Casting process method of high-grade as-cast nodular cast iron cylinder head for diesel locomotive

Abstract

The invention discloses a casting process method of a high-grade as-cast nodular cast iron cylinder head for an internal combustion locomotive, which comprises the following steps of: S101, molding an outer mold and manufacturing a sand core, designing an appearance mold into a one-mold two-type symmetrical layout, and designing a unique pouring system, exhausting and chilling block riser process, and the exterior mold cavity is molded by adopting a self-hardening furan resin sand process. In addition, sand cores are manufactured, and an air channel core, a water channel core, a bolt hole core and an oil nozzle hole core all adopt hot box method precoated sand cores; s102, smelting molten iron: selecting pig iron, scrap steel, ferromanganese, copper, molybdenum and ferrosilicon as raw materials, weighing the raw materials, and feeding the raw materials into a medium-frequency electric furnace for smelting; s103, spheroidizing inoculation treatment and pouring are conducted, specifically, a yttrium-based rare earth magnesium spheroidizing agent is evenly placed in a spheroidizing dam, and after tamping and flattening are conducted, a ladle bottom inoculant is added for compacting; when the temperature of the molten iron reaches 1425-1435 DEG C, pouring is conducted, and after cooling, a box is opened for shakeout; and S104, post-treatment is conducted, specifically, the casting obtained after sand shakeout is polished and cleaned. According to the embodiment of the invention, the mechanical property and compactness of the cylinder head can be improved.

Description

Technical Field

[0001] This disclosure generally relates to the field of casting technology. More specifically, this disclosure relates to a casting process for high-grade as-cast ductile iron cylinder heads for internal combustion engine vehicles. Background Technology

[0002] The cylinder head is a key component of an internal combustion engine. Together with the piston, it forms the combustion chamber and undertakes core functions such as intake, exhaust, cooling, and fuel injector installation. Cylinder heads for medium- and high-speed internal combustion locomotives must withstand extremely high mechanical and thermal loads; therefore, they are typically made of high-grade ductile iron and designed with complex internal reinforcing ribs. Their technical specifications impose stringent requirements on mechanical properties such as tensile strength, elongation, and spheroidization rate, and they must pass multiple magnetic particle inspections and airtightness tests on the water cavity and valve valve lines.

[0003] However, existing casting processes commonly suffer from low yield and poor quality stability when producing such complex components due to casting defects such as porosity, inclusions, shrinkage cavities, and poor spheroidization. These defects severely restrict the reliability of cylinder heads and fail to meet the stringent requirements of high-performance internal combustion engines for critical components.

[0004] Therefore, there is an urgent need in this field for a casting method that can effectively improve the density, mechanical properties and quality stability of cylinder head castings. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, this disclosure proposes a casting process for high-grade cast ductile iron cylinder heads for internal combustion locomotives in several aspects.

[0006] This disclosure provides a casting process for high-grade cast ductile iron cylinder heads for internal combustion locomotives, including the following steps: S101, External mold design and sand core fabrication: The external mold is designed as a symmetrical layout with two molds in one mold, and the gating system, venting, and chill riser processes are designed. The external mold cavity is molded using self-hardening furan resin sand technology; Sand cores are fabricated, wherein the air passage core, water passage core, bolt hole core, and fuel injector hole core are all coated sand cores using the hot core box method. The external mold is divided into an upper mold and a lower mold along the center line of the intake and exhaust passages. The spring seat surface is set as the top surface of the upper mold, and the combustion chamber fire surface is set as the bottom surface of the lower mold; The gating system adopts a bottom-pouring open filter gating system, and the ratio of the cross-sectional area of ​​the sprue, runner, and ingate is 1:1.7:2 or 1:1.3:1.6, and a foam ceramic filter screen is horizontally set in the runner; S102, Molten iron smelting: Pig iron, scrap steel, ferromanganese, copper, molybdenum, and ferrosilicon are selected as raw materials. After weighing the prepared metal raw materials, they are sent to a medium-frequency electric furnace for smelting. Pig iron, scrap steel, and other metal raw materials are added in sequence. During the smelting process, silicon carbide particles and silicon carbide powder are added. After melting and clearing, slag-collecting agent is sprinkled and slag is removed. The mixture is then allowed to stand at high temperature for further slag removal to complete the molten iron smelting. S103, spheroidizing inoculation treatment and casting: The weighed yttrium-based rare earth magnesium spheroidizing agent is evenly placed into the spheroidizing dam of the baked ladle, tamped and flattened with a chisel, and then the bottom inoculant is added and compacted. During tapping, the iron is... Add in-flow inoculant and remove slag after tapping; pour the molten iron when the temperature reaches 1425~1435℃, and simultaneously inoculate the molten iron during the pouring process; keep the casting warm after pouring, and remove the sand after cooling; S104, post-treatment: grind and clean the casting after sand removal, and then perform artificial aging; after artificial aging, use a handheld shot peening machine to clean each bolt hole, sand removal process hole and air intake and exhaust channel core of the casting, and remove the oxide scale in the inner cavity.

