Process for casting gearbox casting evanescent mode through ceramsite sand

Abstract

The invention discloses a process for casting a gearbox casting evanescent mode by using ceramsite sand, which comprises the following steps: step S1, pre-foaming, step S2, bead curing, and step S3, forming. S4, the mold piece is dried; step S5, bonding and forming; step S6, coating: mixing a dry powder coating with water, and then brushing for four times; s7, box burying and sand filling are conducted, specifically, the model is placed in a sand box containing ceramsite sand bottom sand, the granularity of ceramsite sand is 20-30 meshes, the stacking specific gravity is 1.35-1.45 g / cm < 3 >, and rain type sand filling and vibration are conducted successively till the height of the ceramsite sand is flush with the upper surface of the sand sleeve; and S8, pouring is conducted. According to the design, through the characteristic that the stacking specific gravity of ceramsite sand is relatively small, the weight of sand for a sand box is remarkably reduced, the cost of casting sand for a single ton is reduced, the comprehensive economic cost is remarkably reduced, and compared with ceramsite sand, the ceramsite sand is more environmentally friendly, so that the new sand supplementing amount for casting the evanescent mode later is reduced, the production cost is reduced, and the production benefits of casting castings are improved.

Description

Technical Field

[0001] This invention relates to the field of lost foam casting technology, and more particularly to a process for lost foam casting of gearbox parts using ceramsite sand. Background Technology

[0002] Lost foam casting is a near-net-shape precision casting technique. Its core principle is to replace the traditional wax model or wooden / metal model with a foam plastic model that is exactly the same shape as the final part. The model immediately vaporizes and disappears after pouring, and the molten metal takes its place. After cooling, the casting is formed.

[0003] Currently, the lost foam casting method for gearbox castings typically involves applying a white pattern coating, filling with materials such as silica sand or corundum sand, compacting, and then vacuum pouring. However, silica sand has been gradually phased out by the market due to its large angular coefficient, low recycling rate, high dust content, and poor environmental performance. Corundum sand, with its high bulk density, requires an "electro-melting + blowing" process, resulting in low material utilization, difficulty in particle size control, and unstable yield. It also faces high energy consumption and environmental pressures, making it difficult to offer casting companies more price advantages. The high material cost leads to high production costs during the casting process, which is detrimental to the actual processing and production of lost foam castings. Therefore, a production process is needed that allows for the recycling of filler materials and reduces the processing costs of lost foam castings. Summary of the Invention

[0004] This invention addresses the technical problems of unstable yield, low recovery rate, and high economic cost associated with using expanded polystyrene beads as filler material in the lost foam casting process of gearbox castings. It provides a process for casting gearbox castings using expanded polystyrene beads with expanded polystyrene beads. The process includes the following steps: Step S1: Pre-foaming, where expandable polystyrene beads are heated to spherical shape using steam; Step S2; Bead maturation: The spherical beads are placed into a maturation chamber for maturation, wherein the volatile matter content is controlled at 7%~8%; Step S3: Molding. The cured beads are molded under a steam pressure of 0.5~0.7 MPa to obtain a mold. Step S4: Mold drying. Place the molded mold in a drying room to dry, controlling the residual volatile matter in the mold to 2.3%~3%. Step S5: Bonding and molding, bonding each mold piece in sequence, and using hot glue to bond the gating and riser; Step S6: Coating. The dry powder coating is mixed with water and then applied in four coats. The first coat has a Baumé degree of 85±1°Be, the second and third coats have a Baumé degree of 81±1°Be, and the fourth coat has a Baumé degree of 100±5°Be. Step S7: Fill the sand box with sand. Place the model into a sand box containing ceramsite sand as the base sand. The ceramsite sand has a particle size of 20-30 mesh and a bulk density of 1.35-1.45 g / cm³. 3 The process involves sequentially filling and vibrating the sand in a rain-like manner until the height of the ceramsite sand is flush with the upper surface of the sand jacket. During sand filling, the distance between the model and the side of the sand box is 100~150mm. Step S8: Pouring. Pouring is carried out under a negative pressure environment of 0.04~0.06MPa, and pressure is maintained for 8~10 minutes after pouring.

