I am looking for advice here in terms of building a moderately sized brazing furnace.
Background: I have working on and off for years to make a copper cowboy hat. This problem has proven to be very challenging. I had hoped to weld the brim on, but shrinkage became a big problem, so I gave up on that approach. In order to braze, I ended up building a three sided furnace with a propane torch to preheat, and using an oxy-actetylene to weld. But brazing had shrinkage problems also I decided to try what I thought would be a simpler project, which was to make a steel top hat by tin-lead soldering the pieces together. with an acetylene-air torch. That turned out to be difficult as well, due to the pieces shifting when they were heated. (See the photo of a top hat, approximately 14 inches by 12 inches by 5 inches.) I decided to make a kind of scale model, and see if I can solve the problem at a smaller scale. I think now that I may have solved the problem by using an oven. The oven produces fairly uniform heat, and I am able to clamp the pieces together. See the photo. I was able to use the kitchen oven for soldering. But my goal is to braze a copper cowboy hat, and I want the color match of silicon bronze, not a silver line of tin at the join.
What I am thinking that I need to do is to build a medium sized brazing furnace, propane fueled. Furnace brazing is a standard industrial process. The inside of the furnace would need to be at least 16 inches by 14 inches by 8 inches tall, for a volume of about 1800 cubic inches, or around 1 cubic feet. I would probably build it from the usual white soft insulating fire bricks. So I have some questions.
What burners should I use? How many? I made my own burners for my blacksmithing forge, but was disappointed that I could not get it close to welding heat. On the other hand, I do not need welding heat, maybe just build two or three Reil type burners. Or just buy a few burners off of Amazon or wherever. Who makes good burners?
What should I do for the roof of the furnace? I could simply use a large plate/sheet of steel, and then put fire bricks on top of it. This would have the advantage that I could easily take it apart, and perhaps reconfigure it at a future date. For a more permanent solution, I could weld wire mesh to a large plate/sheet, and then glue the fire bricks to it. What could I use to bond the bricks to a sheet of metal? Given my situation, a furnace that can be reconfigured for each project is probably the way to go.
The clamping arrangement shown in the photo uses 1 inch square tubing, 16 ga wall thickness. This will probably be inadequate at brazing temperatures; Perhaps use 1” by 1/2 inch bar.
Richard Ferguson