[0007] In some embodiments, during the outer mold molding and sand core fabrication steps, a composite chilling system is provided for each type of casting. The system includes: at least four heating risers arranged at the hot joint of the spring seat surface; heating side risers arranged at the hot joints of the process hole mounting surfaces on both sides; at least four rectangular cast iron chills and one cross-shaped cast iron chill in the nose bridge area arranged around the combustion chamber surface. The cross-shaped cast iron chill has a through round hole in the middle. A steel round bar is inserted during the outer mold molding process. After demolding, the round bar is left in the sand mold as a core support steel column to support the oil nozzle hole sand core.

[0008] In some embodiments, the push rod hole of the spring seat surface is designed as a cast hole, and a CNC-machined graphite chill is inserted into the hole; the graphite chill is used to press down the intake and exhaust channel sand core while chilling the area, preventing it from floating and moving.

[0009] In some embodiments, silica sand is used for core preparation, with a particle size range of 50~100 mesh. The resulting sand core has a room temperature tensile strength ≥2.8MPa, a room temperature flexural strength ≥6.0MPa, and a gas generation ≤15ml / g. The core injection pressure is controlled at 0.6~0.8MPa, the core preparation temperature is controlled at 250℃~280℃, and the holding time is 180S~300S.

[0010] In some embodiments, during the outer mold shaping and sand core making steps, the dimensional shrinkage rate of all molds is uniformly set to 0.8%, and a wall thickness correction of 3mm is set in the wall thickness area of ​​the bridge of the nose.

[0011] In some embodiments, the chemical composition of the molten iron obtained after the molten iron smelting step is as follows by mass percentage: C: 3.4%~4.1%, Si: 1.7%~2.3%, Mn: 0.20%~0.45%, P: ≤0.1%, S: ≤0.01%, Mo: 0.3~0.6%, Ni: 0.9~1.4%, Mg: 0.04%~0.07%, Cu: 0.4~0.6%, with the balance being Fe and unavoidable impurities.

[0012] In some embodiments, the spheroidizing inoculation treatment and casting steps include spheroidizing treatment, in-flow inoculation during tapping, and in-flow inoculation during casting. The spheroidizing treatment uses yttrium-based rare earth magnesium spheroidizing agent, and its addition amount is 0.8% to 1.2% of the mass of molten iron. The in-flow inoculation during tapping uses barium silicon inoculator, and its addition amount is 0.7% to 1.3% of the mass of molten iron. The in-flow inoculation during casting uses zirconium silicon manganese inoculator, and its addition amount is 0.1% to 0.2% of the mass of molten iron.

[0013] In some embodiments, the chemical composition of the yttrium-based rare earth magnesium spheroidizing agent by mass percentage is as follows: Si: 42%~45%, Mg: 6%~8%, Re: 2%~3.5%, Ca: 2%~3%, Al < 1%, and Fe as the balance; wherein, in Re, the mass percentage of yttrium is 50%, the mass percentage of lanthanum is 25%, and the mass percentage of cerium is 25%.

[0014] In some embodiments, the temperature of the molten iron is controlled at 1425~1435°C during casting.

[0015] In some embodiments, the positioning cores of the air channel core and water channel core are provided with sand cleaning holes. After the loose sand in the inner cavity is cleaned by high pressure, it is dipped in a high-temperature resistant coating and dried.

