Registered: 1442538912 Posts: 1,810
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Have a customer with a single-roll rock crusher. Crusher roll has an 88T bullgear driven by a 16T pinion gear (spur gears) on a jackshaft driven via a very large sheave and belts and a surprisingly small motor (probably 75 hp). Motor runs 1785 rpm or so, jackshaft 349 rpm, crusher roll 63.5 (5.5:1 ratio). This unit sits about 8 ft off the ground on a structural steel frame. The initial issue a year ago was excessive vibration, part of which was lack of stiffness of the structure (mostly corrected before I got involved), but also excessive clearance in the gear-end jackshaft bearing (SKF2236 CCK/W33). Basically, when it was installed (machine was rebuilt by the original mfg) they didn't take the clearance up properly. We reset it to the proper clearance and haven't had any more issues, until recently.
This thing is pretty noisy with rock going through it, as you'd expect. But it was really not much different from a year ago. But "noise" could be felt and heard, more at the sheave-end jackshaft bearing than the gear-end. We opened the sheave-end bearing up and it looked perfectly normal with a normal clearance of 0.004". Can't find any bearing defect frequencies, not even in PeakVue. Vibration is dominated by 1X jackshaft RPM and what appears to be 12X the crusher roll rpm (not sure how it's constructed internally). Loaded data showed 16X as expected and some 32X. We inspected the gears as best we could through a "port" in the guard and found no damage; the gears are not meshing squarely, but it doesn't look too bad -- I've seen much worse. Just wasn't seeing anything to account for the noise. Except, when data was collected while running unloaded (no rock), the 16X was replaced by a 15X peak, with a small 16X present. There was also a cyclical "scrubbing" sound coming from inside the guard. I learned recently from my doctor daughter that "the story" is as significant as anything else when she's making a diagnosis, so I've doubled down on that. They really weren't telling me much about what had happened, but when pressed told me that "something" had happened and two of the four 1-1/4" bolts that secure the gear-end bearing on the pinion shaft had "snapped off" and the other 2 were stretched. I guess they didn't think that was particularly important? My theory is something (possibly a hunk of metal) "jammed" the mill and all the energy of the sheave/flywheel was transferred to the pinion gear, bending the shaft and shearing the bearing bolts. I recommended they inspect the gears carefully and do runnout checks on the pinion shaft. So we'll see. Does this sound like a plausible scenario? Site is 5 hours away, so not something I can follow up on, unless they call me to come back. And yes, I seem to be having a bad run of cases where the diagnosis is elusive. Am I just getting old?
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Registered: 1459670321 Posts: 204
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I think that's not about your age. I experience some customers often call us - smaller companies in the most complicated cases. Why. It is possible that the available price for one machine measurement (despite complex) is not tempting the other big players as they know the price would sometimes not be reasonable as to what the situation is. I don't know the situation in your state but here I guarantee that a self employed person makes his best while big players' workers are often just workers and think more when they will go home or eat a donut. Their analysis often gets into some unwanted routine and every special case could be too much to bare. It is also possible that you were not the first one at the machine but some other couldn't find the solution
From the spectra I would more concentrate to unloaded condition as crushing often masks over some important frequencies. There can be seen some rotation harmonics which could indicate some mechanical looseness. About changing GMF I have some thoughts about sliping belts (although strange that GMF would be higher at loaded condition). But what if your GMF is more accurate on the second spectrum? It is not that obvious on the first one. Is the FFT resolution in both conditions the same? They look very different.
Registered: 1443864758 Posts: 1,918
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Maybe the belts are biting better under load and slipping more unloaded? Anything can happen.
I had this CBI3000 crusher where they got a Volvo B18 engine block that broke the safety pins, as it was end of the day they didn't bother and locked it up firmly and yes if you have 1 engine you have 2 engines and they bent like a 20+T rotor with the 2nd. Nothing 30-40 Kg balancing wouldn't improve but the rotor was never really good until it was scrapped if you ever could say crusher rotors are good anyway. __________________ Good Vibrations since early 1950's, first patented vibrometer 1956 in the US. http://www.vtab.se