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.
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.
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.
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.
Irregular, noisy running is always used as a quality assessment criterion and so vibrations can have a substantial negative effect on a product's competitiveness: A highly vibrating household appliance and a noisy car are products which will not be successful on the market.
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 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: