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(a) Select any two of the following: (i) Compare the impact of soaking with the impact of water cooling in heat treatment; (ii) Distinguish between the optical pyrometer and the thermo-electric pyrometer; (iii) Describe the normalising process - Leaving Cert Engineering - Question 3 - 2010
Question 3
(a) Select any two of the following: (i) Compare the impact of soaking with the impact of water cooling in heat treatment; (ii) Distinguish between the optical pyr... show full transcript
Worked Solution & Example Answer:(a) Select any two of the following: (i) Compare the impact of soaking with the impact of water cooling in heat treatment; (ii) Distinguish between the optical pyrometer and the thermo-electric pyrometer; (iii) Describe the normalising process - Leaving Cert Engineering - Question 3 - 2010
Step 1
Compare the impact of soaking with the impact of water cooling in heat treatment
Answer
Soaking is a heat treatment process where metal is heated to a specified temperature, allowing for uniform heating and phase transformations. This process ensures proper austenitization before quenching.
In contrast, water cooling is a quenching method used after soaking. Water cooling typically results in a rapid drop in temperature, promoting hardening but increasing the risk of cracking and warping. While soaking aims to alleviate internal stresses, water cooling may cause them to intensify due to rapid changes in temperature.
Step 2
Distinguish between the optical pyrometer and the thermo-electric pyrometer
Answer
An optical pyrometer operates by measuring the intensity of light emitted from a hot object, such as the filament of a lamp. By adjusting the resistance, the brightness can be matched, and the temperature can be inferred from this calibration.
Conversely, a thermo-electric pyrometer utilizes electrical current generated by heating two dissimilar metals. The temperature reading is derived from measuring the electrical potential difference generated at the junctions of these metals.
Step 3
Step 4
Describe, with the aid of a diagram, the crystal structure of martensite
Answer
Martensite has a unique needle-like structure, where carbon is trapped in the crystal lattice of iron during rapid cooling. It results in a strong, yet brittle, material due to distortion caused by the high carbon content. Below is a simplified representation:
Diagram: Martensite Structure
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Step 5
Identify a suitable heat treatment process to prevent wear on the guideways
Answer
A suitable heat treatment process for the guideways would be induction hardening. This process hardens the surface by using induction heating to rapidly increase the temperature, followed by quenching to harden the material.
Step 6
Describe, with the aid of suitable diagrams, this heat treatment process
Answer
Induction hardening involves the use of an induction coil to generate an alternating magnetic field, which induces eddy currents in the metal component. This rapid heating increases the surface temperature quickly. Following this, water jets are often used for quenching, which cools the surface swiftly to form a hardened layer.
Here’s a basic diagram illustrating the process:
Diagram: Induction Hardening Process
AC Supply
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Water jets