Using annealed 4140 without heat treat 1

[jande]

Is there ever a case where using annealed 4140 without heat treatment (185-225 BHN) would work for the pinion of a gear set if the stresses are low enough? (12 ksi beam stress, 42 ksi contact, 60 rpm, 2 inch pitch Ø)

 

[dimjim]

Why would you use annealed 4140 when you
could simply use 1050 normalized or some
other steel? Yes you could use it, but
is would not be cost effective.

 

[tbuelna]

I agree with dimjim. The only reason for using a CrMo steel alloy like 4140 in the first place, is that it responds nicely to heat treat. For a pinion gear with bending stress of 12KSI and Hz stress of 42KSI, why not use a material that is much less expensive, produces a much nicer machined finish, machines much easier and has a higher production rate, and wears much better under marginal lubrication conditions?

You might want to consider ductile iron (65-45-12), free machining steels (12L14)or silicon-bronze/aluminum-bronze alloys. Just make sure that the pinion gear material & condition you select is a compatible match for its mating gear.

This company produces a very nice, continuous cast ductile iron bar:

http://www.dura-bar.com/

 

[jande]

The mating gear would be ferritic nitro carburized, so it would have a very hard wear surface. My main concern is the wear characteristics of the soft part against this hard gear. If this is going to be a problem, no matter the material, we'll need to heat treat the pinion.

 

[TVP]

If the mating gear is nitrocarburized, then you should heat treat the pinion. I would not use 4140 in the annealed condition for the same reasons that the others mentioned.

 

[JCJackson]

I concur with everybody vis-a-vis the alloy. Power capacity is directly proportional to hardness up to about 660Hv (thereafter it levels off) for contact stress and up to 350Hv for bending. For elevated hardnesses it is a little more complex for bending.

Establish the minimum hardness material combination which will sustain your power requirements and select the most cost effective materials. Do not incur heat treatment costs unless you need to. The more you mess around with materials, the bigger the problem if anything goes wrong.

 

[plasgears]

By the way,
a good reason to use gears non HT is to reduce noise. We combined non HT helical pinions with extended addendum, and the noise reduction was dramatic. we ran this pinion against both aluminum gears and brass gears.
(This was in a noise reduced breast pump assy! Apparently the boys in the office were picking up strange noises during lunch hour.)