Shop balancing is always preferred in case of new machines and in case of running machines where high degree of balancing is required. Moreover, some machines such as totally enclosed motors, pumps, compressors and others not easy to balance in-situ because extensive disassembly is required to gain access to the rotor for adding or removing balance weight. In these instances, the machine is disassembled and rotor is balanced on a balancing machine.
In-situ balancing will generally produce better results in terms of vibration. However, balancing on a balancing machine will generally produce a better balance. To clarify, the balancing machine is better at measuring and correcting for unbalance, especially two plane or dynamic unbalance. It can not compensate for field installation factors. Two plane balancing on a balancing machine usually produces better results than two plane balancing in the field because the compounding field installation factors like bearing clearances, support stiffness and resonance response, additional components attached to the rotor like coupling, keys, fasteners etc. and alignment are not present. The primary advantage of balancing machine operations is that the unbalance effect is directly measured. The disturbing factors that can cause 1xrpm vibration are not present, so unbalance can be evaluated without these other complications. Balancing machine operations are not so severely troubled by cross effect because they have very flexible supports or they employ plane separation technique. Balancing can be done by either of the methods described earlier depending upon type of rotor, type of unbalance, normal operating speed of the rotor, etc. Some basics of the balancing machines are explained in the coming sections.
In-situ balancing will generally produce better results in terms of vibration. However, balancing on a balancing machine will generally produce a better balance. To clarify, the balancing machine is better at measuring and correcting for unbalance, especially two plane or dynamic unbalance. It can not compensate for field installation factors. Two plane balancing on a balancing machine usually produces better results than two plane balancing in the field because the compounding field installation factors like bearing clearances, support stiffness and resonance response, additional components attached to the rotor like coupling, keys, fasteners etc. and alignment are not present. The primary advantage of balancing machine operations is that the unbalance effect is directly measured. The disturbing factors that can cause 1xrpm vibration are not present, so unbalance can be evaluated without these other complications. Balancing machine operations are not so severely troubled by cross effect because they have very flexible supports or they employ plane separation technique. Balancing can be done by either of the methods described earlier depending upon type of rotor, type of unbalance, normal operating speed of the rotor, etc. Some basics of the balancing machines are explained in the coming sections.
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