general questions on composite castings

[BobM3]

We use gear blanks that currently are sand cast aluminum bronze. This material is getting quite expensive. I'd like to use a composite casting. I was thinking the rim would be aluminum bronze and the hub would be steel. It looks like centrifugal casting can be used to produce these. Is the bond between the 2 materials a metallic bond or a mechanical bond? Also, it would be great if the hub could be aluminum but I haven't heard of this. Can you make a composite with aluminum bronze and aluminum?

 

[CoryPad]

Centrifugal casting with two materials usually results in metallic bonding (or a reaction layer composed of an intermetallic compound). The bond can be weak, so testing is advised.

Obviously Al and Cu have mutual solubility (hence the material that is aluminum bronze), so you could use centrifugal casting to produce a part with an outer layer of Al bronze and an inner layer of Al. You will need to optimize the process to achieve the highest possible bond strength, but beware that this still may not meet your needs.

Regards,

Cory

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

 

[arunmrao]

You can static cast with 2 dissimilar metal. The core or hub can be cast iron and the outer rim can be aluminium bronze. This will be cost effective and functional too. On the outer layer of CI provide some grooves and slots so that there is good bonding.

This is a regular practice locally.Last week for one of my gears I replaced the outer ring retaining the inner CI hub with the same shaft bore.

 

[BobM3]

So it sounds like if I use similiar materials I can get a metallic bond but with dissimiliar materials I get a mechanical bond. I've seen the aluminum bronze/cast iron combination. I would think to ensure a good mechanical bond you would want the rim to "shrink" onto the hub material during solidification so there would be residual stresses on the ID of the rim and the OD of the hub. Does this naturally occur during the casting process?

The aluminum hub/aluminum bronze rim intrigues me because of the low weight. I've not see such a combination though. Has anyone seen these two materials used together for a gear blank?