pinion to gear hardness ratio 1

[j8715]

Hi

Currently I have a system from a vendor with a 1.25:1 ratio. The Gear is 84 Hrb and the pinion is around 42 Hrb (I can't really get to it to test it easily, I'm guessing from a material book). No surprise the pinion is failing very quickly. My question is how much harder do I make the pinion for best performance? I have a book that suggests the pinion should be 20 to 70% harder, that seems like an awfully large range. I assume it should be dependent on the ratio of the drive, since the ratio isn't extreme do I stay on the low side, say 20-30% harder?

Thanks

 

[CoryPad]

You need to separate strength from surface hardness. If the pinion has fewer teeth, then it may need to be stronger since each tooth will see more cycles per unit time. But, that is for strength (static, fatigue, impact). Are your gears fracturing? Or is it wear? Your gears are not surface hardened, so they are susceptible to wear. Are these steel? If so, then you should consider surface hardening both gears, targeting something like 50 to 60 HRC.

 

[j8715]

Yes it is wear not a fracture failure.

The gear is 303 so hardening is out, its a difficult system to explain but I do not want to change anything on the gear. The pinion is some sort of brass/bronze. I want to replace the pinion with something that is a better match to the 303 stainless.

 

[israelkk]

Are you sure you are not using the system beyond its capabiliies. Did you make any sort of calculations that may indicate that the pinion will wear?

Can you provide more details?

 

[dinjin]

Why do you believe in e-mails for answers instead of books which are published for all to view and critisize? Is your book by a noted author? Many books are the result of many tests and studies. Have you looked at long and short addendum gears? Is the pinion always the driver? Normally pinions are harder than the gears.

 

[tbuelna]

j8715,

You have not provided enough information about your gear mesh and its operating requirements to establish a satisfactory reply.

CoryPad makes an excellent point. One of the basic principles of good gear design is to equalize the tooth strength, fatigue life, etc. of both gears. This is usually accomplished by careful selection of materials and heat treatments, tooth geometry modifications, adjustments in face widths, lead corrections, etc.

It would be very unusual to intentionally design one gear in a mesh to have a much reduced life versus its mating gear. The only instances where I've seen this done is where there is a possibility of jamming or overload. The one gear is made much weaker, and will hopefully fail without causing damage to its mate, because it is easier and less expensive to replace.

Good luck.
Terry

 

[Tmoose]

What is pitch line velocity? Are they lubricated? If so, there may be lubricant upgrades that would help. What is the surface finish of the 303 gear? Any possibility of a run-in cycle?