Soldering

Two questions (greedy in one post, I know).

I'm trying to do some silver soldering. I've done electronics soldering and plumbing soldering, but I seem to be getting this one wrong.

Top right of the picture is what I'm trying to solder. a bit of 1 inch square mild steel onto a mild steel bracket.

I've tried with the newly bought silver solder (and flux powder) and then with my plumbers solder and flux.

In the case of the silver solder, I got the items to dull read heat, but the solder would not melt when placed on the join. It would soften in the heat of the blowtorch.

In the case of the plumbers solder the metal was hot enough to melt the solder on contact, but it would not flow under the join.

In both cases, I'd sanded of filed the surfaces back to metal. In the first try I'd raised little bumps with a centre punch all over to make sure there is a gap (having read conflict views in this forum, I thought I'd try both!). This was likely filed of prior to the plumbers go.

My second question is 'can I use the plumbers solder and flux on steel and the like?'. As I already have it and silver solder and flux is not cheap.

As usual any help would be much appreciated!

Iain

Hmm.

Either you could look at the picture in a mirror - or allow me to correct 'top right' to 'top left'. Gawd! No wonder my pieces come out wrong...

Iain

If you are struggling to get the job hot enough for the silver solder to melt you may be also exhausting the flux. Silver soldering flux is an active material and does not last forever. I think you need a brighter red than dull to melt silver solder. Soft solder will contaminate the job and inhibit silver soldering. Your soft solder flux says it is ok for mild steel but i prefer a more aggresive flux like bakers fluid. If you overheat the job for soft soldering you will form an oxide film that soft soldering flux will not be able to clean and again flux cannot do its job indefinately.

Mike

Call it 'stage right' Iain

MichaelG.

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P.S. ... I'm sure that CuP will be along soon, to explain about the Soldering.

FWIW.. I would Braze the mild steel pieces with Brass/Bronze rod; you need to get the steel to a bright cherry red ( the larger steel block will take some heating ) & use a brazing flux such as Sifbronze to have any meaningful result. otherwise it would be better to weld the pieces using MMA/TIG/MIG

George.

First off, plumber's solder and silver solder are very different things and require totally different temperatures and fluxes to flow. Plumber's solder melts at around 230-250C and silver solder around 650-750C. Both require a flux to prevent oxides forming when heat is applied, but the fluyxes are very different. Silver solder creates far stronger joints than plumber's solder., but although either can be used to join steel items, silver solder is the recommended way to go.

The flux for silver solder is usually sold as a powder that is mixed with a little water to form a thin paste with the consistency of thickish cream. A drop of washing-up liquid will help it wetting the work. It is also possible to get the flux as a liquid.

The basic process is to flux the surfaces that you want to solder and then start heating the joint area with a blowlamp. The joint area must be clean - solder will not flow over dirt or oxide. The flux does a certain amount of cleaning, but don't rely on it entirely.

Initially, the flux will bubble and become slightly foamy, but will clear with continued heating. Typically, the solder wire/rod is dipped into some flux and then touched onto the joint area. If the joint is hot enough the solder will melt and flow into it, otherwise remove the solder and continue heating. The solder will flow towards the heat, so it is important to heat the joint and remember that small items heat up quicker than large items. Play the flame mostly on the large item so that the joint area for both reaches the correct temperature at the same time. If the solder melts into balls that don't flow into the joint then the the joint isn't hot enough - or you have taken too long and burnt the flux. Two or three minutes is too long. If this occurs, cool the job down, remove the burnt flux, clean the joint and start again.

I hope this helps.

If the silver solder won't melt when touched to the work, then the answer is simple - it isn't hot enough.

Plumbers solder will work on steel, but is much less strong. The Laco flux is rosin based and I don't find it aggressive enough for bulk steel, try Fry Powerflow which is a paste that contains hydrochloric acid. Powerflo is not nice stuff and will cause corrosion if you don't claen off every trace of it afterwards.

Neil

Hello Iain.

Not to be sidetracked I return to your original request about soldering.

