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Select any two from (i), (ii) or (iii) below and explain the difference between the terms in each: (i) Optical pyrometer and thermocouple pyrometer; (ii) Grey cast iron and white cast iron; (iii) Upper critical temperature (UCT) and lower critical temperature (LCT). - Leaving Cert Engineering - Question c - 2021
Question c
Select any two from (i), (ii) or (iii) below and explain the difference between the terms in each: (i) Optical pyrometer and thermocouple pyrometer; (ii) Grey cast... show full transcript
Worked Solution & Example Answer:Select any two from (i), (ii) or (iii) below and explain the difference between the terms in each: (i) Optical pyrometer and thermocouple pyrometer; (ii) Grey cast iron and white cast iron; (iii) Upper critical temperature (UCT) and lower critical temperature (LCT). - Leaving Cert Engineering - Question c - 2021
Step 1
Optical pyrometer and thermocouple pyrometer
Answer
The Optical pyrometer is a device that measures the temperature of an object by comparing the intensity of light from its surface to a reference light source, usually from a filament. The measurement relies on the matching color of the filament with that of the object to deduce the temperature.
Conversely, the thermocouple pyrometer operates based on the principle of electrical conduction. It consists of two dissimilar metals joined at a junction, producing an electrical voltage proportional to the temperature difference between the junction and the reference point. This device reads temperature directly as an electrical reading instead of comparing colors.
Step 2
Grey cast iron and white cast iron
Answer
Grey cast iron is characterized by its graphitic flakes, which result from its structure and give it a gray appearance when fractured. The flakes enhance machinability and reduce brittleness, making it common in various industrial applications.
On the other hand, white cast iron features a crystalline structure with a shiny appearance and offers greater hardness and brittleness, making it less machinable. It is often used in applications that require wear resistance.
Step 3
Upper critical temperature (UCT) and lower critical temperature (LCT)
Answer
The upper critical temperature (UCT) refers to the temperature point in the iron-carbon phase diagram where the phase changes occur, marking the transition to austenite upon heating. It typically corresponds to the maximum carbon content that remains in solution.
In contrast, the lower critical temperature (LCT), set at approximately 723°C, indicates the temperature where austenite begins to transform into pearlite upon cooling. Understanding these critical temperatures is essential for controlling the microstructure and properties of steel and cast iron during heat treatment.