Balancing Advantages

ADVANTAGES OF  PREDICTIVE  MAINTENANCE :  

  •   Provides increased component operational life and availability 
  •   Allows for preemptive corrective actions
  •   Results in decrease in equipment and/or process down time 
  •   Lowers costs for parts and labor
  •   Provides better product quality 
  •   Improves worker and environmental safety 
  •   Raises worker morale
  •   Increases energy savings 
  •   Results in an estimated 8% to 12% cost savings over which might result from a
  •   predictive maintenance program

There are many advantages of using a predictive maintenance program. A well-orchestrated predictive maintenance program will all but eliminate catastrophic equipment failures. Staff will then be able to  activities to minimize or eliminate overtime costs. And, inventory can be minimized, as parts or equipment will not need to be ordered ahead of time to support anticipated maintenance needs. Equipment will be operated at an optimal level, which will also save energy costs and increase plant reliability.

Past studies have estimated that a properly functioning predictive maintenance program can provide a savings of 8% to 12% over a program utilizing preventive maintenance strategies alone. Depending on a facility's reliance on a reactive maintenance approach and material condition, savings opportunities of 30% to 40% could easily be realized. In fact, independent surveys indicate the following industrial average savings resulted from initiation of a functional predictive maintenance program:

  •   Return on investment: 10 times 
  •   Reduction in maintenance costs: 25% to 30% 
  •   Elimination of breakdowns: 70% to 75% 
  •   Reduction in downtime: 35% to 45% 
  •   Increase in production: 20% to 25%

When unbalance has been identified with the help of FFT vibration analyzer,then the correction is straightforward. Weight has to be either added orr emoved from the rotating equipment. 

Unbalance is measured and reported in two ways. One is a measure of the  effect of the vibration and the other is a measure of the heavy spot.  measure is used in fieldwork and embodies the speed characteristics of centrifugal force effects. In field balancing rotors runs at their own operating speed, with minimum disassembly. A basic requirement in place balancing is that the rotor has to be accessible to make corrections.

The technique of field balancing offers some distinct advantages as:

Balancing is performed on the complete assembled machine and hence  compensates the assembly tolerances.

The cost and time to dismantle the machine is saved.

The possibility of damage to rotor in dismantling and carrying it to balancing station is eliminated.

The effects of temperature, pressure, distortion and other environmental influences can be incorporated.

The vibration level measured at the 1*rpm issued as an indicator of the amount of unbalance. The location is determined by measuring the phase. Phase, is measured by an indicator in the instrument,triggered by a photocell.

UNBALANCE :

The common language definition of unbalance is the unequal distribution of the weight of a rotor about its rotating center line.

The Formal definition of unbalance is that condition which exists in a rotor when vibratory force or motion is imparted to its bearings as a result of centrifugal forces.

MEASURES OF  UNBALANCE :

Perfect balance is unachievable. Perfect balance is not measurable either.To detect unbalance, it is necessary to measure the forces that are created due to the unbalance. These oscillatory forces become smaller and smaller as better balance is achieved. At zero unbalance, there is nothing to measure. In reality every rotor has some residual unbalance. If the speed is increased, this smallun balance causes a much greater force and greater vibration. Therefore, a speed increase usually results in greater vibration for rigid rotors.

Unbalance is measured and reported in two ways. One is a measure of the effect, vibration, and the other is a measure of the heavy spot. The vibration measure is used in fieldwork and embodies the speed characteristics of centrifugal force effects. The heavy spot measure is used in balancing machine work and is simply an expression of the amount of the heavy spot and its distance from the center of the rotation.

STATIC UNBALANCE :

Static unbalance is when the principal mass axis is displaced parallel to the shaft axis. The principal axis passes through the center of gravity with equally distributed mass on both sides of the axis line. The shaft axis is the straight line joining the journal centers. For machines with rolling element bearings, the shaft axis is not the same as the rotational axis because of the eccentricity in the bearings. This factor makes some machines with rough bearings unbalance able below a certain level.

QUASI-STATIC UNBALANCE :

Quasi-static is that condition for which the principal axis intersects the shaft axis at a point other than the c.g. from a definitional perspective; the important difference for quasi-static unbalance is that the principal axis is no longer parallel to the shaft axis.

COUPLE UNBALANCE :

Couple unbalance is when the principal mass axis intersects the shaft axis at the c.g. Product of inertia is synonymous with couple unbalance.

DYNAMIC  UNBALANCE  :

The more typical situation is a combination of static and couple unbalances present in varying degrees, called dynamic unbalance, which is when the principal mass axis and the rotating shaft center line do not coincide or touch.

VIBRATION ANALYSIS  :

If machines exhibit unacceptably strong vibrations, how they are caused is the question, which faces the operator and manufacturer.

Of course, sources of vibration can be found by the step-by-step replacement of components, such as drive motor, coupling, bearing, drive shaft or gearbox.This procedure is however expensive, since it requires a very large stock of replacement parts and possibly many parts are replaced which are still completely in order.

