Instrumentation Provides Process Control & Balance

Rotor balancing is not the only benefit of a balancing machine.

Written by:
Joseph Palazzolo
Published:
July 24, 2012

In a pump manufacturing or repair facility, the balancing instrument can provide important information that, if used correctly, will improve the facility’s workflow and throughput.

The balancing machine can do more than simply obtain the unbalance measurement or define the correction needed for a single rotor.

The balancing machine and its selected instrumentation can also share, store and evaluate data on every rotor. This collective data can be examined and used to make improvements in many areas of a manufacturing or repair facility. Data collection makes the balancing instrument not only an important part of daily balancing activities but an asset to total facility operation. Many instrumentation features are available to help the operator balance effectively and efficiently on a daily basis.

Electronic Protractor

The electronic protractor (visual angle indicator) feature assures accurate location of the unbalance correction. This accuracy will enhance the operator’s ability to decrease the required balancing time for any given rotor. Note that an unbalance angle correction error of only 6 degrees would create an overall error amount in excess of 10 percent, resulting in under-correction of the rotor and additional time to complete the balancing task. By minimizing errors caused by improper transfer of unbalance angle to the rotor, the electronic protractor reduces balancing time. With the instrument’s ability to provide previous run history and mark the previous runs, the operator can evaluate the correction steps being taken to ensure correct angle and expected behavior.

Marking Feature
The ability to mark each run and visually indicate a group of measurements all on the same screen will help prove-out repeatability of the rotor and/or the rotor’s tooling. Run-to-run measurements are marked individually and the “scatter” of the grouping analyzed (see Figure 1).

This shows the marking of each run. Note the scatter grouping of the five marked runs showing the on-off repeatability of a pump on its arbor.

Figure 1. This shows the marking of each run. Note the scatter grouping of the five marked runs showing the on-off repeatability of a pump on its arbor.

Using the marking feature along with an averaging function allows the operator to perform a residual unbalance traverse test, similar to the American Petroleum Institute (API) residual unbalance test used in the petroleum, chemical and natural gas industries. The averaging function will indicate each run on the instrumentation’s display screen and then perform an averaged value of the marked runs, indicating the resultant residual unbalance. These tools aid in checking the balancing machine and balancing process (see Figure 2).

This vector display shows the marked measurements of the traversed weight and the resultant residual unbalance shown as the blue and white point within the green shaded tolerance band.

Figure 2. This vector display shows the marked measurements of the traversed weight and the resultant residual unbalance (average) shown as the blue and white point within the green shaded tolerance band.

Tooling Compensation

Tooling compensation is another area in which the balancing instrument aides the operator and streamlines production. Index balancing helps ensure that the unbalance measured is the component’s unbalance and is not significantly influenced by tooling. The tooling influences the component’s unbalance measurement. This influence is a combination of the errors introduced by tolerance stack ups and clamping errors and the unbalance and geometric error of the tooling itself.

The geometric error of the tooling causes the rotor to be eccentrically positioned when it is installed onto the tooling. An index compensation procedure is carried out as a result, and the balancing instrument electronically compensates for the tooling influence. The instrumentation then displays the unbalance of the component itself.

Single Compensation

The balancing instrument also features single compensation. This software is ideal for  the shaft and component set during the multistage impeller balancing process. After each stage is added to the shaft and balanced, the assembly is electronically compensated so that the residual unbalance is not corrected in each subsequent stage. This compensation is used after stacking each stage onto the assembly as a multistage impeller is built up.

Key Compensation

Key compensation acts as another useful instrumentation feature that calculates the unbalance effect of a shaft key. This allows the balancing of the remaining series of rotors without ever attaching a half-key again for this rotor type.

North American industry has standardized the half-key method in which shafts with keyways—in addition to mating components, such as impeller stages—are individually balanced with half-keys fitted to fill the void that the keys would have occupied in the final assembly. The instrumentation software intuitively takes the operator through the steps and then applies the compensation to the measurements going forward.

Rotor Photo Storage

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