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Bouncing Dryer on Steel Frame


Here at the A.E.Staley plant in Loudon, TN, we have a direct fired rotary drier that has a constant bouncing motion. This dryer is mounted on a structural steel frame about twenty feet above a concrete floor. There is another dryer fifty feet away that doesn't have this same problem. They are both constructed the same way, the one dryer that has this problem does have some bow from end to end. Also both of these dryers are continuously breaking bull gear bolts. I would greatly appreciate any advice that you might have.

Without having seen the unit, it's difficult to tell but the typical problems causing these kinds of symptoms, in order of likelihood, are: 1. Gear and pinion bottoming out or disengaging because of a bent shell or bad alignment 2. badly skewed (toed in rollers) 3. Loose steel support structures, particularly bases 4. drive harmonics setting up vibrations in the steel structure 5. other A bent shell is common and in itself should not be a source of vibration unless in conjunction with one of the above. By process of elimination the above can be sorted out. For 1) Is the vibration constant or come and go with each rotation? Perform a gear run-out analysis. Axial and radial run-out should be less than 1/8". Inspect the gear teeth for ridges near the root or any other signs of concentrated wear. For 2) check the roughness of the support rollers. Are they striped or ridged in any way? If they are dull, gray and fretted they are stressed due to excessive/incorrect skew. Ideally they should be flat cylindrical, shiny, chrome polished and mirror like in appearance. For 3) Using a hammer lightly tap anchor bolts and hold down nuts for tightness and looseness. Check for cracks in flanges or webs. For 4) Can you vary the speed of the drum? Does the vibration increase with increase in speed? Vibration monitoring to see if the frequency or harmonic of the frequency relates to the gear/ pinion tooth engagement frequency. Proper selection of durometer ratings on Elastomeric Coupling's insert on the high speed side of the speed reducer are the usual fixes for these kinds of problems. This assumes of course that this type of coupling be employed. These are the obvious points to investigate. The findings should then lead towards isolating the source which, when identified, opens the options for rectification. Identification = Resolution, as we preach in our seminars.



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