[0016] The high-grade cast ductile iron cylinder head casting process for internal combustion engine vehicles provided above, through the four production steps of external mold molding and sand core making, molten iron smelting, spheroidizing inoculation treatment and pouring and post-treatment, can improve the quality stability of the cylinder head, meet the stringent requirements of high-performance internal combustion engines for key components, and solve casting defects such as porosity, slag inclusions, shrinkage porosity and poor spheroidization in traditional casting processes. Attached Figure Description

[0017] The above and other objects, features, and advantages of exemplary embodiments of this disclosure will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein: Figure 1 An exemplary flowchart of a casting process for high-grade as-cast ductile iron cylinder heads for internal combustion locomotives, according to some embodiments of this disclosure, is shown. Figure 2 An exemplary perspective view of a first component of a ductile iron cylinder head for an internal combustion engine according to some embodiments of this disclosure is shown. Figure 3 An exemplary perspective view of a second component of a ductile iron cylinder head for an internal combustion engine according to some embodiments of this disclosure is shown. Figure 4 An exemplary perspective view of a first component of a ductile iron cylinder head for an internal combustion engine according to some embodiments of this disclosure is shown. Figure 5 An exemplary perspective view of a second component of a ductile iron cylinder head for an internal combustion engine according to some embodiments of this disclosure is shown. Figure 6 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 7 An exemplary perspective view shows the casting process structure of the second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 8 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 9 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 10 An exemplary perspective view shows the casting process structure of the second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Detailed Implementation

[0018] The technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, not all of them. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0019] It should be understood that the terms “comprising” and “including” used in this disclosure and claims indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0020] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this disclosure. As used in this disclosure and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this disclosure and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0021] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0022] This disclosure provides a casting process for high-grade cast ductile iron cylinder heads for internal combustion engine vehicles. Through four production steps—outer mold shaping and sand core making, molten iron smelting, spheroidizing inoculation treatment, and pouring and post-treatment—it can improve the mechanical properties and density of the cylinder head, meet the stringent requirements of high-performance internal combustion engines for key components, and solve problems such as loose structure, shrinkage defects, and unstable performance in traditional casting processes.

[0023] The specific embodiments disclosed herein will now be described in detail with reference to the accompanying drawings.

[0024] See Figures 1 to 5 , Figure 1 An exemplary flowchart of a casting process for high-grade as-cast ductile iron cylinder heads for internal combustion locomotives, according to some embodiments of this disclosure, is shown. Figure 2An exemplary perspective view of a first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure, is shown. Figure 3 An exemplary perspective view of the second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure, is shown. Figure 4 An exemplary perspective view of a first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure, is shown. Figure 5 An exemplary perspective view of a second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure, is shown.

[0025] According to some embodiments disclosed herein, the ductile iron cylinder head for internal combustion engine vehicles is a core component of the internal combustion engine. It generally includes a first part and a second part that are interlocked and connected. The total weight of the casting is approximately 105 kg, and its outer dimensions are approximately 350 mm × 350 mm × 300 mm. Figures 2 to 4 As shown. Valve cover mounting surface 1 is used to install the valve cover and seal the engine oil. Spring seat surface 2 mainly provides mounting reference and support for the valve spring. Combustion chamber firing surface 3 directly bears the impact of the combustion flame and high temperature. Process hole mounting surface 4 is mainly used to install water plugs or oil plugs to seal the casting process holes. Four bolts, through bolt holes 5, engage with corresponding threaded holes on the cylinder block, and with a large and precise preload, firmly clamp the cylinder head, cylinder head gasket, and cylinder block together to form a rigid integral structure. The fuel injector mounting hole 6 is used for precise positioning and sealing of the fuel injector. Cooling water chamber 7 is used to contain circulating coolant to cool high-temperature components such as the combustion chamber and exhaust manifold. The intake manifold 8 is divided into intake and exhaust manifolds, which connect to the engine to serve as the engine's intake and exhaust channels, and have a crucial impact on the engine's performance, efficiency, and emissions. Pushrod hole 9 provides a channel for the pushrod to pass through the cylinder head; each valve corresponds to one pushrod hole.

[0026] Regarding the aforementioned ductile iron cylinder heads for internal combustion locomotives, this disclosure provides a casting process for high-grade as-cast ductile iron cylinder heads for internal combustion locomotives: Example 1 S101: External mold design and sand core fabrication. The external mold is designed with a symmetrical layout of two types in one mold, and features a unique gating system, venting, and chill riser process. The external mold cavity is modeled using a self-hardening furan resin sand process. Sand cores are also fabricated, including air duct cores, water duct cores, bolt hole cores, and fuel injector hole cores, all using a hot core box method with a coated sand core.

[0027] S102. Melting molten iron: Select pig iron, scrap steel, ferromanganese, copper, molybdenum, and ferrosilicon as raw materials; weigh the prepared metal raw materials and send them into a medium-frequency electric furnace for melting.

