Nozzle ring pouring system and investment casting grain refining process

Abstract

The invention discloses a nozzle ring pouring system and an investment casting grain refinement process, the pouring system comprises a pouring head, a first cross gate is connected below the pouring head, the middle and two ends of the bottom of the first cross gate are connected with vertical gates, and the bottom of the middle vertical gate is communicated with the bottoms of the vertical gates at the two ends through second cross gates; a plurality of arc-shaped grooves are formed in the front side face and the rear side face of the vertical pouring gate at equal intervals, the surfaces of the planes of the upper side and the lower side of each arc-shaped groove are used for welding wax pieces, the bottom end of the middle vertical pouring gate is connected with a rotating base, and the investment casting grain refining technology adopting the pouring system comprises the steps of tree assembling, shell manufacturing, smelting pouring and the like. According to the method, the distance between the adjacent wax pieces is increased in the tree assembling process, the adjacent wax pieces are connected through the supporting columns to reduce the thickness of the mold shell, the cast piece rotates under the blowing environment after pouring, the heat dissipation speed of the cast piece is increased, meanwhile, rare metal is added by pouring molten steel, the grain refining effect is achieved, and therefore the nozzle ring cast piece with the grain size controlled to be ASTM 4-6 is obtained.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology for nozzle rings, specifically to a nozzle ring gating system and an investment casting process for refining grain size. Background Technology

[0002] Nozzle ring products are generally automotive parts, manufactured at high temperatures. Conventional investment casting processes typically produce castings with relatively coarse grains (grain size can range from level 3 to level 4). While finer grains generally result in better mechanical properties, this product series operates at high temperatures. When casting temperatures exceed 800°C, excessive grain refinement must be prevented. Furthermore, a grain size greater than level 7 (<22μm) accelerates high-temperature grain boundary slip, reducing creep life.

[0003] In view of the above, this application proposes a nozzle ring gating system and a grain refinement process for investment casting of nozzle rings using the above gating system to solve the aforementioned technical problems. This application addresses the issue that pouring temperature and rare metals affect the grain size of the product. By accelerating the heat dissipation and cooling of the mold shell formed by the gating system and adding suitable rare metals, the grain size is refined, producing nozzle ring castings with a grain size controlled within ASTM 4-6. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a nozzle ring gating system and a grain refinement process for investment casting.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A nozzle ring casting system includes a pouring head, a first horizontal sprue connected below the pouring head, a first vertical sprue connected to the bottom of the middle of the first horizontal sprue, and second vertical sprues symmetrically connected to the bottom of both ends of the first horizontal sprue. The two second vertical sprues are arranged parallel to the first vertical sprue. The bottom ends of the first vertical sprue are respectively connected to the bottom ends of the two second vertical sprues through the second horizontal sprues. The front and rear sides of the first vertical sprue and the two second vertical sprues are provided with a plurality of arc-shaped grooves at equal intervals. The surfaces of the upper and lower planes of the arc-shaped grooves are used for welding wax parts, and two adjacent wax parts are connected by a support column. The bottom ends of the first vertical sprue and the two second vertical sprues are all sealed, and the bottom end of the first vertical sprue is connected to a rotating seat for mounting on a free-rotating hook.

[0006] In a preferred embodiment of the present invention, the top of both ends of the first horizontal runner are symmetrically connected with venting channels, and the first horizontal runner is connected to the pouring head through the venting channels.

[0007] In a preferred embodiment of the present invention, the pouring head, the first horizontal runner, the first vertical runner, the second horizontal runner, the second vertical runner, the venting channel, and the rotating seat are an integrated structure.

