Omkar Engineers, Inc

Misalignment unfailing results in damage to the coupling, bearing and, if severe, to the shaft as well, beyond repair. Accurate alignment, therefore, is of the UTMOST importance and involves three basic operations : axial positioning, paralleling and centering of shaft. These operations are dealt with in detail below.

6.1 Axial positioning of shafts
Ensure that the individual half-coupling are firmly secured to the corresponding shafts. The motor should then be so paralleled that the gap between the faces of the two halves of the coupling as specified by its manufacturer is obtained. This gap should be obtained with the motor shaft fully drawn out in the direction of the driven apparatus. This operation requires a further refinement where the shaft of the driven apparatus is not axially located or can suffer axial displacement such as by wear of the valve in a balance valve located pump. In such cases, reference must be made to the Company for details.

6.2Paralleling of shafts in vertical and horizontal planes. The condition for parallelism is that, if the disconnected half - coupling are rotated together, the measured coupling gaps at two diametrically opposite ends are equals, or in any case the algebraic differences between the two are equal, in all the angular positions of the coupling.

The procedure as illustrated in Fig 2A & 2B consists in applying this condition to obtain parallelism in the vertical and horizontal planes, in turns, to ensure total parallelism.

Paint two lines on two points diametrically opposite to each other on both the half-coupling, extending axially across their rims.

Keeping the lines in the vertical plans, measure the coupling gaps accurately with a feeler gauge at 6 o'clock and 12 0'clock positions (side view) and record their difference. Turn the two couplings through 180o until the lines are again in the vertical plane. This must be rectified by adding or removing shims under the motor feet, until the two differences do not differ by more than 0.01% of the value of the coupling diameter.

By similar means ensure horizontal parallelism by taking reading at the 3 o'clock and 9 o'clock positions with the line brought in the horizontal plane for each reading.

6.3 Centering of the shaft ends (height and sideway setting)

Centering of the shaft ends should ideally be done with the driving and driven machines at their normal working temperatures but if this is impracticable, an allowance must be made when the centering is done with both machines at the same temperature, say ambient temperature, to account for the difference in shaft centre height due to differential thermal expansion during normal operation.

Assuming the motor (driving machine) to be the hotter of the two machines, an average excess of the shaft centre height of the motor over that of the shaft centre height of the motor over that of the driven apparatus of about 0.03 per cent of the nominal shaft centre height may be assumed for a temperature rise of 50oC measured on the frame of the motor.

Clamp a dial gauge securely to one half-coupling with the gauge needle resting initially, for check-coupling and take dial gauge readings for various positions. Any variations of the reading indicates abnormality or instability in the mounting of the dial gauge, which must be correct by tightening the fixing clamps or by modifying the mounting arrangement.

Without disturbing the dial gauge mounting, shift its gauge needle over to and firmly resting on the other half coupling. Rotate this other half coupling till the paint mark on the two half couplings are in one complete revolution taking reading of the dial gauge when it is in each of 3 o'clock, 6 o'clock, 9 o'clock and 12 o'clock positions. For perfect centering all the four reading must be equal. If this is not the case, the shaft ends are eccentric to the extent of half the difference between. Rectification must be affected by shimming and/or sideways setting as required.

The shims should be so arranged under the foot that the thickest shims is at bottom and thinnest at the top. The shims should be placed under the motor or the driven equipment depending on their centre heights.

Rechecking

As each operation will almost certainly disturb results achieved in the previous operations to some extent, it is necessary that the following sequence of operations be followed for correct aligning of the shafts.

6.4.1 Axial positioning

6.4.2 Vertical paralleling6.

6.4.3 Centering (height and sideways setting)

6.4.4 Horizontal paralleling

6.4.5 Centering (side setting only as height will remain unchanged after operation 3)

6.4.6 Recheck operations 1, 2 and 3 with the foundation bolts fully tightened. The shafts are aligned if the desired results are obtained with out variation.