Misalignment & Shaft Alignment Methods

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.