Systems and Methods for Improving Iron-Based Camshaft Fatigue Life

This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/353,743, filed Jun. 20, 2022, the content of which is herein incorporated by reference.

The present application relates generally to the field of camshafts for use in internal combustion engine systems, fuel systems, or the like.

Internal combustion engines include at least one cylinder which receives fuel and air and which combusts the fuel to produce mechanical energy. This mechanical energy is harvested via a piston which translates within the cylinder. Intake valves open to let the cylinder fill with air and exhaust valves open to allow combustion gases to leave. The opening and closing of the valves are controlled by one or more camshafts. In some applications, camshafts can undergo rolling contact fatigue (RCF), a wear mechanism that occurs when the camshafts are subjected to rolling stresses.

Embodiments described herein relate generally to systems and methods for providing improved iron-based camshaft fatigue (e.g., rolling contact fatigue) life.

At least one aspect of the present disclosure is directed to a method of casting a camshaft including iron. The method comprises determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method further comprises casting the camshaft including cooling the camshaft in a chiller based on the cooling rate profile. The method still further comprises imparting the camshaft with a microstructure including carbide and pearlite.

In some embodiments, the method comprises austempering the camshaft to homogenize the pearlite. In some embodiments, the cooling rate profile includes a cooling rate that changes over time. In some embodiments, the cooling rate profile includes a cooling rate that is constant over time. In some embodiments, the cooling rate profile is determined further based on a geometry of the chiller, a size of the chiller, a wall thickness of the chiller, a mass of the camshaft, a thickness of the camshaft, a size of the camshaft, a target hardness of the camshaft, or combinations thereof. In some embodiments, cooling the camshaft decreases an amount of graphite nodules in the microstructure of the camshaft. In some embodiments, casting the camshaft further includes pouring molten iron into a mold before cooling the camshaft such that the cooled camshaft comprises chilled ductile iron. In some embodiments, imparting the camshaft with the microstructure includes realizing the microstructure based on the chemical composition of the camshaft and the cooling of the camshaft according to the cooling rate profile.

At least one aspect of the present disclosure is directed to a method of casting a camshaft comprising iron. The method comprises determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method comprises casting the camshaft including cooling the camshaft in a chiller based on the cooling rate profile. The method further comprises imparting the camshaft with a microstructure comprising carbide and ledeburite. The method still further comprises austempering the camshaft to treat the microstructure.

In some embodiments, the cooling rate profile includes a cooling rate that varies over time. In some embodiments, austempering the camshaft homogenizes the microstructure. In some embodiments, the microstructure further comprises pearlite, and austempering the camshaft transforms the pearlite into ausferrite. In some embodiments, cooling the camshaft includes treating the camshaft in the chiller at different temperatures over different periods of time. In some embodiments, cooling the camshaft is further based on a wall thickness of the chiller. In some embodiments, casting the camshaft further includes pouring molten iron into a mold before cooling the camshaft. In some embodiments, imparting the camshaft with the microstructure includes realizing the microstructure based on a chemical composition of the camshaft and the cooling rate profile.

At least one aspect of the present disclosure is directed to a method of casting a camshaft including iron. The method comprises determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method comprises casting the camshaft including cooling the camshaft in a chiller based on the cooling rate profile. The method further comprises austempering the camshaft to impart the camshaft with a microstructure comprising carbide and ausferrite.

In some embodiments, the method still further comprises imparting the camshaft with the microstructure comprising carbide and pearlite. In some embodiments, austempering the camshaft homogenizes the pearlite in the microstructure to form the ausferrite.

Those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings.

It will be recognized that some or all of the figures are schematic representations for purposes of illustration. The figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.

Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for improving iron-based camshaft fatigue life. The various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

Internal combustion engines include camshafts that may undergo rolling contact fatigue (RCF). Rolling contact fatigue can be caused by camshaft and follower spalling, Hertzian contact stress, and/or subsurface initiation. Steel is commonly used as a material for camshafts due to its hardness. However, camshafts made of steel (e.g., steel-based camshafts) may be more expensive than camshafts made of iron (e.g., iron-based camshafts).

Implementations described herein relate to methods of casting camshafts including iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, which includes cooling the camshaft in a chiller based on the cooling rate profile. The method includes imparting the camshaft with a microstructure including carbide and pearlite.

Implementations described herein relate to methods of casting camshafts including iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft including cooling the camshaft in a chiller based on the cooling rate profile. The method includes imparting the camshaft with a microstructure comprising carbide and ledeburite. The method includes austempering the camshaft to treat the microstructure.

