Silver Solder vs. Loctite Retaining Compound

PS - I've heard that, for soft solder, milk of magnesia works as an anti-flux. I've also heard that soft solder is an anti-flux for brazing.

Another PS - I generally use propane with Stay-Brite. As Mikey pointed out, it has a very nice, low melting point. Matter of fact, I once used a heat gun to join parts with Stay-Brite. Don't recall the exact reason, but I think it had to do with the need to limit overheating.
 
Stay-Brite has a melting point very close to the same as soft electrical solder. depending on which one you get 430 to 535°F. I have used a soldering iron with Stay-Brite on very small parts. I now use mostly Hi-Force 44 silver solder from Brownells, It is a bit stronger than Stay-Brite and still has a fairly low melting temp. That will easily work with propane, or even a good soldering gun for very small parts.
 
Alright folks, I gave it the ole' college try and it actually came out pretty reasonable.

Here's my setup. I heeded some of the advice given here, but not all. Not because I didn't think it was good advice, but because I was too antsy to get started to wait on ordering more supplies. For example, (1) I used regular pavers instead of fire bricks (which had been sitting out in the rain for years and worked just fine) because Home Depot didn't have any in stock, and (2) I used 1/16" dia. silver solder rather than some of the thinner jewelry stuff because it came in a 'kit' with the flux on eBay.
IMG_7931.JPG

I prepped a trial run using similar materials and sizes to the gear assembly that I need to do for my Edwards radial 5 (forgot to take some 'before' photos). It's basically two steel gear blanks slipped over a bronze bushing with about 0.002" clearance. I made sure everything was super clean and then gave a light brushing of flux on the joints I wanted soldered. I just wiped off the excess with a paper towel wherever it squeezed out.

Well, then I just gave it a rip. Threw a bunch of heat at it and dabbed the silver solder at the joints every now and then to see if it was at temperature. I saw a little bit of solder get sucked up into the joint at the top, but it seemed like very, very little. So I kept on going. Probably too long and too hot, and made a little mess of things trying to add more and more solder.

Experts: how hot is too hot? I ended up getting it cherry red. The solder was certainly molten at that point, so I'm sure I was quite a bit too hot.

Here's the outcome after I hit it with a wire wheel. A couple extra blobs of silver solder, but nothing too bad.
IMG_7926.JPG

At this point, I had no idea if any silver solder got into the joints. I was actually pretty confident that it had not, because I just kept on dabbing in the solder and wasn't seeing anything get sucked in. So I sectioned it with a hacksaw and polished it up to take a look.
IMG_7930.JPG

Not sure you can tell from the photo, but there is a clear line of silver solder between the two steel gear blanks (not quite the full way across, but close). It's extremely difficult to tell if there's a similar solder joint between the gears and the bronze bushing because the silver solder is the same color as the bronze. I even looked at it using a microscope under 120x magnification and still couldn't definitively say the solder had wicked all the way through. BUT, (1) there was no indication of the clearance gap, and (2) the bushing didn't fall right out when I slit it in two. Those factors lead me to believe that the entire joint got adequately filled with silver solder.

Anyway, I think I'm ready to go now with the real thing. It really wasn't a difficult process at all, though I think I'll get some proper fire bricks, and I'll certainly order some thinner silver solder.

Thanks again for all the fine suggestions.
 
Also, in the real silver solder job, I plan to chamfer all parts much better than I did for this trial run. Thank for the suggestion, @machPete99.

If you zoom in on my last photo above, you may be a able to see a very small chamfer full of solder. Seems a good idea to go bigger.
 
cherry red is fine but really it's the heat needed to get good flow of the solder,, most important is clean,clean,, I clean and prep all the parts,1. abrasive paper, steel wool,2. some form of solvent (acetone, brake cleaner) safety always.. 3 final cleaning with fresh fine steel wool, no touching parts with fingers,, 4. flux up and solder away.. I estimate how much solder the job will take and clean (fresh fine steel wool) and flux that amount..
 
JRaut said:
I used regular pavers instead of fire bricks
Click to expand...
Can’t say that proper refractory bricks would make a huge difference but they would some. Also, if you can put a fourth brick (or paver) even partially along the top to form a little roof it will do a lot for holding your heat. Sometimes it’s tough because you need to see the part, but it will help contain it.

