# Silver-Solder Question



## Korben (Oct 20, 2015)

I know silver-solder is required when fastening fittings to copper steam pipe.  I looked on Wikipedia and found there are many silver-solder alloys with different melting points.  Silver-solder with a melting point of 400-450 degrees Fahrenheit is available in most hardware store plumbing departments.  Is this the right stuff to use when assembling steam piping?  

Regards,
Korben


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## 10K Pete (Oct 20, 2015)

No. The problem stems with the terms. What you want is properly called
silver _brazing_ alloy. Too many folks who should know better use the term
silver solder when they mean brazing. The difference is the temperature.
Soldering is low temp (up to about 800*F) and brazing is above about
1100*F.

The usual for general use, like your fittings, contains 45% silver and goes
by many trade names.


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## Korben (Oct 21, 2015)

Thank you for the information.  I asked because I was confused about the terminology and I really don't want the thing to blow up in my face.  Is silver-brazing something I could learn to do with a Bernz-O-Matic type torch or should it be left to a more experienced hand with more sophisticated equipment?  

Korben


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## kiwi2 (Oct 21, 2015)

Hi Korben,
                  Although silver solder (sorry brazing alloy) can be useful, I have found that the resin cored tin/lead solder used for electronics is strong enough to be used for low pressure steam lines (up to say 20psi?) as long as the lines aren't in danger of being heated by a flame.
It's a lot easier to use than silver solder. Buy some liquid flux such a Duzall, apply it to both sides of the contact faces using a toothpick, heat up the work gently and touch the solder to the joint. It should give a nice neat joint.
Now I will wait for the howls of disapproval from people who probably know more about these things.
Regards,
Alan C.


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## bazmak (Oct 21, 2015)

Plumbers soft solder is low temp and should not be used on high pressure steam boiler assy.It can be used to give a steam seal on mechanical joints
Ie if you have say a rivetted joint than is mechanically adequate the soft solder will seal the joints.Silver solder is high temp and most commonly used is 45% silver this will give an adequate joint for working pressures of say 200psi
and can be used to join dissimilar metals together ie steel,copper,brass SS etc
Small joints can be done with a mapp brasing torch,larger ones ie boilers need 
oxy/acetelene.  Brasing or bronze welding is a higher temp and gives a stronger joint to include cast iron.Most model engs will use silver solder
for boilers and fittings.Most boiler assys are rivitted or screwed for ease of assy then silver soldered.Silver solder and soft solder do not mix.No doubt many others will want to comment. Regards barry


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## Swifty (Oct 21, 2015)

Korben, depending where you live, it will either be called silver solder or silver braze. It is confusing having different terminology between countries for the same thing. Here in Australia the use of silver based alloys is called silver soldering, whereas brazing is done using brazing rods, often bought coated in flux or used with a flux powder. The brazing rods don't flow well into gaps, but are great for building up nice corners when attaching parts together.

Paul.


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## V22 (Oct 21, 2015)

I use Oxy/MAPP for hard soldering. I also use the high silver content paste. The little oxy/MAPP torch does a great (fast) job that risks melting brass if I'm not careful. Cylinders are throw-away and purchased from the hardware store. They last remarkably long given their small size. Bernzomatic make one. MAPP was near useless on its own for hard silver brazing.


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## abby (Oct 21, 2015)

Just a couple of points V22 you are the only person to refer to hard soldering , the correct description for silver soldering .
Originally jewellers would use scraps of silver or even clippings from silver coins , generally  silver solders contain at least 50% silver and have melting points above 650°C
Brazing is a method for joining ferrous metals with brass rod or wire ,  and should not be confused with sifbronze welding where commercially supplied bronze rod is used with oxy-acetylene to form a fillet joint between ferrous items .
In the former the job is heated above the melting point of the braze which then flows by capillary action into the joint , in the latter the localised heat of the flame keeps a pool of molten metal progressing along the joint rather like gas welding.
For those who are interested copper wire can be substituted for the brass if enough heat is available , borax mixed with water to a creamy consistency makes a cheap flux.
As already stated some solders containing a small amount of silver  should be called soft solder , the bulk will be lead , tin or bismuth depending on its age or origins.


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## gus (Oct 21, 2015)

V22 said:


> I use Oxy/MAPP for hard soldering. I also use the high silver content paste. The little oxy/MAPP torch does a great (fast) job that risks melting brass if I'm not careful. Cylinders are throw-away and purchased from the hardware store. They last remarkably long given their small size. Bernzomatic make one. MAPP was near useless on its own for hard silver brazing.




Please advise source for High Silver Content Paste and Soft Solder Paste.


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## goldstar31 (Oct 21, 2015)

gus said:


> Please advise source for High Silver Content Paste and Soft Solder Paste.


