Silver soldering (Brazing ?) and Flux

[picclock]

Hi

I'm just about to try my first silver soldering on some steel using Tenacity 5 flux and 842 silver solder. I've read the threads about preparation and I think I'm OK there.

The flux comes in powder form with instructions to mix to a creamy paste with water. Once mixed will this keep in an airtight container (if so how long), or is it necessary to mix it fresh every time ?

Some suggest adding a small amount of washing up liquid to the flux, presumably to improve the wetting action of the paste. Is this is needed or advisable ? I presume we're talking about a very small amount, possibly of the order of two drops in a mugfull of water which is then used to mix the flux paste with.

I have an infrared thermometer gun which can measure temperature. Sadly it only works up to 500C. I'm wondering if I can increase the range by fitting an aperture to the infrared lens (just a cardboard washer or similar). Has anyone else done something similar ? or is there a better way of measuring the temperature (I know about the flux turning clear thing - but I'm more concerned about inadvertent overheating).

For holding the pieces together I'm making up a couple of steel clamps.

I'm hoping to attempt one or two practice joints today, which I intend to cut open to see how well the joint has penetrated.

Best Regards

picclock

 

[Blogwitch]

An old film canister is ideal for storage. A heaped teaspoon of flux, the tiniest spot of washing up liquid and add water to the correct fluidity. I have it so that it doesn't drip off the brush.

Mine has been on the go for well over a year now. As it dries a little, even to the stage of going solid in the bottom, I just add a drop more water and give it a good stir, that way it is ready for use anytime.

As always, heat the major part, NOT the joint, try to keep the flame well away from the flux and solder on the surface, both will flow towards the heat automatically as the part heats up, and so forms the joint. You will see it all happen in a couple of seconds from reaching the correct temperature, and then you remove the heat.

If possible use pallions rather than feeding by rod, only after those have melted and run should you attempt to feed a bit more in by hand, just to fill any gaps or make larger fillets. If you have the correct sized pallions, you shouldn't really need to feed any by hand, it is a waste of the solder. You will gain no more in the strength of the joint by piling more solder into it.
Be careful if you are feeding by rod, you can waste a lot by the solder running thru the joint and dripping out the other side, where you can't see it.

Forget all your mumbo jumbo about temp gauges etc., everything will happen so fast, if you start to play about with silly things like that, you will cook the part. Just get the joints set up and heat it up, if you've prepped right and got the heat source coming from the right direction, you should end up with a good joint, if you don't, then you are doing something drastically wrong.

BTW, forget all about using clamps. Not only will they take the heat away from the job, they will also close up the gap that is required for the solder to flow.
What I do usually is assemble the parts to be joined and if needed, gently rest a small bar of steel on the top to hold them in position (make sure it can't be soldered to the job). As the solder flows, there will be enough force due to capillary action to allow full penetration. The other way is to wire wrap the parts together, I sometimes use thin garden wire with the plastic coating stripped off, just enough to hold the parts in position. Keep the heat away from the wire, as it will melt it if you get too close.

Most times, I use nothing at all except for the good fitting of the parts together initially to keep them in position.

Bogs

 

[John Rudd]

If possible use pallions rather than feeding by rod, only after those have melted and run should you attempt to feed a bit more in by hand, just to fill any gaps or make larger fillets. If you have the correct sized pallions, you shouldn't really need to feed any by hand,


Bogs

Bogs, What are pallions please? Not heard that expression before... :-[

 

[cidrontmg]

Bogs, What are pallions please? Not heard that expression before... :-[

Small (1 cm2 or less) square bits of thin metal sheet. In this case silver solder sheet cut into small pieces.
Pallions/paillons (same thing) are square, paillettes/palliettes (same thing) are round.
Sequins are larger (small coin size but thinner), usually round (but can be square also), same sort of things.

P.S. In this case, if you don´t have solder in sheet form, you can also do pallions with hammering a round stick of solder flat, and cutting it then to pieces.

 

[Blogwitch]

John,

Olli has it spot on, but I usually refer to pallions as small pieces of solder laid around or along the joint, sitting on top of the previously flux painted area. If soldering say a tube into something, I will put a ring of formed solder wire around the joint where the pipe enters the part.

I also very rarely use the larger 1/16" (1.5mm) rods, preferring to use the 0.020" (0.5mm) wire instead, but I also use sheet form that is about 0.004" (0.1mm) thick. The main reason being that the more you use on the joint, as in hand feeding, the more solder is wasted. If the gaps are correct, 0.002" (0.05mm) for an average joint, only a tiny amount of solder is required to completely fill that joint. Any more and you will be cleaning and filing it off afterwards to tidy things up.

This shows how it works.

The clean parts are assembled with flux down into the joint, a little more flux is added to the top of the joint and a small 1/3rd of a ring of solder (my pallion) embedded into the flux.

Transferred onto the hearth, you can see the tiny bits of raw solder.

The parts were heated up by playing the torch (a standard throw away can plumbers torch) at the bottom where the parts are resting on the fire brick. You can see the burn marks on the firebrick where it was heated up. The solder flowed within a matter of seconds, as I progressed along the line.

Half an hour in the citric acid pickle bath. You can see that there are just perfectly formed joints with no solder wastage

After a little clean up with wire wool and assembled with other parts.

No eye of newt, tail of guinea pig or any black magic or mumbo jumbo at all. Just clean, assemble with flux and place solder, heat up, take the torch away as the solder flows, clean up.

Job done.

I can't remember how many times I have gone thru this teaching routine, but people still have problems. I just can't explain it any easier.

For people who don't believe only tiny amounts of solder are required. This copper tube/steel joint was taken to the point of destruction, and the joint showed no signs of giving way.

Bogs

 

[compspecial]

That's amazing Bogs, that silver solder is tough stuff and you have really got it bonded to the other metals! great technique.

