Alignment of Machinery

On board ship there are hundreds of motors that drive machinery like pumps, fans, purifiers, winches, and other rotating equipment. The main engine itself is coupled to the propeller through shafting. Diesel engines or turbines drive alternators.

Whenever some of the motors or driven machinery are dismantled or even when the machines are not running smoothly, alignment is done.

The purpose of alignment is to ensure that the centerline of the motor rotor shaft coincides exactly with the centerline of the driven machinery. Alignment is essential to ensure that the machine runs smoothly with minimum vibration.

Provided the two shafts are not bent crooked, the two alignments to be checked and adjusted are: Offset alignment and Angular alignment.

Most of the alignments on ship are rough alignment that can be done using straight edge ruler and feeler gages. However for precision alignment, the use of dial gauges with magnetic bases can be used.

Offset Alignment
offset alignment of the shaft coupling using a straight edge to adjust the difference in heightThe radial alignment is checked using a straight edge ruler. By placing the ruler across the coupling halves at the top, bottom and both sides any gaps between the 2 coupling halves will indicate that the shaft is offset slightly. The misalignment can be corrected by shifting the motor or by putting shims to raise up the motor or driven machine.

Angular alignment
angular alignment of the shafts at the coupling using a feeler gauge to check the gaps at different places and to adjust until they are equalBy inserting a feeler gauge between the coupling faces and rotate both coupling halves simultaneously we can check whether the shafts have any angular displacement between them. The feeler gauge readings at checked at four points on the shaft coupling. Again the alignment is corrected by shimming or shifting the machinery.

The motor and the driven machine should be bolted solidly to the base after finalizing the alignment positions of the equipment.

Flexible Coupling

 

Speed, in r.p.m. Offset Tolerance, in mm Angular Tolerance for Coupling Diameters up to 400 mm Angular Tolerance for Coupling Diameters from 400 to 600 mm
2500 ~ 4000 0.010 0.020 0.030
1300 ~ 2500 0.025 0.050 0.070
Below 1300 0.040 0.080 0.100

 

Rigid Coupling

 

Speed, in r.p.m. Offset Tolerance, in mm Angular Tolerance for Coupling Diameters up to 400 mm Angular Tolerance for Coupling Diameters from 400 to 600 mm
2500 ~ 4000 0.010 0.020 0.020
Below 2500 0.015 0.030 0.030