Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation

 

 

Case Study No. 53 - Evaluating the Field of Influence from Hammer Impacts on a Steel Shell

HURDLE No. 5 - DEBUNKING THE "JOLTERS"

Jolter Hammer RigsTo the left are impact machines that impart a high amount of energy to what they're hitting which in turns knocks sticky stuff off the other side of where the hammers are hitting. If you're thinking of banging on something you might want to determine your field of influence generated by each impact, otherwise you might be wasting your time. Here's an example of evaluating impact energy on a machine known as a "jolter."

There was one very-important piece of equipment that proved itself invaluable over the years in helping to make the rotary dryer perform up to expectations. It was known as "the jolter." There were several of them. When they weren't performing well, the rotary dryer wasn't performing well. Production personnel were very concerned with the term "stiffening ring." To them that meant the rings would stiffen the shell to the point where the jolters would not be able to deflect the shell and hence, dislodge the product. A recommendation that could ruin jolter performance would not be favorably received.

Dynamic Waveform of Hammerhead Response It was important to understand how the jolters worked, so it was time to learn. Vibration waveform analysis was utilized to capture the dynamic energy imparted by the jolter hammer head. The jolters were positioned closely together. If one jolter failed while in service, the product would build up immediately. Therefore, it was safe to assume that the effective field of influence of a jolter wasn't large. The questions to answer were what made the jolter effective, and what was the distance before they became ineffective? The vibration study showed that the energy imparted by the hammer head blow was equivalent to a short 5,900 kg (13,000 lb.) burst of energy lasting less than 10 milliseconds (Figure 1: left). This amounted to a unit stress on the shell itself of only 3.2 Mpa (460 psi). As the pulse traveled away from the hammer head, the pulse RMS energy level decreased significantly when compared with the average RMS energy level (Figure 2: lower left). Therefore, it was the pulse of energy that did all of the work, and not the average energy. This wasn't a surprise. The surprising thing was that the energy dissipated so quickly. It was noted that there was a dead spot in-between each jolter where there was very little pulse energy. From this, it was determined that the location of the stiffening rings would be out of the field of influence of each jolter. Now it was just a matter of convincing the Production personnel. This was accomplished in the presentation. An appropriate analogy was used, something everyone understood.

 

Dynamic Waveform Shell Response 9" Away from Hammerhead To be Continued.....
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