Brazing Mild Steel

[MWParticipant @mw27036]

I can vouch for that, the advice on CuP really helped me understand what was going on when soldering, why using the right type of flux is very important etc..

I do believe CuP has written a guide you can buy, which i suspect i will do myself, in good time.

Not to be sniffed at!

Michael W

[Tim StevensParticipant @timstevens64731]

I think that the need for a gap in a soldered or brazed joint is because of the nature of the melting process. Unless you have a eutectic alloy, the melting process starts with pasty rather than completely runny metal. This is because some of the metal melts first, and what is unmelted comprises small crystals. And it is these crystals that prevent or interfere with flowing into the joint. Once the whole joint, filler and all, are up to a higher temperature, the crystals dissolve and flow properly. And this is, of course, what you need, as otherwise your joint will be partly eutectic, and partly some other alloy, rather than uniformly the same.

Another cause of poor flowing is the presence of dust from the air and minute solid particles remaining in the melted flux. Some dusts (especially emery, for example) act to repel the flux so that flow is impeded, and a wide joint gap may help to allow any grains to be flushed out by molten flux or brazing alloy.

I would be keen to learn of any more scientific explanation (based on tests rather than experience etc).

And PS – silversmiths always relied on borax until fancy modern fluxes were made available. I think this was in the early part of last century – but for may, borax is still generally used, for silver and gold solders.

Regards, Tim

[Bill PhinnParticipant @billphinn90025]

Posted by Tim Stevens on 02/11/2018 12:08:48:

And PS – silversmiths always relied on borax until fancy modern fluxes were made available. I think this was in the early part of last century – but for may, borax is still generally used, for silver and gold solders.

Regards, Tim

That's right, Tim. I mentioned my use of borax in jewellery making earlier.

The "fancy" flux I sometimes use instead (on heating it bubbles up less than borax) is auroflux. It works well on gold and silver. I'd like to know what's in it.

One other thing jewellers often use is a boric acid slurry brushed on before soldering to reduce the dreaded fire-scale you can easily get when soldering sterling silver, and even with some gold alloys. Some people say the boric acid improves solder flow. I use it a lot but I'm not sure whether it does help, nor whether its help (in addition to the flux) is really needed if your soldering discipline is good.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bill Phinn on 02/11/2018 15:42:14:

The "fancy" flux I sometimes use instead (on heating it bubbles up less than borax) is auroflux. It works well on gold and silver. I'd like to know what's in it.

.

Bill,

Have a look at section 2.2 of the Safety Data Sheet

It wasn't difficult to find …  under 'Questions & Answers' on the link that you provided .

MichaelG.

Edited By Michael Gilligan on 02/11/2018 16:23:23

[Bill PhinnParticipant @billphinn90025]

Posted by Michael Gilligan on 02/11/2018 16:15:54:

Bill,

Have a look at section 2.2 of the Safety Data Sheet

It wasn't difficult to find … under 'Questions & Answers' on the link that you provided .

MichaelG.

Edited By Michael Gilligan on 02/11/2018 16:23:23

Sorry, Michael, I've searched the questions and answers section of that link high and low and I can see no safety data sheet.

[MeunierParticipant @meunier]

Bill, it took me 2 attempts to get there but here is a link to the SDS,

**LINK**

DaveD

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bill Phinn on 02/11/2018 17:03:28:

Sorry, Michael, I've searched the questions and answers section of that link high and low and I can see no safety data sheet.

.

Bill,

The second item on the Questions & Anwers tab is:

Do you have a safety data sheet for this product ?

… now click the little 'down arrow' [or the text] and you will see the answer.

MichaelG.

.

Note: Meunier kindly provided a direct link, but I thought you might also find 'how to' useful for future navigation of Cookson's site.

Edited By Michael Gilligan on 03/11/2018 20:33:38

[Bill PhinnParticipant @billphinn90025]

Thank you, Meunier and Michael!

I've worked out why I couldn't see what you were seeing, Michael; I was viewing the page on my desktop, which has a browser extension that blocks ads, trackers etc. I had to disable the browser extension in order to be able to see the actual questions and answers lurking beneath the tab of that name.

