machineryalignmentsolutions.com - Jack-load and Power-Torque measurement

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Jack-load and Power-Torque measurement

Jack- load (sag and gap method);

The proper alignment of the propeller shaft is of vital importance for marine propulsion installation. For this, Machinery Alignment uses the sag and gap method of calculation. This method ensures and acceptable distribution of the bearing load over all bearings in the installation over all operating conditions (from cold start to operating in hot engine rooms). Furthermore, it is often the only method which makes it possible to accurately predict resulting bearing reaction forces on the gearbox bearings, for which manufacturers often give stringent specifications

How does it work?

On the basis of available data on shaft, couplings, propeller, gearbox etcetera, a computer model is prepared of the complete propulsion shaft installation. Using a zero offset reference line, bearing reaction forces and elastic line of the shaft are calculated. This “zero” condition (to be compared to a laser-line alignment) is very often a far from optimal condition.

Then, using unit displacements for each bearing, a sensitivity matrix is obtained, which enables the calculation of optimal bearing positions. Usually, this can be fully achieved by virtually displacing the gearbox bearings (plan-parallel or tilted). The resulting ideal alignment is then corrected for thermal expansion of the gearbox during its increase in temperature from cold start to operating temperature.
When the ideal bearing positions are established, the flanged connection(-s) are opened. The shaft will then bent as a result of gravity forces applied on the installation. The resulting values for sag and gap are determined.

When these values are applied during alignment, the installation will behave as predicted in the calculation. The result: optimal shaft alignment and highest reliability!

Power - Torque;

Machinery Alignment can perform accurate shaft power, stress and strain measurements by using strain gauge techniques on almost every type of rotating installation. The purpose of these strain gage measurements can be many. They can be applied in static situations, and often the purpose of the measurements is stress or strain. In dynamic conditions, they can be applied in the measurements of vibrations, and they are especially suited in the measurement of torsional vibrations, since they yield information on both the vibrations (phase, magnitude and frequentation) as well as distortion, which can be related to torsional stress or torque (and power)

A typical example is to guard the stress and strains to which a large construction is exposed during transport or manipulation.

Another example of the purpose of strain gauge stress measurements is to determine the actual stress level for locations which can only be estimated by normal calculation methods or it is possible, with a high level of accuracy, to measure a Torque of a shaft and with the rotating speed known through rpm measurements, also the Power going through the shaft.