Implementations described herein relate to methods of casting camshafts including iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, which includes cooling the camshaft in a chiller based on the cooling rate profile. The method includes austempering the camshaft to impart the camshaft with a microstructure comprising carbide and ausferrite.

The methods described herein provide iron-based camshafts that have improved rolling contact fatigue life compared to that of steel-based camshafts or conventional iron-based camshafts. The improved iron-based camshafts may be less expensive than steel-based camshafts.

illustrates a schematic diagram of a casting system.illustrates the casting system. The casting systemincludes one or more castings(e.g., chilled ductile iron castings, chilled austempered ductile iron castings, etc.). The composition of the one or more castingsinclude iron (Fe). The one or more castingscan include carbon (C), chromium (Cr), copper (Cu), molybdenum (Mo), and/or nickel (Ni). For a low-alloy white cast iron, the one or more castingscan include less than 5 wt % chromium, copper, molybdenum, and nickel. For a high-alloy white cast iron, the one or more castingscan include greater than 5 wt % chromium, copper, molybdenum, and nickel.

The casting systemincludes one or more chillers. The one or more chillerssurround the one or more castings. Each of the one or more chillershas a wall thickness. According to various embodiments, each of the one or more chillerscan have a wall thicknessof between 2 mm and 15 mm (e.g., 2 mm, 2.5 mm, 3 mm. 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, 14 mm, 14.5 mm, or 15 mm).

The one or more chillerscan include a first chiller having a first wall thickness and a second chiller having a second wall thickness. The first wall thickness can be greater than the second wall thickness. The first chiller can provide a greater cooling rate than the second chiller. The one or more chillerscool the one or more castings. For example, the one or more chillerscan cool the one or more castingsbased on a chemical composition of the one or more castings. The one or more chillerscan cool the one or more castingsbased on a target bearing life of the one or more castings. Each of the one or more chillershas a cavity. Each of the one or more chillerscan have a geometry that produces a camshaft lobe.

illustrates a flowchart of an example process(e.g., method, procedure, etc.) for casting a camshaft including iron (e.g., iron-based camshaft, iron-based camshaft lobe, etc.). The camshaft can be an engine camshaft or a fuel system camshaft. The camshaft can include chilled ductile iron (CDI) or chilled austempered ductile iron (CADI). Chilled ductile iron is formed by chilling or cooling molten iron. Chilled austempered ductile iron is formed by chilling molten iron to produce chilled ductile iron, and then austempering the chilled ductile iron to produce chilled austempered ductile iron. The processcan be used for forming camshafts, camshaft lobes, rollers, or other vehicle components.

The processstarts atwith determining a cooling rate profile based on a chemical composition of the camshaft (e.g., camshaft lobe) and a target bearing life of the camshaft. The cooling rate profile includes the rate of cooling of the camshaft. The rate of cooling can stay constant or vary over time. The cooling rate profile can be determined based on the geometry or size of the one or more chillers, the wall thicknessof the one or more chillers, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, and/or the target hardness of the camshaft. The cooling rate profile can be determined by the target microstructure of the camshaft.

The cooling rate can vary for a given chemical composition of the camshaft. The camshaft can have a chemical composition similar to or the same as the one or more castings. Each camshaft lobe can have a chemical composition similar to or the same as the one or more castings. For example, the composition of the camshaft or each camshaft lobe includes iron. The composition of the camshaft or each camshaft lobe can include carbon, chromium, copper, molybdenum, and/or nickel. For a low-alloy white cast iron, the camshaft can include less than 5 wt % chromium, copper, molybdenum, and nickel. For a high-alloy white cast iron, the camshaft can include greater than 5 wt % chromium, copper, molybdenum, and nickel.

The target bearing life of the camshaft includes the length of time the camshaft is expected to perform based on predefined or target operating conditions. Determining the cooling rate profile can include running a simulation based on desired or target properties of the camshaft. For example, the target properties of the camshaft can include the target bearing life of the camshaft. The simulation can be calibrated based on the properties and the chemical composition of the camshaft.

The processcontinues towith casting the camshaft. Casting the camshaft includes cooling the camshaft in a chiller based on the cooling rate profile. For example, cooling the camshaft in a chiller based on the cooling rate profile can include cooling the camshaft in one or more chillersbased on the cooling rate profile. Casting the camshaft can include pouring molten iron having a chemical composition similar to or the same as the one or more castingsinto a mold to form the camshaft.

