Method and apparatus for improved heat extraction from aluminum castings for directional solidification

Abstract

Method and apparatus for improving the quality and mechanical properties of an aluminum alloy engine cylinder block or other large or complex castings by providing sand molds bound with a soluble binder only at locations on said casting from which rapid cooling for directional solidification and/or improved localized mechanical properties are desired with said molds being otherwise bound at the remaining locations only with a more typical insoluble binder.

1 . A sand mold for defining a cavity for forming an aluminum alloy casting, comprising at least one first portion formed with a binder soluble in a given solvent and at least one second portion formed with binder insoluble in said solvent.  
   
   
       2 . A sand mold according to  claim 1 , wherein said soluble first portions are each externally accessible to a flow of solvent and also are positioned at a respective location to define an area of the casting cavity where relatively rapid cooling of the molten casting is desired; with one or more second portions positioned to define the remainder of the casting cavity.  
   
   
       3 . A sand mold for a large complex casting according to  claim 2 , wherein the solvent is water.  
   
   
       4 . A sand mold for a large complex casting according to  claim 2 , wherein at least one first portion formed with a soluble binder has a preformed hollow shaped to receive a dissolving and cooling flow of solvent with a hollow depth accelerating removal of the respective first portion from the casting surface while initially supporting the initially molten poured casting at said area until the casting at such area is self-supporting.  
   
   
       5 . A sand mold for a large complex casting according to  claim 2 , wherein at least one of said insoluble second portions is positioned and shaped to help focus and aid the flow of cooling water to at least a respective one of the defined areas for rapid cooling.  
   
   
       6 . A sand mold for a large complex casting according to  claim 5 , wherein at least one first portion formed with a soluble binder has a generally V-shape  
   
   
       7 . A sand mold according to  claim 1 , wherein said soluble first portions are each externally accessible to a flow of solvent and also are positioned at a respective location where relatively rapid cooling of the molten casting is desired, wherein said second portions define the entire area of the casting cavity attributable to the sand mold, wherein said second portions at the aforesaid locations are thinner so as to allow more rapid cooling thereacross while still presenting a uniform surface to the mold cavity, and wherein said second portions at the aforesaid locations are backed up structurally by respective first portions.  
   
   
       8 . A casting apparatus, comprising: 
 a source of molten metal;    a mold according to  claim 2  for receiving molten metal from said source;    a source of said solvent; and    at least one nozzle positioned to spray solvent from its source to impinge on a respective one of said first portions, formed with a soluble binder, for washing away said first portion to impinge upon and rapidly cool said casting at the resulting area of impingement.    
   
   
       9 . An apparatus for casting an aluminum alloy engine cylinder block, with a crankcase housing and with seats for cylinder head bolts, in a sand mold according to  claim 1 , further comprising: 
 one of said soluble first portions being a core forming a mold cavity portion for defining a crankcase housing portion for said block; and    others of said soluble first portions being inserts forming a mold cavity portions at locations for said bolt seats.    
   
   
       10 . A method for forming an aluminum alloy casting in a sand mold, comprising: 
 providing a sand mold defining a cavity for forming said casting with at least one first portion of said mold formed with a binder soluble in a given solvent and at least one second portion formed with binder insoluble in said solvent, said one first portion being positioned to define an area of the casting cavity for achieving localized rapid cooling of the casting;    filling said mold with liquid aluminum alloy;    directing at least one cooling stream of solvent onto at least one first portion to wash out such respective first portion to expose and directly cool the solidifying casting to give accelerated cooling of the defined area.    
   
   
       11 . A method according to  claim 10 , wherein each cooling stream is initiated while the casting is still molten with the thickness of the respective first portion and the removal thereof by such cooling stream being adjusted to have the respective first portion remain intact sufficiently to support the molten casting during initial cooling at the respective defined area as needed, with removal to expose such area to direct impingement being accomplished once the casting in such defined area becomes self-supporting and maintaining said impingement on said casting for a time effective for improving the cooling rate and the mechanical properties of said casting at least in the region proximate to the respective defined area.  
   
   
       12 . A method for forming a large complex aluminum alloy casting according to  claim 11 , wherein said respective defined area is positioned to achieve directional cooling remote from and directed towards a source of said liquid aluminum in a manner to avoid voids and shrinkage porosity.  
   
   
       13 . A method according to  claim 10  for low pressure casting of an aluminum alloy engine cylinder block in a sand mold having areas defining a crankcase housing and seats for bolts further comprising setting one of said first portions as a sand-core to define the crankcase housing and setting other first portions as cores to define seats for bolts.