Maintenance Excellence Part 1- Machine Alignment

Are you encountering….

1. Premature bearing, seal, shaft or coupling failures?
2. Is axial vibration high?
3. Oil leakage from seal area?
4. Loosening of foundation bolts?
5. Frequent breaking of coupling bolts?
6. Shaft shearing from hub or bearing area?
7. Accumulation of grease inside coupling guard?

If any of the answer is YES, then it is the problem of alignment.

After lack of lubrication & deviation from standard condition, alignment is the biggest reason for downtime across industries. There are multiple reasons for this, prime being related to understanding the importance & having the skill.

Understanding misalignment

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. The deviation of relative shaft position accounts for the measured difference between the actual centerline of rotation of one shaft and the projected centerline of rotation of the other shaft.

              Biggest Misnomer- FLEXIBLE COUPLING

These couplings are designed to accommodate slight misalignment not everything.

Method of Alignment

1-     Straight edge- Using Engineering scale. Used maximum in Industry as the easiest. But should only be used as initial rough purpose, in case of very high initial misalignment.

2-     Dial Gauge- One of the best method, but require highly skilled workmen.

3-     Laser alignment- Easy to do but with care.

Dial gauge is the basic of all alignment. Let us try to understand this.

Dial Gauge alignment

Few fundamentals:

·        Least count of dial gauge is 0.01 millimetre. One 360-degree rotation of needle moves plunger by 1 mm and dial is divided into 100 parts.

·        Soft foot- Soft foot can make an alignment job much more difficult and sometimes impossible. Soft foot is a condition "when rotating equipment is set into place on its base, frame or sole plate, one or more than one of the 'feet' are not making good contact at the foot points of the frame.” Soft Foot usually gives rise to a 1x Harmonic of the rotation frequency in the spectrum when Radial (Horizontal or Vertical) vibration measurements are taken.

·        LOTO (Lock out and Tag out) of electrical drive is the first thing to do. Also, Look for Mechanical/ hydraulic force and isolate, if present.

·        Sag check- A sag check is a test that determines the amount an indicator bracket will sag at a given distance.

·        Hot alignment- is used where the operating temperature is very high as compared to normal ambient temperature such as turbine or turbo machinery. Based on the thermal expansion of the metal, cold condition alignment is done with calculated misalignment. Such machines are preheated before start and coupling comes to the perfectly aligned condition before actual power input.

  Golden thumb Rule-

  Dial Reading: Top + Bottom = Left + Right

If above equation hold true that indicates-

• No looseness in the alignment brackets.
• Dial indicators are working fine.
• Reading are true reflection of misalignment.

 Required Tools-

Master Level, Vee Block, Engineering Scale, Wire Brush, Brass/ Steel Shims, Shim Cutter, Dial Indicator, Micrometre, Emery Paper, Alignment Brackets, Feeler gauge, Fine flat file, Tool box

 Method-

a-      Isolation and permit to work.

b-     Alignment needs to be done w.r.t. the equipment, which is difficult to move such as gear box, pump, fan and so on. In maximum cases, adjustment to be done in the drive unit i.e. motor.

c-      Initial checks.

1.      Driven unit is levelled. Use Master level.

2.      Driven unit is firmly tightened. No Soft foot. Use feeler gauge to confirm.

d-     Initial steps-

1. Make the coupling hub free from each other.
2. Remove all existing shims from under the feet of drive unit (in most of the cases).
3. Clean the base thoroughly.
4. Examine the base bolts and holes. Replace bolt if necessary.
5. Check for coupling face and diameter eccentricity.
6. Scrape and file all the rust, nicks, or burrs.
7. Check for shaft trueness. Use dial indicator for the same.
8. Remove all the grease from the bearing to the extent possible.

e-     Check for shaft level (of driven unit) using Vee block and Master level.

f-       Install alignment brackets.

g-      Install Dial indicators. One in radial and another in facial position. Check dial indicator for sticking or loose needle. Aim indicator stem directly towards centre line of shaft.

h-     Sequence of alignment is – first axial/ facial and then radial.

i-       Few important measurement before calculating shims.

1. Air gap between coupling hub.
2. Distance between driven unit coupling face to first (nearest) feet.
3. Distance between front and rear feet.

j-       Axial/ facial alignment requires adjustment of air gap between coupling hubs. Feeler gauge will be handy in this condition. For cross verifying the dial reading.

k-      Radial alignment of driven unit with drive unit may require shims under all feet, of different sizes.

l-       Go for the minimum numbers of shims. Too many shims can cause soft foot (springy foot).

m-   Tighten all bolts and recheck the indicator readings.

 Important Points-

a-      False shaft arrangement to be used, wherein the distance between coupling hubs are large. Laser method will be much easier than dial indicator.

b-     In highly corrosive ambient condition, SS shims will be better.

c-      Extra care to be taken while cutting shims as edge needs to be free from all burrs or projections.

d-     If possible, move both coupling hubs together for taking reading. This will nullify any eccentricity in the coupling halves.

Do Remember – Excellence is a continuous journey, made from tiny steps.