Difference between revisions of "Balancing single/dual plane"

A rotor is a shaft rotating around its axis during service. In general such a rotor consists of a shaft with one or more discs fitted to the axle. Such discs can be fly wheels, grinding wheels, turbine wheels, etc. The shaft is usually running in bearings allowing the rotation of the body. Depending on their rotational speed, two basic categories can be defined to classify rotors: <u>rotors with rigid shaft</u>, and <u>rotors with flexible shaft</u>. <br>

If the operating speed remains below half of the first critical bending speed, the shaft does not deflect : it may be considered as a rotor with a rigid shaft. At such operational speeds and due to the non circular cross section of the rotor, the axis of rotation (Z) and the inertial axis (&Delta;) does not coincide (e.g. the mass is not evenly dispatched in a section of the shaft). This may results in a tumbling movement of the structure, which amplitude depends on the bearing clearance and stiffness. In any case, the bearings are subjected to unnecessary or even non allowed loads.  

[[Image:Unbalanced_shaft_schem.png|framed|center|''Unbalance : inertial axis does not coincide with rotational axis.<br> The unevenly mass distribution is represented by "m"'']]<br>

The measurement direction of the accelerometer must be referred to the tach sensor position. This can be done by the "Angular correction" in the analyzer setup. In our example in '''Sketch 1,''' the '''angular correction''' </font>is '''90°''' and the <font color="#339966">'''offset''' </font>is -'''15 °'''.

The <u>initial run</u> analyses the behavior of the rotor due to its initial unbalance.

For <u>balancing in one plane</u>, just one test mass and one test run is necessary. It is important that the angular position of the initial unbalance is changed   significantly by the test mass. Take this into account, when choosing test weight and position.

When <u>balancing in two planes</u>, two test runs are necessary. For each run only one test mass is necessary positioned in one of both planes respectively. Again in both test runs the position of the unbalance must be changed by the test masses.

Imagine a rotating machine to be balanced when standing untightened on the floor. After the test mass is mounted the increased unbalance       causes the machine to move. Holding or fixing the machine during the test run will cause wrong balancing results. To overcome this chose lower test mass or position to reduce the unbalance. If this doesn<nowiki>'</nowiki>t work you could fix the machine during the <u>complete</u> balancing procedure. After this basic balancing execute a second complete balancing procedure with the machine unfixed (in normal operating conditions).

to set the tachometer, you need to go into the "Speed" tab :

To set a phase adjustement, you can specify the position of the sensors. To enter the menu, click on "Position":

This is now the last project that has been used

Set mass and position of the mass you want to use in column "Mounted Mass". The software automatically calculate the expected residual unbalance (green point in polar graph).

In this example, we only had a mass of 5 gram available instead of the calculated 4.685g mass to add at the 7th position. The prognosis shows that the residual unbalance (blue point in polar graph) moves to the green point inside the blue circle.