soft or silver solder it

Mamod boilers themselves are made of a good grade of quality brass, and are soft soldered together with a high melting point soft solder (Pewter grade), not silver solder.

Oh and in our modern world..lead free solder would be “required” stuff…so again are designs intended for that jointing material.and any?difference?in material properties. ..

Ordinary No-lead 'soft' solder has a rather higher melting point than old-fashioned soft solder (183C is the lowest for tin/lead, 227C for the cheapest tin+ 0.7% copper solder, more complex alloys can be lower (or higher)), with strength not much different. Some soft solders do contain a small % (less that 4%) of silver, but it is confusing to call them 'silver solders'. Soft solders rely on resin-based fluxes, or 'killed spirit' which is zinc chloride solution with some free hydrochloric acid. Some early bicycles were soft-soldered together (eg Dursley Pederson).

Silver solder (also called 'hard solder&#39 is quite a different set of alloys, requiring a different range of fluxes, usually borax based, and applied as a paste in water or alcohol, or dry powder. As well as a much higher melting point range, they are stronger, and tougher, so more suited to the higher pressures as well as temperatures. Many silver solders – which contain 50% silver or more – are silver-white in colour, some a bit nickel-pale-yellow.

Brazing involves a further range of brass, bronze, and similar alloys, with an even higher melting temperature. But the distinction between soft and hard solder is much clearer that between silver solder and braze. The answer to your question is 'yes, but don't expect worthwhile performance'.

Cheers, Tim

Edited By Tim Stevens on 28/04/2014 18:00:43

Soft solder is ok… until the boiler runs dry of water and gets a bit too hot.

Hi Brian,
I agree with Michael's comments about contamination with soft solder. Also I do not think brass is a good material for a high pressure boiler as it can loose part of it's zinc content over time and becomes brittle.

Les.

Interesting article OK it's related to plumbing but it still applies

**LINK**

My concern with that boiler would be, not the soft solder, but that I can't see any safety pressure relief valve in the pictures. If there isn't one I would fit a Mamod type valve.

Russell.

I read about this recently in one of my old Model Engineer magazines, I think from the late 1950's.

Originally most model boilers were soft soldered, the main disadvantage being that soft solder can melt if the boiler runs dry.

Brazing with brass was said to be melt proof and stronger but much harder to do than soft soldering.

Brazing with phosphorous/brass is melt proof, strong and easier to do BUT the joint is seriously attacked by firebox sulphur. Examples of boiler failures were given. Avoid!

Silver solder (cadmium/silver/brass) was recommended because it's strong, melt proof, resists corrosion and – apparently – is not that much harder to use than soft solder, just requiring more heat. I say "apparently" because I've never made a boiler and am only reporting what I've read.

Welding was mentioned as producing the best possible joints. However, it was said to be impractical for most amateurs as well as being unnecessary in practice.

That's what the old guys thought. Has anything changed?

Dave

I know. It's not a good time to suggest it though. Michael_w PM'd me instructions for sure fire twist drill sharpening yesterday. Now I've retreated to my computer after making a complete mess of grinding one. Michael's instructions are fine. So is the grinder. The problem is me.

I shall try again after kicking the cat.

Dave

I know this is an old thread but I only just joined for smaller boilers you might want to consider Comsol, it's not as good as silver solder, but much better than ordinary soft solder

The data sheet for Comsol gives melting point as 296 C, even superheated steam only gets to around 130 C so comsol is well within acceptable safety margins temperature wise. Its also very "creep resistant", unlike ordinary soft solder, and it's been tested to pressures above what you would encounter in most small static boilers (not sure about locos and bigger stuff). And probably most importantly, its no harder to use than soft solder, a small propane or butane torch works fine.

I'm not saying its the answer to everything, I'm only saying it's a much better option than soft solder, if in doubt contact the supplier.