Use of Harris Safety-Silv 56

Silver brazing is a great way to join things provided the joint is designed for brazing. The biggest drawback is the cost of the alloy, but you only use a very small amount.

They use silver brazing for through hull joints on submariens. There the disadvantage is that using xrays to check the work does not work well.

Lucas Milhaupt has a great booklet on brazing. You can download it here.

Dan

for brazing. The biggest drawback is the cost of the alloy, but you only use a very small amount.

disadvantage is that using xrays to check the work does not work well.

Thanks Dan,

Wilby

The main difference & drawback is strength. Silver "solder"/brazing is often plenty strong, but is not as strong as welding. A welded joint is as strong as the base material, because of the fusion between the added material and the base. Silver solder is more like glue in that the strength depends upon the bond between the solder and the base material, as well as the strength of the solder itself, whichever is less.

In practice this means that I use brazing to avoid the higher heat of welding, when the object is some gizmo that I'm making where full strength isn't needed. Even when strength isn't a big deal, I weld because it's faster (if heat isn't a problem).

You should be OK - just don't try to build a trailer with silver solder.

Bob

******************************* I was told that the flux for silver solder contained cadium...

It is normally the rod that contains cadmium and Safety-Silver specifically does not contain cadmium. In fact it is a recommended replacement for cadmium containing silver solder. (I suspect that is the reason for the name :-).

Cadmium added to silver solder decreases its melting temperature and makes it more liquid so that it flows better. But also damages the lungs and kidneys.

That depends.

A good 56% silver brazing/soldering alloy has a yield strength of over

60 ksi and an ultimate tensile strength of over 70 ksi (it's three times stronger than brazing brass, and it's stronger than mild steel) - that's the same as a E70xx series rod.

More, if used in joints with thin but well-controlled gaps a well-made joint can have a yield strength considerably higher than the bulk strength of the filler, sometimes in excess of 130 ksi - that's nearly four times the yield strength of A36 mild steel, and stronger than all but a E130xx welding rod (do they make them?).

It's tough stuff.

Yes, if the joint is badly designed or badly made it won't be strong - but the same is true of a welded joint.

Technique is different, but neither seems to me to be much harder to get right than the other (I have done quite a lot of silver soldering/brazing over the years, but only occasional stick welding).

The real reason for not making a trailer with silver solder is however simple - it's expensive!!

-- Peter Fairbrother

A welded joint is

Thanks to all for the information and suggestions.

I'll skip the trailer project and let you real welders build them.

I only wish that I knew about this stuff when I was a teenager, it would have made many projects a reality rather than a dream. On the other hand I might have used a cadmium alloy and now be a basket case who culdntt spll ur ritte sooo wellle, hee hee.

Wilby

You do not have to be a "real weldor" to make trailers.

My first real welding project was a trailer. Everything before was just a few pieces of this and that welded together for practice.

To make this trailer, I used 7018 stick welding and a generous amount of advice from this newsgroup.

Five years later, I still use this trailer often to make money and move small stuff, it is a great trailer. I send my guys with it behind a pickup truck, anyone can tow it without any problems. I painted it with cold galvanizing panit and it is not even rusting.

i

Ignoramus:

Thanks for the encouragement, the trailer looks great. I believe I'll stick to smaller jobs for now.

Wilby

Good to know, thanks. A man who clearly knows more about it than I do ;-). (The beauty of usenet - always learning something.)

Will the badly made joint still have the "bulk" yield strength of the silver solder? I.e., is what's lost is the extra strength of the well-controlled gap?

Bob

That depends largely on how badly the joint is made. Assuming that you got adhesion throughout the joint then the worst off you will be is the material strength of the joining material.

Brazed joints are usually designed to equal or exceed the strength of the parent material due to area. If your braze material has a tensile strength of, say 50,000 psi and you design a joint with two square inches of surface then, assuming good technique, one ends up with a joint that will support 100,000 psi.

If the parts are well-wetted, then usually the joint will have the strength of the bulk solder. If they aren't - perhaps the surfaces are only wetted in parts, or there is a layer of summat between metal and filler - they can be really weak.

There are other possible causes of weakness, like inclusions, or material incompatibilities, but by far the most common cause of unexpected failures is bad wetting (usually caused by dirt on the parts, or sometimes lack of heat or flux, or too much heat).

Ahh, that's magic. :)

Suppose the thickness of the filler is such that a very strong crystal grows from one part to the other. In the bulk material, the crystals can slide against one another with comparative ease, but in a thin layer you have to break the crystals to break the layer.

It's not quite that simple, but roughly.

Peter F