Hard- Surfacing, Building Fusion Welding Carbon Welding Non-Ferrous Metals Heating & Heat Treating Braze Welding Welding Cast Iron Welding Ferrous Metals Brazing & Soldering Equipment Set-Up Operation Equipment For OXY-Acet Structure of Steel Mechanical Properties of Metals Oxygen & Acetylene OXY-Acet Flame Physical Properties of Metals How Steels Are Classified Expansion & Contraction Prep For Welding OXY-Acet Welding & Cutting Safety Practices Manual Cutting Oxygen Cutting By Machine Appendices Testing & Inspecting
2 fire would probably burn flat in a matter of minutes, rather than hours. If there’s one thing you must remember about oxygen, it’s that things burn much faster in pure oxygen (or even in a mixture of half oxygen, half nitrogen) than they do in air. That’s why passing a lighted cigarette to a person in an oxygen tent is almost equivalent to signing his death warrant. The other thing you must remember is this: that when surrounded by pure oxygen, some oils and greases oxidize rapidly, fast enough to reach kindling temperature in a short time. That’s why you must always keep oxygen away from oils and grease, and keep oil and grease from getting into an oxygen regulator or hose. The only lubricants which can be used with oxy-acetylene apparatus – and then only on threads and O-rings – are special products approved for such use. Acetylene Acetylene is a ”hydrocarbon”, just as are propane, methane, and virtually all the components which make up gasoline and fuel oils. However, it differs from those hydrocarbons in this respect: in the acetylene molecule, made up of two carbon atoms and two hydrogen atoms, the carbon atoms are joined by what chemists call a ”triple bond”. When acetylene reaches its kindling temperature (and under some other conditions as well, which we’ll cover shortly) the bond breaks and releases energy. In other hydrocarbons, the breaking of the bonds between the carbon atoms absorbs energy. The triple bond is the reason why the oxy-acetylene flame is hotter than the flame produced by burning any other hydrocarbon gas with oxygen. Acetylene is almost unknown in the natural world. There are ways to produce acetylene from natural gas, but they are economical only on a large scale. Virtually all the acetylene distributed for welding and cutting use is created by allowing calcium carbide, an electric furnace product, to react with water. As mentioned in Chapter 2, the discovery of the electric furnace method of producing calcium carbide was accidental. It turned out to be a lucky accident. The nice thing about the calcium carbide method of producing acetylene is that it can be done on almost any scale desired. In tightly-sealed cans, calcium carbide keeps indefinitely. For years, miners’ lamps produced acetylene by adding water, a drop at a time, to lumps of carbide. Before acetylene in cylinders became available in almost every community of appreciable size, as it is today, many users of acetylene produced their own gas from calcium carbide, using acetylene generators which ranged in output from as little as 20 to as much as 1000 cubic feet per hour (cfh).