The molten iron can be cooled according to the cooling rate profile. For example, the molten iron can be cooled at a first temperature for a first period of time. The molten iron can be cooled at a second temperature for a second period of time. The molten iron can be cooled at a third temperature for a third period of time. The cooling rate profile can include different temperatures and different periods of times. For example, the cooling rate profile can include the first temperature, second temperature, and third temperature and the first period of time, second period of time, and third period of time. The cooling rate profile can include additional temperatures and additional periods of time. The cooling rate profile can include a series of temperature changes over time. Cooling the camshaft can decrease the presence of graphite nodules in the microstructure of the camshaft.

The processcontinues towith imparting the camshaft with a microstructure. The microstructure (e.g., primary microstructure) comprises phases including carbide, pearlite, and graphite, where the amount of each phase is measured in volume fraction or area fraction. The camshaft can include less than 1% graphite (e.g., 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.95%, etc.). The camshaft can include at least 50% carbide (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.). The camshaft can include an average of 50%-60% carbide. The camshaft can include 70% carbide locally (e.g., a volume of the camshaft that is less than the entire volume of the camshaft), while the remaining volume fraction of the camshaft can include pearlite (e.g., 49%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.).

In some embodiments, referring to, the microstructure of the camshaft includes various combinations, at various volume/area fractions, of carbide, dendrite (including primary austenite and/or globular pearlite), graphite, and/or ledeburite (including lamellar-growth ledeburite and/or rod-growth ledeburite). In some embodiments, the camshaft includes at least 15% (in area fraction) lamellar-growth ledeburite (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.). In some embodiments, the camshaft includes at least 25% lamellar-growth ledeburite. In some embodiments, the camshaft includes less than 35% (in area fraction) carbide (e.g., 30%, 25%, 20%, 15%, 10%, 5%, etc.). In some embodiments, the camshaft includes less than 25% carbide (e.g., 20%, 15%, 10%, 5%, etc.). In some embodiments, the camshaft includes less than 40% (in area fraction) dendrite (e.g., 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.). In some embodiments, the camshaft includes less than 30% dendrite (e.g., 25%, 20%, 15%, 10%, 5%, etc.). In some embodiments, the camshaft includes less than 0.05% (in volume fraction) of graphite (e.g., 0.04%, 0.035%, 0.03%, 0.025%, 0.02%, 0.015%, etc.). In some embodiments, such as for an improved CDI specimen with chromium cast in a chiller with a wall thickness of 5 mm (represented by “I-C2”) and an improved CDI specimen without chromium cast in a chiller with a wall thickness of 10 mm (represented by “B-C4”), the camshaft includes at least 25% lamellar-growth ledeburite, less than 25% carbide, less than 30% dendrite, and less than 0.05% graphite. In some embodiments, the I-C2 and the B-C4 specimens demonstrate higher RCF life than specimens with less wall thickness and with no chromium (e.g., specimen represented by “B-C1” as described below).

Imparting the camshaft with the microstructure can include realizing a microstructure for a given chemical composition of the camshaft through a processing treatment (e.g., cooling). For example, the manner in which the camshaft cools and the chemical composition of the camshaft can determine the microstructure of the camshaft. The microstructure can determine the RCF life or fatigue life of the camshaft (e.g., iron-based camshaft fatigue life, iron-based rolling contact fatigue life, rolling contact fatigue life, etc.).

According to various embodiments, the target bearing life of the camshaft corresponds to an L(e.g., Llife, Blife) of at least 2×10life hours for smooth ball bearings with the microstructure provided herein. The Lcan include a minimum expected life or the bearing life associated with 90% reliability. For example, the target bearing life of the camshaft can correspond to an Lof 2.35×10life hours for smooth ball bearings with the microstructure including carbide and pearlite. The target bearing life of the camshaft can correspond to an Lof at least 3×10life hours for smooth ball bearings with the microstructure provided herein. For example, the target bearing life of the camshaft can correspond to an Lof 3.076×10life hours for smooth ball bearings with the microstructure including carbide and pearlite.

According to various embodiments, the target bearing life of the camshaft can correspond to an L(e.g., Llife, Blife) of at least 3×10life hours for smooth ball bearings with the microstructure provided herein. The Llife can include an average life or the bearing life associated with 50% reliability. For example, the target bearing life of the camshaft can correspond to an Lof 3.6×10life hours for smooth ball bearings with the microstructure including carbide and pearlite. The target bearing life of the camshaft can correspond to an Lof at least 2×10life hours for smooth ball bearings with the microstructure provided herein. For example, the target bearing life of the camshaft can correspond to an Lof 2.59×10life hours for smooth ball bearings with the microstructure including carbide and pearlite.

