False Brinelling in Gears with clutchable drive.

[Gooty]

I require some inputs from the members here regarding the false brinelling wear observed on the gear.

The shaft carries two helical gears. Only one gear is engaged during power transmission and the other freewheels. The gears are mounted on tapered roller bearings (TRB) and at one end of the shaft there is a Cylindrical roller bearing (CRB) and at the other end there is another similar cylindrical roller bearing along with two angular contact ball bearings (ACBB). The schematic is as given below.

O/p Coupling---CRB---GEAR1---Clutch---GEAR2---CRB---ACBB---

Now we observe some false brinelling on both the gear teeth. Note that the TRB's are pre-loaded to 0.003" to 0.005". Currently the oil used is ISOVG 100. My questions regarding this problem are:

1. What might be causing the false brinelling.
2. Will using EP oil with or without antiwear additives help?
3. Is it better to have a heavier viscosity oil for these applications.
4. Is there a desired activation temperature for EP or antiwear additives in the oil?
5. Is there a specific EP and or anti-wear additive package / types of package good for this sort of applications (like sulfer, chlorine, boron etc.).

Thanks in advance for your response.

 

[diamondjim]

False brinelling is common in bearings as
well as gears if there is not a load constantly
applied to them. I do not know if it is
possible to impose a spring device to keep
the gear loaded at all times. I would think
a heavier grease would help. There should be
many studies in the bearing industry which should
shed some light on this. I assume it is the
vibration thru the system which is causing on
and off loads causing this fretting condition.

 

[Carburize]

False Brinelling is not a term that is normally applied to gear wear - can you take a look at AGMA 1010 "Appearance of Gear Teeeth - Terminology of Wear and Failure" or the ISO equivalent 10825 and perhaps describe the damage you are seeing using the terms in that document?

 

[Gooty]

Thanks for your responses. Diamondjim, I feel the same, that there are vibrations transmitted onto the gears from an external source or a machinery which might cause false brinelling, when the equipment is not in operation.
However, in this case even after pre-loading the bearings, we observe false brinelling and that is something which we are thinking off. I cannot think of any spring for the gear, but using a thicker oil should improve the film thickness and reduce this type of wear.

carburise, Let me look into the AGMA standards and get back.

 

[diamondjim]

False brinelling and fretting corrosion
look very much alike. Carburize may be
correct that it is the latter that you
have been experiencing. The bearings
are not causing this if they are
preloaded or non preloaded.
Mico pitting may be small welding
taking place at the surfaces
and causing material to shift from one
surface to the other due to lack of
lubricant or contaminants in the lubrication
being caustic. Keep us informed in
your progress.

 

[GearmanPE]

Is the appearence that of a line with a red or brown color? This is fretting and is caused by repeated contacts without rotation. The protrctive oil film is squezed out of the contact zone and fretting starts at the microscopic level. The particles aid in further wear, and their build-up around the edges help prevent lubricant from entering. If severe, will cause functional damage.

This is a not uncommon problem with parked wind turbines that have brakes applied. I have seen the problem result in thumping noise so great as to require imediate replacment of the drive. One would expect these conditions to be evidenced in the bearings as well.