[0008] The present invention also discloses a process for refining grains using the nozzle ring investment casting of the above-mentioned gating system, comprising the following steps: Step 1: Wax Design: Design wax parts and sprue gates for connecting the wax parts to the gating system according to the product shape and size; Step 2: Tree Assembly: Weld the wax parts equidistantly to the front and rear sides of the first and two second sprues, with adjacent wax parts connected by support columns to form a tree assembly; Step 3: Shell Formation: Apply paint, sprinkle sand, and allow to dry and harden on the surface of the tree assembly. Repeat this process to form a mold shell with 3.5 layers of shell material on the surface of the tree assembly. The 0.5 layer of shell material is formed by the final sealing slurry. The first layer of slurry uses zirconium slurry, and the sand is made of magnetic fluorite. The second, third, and sealing slurries all use mullite slurry, and the sand for the second and third layers is made of mullite; Step 4: Steam dewaxing: The mold shell coated with the mold shell material is dewaxed by steam; Step 5, Firing: The dewaxed mold shell is placed in a firing furnace for firing; Step 6, Melting and casting: The steel is melted into molten steel using an induction furnace, and the molten steel is adjusted to a material grade of 1.4848. Then, 0.02-0.04% niobium (Nb) and 0.01-0.03% rare earth (RE) are added. After adding, the molten steel is added into the mold shell. After casting, the mold shell containing molten steel is hung on a free-rotating hook and rotated around the center of the first vertical runner in a blowing environment to accelerate the heat dissipation of the casting; Step 7, Post-processing: The casting with risers is separated from the mold shell by cutting. After separation, the risers of the casting are ground, sand is removed, and the casting is inspected to obtain a qualified casting.

[0009] In a preferred embodiment of the present invention, the length of the sprue of the wax part in step 1 is 7~9mm, and the width of the sprue of the wax part is 4 / 10~5 / 10 of the outer diameter of the wax part.

[0010] In a preferred embodiment of the present invention, the distance between two adjacent wax pieces in step 2 is 30-40 mm, and the diameter of the support column is 6 mm.

[0011] In a preferred embodiment of the present invention, in step 3, the viscosity of the first layer of zirconium slurry is 45-50S, the viscosity of the second layer of mullite slurry is 25-30S, the viscosity of the third layer of mullite slurry is 14-16S, and the viscosity of the mullite slurry used for sealing is 10-12S; the first layer of magnetic fluorite is 80-120 mesh, the second layer of mullite is 30-60 mesh, and the third layer of mullite is 16-30 mesh; the drying time of the first layer of shell material is 8-12 min, and the drying time of the second and third layers and the shell material used for sealing is not less than 8 min.

[0012] In a preferred embodiment of the present invention, the dewaxing temperature in step 4 is 150°C and the dewaxing time is 5-10 minutes.

[0013] In a preferred embodiment of the present invention, the roasting temperature in step 5 is 950-1150°C and the holding time is 45 min.

[0014] In a preferred embodiment of the present invention, in step 6, the rotation speed of the mold shell containing molten steel is 20~40 rpm, the distance of the air source in the blowing environment is 3~5 m, and the air source speed is 3~5 m / s.

[0015] In a preferred embodiment of the invention, the qualified grain size of the casting in step 7 is controlled to be ASTM 4-6.

[0016] Compared with existing technologies, the present invention has the following advantages: The present invention uses three vertical sprues in the casting system, each with several equally spaced arc-shaped grooves on its front and rear sides. Wax pieces are welded to the upper and lower surfaces of these arc-shaped grooves, with a distance of 30-40mm between adjacent wax pieces. Compared to conventional processes (distance 10-20mm), this provides sufficient ventilation and better heat dissipation after casting. Adjacent wax pieces are connected by support columns, reducing the number of mold layers to 3.5 during the shell-making process. The mold thickness is controlled at 3-5mm, compared to conventional processes (5.5 layers, 5-7mm thickness). This reduces the number of layers by two and the mold thickness by 2mm, accelerating heat dissipation and cooling. Simultaneously, the intermediate... A rotating seat is added to the bottom of the first vertical runner. After pouring, the casting rotates on a free-rotating hook mounted on the rotating seat under airflow. The airflow accelerates the rapid heat dissipation of the casting, and the casting cools to a stable state before the grains grow, thus refining the grains. In addition, after the steel is melted into molten steel and adjusted to a material of 1.4848, 0.02-0.04% niobium (Nb) and 0.01-0.03% rare earth (RE) are added. During the solidification process of niobium (Nb), the density of ferrite nucleation points is increased by 30-50%, which also refines the grains. The heterogeneous nucleation and proliferation of rare earth (RE) grains disrupts the growth of the original grains, thus refining the grains. Therefore, by refining the grains, a medium-grained nozzle ring casting with a grain size controlled at ASTM 4-6 is produced, instead of the coarse-grained nozzle ring casting produced by conventional processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the wax component structure of the present invention.

