Method for manufacturing gray cast iron cylinder head and gray cast iron cylinder head

Abstract

This invention provides a method for preparing a gray cast iron cylinder head and the gray cast iron cylinder head itself, comprising: selecting a target mold, a target sand core assembly, and a gating system, wherein the target mold has a cavity, and the target sand core assembly is configured to match the cavity; placing the target sand core assembly into the cavity; melting initial furnace charge into gray cast iron liquid, wherein the initial furnace charge includes recycled iron, iron filings, and scrap steel, and the scrap steel includes forging scrap steel; pouring the gray cast iron liquid into the cavity through the gating system; and cooling the gray cast iron liquid in the cavity to obtain a sample of the gray cast iron cylinder head.

Description

Technical Field

[0001] This invention relates to the field of resin metering system fault diagnosis technology, and more specifically, to a method for preparing a gray cast iron cylinder head and the gray cast iron cylinder head itself. Background Technology

[0002] In existing technologies, the cylinder heads of natural gas engines for commercial vehicles are typically made of high-grade gray cast iron HT300 due to the high combustion chamber temperature and high explosion pressure. However, high-grade gray iron has strict requirements for scrap steel and is used in large quantities, which leads to an imbalance in the furnace charge ratio and high material costs. At the same time, high-strength gray iron has a high tendency to be porous due to the addition of more alloys, which makes it prone to defects such as hole leakage, sand holes, and water leakage in the gas passage. The scrap rate after processing is high, and the traditional casting system has redundancy, resulting in a low process yield. It is difficult to achieve low cost, high quality, and high yield.

[0003] There is currently no effective solution to the above problems. Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing gray cast iron cylinder heads and a gray cast iron cylinder head, so as to solve the technical problems of high smelting cost, high scrap rate, low process yield and waste of molten iron caused by redundancy in the casting system of existing high-grade gray cast iron cylinder heads.

[0005] According to one aspect of the present invention, in order to achieve the above-mentioned objective, a method for preparing a gray cast iron cylinder head is provided, comprising: selecting a target mold, a target sand core assembly, and a gating system, wherein the target mold has a cavity, and the target sand core assembly is configured to match the cavity; placing the target sand core assembly into the cavity; melting an initial furnace charge into gray cast iron liquid, wherein the initial furnace charge includes recycled iron, iron filings, and scrap steel, and the scrap steel includes forging scrap steel; pouring the gray cast iron liquid into the cavity through the gating system; and cooling the gray cast iron liquid in the cavity to obtain a sample of a gray cast iron cylinder head.

[0006] Furthermore, after obtaining a sample of the gray cast iron cylinder head, the method also includes: removing the gating system, taking out the sample after the target mold has cooled to a preset temperature; and removing excess material from the outer surface of the sample to obtain the finished gray cast iron cylinder head.

[0007] Furthermore, when the initial furnace charge is smelted into gray cast iron, the temperature is controlled at 1510℃~1530℃ before tapping; the method also includes one-time inoculation and two-time in-flow inoculation, with a pouring temperature of 1420℃~1435℃, and the time from the start to the end of pouring a ladle of gray cast iron is controlled within 8 minutes.

[0008] Furthermore, the gating system includes a sprue, a main runner, a secondary runner, an upper runner, an ingate, and a filter screen. There are two secondary runners and two filters. The filters are located between the secondary runners and the ingate, and the length of the filters is along the width of the cavity.

[0009] Furthermore, the diameter of the sprue is 58mm, the size of the main runner is 54mm×45mm, the size of each of the secondary runners is 50mm×40mm, the size of the upper runner is 38mm×38mm×7, the ingate includes an ingate with a size of Φ12mm×8mm and an ingate with a size of 6mm×25mm×10; the size of the filter screen is 125mm×65mm×22mm.