Only a method of approach that places a systematic determination of the causes of vibration before replacement of machine parts is economically justifiable. A proved method for this is frequency analysis. In this, the existing mixture of vibrations is split up into its separate components. The origin is determined from the frequencies of the partial vibrations.

The most commonly used method for rotating machines is called vibration analysis. Measurements can be taken on machine bearing casings with seismic orpiezo-electric transducers to measure the casing vibrations, and on the vast  majority of critical machines, with eddy-current transducers that directly observe the rotating shafts to measure the radial (and axial) vibration of the shaft. The level of vibration can be compared with historical baseline values such as former start-ups and shutdowns, and in some cases established standards such as load changes, to assess the severity.

Interpreting the vibration signal so obtained is a complex process that requires specialized training and experience. Exceptions are state-of-the-arttechnologies that provide the vast majority of data analysis automatically and provide information instead of data. One commonly employed technique is to examine the individual frequencies present in the signal. These frequencies correspond to certain mechanical components (for example, the various pieces that make up a rolling-element bearing) or certain malfunctions (such as shaft unbalance or misalignment). By examining these frequencies and their harmonics,the analyst can often identify the location and type of problem, and some times the root cause as well. For example, high vibration at the frequency corresponding to the speed of rotation is most often due to residual imbalance and is corrected by balancing the machine. As another example, a degrading rolling-element bearing will usually exhibit increasing vibration signals at specific frequencies as it wears. Special analysis instruments can detect this wear weeks or even months before failure, giving ample warning to schedule replacement before a failure which could cause a much longer down-time. Beside all sensors and data analysis it is important to keep in mind that more than80% of all complex mechanical equipment fail accidentally and without any relation to their life-cycle period.

Most vibration analysis instruments today utilize a Fast Fourier Transform(FFT) which is a special case of the generalized Discrete Fourier Transform and converts the vibration signal from its time domain representation to its equivalent frequency domain representation. However, frequency analysis(sometimes called Spectral Analysis or Vibration Signature Analysis) is only one aspect of interpreting the information contained in a vibration signal.Frequency analysis tends to be most useful on machines that employ rolling element bearings and whose main failure modes tend to be the degradation of those bearings, which typically exhibit an increase in characteristic frequencies associated with the bearing geometries and constructions. In contrast, depending on the type of machine, its typical malfunctions, the bearing types employed, rotational speeds, and other factors, the skilled analyst will often need to utilize additional diagnostic tools, such as examining the time domain signal, the phase relationship between vibration components and a timing mark on the machine shaft (often known as a key phase or),historical trends of vibration levels, the shape of vibration, and numerous other aspects of the signal along with other information from the process such as load, bearing temperatures, flow rates, valve positions and pressures to provide an accurate diagnosis. This is particularly true of machines that use fluid bearings rather than rolling-element bearings. To enable them to look at this data in a more simplified form vibration analysts or machinery diagnostic engineers have adopted a number of mathematical plots to show machine problem sand running characteristics, these plots include the bode plot, the water fallplot, the polar plot and the orbit time base plot amongst others.

There is no limit to the number of products that rotate. Using cars as an example, they consist of tires, shafts,flywheels, gears, and crankshafts, to name just a few. In our homes, we have a variety of equipment, including fans, vacuum cleaners, refrigerator compressors, video heads, DVD and CD systems, and computer hard drives. It would be impossible to count all the types of rotating objects and how many exist.

When these rotating parts or materials rotate, they generate centrifugal forces. Normally, the sum of these centrifugal forces equals zero, however, if they do not, that rotating object will generate vibration and noise. Dynamic balancing machines measure the amount and angle of this vibration


ADVANTAGES OF HORIZONTAL BALANCING :   
  • Produces highest accuracy
  • Virtually all types of rotors can be balanced
  • Components with its own journals can be balanced without tooling
  • Easy access for loading and correction
  • Large weight capacity

ADVANTAGES OF VERTICAL BALANCING :

  • Ideal for rotors with large diameter to thickness ratios / disc type rotors
  • Option of automatic tooling
  • Fast unbalance measurement
  • Simple and fast loading and unloading

Precision Balancing provides extremely accurate balancing of high-speed (greater than 5000 rpm) components. Many customers utilize this service during R&D to ensure very precise balance before installing the component in the turbo-machinery equipment for testing.

At-Speed Balancing (or Operational Speed Balancing) is for high-speed rotating components where standard "low-speed" balancing (less than 3000 rpm) is not sufficient. Typically, at-speed balancing is required when additional vibration modes (critical speeds) or radial growth of components are encountered at operational speed.

Production Balancing is for customers who fabricate lot size quantities of rotating turbo-machinery components that require balancing prior to delivery or installation. Each rotor is balanced to meet customer specifications and requirements, then either returned to the customer or shipped directly to the end user with Balance Certifications.





























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