[0028] S103, spheroidizing inoculation treatment and casting: The weighed yttrium-based rare earth magnesium spheroidizing agent is evenly placed into the spheroidizing dam of the baked ladle, tamped and flattened with a chisel, and then the bottom inoculant is added and compacted; when the temperature of the molten iron reaches 1425-1435℃, casting is carried out, and after cooling, the ladle is opened and the sand is removed.

[0029] S104 post-treatment involves grinding and cleaning the castings after sand removal.

[0030] Step S101 (outer mold design and sand core fabrication) is the foundation of the entire process, its core being a systematic design scheme to ensure the internal quality of the casting. This includes: employing a bottom-pouring open gating system and foam ceramic filters to achieve stable and clean filling, effectively reducing air entrapment; designing reasonable venting channels to ensure smooth gas discharge from the cavity; and scientifically arranging heating risers and cast iron chills to establish effective sequential solidification conditions, precisely feeding and quenching hot spots in the casting. These designs are crucial to avoiding defects such as porosity and shrinkage in the casting. Step S102 (molten iron smelting) provides molten iron with qualified chemical composition for casting, laying the foundation for the basic material properties of the casting. Step S103 (spheroidizing and inoculation treatment and pouring) is the core step that determines the final metallographic structure of the casting. Through precise spheroidizing and multi-stage inoculation treatment, the molten iron is transformed into a casting with the target morphology and high performance. Step S104 (post-treatment) cleans the casting to meet the initial requirements for appearance and internal cavity cleanliness. The above four steps constitute a continuous and systematic precision control process, which significantly improves the stability of casting quality.

[0031] See Figures 6 to 10 , Figure 6 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 7 An exemplary perspective view shows the casting process structure of the second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 8 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 9 An exemplary perspective view shows the casting process structure of the first component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure. Figure 10 An exemplary perspective view shows the casting process structure of the second component of a ductile iron cylinder head for internal combustion locomotives, according to some embodiments of this disclosure.

[0032] Further, or optionally, the outer mold design adopts a symmetrical layout of two molds in one mold. The outer mold of the casting is divided into upper and lower molds along the center line of the air intake and exhaust channels. The spring seat surface is set as the top surface of the upper mold, and the combustion chamber fire surface is set as the bottom surface of the lower mold. By dividing the mold into upper and lower molds along the center line of the air intake and exhaust channels, the overall casting layout is split, and this structural setting achieves precise layout of key surfaces. The symmetrical layout of two molds in one mold can improve production efficiency and reduce mold manufacturing costs. Dividing the mold into upper and lower molds along the center line of the air intake and exhaust channels facilitates mold opening and closing and casting removal, reducing damage to the casting during demolding. The positioning of the spring seat surface and the combustion chamber fire surface can ensure uniform machining allowance for these two key functional surfaces, improving the convenience and accuracy of subsequent machining.

[0033] Further or optionally, in the outer mold design of step S101, the gating system adopts a bottom-pouring open gating system, and the overall gating system presents an "I-shaped distribution," which is divided into 1 sprue (structure 10), 4 horizontal sprues (structure 11), and 8 ingates (structure 12). The ingates are introduced from both sides of the edge of the fire face. The total cross-sectional ratio is ΣA_straight (2000mm). 2 ) :ΣA horizontal (3500mm 2 ): Within ΣA (4000mm 2 The ratio of the cross-sectional area of ​​the sprue 10, branch runner 11, and ingate 12 is 1:1.7:2. Simultaneously, two 100×100×22mm 10ppi ceramic slag screens (structure 13) are placed symmetrically and horizontally in the main and branch runners. The cross-sectional area ratio of the sprue 10, branch runner 11, and ingate 12 follows the flow law of molten iron. The sprue 10 serves as the main channel providing stable material supply, the branch runner is responsible for diversion and buffering, and the ingate 12 ensures uniform injection of molten iron into the mold cavity. By setting the cross-sectional area ratio of the three as described above, the smooth flow of molten iron can be ensured, avoiding excessively fast or slow flow rates within the channels, and reducing defects caused by oxidation and vortices. The horizontal placement of the foam ceramic filter screen ensures full coverage filtration of the molten iron. Its size is adapted to the corresponding channels of the casting system, and its porosity determines its reasonable filtration accuracy, effectively intercepting oxide slag and impurities in the molten iron, reducing the incidence of slag defects, and preventing obstruction of molten iron flow.

