Patent Grant
8079401
This disclosure is related to metal casting processes for forming a casting.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Casting processes for forming articles using molds and cores employ casting chambers including outer molds and inner core elements each having features and reliefs that form details, recesses, and cavities in a casting when molten material such as liquid metal is poured into the mold. One casting formed by such a casting process is an engine block formed from molten cast iron or molten aluminum alloys. Inner core elements can be constructed from bonded sand. The inner core elements are extracted from the casting subsequent to the forming process. Portions of the casting may be subject to high-stress in-use, and it may be desirable to impart varying metallurgical properties to those portions. For example, a time-rate of removal of thermal energy from liquid metal during casting affects grain structure, with increased cooling and solidification of the poured liquid metal leading to an improvement, in general, of material properties such as tensile strength, fatigue strength, and in some cases machinability.
Known casting processes use thermal chill devices in proximity to specific portions of a casting in place of or in conjunction with features on the mold and core elements. This includes using chill devices at bulkheads and crankshaft bearing surfaces on engine blocks.
Known casting processes can include quiescently feeding molten metal upwards into a casting chamber in a counter-gravity fill process. The casting process can include subsequently inverting the casting chamber to allow molten metal to gravity-feed into the inverted casting chamber to fully form the casting.
A casting chamber configured to form a casting from molten material includes an outer mold, a plurality of inner core elements, and a surface portion of a thermal chill device. The thermal chill device includes first and second interchangeable elements with the surface portion of the thermal chill device including one of a first surface portion of the first interchangeable element and a second surface portion of the second interchangeable element. The first surface portion of the first interchangeable element includes an insulating material and the second surface portion of the second interchangeable element comprising a metallic material.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The casting chamber 10 is formed using an outer mold 20, an inner core element 30, and a first outer surface portion 45A of a rotatable thermal chill device 40 of a thermal chill assembly 35. In one embodiment the inner core element 30 is a sand core element formed from silica sand mixed with a polyurethane binding material and formed into an appropriate shape associated with the casting. Inner surfaces of the outer mold 20 and the inner core element 30 and the outer surface portion 45A of the rotatable thermal chill device 40 define the casting chamber 10 for producing the casting 5.
The casting process includes forming the casting 5 in the casting chamber 10 by feeding molten material into the casting chamber 10 which subsequently solidifies as it cools below its solidification temperature. In one embodiment, the molten material feeds into the casting chamber 10 in a counter-gravity fill process. The casting 5 is depicted as an engine block for an internal combustion engine. A skilled practitioner can apply the principles described herein to form a multiplicity of other castings. In one embodiment the molten or liquid material is an aluminum alloy.
In one embodiment, the first outer surface portion 45A is formed from high-temperature insulating material 42 and is configured to contact the casting 5 during a first period or step in the casting process. The second outer surface portion 46A is constructed from metal and is configured to contact the casting 5 during a second subsequent period or step in the casting process.
As shown, the rotatable thermal chill device 40 includes a cylindrically shaped metallic element having an annular cross-section. A recess 48 is cut into the semi-cylindrical element of the first element 45 coincident with the first outer surface portion 45A. The recess 48 is laminated with high-temperature insulating material 42 that is preferably cured in place such that the first outer surface portion 45A has a cross-sectional form that is geometrically identical to the second outer surface portion 46A, with both being semi-cylindrical surfaces in this embodiment. The insulating material 42 is constructed from insulating or refractory material that is mounted to the recess 48 by one of an adhesive or metal glue and mechanical fixturing, or can be cast in place. The insulator material can include alumina, magnesia, silica, silicon carbide, or a combination thereof, or bonded sand similar to that used in making a sand core. Alternatively, the first outer surface portion 45A is a unitary piece formed completely from the insulating material and having a cross-sectional form that is geometrically identical to the second outer surface portion 46A. An embodiment depicting the first outer surface portion 45A as a unitary piece is shown with reference to
The rotatable thermal chill device 40 includes a plurality of radial pass-through holes 44 located along a longitudinal axis that pass through the second outer surface portion 46A of the second semi-cylindrical surface element 46. Each of the pass-through holes 44 provides a fluidic flow passageway between the inner chamber 47 and the second outer surface portion 46A of the second element 46. A fluid dispensing mechanism 49 including a fluidic pipe fluidly connected to a plurality of radial jets 43 is inserted into the inner chamber 47 and is configured to inject a cooling fluid to contact a portion of a surface of the casting 5 contiguous to the second outer surface portion 46A of the rotatable thermal chill device 40. The radial jets 43 pass through a portion of the radial pass-through holes 44 and have openings on distal ends thereof. Cooling fluid injected through the radial jets 43 contacts the surface of the casting 5 contiguous to the second outer surface portion 46A to effect cooling thereof, and flows through the radial pass-through holes 44 to the inner chamber 47 for removal, e.g., via a vacuum system. Injecting the cooling fluid through the radial jets 43 and subsequent evacuation of steam is timed to achieve a maximum cooling benefit with acceptable amount of steam generation.
The fluid dispensing mechanism 49 is an element of a cooling fluid dispensing system that is housed in the thermal chill assembly 35 in one embodiment. The fluid dispensing system includes a pump mechanism that is configured to pump cooling fluid, e.g., water to the fluid dispensing mechanism 49.
