Aluminum on Steel Spline?

[Cryo1]

I have a steel external spline. The new retrofit housing that fits on the spline will be aluminum 7050-T6 condition with hard anodize coating. The assembly is turned by an human, not a motor. There is no sliding on the spline. Stresses look OK but....

?Will this steel/aluminum interface wear out? We don't have experience in mixing the two. Any helpful, everyday experience out there?

 

[dimjim]

You will have to be more specific.
What are the loads, size of the
spline, width, etc. If the loads
are light, no problem. I assume
because this is done by hand, that
the loads are light and that the
aluminum would be acceptable.
Normally it has about 1/2 the strength
of steel.

 

[Cryo1]

Nominal Force: 150 in-lb
1" length
1" nominial pitch dia.
48 teeth
SAE Standard 1946

The issue isn't the strength but the wear that may occur with the combo of steel+aluminum.

 

[israelkk]

If there is no sliding there is no wear. However, the hard anodize coating may crack if the loads are too high because the backing compressive strength of the aluminum is very weak compared to the 35-40RC of a steel core used with nitriding etc.

 

[CoryPad]

There are steel/aluminium spline couples used for automotive propshafts. Here is one example:

http://www.visteon.com/products/automotive/media/slipintube_spec.pdf

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dimjim]

You might want to check with Loctite.
I do not know if they have a product
that you could coat the spline with
before assembly. As israelkk states
if it does not slide, wear should
not be a consideration unless you
are using a much smaller spline
ie fewer teeth to drive the internal
spline. I assume this is not the case.

 

[Philrock]

Are you using a lubricant?

Are there any radial or moment components to the load?

 

[Cryo1]

Philrock,

There is no lubricate. The moment force around the splines longitudinal axis is 150 in*lbs.

So what do you think?

 

[dimjim]

Go for it.
If I simply used the old Lewis equation
Wn = SfY/Dp Yields
78000 x 1.00 x .6/48 yields 975 pounds.
at at .50inch radius would yield 487 inch pounds.
And this assume no tooth load sharing.
The Y factor of .6 that I chose is probably
also conservative. I assume too that you
are talking about a 30 degree involute spline.
S = Maximum Tensile Stress
f = face width
Y = Lewis equation constant (.60 is an assumption)
Dp = Diametral Pitch

 

[Cryo1]

Thanks for the Lewis formula dimjim. What I am concerned about is fretting and wear. Does any one in this world mate steel to aluminum splines in a non-slip application?

 

[dimjim]

What kind of revolutions or cycles do you have
with a hand operation that you would worry
about fretting and wear? Fretting normally
is high cycle vibration phenomenom and wear is
caused from sliding operations which you do
not have as mentioned by israelkk.

 

[Heckler]

I'm with israelkk that the HA may crack under repeated loading. If you must use aluminum I would either just use Chemfilm or electroless nickel w/teflon codeposit. I have had a lot of good experience with Coating Technologies NP3 process

http://www.coatingtechnologiesinc.com/services_plating_np3.html

I have an application that an aluminum body runs in a 17-4 SS ring. The system is sees 850 lb-ins of torque.

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[Cryo1]

Personally, I'm not worried. I think we can work the system out to hand the mechanics and strengths. The problem is others who have never seen a system like that and are risk adverse.