[0034] Further or optionally, in the outer mold shaping in step S101, a total of 8 air vents are arranged on the upper spring seat surface of the outer mold, each air vent having a cross-sectional area of ​​6000 mm². 2In addition, a total of 12 air vents with a diameter of 10-25mm are installed at the parting surface water channel core, air channel core head, and sand filling core positioning points. Each mold has four 10 / 13k heating risers 14 at the hot spot on the spring seat surface, and two 8 / 11k heating side risers 15 at the hot spots on the process hole mounting surfaces on both sides. This arrangement of heating risers 14 forms a targeted feeding structure connection. The spring seat surface is the main hot spot area of ​​the cylinder head, corresponding to the higher-power 10 / 13k heating risers 14. The hot spots on the process hole mounting surfaces on both sides are relatively less important, so the lower-power 8 / 11k heating side risers 15 can be arranged accordingly. This precise arrangement enables directional feeding. The heating risers 14 continuously release heat, providing sufficient liquid metal to the hot spots of the casting, filling the shrinkage voids generated during solidification, effectively solving the problem of frequent shrinkage porosity and shrinkage cavities at the hot spots in traditional processes, and improving the density of the casting.

[0035] Further or optionally, four rectangular cast iron chills 16 and one cross-shaped cast iron chill 17 are arranged around the perimeter of each type of combustion chamber surface. The chills cover the combustion surface and are 40 mm thick. A 25 mm through hole is designed in the center of the cross-shaped cast iron chill 17. A steel rod is made and inserted into the hole when the outer mold is molded. After the outer mold is removed, the rod is left in the sand mold along with the chill. The steel rod serves as a core support column to support the nozzle hole core.

[0036] Specifically, the rectangular cast iron chill 16 and the cross-shaped cast iron chill 17 in the nose bridge area complement each other, jointly covering the high-temperature critical area of ​​the combustion chamber surface. The special shape of the cross-shaped cast iron chill 17 is adapted to the structure of the nose bridge area, and the through-hole in the middle provides a mounting base for the steel round bar. The steel round bar and the chill form an integrated structure, combining the chill's chilling function and the core support function. The 40 mm thick cast iron chill has a good chilling effect, which can accelerate the solidification speed of the combustion chamber surface, refine the grains, and improve the mechanical properties of this part. At the same time, it works with the riser to form a sequential solidification of the entire casting. The cross-shaped cast iron chill 17 acts precisely in the nose bridge area, and the steel round bar, as a core support column, effectively supports the injector orifice core, preventing it from shifting during the casting process. This ensures both the forming accuracy of the injector orifice and strengthens the structural stability of the nose bridge area.

[0037] Further, or optionally, the valve spring seat pushrod hole is designed as a cast hole, into which four CNC-machined graphite chills 19, each 25 mm in diameter, are inserted. These graphite chills 19, while chilling the cast hole area, also press down on the intake and exhaust manifold cores to prevent them from floating or moving. The cast hole design reduces subsequent machining steps. The graphite chills 19 precisely fit the cast hole, simultaneously connecting the chilling and pressing functions, acting on the cast hole area and assisting in the fixation of the intake and exhaust manifold cores. The CNC-machined ø25 mm graphite chills 19 have high dimensional accuracy. The chilling effect densifies the microstructure around the pushrod hole, improving the dimensional accuracy and surface quality of the hole. Furthermore, their pressing effect effectively suppresses the upward movement of the intake and exhaust manifold cores under the buoyancy of the molten iron, preventing displacement or deformation of the air and water passages, and ensuring the smooth flow of the engine's "breathing system."

[0038] Further, or optionally, in step S101, the shrinkage rate of all mold dimensions is set to 0.8%, while a wall thickness correction of 3mm is set in the bridge area. The 0.8% mold shrinkage rate is a general adjustment for the overall solidification shrinkage of the casting, while the 3mm wall thickness correction in the bridge area is a specific compensation for this critical local area. The two work together to achieve precise control of both overall and local dimensions. The 0.8% shrinkage rate offsets the volume shrinkage during the solidification process of cast iron, preventing the overall size of the casting from being too small. The 3mm wall thickness correction in the bridge area compensates for insufficient wall thickness caused by linear shrinkage in this region, while ensuring the strength and rigidity of the bridge area, preventing fracture or deformation under high temperature and high pressure conditions.

