Iron mold sand-coating retarder type production process of agricultural machine axle housing

Abstract

The application provides an iron mold sand-coated retarding type production process of an agricultural machine axle housing and relates to the field of agricultural machine axle housing casting technology. The process comprises the following steps: preparing an internally hollow cast iron core, one end of which is sealed and the other end of which is open, and the pipe wall of the cast iron core is provided with an exhaust plug; coating the outer wall of the cast iron core with sand; preparing an iron mold, adopting middle parting, and dividing the iron mold into an upper iron mold and a lower iron mold, and coating the cavity surfaces of the upper iron mold and the lower iron mold with sand; assembling the core and the mold, and connecting a vacuum device to the open end of the cast iron core at the outer end of the iron mold; performing spheroidizing treatment on the molten iron; starting the vacuum device to form a negative pressure cavity, and then pouring, cooling, opening the mold in sequence, and obtaining the agricultural machine axle housing casting. The four technical problems of thin wall filling, strengthening sequential solidification, inhibiting graphite floating and no riser can be solved simultaneously.

Description

Technical Field

[0001] This invention relates to the field of agricultural machinery axle housing casting technology, specifically to a production process for agricultural machinery axle housing using an iron mold with sand coating and slow setting. Background Technology

[0002] In casting production, to prevent shrinkage porosity in bridge shell castings, the first consideration is how to use risers for feeding. The weight of risers in the entire gating system accounts for 10% to 30% of the total weight of molten iron, depending on the weight of the casting. This greatly reduces the process yield of castings. For example, in clay sand molding and self-hardening resin sand molding, the process yield of castings is generally 50-80% in order to solve shrinkage porosity defects. This results in a huge waste of molten iron and makes the smelting cost of castings very high. According to the current market price, every 1% increase in yield will increase the cost of castings by 40-50 yuan / ton.

[0003] Currently, in cast iron casting processes, to prevent shrinkage cavities and porosity in castings, regardless of the design philosophy, the feeding function of risers is emphasized, making riserless casting difficult to achieve. The difference lies in the chosen process, such as clay sand casting, self-hardening resin sand molding, and iron mold sand-covered molding, which results in different riser sizes, but all still struggle to achieve riserless casting. Furthermore, in existing casting techniques, if the carbon content of the molten iron is high, graphite floating problems can occur.

[0004] In addition, for ultra-thin agricultural machinery bridge shells with a thickness of less than 10mm, during the casting process, the edges or gaps of the bridge shell may not be able to be cast or the casting may be uneven due to the excessive thinness, which will also lead to a low process yield. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a process for producing agricultural machinery bridge housings using a sand-coated iron mold with a slow-setting process. By controlling the high silicon-to-carbon ratio to increase the eutectic degree of molten iron to between 1.06 and 1.14, sufficient graphitization expansion is provided as a foundation. The iron mold with sand coating serves as a rigid outer shell and a rapid cooling method, ensuring that the expansion force is effectively utilized and rapid cooling is achieved. With "negative pressure" as the core catalyst, this process can simultaneously solve four major technical challenges: thin-walled filling, enhanced sequential solidification, suppression of graphite floating, and the absence of risers.

[0006] This invention provides a production process for a sand-coated, slow-setting type of agricultural machinery axle housing, comprising the following steps:

[0007] S1: Prepare a hollow cast iron core, sealed at one end and open at the other end. The tube wall of the cast iron core is equipped with an air vent; the outer wall of the cast iron core is coated with sand.

[0008] S2: Prepare the iron mold, using the middle parting method, dividing it into an upper iron mold and a lower iron mold, and apply a coating sand to the cavity surfaces of the upper iron mold and the lower iron mold;

[0009] S3: Core assembly box, the open end of the cast iron core frame is located at the outer end of the iron mold and is connected to the vacuum device;

[0010] S4: The molten iron is spheroidized. The composition of the spheroidized molten iron by mass fraction includes: C: 3.9-4.1%, Si: 2.1-2.4%, Mn: 0.2-0.6%, S: <0.02%, P: <0.035%, and the remainder is iron.

[0011] S5: Start the vacuum device to form a negative pressure cavity, then pour the casting, and after cooling and opening the mold, the agricultural machinery bridge shell casting is obtained.

