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Danny Harvey

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Reply with quote  #31 
John,

Someone (maybe you?) once commented that 2 x gmf can be caused by micro pressure and suction bursts in the lubricant when the mesh enters and exits.

Do you have any thoughts on that possibility? 
Walt Strong

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Reply with quote  #32 
Rusty & SNORMAN,

I had second thoughts on measuring backlash for this OP. I have used a dial indicator with a tangential setup. I would probably mount the indicator with magnetic base on mill gear and put small target with magnetic base on pinion gear. I expect that mill would have to be rotated to several index angle positions so that an average, minimum and maximum backlash could be obtained from several measurements. There is a lot of general information and specific ball mill gear information on Internet. Here are a few search links:

Search: measuring gear backlash indirect method

https://www.bing.com/search?q=measuring+gear+backlash+indirect+method&form=EDGTCT&qs=AS&cvid=9fc24559e7f245adb05f2cf0a9ba8295&cc=US&setlang=en-US&elv=AY3%21uAY7tbNNZGZ2yiGNjfMpp9NnEzovRcBoEhS75h4V5m1zccsVlaevGgMqdqy4*%2145od2rQn9iVEC1qZv1rHykQkc3e8uPFXqXMPGlhL%21U

 

Search: measuring gear backlash for ball mills

https://www.bing.com/search?q=measuring%20gear%20backlash%20for%20ball%20mills&qs=n&form=QBRE&sp=-1&pq=measuring%20gear%20backlash%20for%20ball%20mills&sc=1-38&sk=&cvid=A40E5BFC36B94BE89D45153CB70ADE59

 

measuring backlash - Search Results - Articles About measuring backlash

 

From <https://www.geartechnology.com/subjects/measuring_backlash/>

 

https://www.bliksembeveiligingepa.be/Feb-05_31300/how-to-set-backlash-ball-mills

 

http://www.newcambridgeschool.com/19697_how/to/set/backlash/ball/mills.html


I learn something new each time I search the Internet, and found this "Mill Frequency Calculation" that may or may not be related to the unusual vibration modulating frequency of the OP.

Mill Speed - Critical Speed

Note the Formula for calculation of Mill Critical Speed

From <http://www.pauloabbe.com/size-reduction/resources/mill-speed-critical-speed>

 
Walt

SNORMAN

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Reply with quote  #33 
Sounds good thanks for the input guys
John from PA

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Reply with quote  #34 
Quote:
Originally Posted by Danny Harvey
John,

Someone (maybe you?) once commented that 2 x gmf can be caused by micro pressure and suction bursts in the lubricant when the mesh enters and exits.

Do you have any thoughts on that possibility? 


It wasn't me, at least as to the creation of a 2X mesh.  Having said that, there is something unique to the meshing action that occurs in high speed gearing, and by high speed I mean a pitch line velocity of 20,000 ft/min (100 meters/sec) or higher. That number may vary a bit manufacturer to manufacturer.

When teeth enter mesh, the driver "pushes" a wedge ahead of the pitch line. Once the pitch line of the two members roll across each other, there is a pulling action. The lubrication during the pulling action is not a good as that during the push phase. These phases are called approach and recess. When the teeth are disengaging there is a void created and thus a vacuum. This vacuum can draw oil into the area of the void. This is the reason that in high speed gearing, perhaps 75% of the oil is sprayed into the leaving side of mesh and about 25% is sprayed into the entering side. To spray all the oil into the entering side would drive power losses up. The leaving side literally sucks the oil into the mesh area.

entering_leaving.jpg  


Danny Harvey

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Reply with quote  #35 

Thanks very much. That sounds like what I remember. I must have attached the 2 x gmf in error myself.

I note that this is directly pertaining to high speed gearing and oil lubrication. Could the same logic be applied to lower speed gearing that is grease lubricated or perhaps dipped in an oil sump?

If it wouldn't generate vibration at 2 x gmf, what would it generate?

Pomegranite

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Reply with quote  #36 
Can you access the pinion while the mill is running?
We used to conducted thermal scans on all mill pinions, as they didn't like stopping them, temperature difference across the pinion is an excellent way of confirming misalignment, without causing downtime. 
RustyCas

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Reply with quote  #37 
Walt, I don’t see anything in your links that actually shows how to measure backlash. Or am I missing something?

