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

Abstract

A process for high integrity large thin-walled castings of metals and their alloys using a single downsprue 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.

1 . A process for making a large thin-walled casting free from shrinkage porosity using one single downsprue that serves as a single feeder or a single riser, comprising the steps of:
 preparing sand molds containing at least an aggregate and a binder to form a cavity to make a casting, wherein the binder may not be water-soluble;   preparing a coolant delivery device that is capable of traveling over the casting from its distal end to the downsprue or feeder at controllable speeds;   heating at least one mold to predetermined elevated temperatures with a certain temperature distribution;   introducing a molten material into the mold cavity from the single downsprue to form the casting;   delivering a predetermined amount of a selected coolant at predetermined rates, times, and durations to contact the surfaces of the casting during its solidification and to maintain an acceptable level of progressive solidification from a distal end of the casting to the feeder or the riser; and   controlling the cooling of the casting to maintain a distance between dendrite front and solidus front within a predetermined range during the solidification of the casting by controlling mold temperatures and coolant cooling until the casting is totally solidified.   
     
     
         2 . The process of  claim 1 , wherein the heating of the mold is achieved by a method including torch heating, oven heating, and infrared heating. 
     
     
         3 . The process of  claim 1 , wherein the temperature distribution of the mold can be managed by using materials and methods including insulation materials, exothermic materials, and embedded heating devices in the mold. 
     
     
         4 . The process of  claim 1 , wherein the mold temperature is heated to a temperature above 200° C. for a thin-walled casting. 
     
     
         5 . 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 casting to achieve high cooling rates at the region of contact until the casting is cooled to predetermined temperatures. 
     
     
         6 . The process of  claim 1 , wherein contact regions of the coolant to the casting move from the distal end to the feeder of the casting at controllable speeds. 
     
     
         7 . The process of  claim 6 , wherein the controllable speeds are variable and are between a range of 0 mm/s to 100 mm/s. 
     
     
         8 . The process of  claim 6 , wherein the controlled speeds are variable and are between a range of 2-40 mm/s. 
     
     
         9 . The process of  claim 1 , wherein the molten material is a molten aluminum alloy. 
     
     
         10 . The process of  claim 1 , wherein the molten material is a molten magnesium alloy. 
     
     
         11 . The process of  claim 1 , wherein the distance between the dendrite front and the solidus front along the centerline of the wall of the casting is between a range of 1 to 10 times an average wall-thickness of the casting. 
     
     
         12 . The process of  claim 1 , wherein the distance between the dendrite front and the solidus front along the centerline of the wall of the casting is between a range of 4 to 10 times the average wall-thickness of the casting. 
     
     
         13 . A process for making a large thin-walled casting with controlled porosity distribution using one single downsprue that serves as a single feeder or a single riser, comprising the steps of:
 preparing sand molds containing at least an aggregate and a binder to form a cavity to make castings, wherein the binder may not be water-soluble;   preparing a coolant delivery device that is capable of traveling over the casting from its distal end to the downsprue or feeder at controllable speeds;   heating at least one mold to predetermined elevated temperatures with a certain temperature distribution;   introducing a molten material into the mold cavity from the single downsprue to form the casting;   delivering a predetermined amount of a selected coolant at predetermined rates, times, and durations to contact the surfaces of the casting during its solidification and to maintain an acceptable level of progressive solidification from a distal end of the casting to the feeder or the riser; and   controlling the cooling of the casting to maintain a distance between dendrite front and solidus front within a predetermined range during the solidification of the casting by controlling mold temperatures and coolant cooling until the casting is totally solidified.   
     
     
         14 . The process of  claim 13 , wherein the heating of the mold is achieved by a method including torch heating, oven heating, and infrared heating. 
     
     
         15 . The process of  claim 13 , wherein the temperature distribution of the mold can be managed by using materials and methods including insulation materials, exothermic materials, and embedded heating devices in the mold. 
     
     
         16 . The process of  claim 13 , wherein the mold temperature is heated to a temperature above 200° C. for a thin-walled casting. 
     
     
         17 . The process of  claim 13 , 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 casting to achieve high cooling rates at the region of contact until the casting is cooled to predetermined temperatures. 
     
     
         18 . The process of  claim 13 , wherein contact regions of the coolant to the casting move from the distal end to the feeder of the casting at controllable speeds. 
     
     
         19 . The process of  claim 13 , wherein the distance between the dendrite front and the solidus front along the centerline of the wall of the casting is between a range of 1 to 10 times an average wall-thickness of the casting.