[0010] Furthermore, the target mold also includes a spring-loaded air-hole needle, which includes a needle body, a pin sleeve, and a spring. The pin sleeve is fitted onto the needle body, and the spring is positioned between the pin sleeve and the mounting surface. The height of the needle body is greater than 280mm. During molding and extrusion, the spring is compressed to avoid the pressure block and to allow the air-hole to be formed directly.

[0011] Furthermore, the airway sand cores in the target sand core group are prepared using ceramic sand and resin, with the amount of resin added being 1.3% to 1.9% of the mass of ceramic sand.

[0012] Furthermore, the initial furnace charge includes: 30%–35% recycled iron, 25%–30% iron filings, 8%–10% baled scrap steel, 7%–9% forging scrap steel, 15%–17% guide rail scrap steel, 1.0%–1.2% carbon raiser, 0.03%–0.05% ferrosilicon, 0.7%–0.8% silicon carbide, 0.15%–0.2% ferromanganese, 0.1%–0.12% iron sulfide, 0.65%–0.7% copper, 0.04%–0.05% tin, 0.1%–0.15% ferromolybdenum, 0.29%–0.3% silicon-strontium inoculant, and 0%–0.05% ferrochrome.

[0013] Furthermore, the method also includes: adding 0.1% to 0.3% ferrochrome powder during tapping, adding 0.1% to 0.3% silicon-strontium inoculant during the first inoculation in the ladle, performing a second inoculation in the pouring process and adding 0.1% to 0.2% silicon-strontium inoculant, the pouring temperature being 1420℃ to 1435℃, controlling the pouring time of one ladle of gray cast iron molten iron from the start to the end of pouring to within 8 minutes, and cooling the casting to 600℃ in the sand mold before removing it from the mold and removing it from the sand.

[0014] According to one aspect of the present invention, in order to achieve the above-mentioned objective, a gray cast iron cylinder head is provided, which is prepared by the above-described method for preparing a gray cast iron cylinder head.

[0015] By applying the technical solution of this invention, the initial furnace charge containing recycled iron, iron filings, and forging scrap steel is used to smelt gray cast iron. Combined with the target sand core group and gating system for casting and cooling, the cost of furnace charge is effectively reduced, and the amount of scrap steel and alloys added is reduced. At the same time, with the subsequent process optimization, the cost per unit and the annual cumulative cost of natural gas cylinder heads are significantly reduced, the processing scrap rate is significantly reduced, and the process yield is improved. The tensile strength, Brinell hardness, and pearlite content of the casting body all meet the requirements of high-grade gray cast iron. This solves the technical problems of high smelting cost, high processing scrap rate, low process yield, and waste of molten iron due to redundancy in the gating system of existing high-grade gray cast iron cylinder heads. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 A flowchart of a first embodiment of a method for preparing a gray cast iron cylinder head according to the present invention is shown. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0021] Exemplary embodiments according to this application will now be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of this application is thorough and complete, and that the concept of these exemplary embodiments is fully conveyed to those skilled in the art. In the drawings, for clarity, the thickness of layers and regions may be exaggerated, and the same reference numerals are used to denote the same devices, and therefore their description will be omitted.

[0022] In the current technology, with the adjustment of energy structure and increasingly stringent emission regulations, natural gas engines for commercial vehicles are gradually becoming a growth product in the market due to their advantages such as low operating costs and low emissions. Compared with diesel engines of the same displacement, natural gas engines have higher in-cylinder combustion pressure and higher combustion chamber operating temperatures, resulting in the cylinder head bearing higher thermal and mechanical loads. Therefore, the cylinder head of a natural gas engine for commercial vehicles usually needs to be made of high-grade gray cast iron, such as HT300 or even HT350. Taking the cylinder head of a China VI natural gas engine as an example, its bottom combustion chamber area often requires a Brinell hardness greater than 220HB and a tensile strength greater than 300MPa, with the material reaching the HT300 grade; while traditional gray cast iron cylinder heads without Cr and Mo elements have a hardness of only about 190~200HB and a tensile strength of only about 260~280MPa, usually only reaching the HT250 grade, which is difficult to meet the increasingly higher performance requirements of natural gas engines.