[0005] Preferably, in the above technical solution, the density of the spherical beads in step S1 is 19~20 g / L.

[0006] Preferably, in the above technical solution, the spherical beads are matured for 12 to 48 hours in step S2.

[0007] Preferably, in the above technical solution, the mixing weight ratio of dry powder coating and water in step S6 is in the range of 1:0.65 to 1:0.7.

[0008] Preferably, in the above technical solution, after the first application in step S6, the surface needs to be placed under ventilation for 1.5 hours before being heated and dried, and drying is required after each application, with a drying time of 8 to 12 hours.

[0009] Preferably, in the above technical solution, the thickness of the bottom sand in step S7 is ≥180mm, and it is vibrated and tamped flat.

[0010] Preferably, in the above technical solution, in step S7, the sand filling height is 100~300mm each time, and after each sand filling, it needs to be vibrated for 15~30s before sand filling is carried out again.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the relatively low bulk density of ceramsite sand to significantly reduce the weight of sand used in sand boxes, thereby reducing the cost of sand per ton of foundry sand and resulting in a significant reduction in overall economic costs.

[0012] In this invention, the recycling rate of ceramsite sand is as high as 98%, which is more environmentally friendly than abrasive sand. This reduces the amount of new sand needed for subsequent lost foam casting, thereby reducing production costs and improving the production efficiency of castings.

[0013] The ceramsite sand in this invention has a good cooling effect, which can effectively shorten the sand removal time of the casting after pouring, and improve the quality and density of the produced castings. Attached Figure Description

[0014] Figure 1 Microscopic images of ceramsite sand used in the lost foam casting process of gearbox parts using ceramsite sand according to the present invention. Figure 2 This invention relates to the microstructure of HT200 (gray cast iron) in the lost foam casting process for gearbox components using ceramsite sand. Figure 1 ; Figure 3 This invention relates to the microstructure of HT200 (gray cast iron) in the lost foam casting process for gearbox components using ceramsite sand. Figure 2 . Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1

[0017] This invention discloses a process for lost foam casting of gearbox parts using ceramsite sand, comprising the following steps: Step S1: Pre-foaming, expandable polystyrene beads are heated with steam to spherical beads with a density of 19~20 g / L; in this process, an automatic intermittent steam pre-foaming machine is used to control the steam pressure and heating time parameters according to the pre-foaming material and density requirements to ensure that the steam heating obtains spherical beads with a certain density requirement.

[0018] Step S2; Bead Curing: Place the beads in a curing chamber for curing for 12-48 hours, with a volatile content control point of 7%-8%. After curing in the chamber, qualified beads generally have a smooth, glossy surface and good resilience when squeezed by hand. Curing is carried out in a naturally ventilated environment, allowing air to penetrate into the pores of the beads, making them dry and elastic, thus increasing their expansion capacity during pattern forming and their resistance to deformation and shrinkage under external pressure after pattern forming. Volatile content refers to the foaming agent pentane (C5H) in the foam beads. 12 The content of pentane is controlled. Pentane gradually volatilizes during pre-foaming and curing, causing the beads to expand and form a honeycomb structure. The volatile content is controlled at 7%~8% to ensure that the beads have sufficient foaming power during molding heating, avoid incomplete fusion, and prevent excessive foaming that could lead to white mold deformation, surface roughness, or dimensional deviations.

[0019] Step S3: Molding. The matured beads are molded in an environment with a steam pressure of 0.5~0.7 MPa to obtain a mold plate. First, air is ventilated in the forward direction (air intake of the fixed mold), then in the reverse direction (air intake of the moving mold), and finally in both directions simultaneously to ensure that the beads are foamed and fused evenly.

