I want to talk a little bit about Brazing and Torching in this article.
First the definition of Brazing:
verb (used with object), brazed, brazing. Metallurgy.
- to unite (metal objects) at high temperatures by applying any of various nonferrous solders.
Origin: 1575-85; French braser to solder (MF), burn ( Old French) <Germanic;compare Swedish brasa, Danish brase to roast>
So like with welding, it is joining two different pieces of metal together. The difference is that a filler material is used. One of the most common examples of brazing is soldering. If you have ever watched a plumber install a new water line , you have seen brazing in action. There are many other instances of the use of brazing. It is used when much greater tolerances are required. The parts to be joined can be fitted together with great accuracy for shape, size and angle of joining so that the proper results can be achieved.
Brazing is used in just about every industry when accurate joined pieces are required. Depending on materials and usage, different techniques are used. Materials and conditions apply. Some brazing must be done in a chamber filled with an inert gas such as Nitrogen. When Brazing, different alloys of filler metals, usually a combination of metals with low melting points like gold, copper or silver are used to join the parts in the assembly. Torching is the overwhelmingly most common technique for brazing. Other types are furnace, vacuum and dip brazing. In all of these, the proper temperature and the time it is applied are critical.
It is the accuracy of fit that makes brazing a viable technique for industry and the arts. The drawback is that the joint strength is not as great as when welding. The parts to be joined must be very close fitting. They also need to be very clean and smooth to allow capillary action of the filler material to flow between the joints and make a good connection. If you have ever seen water running down the sides and then under the bottom of a flat bottom glass on a summer day, you have seen capillary action happening.
An entire article can be written about the different types and uses of flux in brazing. We will simply let you know that it is a helper material, usually in the form of a paste that causes the filler material to melt more easily and to flow between the parts to be joined. It also makes the operation anaerobic, that means it keeps oxygen away from the heated metals. When you heat metals they begin to oxidize (rust is oxidation of iron) and this will cause the bond to be weak.
Different materials are used for flux. Some common ones are rosin, acids and phosphors. Rosin is good old pine tar. Purified and refined of course, and one of the earliest fluxes used. Different combinations of acidic or phosphoric chemicals are also used depending on the type of metals to be joined and the specific conditions.
As I said earlier, torching is most commonly used to heat the joint to be brazed. The word ‘torch ‘comes from the old French “Torche” literally meaning “a twisted thing” That is because in early times, people made sticks they could burn for light. They were called torches and were used throughout early history for light and keeping a flame going for cooking and warmth.
In modern days, torching is used for many different processes. One is to cut metal plates. Very thick metal plates can take a lot of time and many saw blades to cut to size, so what are called Oxy-Acetylene cutting torches are commonly used. These are a combination of Oxygen and flammable acetylene gas pied into a wand that can direct the super-hot, pinpoint flame.
Torching is also used in heat treating of metals to make them stronger or to shape them. The glass industry also uses torches for many different purposes. Some of them are drawing glass into fibers, to molding, cutting and shaping glass. More will be explored in a future article on hot glass working. Many other processes that require a source of heat to be applied use torching. Some examples are hot tar roofing, blacktop installation and firefighting.
So since man first learned of fire, we have devised methods to control it and to use it to make our lives more comfortable by creating warmth, light and tools that we can use for living. Torching and Brazing are just two examples of this, and I hope you have learned a bit about them today.
In Part 3 of this series we will look at safety aspects of Brazing, Welding and Torching. Including OSHA regulations and the use of eye protection while performing each process.