Gear Mesh Vibration in Coal Pulverizer
Gear Mesh Vibration in Coal Pulverizer
(OP)
I have a pulverizer that was vibrating at 1 ips measured at various bearings within the gearbox. This vibration appeared after the gearbox was overhauled. It is a double reduction gearbox. %99 of the vibration is occuring at 332 Hz, which corresponds to the gearmesh frequency of the first reduction. The 1x pinion speed sidebands are almost invisible.
Last night the machine was brought offline and all of the gears were realigned. The vibration is now at .8 ips. My question is: should I really be concerned? Are the gears "wearing in to each other"?
Last night the machine was brought offline and all of the gears were realigned. The vibration is now at .8 ips. My question is: should I really be concerned? Are the gears "wearing in to each other"?





RE: Gear Mesh Vibration in Coal Pulverizer
RE: Gear Mesh Vibration in Coal Pulverizer
Then, the gears were aligned to try to eliminate the vibration. I don't fully understand the alignment procedure. I believe the bullgear and small intermediate gear had some angular misalignment, as indicated by the new wear pattern. The lash was also checked and adjusted. The high speed pinion was then realigned to the large intermediate gear. This gearmesh is the one that corresponds to the high vibration. The wear patterns did not indicate anything wrong with this one the first time. The vibration is now at 1.1 in/s @ 332 Hz. I don't know whether we should run it until our next opportunity to take it down (probably this weekend), or shut it down before permanent damage occurs.
RE: Gear Mesh Vibration in Coal Pulverizer
RE: Gear Mesh Vibration in Coal Pulverizer
If the teeth are cut inaccurately, then the inaccurate cut is consistent with all of the teeth. The vibration is not modulated in any way.
RE: Gear Mesh Vibration in Coal Pulverizer
Another thing you could check is the lowest point of single tooth contact -its possible that you are digging into the root for some reason.
Were the new gears made to the original drawings, or did someone come up with what they thought the original gears were supposed to be ?
How does it compare to the others when you don't have any noise sources other than the gears themselves? (Just curious).
You probably need to get production out of it, so your options may be limited. If you are seeing the tooth pass frequency, I can't think of anything else to check other than the tooth profiles - maybe someone else has an idea.
RE: Gear Mesh Vibration in Coal Pulverizer
Sounds like you’re on top of the problem doing your vibration homework very thoroughly, and properly. Most plants would not know about the problem, due to all the other equipment noise involved. Pre-mature gearbox failure would be their first indication, and then the cause of the problem would be very hard to diagnose (without the data you’re collecting), after a catastrophic gearbox failure.
Gear quality control is most likely a serious issue in your case as EnglishMuffin has defined. I know of a very good AGMA gear expert you could contact. I’ve used him in Portland cement plants, and my brother has used him in food plants, to deal with improperly manufactured OEM and replacement gears. He’s a nice guy, very helpful, and relatively inexpensive since he’s an independent consultant.
If you need more information, call me at 641-423-9363 with more details about your application. Good Luck, Paul Juhnke, Maintenance Engineering Services.