[0023] However, high-grade gray cast iron has stringent requirements for furnace charge. To ensure material properties, traditional smelting formulas require the use of large amounts of scrap steel, such as a charge structure of approximately 70% scrap steel and 30% recycled iron. The proportion of recycled iron is difficult to increase, resulting in high levels of scrap steel, pig iron, and alloys, making it impossible to achieve a balanced charge ratio and leading to high material costs. Simultaneously, to achieve the required strength and hardness, high-grade gray cast iron often requires the addition of significant amounts of alloying elements such as Cu, Sn, Cr, and Mo. While these alloying elements can strengthen the matrix structure, stabilize pearlite, and improve strength and hardness, they also increase the tendency of molten iron to shrink and the material to become porous. This makes castings prone to defects such as shrinkage cavities, porosity, leakage, sand holes, and water leakage in hot spots or thin-walled, complex areas like grease fittings, bolt holes, guide tube holes, and gas passages. The scrap rate after processing is relatively high. For example, the scrap rate of natural gas cylinder head processing under traditional processes can reach about 3.33%. Among them, defects in oil nozzle holes, leakage, and sand are the main types of scrap, which seriously affect the yield and customer quality targets.

[0024] Furthermore, the traditional gray cast iron cylinder head casting system design suffers from redundancy. The cross-sections or number of components such as the sprue, main runner, secondary runners, upper runner, and overflow block are excessively large, along with a large number of filters, resulting in high weight per casting and low process yield. For example, the original casting system had a sprue of Φ70, a main runner of 70×50, four secondary runners of 46×44, an upper runner of 40×40×7, an overflow block thickness of 30mm, and four filters of 75×75. Each casting weighed approximately 95.6kg, resulting in a heavy system and significant molten metal waste. Additionally, the traditional vent needle height is limited, requiring manual piercing, and the back of the sand box easily forms a "bowl" shape, leading to excessive molten iron pouring. The aforementioned problems make it difficult for existing technologies to achieve a balance between low cost, high quality, and high yield: reducing the proportion of scrap steel or reducing the amount of alloy added will damage the material properties, while ensuring the material properties will lead to increased costs and an increase in defects such as shrinkage porosity and leakage; insufficient weight reduction of the gating system makes it difficult to improve the process yield.

[0025] Therefore, there is an urgent need for a low-cost, low-scrap, and high-yield method for manufacturing gray cast iron cylinder heads suitable for commercial vehicle natural gas engine cylinder heads. This method aims to optimize the furnace charge ratio, reduce alloy costs, improve material porosity, reduce defects such as pore leakage and gas passage leakage, and increase the yield of the process while ensuring the material properties of HT300 and above.

[0026] Combination Figure 1 As shown, according to a specific embodiment of this application, a method for preparing a gray cast iron cylinder head is provided.

[0027] Specifically, a method for preparing a gray cast iron cylinder head includes:

[0028] Step S1: Select the target mold, the target sand core assembly, and the gating system. The target mold has a cavity, and the target sand core assembly is set to match the cavity.

[0029] Step S2: Place the target sand core assembly into the cavity;

[0030] Step S3: Melt the initial furnace charge into gray cast iron liquid. The initial furnace charge includes recycled iron, iron filings and scrap steel. The scrap steel includes forging scrap steel.

[0031] Step S4: The gray cast iron molten metal is poured into the mold cavity through the gating system; the gray cast iron molten metal in the mold cavity is cooled to obtain a sample of gray cast iron cylinder head.

