1. Cutting with Oxyfuels and Other Gases
Unit 24

2. 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

4. 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

5. 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

6. 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

7. 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

8. 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

10. 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

11. 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

12. 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

13. 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

18. 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

22. 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

27. 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

28. 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

30. 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

33. 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