Silver soldering/Brazing technique

[sunworksco]

The best gas combination is propane and oxygen. These gases leave less carbon residue and give the best temperature range. It is also less expensive to purchase. Yes. You can use only propane but it is a PITA.
Also, if you have access to a kiln, this is a very clean and efficient way to silver solder. Just clean, flux and place the solder on the joints.

 

[MuellerNick]

So - applying the flux after the preheat and slightly before the metal is probably the way to go. The question is - how are you getting the flux onto the joint?

With the silver solder rod. Or a screwdriver or whatever is near.

I don't see how you could do it in the manner of rod brazing (ie on the rod) since you normally snip off as smaller piece of silver braze as will do the job.

I almost never snip off the braze. I just use it off the rod. This implies that the rod melts when contacting the work, I never melt it with the flame because that makes the blobs some here do talk about.
If needed, you can chase the melt with the flame or with a steel pin to where it didn't want to go.

Also - I've been using oxy-acetylene as my heat source. Certain authorities (E.g. Kozo Hiraoka) say that propane is the way to go. Any thought on that?

Well, if someone tells you that you need propane, he is ruling himself out as authority. At least in my eyes. I do have 4 different burners, each one is good for some job, none is good for all jobs. O/A for big pieces, 2 propane for smaller ones and a micro propane/oxygen for small jobs.
With O/A, a rose butt is advisable. If you don't have one, use a soft flame and only the blue cone of the flame to heat up. Takes some practice.

Nick

 

[Jasonb]

There is another Silver soldering thread on another forum about type of torch and gas to use and this is the reply from one of the trade solder suppliers that has 35 years in the industry working for both Johnson Matthey and running his own company, I'm sure he won't mind me posting it here

"Beginners should steer clear of oxy-gas systems. The heat is too concentrated and you may find it difficult to heat the joint properly to achieve the necessary capillary attraction required to attain the complete penetration of the alloy and strong leak free joints.

Go for propane, it is cheap, effective, efficient and versatile. Get a variable 1 - 4 bar regulator. This will set you up to produce between 84 and 0.25 kw of heat from your burners. The best in the range is undoubtedly Sievert."

 

[sunworksco]

I have been a pipe fitter since 1969 and have used propane, Mapp gas, acetylene, acetylene/oxygen, oxygen and oxygen/propane and have soldered copper tubing over 6" in diameter. Oxygen/propane is by far the fastest and most efficient for my silver soldering. I not only use a full sized torch setup but also use the French made MiniFlam. It has the tiniest flame for jewelry. Over the years I have soldered over 100,000 joints. The best thing to do is start learning to silver solder with the less expensive Silfos solder and then graduate to the more expensive higher content solder after that. Silfos solder is ok as long as it is not used for a boiler.
I use a titanium stick for moving solder since solder will not stick to it.

 

[gus]

Hi Jason

Will stock some silver rods of 45% silver. IS this rod overdone for copper boliers?

Gus

 

[chucketn]

I want to thank all who have commentedand offered advise on the techniques of silver soldering/brazing. Alot of good info to think about and apply.

A little background on me. I havesoldered for electronics for many years. I actually taught highreliability soldering for the USAF for many years. I have also donesome plumbing soldering over the years using propane and mapp gas,even an old kerosene blowlamp. I have only silver soldered/brazedonce, and can't find that part now! So, I am familiar with theprocess and what solder flow and wicking look like.

I have my Dad's Proto torch set,regulator and acetylene tank that I intend to use for silversoldering/brazing. It needs a new hose, as the original is lookingdry rotted and I don't trust it. I'm looking for firebrick to make ahearth, and have found a local supplier for the solder and flux, anda replacement hose.

I have uploaded a photo of the parts Ineed to silver solder/braze.

http://i571.photobucket.com/albums/ss157/chucketn/DSCF1344.jpg

The part, shown assembled at the top,and the 3 components at the bottom, is a connecting rod for a modelsteam engine. The clevis on the right end does not get soldered. Theflat part on the left gets soldered to the end of the rod in theposition shown at the top. The rod part is run of the mill 3/16”CRS rod, not modified other than faced in the lathe and threaded forthe clevis. The flat piece is 1/16” crs plate, drilled and tapped2-56 on the outaide holes and drilled 3/16” in the center.

