Method of casting metal parts such as valve seat inserts and casting apparatus

Abstract

A method of casting metal parts such as valve seat inserts comprises pouring molten metal into a gating system of a mold plate stack wherein mold plates are located between a cover mold and a bottom mold, the gating system including a casting header, down-sprue, at least one distribution runner, at least one up-sprue, runners and gates in fluid communication with mold cavities configured to form metal parts, and the gating system including at least one internal passage in the cover mold in fluid communication with the up-sprue and the down-sprue. During filling of the mold cavities with the molten metal, air trapped in the mold plate stack is expelled to surrounding atmospheric air via the up-sprue, the internal passage and an upper end of the down-sprue. The molten metal is solidified to form cast metal parts interconnected by solidified metal in the down-sprue, distribution runner, runners and gates, up-sprue and internal passage.

What is claimed is: 
     
         1 . A method of casting metal parts, comprising:
 pouring molten metal into a gating system of a mold plate stack wherein mold plates are located between a cover mold and a bottom mold, the gating system including a casting header, down-sprue, at least one distribution runner, at least one up-sprue, runners and gates in fluid communication with mold cavities configured to form metal parts, and the gating system including at least one internal passage in the cover mold in fluid communication with the up-sprue and the down-sprue;   filling the mold cavities with the molten metal while expelling air trapped in the mold plate stack to surrounding atmospheric air via the up-sprue, the internal passage and an upper end of the down-sprue;   and solidifying the molten metal to form cast metal parts interconnected by solidified metal in the down-sprue, the distribution runner, the up-sprue, the runners and gates, and the internal passage.   
     
     
         2 . The method of  claim 1 , wherein the cover mold is a 3D printed sand composition. 
     
     
         3 . The method of  claim 1 , wherein the mold plates have a plurality of up-sprues, the bottom mold has a plurality of distribution runners in fluid communication with the down-sprue and the up-sprues, and the cover mold has a plurality of internal passages in fluid communication with the up-sprues and the down-sprue, whereby during filling of the mold cavities with the molten metal air trapped in the mold plate stack is expelled to the surrounding atmospheric air via the up-sprues, the internal passages and an upper end of the down-sprue. 
     
     
         4 . The method of  claim 3 , wherein the internal passages include horizontal and vertical sections, the horizontal sections extending radially outward from the down-sprue in the cover mold, the vertical sections comprising vertically extending recesses in a lower surface of the cover mold, each of the vertically extending recesses in fluid communication with one of the horizontal sections of the internal passages and one of the up-sprues, whereby air escaping the mold cavities passes into the up-sprues and then through the recesses, the horizontal sections of the internal passages and the upper end of the down-sprue before being expelled to the surrounding atmospheric air. 
     
     
         5 . The method of  claim 1 , wherein the cover mold prevents surrounding atmospheric air from contacting the molten metal during filling of the mold cavities. 
     
     
         6 . The method of  claim 1 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least two circumferentially spaced openings corresponding to up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least two ring-shaped mold cavities extending into the upper surface of the mold plate, at least two circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least two runners arranged such that at least one of the runners extends from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the method including solidification of the molten metal and forming a mold stack of parts comprising valve seat inserts. 
     
     
         7 . The method of  claim 6 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least four circumferentially spaced openings corresponding to the up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least eight ring-shaped mold cavities extending into the upper surface of the mold plate, at least eight circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least eight runners arranged such that at least two of the runners extend from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the method including solidification of the molten metal and forming a mold stack of parts comprising valve seat inserts. 
     
     
         8 . The method of  claim 6 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least six circumferentially spaced openings corresponding to the up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least eighteen ring-shaped mold cavities extending into the upper surface of the mold plate, at least eighteen circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least eighteen runners arranged such that at least three of the runners extend from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the method including solidification of the molten metal and forming a mold stack of parts comprising valve seat inserts. 
     
     
         9 . The method of  claim 1 , wherein the molten metal is a wear and corrosion resistant alloy, nickel-base alloy, cobalt-base alloy, or intermetallic-base alloy the method further comprising maintaining a substantially uniform temperature distribution of the molten metal in a vertical direction during solidification of the molten metal. 
     
