Alternate Gear Material 3

[Flesh]

I had a request to make a gear set lighter. My colleague asked about using Titanium alloy. I need 166ksi UTS material with a wear resistant surface. Is this strength obtainable with titanium? Can I make its surface wear resistant via some modification treatment (nitriding, anodize, PVD, etc)? What about an aluminum alloy?

 

[metengr]

The following thread has some interesting posts with excellent reference material on Titanium alloys. The technical literature provides answers to your questions regarding mechanical properties and surface treatments for the various Ti alloys;

thread330-110611

 

[Carburize]

You do not need to go to titanium to achieve the mechanical properties you are looking for - there are a number of available carburizing alloys will give you the hardness/strength you need plus they can obviously be "surface treated" by carburizing.

 

[TVP]

Flesh,

The current state of technology really does exist for creating robust titanium alloy gears. Titanium alloys can be processed to your recommended strength level, and they can be treated by diffusion processes involving oxygen or nitrogen for surface hardening, but these processes do not create the fatigue resistant surface that carburizing does for steel. Your best bet for reducing gear weight is to increase the surface stress on a steel design, and make the steel design very strong. This can be done by using the best steel grades (low inclusions, high temper resistance), optimal heat treating parameters that create the best microstructures (no intergranular oxidation, no non-martensitic transformation products, optimized carbide structures & retained austenite, etc.), shot peening to create residual compressive surface stresses, and some type of finishing treatment to reduce surface roughness, such as the isotropic finishing done by REM. The following links have some excellent information on this subject:

http://www.grc.nasa.gov/

http://WWW/5900/5950/Research.htm

http://www.grc.nasa.gov/

http://WWW/RT1998/5000/5950krantz.html

Also, you should contact Carburize to discuss this project, as he is intimately involved in gears and gear heat treating.

 

[Flesh]

Thank you all for your replies. I don't have my exact weight measurements yet, but consider this: a 40 lbs gear, 8620H, carburized. I want to cut this weight in half.

TVP: Is this really feasible with the optimized steel design you speak of?

Also, thanks for the links. I will definitely check them out over the holidays. Cheers.

 

[EdStainless]

Cutting it in half might be tough, but you can lighten it significantly.
I have seen some gears that use Ti for a hub and spyder, and use high strength tool steel for the rim & teeth. With PM tool steels a lot is possible.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

There are numerous ways to lighten your gear by machining if this hasn't been done by design.
Holes and reduced hub section are two points.

 

[Carburize]

One of the challenges associated with going away from one of the more "usual" gear materials is how do you rate the new material in terms of pitting resistance and bending strength? Titanium, for example, because of its low modulus of elasticity needs very careful analysis of tooth bending phenomena.

 

[TVP]

Flesh,

The last three responses from EdStainless, unclesyd, and Carburize offer significant insight when discussing TOTAL mass of the system. I agree with EdStainless that a 50% reduction may not be possible, but it really depends on the details of gear type, lubrication, temperature, etc. By the way, I meant to say that "the current state of technology really does NOT exist for creating robust titanium alloy gears" in my previous post. Sorry for any confusion.

 

[Carburize]

Flesh - how are the present gears rated? Which standard is used? It is possible as suggested by others that an upgade of material quality to an AGMA 2001 Grade 3 would enable the size of the gear to be reduced by permitting higher tooth loads to be applied.

 

[Matt51]

http://www.titaniumgears.com