Getting the right balance for rotors

Rotors are used in a wide number of different devices, including industrial machinery and vehicles. They are designed to be properly balanced and revolve around a perfect mass centre axis, but this can be difficult to achieve. There are several reasons why this is so including the number and location of bolts, the fitting or parts and bearings. As a result the rotor will revolve around a different centre of mass and produce vibrations. These can then cause wear to bearings and casings, reducing the lifespan of the part. The vibrations and wear will also create noise.

To understand how to improve balancing and reduce vibrations, you need to know the two different types of rotor and three types of unbalancing. Rotors are either rigid or flexible. The first type is designed to be sturdy and not change at various rotational speeds. The second are more versatile meaning the centre mass of the part will change at speeds.

The three types of unbalance are static, couple and dynamic. Static means that the mass axis is only displaced in one place, parallel to the shaft axis. Couple unbalancing occurs when the mass and running axes intersect. The final type of unbalance is the most complex because it is a combination of the first two types. It occurs when the mass and rotational axes don’t coincide.

Rotors need to be properly balanced to dampen vibrations and improve their longevity. This process is called dynamic balancing and is done by adding or removing weight to different sides of the part to bring perfect mass and operating centres closer together. Static balancing is done by adding weight to one plane. The other two types of unbalance need to be fixed in two planes.

Rigid rotors are the easiest to balance because they don’t change. All you need to do is rotate the part slowly to produce a centrifugal force and reveal the extent of the problem. You can then add or remove weight to correct it. Flexible rotors are a little trickier to work with. You’ll need to work in stages, starting off with a slow rotation and a balance before gradually increasing the speed and balancing again whenever necessary.

Dynamic balancing takes care and precision to get right, particularly when working with high speed components. It is best to call on an experienced professional to do the job for you, especially if the component is going to need adapting. The last thing you want to do is try adding or removing weight yourself because you could make the device more dangerous. we specialise in dynamic balancing and can provide all the assistance you need – just get in touch to find out more.