     
         10 . The method of  claim 3 , further comprising solidifying the molten metal after the molten metal fills the internal passages, the cover mold allowing escape of trapped air into the down-sprue and providing sufficient thermal insulation in a vertical direction to improve surface quality of the cast parts. 
     
     
         11 . An apparatus for casting metal parts, comprising:
 a mold plate stack comprising mold plates located between a cover mold and a bottom mold, and a gating system including a casting header, down-sprue, at least one distribution runner, at least one up-sprue, and runners/gates in fluid communication with mold cavities configured to form the metal parts;   the mold cavities located in upper surfaces of the mold plates;   the cover mold including at least one internal passage in fluid communication with the up-sprue and the down-sprue, the internal passage in the cover mold allowing trapped air to be expelled through an upper end of the down-sprue during a casting operation in which molten metal sequentially fills the down-sprue, the distribution runner, the up-sprue, the runners/gates, and the mold cavities in each mold plate, and after filling the up-sprue of each mold plate the liquid metal fills the internal passage and contacts the liquid metal in the upper end of the down-sprue of the cover mold.   
     
     
         12 . The apparatus of  claim 11 , wherein the cover mold is a 3D printed sand composition. 
     
     
         13 . The apparatus of  claim 12 , wherein the mold plates have a plurality of up-sprues, the bottom mold has a plurality of distribution runners in fluid communication with the down-sprue and the up-sprues, and the cover mold has a plurality of internal passages in fluid communication with the up-sprues and the down-sprue. 
     
     
         14 . The apparatus of  claim 13 , wherein the internal passages include horizontal and vertical sections, the horizontal sections extending radially outward from the down-sprue in the cover mold, the vertical sections comprising vertically extending recesses in a lower surface of the cover mold, each of the vertically extending recesses in fluid communication with one of the horizontal sections of the internal passages and one of the up-sprues. 
     
     
         15 . The apparatus of  claim 13 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least two circumferentially spaced openings corresponding to up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least two ring-shaped mold cavities extending into the upper surface of the mold plate, at least two circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least two runners arranged such that at least one of the runners extends from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the ring-shaped mold cavities configured to form valve seat inserts. 
     
     
         16 . The apparatus of  claim 13 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least four circumferentially spaced openings corresponding to the up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least eight ring-shaped mold cavities extending into the upper surface of the mold plate, at least eight circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least eight runners arranged such that at least two of the runners extend from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the ring-shaped mold cavities configured to form valve seat inserts. 
     
     
         17 . The apparatus of  claim 13 , wherein each of the mold plates is a circular sand mold plate having a central opening corresponding to the down-sprue extending vertically between upper and lower surfaces of the mold plate, at least six circumferentially spaced openings corresponding to the up-sprues extending vertically between the upper and lower surfaces of the mold plate, at least eighteen ring-shaped mold cavities extending into the upper surface of the mold plate, at least eighteen circular recesses extending into the upper surface of the mold plate at locations such that each ring-shaped mold cavity surrounds one of the circular recesses, at least eighteen runners arranged such that at least three of the runners extend from each of the circumferentially spaced openings and each of the runners/gates is in fluid communication with one of the ring-shaped mold cavities, the ring-shaped mold cavities configured to form valve seat inserts. 
     
     
         18 . The apparatus of  claim 13 , wherein the cover mold includes a central opening extending vertically between upper and lower surfaces of the cover mold, each of the internal passages including a horizontal section extending radially outward from the central opening and a vertical section extending vertically from the lower surface of the cover mold. 
     
     
         19 . The apparatus of  claim 18 , wherein the horizontal section is formed by a cylindrical passage having an inner end extending from the central opening and an outer end spaced inwardly of an outer periphery of the cover mold, and the vertical section is formed by a cylindrical recess having a lower end extending through the lower surface of the cover mold and an upper end extending from the outer end of the cylindrical passage. 
     
     
         20 . The apparatus of  claim 12 , wherein the mold cavities extend vertically into an upper surface of each mold plate.