phosphor bronze  or aluminium bronze

Hi Guys i am at the stage of making the parts for brazing on a steam boiler

do i need phosphor bronze or aluminium bronze

Thanks Kevin

Gun metal ! or a normal Cu/Sn alloy ! Phosphor bronze is for bearings, and aluminium bronze is a high strenght alloy. Noel.

Ally bronze is VDiff to drill and tap, and not at all easy to silver solder. SAE660 or Colphos would be my preference

On no account use aluminium bronze on a boiler. Although technically speaking it can be brazed using special fluxes, you can't guarantee perfect sealing with it.

You should be using PB102 bronze for boiler bushes (PB1 is acceptable) that are silver soldered to a copper boiler shell. The other bronzes mentioned contain lead (gunmetal LG2 5%, colophos 90 4%, SAE660 7%) and zinc, and there are reports that this can affect the silver solder joint. I think the Australian code says something about it but I am speaking from memory.

For a boiler to be tested the materials used should be certified.

However, I am sure that the use of gunmetal has been common, especially for turrets, and I would guess that people have been using colophos and SAE660 with no apparent failure. Some suppliers sell 'phosphor bronze' without being aware of the differences.

Edited By norm norton on 08/01/2022 15:00:51

I'm glad you said should be certified rather than shall be Norm ! For boilers built to standard or recognised plans for small ish boilers there's no requirement in the UK under club rules Etc. I've not heard of anyone here talking about the arsenic content of copper supplied to the ME trade for boilers Etc. Noel

DataSheet for SAE660, note 'brazing good' 660

info from Noggin End 'contrary to popular belief Colphos can be silver soldered' colphos

Extract from AMBSC acceptable materials bushes, Alloy 836, which is near as dammit the same as colphos in chemical composition.

Thanks for the info i will have a good look for the best action

thanks Kevin