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Low Temperature operation of Carburized Gears

Low Temperature operation of Carburized Gears

(OP)
A customer intends testing a vehicle of ours after conditioning it to -46 C (-50F).  The vehicle has an axle and hub reduction which use case-carburized 8620 and 4820 gears.  Does anyone have any experience of operation of such gears at these kind of temperatures?  Obviously after a few minutes driving they will warm up, but I am concerned about possible brittle fracture of a tooth at startup.  At the moment we are just warning them not to apply any shock loads until after the driveline has warmed up, but I'd appreciate any more detailed advice/experience.

RE: Low Temperature operation of Carburized Gears

Normal axle lube is pretty stiff at that temperature, and might provide some extra shock protection just by making it difficult to make _anything_ move.

Tell me you didn't specify ATF...


 

Mike Halloran
Pembroke Pines, FL, USA

RE: Low Temperature operation of Carburized Gears

1MarcoD,

That's an interesting question. Normally with carburized gear steels, you're worried about exceeding the tempering limit. I've done some aircraft transmission gears in carburized 9310 that were qualified for -65degF startup, and it was not necessary to derate them.  But aircraft transmissions are usually treated more carefully than a truck drivetrain.

Something else to note, rolling element bearings are a concern at low temps, especially with housing materials (like aluminum) that have a CTE mismatch with the bearing.  It is quite easy to lose all of the bearing radial clearance at low temp exposures, and operating the bearing under such a condition would likely cause damage.

Hope that helps.
Terry

RE: Low Temperature operation of Carburized Gears

(OP)
Thanks everyone.  No, we didn't specify ATF - we told them to use a low-temp gear oil e.g. 75W-90 rather than our usual 80W-90.

FWIW, the general advice I've got elsewhere is also that it shouldn't be a problem for the gears, but we'll see...

RE: Low Temperature operation of Carburized Gears

"Low temp gear oil" - what is the pour point?  I would be most concerned that you don't have bearings or gear barely immersed which will be left dry when the thick cold oil surface is deformed by the flow.

RE: Low Temperature operation of Carburized Gears

(OP)
Hi geesamand. Yes we did have to change the oil spec because of pour point and I never posted to this thread.  Shell recommended Donax TD Low Vis which is a tractor oil with a pour point of -51C

RE: Low Temperature operation of Carburized Gears

One of my chem prof's worked for the army in alaska in the wayback when's. He said all kinds of stuff broke, rifle breeches were the scariest.

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