Brazing advice needed!!

[velocette]

Here Goes I'll stick my Totally Biased Opinion on good Brazing-Silver Soldering technique. All advice offered so far is good practice.
The bit that I would like to add is that you use the flame and hot gas stream to protect the area of molten metal at all times by NOT flicking the flame sideways on and off the area to be Joined!!!
Move the Torch closer or further away from the joint keeping the flame on the area you are working on this will allow you to control the temprature of the molten puddle from liquid to solid.
The Enemy of molten Silver Solder is AIR.
Whatever source of heating is used it is the hot and almost inert gas that is the flame and hot gas stream that will protect the puddle.

 

[C.BRAXMAIER]

I have found that tinning flux works great too.


http://www.oatey.com/Channel/Shared/ProductGroupDetail/76/No_95_Tinning_Flux.html

 

[sunworksco]

I have used the Oatey #5 for soft solder for decades haven't tried the silver solder paste. I may try that soon. I have used a boron-based flux for decades for high-temp silver soldering with great success. I use silflos stick solder for everything except steam boilers.

 

[Jasonb]

I have found that tinning flux works great too.


http://www.oatey.com/Channel/Shared/ProductGroupDetail/76/No_95_Tinning_Flux.html

Don't think that is for hard soldering eg silver brazing or silver soldering as we call it in the UK which is whats being discussed here. Its made for lower temp solders which we call soft solder and you call silver as it looks that colour.

J

 

[Ken I]

The bit that I would like to add is that you use the flame and hot gas stream to protect the area of molten metal at all times by NOT flicking the flame sideways on and off the area to be Joined!!!

I agree with Velocette - once you start you do not remove the flame until the job is finished (not even to have a look see) - also the flame should be slightly on the rich side (particularly with oxy-fuel) which makes it a reduction atmosphere flame (it has an appetite for Oxygen which we want to keep off our work).

With large parts, a firebrick box not only keeps the heat in but keeps the parts shrouded in flame or reducing atmosphere from the flame - keeping the air out.

Ken

 

[terryd]

Bogstandard, you have taken my comments out of context. I never said that you couldn’t braze joints with a fuel-air torch.

To add further clarification - when accomplishing a socket-type brazed piping joint, or joining boiler tubes to a tube sheet, it is desirable to have the brazing material wet out and readily flow over the work piece - in which case a fuel-air torch could be used.

If you are attempting to join two “widgets” together, using a fillet joint for example – you are unlikely going to obtain a pretty and uniform fillet bead along the joint (one that looks like a weld), if you blast the parts with a fuel-air torch. The filler metal will tend to wet out all over the work piece, leaving a very thin and weak fillet at best.

The overall heat input into the part is minimized when you have a very hot and localized heat source. Oxy-fuel torches make it easier to contain the filler material within the joint (to create actual fillet beads – like they’ve been made with a TIG torch in a welding process.)

For this reason, oxy-fuel torches are MUCH better suited for joining “parts” together.

There is little difference between bronze brazing, silver brazing, and soldering – other than the heat input and flux requirements.

Just a point here. To prevent what you describe as 'filler wetting' all over the place, it is usual to use a resist. This can be as simple as a line of correction fluid (we use one called Tippex) drawn next to the joint. In the past in silversmithing which involves rather complex fabrications such as coffee pots down to small delicate items the material we used was loam - very pure soil - as a resist. A paste was made with water and a simple line of this painted next to both sides of the joint with an artists paintbrush. Solder (braze) will not run beyond this and remain in the joint. We always used a gas air torch. Solder creep is a very undesirable thing in silversmithing as you can appreciate. Such resists are easily washed off.

'Braze' is derived from 'Brass' so in the UK we tend to refer to the use of brass based filler rod as brazing, while the use of silver bearing solder is 'silver soldering and tin/lead as soft soldering (aka 'soddering' in the US which I believe stems from the French 'soudure' rather than the English 'solder'). However the terms silver soldering and brazing are often interchanged even here in the UK, which I think is a shame as it leads to confusion at times as we have seen in these debates before.

I find that oxy - fuel flame is too hot and localised, it is too easy to burn the job if the flame is not reducing and stresses can be set up in the finished product. In critical situations such welds need to be stress relieved.

Regards

Terry