In some embodiments, the processcontinues towith austempering the camshaft. Austempering the camshaft homogenizes the pearlite contained in the microstructure of the camshaft. Austempering can improve the RCF life of chilled ductile iron. Austempering can transform the pearlite into ausferrite. Austempering can harden the camshaft and lower the hardness variation among different phases of the camshaft. Austempering can improve the wear resistance and fatigue performance of the camshaft. The austempering process can further harden the chilled ductile iron. The austempering process can further refine and homogenize the microstructure of the chilled ductile iron, thereby producing chilled austempered ductile iron.

illustrates a micrographof the microstructure of chilled ductile iron. The microstructure of the chilled ductile iron includes carbideand pearlite. The carbideis represented by the dark phase and the pearliteis represented by the light phase. The microstructure of the chilled ductile iron can include graphite nodules. The graphite nodulescan be involved with a failure mode (e.g., cracking) of the camshaft. The camshafts or the camshaft lobes can be made of such chilled ductile iron. The camshafts or the camshaft lobes can have a microstructure that includes the carbideand the pearlite. The camshafts or the camshaft lobes made of chilled ductile iron can have an improved RCF compared to camshafts or camshaft lobes made of chilled iron or austempered iron. The camshafts or the camshaft lobes made of chilled ductile iron can have a similar RCF compared to camshafts or camshaft lobes made of steel. The camshafts or the camshaft lobes made of chilled ductile can provide wear resistance.

illustrates the microstructure of chilled austempered ductile iron. The camshafts or the camshaft lobes can be made of such chilled austempered ductile iron. The camshafts or the camshaft lobes can have a microstructure that includes the carbideand the pearlite. The camshafts or the camshaft lobes made of chilled austempered ductile iron can have an improved RCF compared to camshafts or camshaft lobes made of chilled iron or austempered iron. The camshafts or the camshaft lobes made of chilled austempered ductile iron can have a similar RCF compared to camshafts or camshaft lobes made of steel. The camshafts or the camshaft lobes made of chilled austempered ductile can provide wear resistance.

illustrates a tablecomparing the RCF life of different chilled ductile iron specimens. The different chilled ductile iron specimens include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (represented by “2.5 no Cr”), and an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (represented by “5 no Cr”). The testing was performed at 3.9 GPa using smooth ball bearings. The CDI specimens can correspond to camshaft lobes.

The target bearing life of the baseline CDI can correspond to an Lof 3.3×10life hours for smooth ball bearings. The target bearing life of the baseline CDI can correspond to an Lof 1.4×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 2.5 mm can correspond to an Lof 2.35×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 2.5 mm can correspond to an Lof 3.6×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 5 mm can correspond to an Lof 3.076×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 5 mm can correspond to an Lof 2.59×10life hours for smooth ball bearings.

illustrates a plotcomparing the RCF life of different chilled ductile iron specimens. The plotincludes the different chilled ductile iron specimens illustrated in table. The different chilled ductile iron specimens include the baseline CDI, the improved CDI without chromium cast in a chiller with a wall thickness of 2.5 (represented by “2.5 no Cr” or “B-C1” as described below) and the improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (represented by “5 no Cr” or “B-C2” as described below). The RCF life of the different chilled ductile iron specimens are plotted in a Weibull distribution using maximum likelihood estimation.

illustrates a plotof cooling curves for different chiller wall thicknesses. The cooling curve can represent the cooling rate profile. The 2.5 mm curve represents a specimen or casting cooled by a chiller with a wall thickness of 2.5 mm. The 5 mm curve represents a specimen or casting cooled by a chiller with a wall thickness of 5 mm. The 7.5 mm curve represents a specimen or casting cooled by a chiller with a wall thickness of 7.5 mm. The 10 mm curve represents a specimen or casting cooled by a chiller with a wall thickness of 10 mm.

The cooling rate varies over the solidification time. The cooling rate profile can include the varying cooling rates or changing cooling rates. The cooling rate profile can include a cooling rate that is constant or that changes over time. The cooling rate profile can be determined based on the geometry or size of the one or more chillers, the wall thicknessof the one or more chillers, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, and/or the target hardness of the camshaft. The cooling rate profile can be determined by the target microstructure of the camshaft. The cooling rate can vary for a given chemical composition of the specimen.

illustrates a tablecomparing the RCF life of different chilled ductile iron specimens. The different chilled ductile iron specimens include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (represented by “B-C1”), an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (represented by “B-C2”), and an improved CDI with chromium cast in a chiller with a wall thickness of 5 mm (represented by “I-C2”). In some embodiments, the amount of chromium in the I-C2 specimen has a range of 0.5 wt % to 1 wt %. The testing was performed at 3.6 GPa using smooth ball bearings. The CDI specimens can correspond to camshaft lobes.

