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LOST WAX INVESTMENT CASTING - PREPARING THE INVESTMENT MIXTURE

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Lost wax casting is a process whereby, a wax model of the final product is used to manufacture a mould. A mould composed of ‘rubber’ or ‘investment’ is formed around the wax model. The wax is either removed or melted by heating in an kiln / oven. The molten metal is poured into the mould, cooling to form the final product.
 

A wax model of the finished product is manufactured, normally by hand. This is a skilful process, as the wax model must be perfect. Any imperfections at this stage, would show up on the ‘cast’ final product. The example shown opposite is a wax model of a simple ring.

Sprues are added to the model. The bottom sprue supports the model, when making the mould and allows the melting wax to escape. The top sprue forms the hole down which the molten metal is poured.

 
 
 
 
PREPARING INVESTMENT
 
‘Investment’ is the term given to the powder that is combined with water, to produce a mixture, that is poured around the wax model. A dust mask is advisable when mixing, as investment includes silica. Always follow the manufacturers instructions when mixing, ensuring that accurate measures of investment and water are used.
 
1. Weigh the correct measure of investment powder.  
     
2. Measure accurately, the amount of water required.  
     
 
     
3. Add the investment powder to the water and mix for 2 - 3 minutes.  
     
4. Place the investment mixture in a vacuum for 3 minutes, to remove any air. The mixture expands as it ‘boils up’ (bubbles) filling the bowl. Then it returns to its original height in the container. Pour it into a pouring container / jug.  
     
Investment mixture - ready for the next stage.  
     
 
 
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