Rotors unbalanced

If silica (in the form of volatile silicic acid) is present in steam at concentrations greater than 0.02 ppm Si02, turbine deposit problems result. In some cases, volatile silica appears not to significantly affect superheaters but certainly will always form deposits in turbines. Silica appears in different forms, depending on the steam pressure, and affects all turbine surfaces, It is most noticeable on the blades, which eventually results in rotor unbalancing. 

Sometimes, as a result of an unbalanced magnetic field, causing an air gap eccentricity or excessive shaft deflection, the motor is not able to maintain the small air gap between the rotor and the stator and this may lead to failure. 

The unbalanced voltage will produce an additional rotor current at nearly twice the supply frequency. For example, for a 2% slip, i.e. a slip of 1 Hz, the negative sequence stator current, due to an unbalanced supply voltage, will induce a rotor current at a frequency of (2/- 1) = 99 Hz for a 50 Hz system. These high-frequency currents will produce significant skin effects in the rotor bars and cause high eddy current and hysteresis losses (Section 1.6.2(A-iv)). Total rotor heat may be represented by... 

Bearing strength to avoid damage if the rotor should be unbalanced by ice deposits, or damaged by erosion... 

Rotating machines subject to imbalance caused by turbulent or unbalanced media flow include pumps, fans, and compressors. A good machine design for these units incorporates the dynamic forces of the gas or liquid in stabilizing the rotating element. The combination of these forces and the stiffness of the rotor-support system (i.e., bearing and bearing pedestals) determine the vibration level. Rotor-support stiffness is important... 

Mechanical Scrubbers Mechanical scrubbers comprise those devices in which a power-driven rotor produces the fine spray and the contacting of gas and liquid. As in other types of scrubbers, it is the droplets that are the principal collecting bodies for the dust particles. The rotor acts as a turbulence producer. An entrainment separator must be used to prevent carry-over of spray. Among potential maintenance problems are unbalancing of the rotor by buildup of dust deposits and abrasion by coarse particles. 

The peak to peak displacement of the unbalanced rotor at the point(s) of maximum displacement shall not exceed 35 percent of the diametral running clearance at that point. 

For one thing, steam produced from hot-lime-softened water will have some amount of silicates. These silicates tend to deposit on the rotor blades of turbines, which use the motive steam as a source of energy. The silicate fouling of the turbine blades reduces the turbine s efficiency. But, more importantly, from an operator s point of view, the silicate deposits eventually break off of the blades. This unbalances the rotor. An unbalanced rotor is the fundamental cause of vibration, Vibrations lead to damage of the shaft bearings and seals. Eventually, vibrations will destroy the turbine s internal components. 

So, the turbine slowed down. And what was the only possible speed that it could slow down to Why, the critical speed, of course. The turbine and blower began to vibrate. The bearings were damaged. The turbine s rotor became unbalanced. A rotating element on the air blower touched a stationary component in the blower s case. The stationary component broke off and wrecked the blower. That was the end of K-805. 

The most cost-effective way to produce a high polytropic head is to increase the number of wheels on the rotor. But the longer the rotating assembly, the more difficult it is to properly balance the rotor. Especially for high-speed machines, rotors which become unbalanced are subject to destructive vibration. Therefore, for low-molecular-weight gas services (less than 10), it is not uncommon to use reciprocating compressors. 

Thrust Bearings The most important function of a thrust bearing is to resist the unbalanced force in a machine s working fluid and to maintain the rotor in its position (within prescribed hmits). A com-... 

Unbalanced rotor or warped shaft due to severe rubbing. 

An unbalanced rotor causes excessive vibrations and mechanical stresses while spinning that can cause breakage. 

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