[Public-List] questions about bronze fasteners

[Gordon Laco]

Hello George - 

I can't definitively answer your question because there are so many alloys
within the families of aluminium bronze and silicone bronze.  I learned the
hard way a number of years ago.

I was supplying alum bronze lifeline stanchions to a large new Alden
schooner being built in the States; I specified the alloy I wanted the
machine shop to use.  Somebody there reckoned alum bronze is alum bronze and
decided to use a much cheaper alloy.  The one I needed is AB2... 83% copper
10% aluminium 5% nickel 3% iron.      The one he chose had no nickel.  It
turns out that it is the iron that gives the stuff its astounding strength
but without the nickel to 'imprison' the iron, it rusts.  Imagine my horror
when the schooner's owner called me from Bermuda to tell me that the
'bronze' lifeline stanchions were rusting....

The machine shop were good about it when they realized what had happened and
made me a new set of proper alloy stanchions to rush to the schooner.

AB2 aluminium bronze is twice the strength of gunmetal bronze (LG2 85%
copper 5% lead 5% tin and 5% zinc)

LG2 is preferred for making things like cleats and portlights were a bit of
give in it is a benefit.  Oh, it used to be the preferred stuff to make
artillery of too, for the same reason.

So, to get back to your question, George, I would not recommend anybody
guess at the properties of bronze of unknown origin or from a part of the
world where suppliers might be more inclined to tell you what will make you
happy, than a truth which might not make you happy.

I have heard of people getting into trouble by ordering winches or
windlasses normally supplied with a chromed finish... Delivered bare bronze.
If the alloy of bronze was not intended to be exposed to the elements,
rusting, pitting etc can happen.

Which leads me to another memory involving sitting here at my desk staring
at two turnbuckles, each claiming to be made of the same AB2 aluminium
bronze; each claim being supported by the respective manufacturer's military
specification certificate (I've learned to ask for such documents)  One
turnbuckle from my English supplier, had that pale yellow caste I know is
characteristic of top quality alum bronze.  The other, from a place further
away, was more 'carroty'.  Hmmmmm. The documents said they were the same.
Which ones do you think I had the courage to represent?

Gord #426 Surprise





On 10/05/11 3:11 PM, "George Dinwiddie" <gdinwiddie at alberg30.org> wrote:

> On 5/10/11 8:54 AM, Gordon Laco wrote:
>> There are alloys of bronze that are 'stronger' than stainless steel... An
>> example would be aluminium bronze.  However, most such alloys are
>> considerably more expensive than stainless steel.   Because there are so
>> many alloys of bronze available, it is important to have good reasons to
>> have faith in the veracity of your bronze gear's maker's claims of what
>> alloy they supply.  That's a whole separate topic and I have amusing stories
>> I could tell with a beer in front of me.
> 
> Do you know how, in general, aluminum bronze compares with silicon
> bronze in a marine environment?  I've noticed that off-cuts of aluminum
> bronze are generally available on eBay, but not much silicon bronze.
> 
>> Another issue with stainless steel is that it needs to be exposed to O2 in
>> air for the anti-corrosive properties 'work'.  It is for this reason that
>> appropriate alloys of bronze are better for fastenings in places where they
>> will live buried in the materials they hold or underwater, than stainless
>> steel.  So wrapping it with too much tape,  or putting plastic bags over
>> various rigging components (or anything) during winter lay-ups are counter
>> productive practices when dealing with stainless steel rigging.
> 
> I've got a good photo of what happens with underwater stainless on
> http://alberg30.org/maintenance/Steering/CreviceCorrosion/
> 
>   - George



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