[Eddy CurrParticipant @eddycurr38053]

Posted by CuP Alloys 1 on 02/11/2018 10:08:53:

Posted by Neil Wyatt on 01/11/2018 16:44:53:

Posted by Con Nicoll 1 on 01/11/2018 15:54:01:

I attended the Silver soldering lecture at the Fosse the other week. It was stated there you should mix the flux with water and washing up liquid before applying it to the job. Will the washing up liquid not contaminate the job?

Con Nicoll

Only use a drop. It doesn't seem to do any harm and helps the flux 'wet' the metal.

Neil

The amount of detergent used in making the paste has no deleterious effects.

Keith

Washing up liquid or dish detergent is a surfactant, a "compound that lowers surface tension between … a liquid and a solid."

As indicated by Neil, adding detergent to the water used with the flux paste facilitates improves dispersion or wetting action of the flux by reducing the surface tension between the flux mixture and the surfaces it is applied to.

While I defer to CuP Alloys 1 in all matters brazing, a little detergent goes a long ways.

[Brian HParticipant @brianh50089]

The 'drop' of detergent is specified in Rolls-Royce Aero literature (or used to be). They also specify surgical spirit instead of water. When a flame is applied the spirit burns and bakes on the flux (I always use Tenacity 5)

Brian

[not done it yetParticipant @notdoneityet]

Posted by Eddy Curr on 11/11/2018 20:10:03

Washing up liquid or dish detergent is a surfactant, a "compound that lowers surface tension between … a liquid and a solid."

I think they work on liquids to liquids, too. Think here – those dirty dishes or oil slicks?

[Eddy CurrParticipant @eddycurr38053]

Posted by not done it yet on 11/11/2018 21:55:59:

Posted by Eddy Curr on 11/11/2018 20:10:03

Washing up liquid or dish detergent is a surfactant, a "compound that lowers surface tension between … a liquid and a solid."

I think they work on liquids to liquids, too. Think here – those dirty dishes or oil slicks?

Yes.

The ellipsis in the quotation denotes words left out. Liquid-to-liquid and gas-to-liquid seemed superfluous to the discussion at hand.

The full phrase reads as follows:

"Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants."

Source: Wikipedia

[Eddy CurrParticipant @eddycurr38053]

Posted by Tim Stevens on 02/11/2018 12:08:48:

I think that the need for a gap in a soldered or brazed joint is because of the nature of the melting process.

I would be keen to learn of any more scientific explanation (based on tests rather than experience etc).

No, the need for enough, but not too much gap is to facilitate: 1) capilliary movement of the braze filler metal along the length of the joint between parent metals; and 2) joint strength.

The article in the following link discusses aspects of gap size, joint tensile strength, flux voids and brazing atmosphere.

"The Famous Joint-Strength vs Joint-Clearance Chart" Dan Kay. 2013.04.07

While the conclusions hold implications for industry and obsessives, hobbiests such as myself can continue to follow age-old practice to enjoy satisfactory results.

[HopperParticipant @hopper]

Interesting reading there, Eddy. I always think that if the ideal gap is somewhere around half to one-and-a-half thou, depending on which chart you follow, any two pieces of metal will have about that clearance between them unless they have been blued and hand scraped to a better fit, or perhaps surface ground and micro polished.

Most pieces of metal in the home workshop cut straight from stock, or even milled to shape, and given a bit of a rough up with some coarse emery paper before brazing will have a tiny gap in this range due to surface imperfections, lack of true flatness etc.

I remember from apprentice days the weeks of painstaking filing it can take to get two pieces of steel to mate within less than one thou. It's a lot harder than many people think.

[J HancockParticipant @jhancock95746]

Just be careful that the mild steel is not leaded.

The joint will look good but a good smack with a hammer will show the problem.

[Chris TriceParticipant @christrice43267]

I've used neat washing up liquid (no water) in my flux mix with no discernible drawbacks and it's easier to control how many drops of detergent you add than drops of water. Usually it's a 50/50 mix of water and detergent though.

[Ron LadenParticipant @ronladen17547]

I have a complete beginners question here as I know nothing about welding, brazing/silver soldering etc. I also know nothing of all the technical terms used.

I had it in my head that when welding say two steel parts together the welding process by whatever method melted the steel and the molten metal from both parts fused together with or without filler rod and once set that was a welded joint.

I am probably missing the obvious but how does brazing/solver soldering work with steel, if the steel doesnt melt but the filler rod does, how do you get a strong joint between the parts..? It obviously does work but I cant get my head around how..?, I am imagining the lower temp filler rod just lying on the surface of the steel with no real connection.

