Rotors balancing

Mechanical imbalance is one of the most common causes of machinery vibration and is present to some degree on nearly all machines that have rotating parts or rotors. Static, or standing, imbalance is the condition when there is more weight on one side of a centerline than the other. However, a rotor may be in perfect static balance and not be in a balanced state when rotating at high speed. 

This section provides information needed to understand and solve the majority of balancing problems using a vibration/balance analyzer, a portable device that detects the level of imbalance, misalignment, etc., in a rotating part based on the measurement of vibration signals. 

TW o major sources of vibration due to mechanical imbalance in equipment with rotating parts or rotors are (1) assembly errors and (2) incorrect key length guesses during balancing. 

Even when parts are precision balanced to extremely close tolerances, vibration due to mechanical imbalance can be much greater than necessary due to assembly errors. Potential errors include relative placement of each part s center of rotation, location of the shaft relative to the bore, and cocked rotors. 

Assembly errors are not simply the additive effects of tolerances, but also include the relative placement of each part s center of rotation. For example, a perfecdy balanced blower rotor can be assembled to a perfecdy balanced shaft, and yet the resultant imbalance can be high. This can happen if the rotor is balanced on a balancing shaft that fits the rotor bore within 0.5 mds (0.5 thousandths of an inch) and then is mounted on a standard cold-rolled steel shaft allowing a clearance of over 2 mils. 

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Vibration grade signifies the accuracy of rotor balancing, e.g. N = normal, R = reduced, S = special. This may be based on the type of installation and the accuracy of the function the motor may have to perform. 

Cleanliness Hardness Hydrostatic Tests Blade Shaker (Static) Rotor balance O Standard O High Speed Final Surface Inspection Crating inspection Spare Rotor Fit ... 

Flexible rotor balancing must be performed with the rotor whirl configuration approximating the mode in question. The operating speed(s) is in the vicinity of a major flexible mode resonance (damped critical speed). As these two speeds approach one another, a tighter... 

Tessarzik, J.M., Badgley, R.H., and Anderson, W.J., Flexible Rotor Balancing by the Exact-Point Speed Influence Coefficient Method, Transactions... 

The value is lower than the. Ig would call for, but most users would prefer to install a compressor rotor balanced with some residual unbalance margin. 

Examination of the drive ratios shows that if both motors have ISOOrpm synchronous speeds that the pony motor is made to operate near 3600rpm when the big motor is operating. This is typically not a problem as to rotor balance or bearing duty because manufacturers make 3600 rpm versions of these same motors. Nevertheless, the duty should be checked and if this is a problem, the small motor can be changed to a 900 rpm model and the synchronous speeds of each motor will not be exceeded. 

Rotor balancing shall be performed as required in the specific pump sections. 

For rotor balancing, any vacant single keyways shall be filled with crowned half keys. 

Certified rotor balance data for multistage pumps. ... 

Make sure that the outsidb of the centrifuge tubes, the sample holders and sample chambers are dryr any liquid present will" cause an imbalarfce during centrifugation (as well as potentially causing corrosive damage-.to the rotor). Balanced tubes must be placed opposite each other, use a simple code if necessary, to prevent errors/... 

These experimental demonstrations confirm that silicon microfabrication is a valid approach to implement microturbines. The relatively simple stmctures survived the centrifugal loads at high speeds. In addition, rotor balancing was not... 

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