[0018] Figure 2 This is a schematic diagram of the nozzle ring casting system of the present invention.

[0019] Figure 3 This is a tree diagram illustrating the grain refinement process in nozzle ring investment casting according to the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1. First horizontal runner; 2. First vertical runner; 3. Second vertical runner; 4. Second horizontal runner; 5. Sprue; 6. Arc-shaped groove; 7. Rotary seat; 8. Vent channel; 9. Wax part; 901. Wax part sprue; 10. Support column. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Example 1 like Figure 2 and Figure 3 As shown, this embodiment provides a nozzle ring casting system, including a sprue 5. A first horizontal sprue 1 is connected below the sprue 5. A first vertical sprue 2 is connected to the bottom middle of the first horizontal sprue 1. Second vertical sprues 3 are symmetrically connected to the bottom ends of the first horizontal sprue 1. The two second vertical sprues 3 are arranged parallel to the first vertical sprue 2. The bottom ends of the first vertical sprue 2 are connected to the bottom ends of the two second vertical sprues 3 through the second horizontal sprue 4. Several arc-shaped grooves 6 are provided at equal intervals on the front and rear sides of the first vertical sprue 2 and the two second vertical sprues 3, which helps to dissipate heat after casting, i.e., accelerates the casting process. The surfaces of the upper and lower planes of the arc-shaped groove 6 are used for welding wax parts 9, so that there are gaps between the castings after pouring, which has a good ventilation and heat dissipation effect. The two adjacent wax parts 9 are connected by the support column 10, which reduces the number of mold shell layers in the shell making process. The bottom ends of the first vertical sprue 2 and the two second vertical sprues 3 are all sealed. The bottom end of the first vertical sprue 2 is connected to a rotating seat 7 for mounting on the free rotation hook, so that after pouring, the mold shell containing molten steel can be hung on the free rotation hook and rotated around the center of the first vertical sprue 2, so that the mold shell is cooled evenly in the blowing environment after pouring.

[0023] In this embodiment, as Figure 2 As shown, the top of both ends of the first horizontal runner 1 are symmetrically connected with venting channels 8. The first horizontal runner 1 is connected to the gating head 5 through the venting channels 8. The venting of the venting channels 8 promotes the diffusion of alloying elements, making the chemical composition inside the casting more uniform, thereby optimizing the crystal structure and improving mechanical properties such as strength and toughness. At the same time, through reasonable layout, it helps to control the temperature gradient during the solidification of the casting and reduce the risk of deformation or hot cracking.

[0024] In this embodiment, as Figure 2 As shown, the gating head 5, the first horizontal gating 1, the first vertical gating 2, the second horizontal gating 4, the second vertical gating 3, the venting channel 8, and the rotating seat 7 are integrated into a single structure, which effectively controls the flow and solidification process of the molten metal, improves the quality of the casting, and can adapt to the needs of castings with complex shapes. By adjusting the layout and position of the gating system, the temperature field distribution can be optimized.

