Re: [CR]Bonding of aluminum lugs with steel tubes (not related to any bike, but theoretical)


Example: Racing

Date: Sat, 13 May 2006 13:04:22 -0700
From: Steve Maas <stevem@mail.nonlintec.com>
To: classicrendezvous@bikelist.org
Subject: Re: [CR]Bonding of aluminum lugs with steel tubes (not related to any bike, but theoretical)
References: <21c9ea8f6c10461172949d98a6c95ba8@comcast.net>
In-Reply-To: <21c9ea8f6c10461172949d98a6c95ba8@comcast.net>


From The Brazing Manual, American Weldering Society, 1976:

"Aluminum can be brazed to certain other metals...Steel surfaces must be protected from oxidation during heating. Bare steel parts can be brazed to aluminum in vacuum or very low dew point intert atmosphere. Steel parts can be electroplated with nickel or hot-dip coated with aluminum for torch, furnace, or dip brazing applications. Aluminum-coated steel parts are readily brazed to aluminum using conventional filler metals and commercial flux. During brazing, aluminum and steel will alloy together to form a brittle intermetallic layer at the interface. [Doesn't THAT just give you the willies?!]...Bimetal joints require special treatments to insure adequate corrosion performance. Because of differences in electrochemical potential, bimetallic joints could corrode rapidly in aggressive environments."

I suppose you could join the tubes to the lugs with adhesives, but then the difference in thermal expansion could eventually crack them. Also the corrosion problems would have to be addressed, probably by using an adhesive (epoxy?) which would fill the joint well and be flexible enough to stand the thermal stresses.

All this to save about as much weight as you'd lose by taking a pee.

Moral: the fact that you can do something does not necessarily make it a good thing to do. There are always trade-offs.

Steve Maas Long Beach, California

Bianca Pratorius wrote:
> Yes, I know that in 1990 the 753 Team Raleigh used this same principle,
> but I am not referring to an OT subject but only a theoretical
> discussion. Would using aluminum lugs and high quality steel tubing
> result in a weight saving? Would it cause stress risers? Would it create
> a more uniform frame/ Would it be durable?
>
> Garth Libre in theoretical Miami Fl.