Product category:
Accelerometers and Vibration Sensors
News Release from: Datastick Systems | Subject: Datastick VSA vibration spectrum analyser
Edited by the Engineeringtalk Editorial
Team on 24 July 2007
Vibration analyser used for inaccessible
fans
Distortion and warping of fans due to rapid temperature change led to excessive vibration and the Datastick VSA vibration spectrum analyser was used to track down the problem.
A single-channel Datastick VSA vibration spectrum analyser can be used to measure vibration and perform balancing of an industrial cooling fan, even in a harsh environment In the process of manufacturing carbon electrodes used in the Bessemer process of making steel, the electrodes are loaded into large furnace for final curing and to bake out all volatile organic compounds
This article was originally published on Engineeringtalk on 13 Nov 2002 at 8.00am (UK)
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The furnace is gas fired with air introduced through burners.
The extremely hot air is extracted through fans in the roof.
At the end of the cycle, the fans are reversed and water spray is added to accelerate cooling.
The unfortunate side effect of this is distortion and warping of the fans due to rapid temperature change.
In this particular example, fan vibration was excessive.
The client had already made several unsuccessful attempts to balance the fans.
The project was to determine actual root cause of problem, and fix it.
Out on the roof, the fan was tested for vibration with a VSA handheld.
Overall vibration was more than excessive, so the fan was shut down after just one reading.
As the outside temperature was below freezing and snow was falling, the actual vibration analysis was done indoors after the read was recorded on the VSA handheld.
Vibration at 1Xrev/min was less than 1/3 of the total vibration.
The spectrum signature indicated looseness and lack of lubrication (harmonics of 1Xrev/min along with high levels of high frequency noise).
However, the bearings were damaged beyond the point where added lubrication would help.
The bearings were replaced and lubricated according to specification and the fan was run and tested again for vibration.
Although the vibration level was high, the FFT showed 90% of vibration at 1Xrev/min, indicating imbalance.
Because the motor and bearings were on the outside of the roof while the fan itself was on the inside of the furnace, no phase information was available.
This made it impractical to use dedicated balancing hardware for this application.
Instead, balancing was done using the three-point trial-weight method.
This method does not require a phase signal.
A balance procedure was performed and the overall vibration was deemed acceptable.
Since the fan blades warp on each heating/cooling cycle, there was no point in going for precision balance for this particular application.
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