The two components of misalignment are Angular and Offset. The aim of Shaft alignment is to position the rotational centres of two or more shafts to a state whereby they are colinear, when running at normal operating conditions.
Angular Misalignment is the difference in the slope of the shaft of the moveable machine, as compared to the slope of the shaft of the stationary machine. The units for angular misalignment are millimetres per metre (mm/m).
Offset misalignment is the distance between the shafts centres of rotation, measured at the plane of power transmission, typically at the coupling centre. The units for this measurement are millimetres (mm) and micrometre (µm).
Vertical shaft alignment is carried out to determine and correct the relative position of two coupled machines, such as a motor and a pump, so that the rotational centres of the shafts are collinear when the machines are working at normal operating temperature. Correction of vertical shaft alignment is done by moving the flange of the machine until the shafts are aligned to within given or industry accepted tolerances.
Machine Defined Data
Set-up data such as Distances, Target Values and Tolerances can be saved for future alignment jobs but only if one is able to place the sensors in the same place, each time.
When a machine, or identical machines, are measured it can be convenient to pre-enter the relevant parameters. The data that is pre-loaded are:-
the name of the specific machine,
the distance between the sensors where fixtures are installed,
the distance between the centre of the coupling and the M Sensor,
the distance between the M Sensor and the first pair of feet,
the distance between the first and the second pairs of feet,
Target Values as required and
When using Machine Defined Data, the sensors must always be placed according to the pre-entered distances in order to get the correct measurement results.
Most machines develop a certain amount of heat while running. The best case scenario is when both the driving and driven machines are affected equally, thus requiring no input or compensation values. In some applications the driven machine gets either hotter, as in a pump for hot liquid or cooler, as in refrigeration plant, than the driving machine.
Machine manufacturers define the thermal expansion of machines differently but in most cases it is expressed as a factor of deliberate misalignment for both offset and angular values. In the Fixturlaser NXA system, the pre-set target values are entered prior to starting the alignment task. Accepted entries are feet values for angle and offset parameters.
The entered values are Target Values, these are the values at which the machine should be positioned when it is not running and in the cold condition, so as to obtain the correct alignment position when the machine is running at its hot condition.