Process for producing exhaust manifold of cast steel material by using sand mold

Abstract

The application discloses a process for producing an exhaust manifold of cast steel material by using sand moulds, and the cast mould used in the process comprises a corresponding upper mould plate and a lower mould plate; the upper mould plate is provided with a pouring system, an exhaust needle, an exhaust fin, a core and a filter, and the pouring system comprises a sprue cup, a straight sprue, a cross sprue, an inner sprue and a riser; the lower mould plate is provided with a riser seat and a straight sprue seat; the straight sprue is located at the middle position of the upper mould plate; the cross sprue is communicated with the straight sprue, and the filter is located between the cross sprue and the straight sprue; the inner sprue is communicated with the cross sprue; the riser is located on both sides of the inner sprue and is communicated; and the exhaust fin is located at the core head position of the core and is connected with the exhaust needle. The process solves the cold shut problem caused by poor flowability of the molten steel, improves the quality of the castings, and reduces the casting cost.

Description

Technical Field

[0001] This invention belongs to the field of exhaust manifold casting technology, and particularly relates to the process of producing cast steel exhaust manifolds using wet-molded sand. Background Technology

[0002] China has implemented the National VI emission standard, which reduces gasoline pollutants and makes exhaust emissions more environmentally friendly. However, lower emission standards mean the need for smaller displacement engines or more advanced engine technology (more efficient combustion technology). Simultaneously, the exhaust system operates at higher temperatures, placing more stringent demands on its temperature resistance. Previous materials such as silicon-molybdenum and high-nickel alloys are no longer adequate for high-temperature emissions. Currently, major OEMs are increasing their efforts in developing cast steel exhaust manifolds.

[0003] Patent document CN108655348B discloses a casting process for thick-walled cast steel exhaust manifolds. The gating system in this process includes a sprue and a runner, with the sprue and runner vertically connected. A filter is installed in the middle of the runner. The risers include a large-face riser, a triangular flange riser, a heat-insulating riser, and a heat-insulating riser. The heat-insulating riser is located at the end of the runner. Figure 1 The specific location and state of the gating system were disclosed. Although it features a compact overall layout, it cannot guarantee a stable flow of molten steel. In actual casting production applications, during pouring, the convergence of the flow heads in the mold cavity can cause cold shuts in the casting, hindering venting and leading to localized gas blockage, flame scorching, and peeling, resulting in low yield and high manufacturing costs.

[0004] Patent document CN108515149B discloses a method for casting thin-walled heat-resistant steel exhaust manifolds, comprising the following steps: core making, molding, melting, pouring, and sand removal. Through the rational design of the molten iron flow rate in the gating system and the cross-sectional ratio of each unit, as well as strict control of the thickness of the iron mold's sand coating layer, the cavity exhaust system, the pouring temperature, and the sand removal and unpacking time, exhaust manifolds of the required thickness are obtained. During the casting process, on the one hand, the iron mold sand coating process results in high casting costs; on the other hand, the yield rate of castings requires consideration not only of the dimensions and temperature of the gating system but also of the rational design of the entire gating system. Summary of the Invention

[0005] To overcome the above-mentioned defects, the purpose of this invention is to provide a process for producing cast steel exhaust manifolds using wet molding sand, which solves the cold shut problem caused by poor fluidity of molten steel, improves casting quality, and reduces casting costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A process for producing cast steel venting manifolds using wet-molded sand, wherein the casting mold used in the process includes a corresponding upper mold plate and a lower mold plate; the upper mold plate is provided with a gating system, venting pins, venting vanes, a core, and a filter; the gating system includes a pouring cup, a sprue, a runner, an ingate, and a riser; the lower mold plate is provided with a riser holder and a sprue holder; the sprue is located in the middle of the upper mold plate; the runner is connected to the sprue; the filter is located between the runner and the sprue; the ingate is connected to the runner; the riser is located on both sides of the ingate and is connected to it; the venting vanes are located at the core head of the core and are connected to the venting pins;

[0008] The process includes the following steps:

[0009] S1. Place the upper mold plate and the lower mold plate into the worktable of the molding machine respectively. First, turn the upper mold plate to the working position, place the sand box on the upper mold plate, and let the molding machine fill the sand box with moist sand and compact it. Then demold to form a cavity. After being flipped by the box flipping machine, it is placed on the trolley and pushed onto a track.

[0010] S2. Next, rotate the lower mold plate to the working position, place the sand box on the lower mold plate, fill the sand box with moist sand and compact it by the molding machine, then demold to form a cavity, flip it by the box flipping machine and put it on the trolley and push it to another track, repeat the same action, the upper and lower sand boxes are continuously pushed forward.

