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.
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Low Temperature operation of Carburized Gears
- Thread starter 1MarcoD
- Start date
MikeHalloran
Mechanical
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
Tell me you didn't specify ATF...
Mike Halloran
Pembroke Pines, FL, USA
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
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
- Thread starter
- #4
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...
FWIW, the general advice I've got elsewhere is also that it shouldn't be a problem for the gears, but we'll see...
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- #6
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