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Balancing
Unbalances are a commonly occurring machine fault and occur when the center of mass of a rotating element is located outside its axis of rotation.
An unbalance can be recognized by excessive vibration at rotational frequency. In the time signal this is expressed as visible sinusoidal oscillation, in the frequency analysis the speed line is increased and accordingly the 1st order shows large values.
Balancing is carried out in different steps. After an initial run, which determines the vibrations causing the unbalance, test runs are carried out for each balancing plane. These are necessary in order to determine the original unbalance from the changed vibration behaviour of the test masses. After the compensation measures have been carried out, a control run is carried out to determine the remaining unbalance. Acceleration sensors register the strength of the unbalance, while a speed sensor registers its angular position.
In VibroMatrix balancing is done with the InnoBalancer. In principle, balancing should always be carried out in 2 planes, but if there is only one bearing point or the rotor imbalance can already be eliminated by one compensation plane, 1-plane balancing is carried out, as in the following practise example:
Practise example balancing
We enter the rotor data of our model machine and want to use 16 fixed locations. A certain balancing quality does not need to be reached, so we leave the fields empty. Data of often used rotors can be stored.
As balancing aim we want to reach 0.1 mm/s vibration velocity. Of course, a certain balancing quality, unbalance in gmm or unbalance mass could also serve as a balancing target.In the Vibration Measurement tab, the measurement channel is set on the InnoBeamer. We accept the settings.
At measurement of rot. speed you can select from when you want to evaluate speeds. The number of revolutions to be collected for a measuring run and maximum speed deviation can also be set. We're setting 300 rpm.
We do not want to use the test mass advice feature and therefore do not make any settings. We also leave the settings in the measuring procedure unchanged.
The definition of the zero angle and the counting direction are often the subject of irritation. Therefore the following comments: It is not possible to detect the direction of rotation, so it is agreed that positive angles are counted against the direction of rotation. The VibroMatrix Kits contains an angle measuring disc as an accessory. Depending on the direction of rotation, this represents the correct angle count.
In the Polar Graphics tab you can also adjust the representation of the polar graphic. The internal calculation remains unaffected.
The zero angle can be set in 3 different ways:
method 1: Speed mark and test mass at same position, zero angle
method 2: Specify an angle between test mass and speed mark. The zero angle is at the speed mark, the test mass is taken into account by the program.
method 3: Test mass at any position and input of angle = 0°. Now the test mass position is the zero angle.
Now to the practical balancing. But which speed should be selected? This question is answered by a run-up analysis. So let's have a look at the result from the Practical example. We had found that from 1750 rpm it was possible to balance. But why not at lower speeds?
Balancing processes are always associated with mass changes. However, these can shift the resonance point and thus strongly change the phase angle. Since test masses also influence the phase angle, the influence of this mass change can no longer be determined exactly. Therefore, a constant phase angle should preferably be maintained at the balancing speed.
We want to balance at 2000 rpm. After starting the machine, measurement is only started at constant speed.
Switching on the single vector display makes it possible to estimate the scatter of the individual measurements. After 300 collected revolutions we see that 5.302 mm/s were determined at 220.1°. We find out which unbalance corresponds to this in the test run and continue the measurement. As a test mass, we add 0.906 g at fixed position 9 (202°). This is done by attaching a screw.
After confirmation, the test run can be carried out.The unbalance is then determined. Here it is 39.616 gmm or 2.669 mm/s at 51.8°.
Now the test mass can be removed. The software suggests compensatory measures to eliminate the imbalance. Since we work with fixed places, two masses must always be added here in order to meet the angular position of the unbalance.
The masses are weighed and placed. A scale for weights up to 500 g is already included in the VibroMatrix balancing kit.
A subsequent control run determines the residual unbalance. This is smaller than the targeted 0.1 mm/second, the balancing process was successful.
The balancing process can be traced in the Tools tab. The test mass has already reduced the unbalance, but the angle was not correct. The control run shows the correct mounting of the compensation in angle and mass.
Balancing can be easily documented using the built-in reporting function. At the click of a button, a report is created as a pdf file. The report templates can be customized in various ways. The balancing history can also be saved, so that it can be viewed at a later time and the report created.
When 2-plane balancing is performed, the procedure is similar. In addition, there is a second test run and the application of compensation masses on the second plane.
The InnoBalancer has other useful functions:
Thus, the unbalance can already be reduced with the test mass by using a proposed test mass. For this purpose, it is necessary to specify the value of the vibrating mass and the type of placement of the machine. Furthermore, the accelerometer and speed sensor should be in line. This option is particularly interesting for machines with long run-up and run-down times.
Various possibilities are implemented as compensation measures: masses can be added or removed, radial drilled or milled, masses can be moved concentrically or radially to the middle or to the border or a separate mass list can be defined from which the program selects suitable combinations for compensation.
In some cases, additional masses are attached to the rotor during later assembly steps. In order to avoid resulting imbalances, a target imbalance can also be obtained. The program will display zero, but the target unbalance is actually generated.
Balancing is an important topic for rotating machines. The InnoBalancer therefore guides you step by step through the balancing process.
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