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Balancing :
Procedure by which the mass distribution of the rotor is checked and if necessary adjusted to ensure that the residual unbalance or the vibration of the journal and / or forces on bearings at a frequency corresponding to service speed are within specified limits. |
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Rotor :
Body capable of rotation, generally with journals, which are supported by bearings.
Rotors are classified in three groups - Rigid, Quasi rigid and flexible |
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Rigid Rotor :
A rotor is considered to be rigid when its unbalance can be corrected in any two planes. After correction residual unbalance does not change significantly at any speed up to service speed and when running under conditions which approximate closely to those of the final supporting system.
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Flexible Rotor:
Rotor not satisfying the above condition because of elastic deflection due to its running at and above critical speeds. Such rotor is to be balanced at high speed or at actual speed. Turbine and two pole generator rotors are generally flexible rotors
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Static (Single plane) balancing:
Procedure by which mass distribution is corrected in one plane to ensure that residual static unbalance is within the limit. (Only forces are balanced). |
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Dynamic (Two Plane) balancing:
Procedure of balancing by which unbalance are corrected in two planes such that residual forces and couple are within the specified limit. |
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Multi Plane balancing: -
Corrections are carried out in more than two planes e.g. Crankshaft |
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Field (on site) balancing: -
Process of balancing of a rotor in it’s own bearing and supporting structure at site rather than in a balancing machine.
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Low speed (Rigid rotor) balancing: -
Procedure of balancing at low speed where the rotor to be balanced can be considered to be rigid. |
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High paced (Flexible rotor) balancing: -
Procedure of balancing at a speed where the rotor to be balanced cannot be considered rigid. This is done near the critical speed of the rotor. |
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Rotor Critical Speed:
A speed of the rotor at which thee is maximum bending of the rotor and where this bending is significantly greater than the motion of journals. |
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At speed balancing:
Balancing of rotor on balancing machine or at test bed at actual (Full) speed. |
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Trim Balancing:
Balancing of rotor at site at actual speed to reduce unbalance and vibrations arising due to mounting errors in assembling at site. |
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Mandrel:
Machined shaft on which rotor is mounted for shop balancing. |
List of various ISO, IS, BS & VDI Standards of vibrations: |
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ISO 1940-1:1986 (IS 11723:1992): |
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Mechanical vibration: Balance quality requirements of rigid rotor. |
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ISO 5343:1983 (IS 13279: 1992): |
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Criteria for evaluating flexible rotor balance. |
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ISO 5406: 1980 (IS 13280: 1992): |
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The mechanical balancing of flexible rotor. |
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ISO 11342 4994(E): |
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Mechanical vibration:- Methods and criteria for the mechanical balancing of flexible rotor. |
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IS0 2372-I974 (E) (IS 11724: 1985) VDI 2056- BS4675: |
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Mechanical vibrations of machines with operating speed from 10 to 200 rev/s (600 to 12000 R.P.M.) – Basis for specifying evaluation standards |
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IS0 3945 - 1985 (IS 11727 - I985) |
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Measurement and evaluation of vibration severity in situ of large rotating machines with speed range from 10 to 200rev/sec. |
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ISO 2953 : 1985 (IS 13277:1992) |
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Balancing Machines- Description and Evaluation. |
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ISO1925 : 1990 (IS 13274:1992) |
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Mechanical Vibration – Balancing – Vocabulary |
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ISO 2017 : 1982 (IS 14259 :1995) |
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Vibration and Shock – Isolators – Procedure for specifying characteristics |
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IS 4758 - 1989 : Methods of measurement of Noise emitted by Machines. |
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IS 4894 – 1999 : Specification for Centrifugal fans |
