Can we have a really clear distinction between Silver Soldering and Brazing

Hi, I have looked at some old posts on this forum and on the web to define the difference between brazing and silver soldering but I don't quite get it.

If it was me I would say the two processes are the same in that you make a joint by heating the metal to be joined and a filler metal joins the metal. In soldering there must be overlap or a very small gap and the solder flows into this. With brazing the gap can be larger and the filler metal also flows around the joint area making for a stronger joint.

Feel free to add, subtract amend?

Chris

Well Brazing usually is done with an oxy acelylene torch, or that's how I always did it. You need a lot more heat for brazing.??? Both are only gluing the metal together hence years back I had a MOT failure on a car because I had brazed sill on. With silver solder when it reaches is melting point the solder flows instantly & sinks in to the joint. Brazing does in a way but so much so.

Keith Hale always maintains that silver soldering is a brazing process. He has presented many lectures on silver soldering at shows and clubs, I think he knows a bit about silver soldering.

Mike

Silver solder contains a proportion of, wait for it, silver? Brazing filler rod is mainly brass. Silver solder has a low viscosity when fluid and flows easily into small gaps - essential property that is always laboured. Braze has a higher viscosity when fluid and likes bigger gaps. Main differential between basically the same process is the temperature it becomes fluid at. Silver solder more suited to smaller sections and potentially lower melting temp parent metal and whilst fillets can be formed they are relatively small. Braze better suited to bigger sections and higher melting temp parent metal and capable of forming larger fillets.

Paul.

Take a bit of time to read the Workshop practice book No 6 by Tubal Cain , the late TD Walshaw . One will learn and understand all one ever needs to know about soldering, silver soldering and brazing and the distinctions between them. It may be dated in relation to its references to cadmium based products ( at least my older copy is ) but that doesnt in any way affect the superb explanations of the theory and practical aspects of this interesting and much misunderstood process. Happy reading and you will certainly achieve better joints after studying this straightforward and well written book.

This site explains the difference fairly well I think Chris...

https://vacaero.com/information-resources/vacuum-brazing-with-dan-kay/1345-brazing-vs-soldering.html

Regards,

IanT

RRMBK mentions Workshop Practice book no. 6, but I have a copy of soldering and brazing, no. 9. No. 6 is measuring and marking metals.

Silver soldering as we think of it should really be called silver brazing as mentioned by Mike. Any joining process involving temperatures over 450°C(?) is classed as brazing, below that is classed as soldering.

John

In the days of yore, including Tubal Cain's heyday, silver soldering referred to what is now commonly called silver brazing. The terminology seems to have changed over the years. In those olden days, brazing was commonly believed to refer only to using brass filler rod and an oxy torch to flow it into the joint. And in those olden days, silver soldering was usually done with high silver content rods and could be done with oxy or propane torches. But that now seems to be called commonly silver brazing.

Keith Hale of CupAlloys who posts on here regularly has a good site with some explanation and he has written what is often considered the definitive modern book on soldering and brazing. His site: **LINK**

But even his site is confusing, listing "Silver Solder" in the headings but referring to it as "a silver brazing alloy" in the fine print.

To add to the confusion, old fashioned lead and tin plumbers and electrical solder has been replaced by a 5 or even 2 per cent silver-bearing tin solder that is marketed as "silver solder" but really is not, in the traditional sense.

In answer to the question - obviously not! Why do you need one?

One thing to clarify from the OP though: the size of the gap does not define brazing versus silver soldering. Both use capillary action to "flow" the molten rod material into the joint and while there may be some variation in the gap people like to leave, it is not definitive.

But to add to the confusion, there is also a process sometimes called bronze welding, or sometimes sif-bronze welding, where the joint is not overlapping and not relying on capillary action, but a bead of bronze/brass welding rod material is built up along the joint something like the way a bead of arc weld or TIG weld would be laid on. This process has been popular with bespoke motorcycle frame builders for many years, including some of those making replica Norton Featherbed frames for classic bike racing today.

Just to add to the confusion where I served my time brazing was referred to as bronze welding!, was this a regional thing or is there a difference between bronze welding and brazing?

I have seen brazing done with brass rod and a gas/air torch allowing the filler to flow into the joint, much as silver soldering, but we always used oxy/ acetylene and built up a fillet. There was great pride amongst the fabricators in a neat and even fillet, I only got a few months in the fabrication shop and sadly never achieved anything like perfection!