C,mon guys put me right.

[ZanParticipant @zan]

 

It bonds at an atomic level into the parent metal and is almost as strong as the parent steel. Capillary action if the joint is made correctly will pull the solder through the joint so that all surfaces are covered. For this reason a tiny gap is required. For flat faces, some people recommend light punch marks to ensure the gap, although iv found that even with clamped faces there seems to be few problems. Some grades are better at gap filling than others, but the gap should be small ideally well under 10 thou no gap = no penetration

Edit….note that both pieces being joined must be at the temperature at which the solder melts- at least a dull red hot – or the solder will form a bead on the outside of the joint and will not penetrate.  Solder flows to where the metal is hottest provided it is fluxed to keep the oxides away

Edited By Zan on 12/11/2018 14:10:41

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ron Laden on 12/11/2018 13:40:56:

I am probably missing the obvious but how does brazing/solver soldering work with steel, if the steel doesnt melt but the filler rod does, how do you get a strong joint between the parts..? It obviously does work but I cant get my head around how..?

C,mon guys put me right.

You went right off the rails when you said 'I am probably missing the obvious', Ron! It's far from obvious what's going on.

In 1954 Dr Linus Pauling (16th most important scientist in history) got the Nobel Prize for Chemistry for his work on the nature of the chemical bond. Dr Pauling was a Quantum Chemist.

Various levels of understanding available:

1. You know it works and can follow the instructions. This is more than sufficient for most of us!
2. You imagine the metals have melted and somehow intertwined at the surface. You know about flux and other practical details like temperature and can make consistently good joins without knowing much about the actual mechanism. Quite rightly, you understand important practical details.  Perhaps you weld for a living.
3. With some knowledge of Physical Chemistry (introduced at A-Level), you know that electrons orbit atoms in specific numbers and energy levels and that nature prefers stable combinations. Stable combinations can be achieved by electrostatic and by orbital sharing. How stable, or not, a particular combination of electrons is determines how reactive the molecule is, and the whether they have a shortage or surplus of electrons decides what else they will react with. In this explanation, brazing creates electronic bonds between iron, copper and zinc copper at the surface layer. The chemical reaction does not require melting before it will start. Consider rusting, where oxygen bonds with steel at room temperature. Brazing creates a relatively weak join because bonding only takes place close to the surface. It's inferior to a weld where the join is much closer to being a true mingling of the original metals.  Knowing this stuff may not help much.
4. At university level you have a much more codified understanding of the various types of bond and the rules that govern them. At this level what's necessary to manipulate bonds to a goal can be predicted. You're likely to become a metallurgist, organic chemist, or similar.
5. Then comes pure science! Rather than depending on practical simplifications, you have a strong grasp of Quantum Mechanics and can do the maths necessary to generalise and predict any bond.

As model engineers, I suggest we only need concern ourselves with theory where it helps get the job done. In my workshop, although the science is interesting, it's usually lack of practical skills that let me down!

Dave

 

Edited By SillyOldDuffer on 12/11/2018 16:07:24

[Tim StevensParticipant @timstevens64731]

It might help you to know that a key factor in brazing ( and silver soldering which is 95% the same thing) and soft soldering (which is 75% ditto) is that under the right conditions molten or nearly-molten metal can wet the surface of another metal. It is the wetting chemistry that Pauling was looking at. Not all metal combinations can do this wetting trick, but over the years engineers (at all levels of understanding – see Dave above) have worked out what does work. And some combinations result in 'alloys' which are weak or brittle (etc) too, so you get wetting but a duff joint.

The surfaces must be clean for the wetting to work, and this is where the flux has a vital role.

And don't forget that welding – same metal in both bits – will sometimes work below the melting point, and it doesn't always need a filler. Iron will do it when hammered together at sparky-red heat, and lead will do it at room temperature.

It is very common in the world of inventing things that the device or process can be made to work long before the real reasons are sorted out, and that is one reason that it is all so interesting.

Regards, Tim

[Chris TriceParticipant @christrice43267]

I've always understood that soldering or brazing is an exercise in alloying at the very surface of metal. That's why it takes slightly more heat to break a joint than it did to make it because the solder is no longer in its pure form, at least in a close fitting joint.

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