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ANNEALING METALS

V. Ryan © 2005 - 2009

 

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Annealing is a heat process whereby a metal is heated to a specific temperature /colour and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily. Mild steel, is heated to a red heat and allowed to cool slowly. However, metals such as aluminium will melt if heated for too long.

Aluminium can be annealed but care must be taken whilst heating. The flame should be held at a distance to the aluminium so that it gives a generalised heating to the metal.
A ‘trick of the trade’ is to rub soap on to the surface of the aluminium and then heat it on the brazing hearth. It takes only a short time for the soap to turn black. The brazing torch should be turned off immediately and the aluminium allowed to cool slowly. It is now annealed and should be very soft and malleable.

 
 
 

PHYSICAL PROPERTIES: Annealed metals are relatively soft and can be cut and shaped more easily. They bend easily when pressure is applied. As a rule they are heated and allowed to cool slowly.

The animation above shows that an annealed metal is usually softer and can be deformed more easily than metals that are not annealed.

 

PHYSICAL PROPERTIES: Hardened metals are difficult to cut and shape. They are very difficult if not impossible to bend. As a rule they are heated and cooled very quickly by quenching in clean, cold water.

The animation above shows that metals that have not been annealed are very difficult to deform.

 

 

 

QUESTIONS:
1. Describe, with the aid of diagrams, the hardening and tempering process for mild steel.
2. What is case hardening ?
3. Describe why it is necessary to rub ‘soap’ on to the surface of aluminium sheet when annealing it.

   

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