Unbalance exists when the centre of mass does not coincide with the centre of rotation, when the mass centre axis is different to its running centre axis. The forces which result in vibration are primarily due to minor imperfections in the rotating components. Practically all newly machined parts are non symmetrical due to blow holes in castings, uneven number/position of bolt holes, parts fitted off centre, machined diameters eccentric to the bearing locations, etc.
Balancing is the procedure where the mass distribution of a product (roller, impeller, etc.) is checked and adjusted in order to ensure that the forces on the bearings, at a frequency corresponding to the devices operational speed, are within specified limits as specified in International Standards.
An uneven distribution of the mass is called unbalance. Because the bearings restrict this movement, the centrifugal force due to the unbalance causes the device to vibrate. This vibration causes wear to the bearings, creates unnecessary noise, and can result in complete failure.
Balancing is the process of improving this mass distribution of a body so that it rotates in its bearings without unbalanced centrifugal forces. The process of "balancing" is the removal or addition of weight to the unit such that this effective mass centre line approaches the true axis adding or removing weight so as to make the two centres coincide.
