Transmission Gears 5

[RATENGINEERING]

I am currently designing an automotive transmission for a high horse power / high RPM application. My question is the gear material (Steel) selection and heat treat process?

Is there a better choice than ASTM 4140 case hardened?

I would truly appreciate any input!

 

[Philrock]

Designing an automotive transmission is a huge job. Existing automotive transmissions have evolved over decades of development at a cost of millions (possibly billions) of dollars.

4140, 4340 and ETD150 are good steels for through hardened gears. The highest performance gears are carburized, case hardened, and ground. 9310 is a better choice for carburized gears. Another excellent steel for carburized gears is 17CrNiMo6 - this steel is more widely used in Europe than in the U.S.

 

[patprimmer]

Torque is what breaks gears, not power and rpm.

Torque, rpm and power all contribute to heat build up and wear rates.

Optimum design depends a lot on the application, which is a detail you omitted.

For instance, Drag racers use soft but tough gears as wear is not an issue, but load bearing shock loads and breakages are.

Heavy duty long haul trucks on the other hand need very good load bearing and wear resistance.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TVP]

SAE 8620 is another popular steel for carburized gears. Do you know how to specify the product requirements after heat treatment? Hardness, case depth, etc.?

 

[swall]

8620 steel, carburized,is another common gear steel choice.

 

[cnova]

Why not consider using "off the shelf" gears from Hewland, Extrac, Emco... who all manufacture racing gearboxes (high hp, high revs). They will give you almost endless ratios and they have already figured out the materials, processes.

Stupidity is the basic building block of the universe. F.Z.

 

[NickE]

I've often thought that fully hardened S7 would make a good gearset. (expensive though.)

 

[RATENGINEERING]

Thanks for the input about material choices. What is the suggested tooth form? Would a common spur gear 12 Diameteral Pitch with 20 degree PA be acceptable?

 

[paulliu]

Helical gears are preferred whenever possible.
The pressure angle of 20 degree is OK. The 25
degree of pressure angle is alos widely used.

 

[Frederick]

A true cryogenic treatment after heat treat will give almost any gear both better impact reisistance and wear resistance. Don't be fooled by a -140F cold treatment, and don't let them dip the gear in LN2. Do your final tempering after the cryogenic treatment.

 

[azgearpro]

8620 material being carburized at a .015/.030 case depth with a agma level of 11/13 is seen alot in turbine engines also most transmisions have helical planet and sun gears. this case depth seems to work really well.The only problem we see with carb is distortion.

Aerospace Gear and Spline specialist