[0032] By applying the technical solution of this invention, the initial furnace charge containing recycled iron, iron filings, and forging scrap steel is used to smelt gray cast iron. Combined with the target sand core group and gating system for casting and cooling, the cost of furnace charge is effectively reduced, and the amount of scrap steel and alloys added is reduced. At the same time, with the subsequent process optimization, the cost per unit and the annual cumulative cost of natural gas cylinder heads are significantly reduced, the processing scrap rate is significantly reduced, and the process yield is improved. The tensile strength, Brinell hardness, and pearlite content of the casting body all meet the requirements of high-grade gray cast iron. This solves the technical problems of high smelting cost, high processing scrap rate, low process yield, and waste of molten iron due to redundancy in the gating system of existing high-grade gray cast iron cylinder heads.

[0033] Furthermore, after obtaining a sample of the gray cast iron cylinder head, the method also includes: removing the gating system, taking out the sample after the target mold has cooled to a preset temperature; and removing excess material from the outer surface of the sample to obtain the finished gray cast iron cylinder head.

[0034] This embodiment effectively ensures uniform casting structure and dimensional stability by removing the sample and cutting off excess material from the outer surface after the target mold has cooled to a preset temperature, thereby reducing deformation, cracking, and internal stress, and thus improving the yield and precision of gray cast iron cylinder heads.

[0035] Specifically, when the initial furnace charge is smelted into gray cast iron, the temperature is controlled at 1510℃~1530℃ before tapping. The method also includes one-time inoculation and two-time in-flow inoculation, with a pouring temperature of 1420℃~1435℃. The pouring time for one batch of gray cast iron is controlled within 8 minutes from the start to the end of pouring.

[0036] This embodiment controls the temperature before tapping at 1510℃~1530℃ and the pouring temperature at 1420℃~1435℃, and combines one inverted inoculation and two in-flow inoculation, completing the pouring within 8 minutes. This effectively prevents overheating of the molten iron and inoculation decline, refines the grains, and reduces shrinkage porosity and white cast iron tendency, thereby obtaining a high-strength gray cast iron cylinder head with uniform structure and stable performance.

[0037] In this embodiment, the gating system includes a sprue, a main runner, a secondary runner, an upper runner, an inner runner, and a filter screen. There are two secondary runners and two filters. The filters are located between the secondary runners and the inner runners, and the length of the filters is along the width of the cavity.

[0038] This embodiment reduces the number of horizontal runners to two and the number of filter screens to two, which are arranged along the width of the cavity between the horizontal runners and the ingate. This effectively reduces the weight of the gating system and improves the process yield, while ensuring stable filling and sufficient filtration, thus reducing inclusions and scrap rates.

[0039] In one exemplary embodiment, the diameter of the sprue is 58mm, the size of the main runner is 54mm×45mm, the size of each of the secondary runners is 50mm×40mm, the size of the upper runner is 38mm×38mm×7, and the ingate includes an ingate with a size of Φ12mm×8mm and an ingate with a size of 6mm×25mm×10; the size of the filter screen is 125mm×65mm×22mm. While ensuring stable filling and filtration effect, this significantly reduces the weight of the gating system, improves the process yield, and reduces the scrap rate.

[0040] Furthermore, the target mold also includes a spring-loaded air-hole needle, which includes a needle body, a pin sleeve, and a spring. The pin sleeve is fitted onto the needle body, and the spring is positioned between the pin sleeve and the mounting surface. The height of the needle body is greater than 280mm. During molding and extrusion, the spring is compressed to avoid the pressure block and allows the air-hole to be formed directly, thereby eliminating the need for manual piercing of the air-hole, reducing labor intensity, preventing the formation of a "bowl" shape on the back of the sand box, reducing the amount of molten iron poured, and improving the process yield.

[0041] Specifically, the air passage sand core in the target sand core group is prepared using ceramic sand and resin, with the amount of resin added being 1.3% to 1.9% of the ceramic sand mass. This reduces resin usage and auxiliary material costs while ensuring the sand core's tensile strength meets requirements, thereby reducing defects such as air passage leakage and sand inclusions, and improving the yield of gray cast iron cylinder heads.

