Silver solder or braze

[Gordon]

I am making a crank shaft for a hit and miss engine. In the past I have machined the crank from solid. Many folks here seem to make the crank from individual pieces and silver solder the pieces together so I thought I would try it. My question is whether it is better to silver solder or braze. I have the equipment and supplies for either. Actually I have done much more brazing than silver soldering. Any thoughts?

Gordon

 

[dnalot]

Silver brazing is the way to go. Done correctly the joint will wick in the brazing material.

Mark T

 

[BobsModels]

Braze it, on my first one used low temp silver solder ie Harris stay brite #8. I have been soldering and brazing for over 30 years at the time I made that crank and it was my first failure - ie joint failure. After about 30 hours of running the joints failed, it could not handle the pounding of the ignition. Since then either made crank from solid (4140,1144) or brazed no more failures. My latest was a bit complicated so it was silver brazed.
Given your equipment and experience braze it, you will need lots of heat as it is a one shot. See attached the wicking can be seen clearly from the finish cuts taken.

Bob

 

[Gordon]

I am a little bit confused here about terms. I thought that there was brazing done with brass rod or silver solder done with silver content (45% in what I have). Is silver brazing something else?

 

[GrahamY]

When people talk about silver soldering they are "normally" talking about the high temp silver "brazing" where the temp is above 450 degrees Celsius (as dnalot was). Bobs Models was talking about low temp soldering with solder that has 6% silver (220-280 degrees Celsius) - this is more like electrical soldering.

 

[Apprentice707]

I silver solder my small steam engine cranks (55% silver) and I have never had a failure yet, some are 40 years old. I am sure someone knows the advantages of silver solder over brazing (besides the melting temperature) but I am not that technical. I just know what works for me.

x

B

 

[BobsModels]

I guess it is terminology. Brazing is when the melting point of the filler material is above about 840 F. Soldering is when the melting point is below 840 F. You need to check your spec on the material you are using, dependent on silver content, tin content etc.
Either way the stuff we are recommending is with a melting point above 840F. For example Harris Safety Silv 56 is Cu 22%, Zn-17%, Sn-5%, Ag-56% and is solidus at 1145F and liquid at 1205. Here is link to all their stuff - Safety-Silv® 56 | The Harris Products Group just click on any item in the left column and you can get all the data.

It is very useful to have brazing materials at different temperatures to allow stepped brazing sequences. I had to braze 19 pieces of different thickness brass together to form a crankcase for a model took 4 different temperatures. All the sides are tapered, the end rings are tapered ie thin on the bottom in order to end up with horizontal lines when looking at the base. So lots of careful setup. It took about 4 days of brazing a section, cooling, pickling, and then repeat. Parts were held together with clamps, screws etc. I used my heat treat oven to bring the parts up to about 1000 degrees, moved the parts to a make shift open oven to contain heat. I used a Sievert Torch with various heat tips. See photos (click on them for full size).

Bob

---------the parts--------------------the layout-------------------sub sections at one temp-----finished main body------different temp for end rings

------another temp-----------cleaned up ready for machining---all machined

 

[JohnS12]

That's beautiful work. I am working on a simpler crankcase and have two questions - how do you cool? I have seen people that recommend immersing in water while hot to remove flux or do you just air cool? My limited experience is that fast cooling causes distortion. Secondly how do you remove the copper colored sections, I use citric acid which removes flux and tarnish, but it leaves the copper color in some areas as can be seen in your pictures

 

[BobsModels]

John

One of the reasons it took me over four days is my process. I did one joint at time. Lets take just center section. It is held together by screws, the surface area to be brazed had punch marks to keep a small distance for the braze to wick into. The entire metal was fluxed, I mix my flux so it is runny and can be brushed on. Part is set at slight angle and silver Braze laid against the joint. Heat applied under the joint and on the center section, minimal heat if any on the joint itself, I want the material hot. Finally the braze wicks in and if more is needed it is applied. I now take the part and set it on some firebrick that is not hot up on some spacers for air flow. I let it air cool, maybe an hour or until I can pick it up in my bare hand without burning myself. Next I have one of those slow cookers that is about a 1 1/2 gallons. In that is Sparax 2, 1 gallon. I clean the part first in warm water and a brass brush to get loose stuff off. Then in the warm pickle bath for maybe 10 to 20 minutes at most. When done with that it goes in to a water bath for a rinse, then a soda bath to neutralized the acid, then water to clean it all up for the next cycle. I am using a brush at each stage to clean off flux and oxidation. If you look at the forth picture over that is how each stage looks when I cool and before I clean. Fifth picture is cleaned and another part being brazed on.