The target bearing life of the baseline CDI can correspond to a Bio of 3.3×10life hours for smooth ball bearings. The target bearing life of the baseline CDI can correspond to a Bof 1.4×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (“B-C1”) can correspond to a Bof 2.35×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 2.5 mm can correspond to a Bof 3.6×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 5 mm (“B-C2”) can correspond to a Bof 3.07×10life hours for smooth ball bearings. The target bearing life of the CDI without chromium cast in a chiller with a wall thickness of 5 mm can correspond to a Bof 2.59×10life hours for smooth ball bearings. The target bearing life of the CDI with chromium cast in a chiller with a wall thickness of 5 mm (“I-C2”) can correspond to a Bof 1.48×10life hours for smooth ball bearings. The target bearing life of the CDI with chromium cast in a chiller with a wall thickness of 5 mm can correspond to a Bof 5.13×10life hours for smooth ball bearings.

illustrates a plotcomparing the RCF life of different chilled ductile iron specimens. The plotincludes the different chilled ductile iron specimens illustrated in table. The different chilled ductile iron specimens include the baseline CDI, the improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (“B-C1”), the improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (“B-C2”), and the improved CDI with chromium cast in a chiller with a wall thickness of 5 mm (“I-C2”). The RCF life of the different chilled ductile iron specimens are plotted in a Weibull distribution using maximum likelihood estimation.

illustrates a tablecomparing the RCF life of chilled ductile iron and 1080 steel specimens. The chilled ductile iron specimen can include an improved CDI without chromium cast in a chiller with a wall thickness of 10 mm (represented by “B-C4”). The 1080 steel is represented by “IH 1080”. The testing was performed at 3.6 GPa using roughened ball bearings. The specimens can correspond to camshaft lobes.

The target bearing life of the cast iron can correspond to a Bof 7.97×10life hours for roughened ball bearings. The target bearing life of the cast iron can correspond to a Bof 3×10life hours for roughened ball bearings. The target bearing life of the 1080 steel can correspond to a Bof 1.52×10life hours for roughened ball bearings. The target bearing life of the cast iron can correspond to a Bof 5.0×10life hours for roughened ball bearings.

illustrates a plotcomparing the RCF life of cast iron and 1080 steel specimens. The plotincludes the cast iron and 1080 steel specimens illustrated in table. The RCF life of the cast iron and 1080 steel specimens are plotted in a Weibull distribution using least squares estimation.

illustrates the casting system, according to an embodiment. The casting systemcan include one or more risers. For example, the casting systemincludes a first riser (riser 1), a second riser (riser 2), a third riser (riser 3), and a fourth riser (riser 4). The casting systemcan include a sprue well. The casting systemcan include one or more cavities. For example, the casting systemincludes a first cavity (cavity 1), a second cavity (cavity 2), a third cavity (cavity 3), and a fourth cavity (cavity 4). The first cavity has a wall thickness of 2.5 mm. The second cavity has a wall thickness of 5 mm. The third cavity has a wall thickness of 7.5 mm. The third cavity has a wall thickness of 10 mm.

shows a plotof temperatures vs. time for different locations of the casting system. One or more thermal couples can be located at the different locations of the casting system. The temperatures at various points in time of a thermal couple located in the sprue wellare plotted. The temperatures at various points in time of a thermal couple located in the first riser are plotted. The temperatures at various points in time of a thermal couple located in the second riser are plotted. The temperatures at various points in time of a thermal couple located in the fourth riser are plotted.

shows a plotof temperatures vs. time for different locations of the casting system. The temperatures at various points in time of a thermal couple located at the bottom of the first cavity are plotted. The temperatures at various points in time of a thermal couple located at the top of the second cavity are plotted. The temperatures at various points in time of a thermal couple located at the bottom of the third cavity are plotted. The temperatures at various points in time of a thermal couple located at the top of the fourth cavity are plotted.

demonstrate various testing results and analyses pertaining to the improved CDI specimens including the B-C1, the B-C2, the I-C2, and the B-C4, which were obtained by cooling the specimens according to the cooling curves illustrated in. For example, the B-C1 specimen was cooled according to the cooling curve corresponding to the chiller with the wall thickness of 2.5 mm; the B-C2 and the I-C2 specimens were cooled according to the cooling curve corresponding to the chiller with the wall thickness of 5 mm; and the B-C4 specimen was cooled according to the cooling curve corresponding to the chiller with the wall thickness of 10 mm.