[0042] In this embodiment, the initial furnace charge includes: 30%–35% recycled iron, 25%–30% iron filings, 8%–10% bundled scrap steel, 7%–9% forging scrap steel, 15%–17% guide rail scrap steel, 1.0%–1.2% carburizing agent, 0.03%–0.05% ferrosilicon, 0.7%–0.8% silicon carbide, and 0.15%–0.2% [unclear - possibly referring to a specific component or component]. The material contains ferromanganese, 0.1%–0.12% ferric sulfide, 0.65%–0.7% copper, 0.04%–0.05% tin, 0.1%–0.15% ferromolybdenum, 0.29%–0.3% silicon-strontium inoculant, and 0%–0.05% ferrochrome. This process significantly reduces the amount of scrap steel and alloys added, balances the furnace charge ratio, and reduces shrinkage porosity and scrap rate while ensuring the performance of high-strength gray cast iron.

[0043] In one exemplary example, the method further includes: adding 0.1% to 0.3% ferrochrome powder during tapping, adding 0.1% to 0.3% silicon-strontium inoculant during the first inoculation in the ladle, performing a second inoculation in the pouring process and adding 0.1% to 0.2% silicon-strontium inoculant, and the pouring temperature is 1420℃ to 1435℃. The pouring time for one batch of gray cast iron is controlled within 8 minutes from the start to the end of the pouring process. After the casting is cooled to 600℃ in the sand mold, it is removed from the mold and the sand is removed. This effectively reduces shrinkage porosity, white cast iron, and deformation cracking, resulting in a high-strength gray cast iron cylinder head with uniform structure, stable performance, and high yield.

[0044] Example 1

[0045] This embodiment provides a method for preparing a gray cast iron cylinder head for a commercial vehicle natural gas engine, specifically including the following steps:

[0046] Select the target mold, target sand core assembly, and gating system. The target mold has a cavity corresponding to the gray cast iron cylinder head, and the target sand core assembly is matched and set to the cavity. The air passage sand core in the target sand core assembly is prepared using ceramic sand and resin, with 100 kg of ceramic sand and 1.5 kg of resin added. The gating system includes a sprue, main runner, secondary runners, top runner, ingate, and filter screen. The sprue diameter is 58 mm, the main runner size is 54 mm × 45 mm, there are two secondary runners, each with a size of 50 mm × 40 mm, the top runner size is 38 mm × 38 mm × 7, the ingate includes an ingate with a size of Φ12 mm × 8 mm and an ingate with a size of 6 mm × 25 mm × 10, and there are two filters with a size of 125 mm × 65 mm × 22 mm. The filters are placed between the secondary runners and the ingate, with the length of the filters along the width of the cavity. The target mold also includes a spring-loaded air-hole needle, which includes a needle body, a pin sleeve, and a spring. The pin sleeve is fitted onto the needle body, and the spring is positioned between the pin sleeve and the mounting surface. The needle body is 300mm high. During molding and extrusion, the spring is compressed to avoid the pressure block and allow the air-hole to be formed directly.

[0047] Step S2: Place the target sand core assembly into the cavity.