[0012] Furthermore, the iron mold sand-coated slow-setting casting process for agricultural machinery bridge housings in this application controls the high silicon-to-carbon ratio to increase the hypereutectic degree of molten iron to between 1.06 and 1.14. This high eutectic degree, during solidification, causes the precipitation of a large amount of graphite, resulting in graphitization expansion. This counteracts the liquid shrinkage of the molten iron during solidification, laying the foundation for subsequent riserless casting of the bridge housing and preventing graphite floating issues. The rapid cooling effect of the iron mold sand coating (metal mold + thin sand layer) allows the casting to cool quickly, with the entire casting reaching the eutectic temperature almost simultaneously, thus causing synchronous and rapid graphitization expansion. Negative pressure enhances venting and solves the problem of thin-walled filling. For ultra-thin sections of 3-4 mm, the flow resistance of molten iron is high, and gas in the mold cavity is the main obstacle. Negative pressure can quickly remove gas from the sand core and mold cavity, greatly reducing filling resistance and allowing molten iron to smoothly fill every thin-walled corner, preventing incomplete filling and cold shuts. The negative pressure removes air from the mold cavity, enhancing heat conduction between the mold and the casting and creating a stronger cooling gradient. This gradient causes the parts furthest from the gate to solidify first, with the gate area solidifying last, resulting in ideal sequential solidification. This further optimizes the feeding channel, ensuring maximum self-feeding effect. Furthermore, the rapid cooling caused by the negative pressure significantly shortens the residence time of the molten iron in the liquid state; graphite spheres are quickly fixed as soon as they precipitate, preventing them from floating and ensuring material uniformity.

[0013] Optionally, the eutecticness of the spheroidized molten iron is 1.07-1.14. This ratio can further reduce the risk of shrinkage cavities and porosity, while suppressing graphite floating. For example, the eutecticness of the molten iron can be any point or range of 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14. For example, the carbon content in the molten iron composition can be any point or range of 3.9%, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 4.0, 4.01, 4.02, 4.03, 4.04, 4.05, 4.06, 4.07, 4.08, 4.09, 4.1.

[0014] Optionally, the negative pressure cavity in step S5 is 0.02-0.10 MPa. This application uses a hollow cast iron core to create negative pressure. Under this negative pressure parameter, the solidification time can be shortened, preventing carbon elements from agglomerating and forming large graphite spheres, and preventing graphite from floating. In addition, under this negative pressure condition, the opening time is shortened from 30 minutes to less than 15 minutes, which can improve production efficiency and extend mold life.

[0015] Optionally, in step S1, the outer wall of the cast iron core is coated with sand, and the thickness of the coating sand is 5-8mm.

[0016] Optionally, in step S2, the cavity surfaces of the upper and lower iron molds are coated with sand, and the coating sand thickness is 5-8mm.

[0017] Optionally, the vent plug is a slit-type vent plug with a diameter of 10-20mm. Alternatively, the vent plug is a slit-type vent plug with a diameter of 14-16mm, which reduces the risk of molten iron leakage while ensuring venting.

[0018] Optionally, multiple vent plugs can be installed, arranged longitudinally or laterally on the wall of the cast iron core. For example, the spacing between multiple vent plugs can be 50-80mm to ensure uniform venting. By evenly distributing the vent plugs, the suction effect of the negative pressure can be uniformly distributed along the cast iron core, more effectively removing gas from the entire cavity, avoiding local dead zones, and thus more stably controlling the slow setting process, while also preventing sand leakage. Furthermore, the method of forming negative pressure in the cavity is not limited to this. Alternatively, vent plugs can be omitted, and several small holes with a diameter of 2-4mm can be made on the inner wall of the cast iron core. Under the action of a vacuum device, gas from the entire cavity can be removed through these small holes.

[0019] Furthermore, in the casting process of agricultural machinery axle housings, the hollow cast iron core of this invention serves two main purposes. First, it acts as a sand core skeleton, ensuring sufficient strength and rigidity of the sand core during manufacturing and casting, preventing breakage. Second, as a channel connecting the mold cavity and the vacuum device, the cast iron core facilitates air extraction and creates negative pressure. This negative pressure removes air from the mold cavity, enhancing heat conduction between the mold and the casting, creating a stronger cooling gradient, which is beneficial for filling and a certain degree of sequential solidification (i.e., delayed solidification).

