Material and Treatment for Gears

[MadMango]

Hey all.

I've designed a "gear reducing clutch" for a power window motor, like the ones typically found in vehicles. Running off the pinion gear of the motor, I have a set of 3 planetary gears that perform a reduction of 3:1, then a ring gear.

My problem is that for prototyping, the ring and planetary gears have been made from CRS1018, are were cut on our laser and are untreated. After about 3-4 hours of constant use, the planetary gears are totaly destroyed. The hole in the planetary gears are oblonged, the teeth are "crushed" to half their thickness. We have melonited the ring and planetary gears, but this does not help.

There is no wear on the ring gear or the pinion, only the planetary gears. What would be the best material and treatment method for the planetary gears? I am thinking 4330 with a heat treatment to C50-55. Any suggestions? "The attempt and not the deed confounds us."

 

[TVP]

The reason the melonite treatment did not work is because the steel below the case was insufficient in strength, so the case probably just crushed through it. You are thinking along the right lines with switching to an alloy steel with much higher strength and hardness. Most gears today use a lower carbon content and are carburized in order to obtain the necessary strength properties, without sacrificing too much core toughness. SAE 4320 or 8620 are commonly used. I am not a gear expert, so I do not want to comment right now on case hardness, case depth, or core hardness. I will probably do some research and get back to you. In the meantime, I expect others will contribute.

 

[MadMango]

We had thought that laser cutting alone would be enough treatment to harden the edges of the gear, but obivously this wasn't the case.

We are also seeing the planetary gears "riding up" and "riding down" the pins they are attached to depending on the direction (CW or CCW). I don't have any room for fasteners. Any ideas how to stop this axial movement? "The attempt and not the deed confounds us."

 

[CoryPad]

Yuo say you don't have room for fasteners - not even a snap ring?

 

[MadMango]

Currently we captivate the planetary gears between two plates, and have nylon washers above and below the gears. This is more to prevent the gears from chewing up the plates than it is to stop them from moving (movement is around .040" total). I should say these gears are small, .500" pitch diameter, 6 teeth with a pressure angle of 20 degrees. "The attempt and not the deed confounds us."