Each end has three joints, each done with one sequence of above. If I count correctly there were 16 passes. It is important to flux everything not just the joint you are doing, you really want to keep everything clean all the time. Here is another picture showing stepped braze temp, the small piece was brazed on before the main box was worked on. Those parts and that center section got the highest melt temp silver braze. The next picture shows the top of one side being brazed, the silver braze was inside and the heat applied to the top and side, took lots of heat to get it to flow, you see the heat treat oven that took it up to about 1000 degrees F first. Those are clamps keeping the ends tight while the top joint is brazed. If not clamped the part would just warp out. Due to the thickness of the material it could not be screwed at the top so I used a custom clamp.

I have used citric acid for steel, never tried it with brass.

I am not sure what you mean by the copper colored - the braze material? The brass is kind of a copper color when it comes out of the Sparax. Also the color is somewhat dependent on the light used and if I used a flash. In the end it will get a light bead blast and then painted so any color of the metal will disappear.

Hope this answers your questions.

Bob

 

[bluejets]

10% sulphuric acid to 90% water mix by adding acid to water is used by some.
Don't leave it too long though.

 

[kwoodhands]

I am making a crank shaft for a hit and miss engine. In the past I have machined the crank from solid. Many folks here seem to make the crank from individual pieces and silver solder the pieces together so I thought I would try it. My question is whether it is better to silver solder or braze. I have the equipment and supplies for either. Actually I have done much more brazing than silver soldering. Any thoughts?

Gordon

Why change from solid to soldered joints? Silver solder is hard solder and melts at average temperature above 1100° depending on the make up. There are some hard solders that melt at about 850° and others at a high of about 1400°. Sometimes hard soldering is known as silver brazing or just silver soldering.
I was told hard soldering is the best description between the three.
Soft soldering ,plumbers solder melts much lower and does not require red heat like hard solder. Not positive but I think soft solder melts at less than 400°.
Electrical solder requires the least heat.
I haven't done any brazing so I won't comment on it.

mike

 

[BobsModels]

Yes that is what I used before I came across Sparex 2 in dry crystals, just mix with water.

I think what folks need to realize is the flux is water soluble, you just need to heat up the water and use a wire brush or small pick to remove it. The pickling solution is really used to clean the metal for the flux and silver braze, much like a piece of sandpaper on copper pipe joints before you flux them.

Lots of little subtle tricks that make the job go easier and make for a nice joint.

Bob

 

[bluejets]

I am making a crank shaft for a hit and miss engine. In the past I have machined the crank from solid. Many folks here seem to make the crank from individual pieces and silver solder the pieces together so I thought I would try it. My question is whether it is better to silver solder or braze. I have the equipment and supplies for either. Actually I have done much more brazing than silver soldering. Any thoughts?

Gordon

Why any brazing etc.
Build accordingly and press together.
Works on most commercial level cranks such as this.

 

[TonyM]

Silver solder is way more expensive than plain brazing rod.

 

[Gordon]

I have made them using 45% silver solder. So far it looks good.

 

[peterl95124]

16 passes seems excessive, the box has 6 sides, I would have done it in 6 passes. another trick is to paint the entire work with flux to avoid so much oxidation and reduce the amount of pickling required. finally, to get back to "brass" color after pickling, anything mechanical works, sanding, filing, blasting, etc...

 

[JohnS12]

John

One of the reasons it took me over four days is my process. I did one joint at time. Lets take just center section. It is held together by screws, the surface area to be brazed had punch marks to keep a small distance for the braze to wick into. The entire metal was fluxed, I mix my flux so it is runny and can be brushed on. Part is set at slight angle and silver Braze laid against the joint. Heat applied under the joint and on the center section, minimal heat if any on the joint itself, I want the material hot. Finally the braze wicks in and if more is needed it is applied. I now take the part and set it on some firebrick that is not hot up on some spacers for air flow. I let it air cool, maybe an hour or until I can pick it up in my bare hand without burning myself. Next I have one of those slow cookers that is about a 1 1/2 gallons. In that is Sparax 2, 1 gallon. I clean the part first in warm water and a brass brush to get loose stuff off. Then in the warm pickle bath for maybe 10 to 20 minutes at most. When done with that it goes in to a water bath for a rinse, then a soda bath to neutralized the acid, then water to clean it all up for the next cycle. I am using a brush at each stage to clean off flux and oxidation. If you look at the forth picture over that is how each stage looks when I cool and before I clean. Fifth picture is cleaned and another part being brazed on.

