Bronze alloys

[Graham_Wright]

Following Bananas request, I received data from my non-ferrous material suppliers. An extract follows.
Phosphor bronze is a copper tin alloy.
PB1 has a high tin content for heavy duty bearings, bushes and thrust washers.
PB2 contains more tin for better wear resistance in gears and sliding components.
LPB1 has a lower tin content for improved machinability, less hard than PB1 and PB2.
LB1,2,3 and 5 are leaded bronzes (increasing lead with number) for general purpose bearings tolerant of poor lubrication and size tolerances.
SAE660 is a leaded gun metal with good all round balance of strength, hardness, machinability and abrasion resistance. (I made my stern tube from this).
PB102 is a corrosion resistant phophor bronze used generally for electrical contacts.
CA104, Aluminium bronze is targetted at safety critical marine applications.

The general rule seems to be that hard bronzes should be used as bearings for hard shafts and soft for soft.

BUT, DON'T USE BRASS!



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[Evadne]

Thanks, that is very useful for the metallically illiterate of us. I will add it to reference directory on my PC, if you don't mind, along with the advice page from Classic marine (<A target="_blank" HREF=http://www.classicmarine.co.uk/Articles/metals.htm> here </A>) on corrosion.

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[Ships_Cat]

<<<BUT, DON'T USE BRASS!>>>

In fact you will find that most thru hull fittings, sea cocks (including Blakes) and propellers for small vessels are in fact made from perfectly acceptable corrosion resistant brasses and not from a bronze at all (except in name eg manganese bronze is a brass).

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[Graham_Wright]

So what is a corrosion resistant brass? Naval brass, and manganese bronze which you mentioned are allegedly (and presumably) corrosion resistant. But what gives them this property.
I frightened myself to death removing brass screws from a wash board slide to find that all the zinc had departed leaving a copper sponge.

My Blakes (old) seacocks are definitely bronze of some sort.

For my new boat, I am sticking to 316 stainless; as fittings are stamped (and tube) at least you lnow what you're using!

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[rjp]

My understanding is that Blakes seacocks are a grade of brass known as DZR (DeZincification Resistant), but definitely not bronze. As far as I'm aware this has always been the case - perhaps others know different?

John

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[Ships_Cat]

Well I trust Cliff is around to expand on this 'cause my metallurgical knowledge is limited to the basics in that I just buy from and trust reputable manufacturers to get it right. But brasses come in alpha and beta phases (to do with the molecular structure) and additives such as arsenic, phosphorus and antimony to alpha phase brasses impart good corrosion resistance against dezincification.

The underwater performance of them is fine. For example on my own boat the propellor is corrosion resistant manganese bronze (a brass with manganese to harden it) mounted on a ss shaft insulated from the engine - there are no anodes on the shaft to protect the propellor and it is not bonded to the boat's main anode so it is totally unprotected. After 8 years there is no sign of any corrosion and I would not have expected any - most problems people have are due to their listening to and acting on too many marina and forum myths about anodes and protection, and/or buying cheap propellors in the first place.

I would not rely on 316 as being a better all round alternative as it tends to have its own set of problems as far as corrosion is concerned. The least problematical, where it is practical to use them, are quality glass reinforced plastics.

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[ccscott49]

I think mine are bronze, they are now 40 years old and not protected, by anodes and are like new, the bolts holding them on are most certainly bronze, I put them in.

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[Graham_Wright]

"SS shaft insulated from the engine".

How is it insulated? This is relevant to earlier questions on grounding shore supplies.

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[Ships_Cat]

The shaft to gearbox coupling is an insulated one, normally made with an ordinary plastic disc type flexible coupling between the gearbox flange and the shaft flange. They are common on many boats even if only for the flexible characteristics, in which case bonding fanatics short them out with a conducting strap.

Polyflex (Australian) is but just one of many examples - this is the brand fitted to my own boat and can be seen at <A target="_blank" HREF=http://www.ceaco.com.au/polyflex.html>http://www.ceaco.com.au/polyflex.html</A> where they point out its flexible, shock aborbing and insulating abilities.

John



<hr width=100% size=1>I am the cat but I am only 6.

 

[Graham_Wright]

Thanks for that. I already have a flexi-coupling but it is all metal.

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