[0020] Optionally, by weight, the raw materials for spheroidized molten iron include: 45-50 parts of primary iron, 25-35 parts of scrap steel, 10-15 parts of recycled material, 1-2 parts of ferromanganese, 1-2 parts of ferrosilicon, 1-2 parts of spheroidizing agent, and 1-2 parts of carbonizer.

[0021] Optionally, the preparation method of spheroidized molten iron includes the following steps: smelting primary iron, scrap steel, recycled furnace, ferromanganese, and a carburizing agent to obtain molten iron; adding a spheroidizing agent to the molten iron ladle and compacting it, then adding ferrosilicon and compacting it, pressing it with steel sheets, pouring in the molten iron to spheroidize it, and then removing the slag to obtain spheroidized molten iron. The temperature of the spheroidized molten iron is 1420-1460℃. Overheating should be avoided to prevent graphite from floating.

[0022] Optionally, the molten iron temperature is 1520-1560℃.

[0023] Optionally, the spheroidizing agent is a rare earth magnesium silicon iron alloy; wherein, by mass fraction, Re: 2-4%, Mg: 6-8%, Ca: 2-3.5%, Si: <45%, Al: <1%, Mn: <1%, Ti: <1%, MgO <1%, and the balance is iron.

[0024] Optionally, the particle size of the spheroidizing agent is 5-30 mm.

[0025] Optionally, the carbon raiser is carbon.

[0026] Optionally, step S5 involves pouring, with the pouring time not exceeding 10 minutes.

[0027] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0028] (1) The iron mold sand-coated slow-setting production process of the present invention increases the high eutectic degree of molten iron to between 1.06 and 1.14 by controlling the high silicon-carbon ratio. The high eutectic degree causes a large amount of graphite to precipitate and generate graphitization expansion during the solidification process, which offsets the liquid shrinkage of molten iron during the solidification process, laying the foundation for subsequent riserless casting of bridge shells and preventing the problem of graphite floating.

[0029] (2) The production process of the iron mold covered with sand for slow setting under negative pressure conditions reduces the opening time from 30 minutes to less than 15 minutes, which can improve production efficiency and extend the mold life.

[0030] (3) The negative pressure of the iron mold sand-coated slow-setting production process of the present invention can enhance the exhaust and solve the problem of thin-walled filling. For ultra-thin parts of 3-4mm, the negative pressure can quickly remove the gas in the sand core and cavity, greatly reducing the filling resistance, so that the molten iron can be sucked in smoothly to fill every thin-walled corner, preventing insufficient pouring and cold shut. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 An exemplary embodiment of the production process diagram of the iron mold for sand coating of agricultural machinery axle housing according to the present invention is shown.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1-Cast iron core; 2-Cast iron mold; 3-Cast iron core with sand coating; 21-Upper iron mold; 22-Lower iron mold; 23-Upper cavity; 24-Lower cavity; 25-Cavity with sand coating; 4-Vacuum pump quick connector. Detailed Implementation

[0035] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0037] Example 1

[0038] In an exemplary embodiment of the present invention, this embodiment relates to a mold for a sand-coated production process of an agricultural machinery axle housing. The mold includes a hollow cast iron core 1 and a cast iron model 2. One end of the cast iron core 1 is sealed, and the other end is open. The tube wall of the cast iron core 1 is provided with several vent plugs, which can be arranged longitudinally or laterally on the tube wall of the cast iron core 1. The spacing between the multiple vent plugs is 50-80 mm. The outer wall of the cast iron core 1 is covered with a sand coating layer 3. During the production process, the cast iron core 1 is placed inside the cast iron model.

[0039] The cast iron model 2 is a middle parting, divided into an upper iron model 21 and a lower iron model 22. The upper iron model and the lower iron model surround the cavity (upper cavity 23 and lower cavity 24). The surface of the cavity is covered with a sand layer 25. The sealed end of the cast iron core is located inside the cavity, and the open end of the cast iron core is located outside the cast iron model. During the production process, the open end of the cast iron core is connected to the vacuum pump through the vacuum pump quick connector 4.

