Dissimilar Metals [RE-wrenches]

[Jim Hartley]

Baran Galocy wrote:
> Wrenches,
> 
> Would someone be so kind as to educate me on why it is not advisable to 
> use
> hot-dipped zinc galvanized products in direct contact with aluminum.  
> I've
> been told it is a no-no, but I've not been told the long-term results of
> such an action.

The problem of galvanic corrosion is precisely why plumbers use 
dialectric unions.  The union employs a non-metallic seal that isolates 
the two dissimilar metals from one another.  You can accomplish the same 
thing by using non-metallic spacers prohibiting
dissimilar metals contact.  Ideally, the spacers should be shouldered
so that a sleeved portion penetrates through the hole in both joined 
members.  Your bolt would slide through this sleeve having isolation 
from the surrounding metal surfaces.  Enabling the correct fitted  
tolerances and positioning may be a bit of extra work, but certainly 
do-able.  Usually such dialectric spacers/washers are made of Teflon or 
some similar material. I suspect you can find such things in a good 
hardware store.  If not, you may have to order them from a fastener 
supply house.  In a pinch, you can use just flat non-metallic surface 
washers and dialectric barrels or sleeving cut down to the right length 
which passes through the holes of the two joined metal elements.  
Ingenuity will get you through this problem.

Jim Hartley
http://www.homestead-specialties.com
JamesHartley at homestead-specialties.com
Direct Email: grail at inil.com
630-584-8780
630-584-9092 FAX

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