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THE CASTING PROCEDURE (1)

V. Ryan © 2003 - 2009

 

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The procedure for preparing aluminium ingots for casting must to be carried out carefully as safety is one of the key concerns, whether in a school workshop or in industry. Outlined below are the stages involved in heating and charging a crucible and then pouring the molten aluminium.

   

PREHEATING - The crucible is first preheated. This removes any moisture from the furnace and crucible. Usually the gas is turned half on in order to avoid rapid heating. The aluminium ingots to be used are placed on top of the furnace so that they warm up.

   

CHARGING WITH ALUMINIUM - once the crucible and furnace have been preheated the lid/top is pulled to one side with a steel hook. Aluminium ingots are then placed into the crucible with steel tongs. All steel tools such as tongs are pre-warmed. The gas pressure is turned up to full.

   

 

   

ADDING FLUX - As the aluminium begins to melt a small amount of ‘flux’ is sprinkled over the aluminium. A spoon can be used to sprinkle the flux powder. The flux prevents oxidisation (oxygen entering the molten aluminium). If oxygen enters the molten aluminium, when it is poured into the mould the final casting can have bubbles which can ruin the finish of the cast shape.

 
 
 

ADDING A DEGASSING TABLET - When the aluminium has melted fully and is approximately 700 degrees centigrade the gas is turned off and a degassing tablet is added. This removes any impurities, in the form of gas. It is important that a good extraction system is used to remove the fumes caused by the tablet.

PLEASE NOTE - it is not vital to use flux or a degassing tablet. The degassing tablet causes a lot of fumes which can be a problem in an enclosed workshop.

   

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