[0020] Step S4: Mold drying. Place the formed mold in a drying room to dry, controlling the residual volatile matter in the mold to 2.3%~3%. When the volatile matter is greater than 3%, it will cause excessive vaporization of the foaming agent during casting, generating a large amount of gas and causing porosity, wrinkles, or carbon defects in the casting. When the volatile matter is less than 2.3%, insufficient foaming power may result in incomplete fusion of the mold, forming voids or insufficient strength.

[0021] Step S5: Bonding and molding. Bond the mold pieces in sequence, using hot glue for the gating and riser. First, assemble the smaller pieces above the larger pieces, then bond the larger pieces, and finally assemble the loose block between the two large pieces. To improve bonding strength, the gating and riser can be bonded using hot glue. Mold piece assembly can also be done using hot glue, but the amount of glue applied must be controlled to avoid excessive dimensional errors and excessive hot glue overflow affecting appearance and quality.

[0022] Step S6: Coating. A dry powder coating is mixed with water and applied in four coats. The first coat has a Baumé degree of 85±1°Be, the second and third coats both have a Baumé degree of 81±1°Be, and the fourth coat has a Baumé degree of 100±5°Be. The purpose of the first coat is to provide basic isolation and wetting, filling surface micropores. The purpose of the second coat is to enhance breathability and provide stress buffering, accelerating the release of gases from foam decomposition. The third coat, in conjunction with the second coat, increases the total thickness, delaying heat dissipation from the molten metal to reduce the risk of cold shut-off. The fourth coat further strengthens the surface and enhances erosion resistance, resisting the erosion caused by the molten metal.

[0023] The mixing ratio of dry powder to water ranges from 1:0.65 to 1:0.7. The first coat of coating needs to be left in a ventilated environment for 1.5 hours before being heated and dried. Each subsequent coat must be dried for 8-12 hours. The dry powder is a mixture of refractory aggregate, suspending agent, and additives. The refractory aggregate can be selected from zircon powder, flake graphite, earthy graphite, bauxite, quartz powder, or magnesia powder. A certain amount of mica powder and wollastonite can also be added to improve the high-temperature permeability of the coating. The suspending agent is bentonite. When the dry powder to water ratio is less than 1:0.65, the coating viscosity is too high, resulting in high coating resistance and easily leading to coating accumulation and uneven flow, especially incomplete coverage of complex foam models. When the ratio is greater than 1:0.7, the coating is too thin, the coating thickness is insufficient, the refractory isolation effect decreases, and it easily causes metal penetration and sand adhesion. By precisely controlling the water-to-powder ratio, the coating achieves a three-in-one performance of "high suspension, moderate viscosity, and microporous breathability," simultaneously meeting the needs for ease of application, coating functionality, and defect prevention.

[0024] Step S7: Fill the sand box with sand. Place the model into a sand box containing ceramsite sand as the base sand. The ceramsite sand has a particle size of 20-30 mesh and a bulk density of 1.35-1.45 g / cm³. 3The process involves sequentially filling and vibrating the sand using a rain-like method. Each rain-like sand filling is 100-300mm high, followed by 15-30 seconds of vibration before repeating the process until the ceramsite sand is level with the top surface of the sand jacket. The distance between the model and the side of the sand box during filling is 100-150mm. This distance ensures that, while maximizing the sand absorption around the foam pattern, as many models as possible can be placed in one box, increasing the yield of blanks per box and improving production efficiency. The thickness of the bottom sand should be ≥180mm, and it should be compacted and leveled. This prevents molten iron from being drawn out of the model into the vacuum equipment or from burning through the filter screen on the side wall of the sand box during the casting process, which could cause leakage and affect the casting effect.

[0025] Step S8: Pouring. Pouring is carried out under a negative pressure environment of 0.04~0.06MPa, and pressure is maintained for 8~10 minutes after pouring.

