I am working on a tumbler drive with a history of having completely worn the teeth off of the drive pinion (Spur gearing, 14 1/2 deg pa, 21 teeth, 4340 steel)

The tumbler is a globular drum suspended from 2 12" bore diameter pillow block bearings and rotating at 6 rpm. The drum is about 15,000 lb in mass and material weight of about 10000 lb is added before the tumbling process. The tumbling process takes aboout 9 hours during which the material is heated to as much as 350 deg f.

The drive is an inverter driven brake motor directly coupled to a gearmotor with the 21 tooth pinion on the output shaft and mated with a 144 tooth gear (also 4340) which is mounted to the tumbler shaft.

The non-drive end of the tumbler has piping for vacuum making it unavailable for expansion, therefore the floating bearing is on the drive end. To compensate for axial float the face of the pinion is 1/2" wider than the face of the gear. The gearing was originally lubricated with NLGI 3 EP grease made by Lubriplate, although whether the gears were lubricated at all in the very early stages of use is unclear. (This is newly commissioned equipment). It is now being lubricated with a spray lubricant made by Lubriplate which is called Gear Shield Extra Heavy EP Lubricant. There is no indication of the NLGI number of this lubricant but I am told that it is the same as was in use before, but in a spray form. I plan to go to Lubriplate's website and attempt to find out more about it.

*Added info:

[NLGI grade appears to be 3 in cartridges (originally used) and 2.5 in spray (current).]

After having worn the teeth completely off of the original pinion they have replaced it with a new pinion made of 1040 (I think) which was quickly available for an emergency replacement. The teeth on the gear are also badly worn with about 3/8 of the original tooth thickness eroded.

Vibration data reveals exactly what one would expect in this situation. High amplitudes at harmonics of GMF with sidebands spaced at 6 cpm. High impacting when running "dry" but damped after lubrication (about every 1/2 hour). Assembly phase is evident as would be suggested by the common factor of 3 in the gears.

Questions are:

1. Given that exposed gearing of this type always operates with a fairly high GMF amplitude, what would be considered normal?

2. Is the lubrication practice acceptable?

3. Any opinions about the expansion being on the drive side and the uneven face widths between the pinion and gear?

4. What are the potential causes of such drastic failure of the original pinion and gear? I have my opinions, but would like to consider more. (I'll try to get picture of the pinion, but can't photograph on site.)

5. What backlash setting is suggested for this type of arrangement?

6. How would you best record the high amplitude low frequency "clunking" of badly worn gears?

7. As always, Will it last until year-end shutdown?

Thanks,

This message has been edited. Last edited by: Danny Harvey,

Danny,

Lube or no lube, it sounds like a machine design issue. The gear design may be insufficient to withstand the dynamic torque (torsional vibrations) from the tumbling process. The tumbling process may cause torque reversals that cause gear tooth chatter that is very bad.

I question whether any "magic" lubricant would help that much.

I suggest measuring torque and dynamic torque (torsional vibration) to resolve the root cause of gear failure problem so your customer can get machine upgraded while it is covered by warranty. There may be other methods to alleviate the problem without modifying the gears.

Need assistance?
w_f_strong at msn dot com

Danny

This is not unlike a 7'x 45' Metso kiln that I began collecting data on late in the summer. The pinion (spur) has 21 teeth, the Bull is 144. The pinion is straddled by two large SKF 22226 SRB brgs. The pinion shaft is direct coupled to a gearbox with a ratio of 45 (approx I believe). THe motor is on a VFD. Typically the pinion rpms are around 22 rpm, but can vary widely depending on the product etc.It has to be stobed every time we show up. The pinion gearmesh and harmonics are very dominant all over the machine, even on the carrying roller brgs. The strength of the pinion gearmesh vibration seems to vary with the rotation of the kiln, which would lead me to believe that something in not centered up well so at some point you get good meshing, the rest of the time the gears slap each other pretty good. As far as I know the pinions do wear out over time allthough not that I have seen in the last 3 or 4 months, it makes sense to me that the pinion should be somewhat softer that the bull, because the pinion is easier to change.The lube system from what I can tell is automatic, the drums they draw from are marked with "Swepco", this grease is not unlike electric motor grease, I do not think spraying it is possible.

The spectrum attached here is typical, hope this helps.

Alan

Kiln.doc (24 Kb, 8 downloads)

The amplitudes at gmf in the spectrum and waveform are greatly reduced and the frequency of lubrication is now about every 3 hours instead of every 30 min.

They are pretty sure that it is getting better, but I don't see the gear teeth getting any of their lost material back. I suspect that we are seeing a new wear pattern developing (from new wear or course) and damped vibration due to the heavy lubrication.

Here is a picture of the original pinion. 4340, pre-heat treated, about 2 dp, 14 1/2 deg pressure angle. What would you expect the gear that did this to look like?

This message has been edited. Last edited by: Danny Harvey,

pinion.doc (41 Kb, 11 downloads)