As made, the flat piece is a lightpress fit on the rod. I used a ball pien to tap the rod into the flatpiece on the anvil part of my bench vise to get a flush fit. I cantwist and pull the flat piece off the rod with my fingers. I used a3/16” drill to make the mating hole. If I use a #12 drill the flatpart is loose on the rod.

Hope this clears up your questions andgives you a mental picture of what I'm trying to do.

Chuck

 

[gus]

We have high pressure compresssor C.I. outer head and a steel valve body insert to silver braze.Despite going the highest silver content,reject rate due to porosity was high---------50%.
This was in China 2004 and Gus was the so-called Manufacturing Consultant. Straight off I advised Gus knows nothing on Silver brazing.I recalled Ingersoll-Rand,India Plant used electric furnace to batch silver braze same parts and reject rate was constantly low but parts must be very well degreased and surgically clean.Advised them to use electric furnace. A week later a "thank you" note came.Problem solved!!!! Ha Ha .Gus knows nothing on Silver Brazing!!!!

 

[GWRdriver]

Chuck,
Hmm . . . smallish and delicate assemblies, so by all means do one of these . . . I'm going to assume you will end up with some wire solder, possibly 1/16", or larger. Take a short piece of wire and pound it flat on a flat surface (anvil, railroad rail, steel block, etc, but NOT a machine table) and make as much of a ribbon of it as you can get it. It's hard stuff and is going to take some pounding to thin it out. Once you have a tape or foil snip a narrow slice of the tape use this as you would a stick of solder. The reason for this is, it isn't going to take much solder to make these joints, in fact a WEENSY bit of solder is going to do it and 1/16" or even 1/32" wire is going to leave you with more solder around your joints than you want.

The other option will be to file some wire into a few grains of solder dust, mix it well with a dab of flux, and apply. The point is, it isn't going to take much to make these joints.

 

[Jasonb]

Looking at your parts here are a few thoughts

You definately want a slacker fit, a hammered in part is much too tight so spend some time working out how you will hold them in position, ideally the flat part should have been left over thickness so the finished fabrication can be held in the lathe to skim the face true to the rod, you will still have to do this but the less you have to take off the better.

As GWR says using thinned rod either fed in or made into a ring will save you getting too much on the job. One note on hammering it flat do it on a clean surface with a clean hammer, don't want to embed dirt into the solder.

Apply the heat to the round rod as that is where the bulk of the metal is.



J

 

[MuellerNick]

Theflat part on the left gets soldered to the end of the rod in theposition shown at the top.

I would TIG that.

You made a design error here. The rod should have a recess as long as the plate is thick. So you have a definite reference where the part goes to. Of course, the plate needs a smaller bore then.
A propane burner is the right tool here.
I'd file two flats on the rod's end (0.1 mm), a slight chamfer on the plate and stick the parts together. I wouldn't hammer silver solder plates as working from the stick works perfect. As long as you don't heat the rod with the flame. That is a common error that leads to those "tricks" with filing or hammering the rod.

Working with rings and ribbons is very common, but almost always only when furnace brazing.


Nick

 

[chucketn]

During my research for my silver soldering project, I came across the .pdf linked below. It has good info including pictures of a reducing flame. I had run across several references to a reducing flame but this is the first illustration I've found.

www.richard-whitehouse.co.uk/Soldering%20notes.pdf


Chuck

edited to correct spelling and spacing

 

[GWRdriver]

Chuck,
The URL doesn't work because it also contains a URL for HMEM and it takes us (or at least me) back to the HMEM first page. Simply plug in only "www.richard-whitehouse.co.uk/Soldering%20notes.pdf" and it will come up. Otherwise that is about as clear and thorough an instruction for hobbyists as I've seen.

 

[Ken I]

You can heat the part and let the heat spread to where it is needed but I would disgree with not applying the flame directly - however use a carburising / reduction flame (rich) and never remove the flame once applied until the job is complete - otherwise you allow air to your hot part and scale forms.

Use a firebrick nest to keep the heat and the burned gasses in - to keep the O2 out - and to help get to temperature as quickly as possible.

