Dynamic balancing
Damaged rotor blades can cause imbalance. When this imbalance exceeds the permissible tolerance, vibrations and produced, which wear the bearings and in the long-term cause major damage to the entire turbocharger. Extensive repairs and downtime are then unavoidable.
Before a rotor can be balanced, it is first necessary to check that the runout of the shaft and the deflection of the compressor wheels are still within the permitted tolerances. If these measurements are satisfactory or after remedial work, the rotor is examined for imbalance on a microprocessor controlled test bench, according to the ISO standards.
The complete rotor is placed on the balancing machine and the partition wall is independently supported. Even though unbalance may not have been evident before overhaul and calibration, it is possible that it could be introduced during dismantling and repair procedures and it is therefore paramount that dynamic balancing is carried out before the rotor is returned to service.
If the unbalance is found to exceed the makers limit, it is corrected by grinding down the appropriate correction planes on the rotor. Accurate balancing is of the utmost importance and not a single rotor leaves the SDS workshop without having been tested and, if necessary, corrected.
Why balancing is so important
Why are some machines louder than others? Why does the valve of a bicycle swing downwards when it is allowed to freely rotate? Why does the steering wheel of a car shake at certain speeds? Virtually every day we come across a phenomenon, the effect of which is frequently underestimated - unbalance.
The term 'unbalance' comes from "balance", which in turn comes from "scales". Scales are in equilibrium when the same weight exists on both sides of the scale beam. The mass distribution of a rotor about its rotational axis can be considered in the same way. An uneven distribution of the mass is called unbalance. It causes centrifugal force, vibration and noise during rotation, which become stronger and more uncomfortably noticeable at higher speeds.
Service life
Bearings, suspensions, housings and foundations can be subjected to very high stresses caused by vibration resulting from unbalance and these result in greater wear. Products with unbalanced parts often have a shorter service life.
Safety
Vibrations can reduce the frictional grip of screwed and clamped connections, until components loosen. Electric switches are destroyed by vibration, pipes and cables can fracture at the connections. Unbalance can substantially reduce a machine's operating safety, man and machine are at risk.
Quality
A irregularly running electric tool cannot be precisely used. The user's effort increases they become tired more quickly. Vibrations also have a substantial negative effect on the production result of machine tools: A grinder or high speed woodworking machine produces poor surface quality and produces more rejects if the spindle and tools have not been precisely balanced.
Forces caused by unbalance, disruptive vibration and noise are removed by balancing.
This involves improving the mass distribution of a rotor so that a smaller centrifugal force act in its bearings. In addition, the type of unbalance also has to be taken into account during balancing.
Unbalance types
Unbalance can be divided into different types depending on their effect. Apart from the shape and task of a rotor, the type of unbalance affects the location of the correction plane and the choice of balancing tolerance. The most important types of unbalance are:
Maintenance & callibration
All our balancing machines uses the latest Schenck technology to provide reliable, cost-effective operation for virtually any size rotor. A wide variety of machines are available that can accommodate short runs for prototype development and overhaul applications to large scale production runs.
- All balancing in accordance with ISO, API and MIL specifications
- Hard & soft bearing machines to meet most balancing requirements
- Vertical balancing machines for disc type rotors without journals
- Certification of proving rotors and test masses
- Fully equipped inspection/QC department
- Precision scales and measuring equipment calibrated to NIST standards
- Full documentation for rotors with Certificate of Conformance available
Scope of balancing facility
Schenck balancing machines offering service from
Length: 0 – 3000 mm
Diameter: 0- 1200 mm
SCHENCK H20/H40 BUTL with CAB 920
SCHENCK H10BU with CAB 610
SCHENCK HEC121 with CAB590
Static unbalance
Two unbalances (shown here as arrows) can have the same size and angular position and can be the same distance from the centre of gravity. The same condition results for an individual, twice as large, unbalance that acts at the centre of gravity, i.e. in this case in the middle of the rotor. If such a rotor is supported on two knife edges, it would swing until the "heavy point" was facing downwards. This means this unbalance acts even without rotation; it is therefore called "static unbalance". It causes the centre of mass to shift away from the geometric centre, which in turn causes the rotor to swing oscillate parallel to its rotational axis when it is running.
Static unbalance should be corrected in the centre of gravity plane. This is achieved by removing material at the "heavy point" or attaching material at the opposite side. Correction of static unbalance in one correction plane occurs particularly frequently in disc-shaped rotors. Therefore, vertical balancing machines are most suitable for balancing these.
Couple unbalance
Two unbalances (shown here as arrows) can have the same size, but their angular position is offset by precisely 180° to each other. This unbalance distribution cannot be detected by swinging, because the rotor does not take up a unique position at rest. The rotating rotor executes a wobbling movement about its vertical axis (perpendicular to the axis of rotation), because the two unbalances exert a moment. Ergo, this type of unbalance distribution is called couple (moment) unbalance.
An opposing moment is required to correct the couple unbalance, i.e. two equal-sized correcting unbalances, which are arranged in the two balancing planes at an offset of 180°, corresponding to the original unbalance. It is particularly important to take couple unbalances into account in elongated cylindrical rotors. Therefore, horizontal balancing machines are particularly suitable for correcting this type of unbalance.
Dynamic unbalance
A real rotor does not only have a single unbalance, theoretically it has an infinite number arbitrarily distributed along the axis of rotation. These can be replaced with two resulting unbalances (shown here as arrows) in two random planes, which generally have different sizes and angular positions. As this unbalance condition can only be fully determined during rotation, it is called dynamic unbalance. It can be broken down into a static unbalance and a couple unbalance, whereby one or the other can be the overriding unbalance. Two correction planes are required to completely correct dynamic unbalance. Dynamic balance occurs in virtually all rotors. Therefore, both horizontal and vertical balancing machines are used.
