Shaftmisalignment occurs when the center lines of rotation of two (or more) machinery
shafts are not in line with each other -In more precise terms, shaft
misalignment is the deviation of relative shaft position from a collinear axis
of rotation measured at the points of power transmission when equipment is
running at normal operating conditions.
Type of Misalignments:
Ø Offset
or Parallel misalignment - Occurs when the two shaft centerlines are parallel,
but not in the same line. They are offset horizontally or vertically (or both),
displaced to the left or right, or positioned at different elevations.
-Horizontal
offset misalignment
-Vertical
offset misalignment
Ø Angular
misalignment- The axis of Driven and Driver shaft are at an angle to each
other.
-
Vertical angular misalignment
-
Horizontal misalignment
Ø Combination
misalignment- Occurs when the motor shaft suffers from angular misalignment in
addition to parallel misalignment.
Symptoms
of Misalignment:
Ø Premature
bearing, seal, shaft, or coupling failures.
Ø Excessive
radial and axial vibration.
Ø High casing temperatures at or near the
bearings or high discharge oil temperatures.
Ø Excessive
amount of oil leakage at the bearing seals.
Ø Loose
foundation bolts.
Ø Loose
or broken coupling bolts.
Ø Excessive
amount of grease on the inside of coupling guard
Ø Similar
pieces of equipment are vibrating less or seem to have a longer operating life.
Ø Unusually
high number of coupling failures or they wear quickly.
Ø The
shafts are breaking (or cracking) at or close to the inboard bearings or
coupling hubs.
Ø Excessive
amounts of grease (or oil) on the inside of the coupling guard.
TIR - Total Indicator Reading;
total range of a dial indicator reading when gauging misalignment.
Shaft Runout is
the wobble motion produced by a shaft that is not perfectly true and straight.
Shaft runout is often abbreviated T.I.R. (Total Indicated Runout).
SHAFT
ALIGNMENT METHODS:
There
are three method of coupling alignment
1. Straight
edge& feeler gauge
2. Dial indicators
- Single
dial method
- Double
dial method
3. Laser alignment
Prerequisite
tools for alignment:
Ø Dial
gauge mounting clamp.
Ø Single
dial gauge mounting clamp.
Ø Double
dial gauge mounting clamp.
Ø Spanner
set.
Ø Dental
or plane mirror.
Ø Filler
gauge.
Ø Pre
cut shims.
Ø Measuring
tape.
Ø Jacking
bolts.
Ø Scale.
Ø Micrometer.
Coupling Alignment Procedure:
Coupling alignment involves following steps:
Ø Ends
float assessment and arrest.
Ø Diagonal
Checking for leveling of the equipment on bed.
Ø Vertical
Angular misalignment correction.
Ø Vertical
Offset misalignment correction.
Ø Horizontal
Angular misalignment correction.
Ø Horizontal
Offset misalignment correction.
Ø Final
horizontal angular and offset misalignment correction.
CHECKING SHAFT RELATED RUN OUT:
“TIR” should not exceed 0.025mm per 50mm
distance from bearing”
CHECKING
SHAFT RELATED RUN OUT: TIR should
not exceed 0.025mm per 50mm distance from
bearing.
LEVEL CHECKING: Done for elimination of clearance
between feet of driver and bed.
Angular misalignment checking:
Angular
Misalignment Checking:
Misalignment Existing:
n At
Inboard = L1 / D x A
n At
Outboard = L2 / D x A
L1 = Inboard distance from pivot point in mm
L2 = Outboard distance from pivot point in mm
D = Pivot point diameter
A = Net misalignment reading in mm.
Net misalignment = ( L2 - L1 )
X A / D
(Add shims at Inboard or outboard depending upon
inclination of the driver)
Offset
Misalignment Checking:
CORRECTION METHOD OF HORIZONTAL OFFSET
MISALIGNMENT:
HORIZONTAL ANGULAR MISALIGNMENT CORRECTION
METHOD:
SHIM INSTALLATION AT REAR FOOT OF MOTOR:
SHIM INSTALLATION AT FRONT FOOT OF MOTOR:
ALIGNMENT CORRECTION WITH FEELER GAUGE AND
SCALE:
VERTICAL PUMP ALIGNMENT:
VERTICAL PUMP ALIGNMENT:
SHIMS:
Ø Try to use a maximum of 4 or less shims
under each foot.
Ø It’s not always possible, but try to
minimize the number of shims per foot.
Ø Use pre-cut stainless steel shims. You
can’t cut them for less than you can buy them.
Ø When you insert shims under the foot,
slide them all the way in, then back them out 5mm, so the bolt threads don’t
bend them.
Ø Don’t reuse painted, or badly bent
shims.
Ø Be careful. A 0.05mm shim can cut you like a knife. Keep them neat.