Recommendations for balancing

П.1.1. Rotor balancing in one and two planes of correction.
The quantity of balancing planes is defined with design features of a rotor of the balanced mechanism.

Balancing in one plane ("static") is usually carried out for the narrow disk-shaped rotors with no essential axial beats.
Typical examples of rotors of this class are:

• narrow grinding wheels;
• pulleys of belt drives;
• disk flywheels;
• cogwheels;
• couplings;
• tightening cartridges of lathes;
• narrow fans, etc.

Balancing in two planes ("dynamic") is carried out for long (arched) double-bearing rotors.
Typical examples of rotors of this class are:

• rotors of electric motors and generators;
• rotors for compressors and pumps;
• turbine wheel and fans;
• wide wheels;
• spindles;
• shafts of flour machines with whips, etc.

П.1.2. Features of the balanced machine installation.
As a rule, balancing of the machine is carried out directly on a place of its installation.
The exception takes place when the speed of a rotor gets to one of car resonance ranges. A sign of it is the difference (more than for 10-20%) of results of amplitude and/or a phase measurements from start to start. In case of a resonance identification it is necessary to change the speed of a rotor rotation and in case it is impossible - to change conditions of car installation on the base (for example, having it temporarily established on elastic support).

П.1.3. Choice of speed rotation of a rotor.
Balancing is usually set at operation speed of a rotor rotation. Balancing is usually carried out at the operating speed of the rotor. In the case when applies an actuator with speed change ability, it is advisable to select the highest operation speed.

Attention!
At a choice of rotation speed of a rotor when balancing it is necessary to avoid hit in ranges of resonances of the car (see Ann. Par. 1.2.)

П.1.4. Choice of measuring points and planes of correction.
Bearing supports or pole planes are preferably selected as vibration measurement points.
When balancing in a single plane it is sufficient to have one measuring point (see Fig. Ann. 1.1.).

When balancing in two planes there should be two points of measurement (see. Fig. Ann. 1.2 and Ann. 1.3).
Correction planes, in which occurs the removal (setting) of correction loads on the rotor, should be selected as close as possible to the point of measurement. In case of balancing in two planes distance between the planes should be chosen as large as possible.

Par.1.5. Choice of test load weight.
Weight of the test load may be approximately determined from the empirical formula:

where: Мп - test load weight, g
Мр – balanced rotor weight, g
Rп –test load installation radius, sm
N – rotor speed, rpm
К= from 1 to 5 – coefficient considering conditions of installation of the balanced rotor.

When the weight of test load is correct its installation on the rotor should lead to noticeable changes in the level of vibration. Otherwise, the weight of the test load should be increased.

Par.1.6. Features of sensors installation.
1) The vibration sensor may be installed at the measurement point using:

• Threaded rod (rigid attachment);
• Magnetic sucker;
• transitional probe (clip with a hand);
• direct contact of the sensor with a support (clip with a hand).

2) Phase-angle sensor can be installed on the machine with special devices (e.g., magnetic rack or clamp) and must be oriented on normal to the cylindrical or end surface of the rotor. Mark is applied with a chalk, light-reflecting tape or likewise on the surface of the rotor to reference the phase angle. As a mark also be used the keyways, holes, protruding bolt heads, etc which are available on specific rotors.
For production of the reflecting mark the adhesive mirror reflecting tape or the adhesive light-reflecting tape are included in a dekivery set.
Light-reflecting tape is recommended to be used for severe conditions of the sensor operation (the raised gap, a flare external sources of light radiation).
The gap between the sensor and the rotating surface of the rotor for phase angle sensor of DT 2234C + type must be installed within 10 - 500 mm.
For phase angle sensors of other models, which can optionally be equipped with the device, the allowable range of the operating clearance is set to meet the requirements of technical documentation for the sensor.
It must be understood that the choice of width of "L" mark depends on the rotation frequency of a rotor and radius of mark installation. Approximately it can be calculated on a formula:

where: L – mark width (min), sm
N – rotor speed, rpm
R – mark installation radius, sm

Based on the experience of practical application the recommended width of mark must be min 1 - 1.5 cm.
For midget rotors with the mark installation radius of 10 mm it is recommended to use a narrower label. It is desirable to conduct an experimental verification of correctness of the label width choice.

Attention!
When using the photoelectric phase angle sensor in order to avoid interference, it is desirable to avoid direct sunlight or strong artificial light reflecting on the mark and / or sensor (photodiode).

Par.1.7. Criteria of balance according to the state standard ISO 10816-1-97 ( ISO
2372).
Limit values for vibration level established for the four classes of machines are listed in Table A.1.

*)Note:
- class 1 corresponds to small machines, installed on rigid foundations (analogue - motors up to 15 kW);
- Class 2 corresponds to average machines, installed without separate foundations (analogue - electric power of 15-75kvt), as well as actuators on detached foundations with individual power up to 300 kW;
- Class 3 corresponds to large machines installed on rigid foundations (analogue - the electrical equipment of more than 300 kW);
- Class 4 corresponds to large machines installed on foundations of facilitated type (analog - electrical equipment more than 300 kW).