Versatility of an Oxygen Acetylene Torch for the Metal Artist
The gas torch
In this article, I will be covering the versatility of the gas torch. What I will not cover is how to hook everything thing up, light it, or maintain it. That being said, I will give a quick summary of what a torch entails. It is essentially a devise that generated extreme heat by mixing a strongly exothermic fuel like acetylene with pure oxygen. The flame temperature can exceed 6000 degrees Fahrenheit and it is completely controllable by pressure and tip sizes. These two properties alone can really be very useful for the artist. But believe me, there is more.
One of the main uses is gas welding. Usually this is done with steel but will work for pure copper as well. This is where two pieces of metal to be joined are heated to the melting point and a filler rod of the same metal is added if needed. The tip size and gas pressure determine the thickness of the metal to be welding. Typically, the gas torch is useful for thinner gauge metals that may be damaged by arc welders. It is also good for producing welds without spatter or pinholes.
Braze welding is where two pieces to be joined are heated but not melted. A filler rod of an alloy with a lower melting point is typically used. An example is joining two steel pieces together with a bronze brazing rod. A flux is usually used to prevent fire scale from getting in the weld joint and must be removed before any painting or coating is applied. The beauty of braze welding is completely different metals can be brazed together providing that each metal is compatible with the brazing alloy and the heating process. Examples are brazing steel to copper or stainless steel to mild steel. The main advantages of braze welding are there is minimal heat distortion due to lower heat used, and thin metal can be joined easily with thicker pieces. The disadvantage is the flux can be difficult to remove especially if overheated. One tip I can offer is to quench the still red hot joint into cool water to crack the flux.
Small Steel Sunburst
Examples of Braze Welded Sculpture
As mentioned above, braze welding is the joining of two metals with a lower melting filler metal. In the case of braze welding mild steel, bronze filler rod is often used. It is way cheaper than the silver bearing alloys. Also, it sets up a handsome contrast with the steel for a decorative and distinctive finish. This is just method I use to make my handmade metal art.
Take for instance, this small steel sunburst. It is made from a pipe end cap, and masory square cut nails braze welded together with bronze.
Another useful trait of the gas torch is that it can be used to cut steel. Many torches have attachements and the welding attachment can be changed for a cutting attachment. The cutting torch operates with an oxygen pressure 3 to 5 times the pressure used for welding. It operates by first heating the metal to redness almost melting, then the high pressure oxygen is engage and the metal combust is blown away from the cut. This type of cutting only works for steel as other metals would just merely melt. The advantage is that the metal is quickly and easily cut without mechanical stress on tools or cutting bits. The disadvantages are that it requries a lot of skill and practice to get a clean cut and there typically is a a lot of slag to grind off.
Cutting Steel with Oxy Acetylene
Bending Steel Rod with Oxygen Acetylene
Alas, there is still more that can be done with a torch. That is heat forming. A piece of metal like a rod or a sheet can be heated and formed by heating with a torch and bent with a gloved hand or with a hammer. The size of the tip determines the thickness of metal that can be bent in this fashion. Many torch body manufacturers make a special tip called a rosebud. This tip is a heating tip with multiple orifices to create a bigger and hotter flame. If you want to see the art that I make then check out my Etsy shop.
Types of alloys for brazing
If you have ever broused a welding supply company, you probably come across a significant selection of filler metals for brazing. Here I will give a brief summary of the most common alloys available.
Silver bearing alloys, sometimes called hard solder, find frequent use in jewelry and HVAC. The high cost limits them to specialty applications though. The silver content varies with eash alloy and determines the lsapplication of such alloys. Some are suited for brazing stainless steel alloys, others for copper alloys, and still others for joining dissimular metals such as stainless to a brass fiitting on brewery equipment. The silver alloys are quite fluid and have superior capilliary action. This means they can flow into joints more easily.
Low fuming bronze is the most common copper based alloy. It is actaully a type of brass since it mostly consist of copper and zinc but contains no tin. It is relatively inexpensive, readily available, and it is capable of joining many kinds of metals including dissimular ones. It is offered in both bare and flux coated versions for the convenience of the brazer. The flux coated variety is best for oxidized metals or metals that oxidize easily like brass and stainless.
Aluminum is another metal that can be brazed with an oxygen acetylene torch. Usually, a aluminum/silicon alloy that melts somewhat lower than the parent metals being joined.