Tham khảo tài liệu 'industrial machinery repair part episode 1 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Rotor Balancing 59 bore and the shaft during balancing. When the equipment is reassembled in the plant or the shop the assembler should also use this mark. For endclamped rotors the assembler should slide the bore on the horizontal shaft rotating both until the mark is at the 12 o clock position and then clamp it in place. Cocked Rotor If a rotor is cocked on a shaft in a position different from the one in which it was originally balanced an imbalanced assembly will result. If for example a pulley has a wide face that requires more than one setscrew it could be mounted on-center but be cocked in a different position than during balancing. This can happen by reversing the order in which the setscrews are tightened against a straight key during final mounting as compared to the order in which the setscrews were tightened on the balancing arbor. This can introduce a pure couple imbalance which adds to the small couple imbalance already existing in the rotor and causes unnecessary vibration. For very narrow rotors . disk-shaped pump impellers or pulleys the distance between the centrifugal forces of each half may be very small. Nevertheless a very high centrifugal force which is mostly counterbalanced statically by its counterpart in the other half of the rotor can result. If the rotor is slightly cocked the small axial distance between the two very large centrifugal forces causes an appreciable couple imbalance which is often several times the allowable tolerance. This is due to the fact that the centrifugal force is proportional to half the rotor weight at any one time half of the rotor is pulling against the other half times the radial distance from the axis of rotation to the center of gravity of that half. To prevent this the assembler should tighten each setscrew gradually first one then the other and back again so that the rotor is aligned evenly. On flange-mounted rotors such as flywheels it is important to clean the mating surfaces and the bolt holes. Clean