Use preformed rings of silver solder wire or foil (pallions) using a rod only as an emergency standby filler - there isn't time to try poking it in with the rod - this problem becomes more and more evident on larger / more complex joints.

As suggested in prior posts - practice on something of low value / prior effort.

Ken

 

[chucketn]

Harry, it works for me. I click on the link in my post and the pdf opens.

Ken, thanks for the input, added to my notes.

Chuck

 

[rdhem2]

Ken;
Thank you very much, well said. I am not sure exactly what you said. It may have been how you said it. But all the bells, whistles and lights just came on. I have talked with so many guys about this subject and I have gotton answers as wide as the Montana sky. But you nailed it, I think it was the remark about jacking around with the rod. Also your remarks about keeping the 02 out and co2 in make perfect sense.
Thanks again!!!!!!!!!!!!!!!!!

 

[goldstar31]

I think that you should take the advice of my wife ( who was no mean hand ) and think seriously about preventing silver soldering from running about 'unchecked' She used nothing more involved than a HB pencil around the proposed joints.
As for possible oxidisation, the old recipe was a paste made with ordinary blackboard chalk but there are now proprietory compounds- which I have never tried.

 

[Jasonb]

Tipex type correction fluid is what I use, the solvent based one.

Chuck see my comment on MEM regarding the Stay-brite solder you have bought not being brazing.

 

[Wagon173]

Not to hijack the thread, but as I was reading this I was thinking to myself that I had been quite good at oxy acetylene welding in school and have kept up with it to a degree since I've been out. I know in a few weeks, I'm going to come to a similar point where I need to solder something. Would it be possible to use one of the very small jewlers torches and skip soldering all together? Seems like it would be a whole lot cheaper to buy some sort of steel or aluminum wire instead of 50 bucks on an ounce of high content silver solder. Keep in mind the extent of my soldering experience has been with fixing wiring harnesses in trucks. I was looking at one torch that says it's capable of welding materiel as thin as .001" Obviously that weld would be very weak, but if you could adjust it to get decent penetration, do these small cranks and such warp even with a small weld?

 

[gus]

You can heat the part and let the heat spread to where it is needed but I would disgree with not applying the flame directly - however use a carburising / reduction flame (rich) and never remove the flame once applied until the job is complete - otherwise you allow air to your hot part and scale forms.

Use a firebrick nest to keep the heat and the burned gasses in - to keep the O2 out - and to help get to temperature as quickly as possible.

Use preformed rings of silver solder wire or foil (pallions) using a rod only as an emergency standby filler - there isn't time to try poking it in with the rod - this problem becomes more and more evident on larger / more complex joints.

As suggested in prior posts - practice on something of low value / prior effort.

Ken

Hi Ken.


I place preformed silver solder rings with a wee bitty flux on the copper boiler sockets. Found this to be best shot instead of poking around with rods.At 69 my hands are not that steady. For copper boiler end caps, I place 1/4 circle formed rings. Then clean up ,turn over and braze the other side. Results been good though I get some over runs. I use Mapp Gas. They now have a three burner torches. Have seen air-con tradesmen using it. They gave me some good tips.Come 2013 will dig out and complete a Colonial-Type Boiler kit bought ages ago. Will buy fire bricks to form up a make do brazing hearth.
Will post if it looks good. Need this bigger boiler to power some bigger slide valve engines.

Gus.

 

[gus]

You are right. I messed up two good parts before getting best results on a third piece.Silver Brazing can be very tricky.Brazing temperature got to be right.Tubal Cain has written a book on same subject--------Soldering and Brazing.
Brazing torches must have the power.Rod selection critical.

Gus.

Hi Goldstar Hi JasonB

Bought an air cleaning gun to match up with the China 1hp close couple compressor which cost me US$96.I could buy same for Rmb300 orUS$50 in China.
The Air Gun fitting had to be re-engineered to fit 1/4" hose with 1/4" hose barb.
Took the gurus seriously and used 40% silver rods. Heated the part to dull red heat and avoiding the sliver ring that I put into barb. At red heat and beyond,the silver solder did run beautifully.Mapp gas used.
Gus is very much a green Silver Brazer.Please view attached and tell me if there are any defects or improvement required.
Higher silver content is hard to buy.
Looking forward to expand the scope of my present machineshop activity with air compressor.