Balancing Methodology

DESCRIPTION OF THE OPERATING PRINCIPLES OF BALANCING MACHINES

The "DAS-383" computer system for measuring and localizing unbalance includes the "R-BAL SI–1" measurement and control unit, which consists of a module for preparing and converting signals from vibration sensors and a laser marker sensor, as well as an electronic unit for starting, stopping, and smoothly adjusting the rotational speed of the drive motor.

We will omit the installation of the rotor on the supports of the balancing machine and the placement of the drive belt.

1. It is necessary to apply a mark on the rotor from which the laser beam will reflect. Typically, a reflective marker or a regular white correction fluid mark is used for this purpose. The applied mark is 0 degrees; the count goes up to 360 degrees from it in the direction opposite to the direction of rotor rotation during balancing.

During the balancing process, there is a need to determine the angle at which material is added or removed. If the rotor has characteristic elements (lamellae, protrusions, bosses, blades, etc.), then the mark is applied on or opposite this element, and knowing the angle between the elements, it is easy to determine the required angle for unbalance correction.

When using the automatic rotor indexing system, the operator only needs to press the button corresponding to the required correction plane, and the balancing system itself will rotate the rotor to the necessary angle; the point where the laser beam falls on the rotor surface will be the location for unbalance correction.

When using the manual rotor indexing system, the operator manually rotates the rotor on the balancing machine supports until the arrow on the screen aligns with the mark indicating the unbalance location; at this moment, the arrow of the corresponding diagram and the table of the balancing run history for the corresponding correction plane are highlighted in green.

In the first window of the program interface, we assign a unique name to the part being balanced, select the rotor type (between bearings, overhung, double overhung, etc.), then measure with a ruler or caliper and enter the geometric parameters of the rotor: namely, the distance from the left support to the left correction plane, the distance from the left support to the right correction plane, the distance between the left and right supports. It is also necessary to enter the radii of the correction planes. If the balancing accuracy tolerance is not known in advance, it can be calculated by knowing the required balancing accuracy class (accuracy classes), the rotor mass, and the operating rotational speed.

2. We start the drive to rotate the part being balanced. In automatic mode, the indexing and gear ratio are set, followed by a smooth acceleration to the optimal rotational speed range.

3. Then the system will suggest calibrating the rotor, or will immediately display the unbalance value if the "permanent calibration" mode is used (relevant for sub-resonant systems).

4. Calibration is performed using the three-run method. The first run is described in step 3. After the first run, the "R-Bal" program recommends that the operator place a first calibration weight of known mass in the left correction plane at a known angle relative to the mark - this is typically 0 degrees.

The drive is started, rotation is stabilized, results are measured and saved, and the rotor is stopped. Then the calibration weight is moved to the right correction plane and the procedure is repeated.

After stopping, an interface window appears on the monitor screen displaying, in polar coordinates and numerical values, the angle and the amount of material in grams that needs to be added or removed to balance the rotor.

Subsequently, the rotor calibration data is saved on the computer's hard drive as a file under a unique name, and balancing is performed in a single run.

In most cases, it is not possible to balance a rotor in a single run due to errors associated with removing or adding more or less material than required, as well as angular errors.

For example, an error of 5 degrees, assuming no mass error, will correct 90% of the unbalance in the current correction plane in one run.

When balancing most rotors, material can be removed or added with sufficient accuracy. For instance, knowing the density of the rotor material and the drill diameter or the diameter and thickness of an end mill, the "R-Bal" program can determine the required drilling or milling depth to remove the necessary amount of material. Or, if balancing is done by adding material, knowing the mass of balancing washers or compound, balancing can also be performed accurately enough in 1-3 runs.

In the case of balancing turbocharger rotors, it is generally not possible to accurately remove the required amount of material in one attempt, as the material is typically removed manually using abrasive wheels. Therefore, for high-quality balancing of a turbine rotor, at least 5 runs are necessary, sometimes up to 10 or more.

After balancing any rotor, it is possible to obtain the results in printed form, which will display the rotor name, balancing date, initial unbalance level, and residual unbalance for both correction planes.