[0048] Step S3: Add the initial furnace charge to the medium-frequency electric furnace and melt it into gray cast iron. Based on 1000kg of initial furnace charge, it includes: 338.51kg of recycled iron, 290.15kg of iron filings, 96.72kg of baled scrap steel, 80.60kg of forging scrap steel, 161.19kg of guide rail scrap steel, 11.77kg of carbon raiser, 0.40kg of ferrosilicon, 7.01kg of silicon carbide, 1.53kg of ferromanganese, 1.05kg of ferrous sulfide, 6.53kg of copper, 0.43kg of tin, 1.13kg of ferromolybdenum, 2.99kg of silicon-strontium inoculant, and 0kg of ferrochrome. The forging scrap steel used is 42CrMoHA forging scrap steel, comprising, by mass percentage: Mn 0.75%, Cr 1.16%, Mo 0.23%, Ni 0.05%, Cu 0.03%, with the balance being Fe and impurities. The iron filings are from cylinder block or cylinder head machining, comprising, by mass percentage: C 3.5%, Si 2.2%, Mn 0.5%, P 0.03%, S 0.10%, Cu 1.0%, Sn 0.09%, Cr 0.20%, Mo 0.20%, with the balance being Fe and impurities. Silicon carbide is added for pretreatment during smelting, and a pre-furnace carbonization process is used to reduce the carbon content of the original molten iron. A fully graphitized carbonizer is added as an inoculant before casting, resulting in a sulfur content of 0.11% in the original molten iron. The temperature measured before tapping is 1521℃.

[0049] Step S4: During tapping, ferrochrome powder is added along with the molten iron at a rate of 0.15% of the iron weight. The ferrochrome powder, by mass percentage, comprises: Cr 62%, C 8%, Si 3.0%, with the balance being Fe and impurities, and a particle size of 2mm. After slag removal, the molten iron is transferred from the transfer ladle to the casting ladle, and simultaneously, a silicon-strontium inoculant is added for a single ladle inoculation at a rate of 0.26% of the molten iron weight. The silicon-strontium inoculant, by mass percentage, comprises: Si 75%, Sr 0.8%, Ca 0.05%, Al 0.3%, with the balance being Fe and impurities, and a particle size of 3mm. After the single ladle inoculation, slag is removed, and the temperature is measured to 1425℃.

[0050] Step S5: Hang the casting ladle on the casting machine for casting. During casting, perform secondary inoculation by adding a silicon-strontium inoculant at 0.15% of the tapped iron weight, with a particle size of 0.5mm. The entire process of casting one ladle of gray cast iron should take 7 minutes. After casting, cool the casting to 600℃ in the sand mold, remove the sand, dismantle the gating system, and cut off excess material from the outer surface of the sample to obtain the finished gray cast iron cylinder head.

[0051] The final chemical composition (by mass percentage) of the gray cast iron cylinder head obtained in this embodiment is: C 3.17%, Si 1.90%, Mn 0.49%, S 0.11%, P 0.03%, Cu 0.86%, Cr 0.24%, Mo 0.23%, with the balance being Fe and impurity elements. Testing revealed a body hardness of 220 HBW, a body tensile strength of 300 MPa, a pearlite content ≥95%, and graphite morphology predominantly type A, achieving a material grade of HT300. The processing scrap rate was 2.44%, and the process yield was 68.5%.

[0052] Example 2

[0053] The difference between this embodiment and Embodiment 1 lies in the initial charge ratio and some process parameters.

[0054] The initial furnace charge, calculated at 1000 kg, includes: 338.51 kg of recycled iron, 290.15 kg of iron filings, 96.72 kg of baled scrap steel, 80.60 kg of forging scrap steel, 161.19 kg of guide rail scrap steel, 11.77 kg of recarburizing agent, 0.40 kg of ferrosilicon, 7.01 kg of silicon carbide, 1.53 kg of ferromanganese, 1.05 kg of ferrous sulfide, 6.53 kg of copper, 0.43 kg of tin, 1.13 kg of ferromolybdenum, 2.99 kg of silicon-strontium inoculant, and 0 kg of ferrochrome. The forging scrap steel used is 42CrMoHA forging scrap steel, and the iron filings are from cylinder head processing. Silicon carbide is used as a pretreatment agent during smelting, and a pre-furnace recarburizing process is employed. The temperature before tapping was 1521℃. Ferrochrome powder was added during tapping, and silicon-strontium inoculant was added during the first ingot inoculation. The temperature before pouring was 1420℃, and 0.2% silicon-strontium inoculant was added during the second ingot inoculation. The pouring time for one ladle of molten iron was 5 minutes. After the casting cooled to 600℃, it was removed from the mold and the sand was removed.

