Key Points

Methods

Link:

“In agriculture mechanics, both in construction and repairs, we are constantly in need of people skilled in the process of oxyacetylene cutting.  The oxyfuel process allows us to cut and shape materials for a variety of jobs.  In several industries, agriculture and oil in particular, there are several needs for people skilled in the art of oxcacetylene welding.”

Motivation:

Let us begin this study by examining the gases associated with the oxyfuel process and the properties of each of those gases.  When using an oxyfuel machine, controlling the gasses is extremely important.  If you understand the gasses and their properties, you will do well with the oxyfuel processes.

Overview:

• Identify the gases associated with oxy-acetylene
• Clarify the properties of the gases associated with oxy-acetylene
• Compare and Contrast the different types of gasses and their properties

5 minutes

Teacher led discussion

Teacher led discussion

Key Points

Methods

Today we will start discussing the oxyfuel processes by starting with the types of gasses associated with oxyfuel processes and their properties.

•         Oxyfuel:  the process of combining pure oxygen with a combustible fuel gas to produce a flame

•         Can be used for welding, brazing, cutting, and heating metals

•         Oxygen & fuel gases are stored under pressure in cylinders and are released as individual gases through valves, regulators, and hoses.

–         Mixed as they flow through torch assemblies

–         Burn as they are discharged through special tips

•         Fuel gases:

–         Propane, natural gas, propylene & acetylene

–         Vary in their chemical composition

–         React with the metal in different ways

•         Factors to consider in selecting a gas:

–         Availability & cost

–         Welding process or operation to be performed

–         Thickness of metal & type of welded joint to be produced

–         Physical properties of metals

–         Chemical properties of metals

Propane (C₃H)

•         Supplied in a liquid form under positive pressure, which varies with temperature

•         Most oxyfuel cutting torches can use LP gas, but special hoses and cutting tips are required.

•         Readily available in most areas

•         Due to cost, propane cutting is heavily used in the metal recycling industry.

Propylene (C₃H₆)

•         Has been used for approximately 30 years

•         Stable in both liquid and gas states

•         Economical

•         Produces little slag

•         Has a high heat value

•         Does not have the withdrawal pressure limitations that are necessary with acetylene

•         Approximately 5% propylene, 87% propane & traces of other gases

Acetylene (C₂H₂)

•         Most widely used fuel gas for welding and cutting applications

•         Produces a clean weld and a controllable flame

•         Less stable and more expensive than other fuel gases

•         Performs most functions well and is widely available

Compressed Natural Gas (CH₄)

•         Adaptable for cutting, soldering, brazing, and preheating

•         A water seal or blowback valve to prevent backfiring into the gas supply line must protect the natural gas source

Facts About Oxygen (O₂)

•         Odorless, colorless, tasteless & heavier than air

•         Makes up about 20% of the atmosphere

•         Will not burn by itself

•         Produced commercially by causing air to liquefy

•         Compressed into steel cylinders at 1,800 to 2,400 pounds per in2 (psi)

•         Supports combustion and is explosive if handled improperly

•         Cylinder sizes = 80 to 244 ft3

Facts About Acetylene (C₂H₂)

•         Colorless, but has a very distinct odor

•         Highly combustible

•         Cylinder sizes = 60 to 300 ft3

•         Cylinder contains a porous substance saturated with liquid acetone

•         Acetylene is pumped into the cylinder, displacing some of the acetone

•         Not under extremely high pressure

–         Full cylinder is pressurized to approximately 250 psi

•         May not be withdrawn at a rate higher than 15 psi

Functions of Oxyfuel Heat

•         Oxyfuel cutting of mild carbon steel heats the metal to rekindling temperature (1,400oF to 1,800oF), then oxidizes and blows the slag from the cut with a stream of pure oxygen.

•         Oxyfuel welding fuses two pieces of metal by heating them to the melting point with a combustible mixture of oxygen and fuel gas.

–         Can be done with or without the use of a welding rod

–         Brazing:  the joining of metals by adding bronze filler

–         Soft and hard solders (lead & silver alloys) are the filler materials used in soldering.

•         The oxyfuel flame is also used to bend, shape, preheat, stress relieve, post-heat & temper metal

We will compare and contrast the different types of gasses on the worksheet orally.  We will fill in the chart stating the differences between the gasses as a class.

25 minutes

Power point presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Power Point Presentation

Application/Student Handout (comparison chart)

Key Points

Methods

• Each student will be given a chart used to compare and contrast the properties of the different types of gasses used in oxyfuel processes.
• The class will work together to fill in the missing parts of the chart

10 minutes

Student Handout (comparison chart)

Key Points

Methods

• What is Oxyfuel?

           the process of combining pure oxygen with a combustible fuel gas to produce a flame

• What are the different types of fuel gasses we talked about today?

     Propane, natural gas, propylene & acetylene

• Give me at lease one consideration when selecting your fuel gas.
  • Availability & cost
  • Welding process or operation to be performed
  • Thickness of metal & type of welded joint to be produced
  • Physical properties of metals
  • Chemical properties of metals
• Which type of fuel gas is the most widely used gas?

     Acetylene

• What is the maximum rate of withdraw for acetylene?

15 psi

• What is Brazing?

           the joining of metals by adding bronze filler

5 minutes

Oral Questions