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Brazing Brazing is the process of joining two metals with a third metal. Example: Heating two pieces of steel together till they are red hot and then melting a bronze rod in between the two pieces of steel. The two pieces of steel do not melt but the bonze rod does melt since it melts at a lower temperature than steel. Metals that I braze: Steel, stainless steel, copper & brass You can braze dissimilar metals together such as steel to copper, brass to copper etc. Below is a photo of brazing a copper tube to hot rolled steel.
Brazing is most often done using an oxygen acetylene torch. There are many definitions to brazing but they tend more to confuse rather than to explain. Below is a short video on the actual process of brazing including what not to do. 95 % of the work that I do with the torch is with a neutral flame. Two other flames that I might use; the carbonizing flame and the oxidizing flame. This is explained in the video below. The attention here is on the cone of the flame.
Monitoring your brazing: 1) As I will frequently mention, the cleaner your base metal (metal to be brazed) the more successful the brazed joint. In the chapter on steel I discuss how the mill scale must be removed from hot rolled steel to insure a good braze. 2) In the case of steel the steel must be red hot at the same time as melting the bronze rod. 3) If the steel goes beyond red hot into a yellow or white hot then move you torch away an allow the steel to cool down. 4) After three or four attempts and the braze fails allow the metals to cool down, clean by wire brushing or grinding and then begin again. 5) Use a neutral flame. 6) Oxygen Acetylene regulators set at the proper setting for your torch and the metal you are brazing. 7) Distance between the torch flame (cone) and the work to be brazed. The video below illustrates this.
I use the Victor Performer torch and have my regulators set at acetylene 5 lbs. oxygen 6 lbs. . You can experiment with these setting and then adjust according to your torch and the work that you are brazing. Fluxes: You need flux to braze. Flux is a cleaning agent. Note: Don’t think that the flux is going to clean an oxidized or rusty piece of metal. It won’t! There are numerous fluxes on the market for different types of brazing. I use just two fluxes. The first is borax. I buy flux coated brazing rod which is covered in a borax based flux.. Since I work with new material I scrape most of the flux off. The flux coated brazing rod has a borax powder coating. More on this in the chapter on Finishing. Below is a bare bronze brazing rod and a flux covered brazing rod. The small box with the white powder is the borax flux. The white rod is the same type of brazing rod but it has the flux already on it.
The other flux I use is Stay Silv. It is a paste like flux that I sometimes use with Sil Fos, silicon bronze and silver solder.
If you are using all new material I would suggest using a minimum of flux. Heavy flux presents two problems: 1) It is sometimes difficult to see the actual braze when working with small detail pieces for your sculpture. The flux builds up and looks like sticky molasses. 2) Heavy flux can leaves a glassy surface. Considering that you are going to clear coat ( clear lacquer or clear acrylic) your piece when you are finished; if any flux is left on the piece in a few days the flux will crystallize and pop up through the clear finish. This will leave what I call the powder sugar effect; little spots of white powder. This essentially ruins a piece of sculpture. The only recourse is to wire brush all the joints with and spray another clear coat. Below is an example where the flux was not completely removed before clear coating with a clear lacquer or clear acrylic. You can just imagine how bad your finished sculpture would look if all your brazed joints looked like this.
Sil Fos, Silicon Bronze and Silver Solder: These are joining materials that melt at lower temperature than the bronze brazing rod. I use these so seldom that I am not a good source of information. I use 3/32nd flux coated brazing rod 99.9% of the time. Much of my brazing has a two fold purpose; one is to join two or more pieces of metal together and the other is using the bronze as a contrasting color effect against other metals. Your first brazes may not turn out the way you want. The key is practice. Take some time and decide that you are going to experiment. Don’t try to make something or repair a broken item. Get some scrap metal and practice. If you do this you will get the hang of it fairly quickly. The basics are getting the metal to be brazed to the proper temperature and flowing the bronze rod in the joint between the two metals. For me clean steel is the easiest to braze, especially RG 45, the mild steel gas welding rod as used in the piece below.
Once you master steel to steel then go on to copper, brass and stainless steel. Brazing is not rocket science! You will become very proficient at what you braze most. When you go onto another material it will take some practice before you become proficient at that, although you'll find that it takes less time to master a new material. Brazing light weight metals to heavier metals. Brazing together metals of an equal thickness is one thing but brazing together metals of different thicknesses raises the bar a bit. Below is a video which gives you some pointers on brazing two different thicknesses of metals.
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