This is not a facetious post, I have often wondered about the difference, As an aside on a recent visit to the National Motorcycle Museum I was fascinated by the beautiful bronze welding on the racing bike frames, something to aspire to. Well worth a visit.

Dave

For what it's worth.

It's a shame we don't have a term to describe the joining of metal parts by the introduction into the joint of a molten filler material by capilliary action such that the filler wets the metal and forms the joint by subsequent solidification and does so at a temperature below the melting point of the parent metal that does not in some way refer to the composition of the filler material. Call it Zapping for a moment.

You then get Brass Zapping, Bronze Zapping, 60/40 Tin Lead Zapping, Spelter Zapping etc

:0)

Martin

Welding is where the component parts (and the filler metal, if used) are actually melted or fused together. This is easier to do with a small, localised, hot flame such as an oxy-acetylene set up. Brazing does not involve the substrate being melted - only the filler is actually melted.

All the lower temperature solders are of a similar ilk - the components are not melted but different fillers are used with different melting points and other differing characteristics.

Think here of brazing cast iron. There is no way that the cast iron is going to melt at brazing temperatures - and if it did, the filler would be completely overheated. Both brazing and soldering require fluxes to maintain unoxidised surfaces to facilitate good contact/adhesion. Welding does not - but does require some form of shielding to prevent the metal burning or seriously oxidising until the joint becomes solid. Melting iron and using brass filler would require some very special flux, I reckon! Just think with a modicum of common sense.

If the OP does not know how the joints are formed, he will not understand the differences in the processes. I think he needs to study a book or two on the subject, before asking such questions (ie before knowing the basic knowledge of the processes).

Also, widen the box (while still thinking inside it) - think about plastics. Some can be welded, too. We don’t usually think of lead-working as a form of welding, but it is. Once the OP knows the difference between welding and brazing/soldering, he may be able to understand the differences between what is described as brazing or soldering and realise they are similar processes but with different nomenclatures. There will never be a ‘clear’ distinction between the two as they overlap each other!

Just like biology, for example - a century, or so, ago living things were described only as either animals or plants - two Kingdoms. Nowadays, we know that this is not the case, so more Kingdoms have been introduced to include the organisms that clearly do not fit in either of the two main definitions of organisms- as used in the past. We also know that some parts of the cell nucleus likely started off as a symbiotic relationship between two early organisms.

Knowledge develops all the time and discrete things (as described in the past) can often, now, be separated into entirely separate ‘sub-assemblies’.

Great help, especially this link, recommend it to all. Thanks everyone for the posts

Chris

As already explained soldering and brazing are similar processes but performed at different temperatures. However the distinction may have arisen by the need to discriminate between different types of manufacturing process or equipment needed or take into account the trade or operative qualifications/training and possibly Union they belonged to.

Clive

The definitions are made by reference to the temperature. Below 450C is soldering, above brazing. I always start my talks to the societies with this fact and then go on to say how we still say silver soldering, even at 630C! Even though for example 455 is a silver BRAZING alloy technically, we still refer to it as silver SOLDERING. Confused?

In truth the processes are the same in almost all aspects, with the exception of the temperature.

.

Agreed ... it explains the difference between Soldering and Brazing quite nicely

What it does not do, however, is clearly position true ‘Silver Soldering’ between those convenient extremes.

This list of Silver Solder grades might help:

[quote]

The most common silver solder melting point divisions are:

• IT: The highest melting temperature, used on fine silver when enameling (melting point: 1490 degrees Fahrenheit)
• Hard: Used for bezels and as a first step when doing multiple soldering (melting point: 1425 degrees Fahrenheit)
• Medium: Used mostly when only one or two steps will be done (melting point: 1390 degrees Fahrenheit)
• Easy: Used as a final solder or when soldering on findings (melting point: 1325 degrees F)
• Extra Easy: Used primarily for repairs and is distinctly yellow in color- (melting point: 1270 degrees Fahrenheit)

[/quote]

Source: **LINK**
https://www.interweave.com/article/jewelry/solder-101-its-forms-and-melting-temperatures-for-successfully-soldering-jewelry/

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MichaelG.

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Edit: Posting crossed with Shaun’s

Edited By Michael Gilligan on 21/01/2020 10:30:26

I have never really bothered too much with the detail. As far as I'm concerned, if it's a silver alloy it's silver soldering and if a brass alloy it's brazing.