[0040] Example 2

[0041] This embodiment relates to a production process for a sand-coated slow-setting type of agricultural machinery axle housing. This production process uses the mold from Embodiment 1 and includes the following steps:

[0042] S1: Prepare a hollow cast iron core, sealed at one end and open at the other end. The tube wall of the cast iron core is equipped with a 12mm diameter slit-type vent plug; the outer wall of the cast iron core is covered with 6mm of coated sand.

[0043] S2: Prepare the cast iron model, using the middle parting, dividing it into an upper iron mold and a lower iron mold, and cover the cavity surface of the upper iron mold and the lower iron mold with 6mm of coated sand.

[0044] S3: Core assembly and box closing. Place the cast iron core frame on the lower iron mold, with the open end of the cast iron core frame located at the outer end of the iron mold and connected to the vacuum pump. After fixing it, close the upper iron mold.

[0045] S4: The molten iron is spheroidized. By mass fraction, the composition of the spheroidized molten iron includes: C: 4.0%, Si: 2.4%, Mn: 0.2%, S: 0.005%, P: 0.005%, and the remainder is iron.

[0046] S5: Start the vacuum pump to form a negative pressure cavity of 0.02MPa, then pour the casting, and after cooling and unpacking, obtain the agricultural machinery bridge housing casting.

[0047] The raw materials for the spheroidized molten iron, by weight, include: 48 parts of primary iron, 30 parts of Q235 scrap steel, 12 parts of recycled material, 1 part of ferromanganese, 1 part of ferrosilicon, 1 part of spheroidizing agent, and 1.5 parts of carbon.

[0048] The preparation method of spheroidized molten iron includes the following steps: smelting primary iron, scrap steel, recycled furnace, ferromanganese and carbon to obtain molten iron at a temperature of 1540℃; adding a spheroidizing agent to the molten iron ladle and compacting it, then adding ferrosilicon and compacting it, pressing on Q235 steel sheets, and pouring in the molten iron for spheroidization, with the temperature of the spheroidized molten iron being 1450℃; then removing the slag and covering with an insulating agent.

[0049] The spheroidizing agent is a rare earth magnesium-silicon-iron alloy; wherein, by mass fraction, the rare earth magnesium-silicon-iron alloy contains: Re: 3%, Mg: 7%, Ca: 3%, Si: 30%, Al: 0.2%, Mn: 0.2%, Ti: 0.2%, MgO: 0.2%, with the balance being iron. The particle size of the spheroidizing agent is 10 mm.

[0050] Example 3

[0051] This embodiment relates to a production process for a sand-coated slow-setting type of agricultural machinery axle housing. This production process uses the mold from Embodiment 1 and includes the following steps:

[0052] S1: Prepare a hollow cast iron core, sealed at one end and open at the other end. The tube wall of the cast iron core is equipped with a 15mm diameter slit-type vent plug; the outer wall of the cast iron core is covered with 5mm of coated sand.

[0053] S2: Prepare the cast iron model, using the middle parting, dividing it into an upper iron mold and a lower iron mold, and cover the cavity surface of the upper iron mold and the lower iron mold with 5mm of coated sand.

[0054] S3: Core assembly and box closing. Place the cast iron core frame on the lower iron mold, with the open end of the cast iron core frame located at the outer end of the iron mold and connected to the vacuum pump. After fixing it, close the upper iron mold.

[0055] S4: The molten iron is spheroidized. By mass fraction, the composition of the spheroidized molten iron includes: C: 4.0%, Si: 2.1%, Mn: 0.2%, S: 0.005%, P: 0.005%, and the remainder is iron.

[0056] S5: Start the vacuum pump to form a negative pressure cavity of 0.02MPa, then pour the casting, and after cooling and unpacking, obtain the agricultural machinery bridge housing casting.

[0057] The raw materials for molten iron, by weight, include: 48 parts of primary iron, 30 parts of Q235 scrap steel, 12 parts of recycled material, 1 part of ferromanganese, 1 part of ferrosilicon, 1.5 parts of spheroidizing agent, and 1.5 parts of carbon.

[0058] The preparation method of spheroidized molten iron includes the following steps: smelting primary iron, scrap steel, recycled furnace, ferromanganese and carbon to obtain molten iron at a temperature of 1520℃; adding a spheroidizing agent to the molten iron ladle and compacting it, then adding ferrosilicon and compacting it, pressing on Q235 steel sheets, and pouring in the molten iron for spheroidization, with the temperature of the spheroidized molten iron being 1420℃; then removing slag and covering with an insulating agent.

