Method and apparatus for making directional solidification castings

Abstract

A method and apparatus for producing large, directionally solidified cast articles having a cast height greater than 200 mm, and preferably greater than 300 mm is described. The casting mold reliability, as well as the casting equipment, is improved by proportioned pouring of a molten superalloy into a casting mold where the mold is protected by suspender elements. The cast articles made by the inventive method are of particular interest to aircraft and power generation equipment, and include, but are not limited to, components such as blades, airfoils, buckets, nozzles, and the like.

What is claimed:  
     
         1 . A method of making directionally solidified cast articles, distinguished by having improved reliability of a casting mold or molds, said method comprising the steps of: 
 heating the casting mold to a predetermined temperature in a heating zone in a casting furnace;    pouring molten superalloy into the casting mold in the heating zone in an initial amount sufficient to maintain a level of the molten superalloy above a solidification front of the cast article to prevent disturbance of crystalline growth of the directionally solidified cast article;    simultaneously directionally solidifying the molten superalloy by withdrawing the mold from the heating zone into a cooling zone while further pouring of the molten superalloy into the casting mold at a rate to maintain the level of the molten superalloy above the solidification front; and    finishing the pouring of the molten superalloy into the casting mold so that a height of the solidified portion of the cast article is greater than one half of an overall height of the cast article.    
     
     
         2 . A method according to    claim 1    where the directionally solidified cast articles are single crystal or polycrystalline articles.  
     
     
         3 . A method according to    claim 1    where the casting mold is heated above a melting temperature of the molten superalloy.  
     
     
         4 . A method according to    claim 1    where the initial amount of the molten superalloy poured into the mold is about 20-30% of the volume of the mold.  
     
     
         5 . A method according to    claim 1    where the level of the molten superalloy above a solidification front is about 30-70 mm in height.  
     
     
         6 . A method according to    claim 1    where the cooling zone comprises a liquid metal bath.  
     
     
         7 . A method according to    claim 1    where the cooling zone comprises a chill plate and a space without auxiliary heating.  
     
     
         8 . A method according to    claim 1    where the casting mold comprises more than one interior cavity to make plural cast articles.  
     
     
         9 . A method according to    claim 1    where the casting mold hangs vertically within the furnace, and said mold is embraced by a suspender system.  
     
     
         10 . A method according to    claim 9    where the suspender system comprises horizontal and vertical suspending elements.  
     
     
         11 . A method according to    claim 10    where suspending elements are made from a material selected from the group consisting of molybdenum, graphite, graphite-based composites, and mixtures thereof.  
     
     
         12 . A method according to    claim 1    where the casting mold is made from a pattern having a suspender skeleton.  
     
     
         13 . A method according to    claim 12    where the suspender skeleton has suspender elements placed into outer mold cavities and ends of said suspending elements are sealed with a ceramic slurry.  
     
     
         14 . A method according to    claim 1    where said mold has a pouring riser attached on its lateral side with at least one passageway entering the interior cavity of the mold.  
     
     
         15 . A method according to    claim 14    where said mold has more than one interior cavity and each cavity at least one passageway from the pouring riser entering the interior cavity.  
     
     
         16 . A method according to    claim 15    where said passageway has an angle between about +70° to −70° to a horizontal plane.  
     
     
         17 . A method according to    claim 16    where the passageway has a diameter of about at least 1 millimeter.  
     
     
         18 . A method according to    claim 14    where the pouring riser has a stationary pouring cup that telescopically enters the pouring riser.  
     
     
         19 . An article made according to the method of    claim 1   .  
     
     
         20 . An article according to    claim 14    being a single crystal.  
     
     
         21 . An apparatus for casting directional solidified articles comprising: an induction furnace for heating metal, a heating means connected to the induction furnace to heat the metal; a chamber for preheating a casting mold; a heating means to preheat the mold and chamber; a pouring means in the induction furnace to pour the heated metal into the preheated mold; a mold suspender means in the chamber for preheating the mold; a cooling chamber; and a means to maintain a controlled atmosphere in each chamber.  
     
     
         22 . A casting mold having an interior casting cavity with dimensions for a cast article and exterior cavities for suspender elements.