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Balancing |
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db company ltd. Balancing Unbalance is the most common source of vibration in machines with rotating parts. Unbalance in a rotor is the result of an uneven distribution of mass, which causes the rotor to vibrate, the vibration is produced by the interaction of an unbalanced mass component with the radial acceleration due to rotation, which together generate a cetrifugal force. Since the mass component rotates, the force also rotates and tries to move the rotor along the line of action of the force. The vibration will be transmitted to the rotor’s bearings, and any point on the bearing will experience this force once per revolution. It is a very important factor to be considered in modern machine design, especially where high speed and reliability are significant considerations. Balancing of rotors prevents excessive loading of bearings and avoids fatigue failure, thus increasing the useful life of machinery. Balancing is the process of attempting to improve the mass distribution of a rotor, so that it rotates in its bearings without uncompensated centrifugal forces. This is usually done by adding compensating masses to the rotor at prescribed locations. It can also be done by removing fixed quantities of material, for example by drilling. Field Balancing is the process of balancing a rotor in its own bearings and supporting structure, rather than in a balancing machine. The principle of field balancing is the influence coefficient method. Some important advantages: (1) dismantling the machine and transporting the rotor to a balancing machine are not necessary (time and cost saving); (2) lower capital investment (with a portable, electronic balancing instrument); (3) operationally induced changes can be measured and compensated (e.g. thermal influence, centrifugal force, assemble-induced unbalance); (4) rotors of almost any weight and dimensions can be balanced using the same instrument. Shop balancing is the most economic and practical solution for balancing during the manufacturing or repair stage when the rotor is removed and the correction planes are accessible. An advantage of db’s service is transportable our balancing machine to client’s site, especially with huge rotors (steam turbine, generator, …). General Balancing Procedure (1) Performing a vibration analysis to see whether it is unbalance that is causing the excess vibration or some other fault such as misalignment, looseness, or bearing fault, … By performing a vibration analysis before and after balancing, the reduction in vibration level due to the balancing can also be clearly seen. (2) Selecting the best measurement parameter Velocity is the parameter most often selected. Acceleration is chosen where low frequency noise is a problem. Displacement is used to avoid high frequency noise or using proximity probes. (3) Determining balance quality Based on ISO 1940 (almost for shop balancing) and vibration criteria (such as ISO 10816, ISO 7919) for field balancing. (4) Selection of trial masses (5) Single-plane balancing (6) Two-plane balancing (7) Measurement check to determine the trial mass give suitable results for the balancing calculations. (8) Balancing report It is a good idea to keep a record of each balancing job so that the measurements can be repeated with the same instrument settings if necessary. |
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