 

[IronHorse]

A trick I use from my days as a jeweler, I pound some solder wire flat, cut off several small pieces and place them on the fire brick. I then take a 6" length of coat-hanger wire and file to a point. With the torch I melt the solder into a ball and pick it up on the end of the wire and then I apply it to the joint. I never had much luck placing the solder on the joint first, it always migrates to one side ???


IronHorse

 

[picclock]

That's a very impressive steel copper joint, Bogs. My parts are quite a lot bigger and steel. To be precise a 10mm thick lap joint on a curved piece 15 mm wide. I have read about your method before, but because of the type of the joint (15mm wide and about 20 long) I can only access one edge of the joint so I'll be relying on the flux solder combination to wick it a long way inside.

I have 1.5 mm silver steel so I'll test it with one piece. In theory this should be more than enough to fill a 2 thou gap 20 mm long (assuming I can get a 2thou gap). Like the idea of centre punch marks

I'm not too worried about the cleaning up as I will be machining the part afterwards.

I was hoping to get the test piece done today but the weather is pants. As I have to do it outside I will have to wait for the next dry day .. . :-\

Thanks for the info

picclock

 

[mklotz]

I was hoping to get the test piece done today but the weather is pants.

Ah, British English. Always something new to learn.

For the benefit of my fellow colonials...

Noun/Adj. Nonsense, rubbish, bad. From the standard British English of pants, meaning underwear; also a variation on 'knickers'. E.g."The first half was pants but I stayed until the end and it was actually a great film." [1990s]
Exclam. An exclamation of annoyance or frustration.

 

[Jasonb]

Pat you can get a solder (AG 304) with slightly less silver and a lower melting point that is supposed to be better at gap filling.

The problem with trying to fill a large gap is that teh solder will tend to just run out of the joint at the moment you think you have it filled

It is possible you playing the flam as the solder flows and feding in with the stick of solder when the heat is removed and the part cooling to build up a fillet. I use this method quite a bit when fabricating parts that would have been cast or forged and therefore had internal fillets, you end up with more solder than needed for strength but it looks right.

Like the fillets between the weight and arm on these flyweights or the fillet on the insides of this brace that was fabricated to look like a pressing - dressed on teh externals and filleted on the internals. I think I used 2.5mm rod on that one, any thicker plate and weld would have been a better bet.

J

 

[wesley]

Dam fine work there that man
wes

 

[John Rudd]

Bogs, et -al...

Thanks for clearing that up..Great techniques by the way...

 

[zeeprogrammer]

I can't remember how many times I have gone thru this teaching routine, but people still have problems.

Different people.

Teaching means teaching the same thing to different people (at different times). It's not a forum with always the same people.

I appreciate the patience a teacher has to teach the same thing over and over.

Thanks for being a teacher Bogs.

 

[mklotz]

There are also an astounding number of people who are incapable of learning something until the exact moment when they have need of the knowledge.

 

[dsquire]

There are also an astounding number of people who are incapable of learning something until the exact moment when they have need of the knowledge.

Marv

That statement hits the nail squarely on the head. :bow: :bow:

Cheers

Don

 

[cl350rr]

There are also an astounding number of people who are incapable of learning something until the exact moment when they have need of the knowledge.

or shortly there after

 

[zeeprogrammer]

I reread my post and realized it may have come across sarcastic. Didn't mean to.
I do mean...

Thanks for being a teacher Bogs.

 

[Ken I]

I couldn't possibly improve on what Bog's has to say on the subject but I would add that once you "know" how to do it you quickly forget the frustration of your early attempts - it seems so deceptively simple to a casual observer.

Basic rules are preparation, preparation, cleanliness, cleanliness cleanlness. Preflux apply pallions (new term to me as well) heat as rapidly and evenly as possible starting with the heavier sections.

Do all that right and the silver solder joint happens by magic - if you are poking it around with a rod and struggling - odds are you are doing it wrong - probably started wrong and went from bad to worse.

I love silver soldering things - its one of those jobs I look forward to - it wasn't always so !

Ken

 

[Blogwitch]

I don't know if anyone followed Stew and his building of a 3.5" gauge loco. That is a long term post, but last summer, we both got together at his place to solder his boiler together.

We used exactly the same technique that I showed, but with thicker rods 1/16" (1.5mm) for the pallions instead of my skinny stuff, and I think he used a length of 1/8" (3.2mm) for filling in any gaps by hand.

OK, we did use a couple of much larger propane burners, one for main heat and one for localised heating. But that boiler behaved exactly the same as the small stuff we do, it basically soldered itself together when it got up to temperature. All you have to remember is to put enough solder and flux on the joint to fill the gap, and get enough heat into the job so that the solder will flow. The rules are the same whether it be a small or large job.

Ken has really got it right, and I actually look forwards to doing a little silver soldering (brazing) purely because that, as he says, once you have the 'knack', it is really very easy.


Bogs

 

[Ken I]

Bog's mentioned a plumbers burner for larger pieces - this made me think of something else that hasn't been mentioned.

When using an oxy-fuel torch - it should be set rich - a reduction atmosphere - the surplus fuel tends to "eat" any oxygen molecules and prevents (or at least hinders) it oxidising your work.

Similarly when using a propane torch I try to keep the work immersed in the flame to reduce oxidation. Don't remove the flame to "check" what's going on and try to avoid using too small a torch - it takes too long and if you have to chase the heat all over the place you are going to get a lot more oxidation.

If your torch has an airflow adjuster - keep it slightly on the rich (reducing) side as opposed to lean (oxidising).

Sure the flux will take care of this problem at the joint but if you missed a bit and it oxidises before the flux runs there it will probably cause problems.

The Devil is in the details.

Ken