Method of producing large thin-walled sand castings of high internal integrity

Abstract

A process for high integrity castings of metals and their alloys includes the steps of providing at least a sand mold at desired elevated temperatures, delivering a molten metal into the mold, and supplying a predetermined amount of coolant to contact the surfaces of the casting at desired rates, times, and durations to achieve an acceptable level of progressive solidification from the distal end of the casting towards the riser until the casting has reached desired temperatures.

What is claimed is: 
     
         1 . A process for the casting of metals and their alloys, comprising of the steps of:
 preparing sand molds containing at least an aggregate and a binder to form a cavity to make castings;   bringing at least one mold to predetermined elevated temperatures with a certain temperature distribution;   introducing a molten material into the mold cavity to form castings;   delivering a predetermined amount of a selected coolant at predetermined rates, times, and durations to contact the surfaces of the solidifying casting and to maintain an acceptable level of progressive solidification from the distal end of a casting to the riser or downsprue; and   controlling the cooling of the casting to maintain the distance between the dendrite front and the solidus front within a predetermined range during the solidification of the casting by controlling the mold temperatures and the coolant cooling until the metal is totally solidified.   
     
     
         2 . The process of  claim 1 , where the heating of the mold is achieved by any method that is conventionally used in the casting industry, including, but not limited to, torch heating, oven heating, and infrared heating. 
     
     
         3 . The process of  claim 1 , where the local temperatures of the mold can be managed by using insulation materials, exothermic materials, and embedded heating devices in the mold, or by other means that are conventionally used in the metal casting industry. 
     
     
         4 . The process of  claim 1 , where the mold temperature is heated to in a range between 100° C. to the solidus temperature of the molten material. 
     
     
         5 . The process of  claim 1  wherein the mold temperature is heated to in a range between 200° C. to the solidus temperature of the molten material. 
     
     
         6 . The process of  claim 1  wherein the mold temperature is heated to in a range between 300° C. to the solidus temperature of the molten material. 
     
     
         7 . The process of  claim 1 , where the molten material is introduced into the mold cavity by gravity or by pressure. 
     
     
         8 . The process of  claim 1  wherein the coolant is a liquid, a gas, a mixture of gases, or a mixture of liquids and gases that contact the surface of the introduced metal to achieve high cooling rates at the region of contact until the metal is cooled to predetermined temperatures. 
     
     
         9 . The process of  claim 1 , where the contact region of the coolant to the casting moves from the distal end to the feeder of the casting at controllable speeds. 
     
     
         10 . The process of  claim 9  wherein the controllable speed is variable and is between a range of 0 mm/s to 100 mm/s. 
     
     
         11 . The process of  claim 9  wherein the controlled speed is variable and is between a range of 2-40 mm/s. 
     
     
         12 . The process of  claim 1 , where the molten material is a molten aluminum alloy. 
     
     
         13 . The process of  claim 1 , where the molten material is a molten magnesium alloy. 
     
     
         14 . The process of  claim 1 , where the distance between the dendrite front and the solidus front along the centerline of the wall of a solidifying casting is between a range of 1 to 10 times the wall-thickness of the casting. 
     
     
         15 . The process of  claim 1 , where the distance between the dendrite front and the solidus front along the centerline of the wall of a solidifying casting is between a range of 4 to 10 times the wall-thickness of the casting. 
     
     
         16 . A process for the casting of metals and their alloys, comprising of the steps of:
 preparing sand molds containing at least an aggregate and a binder to form a cavity to make castings;   bringing at least one mold to predetermined elevated temperatures with a certain temperature distribution;   introducing a molten material into the mold cavity to form castings;   delivering a predetermined amount of a selected coolant at predetermined rates, times, and durations to contact the surfaces of the solidifying casting progressively from the distal end of a casting to the riser or downsprue; and   controlling the cooling of the casting to maintain the openness of the feeding channel for the liquid from the feeder to feed the solidification shrinkage of the casting by controlling the mold temperatures and the coolant cooling until the metal is completely solidified.   
     
     
         17 . The process of  claim 16  wherein the coolant is a liquid, a gas, a mixture of gases, or a mixture of liquids and gases that contact the surface of the introduced metal to achieve high cooling rates at the region of contact until the metal is cooled to predetermined temperatures. 
     
     
         18 . The process of  claim 16 , where the mold temperature is heated to in a range between 100° C. to the solidus temperature of the molten material. 
     
     
         19 . The process of  claim 16  wherein the coolant is delivered to the surfaces of the casting progressively towards the feeder with speeds, constant or variable, between the range of 0 mm/s to 100 mm/s. 
     
     
         20 . The process of  claim 16  wherein the coolant is delivered to the surfaces of the casting progressively towards the feeder with speeds, constant or variable, between the range of 2 mm/s to 40 mm/s.