[0025] Example 2 A grain refinement process for investment casting of nozzle rings, using the gating system of Example 1, includes the following steps: Step 1: Design the wax part 9 and the wax sprue 901 for connecting the wax part 9 to the casting system, according to the shape and size of the product. The length of the wax sprue 901 is 7~9mm, and the width of the wax sprue 901 is 4 / 10~5 / 10 of the outer diameter of the wax part 9. In this embodiment, the diameter of the wax part 9 is 70mm, and the width of the wax sprue is 30mm. Figure 1 As shown; Step 2, Tree Assembly: Wax pieces 9 are welded at equal intervals to the front and rear sides of the first vertical sprue 3 and the two second vertical sprues 2. The distance between two adjacent wax pieces 9 is 30-40mm, and adjacent wax pieces 9 are connected by support columns 10 with a diameter of 6mm, forming a tree assembly. Figure 3 As shown; Step 3, Shell Making: Apply coating to the surface of the tree group, sprinkle sand, and dry and harden. Repeat this process to form a mold shell with 3.5 layers of shell material on the surface of the tree group. The 0.5 layer of shell material is formed by the final sealing slurry. The first layer of slurry uses zirconium slurry and magnetic fluorite sand is used for sprinkling sand. The second and third layers and the sealing slurry all use mullite slurry. The second and third layers of sand are both sprinkled with mullite sand. Step 4, Steam dewaxing: Dewax the mold shell coated with shell material using steam at a temperature of 150℃ for 5-10 minutes. Step 5, Firing: Place the dewaxed mold shell into a firing oven and fire it at a temperature of 950-1150℃ for 45 minutes. Step 6, Melting and Casting: Use an induction furnace to melt the steel into molten steel, and adjust the molten steel to a material grade of 1.4848. Then add 0.02-0.04% niobium (Nb) and 0.01-0.03% rare earth (RE). After adding, pour the molten steel into the mold shell. After casting, hang the mold shell containing the molten steel on a free-rotating hook and rotate it around the center of the first vertical runner in a blowing environment. The rotation speed is 20-40 rpm to accelerate the heat dissipation of the casting. Step 7, Post-processing: Separate the casting with riser from the mold shell by cutting. After separation, grind the riser on the casting, clean the sand, and inspect the casting to obtain a qualified casting.

[0026] In this embodiment, the 3.5-layer shell material of the mold shell in step 3, its characteristics, and its drying time are shown in the table below.

[0027]

[0028] In this embodiment, the air source for the blowing environment in step 6 is a fan located 3-5m away from the mold shell, and the fan speed is 3-5m / s.

[0029] In this embodiment, the qualified casting grain size in step 7 is controlled within ASTM 4-6, that is, the qualified casting grain is medium grain with a grain size of 70~32μm. The corresponding grain size is shown in the table below.

[0030]

[0031] In this embodiment, the distance between two adjacent wax parts on the casting system is maintained at 30-40mm. Compared with the conventional process (distance of 10-20mm), there is sufficient gap for ventilation after casting, improving heat dissipation. Adjacent wax parts are connected by support columns, reducing the number of mold layers to 3.5 layers during shell making, with a mold thickness controlled at 3-5mm. Compared with the conventional process (5.5 layers, mold thickness of 5-7mm), this reduces the number of layers by two and the mold thickness by 2mm. The thinner thickness accelerates heat dissipation and cooling. Furthermore, after casting, the wax parts are mounted on a rotating seat and mounted on a free-rotating hook for blowing. Rotation in windy conditions accelerates heat dissipation from the casting, allowing it to cool to a stable state before the grains grow, thus refining the grain size. Furthermore, by adding 0.02-0.04% niobium (Nb) and 0.01-0.03% rare earth elements (RE) to the 1.4848 steel used for casting, niobium (Nb) promotes a 30-50% increase in ferrite nucleation point density during solidification, refining the grain size. Rare earth elements (RE) promote heterogeneous nucleation and grain proliferation, disrupting the original grain growth and further refining the grain size. Therefore, by refining the grain size, the nozzle ring casting is controlled to ASTM 4-6, resulting in a medium-grained design, unlike the coarse-grained nozzle ring castings produced by conventional processes.

[0032] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nozzle ring gating system, comprising a gating head (5), characterized in that, The first horizontal sprue (1) is connected below the sprue (5). The first vertical sprue (2) is connected to the bottom of the middle of the first horizontal sprue (1). The bottom of the two ends of the first horizontal sprue (1) is symmetrically connected to the second vertical sprue (3). The two second vertical sprues (3) are arranged parallel to the first vertical sprue (2). The bottom end of the first vertical sprue (2) is connected to the bottom end of the two second vertical sprues (3) through the second horizontal sprue (4). The front and rear sides of the first vertical sprue (2) and the two second vertical sprues (3) are provided with several arc-shaped grooves (6) at equal distances. The surfaces of the upper and lower planes of the arc-shaped grooves (6) are used for welding wax pieces (9). The two adjacent wax pieces (9) are connected by a support column (10). The bottom ends of the first vertical sprue (2) and the two second vertical sprues (3) are sealed. The bottom end of the first vertical sprue (2) is connected to a rotating seat (7) for mounting on a free-rotating hook.