[0011] S3. After arriving at the core lowering station, the worker puts the sand core and filter into the lower mold plate. Then, the upper mold plate is flipped by the box flipping machine and closed onto the lower mold plate, and they fit tightly together.

[0012] S4. After arriving at the casting station, pour the molten iron from the pouring cup of the upper mold plate, enter the sprue socket along the sprue, and then enter the riser of the lower mold plate along the horizontal sprue of the lower mold plate, and enter the cavity that forms the casting through the riser neck.

[0013] Optionally, the sprue, the runner, and the ingate all have circular cross-sections; the ratio of the cross-sectional areas of the sprue, the runner, and the ingate is S. 直 :S 横 :S 内 = 1:1.2:1.5.

[0014] Optionally, a slag collection zone is provided above the parting surface at a distance of 10 mm above the horizontal runner; the slag collection zone is elongated.

[0015] Optionally, the wet compressive strength of the wet sand is 0.13–0.18 MPa; the compaction rate of the wet sand is 30–40%; the moisture content of the wet sand is 2.8–3.4%; the air permeability of the wet sand is 120–170; the splitting strength of the wet sand is 35–45 kPa; the mud content of the wet sand is 12–15%; the effective bentonite content of the wet sand is 7–10%; and the hardness of the wet sand is ≥90.

[0016] Optionally, the thickness of the exhaust plate is 0.4 mm; the size of the exhaust needle is φ25×180 mm.

[0017] Optionally, a molding sand curing agent can be sprayed into the mold cavity, and the molding sand can be poured after the curing agent dries.

[0018] With the continuous improvement of automotive technology, the heat resistance temperature of automotive exhaust manifolds is increasing, leading to a significant increase in demand for cast steel exhaust manifolds. Compared to cast steel volutes, cast steel exhaust manifolds have a more dispersed structure and more molten iron flow heads, resulting in a longer molten iron flow path during the filling process, greater temperature loss, and a much higher proportion of cold shuts compared to similar volute products. Thick-walled parts, due to their large weight, thick walls, and high viscosity and poor fluidity of the molten steel, require longer filling times, have a greater tendency for shrinkage porosity, making casting extremely difficult and resulting in a very low yield rate.

[0019] Due to the inherent properties of heat-resistant steel, numerous defects such as sand adhesion, cold shuts, slag inclusions, and porosity occur. Common casting processes include negative pressure shell mold casting or iron mold with sand coating, where a coated sand shell mold is used to form the casting, and the shell mold is covered with moist molding sand. While this process improves casting defects somewhat, the casting cost remains high, and the yield is not high. Currently, the shell mold or iron mold with sand coating process is used. Both involve covering the casting with a sand core made of coated sand. Both processes require additional sand cores; the difference lies in the sand core being covered with moist sand in the shell mold process and an iron mold in the iron mold with sand coating process.

[0020] The positive and beneficial effects of this invention are as follows:

[0021] 1) This process eliminates the need for external sand cores in castings, resulting in cost savings, high efficiency, and the possibility of using wet sand casting for heat-resistant steel, thus ensuring the appearance quality of the castings.

[0022] 2) It enables the gating system to fill quickly, avoiding air entrapment or oxidation of molten steel.

[0023] 3) Solve the cold shut problem caused by poor fluidity of molten steel. Ensure smooth mold filling during the pouring process, smooth gas discharge during pouring, and uniform cooling of molten steel within the mold.

[0024] 4) Solve the problem of sand adhering to molten steel at high temperatures. The large heat dissipation area of ​​the damp sand mold reduces the chance of sand adhering. At the same time, a molding sand curing agent is used in the damp sand mold cavity. After the molding sand curing agent dries, the steel is poured, forming a heat-resistant film on the surface of the cavity.

[0025] 5) Solve problems such as slag inclusions. Slag is blocked by filters and gating systems. At the same time, overflow feed risers are set at the top of the casting to allow the slag in the mold to overflow out of the casting, thereby reducing and eliminating slag inclusions.

[0026] 6) Solve the porosity problem. Add venting pinholes to the sand mold to reduce air trapping. Attached Figure Description

[0027] Figure 1 This is a top view of the upper mold plate structure of the process for producing cast steel exhaust manifolds using wet molding sand, as provided in Embodiment 1 of the present invention.

[0028] Figure 2 This is a top view of the lower mold plate structure of the process for producing cast steel exhaust manifolds using wet molding sand, as provided in Embodiment 1 of the present invention.

[0029] Figure 3 This is a schematic diagram of the upper mold plate axial side structure of the process for producing cast steel exhaust manifolds using wet molding sand, as provided in Embodiment 1 of the present invention.

[0030] Figure 4 This is a schematic diagram of the lower mold plate axial side structure of the process for producing cast steel exhaust manifolds using wet molding sand according to Embodiment 1 of the present invention;

[0031] Figure 5 This is a schematic diagram of the front structure of a casting made by producing a cast steel exhaust manifold using a process of producing cast steel using wet molding sand, as provided in Embodiment 1 of the present invention.

