81928
Description
Flashcards by Alec Stevens, updated more than 1 year ago
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Created by Alec Stevens
over 11 years ago
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| Question | Answer |
| Annealing | Done to alleviate the effects of work hardening. Relieves internal stresses. Heat up to required temperature and allow to cool. Aluminium should be covered in soap and heat until soap turns black to ensure it doesn't melt. Copper heated till dull red. When heated copper forms oxides on the surface - must be removed by an acid bath. |
| Tempering | Done after hardening a metal in order to give the right balance of hardness vs brittleness. The hardened metal is cleaned up using emery cloth, and then slowly and carefully reheated until the thin line of oxide on the material changes colour. When the desired temperature/colour is reached, the work is removed and quenched, freezing the iron carbide level. If it wasn't quenched, the metal would simply cool and normalise. |
| Hardening | When carbon steel is heated to 900 degrees (cherry red) and then quenched, it becomes exceptionally hard. This also increases its brittleness and means it can break if put under pressure. Mostly metals are hardened and then tempered to achieve desired result. |
| Normalising | A process undertaken on hardened ferrous metals to return them to their original state. Steel is heated until it is cherry red and allowed to cool in air. This will allow it to lose its hardness and be cut or drilled again. |
| Work Hardening | Occurs when a non-ferrous metal is cold worked (hit, bent or shaped). It becomes so hard and brittle it can eventually fracture. Positive when used for plannishing - where work hardening is used to make something suitably hard for usage. Negative when it means constant annealing during work. |
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