Having made many 100's of items of jewellery over the years I have used all the grades a silver solder on silver, gilding metal, Nickel silver, brass and copper etc.

For steel I have always generally brazed (a term I have used for 50 years). If I use silver silver solder on steel it's silver soldering.

Everyone at my work used a brazing torch for both brazing and silver soldering. We all knew what we were doing and never had any discussions about the correct terminology.

Works for me.

My understanding is the difference can be decided almost entirely by temperature: below 450°C it's soldering, above 450°C it's almost certainly Brazing.

Both processes rely on melting a filler metal at below the joint metals melting point. Filler metals that melt below 450°C include Bismuth, Zinc, Tin and Lead. As Bismuth is expensive and poisonous and Zinc evaporates easily and the fumes are poisonous, most solders are alloys of Tin and Lead. Tin melts at 232°C, and Lead at 326°C, but alloying them reduces the melting point. A solder containing 60% Tin and 40% Lead melts at 182°C making it highly suitable for electronic work. It can be precision melted with an electric iron that's not a fire risk, and the solder usually comes with built in flux. The flux is relatively weak and depends on the joint being clean.

Plumbing solder requires considerably more skill because operations are on a much grander scale. The operator has to choose and apply his own flux, and carefully judge the heat. Copper pipe isn't too difficult, but soldering Lead Pipe is skilled work. Plumbers are trained to do it and some become specialists. In the good old days power cables and communications wiring were often protected by lead sheathed cable that had to be carefully soldered at the joints to keep water out: this also is skilled work.

The disadvantage of soldered joints is they aren't mechanically strong.

The words 'Braze' and 'Brazen' both point to the main filler metal used above 450°C - Brass. Brass is an alloy of mostly Copper and Zinc. Pure Copper melts at 1085°C, but alloying it with Zinc drops the melting point. High Zinc Yellow Brass melts at about 900°C. This is very convenient for jointing Iron and Steel; it's much easier than welding, and done quickly the heat doesn't alter the steel. The disadvantage is that, although considerably stronger than solder, Brazed joints are weak compared with Welded or Rivetted joints. In the past, Brazing was associated with cheap and nasty car repairs - I vaguely remember it being made illegal for garages to mend cars by brazing.

Brazing was originally done with ordinary Brass Filings, and still can be, but 900°C is an uncomfortably hot working temperature. The melting point of Brass can be reduced by further alloying it with other metals notably Silver (expensive) or Cadmium (poisonous). Cadmium has been banned for all but special purposes, shame because it's not particularly hazardous in small workshop quantities. It turns nasty when people have to work with it all day every day, or live downwind of a plant, and if it leaks into the water. Silver solder is good stuff, some alloys melting as low as 620°C. As some Brazing alloys containing a lot of Cadmium melt below 450°C, and some solders melt above 450°C, the border isn't rock solid.

Whilst scientists and engineers try to use consistent technical terms, the same can't be said of trades and practical men! Don't be surprised to find the same word meaning several entirely different things (like Alum), or definitions being blurred as with 'Soldering' and 'Brazing'. Despite the name 'Silver Solder' is usually a Brazing material and process. Some trades say 'Soft Soldering' for less than 450°C, and 'Hard Soldering' for above that. In effect 'Hard Soldering' = 'Brazing'.

Keeping it simple:

1. Soldering - low temperature, mostly easy to do with low tech equipment but joints are weak.
2. Brazing - harder to do, needs more equipment and much more heat, and the joints are medium strength.
3. Welding - Hardest to do, requires special equipment, high temperatures and skills. Properly done, joints will be as strong as the base material.

As always, engineering is about balance. Fit for purpose is the goal. Model Locomotive Boilers are a good example; the Codes all discourage Soldering because soldered joints are borderline in terms of strength. Probably wouldn't go bang, but why risk it? Likewise the Codes discourage Welding because amateurs are likely to make a mess of it in non-obvious ways. It's difficult to prove welded joints are sound, especially when they can't be seen. Brazing is recommended because it's reliable - more than strong enough for the job, relatively lenient, and easy to spot and fix mistakes. A boiler brazed by a skilled expert will be a work of art but I think I could just about make a simple one. (Probably ugly and only after much wasted time and materials. I can't see me ever putting the effort in needed to become proficient!)

Dave