Fugitive pattern for casting

Abstract

A fugitive pattern for making a shell mold for investment casting a metal or alloy comprises a substantially random interpolymer and a low molecular weight polymer in proportions to provide a fugitive pattern having a combination of properties suitable for use in making the shell molds.

We claim:  
     
         1 . A pattern material for making a fugitive pattern of an article to be cast of a metal or alloy, comprising; 
 A) a substantially random interpolymer, and    B) a low molecular weight polymer other than said interpolymer.    
     
     
         2 . The pattern material of  claim 1  including a thermoplastic polymer other than said interpolymer and said low molecular weight polymer.  
     
     
         3 . The pattern material of  claim 1  wherein said interpolymer is prepared by polymerizing one or more α-olefins with one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.  
     
     
         4 . The pattern material of  claim 1  wherein said interpolymer comprises one or more vinyl or vinylidene aromatic monomers and an additional monomer.  
     
     
         5 . The pattern material of  claim 3  wherein said vinyl or vinylidene aromatic monomer comprises from 1 to 65 mol % of said interpolymer.  
     
     
         6 . The pattern material of  claim 5  wherein said vinyl or vinylidene aromatic monomer comprises from 10 to 60 mol % of said interpolymer.  
     
     
         7 . The pattern material of  claim 6  wherein said vinyl or vinylidene aromatic monomer comprises from 30 to 50 mol % of said interpolymer.  
     
     
         8 . The pattern material of  claim 1  wherein said polymer is selected from a low molecular weight polystyrene, tackifier resin, and wax with average molecular weight (Mn) <10,000.  
     
     
         9 . The pattern material of  claim 8  wherein the average molecular weight is <5,000.  
     
     
         10 . The pattern material of  claim 9  wherein the average molecular weight is <2,000.  
     
     
         11 . The pattern material of  claim 1  comprises, in weight %: 10-95% said interpolymer and 5-60% of a low molecular weight polymer.  
     
     
         12 . The pattern material of  claim 11  comprises, in weight %: 30-80% said interpolymer and 10-50% said low molecular weight polymer.  
     
     
         13 . The pattern material of  claim 12  comprises, in weight %: 50-70% said interpolymer and 20-50% of a low molecular weight polymer.  
     
     
         14 . A fugitive pattern material for making a fugitive pattern of an article to be cast of a metal or alloy, comprising; 
 A) ethylene/styrene interpolymer, and    B) a low molecular weight polystyrene.    
     
     
         15 . The pattern material of  claim 14  comprising, in weight %: 50-70% said interpolymer and 20-50% of said low molecular weight polystyrene.  
     
     
         16 . The pattern material of  claim 15  comprising, in weight %: 60% said interpolymer and 40% said low molecular weight polystyrene.  
     
     
         17 . The pattern material of  claim 14  having a melt flow rate of 350 or greater by ASTM D1238.  
     
     
         18 . A fugitive pattern having a shape of an article to be cast from a metal or alloy, comprising the pattern material of  claim 1  or  14 .  
     
     
         19 . The pattern of  claim 18  having an injection molded shape of said article.  
     
     
         20 . The pattern of  claim 18  wherein said shape comprises a gas turbine engine blade or vane.  
     
     
         21 . The pattern of  claim 18  having reduced dimensional variation as an I-beam pattern shape as compared to a wax pattern as an I-beam pattern shape.  
     
     
         22 . The pattern of  claim 18  having higher strength as compared to a wax pattern.  
     
     
         23 . The pattern of  claim 18  having higher toughness as expressed by less brittleness as compared to a wax pattern.  
     
     
         24 . The pattern of  claim 18  having a melt flow rate of 350 or greater by ASTM D1238.  
     
     
         25 . The pattern of  claim 18  having a lower shrink as compared to a wax pattern and a polystyrene pattern.  
     
     
         26 . Combination of a fugitive pattern having a shape of an article to be cast from a metal or alloy and a shell mold invested on said pattern, wherein said pattern comprises the pattern material of  claim 1  or  14 .  
     
     
         27 . The combination of  claim 26  having an injection molded shape of said article.  
     
     
         28 . The combination of  claim 26  wherein said pattern has a shape of a gas turbine engine blade or vane.  
     
     
         29 . The combination of  claim 26  where said pattern has a melt flow rate of about 350 or greater by ASTM D1238.  
     
     
         30 . The pattern of  claim 26  wherein said shape comprises a gas turbine engine blade or vane.  
     
     
         31 . The pattern of  claim 26  having reduced dimensional variation as an I-beam pattern shape as compared to a wax pattern as an I-beam pattern shape.  
     
     
         32 . The pattern of  claim 26  having higher strength as compared to a wax pattern.  
     
     
         33 . The pattern of  claim 26  having higher toughness as expressed by less brittleness as compared to a wax pattern.  
     
     
         35 . The pattern of  claim 26  having a lower shrink as compared to a wax pattern and a polystyrene pattern.  
     
     
         36 . A method of making a shell mold for casting a metal or alloy, comprising providing a fugitive pattern having a shape of an article to be cast of the metal or alloy, said pattern comprising said pattern material of  claim 1  or  14 , investing said pattern in a shell mold, and removing said pattern from said shell mold by melting said pattern without cracking said shell mold.  
     
     
         37 . The method of  claim 36  wherein said pattern is melted by flash heating.  
     
     
         38 . The method of  claim 37  wherein said pattern is melted by steam autoclaving.