine
• Looseness between two normally
stationary parts, such as a foot and a
foundation, or a bearing housing and a
machine

12. Structural Looseness
• looseness between a machine and its
foundation, will increase the 1x
vibration component in the direction of
least stiffness
• Usually the horizontal direction
• Depends on the pshisycal layout of the
machine