[0059] The spheroidizing agent is a rare earth magnesium-silicon-iron alloy; wherein, by mass fraction, the rare earth magnesium-silicon-iron alloy contains: Re: 2%, Mg: 6%, Ca: 2%, Si: 30%, Al: 0.2%, Mn: 0.2%, Ti: 0.2%, MgO: 0.2%, with the balance being iron. The particle size of the spheroidizing agent is 15 mm.

[0060] Example 4

[0061] This embodiment relates to a production process for a sand-coated slow-setting type of agricultural machinery axle housing. This production process uses the mold from Embodiment 1 and includes the following steps:

[0062] S1: Prepare a hollow cast iron core, sealed at one end and open at the other end. The tube wall of the cast iron core is equipped with a 14mm diameter slit-type vent plug; the outer wall of the cast iron core is covered with 8mm of coated sand.

[0063] S2: Prepare the cast iron model, using the middle parting, dividing it into an upper iron mold and a lower iron mold, and cover the cavity surface of the upper iron mold and the lower iron mold with 8mm of coated sand.

[0064] S3: Core assembly and box closing. Place the cast iron core frame on the lower iron mold, with the open end of the cast iron core frame located at the outer end of the iron mold and connected to the vacuum pump. After fixing it, close the upper iron mold.

[0065] S4: The molten iron is spheroidized. By mass fraction, the composition of the spheroidized molten iron includes: C: 3.9%, Si: 2.25%, Mn: 0.2%, S: 0.005%, P: 0.005%, and the remainder is iron.

[0066] S5: Start the vacuum pump to form a negative pressure cavity of 0.04MPa, then pour the casting, and after cooling and unpacking, obtain the agricultural machinery bridge housing casting.

[0067] The raw materials for molten iron, by weight, include: 50 parts of primary iron, 35 parts of Q235 scrap steel, 15 parts of recycled material, 1 part of ferromanganese, 2 parts of ferrosilicon, 1.5 parts of spheroidizing agent, and 1.5 parts of carbon.

[0068] The preparation method of spheroidized molten iron includes the following steps: smelting primary iron, scrap steel, recycled furnace, ferromanganese and carbon to obtain molten iron at a temperature of 1560℃; adding a spheroidizing agent to the molten iron ladle and compacting it, then adding ferrosilicon and compacting it, pressing on Q235 steel sheets, and pouring in the molten iron for spheroidization, with the temperature of the spheroidized molten iron being 1460℃; then removing the slag and covering with an insulating agent.

[0069] The spheroidizing agent is a rare earth magnesium-silicon-iron alloy; wherein, by mass fraction, the rare earth magnesium-silicon-iron alloy contains: Re: 2%, Mg: 6%, Ca: 2%, Si: 30%, Al: 0.2%, Mn: 0.2%, Ti: 0.2%, MgO: 0.2%, with the balance being iron. The particle size of the spheroidizing agent is 20 mm.

[0070] Example 5

[0071] This embodiment relates to a production process for a sand-coated slow-setting type of agricultural machinery axle housing. This production process uses the mold from Embodiment 1 and includes the following steps:

[0072] S1: Prepare a hollow cast iron core, sealed at one end and open at the other end. The tube wall of the cast iron core is equipped with a 14mm diameter slit-type vent plug; the outer wall of the cast iron core is covered with 6mm of coated sand.

[0073] S2: Prepare the cast iron model, using the middle parting, dividing it into an upper iron mold and a lower iron mold, and cover the cavity surface of the upper iron mold and the lower iron mold with 6mm of coated sand.

[0074] S3: Core assembly and box closing. Place the cast iron core frame on the lower iron mold, with the open end of the cast iron core frame located at the outer end of the iron mold and connected to the vacuum pump. After fixing it, close the upper iron mold.

[0075] S4: The molten iron is spheroidized. By mass fraction, the composition of the spheroidized molten iron includes: C: 3.92%, Si: 2.23%, Mn: 0.1%, S: 0.002%, P: 0.002%, and the remainder is iron.

[0076] S5: Start the vacuum pump to form a negative pressure cavity of 0.1MPa, then pour the casting, and after cooling and unpacking, obtain the agricultural machinery bridge housing casting.

