Method of unidirectional solidification of castings and associated apparatus

Abstract

Molten metal is injected uniformly into a horizontal mold from a feed chamber in a horizontal or vertical direction at a controlled rate, directly on top of the metal already within the mold. A cooling medium is applied to the bottom surface of the mold, with the type and flow rate of the cooling medium being varied to produce a controlled cooling rate throughout the casting process. The rate of introduction of molten metal and the flow rate of the cooling medium are both controlled to produce a relatively uniform solidification rate within the mold, thereby producing a uniform microstructure throughout the casting, and low stresses throughout the casting. A multiple layer ingot product is also provided comprising a base alloy layer and at least a first additional alloy layer, the two layers having different alloy compositions, where the first additional alloy layer is bonded directly to the base alloy layer by applying the first additional alloy in the molten state to the surface of the base alloy while the surface temperature of the base alloy is lower than the liquidus temperature and greater than eutectic temperature of the base alloy −50 degrees Celsuis.

What is claimed is: 
     
         1 . A method of casting metal, comprising:
 providing a casting apparatus for casting metal comprising
 a plurality of sides and a bottom defining a mold cavity, wherein the bottom has at least two surfaces, including a first surface and a second surface; 
 at least one metal feed chamber adjacent to the mold cavity; 
 at least one control apparatus between the feed chamber and the mold cavity, the control apparatus being structured to control the flow rates of molten metal being introduced horizontally into the mold cavity, 
 wherein the bottom comprises a substrate having (a) sufficient dimensions, and (b) a plurality of apertures, such that the bottom:
 (i) allows one or more cooling mediums to flow through the apertures and directly contact the metal, wherein a direction of the flow of the cooling medium is from the first surface of the bottom into the mold cavity, and 
 (ii) simultaneously resists the metal initially poured directly onto the second surface of the bottom from exiting through the apertures to the first surface of the bottom; 
 
   introducing a first molten metal into the mold cavity through an inlet;   directing a cooling medium against the first surface of the bottom of the mold cavity to initiate solidification of the first molten metal;   continuing to introduce the first molten metal through the inlet until a desired thickness;   introducing a second molten metal through the inlet and continuing to introduce the second molten metal until a desired thickness;   whereby the molten metal is cooled unidirectionally through its thickness.   
     
     
         2 . A method according to  claim 1 , wherein a rate of introduction of molten metal into the mold cavity is coordinated with the rate of cooling. 
     
     
         3 . A method according to  claim 1  or  2 , wherein the cooling rate is about 0.5.degree. F./sec. to about 3.degree. F./sec. 
     
     
         4 . A method according to  claim 1 , wherein the rate of introduction of molten metal into the mold cavity slows as the casting progresses. 
     
     
         5 . A method according to  claim 4 , wherein the cooling rate slows from about 3.degree. F./sec. to about 0.5.degree. F./sec. as casting progresses. 
     
     
         6 . A method according to  claim 1 , wherein the rate of introduction of molten metal into the mold cavity is about 0.5 in./min. to about 4 in./min. 
     
     
         7 . A method according to  claim 6 , wherein the rate of introduction of molten metal into the mold cavity is slowed as casting progresses. 
     
     
         8 . A method according to  claim 7 , wherein the rate of introduction of molten metal into the mold cavity slows from about 4 in./min. to about 0.5 in./min. as casting progresses. 
     
     
         9 . A method according to  claim 1 , wherein a rate of application of cooling medium is increased as casting progresses. 
     
     
         10 . The method according to  claim 9 , wherein the coolant is applied by spraying against the bottom of the mold. 
     
     
         11 . A method according to  claim 9 , wherein at least one material within the coolant comprises air, water, or a mixture thereof. 
     
     
         12 . A method according to  claim 1 , wherein the casting apparatus further comprises a coolant manifold disposed under the bottom. 
     
     
         13 . A method according to  claim 1  wherein the apertures have a geometry that is equivalent to holes having an equivalent diameter about of 1/64″ to about 1″.