Aluminium and stainless steel gears wear out fast

[transcendgold]

Hello,

I seem to be having problems with two different material gears meshing together. In certain cases, I see a a lot of metallic dust accumulate (as shown in the pictures). I assume that is because of the wear between the two gears.

Detailed info:
The larger gear is made out of aluminium (anti-backlash gear)
The smaller gear is made out of stainless steel
No lubrication is currently used
Rotation speed of the larger gear is very slow, maximum 10 RPM
Rotation is oscillatory covering 90% of the larger gear

How should the design be changed to solve this issue? Should both gears be made out of stainless steel? Should we use a lubricant, which type?

Thanks!

 

[MikeHalloran]

>>How should the design be changed to solve this issue? <<
What issue?
Is the accumulated metal dust a cosmetic problem?
Which metal is dusting? If it's the aluminum, that could be a fire hazard.
Do any of the gears actually fail before the warranty runs out?

Have you measured or estimated the torque being transmitted and calculated the pressure on the tooth faces and the pressure on the bearing surfaces within the anti-backlash pair?

>>Should both gears be made out of stainless steel? <<
Not generally a good idea.
Have you tried anodizing the aluminum gears, i.e. converting their surface to a hard oxide of aluminum?
Is the dust being developed at the pinion/gear mesh, or is it coming from relative movement of the two halves of the anti-backlash gear?

>>Should we use a lubricant, which type? <<
Even ear wax is better than nothing.
Most any grease should work fine; pick one whose color you like.
( There may be environmental or cosmetic reasons to choose a particular grease, but you didn't state any. )



Mike Halloran
Pembroke Pines, FL, USA

 

[transcendgold]

Thanks Mike for your reply.
The larger aluminium gear is being eroded by the smaller stainless gear.
The metallic powder is clearly coming from the meshing. There is no obvious signs of wear between the two halves.
There is practically no torque being transmitted between the two gears. The black box in the lower half of the image is an optical encoder.
The product was designed not to require maintenance on this part. After about 1 year of operation or less, the part has to be replaced.
This is a design flaw and I am trying to find the cause to increase the reliability.
Why shouldn't the two gears be made out of stainless? From my understanding, I should try to maximize my gear surface hardness and aluminium is not that hard.

 

[MikeHalloran]

Stainless on stainless, rolling, sliding, or just sitting there, produces more surprises than you might wish.
Stainless is not all that hard, either, until you try to cut it or bend it, then it work hardens.

Something you can try for very little money is to have the two halves of the anti-backlash gear cut from zinc-plated mild steel sheet. You just need a DXF file of the exact outline you want. Put the outline on layer 0. Put a reference dimension, like a diameter over the teeth, on a different layer. Include the units in the dimension text.
Honestly, I haven't got a sense from the photo of how big a challenge that is, but make a file and send it to some lasercutters just for fun.

Another possibility is doing the anti-backlash gear in plastic. If you can't make do with a stock one, you could probably do it up in nylon or acetal, self-conjugate so you only need one mold, and you may be able to work in a leaf spring or two for the lash. Plastic becomes a practical possibility at substantial production volumes, information not in evidence.





Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

I would think you could just anodize or electroless nickel plate the aluminum gear. There are various additions you can make to either to make them self lubricating.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Tmoose]

Not surviving the warrantee period certainly eats into profits this year or maybe next.

Lasting a few days or even a week beyond the end of the warrantee period is a tale I think heard most often in bitterly unhappy conversations about a product that someone will not buy again, from a dealer they will not use again.

I think Some manufacturers have improved their long term success by routinely lasting a bit beyond the warrantee period.

http://www.motortrend.com/cars/2013/toyota/prius/warranty/

Toyota, including Prius
Drivetrain 5 year / 60,000 miles

 

[imcjoek]

I would suspect the tooth loading actually comes from the anti-backlash mechanism. Is it an off the shelf item? If so, is it available with a weaker spring?