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John from PA

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Reply with quote  #38 
The link at http://lytteltonminingsupplies.co.za/Downloads/DavidBrown/Installation_Maintenance/Mill-and-Kiln-Gears_Installation_Maintenance.pdf provides a David Brown procedure.  The use of feeler gauges is discussed on page 14 (article numbering) or 17 (PDF numbering).

Note the mention of lead wires, that is actually the method I preferred when I did this many years ago.  I used Plastigauge however as opposed to the wire.
RustyCas

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Reply with quote  #39 
John, that’s a very good article. Thanks! The only ones I work with now, neither of the “inching” drives work, so wherever it stopped, that’s what we have to work with. Not an ideal situation. But they buy their pinions from China and they are pretty soft, so wear quickly regardless. They run them for about 18 months, then flip them. Not my favorite job, but once we got the motor and gearbox aligned, and I explained how to get the pinion “close” each time, it’s fairly routine now. I’ve always wondered about how the bull/ring/girth gear was initially setup. I kind of puckered up the first time I did the alignment and the root clearance was specified as 0.110” — that requires a lot of confidence in the ring gear setup.
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John from PA

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Reply with quote  #40 
Quote:
Originally Posted by RustyCas
Walt, that’s a very good article.


Did you mean something that Walt posted, or what I had linked to at http://lytteltonminingsupplies.co.za/Downloads/DavidBrown/Installation_Maintenance/Mill-and-Kiln-Gears_Installation_Maintenance.pdf
RustyCas

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Reply with quote  #41 
John, yes, your article. Wasn’t paying attention. Again, thanks!

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Walt Strong

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Reply with quote  #42 
Rusty,

One common way is to mount indicator such that stem touches the gear tooth flank in a tangential orientation. The magnetic base could be mounted on nearby stationary structure or directly on mill/ring gear. Another way, as mentioned is to attach a magnet target (like accelerometer base) to side of pinion gear and align dial indicator stem to it with a tangential orientation. Here are some additional links:

Search: measuring gear backlash with dial indicator

https://www.bing.com/search?q=measuring+gear+backlash+with+dial+indicator&form=EDGEAR&qs=PF&cvid=6c1b4bcd8614430b86f9df02a9ad158c&cc=US&setlang=en-US&elv=AY3%21uAY7tbNNZGZ2yiGNjfMSohQIxd*MMyB7Lud44I8VSkKR*JBWXubvk56LNE5okITUePvnQTbKfuwTnNiwH9GRl8XUUp3JN7QCLnA*AChv  See Images for many different setup and backlash definition

https://www.amazon.com/backlash-dial-indicator/s?k=backlash+dial+indicator&rh=p_n_condition-type%3A6461716011 for many dial indicators and magnetic bases

How to Inspect a Gearbox

From <https://www.machinerylubrication.com/Read/28765/how-to-inspect-a-gearbox-

An Elementary Guide to Gear Inspection

From <http://gearsolutions.com/features/an-elementary-guide-to-gear-inspection/>


Other inspection methods besides vibrations during mill operation, if IR camera is not available, is to take close-in photos for visual inspection. Use ultrasound meter with close-scan microphone along tooth mesh. For a direct drive without fluid coupling consider motor current spectrum analysis; it works. Use a microphone (sound level meter) placed close to mill surface as a non-contact vibration sensor. To identify cause of frequent failures on an expensive mill consider making torsional vibration measurements with strain-telemetry, vibration-telemetry, or FM-encoder methods. Use the tools you have and get the tools you need!!

Depending on mill drive and operating conditions, conduct measurement during variable speed and/or variable load, since one or more operating points may produce more dynamic force/vibration on drive system.

Happy Meshing,

Walt

John from PA

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Reply with quote  #43 
It perhaps should be noted that backlash as specified on a drawing or installation instructions refers to a measurement done at the pitch line.  I have made service calls with customers that had reported backlash twice and three times nominal, only to find that they were making measurement by mounting a long arm on the end of the shaft (which is often drilled and tapped) and taking the measurement several feet away.  All done for convenience.  [confused]
Walt Strong

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Reply with quote  #44 
Good point John that I did not mention is that dial measurements should be corrected for the radial distance back to the Pitch radius. 

Walt
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