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Silver soldering question

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benchmark:
Til now i have always used tin solder to do my small boiler work.
As my boiler projects get bigger i decided to get some silver solder and use that instead. After watching numerous instructional videos on youtube and reading DIY guides on the net i tried it a couple of times yesterday with poor results.

The flux just gets brown then burns away into a crust without liquifying. From what i have read the flux should liquify to clear flowing fluid indication its time to apply the silver solder. this does not happen i my case .
I have tried on both copper and brass with same disappointing results, could it be that the surfaces need to be cleaned more thoroughly?


I am using this flux and solder (it is specified for model making)
http://cgi.ebay.co.uk/Silver-Solder-1-5mm-Flux-Kit-Brazing-Model-engineer-/360334888469?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item53e5a20e15

and i use a handheld propane/buthane torch

Gerhard Olivier:
Sorry can help, but is very interested in the answer as I have a fair bit of silver soldering that I need to do and dont want to buy the wrong stuff.

Any help here would be appreciated by me also.

Gerhard

PTsideshow:
Can't help with the solder or flux as, I'm on the other side of the pond. I will say that the material to be joined has to be CLEAN, CLEAN, CLEAN. Yes really clean and at the proper temperature for it to flow.

The other thing is it isn't soldering, it is  silver brazing at these temps. So soldering techniques don't work well.

You can use a pickle to clean the parts, rinsing and then dry before soldering,  pool reducer Ph down works good and is cheaper than the Sparex brand. Citrus acid also works, keep finger/skin oils off the parts.

The proper temperature is a must along with keeping the flame tip ahead of the solder. Heating the materials and drawing the solder to the joint. And not overheating the solder or joint.
The 5 most common jewelry alloys have a flow point from 618'C to 809'C  1145'F to 1490'F

With flux at times less is more. The speed at which you move the torch and the distance the tip is away from the join are things that come with practice. the type of metal, the size and thickness all will play a role. The solder also must be clean.

For jewelry/art metal work the paste fluxes which are a lighter weight, and start out either as a petroleum jelly based with borax added, it also can be a mixture of boric acid and gum tragacanth with a little water to form a paste.

And the solders are different in their alloys and flow temperatures, in jewelry the use of easy, medium, and hard solders. Which refer to the melting and flow temps, so complex constructions can be assembled with out previous solder joints coming apart.

The nice thing about the jewelry silver solder is the sheet version can be cut and placed at the join to minimize the excess and to control flow. It is available at any jewelry supply house locally or on the net.

For small scale work it does a great job.

You will have to check on the gas you are using in your torch, for the general temp it hits you will want it to be above the flow point of your solder.

The other thing to remember is that copper and brass are heat sinks and require more input of heat to do the job.

They have a new generation of torches that will raise the temp with propane to high enough temps to silver solder. EZ torch brand is an in house jewelry supply brand here in the states.


This is one, it is sold under the brand of Shark,


This is the other common use torch for silver soldering, whether AC & heating, or silversmithing.
This is an air/acetylene version generically called a prest-o-lite torch

Here is one of the largest producers of brazing wire etc. this is their knowledge base, section be sure to read the brazing book

Hope this helps :thumbup:

Bernd:
Sounds like you aiming the flame right at the flux. Try heating the metal around the flux to a dull red. The flux should start to turn on you and get clear. Apply silver solder and remove heat. Try that on a couple of prcatice pieces. Remember heat the metal not the flux. Let the metal heat the flux.

Hope this helped some.

Bernd

sorveltaja:
Benchmark, it sounds like you have used wrong kind of flux, despite the product's description.

What you described about that flux, how it gets brown and burns away, reminds me of soft soldering flux.

I have used two different brands of silver soldering flux, one works really well, but with another I just can't get good results. Don't know why :scratch:.

So there seems to be differences even between silver soldering flux brands.

One, that has worked for me is Felder's "CUFE Nr. 1".

Better yet, if you can find silver soldering rods, that are coated with flux. Those, that I have used, are yellow coloured, and look quite thick, but inside the flux coat is 1.5mm rod. Works like a treat. There is some specific name/brand for flux coated soldering rods, but I can't remember what it was :hammer:.

Unfortunately it takes sometimes trial and error to find a working combination, when beginning that silver soldering thing.
But when found, silver soldering could be even easier, than soft soldering.

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