First off - neither of the two fluxes in the picture are suitable for use with what appears to be silverflo 40. There is what appears to be a JM label but unless there has been a dramatic turn around I do not believe that the material was supplied to you by JM. They do not supply it by the rod! And CuP do not use JM labels!

So what advice does your supplier offer? I would be interested to know.

Secondly. You should be able to melt the silver solder with a plumbers torch - as long as you are generating enough heat.

If the steel is a dull red the silver solder should melt a 40% silver cadmium free alloy

Thirdly, if you can melt the silver solder but it doesn't flow then change your flux to one with a longer life eg HT5 from CuP Alloys.

Fourthly, if you can't melt the silver solder then use a lower melting point alloy eg 455 from CuP Alloys.

Why do I keep plugging CuP Alloys - because they are the company that can supply good quality materials and give the technical help to get the right results.

Silver solder is expensive ..... especially when it doesn't work!

Keith

Keith if you look closely at the "lable" it is infact a printed photo of a JM cardboard tube with the lable on it, common for e-bay sellers to use this when they split it down into smaller quantities eg 10 (short) rods.

Most sell with Easyflo solder which going by the size of the metal in the photo and a "blowlamp" was probably exhausted before the work got upto temperature.

Iain, Try it on something small and then that will rule out any fault with the flux, that then leaves you needing HT5 or Tenacity No5 and/or a bigger heat source.

Edited By JasonB on 11/12/2018 12:40:49

Iain's photo looks very like my early attempts. The cause in my case was insufficient heat coupled with taking so long trying to get a flow that the flux went off. I don't think my inexperienced technique helped either - I was distinctly sluggish!

I'm still not very good at silver soldering but buying a bigger torch and arranging insulating bricks around the job to keep the heat in made it a lot easier!

Dave

Totally agree, not enough heat , torch too small not delivering the quantity needed but the temperature of the flame is enough to burn off the flux. I tend to find that easy flo flux is not as good as tenacity no5 type ( for extended heating and stainless) when working with steel fabrications. Add a drop or two of washing up liquid to the mix, it helps the flux to “wet” the metal and provides a small measure of cleaning action

Edited By Zan on 11/12/2018 13:39:26

So the long and the short of it appears to be that I can't get enough heat out of the torch to heat up the lump of steel that I have.

That or I need to improve the hearth.

The blowtorch is about the most powerful that B&Q stock (I'm expecting comments here about buying proper kit) - which may not be enough.

It took quite a few minutes to get the metal near red hot by which time the flux had clearly gone.

The flux that came with it is a white powder which I have mixed with water and a drop of fairy. I rather think that I've made it too runny which won't help it stick.

I have managed to (apparently) solder a smaller item, though without cutting it open I don't know how well the solder has spread.

Would putting a brick over the top of the back of the hearth help it heat up quicker, or is it just not enough grunt from the torch?

I think for the moment I will just tap and bolt the bits together. Sigh.

As always many thanks for your help.

Iain

In terms of "sufficient" Iain - sometimes 'retaining' what heat you already have available can make enough difference between it working ok or not.

Ceramic blanket is not too expensive (I think I paid about £6 for my last one) and does help with larger pieces when brazing or silver soldering. It's not perfect for long term use like this but is a good solution if you don't want the bother of a buying a proper brazing hearth.

If you've tried to soft solder these pieces, you will need to completely remove this before attempting silver soldering by filing or machining a few thou off any contaminated surfaces.

Regards,

IanT

My only qualification for offering suggestions is that I had trouble too. There are a few things to get right and it pays to tick all the boxes. I think silver soldering and brazing is much easier to do when you have plenty of heat from a powerful torch. I make do with the cartridge kind, but they are relatively limited.

It's easy to use the wrong sort of firebrick for the hearth. There's a type designed to soak up and retain heat. Heavy, dark and solid. Mine came from a night storage heater. They resist flame extremely well but you probably don't want to use them because they can eat all the heat a small blowlamp can throw at them. Only after you've fully heated a hearth made of these can you start soldering! The other type of firebrick is intended to insulate. Various materials, but typically light weight, whitish and soft. They reflect rather than absorb heat so more of it concentrates on the metal.

