Fluxes

[Dunstan EloiParticipant @dunstaneloi23233]

When I were a lad, my Dad taught me to silver solder using borax ground from a cone with water, and we used this to successfully build a boiler for my steam tug to power a Stuart 10V engine. 

    I am now told by those who sell solders and  fluxes that borax is not suitable and I must use the ‘new’ fluxes that they sell. None of them can, or will, give me a clear technical explanation as to why I must use the modern stuff rather than borax. Vague wafflings about borax breakng down before the solder fusing temperature is reached do NOT match my experience so there must be some proper scientific reason that can be explained in simple terms, for the superiority/necessity to use what is now specified.

    Can anyone help me out?  Dunstan Eloi.

[Dunstan EloiParticipant @dunstaneloi23233]

[Ian S CParticipant @iansc]

Can’t help with why not,but for general use I use Borax bought from a garden shop,a dollar NZ per kilo.My grandfather,a tradesman plumber in Scotland,when on holiday in NZ used Borax with Easyflo.The blokes selling the solders proberbly dont know anything about brazing or fluxes.The borax from the garden shop is granular,a little coarser than white sugar.Ian S C

[CirclipParticipant @circlip]

Bet you used a petrol blowlamp for it Dunstan?? Since everyone uses the modern gassy products, the old nuggets drop into obscurity. While the “New” fluxes may contain the latest black art wonder chemicals, there’s nowt wrong with make do and mend.

 

  Regards  Ian.

 

  Don’t forget a splash of washing up liquid in with it.

Edited By Circlip on 08/12/2009 12:47:08

[Dunstan EloiParticipant @dunstaneloi23233]

Hi SC. Don’t know if garden shops sell borax.  It does need to be anhydrous to avoid cooling as water of crystallization is driven off slowing the procedure down. Thanks, wil look into it.

Hi Ian. We used  town gas with a pumped air blow torch, the same as silversmiths once used.  Thanks.

[chris stephensParticipant @chrisstephens63393]

Hi Circlip, (or should that now be Mo, to go with Curly and Larry)

  

On topic first, mixing with Meths has been mentioned elsewhere rather than water. The theory is that it burns off or evaporates rather than bubbling up and disturbing the little snippets of solder. The water is only there to aid placing the flux where it is wanted and takes no part in the soldering process.

Off topic second, If only the younger generation would adopt the concept of “make do and mend”, we might be able to reduce our balance of payments debt to the Chinese a bit. It might help with “Global Warning” too.

chriStephens

[Ian S CParticipant @iansc]

Hi Dunstan,your garden shops may not have borax,the chemist will,but more expensive.Its best to heat it up,the grind it up again,then mix it either with water with detergent,or meths.I certainly used a petrol blow lamp when I started,but after it missbehaved I got LPG.Ian S C

[Ian S CParticipant @iansc]

Here I am again,been looking on the web,theres a number of places in UK to get borax,Garden Direct 100gm £4 95,500gm £14 95.Jewel Toolcraft.co.uk Soldering-melting-Equipment this site has borax cones £1 99 ea.Borax is handy for getting rid of ants and other bugs,also some weeds.They say it is very good for bigger and better sunflowers.Ian S C

[DMBParticipant @dmb]

Hullo Dunstan,

I expect that retailers trying to rubbish Borax in favour of newer chemicals, which of course they stock, have a vested interest in flogging their more expensive “superior” jollops! Borax + “town Gas” worked well enough for me in school metalwork!

John

[mgjParticipant @mgj]

I understood that the lower temperature fluxes like easyflo2 were fluourite – fluourspar, fluoursomething that you can mine in the Pennines just near Eyam in derbyshire.

 

The high temperature ones like Tenacity were borax substantially.  What additives there are to improve wetting and aggression? I don’t know, but thats what I understood.

[Ockert SchoemanParticipant @ockertschoeman59821]

The reason that borax is not recommended is that its activation temperature is higher than the melting temperature of most of the silver solders. That means that it doesn’t begin to  remove oxides from the surface to be brazed before the silver solder melts. It also leaves a hard glass that is difficult to remove. Having said that borax does work for the high temperature brazing rods (read no or little silver). The different formulations of fluxes are all designed to give the best braze joint for a specific combination of  brazing alloy and material to be joined. A full discussion of the hows and whys of fluxing is a bit long for a post. Maybe it would make a good subject for a article in MEW or ME.

[Ockert SchoemanParticipant @ockertschoeman59821]

The reason that borax is not recommended is that its activation temperature is higher than the melting temperature of most of the silver solders. That means that it doesn’t begin to  remove oxides from the surface to be brazed before the silver solder melts. It also leaves a hard glass that is difficult to remove. Having said that borax does work for the high temperature brazing rods (read no or little silver). The different formulations of fluxes are all designed to give the best braze joint for a specific combination of  brazing alloy and material to be joined. A full discussion of the hows and whys of fluxing is a bit long for a post. Maybe it would make a good subject for a article in MEW or ME.