The rotatable thermal chill device 40 is mounted on the thermal chill assembly 35. In one embodiment a portion of the thermal chill device extends longitudinally outside the thermal chill assembly 35 and contacts a rotating mechanism 56 for rotating the rotatable thermal chill device 40 about its longitudinal axis between a first position and a second position. When the thermal chill device 40 is in the first position (as shown), the first outer surface portion 45A forms and defines the casting chamber 10, preferably during the portion of the casting process when molten material is flowing into the casting chamber 10. The casting process preferably includes rotating the rotatable thermal chill device 40 to the second position, with the second outer surface portion 46A forming and defining the casting chamber 10. The rotating mechanism 56 rotates the rotatable thermal chill device 40 about the longitudinal axis between the first and second positions, preferably rotating to the second position subsequent to the portion of the casting process when molten material is flowing into the casting chamber 10.
During the casting process, the first outer surface portion 45A forms and defines the casting chamber 10 during the portion of the casting process when molten material is flowing into the casting chamber 10. The casting process preferably includes rotating the rotatable thermal chill device 40A to the second position, with the second outer surface portion 46A forming and defining the casting chamber 10. The rotating mechanism 56 rotates the rotatable thermal chill device 40A about the longitudinal axis between the first and second positions, preferably rotating to the second position subsequent to the portion of the casting process when molten material is flowing into the casting chamber 10. Cooling fluid injected through the radial jets 43A contacts the surface of the casting 5 contiguous to the second outer surface portion 46A to effect cooling thereof, during which time the cooling fluid vaporizes. The vaporized cooling fluid passes through the radial pass-through holes to the inner chamber 47 for removal, e.g., via a vacuum system.
In this embodiment, the first element 45′ and the second element 46′ are preferably unitary semicircular portions of the coaxial disks 41 formed completely from homologous materials. The first element 45′ is formed from the insulating material and the second element 46′ is formed from a metal, e.g., H13 steel. The first element 45′ and the second element 46′ have cross-sectional forms that are geometrically identical. Each of the second elements 46′ includes radial pass through holes terminating at an annular opening 44B on one or both the side surface portions 54 of the outer surface. Radial jets 43B pass through radial holes in the second element 46′ and terminate at a radial distance that is less than an outside radius of each coaxial disk 41 and coincident with the associated annular opening 44B. Each of the radial jets 43B has one or more fluidic openings that are orthogonal to the radial axis and preferably parallel to the longitudinal axis of the rotatable thermal chill device 40.
During the casting process, the outer surface portions of the first element 45′ form and define the casting chamber 10 during the portion of the casting process when molten material is flowing into the casting chamber 10. The casting process preferably includes rotating the rotatable thermal chill device 40B to the second position, with the circumferential surface portion 52 and the side surface portion 54 forming and defining the casting chamber 10. The rotating mechanism 56 rotates the rotatable thermal chill device 40B about the longitudinal axis from the first to the second position, preferably rotating to the second position subsequent to the portion of the casting process when molten material is flowing into the casting chamber 10. Cooling fluid injected through the radial jets 43B contacts the surface of the casting 5 contiguous to the annular openings 44B in the side surface portion 54 to effect cooling thereof, and flows through the radial pass-through holes 44A to the inner chamber 47 for removal, e.g., via a vacuum system.
During an initial portion of the casting process, the casting chamber 10 includes the outer mold 20, the inner core element 30, and the first outer surface portion 45A of the rotatable thermal chill device 40C. Subsequently, the rotatable thermal chill device 40C is rotated, and the casting chamber 10 includes the outer mold 20, the inner core element 30, and the second outer surface portion 46A. After a skin has formed on the casting 5, the rotatable thermal chill device 40C is translated linearly to expose a portion of the casting 5 to the cooling section 58. Cooling fluid injected through the radial jets 43 contacts the surface of the casting 5 contiguous to the cooling section 58 to effect cooling thereof, and flows through the radial pass-through holes 44 to the inner chamber 47 for removal, e.g., via a vacuum system. Injecting the cooling fluid through the radial jets 43 and subsequent evacuation of steam is timed to achieve a maximum cooling benefit with acceptable amount of steam generation.
During an initial portion of the casting process, the casting chamber 10 includes the outer mold 20, the inner core element 30, and the first element 72 of the thermal chill device 70. After a skin has formed on the casting 5, the thermal chill device 70 is translated linearly to expose a portion of the casting 5 to the cooling section 58. Cooling fluid injected through the radial jets 43 contacts the surface of the casting 5 contiguous to the cooling section 58 to effect cooling thereof, and flows through the radial pass-through holes 44 to the inner chamber 47 for removal, e.g., via a vacuum system. Injecting the cooling fluid through the radial jets 43 and subsequent evacuation of steam is timed to achieve a maximum cooling benefit with acceptable amount of steam generation.
Subsequent to extracting the thermal chill device 40 from the casting, the casting can be subjected to a spray cooling or misting process, wherein cooling fluid, e.g., water, is sprayed directly onto the casting at the location previously occupied by the thermal chill device 40 to further accelerate cooling thereof. This process also increases rate of solidification of the casting in the portion nearest the location of the thermal chill device 40, thus enhancing quality of the casting due to a refined metallurgical microstructure thereat.
The process described with reference to
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1817388 | Melcher | Aug 1931 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20110094701 A1 | Apr 2011 | US |