To maximise heat from a smallish torch, I find it best to shield the job inside a kind of insulating oven structure made of insulating firebrick with an insulating floor. It has front and side walls and a bit of a roof, leaving just enough access to comfortably access the job. Nothing special or permanent about it - a few loose insulating bricks arranged to suit. You need a lot more heat on an open hearth than a shielded one.

Flux, metal and solder all have to be compatible - see CuP Alloys advice. Flux moistened rather than wet.

In my experience small DIY blowlamps are a bit underpowered for your lump of metal, but I've used the next size up successfully on that size.  I experimented with two small torches and found it didn't help - time wasted faffing with two heat sources spoiled the joint. Someone more skilled might have done better. Butane torches produce more heat than propane.

Practice, practice...

Another mistake I made was not setting the hearth up so it was comfortable to work with. To reduce the fire risk and shelter the flame I built it low and had to sit on the floor to use it. Not smart. I did far better set up outside at waist height on a still day with plenty of room and no distractions. Getting hot quickly and applying solder at just the right moment is important - no dithering. When soldering works properly it's easy. With limited equipment and skills it can be a pig.

Dave

Edited By SillyOldDuffer on 11/12/2018 16:07:48

Iain,

Here is an example of a small fabrication that was brass brazed (which needs more heat than silver solder). It is surrounded by ceramic blanket (to throw the heat back) and also stood on a thin tin stand (which doesn't leech the heat away). So take a little time to make sure everything is both clean and set-up to retain as much heat as possible and then get the heat into the larger piece as quickly as possible - trying to avoid direct flame on the fluxed area to begin with - until you have heated the main mass. Someone else has suggested practicing with some scrap to get an idea of how it all works - and that's a good idea the first time around.

Keep trying - not all of my attempts work first time around - even when you think you've 'mastered' the art. I just go back and clean everything back to clean metal and try again..

Hope this helps - good luck.

IanT

For a lump of steel like that you want a torch that has a burner capable of putting out at least 7kw, although a canister blowlamp may claim to have a hot flame it is the size of that flame that matters more. This will empty a can in no time so really worth getting a decent sized torch and burner from the start and an inexpensive propane bottle, it will work out cheaper in the long run.

You can also help things along by part machining any fabrication to reduce the mass that needs to be heated, for example when I'm silver soldering up steam engine cylinders I will bore them say 2mm under finished size so I'm only heating a "tube" then when they have cooled I can pop the assembly back in the lathe an treat like a cored casting.

Edited By JasonB on 11/12/2018 16:36:07

Iain,

You need something with a lot more muscle like this one https://www.screwfix.com/p/bernzomatic-propane-mapp-gas-trigger-start-brazing-torch/71976 or a much bigger torch on a hose. The Bernz will solder pipes with some water left in them and work upside down. The cheap disposable ones are only good for burning paint and plumbing. It's much cheaper to use a big torch on a hose from a bottle.

If soft solder is good enough for your needs, then tin both surfaces separately first, then put them together and reheat with more flux.

Edited By Dave Halford on 11/12/2018 18:22:22

Can anyone tell me how the Rothernberger, Bernzomatic and Bullfinch compare to the Sievert in terms of power? The Sievert (at least the CuP site) tells me how many kW. I can't find it for the others?

Also, can I use these burners both with disposable canisters and the re-fillable big bottles?

My hearth is a bunch of insulating breeze blocks (forgotten the trade name) which I just put on my bench. If I thought I was going to really go mad, I'd put some metal plate underneath, but they don't seem to need it.. I did buy some firebricks to start with, but they just soak up the heat.

Iain

Benzomatic TS4000 on mapp gas puts out about 2KW/h and the TS800 about 4kw/h Rothenberger will be around the same figures.

Thermalite/celcon won't do a lot to help things you need a refractory brick like with a vermiculite base.

So the Sievert at 8kW (more with the right nozzle) is a lot more powerful?

Iain