John,

I am surprised that nobody else has answered apart from Bill. I have never tried leaded gunmetal – I have only ever used copper but my understanding is that the lead might affect the silver soldered joint. I can't recall where, but I think I have seen photographs of leaded material bushes that simply won't take to the silver solder.

Phil H

If the lead content exceeds 2%, it can affect the brazing operation.

It can form an unwettable dross at the interface.

It can cause cracking.

These effects can be reduced by adequate fluxing and uniform heating without imposed stress.

Source of information – BS EN 14324:2004 Section 5.1.2.8

This document would be of great interest to the model engineer. It defines the process. Silver soldering is part of the brazing process. Silver solders, conforming to BS EN 1044, as used by model engineers, are referred to as silver brazing alloys. Brazed joints can be made with copper, silver, nickel, gold, palladium and aluminium alloys.

It offers guidance on joint design and heating techniques.

Download it

If the model engineer reads and understands this document, he will produce stronger, neater, cheaper joints. Brazing is a simple process, made difficult by not sticking to the basic principles. It is a skillful process, but this document will highlight where to develop your skills. Then, it's practice, practice.

Keith

Hi Martin,

I didn't pay£250 and got it surprisingly easily from the internet at no charge.

A "downloadable" version is available. Set your printer to double sided printing and load 25 sheets l!

Personally, a better option is to buy my book, which is based on this BS and costs considerably less. Regrettably, it is not available from any reputable book shop! It is available from CuP Alloys.

Keith

PS you can also download some of the detail from CuP Alloys website. Free!

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Martin's link goes to SAE 660, and if you look up the tech data sheet it says 6 to 8% lead, this is hardly a trace

Colphos is 4% and is a lot easier to machine than unleaded bronze, and presumably easier to silver solder, I've had no difficulty.

As an aside if you search for I.S EN 14324 you will find exactly the same standard but for only (only?) £71.19 plus vat. Exactly the same standard, just from the Irish standards authority who don't seem to feel the need to rip us off

From the advice given to me, this is what i do.

Copper for the boiler ( obviously )

PB102 for any bushes, or anything that's soldered to the boiler which is tapped or threaded.

SAE660 for fitting that screw into the boiler.