Small gears - lube for life

[MrClean]

I'm working with a small (64 DP) 5-stage gear train. Overall ratio is 591:1. Design load is 3.8 watts @ 6,000 rpm motor speed. Design life is 500 hours at this load, though it will normally be used at much lower loads. Motor pinion is 13 teeth, x = 0.6, Rc 58. Gear for this stage is 69 teeth, HB 210. Pitch line velocity for high-speed stage is 326 fpm. Even though the gear is soft, gearset still has a service factor of 10 per AGMA ratings. Gearbox will be hand held and used at all attitudes. The unit will be manufactured and sold in small to medium quantities (up to 200 units per year).

I'm concerned about lubrication for the 2 highest speed stages. I'd like to lube the gears "for life" at assembly with some kind of grease. Oil is not practical because there are internal feedback electronics that are not sealed well enough.

I'd appreciate any suggestions on a suitable grease.

 

[israelkk]

As far as I know AGMA/ISO/DIN etc. rating formulas are based on well oil lubricated gears that can cool the gears. Grease lubricating is not the same. Therefore, I recommend that you should test the gear. I could not find information how to apply AGMA rating formulas for grease lubricated gears.

 

[israelkk]

6000 rpm for 500 hours is 500*60*6000 = 180,000,000 cycles. Fatigue analysis considers 10,000,000 as infinite life on the S-N curve. I do not think that any analysis can validate 180,000,000 cycles. AGMA rating can tell if it will hold for 10,000,000 but can not say that it will hold the 180,000,000.

 

[plasgears]

We prelubed plastic gears by immersion followed by centrifuging the excess. Prelubing PM gears by dropping into oil bath following sintering and air quench worked well in a challenging application.

At any rate, the cycles seem high, but go ahead and perform a challenging test. If you have no time to test the full cycles, challenge the product by imposing higher temp, higher loads, and other challenges.