It's tough to see end-on, but the tooth profiles look a bit...funky...to me. Are they involute?

How well is the center distance controlled?

I would cast my vote for trying a nylon or acetal gear on one of the pair. Aluminum and stainless both love to gall given half a chance.

 

[Compositepro]

You definitely need lubricant. Aluminum is prone to fretting wear in this type of application. Aluminum forms a protective oxide layer that keeps it from further oxidation. If you wear-off this oxide layer it will again oxidize rapidly. A hard anodize treatment would probably help as well.

 

[BrianE22]

Aluminum tends to corrode when in contact with stainless. Adding a lubricant might make it worse.

 

[gearcutter]

Both stainless and aluminium aren't very good materials to use for gears.
A better combination would be stainless on nylon or cast iron on cast iron.
Given the application though; I'm surprised that the gear mesh is generating so much debris.

Are the two halves of the anti-backlash gear spring loaded or are they adjusted by unbolting to create the offset required?

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[gearcutter]

Looking at the photo again and zooming in for a better look I can see what appears to be evidence of hard meshing. There is damage to the tooth tips.
Are the mating gears set at the correct mounting distance?
It looks to me like they are meshing too close to each other.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[transcendgold]

Wow, what a great turnout. Thanks!
I spoke with one of the engineers that makes the anti-backlash gears (SDP/SI) and we arrived at the conclusion that the two biggest factors involved are : control of the gear distance and lubrication.

The design allows for the encoder to be moved back and forth (thus modifying the clearance between the two gears). Unfortunately, it is too easy to put the gears too close to each other or too far. For these anti-backlash gears, the manufacturer recommendation is center distance = (Ng+Np)/2P + 0.0015". Controlling this distance with more accuracy would certainly reduce wear.

On the topic of lubrication, a dry film lubricant is something that should work well. I'm going to test Molykote 321 (Molybdenum disulfide) on this system. A multi-purpose lithium grease (NLGI 2) could also work, but I'm worried about dust and it falling on the sensitive components below.

If neither of these two solutions work, then I will investigate the materials used and try a different combination such as aluminium on brass.

 

[MikeHalloran]

Molyote works great if the surfaces only have to slide, once.
You may find that it acts as an abrasive in your application. ... depending of course on which of many Molykote products you use, and all of the variables already discussed.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

>>> but I'm worried about dust and it falling on the sensitive components below.<<<

And that explains why it had, and should have, no lubrication.
You might have mentioned that before.

Take a look at a nylon gear. ... Not antibacklash, just a regular gear, jammed into mesh as you seem to be doing that already.

Or go to pulleys and a timing belt. Just have your gorillas spread the pulleys until the belt is nice and tight, then cinch 'em down.



Mike Halloran
Pembroke Pines, FL, USA

 

[mfgenggear]

I would think pre-harden steel gears would work better than what is being used now.
what is the budget & cost concerns. what precision are required for the gears.
any thing you do is putting a band aid on this gear set.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[3DDave]

I've seen the same result before. Small areas of the aluminum stick to the steel part and then get wiped off during the sliding action. The answer is to prevent that sticking. Tried dry film lubricant, but it wears off very rapidly.

Hard anodize should help as the oxide layer won't stick to the steel. Polishing can help to prevent abrasive wear. Adding a felt pad on top of the split gear and adding oil to that should lubricate the mesh just fine without dripping or moving around. That's what's used to lubricate home furnace blower motors.

A remark on the tip damage - at the end of tooth contact there is significant sliding. With adhesion it will tend to pull a burr off the end of the softer teeth. I suppose if it got long enough, the burr would interfere with the root of the mating gear.

As to the use of stainless - The key to picking the right combination is to make sure the two materials do not tend to gall. The reason stainless is stainless is the formation of a protective oxide coating. Just like aluminum, sliding will remove the coating in tiny places, which can then weld and tear loose. Unlike the aluminum, the material could remain stuck and form high spots that continue to do damage. Been there and done that.