Can I do this; Aluminum on Steel?

[vonsteimel]

I'm working on a developmental project on which I cannot give too many details but here's the situation: I have a Stub shaft which can be seen in the attached illustration. This shaft is made from a high-strength steel (exact alloy unknown) and is driving an accessory shaft. It's transmitting up to 120HP @ 7,000rpm for short periods of time (10-15 seconds) but is transmitting between 50-70% of that most of the time...

Space limitations are very restricting and the stub shaft cannot be modified. -- As you'll see in the image, the Stub shaft has a 1:10 taper as does the mating ACC shaft. Up until now, we've tested with a steel Accessory shaft which has worked fine but is way too heavy to be practical.

What I want to do is make this Accessory shaft out of aluminum but I am weary of pressing an Aluminum Accessory shaft (female) onto a Steel Drive shaft (male)... Can I do this? What problems might this cause?

There is no key, only the friction between the tapered surfaces will transmit the load.

There is little-to-no cantilever forces on the joint, as all load is transmitted rotational about the shaft axis. There little shock loading as well, it is mostly smooth transmission.
What’s your input?

Any info or link will be greatly appreciated.
Thanks,

VS

 

[GregLocock]

We press large steel bearing units into aluminium spindles all day long. The joint design is not significantly different to joint design of steel on steel. You'll find that the contact pressure and hence torque capacity is significantly affected by the OD of the aluminium part

A 1:10 taper is rather a lot, do you do this for disassembly?



Cheers

Greg Locock


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[msquared48]

Without knowing the details of the useage, I would be concerned with electrolysis between the dissimilar metals.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dgallup]

I would be concerned about fatigue life of the aluminum accessory shaft. Aluminum has no fatigue limit so with any kind of alternating or transient loads it will eventually fail. What is supplying the power, internal combustion engine or an electric motor or other? How much inertia does the load have? What is your life expectancy?

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[GregLocock]

Another example, more directly relevant, is the outer tie rod, which is a steel taper pulled into the aluminium steering arm on the spindle.

The taper is fairly coarse.

Cheers

Greg Locock


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[MikeHalloran]

It ain't broke; why are you fixing it?


Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

it is broke - "we've tested with a steel Accessory shaft which has worked fine but is way too heavy to be practical."

Cars have had aluminium driveshafts for donkey's years, I'm not saying that aluminium is the ideal material for a driveshaft, but it can certainly be made to work.

Cheers

Greg Locock


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[MikeHalloran]

>>> has worked fine<<< ain't broke.

>>> way too heavy to be practical <<< We have no measurements, of anything, including the threshold of practicality.

Granted, aluminum driveshafts can be perfectly satisfactory.

It's also possible to build a perfectly good airplane out of steel.

This is neither, so far as we know.

Aluminum is not necessarily the best material for the subject auxiliary shaft, just because of its lower density, because its elastic modulus is also lower, by the same factor as the density. I suspect that 'E' is important to the survival of the subject taper drive joint.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Is it possible to whittle some of the objectionable weight off the steel aux shaft, or hollow it out, like a "real" driveshaft?

 

[swall]

GKN made an aluminum prop shaft with steel splined end connections for the Pontiac Aztec (all wheel drive version). The aluminum tube was friction welded to the steel stub shafts and the assembly was powder coated.

 

[IRstuff]

Will the drive shaft connection to the accessory shaft be a loose fit? If so, I would think there might be a potential for galling.

TTFN
faq731-376

 

[GregLocock]

So far as corrosion goes, given that people have been running aluminium wheels on steel hubs for 50 years experience would be that if you aren't in a salty environment you should be OK.



Cheers

Greg Locock


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