Silver brazing problems

[Scota4570]

I fabricated a trigger guard in two pieces of brass plate.  The idea was to jig it and stick the parts together with silver solder.  I have 56% easy wire.  I am using brazing flux and "O" tip on an oxy acetene torch. The flame is neutral.   

The plate boils and melts before the silver braze sticks.  The silver solder is not flowing out properly.  I have used this exact stuff on nose caps without a problem.  Is some brass plate not suitable for silver brazing? 

I have to start over.  I could will use lead solder and make tight joint.  Brass is much easier to work but I guess I could use steel.

Opinions eagerly sought. 

[Daryl]

Too fast/high a heat source, localized heating and melting before the heat can spread out to melt the solder? I am puzzled as well.

[JPK]

+1 to Daryl, slower and less heat.

[Scota4570]

Hmmm??  Could be right.   Perhaps a general heating with a MAP gas torch then a nudge with the oxy acetylene? It is too big to do with MAP alone.

I ended up building up a large blob of regular braze then working it back down.  It is no Longer perfect but good enough I guess. 

[T*O*F]

With some alloys, getting them too hot will burn the zinc out of them and leave a reddish, coppery piece behind.  I've even gotten them too hot with a propane torch.

[Scota4570]

I think I will resupply my spelter  solder.  Bernzomatic used to make something like this.  It was some sort of bronze color alloy that worked at about 800*F.  I am having trouble finding it, anyone?

[smylee grouch]

I agree with too much heat. A regular propane torch is what I thought would work best.

[Stophel]

MAPP is more than sufficient for me to silver solder (I use the silver solder from Brownell's.. I don't know how "easy" it is.. it's the only one I've ever used).  Never had any problems with it.  In fact, it's easier for me to silver solder than soft solder with tin or lead.

Like the others, I think you're hitting it too hard, too fast with your oxy/acetylene torch.

[Not English]

Scot, I'm not sure what you mean by a brazing flux. When I first learned to silver solder (braze) we used a white paste flux. It only worked when the flux dried and then turned liquid again and kind of "boiled" a little. We also fluxed the end of the wire when  first using it to get a clean  silver surface. Only then would the silver solder flow. I agree with those who say you're heating too fast. It doesn't really make any difference what kind of fuel you're using. If it's melting under the flux, I think it's getting too hot too fast before the flux has a chance to do it's thing. Try a different flux.

[davec2]

I've been silver and gold brazing things from the size of a Space Shuttle Main Engine (in a hydrogen furnace the size of a room) down to the finest gold chain you have ever seen for more than 60 years.  I can tell you that, to silver braze a trigger guard, a simple propane torch will supply more than enough heat and oxygen- acetylene is WAY overkill.  (An experienced person would have no trouble doing it with oxygen- acetylene but an inexperienced person will, as other have noted, almost always heat the workpiece WAY too fast and WAY too hot.)  The best way to train yourself is to get several pieces of brass or steel that will simulate the size of the joint you are trying to silver braze and work on those until the heat, the flux, the play of the torch, and the placement of the braze alloy are second nature.  And remember that the braze will ALWAYS flow toward the highest heat, so if you apply heat from the top of the joint and try to apply the braze alloy through the flame, the braze will most often go everywhere except where you want it to go.  Heat the joint from the back side and apply the braze to the front as the heat approaches the melting temperature of the braze alloy.

[G_T]

Make sure the surfaces to be brazed together are bright clean netal with no finger or other oils on them. A light sanding with clean sandpaper is good for that prep.

Flux the surfaces. A good flux is Boric Acid dissolved in some denatured alcohol. Borax is also usable. Paint the flux on the parts, then light the alcohol and let it burn off. That sticks the flux to the surfaces. Put the parts together, then start with LOW heat from the torch! It probably takes less than you think to get it to braze. Don't be afraid to use lots of flux!

Roach powder from a hardware store is Boric Acid. It's a cheap source of a good flux for some uses.

Gerald

[Craig Wilcox]

Lowe's carries Boraxo in the cleaning aisle - great flux for most precious  type metals.  When I was helping a jeweler friend, I believe he used an alcohol/borax mix - brush it on the part, ignite it, and the borax gets left on the joint.  Pickle it when done soldering/brazing, etc.

The Boraxo is also good doing your laundry, add half a cup or so to the normal detergent when washing especially dirty clothes.

Easy, medium, and hard silver solder is determined by the melting point, with "hard" taking more heat than "medium", "easy" taking the least amount of heating.  That way, you can solder up the first joints with HARD, the next series with MEDIUM, and the last with EASY.  Has nothing to do with the actual hardness of the metal, but with the alloy used to make the solder.

Dave C - did you REALLY start at age3 and had to sit in your high chair to reach the workbench?

[Machinist John]

As Dave said you do not need a  lot of heat.   My little Prestolite torch works great for all types of silver brazing.   No Oxygen, just acetylene that mixes with air.   A good soft flame.  Comes with a box of different sized interchangeable tips.



Buy the best silver brazing rod you can find.  My favorite:



Expensive but a pound will outlast you.   44,000 psi tensile.