[0055] The final chemical composition (by mass percentage) of the gray cast iron cylinder head obtained in this embodiment is: C 3.20%, Si 2.01%, Mn 0.53%, S 0.11%, P 0.02%, Cu 0.91%, Cr 0.30%, Mo 0.29%, with the balance being Fe and impurity elements. Testing revealed a body hardness of 240 HBW, a body tensile strength of 320 MPa, a pearlite content ≥95%, and graphite morphology predominantly type A, achieving a material grade of HT350. The processing scrap rate was 2.44%, and the process yield was 68.5%.

[0056] Comparative Example 1

[0057] Comparative Example 1 uses the traditional gray cast iron cylinder head manufacturing process. The initial furnace charge consists of 70% scrap steel and 30% recycled iron, without adding iron filings or forging scrap, and without adding additional Cr or Mo elements. The gating system uses the original design: a Φ70 sprue, a 70×50 main runner, four 46×44 secondary runners, a 40×40×7 top runner, an overflow block thickness of 30mm, and four 75×75 filter screens. The weight of each casting box is approximately 95.6kg. The height of the air vent needle is only 280mm, requiring manual piercing. The air duct sand core is prepared using abrasive sand and resin, with a higher resin content than in this application. The casting temperature and inoculation process are controlled according to the traditional scheme.

[0058] The gray cast iron cylinder head obtained in Comparative Example 1 has a body hardness of 190 HBW, a body tensile strength of 280 MPa, a pearlite content of approximately 92%, and a high proportion of type B, D, and E graphite morphologies, resulting in a material grade that can only reach HT250. The processing scrap rate is 3.33%, the process yield is approximately 62%, and the unit cost is significantly higher than that of the embodiments in this application.

[0059] The gray cast iron cylinder heads prepared in Example 1, Example 2 and Comparative Example 1 were subjected to performance testing, and the test results are listed in Table 1.

[0060] Table 1

[0061]

[0062] As shown in Table 1, compared with Comparative Example 1, Examples 1 and 2 of this application, by using initial furnace charge containing recycled iron, iron filings, forging scrap, and guide rail scrap, combined with silicon carbide pretreatment, pre-furnace carbonization, primary inoculation with ladle pouring, and secondary in-flow inoculation, as well as a lightweight casting system and spring-loaded needles, significantly improved the hardness and tensile strength of the resulting gray cast iron cylinder heads. The hardness of Comparative Example 1 was 190 HBW, and the tensile strength was 280 MPa; the hardness of Example 1 was 220 HBW, and the tensile strength was 300 MPa; the hardness of Example 2 was 240 HBW, and the tensile strength was 320 MPa. As can be seen, this application significantly improves the hardness and tensile strength of gray cast iron cylinder heads while ensuring low cost, low scrap rate and high process yield. This enables the cylinder heads of commercial vehicle natural gas engines to stably meet the requirements of HT300 and even HT350 grades, solving the technical problems of high smelting cost, high processing scrap rate, low process yield and difficulty in balancing hardness and tensile strength in the prior art for high-grade gray cast iron cylinder heads.

[0063] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0064] In addition to the above, it should be noted that the terms "one embodiment," "another embodiment," and "embodiment" used in this specification refer to specific features, structures, or characteristics described in connection with that embodiment, which are included in at least one embodiment described in the general description of this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in connection with any embodiment, the intention is to suggest that implementing such a feature, structure, or characteristic in conjunction with other embodiments also falls within the scope of this invention.

[0065] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of manufacturing a gray cast iron cylinder head, characterized by, include: Select a target mold, a target sand core assembly, and a gating system. The target mold has a cavity, and the target sand core assembly is configured to match the cavity. The target sand core assembly is placed inside the cavity; The initial furnace charge is smelted into gray cast iron liquid, wherein the initial furnace charge includes recycled iron, iron filings and scrap steel, wherein the scrap steel includes forging scrap steel; The molten gray cast iron is poured into the mold cavity through the gating system; The molten gray cast iron in the cavity is cooled to obtain a sample of the gray cast iron cylinder head.