Hi Gus,
            I'm one of the guys with this double distinctions City and Guilds Motor Vehicle Restoration things and this was simply one of the competences.
Soft solder paste should be available at automobile factors who supply suitable lead for filling car body panels. You'll know the lead thing the same as me as you worked for Metal Box 

As for the silver paste, mine came from Chronos in the UK but where else, I simply don't know. I would be having a word with your local dental mechanic, recalling that my late wife was an orthodontic consultant. Certainly, any dental tech. will know where to get borax as a flux. I had difficulty in getting borax from chemists because - it's a poison. However, I bought a clapped out MIG welder to restore and came away with a spare bottle of shielding gas and a jar of a sort of borax mixture which actually works.

Kills cockroaches as well- but I digress:hDe:

Regards

Norman


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## mcostello (Oct 21, 2015)

Has anyone used borax from washing powder to flux with? It is used for fluxing Aluminum when melting.


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## goldstar31 (Oct 21, 2015)

mcostello said:


> Has anyone used borax from washing powder to flux with? It is used for fluxing Aluminum when melting.



Yes but it didn't work. I simply couldn't find the time to experiment further and getting the real stuff was cheap enough. Life with my dear wife took precedence over cockeyed school boy chemistry and penny pinching.


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## Korben (Oct 21, 2015)

Thanks, everyone, this is an interesting and, I realize, complex subject.  

To clarify my immediate interest:  I have a Stuart S-50 stationary mill engine and a Stuart 500 Babcock boiler.  I also have a Stuart steam and exhaust piping set.  I need to shorten the steam pipe in order to make a neat installation in the space I have.  I have all the pieces but need to silver-braze a steam union liner sleeve to the end of my copper steam pipe to make the connection.  

I've done a lot of soldering in my time and I'm familiar with the welding and brazing processes.  I just need to get the supplies and a torch and experiment with silver-brazing.  You've all given me a better sense of direction on this.  

Where is a good place to shop for silver-brazing rod and flux?  

Thanks again,
Korben


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## chucketn (Oct 21, 2015)

Korben said:


> Thanks, everyone, this is an interesting and, I realize, complex subject.
> 
> Where is a good place to shop for silver-brazing rod and flux?
> 
> ...


 
It would help to know where in the world you are, to enable us answer your question.

Chuck


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## Korben (Oct 21, 2015)

Sorry about that.  I am in Southern California, USA.  I was thinking in terms of the type of store (plumbing supply, welding supply, etc.).  I'll also check E-bay.  

Korben


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## bazmak (Oct 21, 2015)

Silver solder 45o and flux can be bought at plumbers. the mapp gas torches 
at the plumbers or hardware stores


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## chucketn (Oct 21, 2015)

Mapps gas torches are available at the big box home improvement stores, silver solder and flux can be found at welding supply stores. Just ask at the welding supply store for someone that has actually done some silver soldering. My local AirGas  counter guy had no clue... Luckily, his boss was close by and heard my question and pointed me in the right direction.
Chuck


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## Dave Sohlstrom (Oct 21, 2015)

Your local welder supply house is your best source for good quality silver brazing alloys. You can also get the two types of flux that you will need, there is white and black. The black is for working with higher temps.
You can also get good propane torches and propane. Do not use oxy- act for silver brazing the flame temp is to high and you run a very good risk of melting the parts you are trying to join. 
When you are working on large parts that take a lot of heat it is a good idea to get some insulating fire brick that you can build a brazing table out of where you can surround your work to help keep the heat in the part. There are propane torches that have big tips on them an put out a lot of heat. Some times on large parts it is even necessary to use 2 torches.

If you are just starting out practice on something that if it does not work out you have not messed up your good parts.

Dave


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## Charles Lamont (Oct 22, 2015)

In the (these days unlikely) event that you have a paraffin (kerosene) blow-lamp lying around, that would do the job in question.


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## V22 (Oct 22, 2015)

gus said:


> Please advise source for High Silver Content Paste and Soft Solder Paste.


Waymill is the companies name. I usually buy via their Ebay listings as their site does funny things on the international shipping calculations. They sell a number of different soldering pastes. From "Easy" (lower temp) through to Hard high temp and 75% silver.

https://www.waymil.com/mobile/Product.aspx?id=38847

As for hard soldering with MAPP alone, I had no luck. My setup involves fire insulating bricks. MAPP would never get even small parts up to hard solder temperature (1300F / 700c). Silver solder is much easier with Oxy MAPP. Even with Oxy MAPP it can still take time to get a part up to the point where the hard solder flows.


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## gus (Oct 22, 2015)

goldstar31 said:


> Hi Gus,
> I'm one of the guys with this double distinctions City and Guilds Motor Vehicle Restoration things and this was simply one of the competences.
> Soft solder paste should be available at automobile factors who supply suitable lead for filling car body panels. You'll know the lead thing the same as me as you worked for Metal Box
> 
> ...



Hi Norman.

