Alignment

Alignment, primarily for rotating machinery is the activity to check that centerlines of two rotating shafts ( of Driver & Driven machine ) are in line i.e. collinear with each other at operating conditions.

Driver

Rotating Machinery

Driver Driven

Rotating Machinery

Driver Connector Driven

Rotating Machinery

Motor Pump

Coupling

Rotating Machinery

Driver Connector Driven

Shaft Alignment Fundamentals, Techniques & Execution Methods

Introduction to shaft alignment Understanding alignment Objectives of accurate alignment Effect of misalignment Types of misalignment Misalignment tolerance guide Pre alignment checks Alignment techniques Symptoms of misalignment Do’s & Don’ts of alignment Conclusion

Introduction to Shaft Alignment

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 condition.

Introduction to Shaft Alignment

Prime interest of alignment is to set the centerline of rotation of shaft for two or more pieces of rotating machinery collinear. However, in practice alignment check is performed on the coupling & it is assumed that coupling hub bore & shaft are concentric with each other. So it’s necessary to ensure that coupling hub bores & shaft centerlines are concentric to each other.

Understanding Alignment

Understanding Alignment

Understanding Alignment

Understanding Alignment

Objectives of Accurate Alignment

Reduce excessive axial and radial forces on the bearings to insure longer bearing life

Minimize the amount of shaft bending Minimize the amount of wear in the coupling

components Reduce mechanical seal failure Maintain proper internal rotor clearances Eliminate the possibility of shaft failure from cyclic

fatigue Lower vibration levels in machine casings,

bearing housings, and rotors

Effect of Misalignment

Effect of Misalignment

Effect of Misalignment

Effect of Misalignment

Types of Misalignment

Types of Misalignment

Types of Misalignment

Types of Misalignment

Misalignment Tolerance

Misalignment Tolerance

Pre Alignment Checks

Shaft run-out Soft foot Distance Between Shaft Ends Rough Alignment Piping strain Tightening Sequence of foundation bolts

Pre Alignment Checks – Shaft Run-out

Pre Alignment Checks – Soft Foot

“Soft-Foot” is the term commonly applied to that condition which exists when all four (4) of the machine feet are not supporting the weight of the machine.

Pre Alignment Checks – Soft Foot

Set the machine in place, but do NOT tighten the hold-down nuts

Attempt to pass a thin feeler gage – check for gap Tighten all hold-down nuts on the machine to be

aligned Secure a dial indicator holder on one foot Set the dial indicator to zero (0) Completely loosen the hold-down nut(s) on that

foot only. Watch the dial indicator for foot movement during the loosening

If the foot rises from the base when the hold-down nut(s) is loosened, the leg is having soft foot

Pre Alignment Checks - DBSE

Pre Alignment Checks – Rough Alignment

Pre Alignment Checks – Piping Strain

Pre Alignment Checks – Tightening Sequence

Machine To Be Moved

The machine which is easy to move & can be moved in least time with minimum effort is preferred for movement i.e.

For Pump & Motor train, motor shall be preferred for movement

For pump & turbine train, turbine shall be preferred for movement

For compressor, G.box & Turbine train, first fixing the G.box & carrying out adjustment on turbine& compressor shall be preferred

Alignment Techniques

Straight edge & feeler gauge

Shaft alignment using dial indicators :

- Face-Rim method~ Two indicator method~ Three indicator method

- Reverse indicator method

Laser alignment method

Alignment Techniques

Straight Edge & Feeler Gauge Method

Advantages :

Simplest & cheapest of all methods. Does not require too many tools. Does not require specialized skills

Disadvantages:

Least accurate of all methods. Too much Scope for human errors

Face-rim Dial Indicator Method

Face-rim Two Dial Indicator Method

Face-rim Three Dial Indicator Method

Reverse Indicator Method

Laser Alignment

Symptoms of Misalignment

Premature bearing or Mech. seal failures Excessive radial and axial vibration High casing temperatures at or near the

bearings Excessive amount of oil leakage at the bearing

seals Loose foundation bolts Loose or broken coupling bolts Unusually high number of coupling failures The shafts are breaking (or cracking) at or close

to the inboard bearings or coupling hubs

Do’s

Always use calibrated dial gauges Adjust the plunger of the dial gauges so that they are

pressed half ways   Ensure that uniform conventions i.e. top, bottom, north

& south is followed throughout the procedure Measure all the readings facing the same direction Follow uniform practice for dial readings-division or mm Before rotating the machine, ensure that bearings are

lubricated Always use pre-cut SS shims Ensure the correctness of readings by taking at least

two set of readings Check the surfaces where measurements are to be

made are free from burrs or marks

Don’ts

Do not hammer the machine feet directly for side movement. Use side jackscrews for movement

Do not use poorly fabricated or rough alignment brackets. Use properly machined & sturdy brackets

Never use magnetic dial stand for alignment Don’t use trial & error method for corrective

movements Don’t grind shank of the holding down bolts if

restricting the movement, enlarge the holes Avoid using too many shims While measuring the readings if you have passed

the 90 Deg. mark never rotate back, complete the whole revolution

Conclusion

Precision alignment reduces maintenance cost

Aligned equipment run longer & smoother

Always align to a known tolerance

Don’t skip the pre alignment checks