When your machine is functioning in balance, most likely, it is operating according to the manufacturers design. Excess vibrations are a result of unbalance in rotating machinery and may cause unacceptable levels of noise and reduce the lifespan of shaft bearings. Most premature failures in rotating machinery are usually a result of imbalance. The unbalance mostly results from uneven mass distribution around the axis of rotation. Dynamic balancing is among the main solutions.
What is dynamic balancing?
One goal of manufacturers when designing any machine is to ensure that it will operate free from vibrations. The other goal is to ensure that the machine runs for the longest time possible. However, in reality, vibrations form part of rotating machinery, and some vibration levels may be unacceptable. Instead of removing all vibration from machinery, the manufacturers try to balance it to the peachiest extent possible. One method of balancing is dynamic balancing. Manufacturers perform dynamic balancing using sensors that they attach to bearing pedals. The sensors allow identification of unbalance on two planes to allow real correction. The balancing uses machinery to identify the imbalance points and rectify it.
Factors affecting the efficiency of dynamic balancing
Various factors affect the efficiency of dynamic balancing. They include installation problems, fabrication problems at the assembly place and a machine that has been serviced for a longer time.
Manufacturing factors
Many manufacturing factors can affect the efficiency of dynamic balancing. They include material issues such as porosity, density, blowholes, and voids. Fabrication issues include eccentric machining, misshapen castings, and poor assembly. Distortion issues include temperature and aerodynamics changes and rotational stresses. The problems arise during the manufacturing process while others arise during the machine’s operational life.

Assembly factors
Unbalance can occur during rotor fabrication due to many reasons. One of them is tolerances stack up. If a manufacturer combines a well-balanced shaft and rotor, the needed assembly tolerances may allow radial displacements. That leads to an imbalance condition. Keys and keyways additions contribute to the problem.

Machine operating factors
Rotors that have been in service for a very long time alongside some other factors may contribute to imbalance condition. The factors may include wear, corrosion, deposit build up and distortion. Deposits may also unevenly break off leading to severe imbalance. That mostly applies to fans, compressors, blowers and some other rotating devices. To minimize the effect, you will need to inspect and clean your machine regularly. However, eventually, you will have to remove the machines from service due to imbalance.

Other factors
The difference between the rotors in the machinery can also cause imbalance. There are two primary types of rotors: flexible and rigid. Rotors operating within 70-75% critical speed – the natural frequency – are flexible rotor. Those operating below the speed are rigid rotors. Rigid rotors are usually at balance at two end planes. In addition, they remain in balance when in service. Flexible rotors require multi-pane balancing. When a rotor is in balance on low speed balancing machine (assuming that it is rigid) and then it becomes flexible in service, unbalance will arise leading to high vibration. Machines in this group include compressors, multistage centrifugal pumps, and gas and steam turbines.

A machine operating in a smooth, properly balanced order has many benefits. When operating the machinery, you will enjoy lower vibrations, low noise, lower operator fatigue, higher operator safety, and lower operational cost. The other benefits include more productivity, longer bearing life, and lower structural stress.

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