[0032] Figure 6 This is a schematic diagram of the back structure of a casting made by producing an exhaust manifold of cast steel using a process of producing cast steel using wet molding sand, as provided in Embodiment 1 of the present invention.

[0033] 1. Venting needle; 2. Venting plate; 3. Core; 4. Riser; 5. Streamline; 6. Filter; 7. Sprue; 8. Ingate; 9. Riser seat; 10. Slag collection area; 11. Sprue seat; 12. Pour cup. Detailed Implementation

[0034] The present invention will be further described below with reference to some specific embodiments.

[0035] Example 1

[0036] like Figures 1 to 6As shown, a process for producing cast steel venting manifolds using wet-molded sand is described. The casting mold used in this process includes an upper mold plate and a lower mold plate that correspond to each other. The upper mold plate is equipped with a gating system, venting pins 1, venting vanes 2, a core 3, and a filter 6. The gating system includes a pouring cup 12, a sprue 7, a runner 5, an ingate 8, and a riser 4. The lower mold plate is equipped with a riser holder 9 and a sprue holder 11. The sprue 7 is located in the middle of the upper mold plate. The runner 5 is connected to the sprue 7, and the filter 6 is located between the runner 5 and the sprue 7. The ingate 8 is connected to the runner 5. The riser 4 is located on both sides of the ingate 8 and is connected to it. The venting vanes 2 are located at the core head of the core 3 and are connected to the venting pins 1.

[0037] The process includes the following steps:

[0038] S1. Place the upper mold plate and the lower mold plate into the worktable of the molding machine respectively. First, turn the upper mold plate to the working position, place the sand box on the upper mold plate, and let the molding machine fill the sand box with moist sand and compact it. Then demold to form a cavity. After being flipped by the box flipping machine, it is placed on the trolley and pushed onto a track.

[0039] S2. Next, rotate the lower mold plate to the working position, place the sand box on the lower mold plate, fill the sand box with moist sand and compact it by the molding machine, then demold to form a cavity, flip it by the box flipping machine and put it on the trolley and push it to another track, repeat the same action, the upper and lower sand boxes are continuously pushed forward.

[0040] S3. After arriving at the core lowering station, the worker puts the sand core and filter 6 into the lower mold plate. Then, the upper mold plate is flipped by the box flipping machine and closed onto the lower mold plate, and they fit tightly together.

[0041] S4. After arriving at the casting station, pour molten iron from the pouring cup 12 of the upper mold plate (fill the molten iron to be level with the top of the pouring cup 12, and the pouring time is generally 8-10 seconds), enter the sprue seat 11 along the sprue 7, and then enter the riser 4 of the lower mold plate along the horizontal sprue 5 of the lower mold plate. It then enters the cavity that forms the casting through the ingate 8 and the neck of the riser 4.

[0042] The functions of the pouring cup 12 are: first, to receive the molten metal poured from the ladle and guide the liquid metal into the sprue; second, to prevent the molten metal from splashing and overflowing, facilitating pouring; third, to reduce the impact of the liquid flow on the mold cavity; and fourth, to separate slag and air bubbles, preventing them from entering the mold cavity.

[0043] This invention eliminates the need for an external sand core in the casting, resulting in cost savings and high efficiency. It solves the cold shut problem caused by poor molten steel fluidity. It ensures stable mold filling during pouring, allowing for smooth gas release and uniform cooling of the molten steel within the mold. It resolves the issue of sand adhering to the molten steel at high temperatures, as the large heat dissipation area of ​​the damp sand mold reduces the likelihood of sand adhesion. It addresses slag inclusions by using a filter 6 and the gating system to prevent slag buildup, and by adding a riser 4 at the top of the casting for overflow feeding, allowing slag to overflow from the mold and reducing or eliminating slag inclusions. Finally, it addresses porosity by adding a venting pin hole in the sand mold to reduce air trapping.

[0044] Due to the poor fluidity and susceptibility of cast steel to air entrapment and slag inclusions, a bottom-pouring process is adopted, where the ingate is placed at a lower position on the casting. To ensure smooth filling, an open gating system is used, with the sprue 7, sprue 5, and ingate 8 all having circular cross-sections; the ratio of the cross-sectional area of ​​the sprue 7, sprue 5, and ingate 8 is S. 直 :S 横 :S 内 =1:1.2:1.5, which allows the gating system to fill quickly and avoids air entrapment or oxidation of molten steel.