2. The nozzle ring casting system according to claim 1, characterized in that, The first horizontal runner (1) has symmetrical exhaust channels (8) at both ends and top. The first horizontal runner (1) is connected to the pouring head (5) through the exhaust channels (8). The pouring head (5), the first horizontal runner (1), the first vertical runner (2), the second horizontal runner (4), the second vertical runner (3), the exhaust channels (8) and the rotating seat (7) are an integrated structure.

3. A process for refining grain size in investment casting using a nozzle ring gating system as described in claim 1 or 2, characterized in that: Includes the following steps: Step 1, Wax Design: Design wax parts (9) and wax sprues (901) for connecting wax parts (9) with the gating system according to the product shape and size; Step 2, Tree Assembly: Weld wax parts (9) at equal intervals to the front and rear sides of the first vertical gating (2) and two second vertical gatings (3), and connect adjacent wax parts (9) with support columns (10) to form a tree assembly; Step 3, Shell Making: Apply paint to the surface of the tree assembly, sprinkle sand, and dry and harden. Repeat this process to form a mold shell with 3.5 layers of shell material on the surface of the tree assembly, of which 0.5 layers of shell material are formed by the final sealing slurry. The first layer of slurry uses zirconium slurry, and the sand is magnetic fluorite. The second, third, and sealing slurries all use mullite slurry. Mullite sand was used for sanding; Step 4, Steam dewaxing: Steam dewaxing was performed on the mold shell coated with the shell material; Step 5, Firing: The dewaxed mold shell was placed in a firing furnace for firing; Step 6, Melting and casting: The steel was melted into molten steel using an induction furnace, and the molten steel was adjusted to material 1.4848. Then 0.02-0.04% niobium Nb and 0.01-0.03% rare earth RE were added. After adding, the molten steel was added into the mold shell. After casting, the mold shell containing molten steel was hung on a free-rotating hook and rotated around the center of the first vertical runner (2) in a blowing environment to accelerate the heat dissipation of the casting; Step 7, Post-processing: The casting with riser was separated from the mold shell by cutting. After separation, the riser of the casting was polished, the sand was cleaned, and the casting was tested to obtain a qualified casting.

4. The grain refinement process for nozzle ring investment casting according to claim 3, characterized in that, In step 1, the length of the wax part sprue (901) is 7~9mm, and the width of the wax part sprue (901) is 4 / 10~5 / 10 of the outer diameter of the wax part (9).

5. The nozzle ring investment casting grain refinement process according to claim 3, characterized in that, In step 2, the distance between two adjacent wax pieces (9) is 30~40mm, and the diameter of the support column (10) is 6mm.

6. The grain refinement process for nozzle ring investment casting according to claim 3, characterized in that, In step 3, the viscosity of the first layer of zirconium slurry is 45-50S, the viscosity of the second layer of mullite slurry is 25-30S, the viscosity of the third layer of mullite slurry is 14-16S, and the viscosity of the mullite slurry used for sealing is 10-12S; the first layer of magnetic fluorite is 80-120 mesh, the second layer of mullite is 30-60 mesh, and the third layer of mullite is 16-30 mesh; the drying time of the first layer of shell material is 8-12 minutes, and the drying time of the second and third layers and the shell material used for sealing is not less than 8 minutes.

7. The grain refinement process for nozzle ring investment casting according to claim 3, characterized in that, In step 4, the dewaxing temperature is 150℃ and the dewaxing time is 5~10 minutes.

8. The grain refinement process for nozzle ring investment casting according to claim 3, characterized in that, In step 5, the roasting temperature is 950-1150℃ and the holding time is 45 minutes.

9. The grain refinement process for nozzle ring investment casting according to claim 3, characterized in that, In step 6, the rotation speed of the mold shell containing molten steel is 20~40 rpm, the distance from the air source in the blowing environment is 3~5m, and the air source speed is 3~5m / s.

10. The nozzle ring investment casting grain refinement process according to claim 3, characterized in that, In step 7, the grain size of the qualified casting is controlled within ASTM 4-6.

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