[0077] The raw materials for molten iron, by weight, include: 50 parts of primary iron, 35 parts of Q235 scrap steel, 15 parts of recycled material, 1 part of ferromanganese, 2 parts of ferrosilicon, 1.5 parts of spheroidizing agent, and 1.5 parts of carbon.

[0078] The preparation method of spheroidized molten iron includes the following steps: smelting primary iron, scrap steel, recycled furnace, ferromanganese and carbon to obtain molten iron at a temperature of 1540℃; adding a spheroidizing agent to the molten iron ladle and compacting it, then adding ferrosilicon and compacting it, pressing on Q235 steel sheets, and pouring in the molten iron for spheroidization, with the temperature of the spheroidized molten iron being 1450℃; then removing the slag and covering with an insulating agent.

[0079] The spheroidizing agent is a rare earth magnesium silicon iron alloy; wherein, by mass fraction, the rare earth magnesium silicon iron alloy contains Re: 2%, Mg: 6%, Ca: 2%, Si: 30%, Al: 0.2%, Mn: 0.2%, Ti: 0.2%, MgO: 0.2%, with the balance being iron.

[0080] Example 6

[0081] Based on Example 2, the main difference is that, by mass fraction, the composition of the spheroidized molten iron includes: C: 3.9%, Si: 2.1%, Mn: 0.2%, S: 0.005%, P: 0.005%, with the remainder being iron. Other steps are similar to those in Example 2.

[0082] Example 7

[0083] Based on Example 2, the main difference is that, by mass fraction, the composition of the spheroidized molten iron includes: C: 4.1%, Si: 2.4%, Mn: 0.2%, S: 0.005%, P: 0.005%, with the remainder being iron. Other steps are similar to those in Example 2.

[0084] Example 8

[0085] Based on Example 2, the main difference is in step S5: starting the vacuum pump to form a negative pressure cavity (0.03 MPa), followed by casting, cooling, and unpacking to obtain the agricultural machinery bridge housing casting. Other steps are similar to those in Example 2.

[0086] Example 9

[0087] Based on Example 2, the main difference is in step S5: starting the vacuum pump to form a negative pressure cavity of 0.06 MPa, followed by casting, cooling, and unpacking to obtain the agricultural machinery bridge housing casting. Other steps are similar to those in Example 2.

[0088] Comparative Example 1

[0089] Based on Example 2, the main difference is that, by mass fraction, the composition of the spheroidized molten iron includes: C: 3.8%, Si: 2.1%, Mn: 0.2%, S: 0.005%, P: 0.005%, with the remainder being iron.

[0090] Comparative Example 2

[0091] Based on Example 2, the main difference is that, by mass fraction, the composition of the spheroidized molten iron includes: C: 4.3%, Si: 2.1%, Mn: 0.2%, S: 0.005%, P: 0.005%, with the remainder being iron.

[0092] Comparative Example 3

[0093] The main difference from Example 6 is that ordinary sand cores are used and no vacuuming is performed.

[0094] Comparative Example 4

[0095] Bridge shells are produced using furan resin self-hardening sand molding.

[0096] Comparative Example 5

[0097] Based on Example 2, the main difference is in S5: starting the vacuum pump to form a negative pressure cavity of 2MPa, then pouring, followed by cooling and unpacking to obtain the agricultural machinery axle housing casting. Other steps are similar to Example 2.

[0098] Test case

[0099] The agricultural machinery axle housings obtained in the examples and comparative examples were subjected to performance tests, as shown in Table 1. Metallographic analysis was performed in accordance with GB / T 9441-2009.

[0100] Wherein, eutectic degree = (mass fraction of C + 1 / 3 mass fraction of Si) ÷ 4.3 × 100%.

[0101] Table 1

[0102]

[0103] Referring to Table 1, the agricultural machinery axle housing produced in this application achieves riserless casting, with a spheroidization grade of 1-3, a graphite size grade of 6-7, and a spheroidization rate >85%, exhibiting high spheroidization grade, graphite size, and spheroidization rate. It possesses a tensile strength of not less than 600 MPa, an elongation of not less than 11%, and a hardness of 180-212 HB, demonstrating excellent mechanical properties. Furthermore, the agricultural machinery axle housing cast in this application is free from graphite floating and casting defects.