Thanks. Will buy tomorrow. Trust all is well at your end. Take care.


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## gus (Oct 22, 2015)

V22 said:


> Waymill is the companies name. I usually buy via their Ebay listings as their site does funny things on the international shipping calculations. They sell a number of different soldering pastes. From "Easy" (lower temp) through to Hard high temp and 75% silver.
> 
> https://www.waymil.com/mobile/Product.aspx?id=38847
> 
> As for hard soldering with MAPP alone, I had no luck. My setup involves fire insulating bricks. MAPP would never get even small parts up to hard solder temperature (1300F / 700c). Silver solder is much easier with Oxy MAPP. Even with Oxy MAPP it can still take time to get a part up to the point where the hard solder flows.




There are Mapp Gas Torch that come with twin torch or triple torch. I have seen Refrigeration Repairman using Mapp Triple Burner Torch to Silver Braze 3/4" Copper Pipe with ease. Foto follows.


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## chucketn (Oct 22, 2015)

I have tried using Boric Acid, sold here in the US as roach bait, as silver solder flux. I could not get it to work.

Chuck


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## abby (Oct 22, 2015)

Borax is the  flux for brazing  see earlier definition , it is not very good for silver soldering(hard soldering) .
Silver solder fluxes melt at a lower temperature than straight borax and contain potash (potassium carbonate) and flourides amongst other constituents.
Flourides when heated release hydroflouric acid which can be dangerous to health if working in badly ventilated areas.
If you can find a tried and tested recipe anywhere I will be suprised and grateful for a copy.
I have read the labels on dozens of products , looked at the specs published on line and done extensive googling but I have yet to find anything useful.
At the end of the day a commercially produced hard soldering flux is not expensive and for most people a 500 gm pack will last many years.
Manufacturers such as Johnson Mathey produce silver solder with varying melting points and fluxes for different substrates.
 Some copper alloys such as aluminium bronze require a very active flux to get an effective join.


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## bazmak (Oct 22, 2015)

Must disagree with the advice not to use oxy/acet.Yes it 
s high temp and thats the point.With care it can get to the temp quickly and with local accuracy.If you take too long getting to temp and the heat spreads too far it make a mess of any joint.As an old school time served welder i never used anything but O/A.Even the real small delicate items with an accurate wave of the tourch and bingo.Yes you have to be careful of overheating but its far worse not reaching temp and trying to melt the s/s with the torch and not the job.As we should all know the job should be got to just red heat then melt the solder with the job.If you put the flux on first and take too long with the torch the flux becomes a black mess and thats bad.I prfer to ore heat local and melt the flux which should be a clear colour the heat to temp and melt the rod ON THE WORK. hope this helps Regards barry


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## 10K Pete (Oct 22, 2015)

Welding supply should have what you need. 45% alloy and white flux.

And I should add that all I've ever used for heat in silver brazing was O/A
for part large and small. It's a very hot flame, yes, but you have the control
over the flame size and application to the work piece. One must learn to use it.

Pete


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## goldstar31 (Oct 23, 2015)

Barry and Pete,
 I must agree  but we understand the skills in using a torch to get into the weld pool and remove the dross or 'dottle' which causes porosity.
 Frankly, the skills of the old welders and other craftsmen are being lost and are being replaced  with something which does not bear thinking about.

However, might I thank you for your attempts to get the message over?

Regards

Norman


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## abby (Oct 23, 2015)

Oxy /acetylene is very useful but the cost of bottle hire and refills especially here in the UK would rule it out for most model engineers , I am lucky enough to have them but for most jobs I use propane .


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## V22 (Oct 23, 2015)

abby said:


> Oxy /acetylene is very useful but the cost of bottle hire and refills especially here in the UK would rule it out for most model engineers , I am lucky enough to have them but for most jobs I use propane .


And hence the Oxy MAPP. No bottle rental. Disposable cylinders.


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## Korben (Oct 23, 2015)

Considering all the good information in this thread, cost, availability, and my immediate need (to braze steam fitting sleeves to 5/32" copper pipe), I'll start by experimenting with a Bernz-O-Matic type torch with disposable gas canisters.  I presume that MAPP gas (without oxygen) produces a hotter flame than propane and would be the better choice.


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## bazmak (Oct 23, 2015)

Yes the mapp gas should work well with with small dia tube to fitting etc
i have no trouble with up to 12mm sq but will try oxy/mapp next if i can find it
Does it work with the mapp torch i have ????


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## V22 (Oct 24, 2015)

bazmak said:


> Yes the mapp gas should work well with with small dia tube to fitting etc
> i have no trouble with up to 12mm sq but will try oxy/mapp next if i can find it
> Does it work with the mapp torch i have ????


Bunnings sell the Oxy cylinders. You will likely need a new torch. The oxy needs its own valve to meter the flow.. The MAPP torches that I have owned only have one valve.


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