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Questions and Answers
What causes metal to rust?
What causes metal to rust?
Rust is the result of corroding steel after the iron (Fe) particles have been exposed to oxygen and moisture.
What principle makes it possible to cut metal by OFC?
What principle makes it possible to cut metal by OFC?
If metal is heated to its ignition temperature, it oxidizes and rusts much faster, allowing for cutting.
How does a cutting torch differ from a gas welding torch?
How does a cutting torch differ from a gas welding torch?
A cutting torch has a central hole for oxygen and smaller pre-heating holes for fuel gas.
What determines the oxygen and acetylene pressure for cutting metal?
What determines the oxygen and acetylene pressure for cutting metal?
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What aids can be used to facilitate an even cut when using OFC?
What aids can be used to facilitate an even cut when using OFC?
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How can it be determined that the OFC cut is penetrating through the metal?
How can it be determined that the OFC cut is penetrating through the metal?
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What is the position of the torch when cutting round stock?
What is the position of the torch when cutting round stock?
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How is it possible to make a bevel cut with a cutting torch?
How is it possible to make a bevel cut with a cutting torch?
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Describe the operation for piercing small holes with a cutting torch.
Describe the operation for piercing small holes with a cutting torch.
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What type of flame is used for cutting cast iron?
What type of flame is used for cutting cast iron?
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How is the torch held when cutting cast iron?
How is the torch held when cutting cast iron?
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What torch motion is used for cutting cast iron?
What torch motion is used for cutting cast iron?
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What is meant by PAC?
What is meant by PAC?
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What types of metals can be cut by PAC?
What types of metals can be cut by PAC?
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What type of electrode is used in the CAC-A process?
What type of electrode is used in the CAC-A process?
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What causes the removal of molten metal when using CAC-A?
What causes the removal of molten metal when using CAC-A?
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What does the term washing mean when using CAC-A?
What does the term washing mean when using CAC-A?
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What precautions should be observed before engaging in any cutting operation?
What precautions should be observed before engaging in any cutting operation?
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Study Notes
Rust Formation
- Rust results from the corrosion of steel when iron (Fe) is exposed to oxygen and moisture.
- Oxidation of iron leads to the formation of Fe⁺⁺ ions, releasing electrons that create hydroxyl ions (OH) upon reacting with oxygen.
- The reaction between Fe⁺⁺ and hydroxyl ions produces hydrous iron oxide (FeOH), commonly known as rust.
Cutting with Oxygen-Fuel Cutting (OFC)
- Metal oxidizes and rusts faster when heated to its ignition temperature, causing a melting action that is swept away by oxygen, enabling cutting.
- A cutting torch has a central hole for oxygen to blow away molten metal, surrounded by pre-heating holes for the fuel gas.
- Oxygen and acetylene pressures for cutting depend on the type of metal, the manufacturer's tip number size, and the thickness of the metal.
Techniques and Tools
- A straight edge or metal bar aids in achieving an even cut with OFC.
- Indication of successful penetration during cutting is evidenced by a shower of sparks from the underside of the cut.
- To cut round stock, position the torch at a 90-degree angle initially, then follow the contour of the material.
Bevel Cuts and Piercing Holes
- Bevel cuts are achieved by holding the torch at an angle rather than perpendicular, with steady movement to ensure uniform cuts.
- Begin piercing small holes with a larger cutting tip held close to the metal surface, heating until cherry red before activating the cutting lever.
Flame Types and Adjustment
- A slightly carburizing flame is recommended for cutting cast iron; proper adjustment can improve cutting effectiveness.
- For cutting cast iron, position the torch at a drag angle of 40 to 50 degrees initially, then adjust to 65 to 70 degrees as cutting progresses.
Plasma Arc Cutting (PAC)
- PAC can cut any electrically conductive metal, typically effective for materials up to 3 inches thick.
- Nonferrous materials like aluminum and copper can also be cut using PAC, with increased speed for ferrous metals under 3 inches.
Air Carbon Arc Cutting (CAC-A)
- CAC-A uses three types of electrodes: DC copper-coated, DC plain, and AC coated, each having specific characteristics for stability and service life.
- Molten metal is removed through a high-velocity air blast that strikes the molten metal behind the arc.
Safety Precautions
- Cutting operations must be performed in designated areas; clear a 35-foot radius of combustibles if moving the work is not possible.
- Maintain fire watches and have a charged fire extinguisher on site; check for smoldering materials after work hours.
- Always wear appropriate protective gear, including filtering lenses, gloves, and clothing made of materials that are not easily flammable.
- Special ventilation is necessary for cutting materials that produce toxic fumes, and relevant safety measures should be consulted with an Occupational Safety Officer.
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Description
Explore the essential cutting operations in welding as detailed in Chapter 25. This quiz will enhance your understanding of how various factors, including moisture and oxygen, affect metal properties. Test your knowledge and skills related to rust formation and its implications in the welding process.