[0045] The ingate 8 and the runner 5 are placed in the lower mold. At the same time, a slag collection area 10 is set above the runner 5, 10mm above the parting surface. The slag collection area 10 is elongated and the filtered residue will be collected in the slag collection area 10. A molding sand curing agent is sprayed into the damp sand cavity to form a heat-resistant film on the cavity surface. The molding sand is poured after the molding sand curing agent dries.

[0046] Specifically, the process parameters for the wet sand are shown in Table 1. The wet compressive strength of the wet sand is 0.13–0.18 MPa; the compaction rate of the wet sand is 30–40%; the moisture content of the wet sand is 2.8–3.4%; the air permeability of the wet sand is 120–170; the splitting strength of the wet sand is 35–45 kPa; the mud content of the wet sand is 12–15%; the effective bentonite content of the wet sand is 7–10%; and the hardness of the wet sand is ≥90.

[0047] Table 1

[0048]

[0049] Further, refer to Figure 5 and Figure 6Both the upper and lower mold plates are made of TL047 material. The mold plates are identical to the formed casting, indicating the absence of a shell core. The upper and lower mold plates are symmetrically distributed on both sides around the pouring cup 12. A venting pin 1 is placed at each of the four corners of each side. Near the middle of the horizontal runner 5, a venting pin 1 and two risers 4 are placed on each side, symmetrically distributed around the horizontal runner 5. The thickness of the venting plate 2 is 0.4 mm; the dimensions of the venting pin 1 are φ25×180 mm. This design can further improve the quality of the casting.

[0050] Verification through actual casting production shows that the process of this invention can guarantee the appearance quality of the castings. Internal dissection, X-ray flaw detection, and machining verification have confirmed that the produced castings are free from defects such as shrinkage porosity and blowholes. Compared with previous processes, this invention saves on upper and lower shell molds, resulting in significant economic benefits.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A process for producing cast steel exhaust manifolds using wet-molded sand, characterized in that, The casting mold used in the process includes a corresponding upper mold plate and a lower mold plate; the upper mold plate is provided with a gating system, venting pins, venting vanes, a core, and a filter; the gating system includes a pouring cup, a sprue, a runner, an ingate, and a riser; the lower mold plate is provided with a riser holder and a sprue holder; the sprue is located in the middle of the upper mold plate; the runner is connected to the sprue; the filter is located between the runner and the sprue; the ingate is connected to the runner; the riser is located on both sides of the ingate and is connected; the venting vanes are located at the core head of the core and are connected to the venting pins; the thickness of the venting vanes is 0.4 mm; the size of the venting pins is φ25×180 mm; a long strip-shaped slag collection area 10 mm above the parting line is provided above the runner; The process includes the following steps: S1. Place the upper mold plate and the lower mold plate into the worktable of the molding machine respectively. First, turn the upper mold plate to the working position, place the sand box on the upper mold plate, and let the molding machine fill the sand box with moist sand and compact it. Then demold the mold plate directly to form the cavity from the moist sand. After being flipped by the box flipping machine, it is placed on the trolley and pushed onto a track. S2. Next, rotate the lower mold plate to the working position, place the sand box on the lower mold plate, and fill the sand box with moist sand and compact it by the molding machine. Then demold the mold, and the moist sand directly forms the cavity. After being flipped by the box flipping machine, it is placed on the trolley and pushed to another track. Repeat the same action, and the upper and lower sand boxes are continuously pushed forward. S3. After arriving at the core lowering station, the worker puts the sand core and filter into the lower mold plate. Then, the upper mold plate is flipped by the box flipping machine and closed onto the lower mold plate, and they fit tightly together. S4. After arriving at the casting station, pour the molten iron from the pouring cup of the upper mold plate, enter the sprue seat along the sprue, and then enter the riser of the lower mold plate along the horizontal sprue of the lower mold plate, and enter the cavity that forms the casting through the riser neck. Before pouring, a molding sand curing agent is sprayed into the mold cavity to form a heat-resistant film on the surface of the mold cavity. Pouring is then carried out after the molding sand curing agent has dried.

2. The process for producing cast steel exhaust manifolds using wet-molded sand as described in claim 1, characterized in that, The sprue, the runner, and the ingate all have circular cross-sections; the ratio of the cross-sectional area of ​​the sprue, the runner, and the ingate is S. 直 :S 横 :S 内 = 1:1.2:1.

5.

3. The process for producing cast steel exhaust manifolds using wet-molded sand as described in claim 1, characterized in that, The wet compressive strength of the wet sand is 0.13-0.18 MPa; the compaction rate of the wet sand is 30-40%; the moisture content of the wet sand is 2.8-3.4%; the air permeability of the wet sand is 120-170; the splitting performance of the wet sand is 35-45 kPa; the mud content of the wet sand is 12-15%; the effective bentonite content of the wet sand is 7-10%; and the hardness of the wet sand is ≥90.

Images