Each end has three joints, each done with one sequence of above. If I count correctly there were 16 passes. It is important to flux everything not just the joint you are doing, you really want to keep everything clean all the time. Here is another picture showing stepped braze temp, the small piece was brazed on before the main box was worked on. Those parts and that center section got the highest melt temp silver braze. The next picture shows the top of one side being brazed, the silver braze was inside and the heat applied to the top and side, took lots of heat to get it to flow, you see the heat treat oven that took it up to about 1000 degrees F first. Those are clamps keeping the ends tight while the top joint is brazed. If not clamped the part would just warp out. Due to the thickness of the material it could not be screwed at the top so I used a custom clamp.

I have used citric acid for steel, never tried it with brass.

I am not sure what you mean by the copper colored - the braze material? The brass is kind of a copper color when it comes out of the Sparax. Also the color is somewhat dependent on the light used and if I used a flash. In the end it will get a light bead blast and then painted so any color of the metal will disappear.

Hope this answers your questions.

Bob

View attachment 114923View attachment 114924

Bob, thanks for the detailed reply. FYI, my crankcase is for the Kozo New Shay. I have screwed my sections together, and punched as you note. But, from my results and your reply I now know I should be doing some clamping as well, since I did have some warping. The copper color I was referring to is from the brazing filler metal. I have not been neutralizing after the acid and as you say, I should do that as well. The citric acid is pretty slow acting, but it does work well, I typically leave it overnight. I do not have an oven, but I do have a refractory area similar to yours and with a large torch I don't have any trouble getting up to temp but I am sure the furnace gives you a much more even temp.

John

 

[tornitore45]

Electrical connection are soldered. Used to be Pb/Sn now a composition w/o Pb with some Silver

Plumber call the 5% Silver solder process Silver soldering becuse is a little better that Lead and Lead is now banned.

Refrigeration people Silver Braze, presumably because of High Pressure, Temperature and Vibration.

Using High Silver around 50% is NOT soldering Is called Silver Brazing
Any joint where the base metal does not melt but the filler melts above 450C is called Brazing.

Is that Simple

 

[werowance]

Using High Silver around 50% is NOT soldering Is called Silver Brazing

well, probably better to say "it shouldn't be called soldering" and it "should be called brazing" however I see it all over different model forrums, high temp high content silver brazing wire around 45% silver or higher - people often call it "silver soldering" when really isn't. its brazing.
and I have to admit that I am guilty of calling it silver soldering instead of silver brazing when using real silver brazing wire. but a lot of others way more experienced than I also call it silver soldering when they are using the hard stuff.

the stay brite as mentioned by someone else is pretty much plumbers solder. just a little better than most and can handle just a little more heat than regular plumbers solder. but just a tad bit more.

they also make stay silv which is the real silver brazing wire ("they" = harris company)

you can also tell a difference between the stay brite solder and the real around 45% or higher silver content brazing wire when you bend it. stay brite bends just like plumbers solder, a piece of silver brazing wire is very stiff and difficult to bend in my opinion


so I can see why its confusing when a lot of folks call the hard 45% high content silver brazing wire and the techniques used to heat and flow that stuff - silver soldering. its not but just understand a lot of us do call it soldering instead of brazing.

 

[BobsModels]

John
Your welcome and good luck on your project, post some pictures.

Peter
With 19 parts, some inside some outside, not being able to physically attach at least 12 of them, doing it in 6 passes would have been a real challenge for me. It took me 6 passes to just do the basic box sides, each of the 6 joints needed the box to be repositioned to get at them. The parts attached to the ends sides and top had to be held by gravity so again not sure how I would have done it in 6 passes. I made lots of stuff for live steam locomotives, and models over the last 45 years and have done so by listening and learning from everyone I have ever met. Not sure I see how to do it in 6 passes for the 19 parts. Give me some hints.

I agree with you about the fluxing as I mentioned that is what I did for every pass it really makes a difference.

All
I know all the terminology issues, seen them discussed and confused often. I saw we really confused one person who missed that high silver content braze wire is not just a brass filler rod used for brazing. I think anyone who has done it knows what is what, and those that have not figure it out quickly. One way is if the silver solder is sold by the pound for the same price several ounces of something else called silver solder, one is soft and one is hard.

Thanks
Bob