Crystal selector pattern

Abstract

A crystal selector pattern for use in forming a mould in an investment casting process, which is formed from a water-soluble organic composition which, in a preferred embodiment, comprises 80% urea.

I claim:  
     
         1 . A crystal selector pattern for forming a crystal selector in an investment casting mould, the crystal selector pattern being formed from a water-soluble organic composition.  
     
     
         2 . A crystal selector pattern as claimed in  claim 1 , in which the water-soluble organic composition is thermoplastic.  
     
     
         3 . A crystal selector pattern as claimed in  claim 1 , which is formed in an injection moulding process.  
     
     
         4 . A crystal selector pattern as claimed in  claim 1 , in which the solubility of the water-soluble organic composition is not less than 500 g/l.  
     
     
         5 . A crystal selector pattern as claimed in  claim 4 , in which the solubility of the water-soluble organic composition is not less than 900 g/l.  
     
     
         6 . A crystal selector pattern as claimed in  claim 1 , in which the water-soluble organic composition comprises hydroxypropylcellulose.  
     
     
         7 . A crystal selector pattern as claimed in  claim 1 , in which the water-soluble organic composition comprises urea.  
     
     
         8 . A crystal selector pattern as claimed in  claim 1 , in which the water-soluble organic composition comprises polyvinyl acetate.  
     
     
         9 . A crystal selector pattern as claimed in  claim 1 , in which the water-soluble organic composition comprises stearic acid.  
     
     
         10 . A crystal selector pattern for forming a crystal selector in an investment casting mould, the crystal selector pattern being formed from a water-soluble organic composition which contains urea.  
     
     
         11 . A crystal selector pattern as claimed in  claim 10 , in which urea is present in the water-soluble organic composition in a proportion not less than 50%.  
     
     
         12 . A crystal selector pattern as claimed in  claim 11 , in which the urea is present in the water-soluble organic composition in a proportion not less than 70%.  
     
     
         13 . A crystal selector pattern as claimed in  claim 10 , in which the water-soluble organic composition comprises polyvinyl acetate.  
     
     
         14 . A crystal selector pattern as claimed in  claim 13 , in which the polyvinyl acetate is present in the water-soluble organic composition in a proportion not less than 10%.  
     
     
         15 . A crystal selector pattern as claimed in  claim 14 , in which the polyvinyl acetate is present in the water-soluble organic composition in a proportion not less than 15%.  
     
     
         16 . A crystal selector pattern as claimed in  claim 10 , in which the water-soluble organic composition comprises stearic acid.  
     
     
         17 . A crystal selector pattern as claimed in  claim 16 , in which the stearic acid is present in the water-soluble organic composition in a proportion not less than 1.  
     
     
         18 . A crystal selector pattern for forming a crystal selector in an investment casting mould, the crystal selector pattern being formed from a water-soluble organic composition which comprises: 
 70 to 90% urea,    10-25% polyvinyl acetate, and    1 to 5% stearic acid.    
     
     
         19 . A crystal selector pattern in accordance with  claim 18 , in which the water-soluble organic composition comprises: 
 80% urea,    18% polyvinyl acetate, and    2% stearic acids.    
     
     
         20 . An investment casting process comprising: 
 making a pattern corresponding to the shape of a desired mould cavity, which mould cavity includes a crystal selector region;    investing the pattern with a hardenable coating of a ceramic material thereby to form a mould cavity about the pattern;    hardening the coating;    removing the pattern from the mould cavity; and    casting an article in the mould cavity,    wherein the pattern corresponding to the crystal selector region is made form a water-soluble organic composition, and wherein the step of removing the pattern corresponding to the crystal selector region comprises steam autoclaving the moulding cavity.    
     
     
         21 . An investment casting process as claimed in  claim 20 , wherein the water-soluble organic composition contains urea.  
     
     
         22 . An investment casting process as claimed in  claim 20 , wherein the water-soluble organic composition comprises: 
 70 to 90% urea,    10-25% polyvinyl acetate, and    1 to 5% stearic acid.    
     
     
         23 . An investment casting process as claimed in  claim 20 , wherein the water-soluble organic composition comprises: 
 80% urea,    18% polyvinyl acetate, and    2% stearic acid.