2. The method of producing a gray cast iron cylinder head according to claim 1, characterized by, After obtaining the sample of the gray cast iron cylinder head, the method further includes: Dismantle the gating system and remove the sample after the target mold has cooled to a preset temperature; Excess material is removed from the outer surface of the sample to obtain the finished gray cast iron cylinder head.

3. The method for preparing a gray cast iron cylinder head according to claim 1, characterized in that, When the initial furnace charge is smelted into gray cast iron, the temperature is controlled at 1510℃~1530℃ before tapping. The method also includes one inverted ladle inoculation and two in-flow inoculation, with a pouring temperature of 1420℃~1435℃. The pouring time for one ladle of gray cast iron is controlled within 8 minutes from the start to the end of pouring.

4. The method for preparing a gray cast iron cylinder head according to claim 1, characterized in that, The gating system includes a sprue, a main runner, a secondary runner, an upper runner, an inner runner, and a filter screen. There are two secondary runners and two filters. The filters are located between the secondary runners and the inner runners, and the length of the filters is along the width of the cavity.

5. The method for preparing a gray cast iron cylinder head according to claim 4, characterized in that, The diameter of the sprue is 58mm, the size of the main sprue is 54mm×45mm, the size of each of the secondary sprues is 50mm×40mm, the size of the upper sprue is 38mm×38mm×7, the ingate includes an ingate with a size of Φ12mm×8mm and an ingate with a size of 6mm×25mm×10; the size of the filter screen is 125mm×65mm×22mm.

6. The method for preparing a gray cast iron cylinder head according to claim 1, characterized in that, The target mold also includes a spring-loaded air-hole needle, which includes a needle body, a pin sleeve, and a spring. The pin sleeve is fitted onto the needle body, and the spring is positioned between the pin sleeve and the mounting surface. The height of the needle body is greater than 280mm. During molding and extrusion, the spring is compressed to avoid the pressure block and allow the air-hole to be formed directly.

7. The method for preparing a gray cast iron cylinder head according to claim 1, characterized in that, The airway sand cores in the target sand core group are prepared using ceramic sand and resin, with the amount of resin added being 1.3% to 1.9% of the mass of the ceramic sand.

8. The method for preparing a gray cast iron cylinder head according to claim 1, characterized in that, The initial charge includes: 30%–35% recycled iron, 25%–30% iron filings, 8%–10% baled scrap steel, 7%–9% forging scrap steel, 15%–17% guide rail scrap steel, 1.0%–1.2% carbon raiser, 0.03%–0.05% ferrosilicon, 0.7%–0.8% silicon carbide, 0.15%–0.2% ferromanganese, 0.1%–0.12% iron sulfide, 0.65%–0.7% copper, 0.04%–0.05% tin, 0.1%–0.15% ferromolybdenum, 0.29%–0.3% silicon-strontium inoculant, and 0%–0.05% ferrochrome.

9. The method for preparing a gray cast iron cylinder head according to claim 8, characterized in that, The method further includes: adding 0.1% to 0.3% ferrochrome powder during tapping, adding 0.1% to 0.3% silicon-strontium inoculant during the first inoculation in the ladle, performing a second inoculation in the pouring process and adding 0.1% to 0.2% silicon-strontium inoculant, the pouring temperature being 1420℃ to 1435℃, controlling the pouring time of one ladle of gray cast iron molten iron from the start to the end of pouring to within 8 minutes, and cooling the casting to 600℃ in the sand mold before removing it from the mold and removing it from the sand.

10. A gray cast iron cylinder head, characterized in that, The gray cast iron cylinder head is prepared by the method described in any one of claims 1 to 9.

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