[0104] Furthermore, the process yield of the agricultural machinery axle housing produced in this application is greater than 90%, while the process yield of the agricultural machinery axle housing produced by self-hardening sand in Comparative Example 4 is less than 70%.

[0105] In Comparative Example 1, the eutectic ratio was too low, and shrinkage cavities and porosity were present at the window, indicating casting defects.

[0106] In Comparative Example 2, excessive eutectic density, graphite floating, and flowering graphite all lead to poor spheroidization, lower spheroidization and graphite grades, significantly reduced tensile strength and elongation, and higher hardness.

[0107] In Comparative Example 3, when no vacuum was applied to create negative pressure, flowering graphite was observed during the casting process, and shrinkage cavities and porosity were present at the windows.

[0108] In Comparative Example 4, it was difficult to achieve riserless casting when using furan resin self-hardening sand molding to produce bridge shells.

[0109] In Comparative Example 5, excessively high vacuum pressure also caused sand adhesion, resulting in serious casting defects.

[0110] The above description is merely an 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 principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A kind of agricultural machinery axle housing's iron mould sand coating delayed production process, it is characterized in that, The iron mold coated sand retarding type production process comprises the following steps: S1: preparing an internally hollow cast iron core bone, one end of which is sealed and the other end is open, the pipe wall of the cast iron core bone being provided with an exhaust plug; coating the outer wall of the cast iron core bone with a film sand; S2: preparing an iron mold, adopting middle parting, and being divided into an upper iron mold and a lower iron mold, the cavity surfaces of the upper iron mold and the lower iron mold being coated with a film sand; S3: assembling the core and closing the mold, the open end of the cast iron core bone being located at the outer end of the iron mold and being connected with a vacuum device; S4: performing spheroidization treatment on the molten iron, the composition of the molten iron after spheroidization including, by mass fraction: C: 3.9-4.1%, Si: 2.1-2.4%, Mn: 0.2-0.6%, S: <0.02%, P: <0.035%, and the rest being iron; S5: starting the vacuum device to form a negative pressure cavity, and then performing pouring, and sequentially cooling, opening the mold to obtain a riserless agricultural bridge shell casting; The eutectic degree of the molten iron after spheroidization is 1.07-1.14; The negative pressure cavity in step S5 is 0.02-0.10 MPa; The exhaust plug is a slit type exhaust plug with a diameter of 10-20 mm.

2. The sand coated iron mold retarder type production process according to claim 1, characterized in that, In step S1, the outer wall of the cast iron core bone is coated with a film sand, and the thickness of the film sand is 5-8 mm; And / or in step S2, the cavity surfaces of the upper iron mold and the lower iron mold are coated with a film sand, and the thickness of the film sand is 5-8 mm.

3. The sand coated iron mold retarder type production process according to claim 1, characterized in that, By weight fraction, the raw materials of the molten iron after spheroidization include: primary iron 45-50 parts, scrap steel 25-35 parts, recycled material 10-15 parts, manganese iron 1-2 parts, silicon iron 1-2 parts, spheroidizing agent 1-2 parts, and carbon additive 1-2 parts.

4. The sand coated iron mold retarder type production process according to claim 3, characterized in that, The spheroidizing agent is a rare earth magnesium silicon iron alloy; wherein, by mass fraction, Re: 2-4%, Mg: 6-8%, Ca: 2-3.5%, Si: <45%, Al: <1%, Mn: <1%, Ti: <1%, MgO <1%, and the rest being iron; And / or the carbon additive is carbon.

5. The sand coated iron mold retarder type production process according to claim 3, characterized in that, The particle size of the spheroidizing agent is 5-30 mm.

6. The sand coated iron mold retarder type production process according to claim 3, characterized in that, The preparation method of the molten iron after spheroidization comprises the following steps: smelting the primary iron, scrap steel, recycled material, manganese iron, and carbon additive to obtain smelted molten iron; adding the spheroidizing agent in the ladle and tamping, then adding the silicon iron and tamping, and pressing the steel sheet, pouring the smelted molten iron for spheroidization, and then removing the slag to obtain the molten iron after spheroidization, the temperature of the molten iron after spheroidization being 1420-1460°C.

7. The sand coated iron mold retarder type production process according to claim 1, characterized in that, In step S5, the pouring time is not higher than 10 min.

Images