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Extreme pitting on an unhardened pinion, need help
5

Extreme pitting on an unhardened pinion, need help

Extreme pitting on an unhardened pinion, need help

(OP)
I am looking at fixing a gear application in an overhead crane where pitting is a problem.  There are about 7 gears in the gear box.  One pinion gear is pitting very badly across the face of the gear from about the pitchline down to close to the root.  Although the gear runs forward and backward, the pitting only occurs on one side of the gear.  None of the gears are hardened.  The material is 1045 and the gears have been replaced twice before using 1045 unhardened material and this pitting did not occur.  What could be the cause?  I appreciate any direction that I can get.

RE: Extreme pitting on an unhardened pinion, need help

The first thing I would do is check the involute form for a possible interference condition. If the tip of the gear (addendum) is heavily contacting the SAP (start of active profile) that would cause your condition. The manufacturer should have an involute machine to check this.

RE: Extreme pitting on an unhardened pinion, need help

Do you have any records on this and the previous parts showing the hardness of the materials? The hardness of the gears and pinions is a key element in their pitting resistance and although the material was not hardened if, by chance, the previous parts were significantly harder that may explain why they survived longer.

RE: Extreme pitting on an unhardened pinion, need help

Jermelle;

"Un-hardened" material could have a wide range of properties. Pitting is strongly related to hardness, but could be result of poor quality.

Suggest you specify replacments from heat-treated 4140. Gear material is typically avaiable in 269-321 hardness. Pinion should be harder, 321-369 BHN.

Request AGMA 2000 Q8 or better, and crown the pinion teeth. Teeth need tip relief on both members, or tip and root relief on the pinion only.

Cranes have load on one side, regardless of rotation, if used in hoisting function.

If you fax me at 262-369-0367 with gear dimensions, we can give you recommendations for specs.

RE: Extreme pitting on an unhardened pinion, need help

If it worked before without pitting,
something is wrong with the new pinions.
When you say they are not hardened, I
assume you mean they are not induction
hardened but have been quench and tempered
to 250 bhn min.?  The fact that is is only
happening on one side means that they are
cut wrong.  Probable cause that the cutter
was not keyed properly and allowed to shift
or rock from side to side.  If these were
hobbed, forget the above.  You know for a
fact that the pinions are splined or keyed
and not allowed to shift radially on the
shafts?
Do you actually have a value for the hardness
range?  Normalized material may be down to
180 BHN.  No size has been mentioned.  If the
pinions cross section is 3 inches or less, the
1045 material might be ok.  If heavier, you should
consider an alloy material as suggested above.
You still should be specifying that they be quench
and tempered to some value above 250.
Can you measure the hardness of the old parts?
Keep us informed.

RE: Extreme pitting on an unhardened pinion, need help

Gear can go in both direction and have the load always in the same direction.  Is the pitting on the loaded side?  

RE: Extreme pitting on an unhardened pinion, need help

i would say its a simple wear problem
i see that it is pitting in one direction it maybe the direction when the winch is under load and pulling up
I would think it is just that the pinion needs to be hardened to take care of the wear, ask the manufacturer to rectify it

RE: Extreme pitting on an unhardened pinion, need help

The lubrication system in a splash lubricated gear reducer can be such as to favour one particular direction of rotation. When the lubrication system relies on one or two gears throwing enough oil up to fill internal oil chanels and splash onto other gear mesh, the direction of rotation, fill levels as well as main load direction can be critical.  It is suggested you check the lubrication function before embarking on radical changes.

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