[0039] Further, or optionally, in step S101, the raw sand for the coated sand core is silica sand with a particle size range of 50-100 mesh, a room temperature tensile strength ≥2.8MPa, a room temperature flexural strength ≥6.0MPa, and a gas emission rate ≤15ml / g. The core injection pressure is controlled at 0.6-0.8MPa, the core-making temperature is controlled between 250℃ and 280℃, and the holding time is 180S-300S. The particle size of the raw sand determines the density of the sand core, the room temperature tensile strength and flexural strength limit the impact resistance of the sand core during casting, and the gas emission rate is directly related to the subsequent venting effect. The core injection pressure, core-making temperature, and holding time together determine the curing quality of the sand core. These parameters work together to ensure that the sand core has sufficient strength to resist the impact of molten iron, control the amount of gas generated to a low range to avoid subcutaneous porosity during casting, and prevent the sand core from deforming during handling and casting, thus ensuring the forming accuracy of complex internal cavities such as air channels and water channels.

[0040] Further, or optionally, the air channel core and water channel core are equipped with manual drilling and sand-cleaning holes at the core head position. After cleaning the loose sand in the inner cavity using a high-pressure air pipe, they are dipped in zircon powder coating and dried in a surface drying furnace. The sand-cleaning holes at the core head position are used to clean the loose sand in the inner cavity, the high-pressure air pipe cleaning is used to remove loose sand, the zircon powder coating forms a protective layer on the cleaned core surface, and the surface drying furnace allows the coating to solidify and adhere. Thus, by using the sand-cleaning holes and high-pressure cleaning, loose impurities inside the core can be further removed, preventing impurities from mixing with molten iron and forming inclusion defects. The zircon powder coating has high-temperature resistance properties; after dipping and drying, it can reduce the probability of sand adhering to molten iron during casting, while also improving the core's permeability, further reducing porosity defects, and ensuring the smoothness of the inner walls of the air and water channels.

[0041] Further or optionally, in the molten iron smelting step S102, raw materials such as pig iron, scrap steel, ferromanganese, copper, molybdenum, and ferrosilicon are selected and batched according to the target composition: C: 3.4%-3.8%, Si: 1.7%-2.0%, Mn: 0.35%-0.45%, P: ≤0.1%, S: ≤0.01%, Mo: 0.5-0.6%, Ni: 1.1-1.4%, Mg: 0.04%-0.07%, and Cu: 0.5%-0.6%. The furnace charge is selected as follows: pig iron (C: 4.57%-4.69%, Si: 0.67%-0.83%, balance being other trace elements and Fe) at 40%-60%; scrap steel (C: 0.12%-0.17%, Si: 0.13%-0.19%, Mn: 0.40%-0.51%, balance being other trace elements and Fe) at 20-30%; and appropriate proportions of recycled materials, ferromanganese, ferromolybdenum, nickel, and copper are added.

[0042] After the bill of materials is prepared, the metal raw materials are weighed and then sent to the medium-frequency electric furnace for smelting. First, pig iron is added. After the furnace charge is completely melted, scrap steel and other metal raw materials are added, including 1% silicon carbide particles (85% content) to improve the metallurgical quality of the molten iron. After all the furnace charge is completely melted, a slag-reducing agent is sprinkled on the molten iron to remove slag. At a smelting temperature of 1560-1600℃, the molten iron is allowed to settle at high temperature for further slag removal. Once the molten iron reaches the tapping temperature of 1500-1540℃, 0.2% silicon carbide powder (0.2-0.7mm particle size) (90% content) is sprinkled into the furnace, followed by tapping. This process provides molten iron with a suitable chemical composition, thus laying the foundation for the basic material properties of the castings.

