Cutting with Oxyfuels and Other Gases Unit 24

Objectives Students will: Write the names and characteristics of common fuels used for cutting. State and apply recommended safety practices for using oxyfuels. Select appropriate pressures for using oxygen and common fuel gases for cutting. Cut steel with oxyfuels Pierce steel with oxyfuels

Important Terms Oxyfuel: combination of pure oxygen and combustible fuel gas to produce a flame Oxyfuel cutting: process in which steel is heated until it burns and is then removed to leave a kerf Kerf: a thin cut Slag: a by-product that is formed during the combination of oxygen with hot steel Brass: mixture of copper and zinc

Important Terms (continued) Base metal: main piece of metal Backfire: a loud snap that blows out the flame Flashback: gases burning back inside the torch that causes a hissing noise Slag box: metal container of water or sand placed to catch hot slag and metal Plasma: a group of charged particles that conduct electrons across a gap

Oxyfuel Processes No one gas is the safest or the best for all jobs Oxyfuels are used for welding, brazing, cutting, and heating metals Oxygen and fuel gases are stored under pressure in tanks or cylinders, carried through valves and hoses, then mixed inside of torch assemblies before being burned as they are released through the tip

Heat Oxyfuels burn between 5,000°F and 6,000°F Temperature is raised enough to soften metal for bending or shaping NO melting takes place Can be used to make a sharp bend in a specific piece Also used to reduce stress from welding

Brazing Process of bonding with metals and alloys that melt at or above 840°F The base metal is heated until the brazing alloy melts, flows, and bonds to it The two metals do not mix

Fusion Welding Joining of metal by melting it together The torch is used to heat two pieces until the metal from each runs together to form a joint Joints are as strong as the base metal itself

Oxygen Not a fuel—will not burn on its own Combines with other substances to cause them to burn at a higher temperature Must be 99.5 percent pure to support the combustion of iron

Acetylene Fuel gas most suitable for welding Produces a cleaner weld than most other fuel gases Produces a more controllable flame Unstable and very hazardous Most stable at pressures below 15 psi

Other Gases Propane and natural gas MAPP® gas Used for general heating and cutting, but not for welding MAPP® gas Mixture of methylacetylene and propadiene gases Qualities similar to acetylene, but more stable Suitable for brazing, cutting, and heating

Oxyfuel Cutting Obtain a neutral flame Mark the line of cut Hold the flame over the corner/edge of the metal at a slight angle Once the metal turns red, press the oxygen lever and move the torch across the metal at a steady rate Keep the flame about 1/8 inch from the metal

Improving Cuts Excessive preheat: if the flame is too hot, or the torch moves too slowly, the surface melts before the metal is heated through Clearance: the distance from the torch to the metal is correct when the tips of the primary flames are almost touching the metal surface

Improving Cuts (continued) Cutting speed Too fast will result in an incomplete cut with rough edges Too slow results in a melted top edge and gouging Gas pressure Too high: dish shape to the kerf Too low: cut is not complete at the bottom

Piercing Pierce: to make a hole Hold the torch at a normal preheat distance above the mark When heated to red color, raise the torch one-half inch or more and slowly press oxygen lever Move the tip sideways in a circular motion until a hole breaks through

Cutting Pipe Small pipe Large pipe Pierce a hole in the top Cut a kerf to the left and one to the right Rotate the pipe and repeat on the underside Large pipe Hold the torch at a right angle to the pipe Move the torch around the pipe to make the cut

Plasma Arc Cutting Used for cutting nonferrous metals Uses an electric arc and argon (an inert gas) Cuts metal faster than conventional oxyfuel torches Not as efficient in cutting thicker metals