-frank
 
I think some of the responders are thinking silver brazing (Very often incorectly refered to as silver soldering) and not the silver soldering that you are doing. The American Welding Society (AWS) defines brazing as such a process which involves a filler metal which has a liquidus above 450°C (842°F).

The silver solder that you are using has a melting point of 435°F. Red hot steel is WAY to hot. Red hot is just a bit on the high side but still ok for silver brazing. Steel starts to turn red at ~1400°F. That much heat will completely vaporize and remove ALL of your flux and very quickly allow the surfaces to oxidize and repel solder. That is why the visible solder on the outsides of the joint is beaded up and looks rough and flaky. Just like in electrical soldering the solder should be bright shiny and smooth. When i use the StayBright 4S silver solder that you have, I usually use a 150 watt soldering iron for the heat, it has a tip temp of just over 600°F. That iron will not make heat fast enough for your parts but just to give you an idea of the temp needed.
On your test piece grab the 2 steel parts with pliers and see if you can get them apart, That will be the sure test as to if you had full penetration of the solder.

You were correct at first that as soon as you saw the solder starting to melt and wick into the joint you were at that point at the correct temperature. Then the trick is to hold the temp for long enough for the heat to get all the way thru to the joint. When the solder first melted the outside of the assembly was at temp but it takes a minute or 2 for that temp to get to the center of the parts. concentrate most of the heat on the bigger gear and test for temp at the other end of the small gear that way once the solder starts to melt you know you have the correct temp all the way through the joint. When I am using a torch, once I get up to temp I just use the outermost tip of the flame not the inner cone, to tickle the part to slowly bring it up to temp. Mapp gas is way more heat than necessary, so go easy with the heat. If you have propane switch to that.
 
All good info, thanks @Flyinfool.

But now I'm thoroughly confused.

The filler material I'm using is Harris Safety-Silv 45, which is described on Harris's website as "General Purpose Silver Brazing Alloy" with a melting point around 1300F (not 435F). And I can tell you for a fact: it was wayyyy hotter than 435F by the time the filler metal melted.

So to be technical about things, I was brazing, not soldering. And I'm apparently one of the folks who confuses the two. :rolleyes:

But I always thought "silver soldering" was more of a colloquial name of the (more technically correct) "silver brazing" process.

I guess a different question would be, is there actually such a thing as "silver soldering" in the technical sense? And if so, what silver-containing filler material would one use to accomplish such a task.
 
Too hot. Cherry red is too hot. You can see from that crusty look that it got too hot. The right temperature is about aluminum melting hot. A slight red glow. Flux up really good. More is better if you are just starting out. Keep touching the flux with the solder. One moment it will give, then it will just rush in. Done! As someone said above, if you wait until good and red, the solder won't stick.

It is easy to reach this temperature with a propane torch on small pieces, especially with the aid of a little refractory cave. It can be super simple, like a sardine can filled with perlite with sand on top or an old charred chunk of wood. Do not leave the wood lying around until it has stopped glowing. If you have a Reil or Mikey burner, you don't even need much refractory. A pile of dirt or sand will work.
 
I'm sorry, My mistake, I did not zoom in on the pic and misread the P/N that you are using.

I am one of those that is a stickler for the correct terminology as I do both brazing and soldering. Terminology will send me down the wrong path if I am not careful. I was not careful and assumed............

Here is your data;

Safety-Silv® 45 | The Harris Products Group

The Harris Products Group is a world leader in the design, development and manufacture of brazing, soldering and welding alloys and equipment, cutting and heating equipment, and gas distribution systems.
www.harrisproductsgroup.com www.harrisproductsgroup.com

But some of my points are still valid, try to tear the test parts apart to see what your penetration looks like. Too much heat will still make a ugly surface on the visible brazing. 1370°F will be a dull red heat, cherry red is still a bit hot. You still want just enough heat to melt and flow the solder and you need that temperature for the full length of the joint,

The silver soldering is more of just soft solder with a bit of silver in it. The "Silver Solder" contains 4% to 7% silver and is often referred to as silver bearing solder, where what you are using is 45% silver. That is why the weight of the spool is measured in troy ounces. and silver solder is just in oz. Silver brazing alloy is also a LOT more expensive than Silver solder, Obviously due to the silver content.

Sorry for the confusion. As for me, I still would have silver soldered those parts. Brazing temps will change the heat treat of the gears.
 
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