[0043] Further or optionally, in the spheroidizing inoculation treatment and casting in step S103, the composition of the yttrium-based rare earth magnesium spheroidizing agent is Si: 42%-45%, Mg: 6%-8%, Re: 2%-3.5%, Ca: 2%-3%, Al < 1%, and Fe balance. The total addition amount of the yttrium-based rare earth magnesium spheroidizing agent is 1.0-1.2%, and the proportion of yttrium in Re is 50%, lanthanum 25%, and cerium 25%. The 50% yttrium content effectively stabilizes the spheroidizing effect, preventing spheroidization degradation of molten iron during a long casting window. Combined with multi-stage inoculation, it can achieve a spheroidization grade ≥ 2 and a carbide grade ≤ 3%, providing a key guarantee for the metallographic stability of the casting. The composition of the inoculant is Si: 70%-75%, Ba: 1.9%-2.5%, Ca: 0.9%-1.5%, Al < 1%, and Fe balance. The total amount of inoculant added is 1.0%-1.3%, with a particle size between 2-7mm. Furthermore, the molten iron needs to reach a pouring temperature between 1425-1435℃ for pouring. A suitable pouring temperature helps avoid cold shuts, porosity, and shrinkage defects, and it is a parameter that balances multiple aspects. Simultaneous inoculation of the molten iron is carried out during the pouring process. The inoculant used is a silicon-manganese-zirconium inoculant with the following composition: Si: 70%-75%, Ba: 1.9%-2.5%, Ca: 0.9%-1.5%, Al < 1%, Fe balance, with a particle size of 0.2-0.7mm to ensure suitable particle size and rapid absorption. The total addition amount is 0.15%-0.2%.

[0044] Example 2 Unlike Example 1, the total cross-sectional ratio of the casting system is ΣA_straight (1500 mm²): ΣA_horizontal (1950 mm²): ΣA_inner (2400 mm²) = 1:1.3:1.6. The target components are: C: 3.8%-4.1%, Si: 2.0%-2.3%, Mn: 0.35%-0.45%, P: ≤0.1%, S: ≤0.01%, Mo: 0.3-0.5%, Ni: 0.9-1.1%, Mg: 0.4%-0.07%, Cu: 0.4-0.5%. The materials are selected and proportioned accordingly. The total amount of yttrium-based rare earth magnesium spheroidizing agent added is between 0.8% and 1.0%, the amount of inoculant added is 0.7%-1.0%, and the total amount of silicon manganese zirconium inoculant added is 0.10%-0.15%.

[0045] The physical and chemical properties of the products cast according to the first and second embodiments described above are shown in the table below:

[0046] The high-grade as-cast ductile iron cylinder head casting process for internal combustion locomotives disclosed in this embodiment integrates optimized mold design, innovative molten iron composition design, and precise spheroidization inoculation process. Combined with a bottom-pouring gating system based on solidification simulation and directional cooling control technology, it achieves coordinated and precise control over the solidification sequence, microstructure, and geometric dimensions of the casting. This systematically solves problems such as shrinkage porosity, abnormal graphite morphology, dimensional deviations, and substandard performance in key parts of the cylinder head, resulting in high-yield, high-performance ductile iron cylinder head castings. The specific process includes four steps: external mold shaping and sand core fabrication, molten iron melting, spheroidization inoculation treatment, pouring, and post-treatment.

[0047] This disclosure also provides a ductile iron cylinder head for internal combustion engine vehicles, which includes a first part and a second part according to some embodiments of this disclosure, and is cast using the casting method described in some embodiments of this disclosure.

[0048] While numerous embodiments of this disclosure have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and intent of this disclosure. It should be understood that various alternatives to the embodiments of this disclosure described herein may be employed in the practice of this disclosure. The appended claims are intended to define the scope of this disclosure and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A casting process for a high-grade as-cast ductile iron cylinder head for an internal combustion engine vehicle, characterized by, Comprise the following steps: S101, the outer mold modeling and sand core making: the shape mold is designed as one mold two patterns symmetrical layout, and the gating system, exhaust and cold iron riser process are designed, the outer mold cavity adopts self-hardening furan resin sand process molding; make sand core, wherein the air channel core, water channel core, bolt hole core and oil nozzle hole core all adopt hot core box method coated sand core, the shape mold is divided into upper mold and lower mold along the center line of the exhaust passage, the spring seat surface is set as the upper mold top surface, and the combustion chamber fire surface is set as the lower mold bottom surface; the gating system adopts an open filter gating system, the cross-sectional area ratio of the direct gate, the horizontal gate and the inner gate is 1:1.7:2 or 1:1.3:1.6, and the horizontal gate is provided with a foamed ceramic filter screen horizontally; S102, smelting molten iron: select pig iron, scrap steel, manganese iron, copper, molybdenum, silicon iron as raw materials, after the prepared metal raw materials are weighed, they are sent into a medium-frequency electric furnace for smelting, pig iron, scrap steel and other metal raw materials are sequentially added, silicon carbide particles and silicon carbide powder particles are added in the smelting process, after smelting, the slag is removed by scattering the slag remover, and the molten iron is completed after high-temperature standing and slag removal; S103, spheroidizing inoculation treatment and pouring: the weighed yttrium-based rare earth magnesium spheroidizing agent is uniformly placed into the spheroidizing dam of the dried pouring ladle, the bottom inoculant is added after the spheroidizing agent is tamped and flattened, and the bottom inoculant is tamped; the stream inoculant is added with the stream when the molten iron is discharged, and the slag is removed after the molten iron is discharged; when the temperature of the molten iron reaches 1425-1435 DEG C, pouring is carried out, and the stream inoculation is carried out synchronously during pouring; after pouring, the temperature is kept, and the mold is opened and the sand is removed after cooling; S104, post-processing: the sand-removed casting is polished and cleaned, and then artificial aging is carried out; After artificial aging, the handheld shot blasting machine is used to clean each bolt hole, sand cleaning process hole and exhaust passage core of the casting, and the inner cavity oxide skin is removed.

2. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, In the outer mold modeling and sand core making step, a composite chilling system is arranged for each casting, which comprises: at least four heat generating risers arranged at the hot section of the spring seat surface; heat generating side risers arranged at the hot section of the process hole installation surface on both sides; at least four rectangular cast iron cold irons and one cross-shaped cast iron cold iron in the nose bridge area are arranged around the combustion chamber surface, a through hole is designed in the middle of the cross-shaped cast iron cold iron, a steel round bar is inserted during molding of the lower mold of the outer mold, and the round bar is reserved in the sand mold as a core support steel column supporting the oil nozzle hole sand core after the mold is removed.

3. The process for casting high grade as-cast ductile iron cylinder head for IC engine vehicle as claimed in claim 2 wherein, The push rod hole of the spring seat surface is designed as a cast-out hole, and a numerically controlled processed graphite cold iron column is inserted in the hole; the graphite cold iron column is used to press the exhaust passage sand core to prevent it from moving upward at the same time of chilling the area.

4. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, The sand core making adopts silica sand with a particle size range of 50-100 meshes, the tensile strength of the prepared sand core at room temperature is ≥2.8 MPa, the bending strength at room temperature is ≥6.0 MPa, and the gas evolution amount is ≤15 ml / g; the core shooting pressure is controlled at 0.6-0.8 MPa, the core making temperature is controlled at 250-280 DEG C, and the holding time is 180-300 S.

5. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, In the outer mold modeling and sand core making step, the size shrinkage rate of all molds is uniformly set to 0.8%, and a wall thickness correction amount of 3 mm is arranged in the wall thickness area of the nose bridge area.

6. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, The chemical composition of the molten iron obtained after the molten iron smelting step is as follows in terms of mass percentage: C: 3.4% to 4.1%, Si: 1.7% to 2.3%, Mn: 0.20% to 0.45%, P: ≤0.1%, S: ≤0.01%, Mo: 0.3 to 0.6%, Ni: 0.9 to 1.4%, Mg: 0.04% to 0.07%, Cu: 0.4 to 0.6%, and the balance being Fe and inevitable impurities.

7. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, The spheroidizing inoculation treatment and pouring step comprises spheroidizing treatment, tapping stream inoculation and pouring stream inoculation, the spheroidizing treatment uses yttrium-based rare earth magnesium spheroidizing agent, the adding amount of which is 0.8 to 1.2% of the mass of the molten iron; the tapping stream inoculation uses silicon-barium inoculant, the adding amount of which is 0.7% to 1.3% of the mass of the molten iron; and the pouring stream inoculation uses silicon-manganese-zirconium inoculant, the adding amount of which is 0.1% to 0.2% of the mass of the molten iron.

8. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 7 wherein, The yttrium-based rare earth magnesium spheroidizing agent has the following chemical composition in terms of mass percentage: Si: 42% to 45%, Mg: 6% to 8%, Re: 2% to 3.5%, Ca: 2% to 3%, Al: <1%, and the balance being Fe; wherein the yttrium element accounts for 50% of the mass of the Re, the lanthanum element accounts for 25%, and the cerium element accounts for 25%.

9. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, The temperature of the molten iron during pouring is controlled at 1425 to 1435℃.

10. The process for casting high grade as-cast ductile iron cylinder head for internal combustion engine as claimed in claim 1 wherein, In the sand core, the positioning core head positions of the air channel core and the water channel core are provided with sand cleaning holes, after high-pressure cleaning of the inner cavity to scatter sand, high-temperature resistant paint is used for immersion coating and drying.

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