[Ockert SchoemanParticipant @ockertschoeman59821]

The reason that borax is not recommended is that its activation temperature is higher than the melting temperature of most of the silver solders. That means that it doesn’t begin to  remove oxides from the surface to be brazed before the silver solder melts. It also leaves a hard glass that is difficult to remove. Having said that borax does work for the high temperature brazing rods (read no or little silver). The different formulations of fluxes are all designed to give the best braze joint for a specific combination of  brazing alloy and material to be joined. A full discussion of the hows and whys of fluxing is a bit long for a post. Maybe it would make a good subject for a article in MEW or ME.

[Ockert SchoemanParticipant @ockertschoeman59821]

Sorry about that but the website gave me a error messages stating that I must try again.

[Dunstan EloiParticipant @dunstaneloi23233]

Thanks for all your replies. What still puzzles me is that my Dad used to do silver smithing to a professional standard. Many of his joints were critical as to location of parts, and the use of minimum solder for assay purposes. I watched him many times and the borax / solder combination always worked perfectly ; firsly the moisture was driven off, then  a dull red appeared in the metal and the borax visibly melted and by the time the solder fusion temperature was reached the flux was like glass and the solder ran perfectly, no bubbling or smoking from overheating or any other adverse effects So is there a metalugical difference between soldering silver & copper that now make borax unsuitable for our modern copper boilers? Perhaps There is a technical expert out there who can enlighten us,. Could Johnson Matthey be persuaded to write an authoritatve article for ME with specific refence to our boiler making activities ?  (ED?) .       Dunstan

[Ockert SchoemanParticipant @ockertschoeman59821]

Dunstan if your dad was doing silver smithing he was probably using an solder that was close to 90% silver. The melting point would probably be in the 800-900 deg C range, right where borax would start to work. Most of your silver solders as used in industry contain less than 50% silver and melt in the 600-700 deg C so you need a flux that will start to melt at about 450 deg C. Unfortunately to get performance at that low temperature you have to live with poor performance at the higher temperatures (flux exhaustion, burning of etc.) Which is why Easyflo flux and Tenacity flux have different applications. Now to your copper boilers; getting enough heat into the boiler to make a good braze joint isn’t easy, and one also doesn’t want undue distortion of the copper. So using a low melting point silver solder alloy (Easyflo, Mattibraze, Silverflo) with the correct flux is the way to go. In industry the use of self fluxing alloys (Silfos, Copperflo) are preferred for copper to copper joints. They have  slightly higher melting points though. Selecting the correct alloy for an application involves trade offs between a lot of things; including how you plan to heat the joint. Johnson Matthey used to have application notes that was very detailed. I presume that they still have them. If you have specific questions, ask and  I’ll try to provide answers that make sense.

[Dunstan EloiParticipant @dunstaneloi23233]

Hello Okert Schoeman. Your advice is just what I am after. When I start to build my boiler I shall be using large nozzle propane torches, with the work shrouded in ceramic heat resistant wool, board or chips, to bring the parts to be soldered up to temperature as quickly as possible. I may also have the use of oxy-acetylene to facilitate more localised final temperature elevation. I will look into the J.M .notes that you mentioned,  Dunstan

[DMBParticipant @dmb]

Hi All,

Soft Solder Flux. I have not yet tried it but someone “at the club” recommended a flux which he said really does work on brass although the makers say its for copper tube in the plumbing industry; Wickes Active Paste Flux.John

[Chris TriceParticipant @christrice43267]

John, brass is an alloy of copper and zinc. The fluxes used for plumbing copper pipes are fine on brass and the DIY tubs of plumbers flux (Powerflux) are good. Definitely for low temperature soft soldering though.

[Richard ParsonsParticipant @richardparsons61721]

 

Be careful of rods like Silfos, Copperflo etc. there was an article in M.E. in the 80s/90s which discloser that these rods are attacked by sulphur.

[Michael Cox 1Participant @michaelcox1]

I have used borax for flux when silver soldering. My technique is to apply the borax as a paste, heat the workpiece(s) up and when the borax melts to a clear glass then apply the solder.  By heating before applying the solder, then you can bring the borax to its active state before filling the joint.

Mike

[Speedy Builder5Participant @speedybuilder5]

Off topic / On topic,  I don’t know,  but the topic is FLUXES. 

 

For lead soldering stainless steel, use Phosphoric acid – Jenolite does well as a flux, but be carefull of the eyes, and if using a lot, do it outside as it doesn’t improve your tools when it condenses on them.

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