Silver Solder

[8ntruck 6,358]

I am finally starting to work on a model steam engine kit that I got back in the 80's.  I am currently starting to assemble the boiler.  The boiler parts are copper and brass. 

 

The recommended solder is silver solder.  A while back, I stopped by the local welding supply house and picked up a couple sticks of cup 5/15% silver solder and some Harris Stay Clean flux.  I tried making a joint last night.  Didn't work out very well.  It looks like the flux cooked off of the joint before the solder melted.  I did manage to get a glob of solder to stick to the work, but not flow into the joint.

 

I'm thinking that the propane torch might not be hot enough, or I need a higher temperature flux.  Checking the spec sheets for the solder and flux indicates that the solder melts about 100 deg. C higher than the max working range of the flux.

 

Does anybody have experience with silver soldering that could give some guidance?

 

Thanks.

[ebinmaine 62,978]

@JCM

Jim / Plunge     can you help this guy out?

 

@squonk. @WHX24

 

[squonk 38,848]

https://www.grainger.com/product/1UYK2?ef_id=EAIaIQobChMI0MW6yp-U7AIVB4bICh1_dw03EAAYASAAEgLsT_D_BwE:G:s&s_kwcid=AL!2966!3!317451745590!b!!g!!&gucid=N:N:PS:Paid:GGL:CSM-2296:9JMEDM:20500731

[ACman 7,505]

You’re going to at least want to use map gas . I used oxy-acetylene and others acetylene with a turbo torch head . I never used flux just clean joints and the parts a nice orange color and many years of practice. This was for AC lines which I didn’t want contamination from the flux .

Edited October 2, 2020 by ACman

[953 nut 51,540]

3 hours ago, 8ntruck said:

propane torch might not be hot enough,

I have alwaysused pre-fluxed silver solder (AKA Hard solder). Oxy-acetylene ids the way to go with this. it has to be nearly as hot as brazing. 

Edited October 1, 2020 by 953 nut

[WHX?? 46,704]

Put up a pic of the solder you are using. Pics of what you are trying to join would help too. There are many many types of silver solder. There is soft and hard. Soft is much like sweating copper joints. Hard is like brazing and takes alot of heat and propane will not do it. Hard you will not need flux soft you will. 

[8ntruck 6,358]

I have done oxy-acetylene brazing in the past on steel without any issues.  I would typically use flux coated brazing rod for those jobs. 

 

Since I am building a pressure vessel, I need to use a hard solder - something stronger than the normal lead free plumbing solder.  I came up with a 15% silver solder, that is listed as having a melting temp of 800 deg. C.

 

Here is a picture of what the project is supposed to look like when it is done:

 

Boiler assembly dry fit:

 

 

1st joint attempt, a water passage across the flue.  Both tubes are brass.  The blob of solder stuck to the work, but did not flow into the joint:

 

 

Solder being used.  It will melt in a propane torch flame:

 

 

Flux:

 

Edited October 2, 2020 by 8ntruck

[WHX?? 46,704]

That's stick style hard solder and for delicate work like that you are going to need  pinpoint heat in the range of 16- 1900 f or maybe better to get a good flow. Will need oxy acetelene for that.

. You will not need flux for that.

I would use Silva Brite soft solder say maybe a 5% or less silver content. Unless fhis thing operates at really high pressures??? Any kind of soft solder you will need flux but not as half important as having cleaned the surfaces well. 

You could use actual  silver solder which is super strong but $$$$$$ Super fluid at  lower temps but gets sold by the troy ounce and mostly used in jewelry. 

[8ntruck 6,358]

Thanks, Jim.  I have another thread running in a model steam forum asking the same question.  Hopefully, I'll get some good advice there.

 

I really have no idea what the operating pressure of this boiler is going to be, but I'll guess that it won't be very high - maybe 10 to 15psi at the most.  Maybe Silva Brite would work for this boiler.  More advanced model steam plants do work at higher pressures that are 3 to 5 times higher than I am expecting, so a stronger solder would be appropriate for those jobs. 

[WHX?? 46,704]

 to that forum Truck? 

This is what I use on most of my refrigeration work. Note the low melting point so a butane micro torch can be used for what you are doing. You can get some real nice filet joints with this.

Edited October 2, 2020 by WHX24

[squonk 38,848]

I forgot to mention you need to get the metal you are soldering hot enough to melt the solder. You do not want the torch melting it. I can't believe that steam pressure is more than a couple of lbs. Even 5lbs. of steam can do a lot of damage

[diesel cowboy 263]

Not sure if this will help, but I watch a few guy on YouTube that redo the old Matchbox cars and one of them bought some solder from here: https://www.muggyweld.com/knowledge-center/#copper-brass-bronze  He used the one for pot metal and had reasonable succses fixing a broken part.  They also have stuff to do copper and brass.  Might be something there that would work with the torch you have

[lynnmor 6,762]

I use the products from McMaster-Carr.  The very small wire diameters are best for model work and I always use their flux as well.  To judge the temperature of the work piece; Google "temperature color chart", typically you want a dull red glow for silver solder.  A propane torch can work on thin parts as they can easily be heated to red hot.  Gap filling solder is best if you need to bridge, otherwise use the product for tight gaps.  I had many small parts to make for a pretzel maker that required both gap filling and regular solder since round and flat parts needed to be connected.

[8ntruck 6,358]

I got some MAP gas today and gave it another go.  Only a slight improvement.  The work was heated red, the solder melted when touched to the work, but it did not flow - almost like the work was too dirty.  I'm still going to try a higher temperature flux.

 

I put pencil to paper and ran stress numbers on the solder joints at a boiler pressure of 20 psi.  Not very high.  Steam temperature at 20 psi ts about 260 deg. F - again, not very high.

 

The 96 tin, 4 silver solder should be plenty strong for this application.  This will definitely be the next step if the new flux does not work. 

 

One answer from the model steam forum is reccomending 20 gage sterling silver solder -just $34 per troy ounce.