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a) Answer any two of the following: i) Describe, with the aid of a suitable diagram, the induction hardening process; ii) Distinguish between the properties of grey cast iron and white cast iron; iii) Explain the function of stress relieving in metals - Leaving Cert Engineering - Question 3 - 2011
Question 3
a) Answer any two of the following: i) Describe, with the aid of a suitable diagram, the induction hardening process; ii) Distinguish between the properties of gre... show full transcript
Worked Solution & Example Answer:a) Answer any two of the following: i) Describe, with the aid of a suitable diagram, the induction hardening process; ii) Distinguish between the properties of grey cast iron and white cast iron; iii) Explain the function of stress relieving in metals - Leaving Cert Engineering - Question 3 - 2011
Step 1
Induction hardening process
Answer
Induction hardening is a heat treatment process that involves the use of high-frequency electrical currents to heat the surface of a metal component. The process typically involves the following steps:
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Induction Coil: A coil carries high-frequency alternating current, creating an electromagnetic field around the component.
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Heat Generation: The induced currents cause the metal surface to heat rapidly, transforming it into austenite.
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Quenching: After reaching the desired temperature, the surface is cooled quickly using a water spray or oil, which transforms the austenite into a harder structure.
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Depth of Hardening: The frequency of the current influences how deep the hardening effect penetrates the material, allowing for control over hardness and wear resistance.
Step 2
Distinguish between the properties of grey cast iron and white cast iron
Answer
Grey cast iron and white cast iron differ primarily in their microstructure and mechanical properties:
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Grey Cast Iron: Contains graphite flakes, which provide a softer, more ductile material. It has excellent castability, good machining properties, and high wear resistance, making it suitable for engine blocks and machine bases.
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White Cast Iron: Characterized by a cementite structure without graphite, it is harder and more brittle. It is often used in wear-resistant applications, such as in some types of grinding mills, but its brittleness limits its use.
Step 3
Explain the function of stress relieving in metals
Answer
Stress relieving is a heat treatment process aimed at reducing residual stresses in metals, which can be introduced during processes like welding, machining, or forming. The primary functions include:
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Reducing Internal Stresses: It helps to decrease the potential for warping or distortion during subsequent manufacturing processes or during service.
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Enhancing Structural Integrity: By relieving stress, the process improves the overall mechanical performance of the metal, extending its life and preventing unexpected failures.
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Improving Workability: Stress-relieved metals tend to be more ductile, allowing for easier machining and forming.
Step 4
Step 5
Outline the effect of cooling 0.4% carbon steel quickly from 900 °C
Answer
Rapid cooling of 0.4% carbon steel from a temperature of 900 °C results in the formation of martensite. This microstructure is characterized by a hard and brittle configuration:
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Formation of Martensite: The structure develops due to the trapped carbon atoms in the iron matrix as the temperature drops too quickly for carbon to diffuse out.
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Increased Hardness: The transition creates a material that is significantly harder than its initial state, often at the expense of ductility, making it more susceptible to cracking under stress.
Step 6
Step 7
Describe the principle of operation of the pyrometer, making reference to diagrams A, B and C
Answer
The disappearing filament pyrometer operates based on the comparison of light intensity:
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Diagram A: Shows the filament glowing brighter compared to the surrounding area. When the temperature of the furnace is too low, the filament’s light can be easily seen.
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Diagram B: Indicates an ideal condition where the filament matches the brightness of the furnace’s light, allowing for accurate temperature measurement.
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Diagram C: Represents a situation where the filament appears darker due to excessive temperature, indicating that the reading may be too high, and adjustments are necessary to achieve balance between the lamp and furnace light.