[0026] In this embodiment, the lost foam casting method using ceramsite sand is employed. Utilizing the relatively low bulk density of ceramsite sand, the weight of sand used in the sand box is significantly reduced, lowering the cost per ton of casting sand and resulting in a significant reduction in overall economic costs. Furthermore, ceramsite sand has excellent cooling properties, effectively shortening the time for casting to fall off the sand after pouring, thus improving the quality and density of the produced castings.

[0027] Example 2

[0028] This invention discloses a process for lost foam casting of gearbox parts using ceramsite sand, comprising the following steps: Includes the following steps: Step S1: Pre-foaming, expandable polystyrene beads are heated with steam to form spherical beads with a density of 19~20 g / L; Step S2; Bead maturation: Place the spherical beads into a maturation chamber for maturation for 12-48 hours, during which the volatile matter content is controlled at 7%-8%. Step S3: Molding. The cured beads are molded under a steam pressure of 0.5~0.7 MPa to obtain a mold. Step S4: Mold drying. Place the molded mold in a drying room to dry, controlling the residual volatile matter in the mold to 2.3%~3%. Step S5: Bonding and molding, bonding each mold piece in sequence, wherein the gating and riser are bonded with hot glue; Step S6: Coating. Apply four coats of dry powder coating mixed with water. The first coat has a Baumé degree of 85±1°Be, the second and third coats both have a Baumé degree of 81±1°Be, and the fourth coat has a Baumé degree of 100±5°Be. The mixing ratio of dry powder to water ranges from 1:0.65 to 1:0.7. The first coat needs to be left in a ventilated environment for 1.5 hours before being heated and dried. Each coat must be dried for 8-12 hours.

[0029] Step S7: Fill the sand box with sand. Place the model into a sand box containing ceramsite sand as the base sand. The ceramsite sand has a particle size of 20-30 mesh and a bulk density of 1.35-1.45 g / cm³. 3 The sand is filled and vibrated sequentially using a rain-like method. Each rain-like filling is 100-300mm high, and after each filling, it is vibrated for 15-30 seconds before filling again, until the height of the expanded clay sand is flush with the top surface of the sand jacket. The distance between the model and the side of the sand box during filling is 100-150mm. The thickness of the bottom sand is ≥180mm, and it is then compacted and leveled.

[0030] Step S8: Pouring. Pouring is carried out under a negative pressure environment of 0.04~0.06MPa, and pressure is maintained for 8~10 minutes after pouring.

[0031] In this embodiment, the recycling rates of ceramsite sand and commonly used molten ceramic sand (jewel sand) will be compared experimentally. Under the same lost foam casting conditions, a comparative embedding box test was conducted using ceramsite sand and molten ceramic sand: Because molten ceramic sand (ceramsite sand) is produced using an "electrofusion + blowing" process, material utilization is low, particle size control is difficult, and the yield is only 40%-60%, resulting in high production costs. It also faces pressure from high energy consumption and environmental concerns, making it difficult to offer the foundry industry more room for price reduction. In contrast, ceramsite sand is produced using a "granulation + sintering" process, resulting in high material utilization, controllable particle size, a yield of 80%-90%, relatively low production costs, and is a green and environmentally friendly production method.

[0032] Electrofused ceramic sand has weak magnetism, resulting in some loss at the magnetic separation station in the sand line. In contrast, ceramsite sand is non-magnetic, thus reducing losses compared to electrofused ceramic sand.

[0033] The bulk density of expanded clay aggregate is 1.35~1.45 g / cm³. 3 The electrofused ceramic sand has a density of 1.95~2.05 g / cm³. 3 Comparing the recycling rates, with a production cycle of 10 days and 36 recycling cycles per year: Recycling rate: 98%-99%. Ceramsite sand: Recycling recovery rate: 98%; after 36 recycling cycles, 48.3% remains. Fused ceramic sand: Recycling recovery rate: 95%; after 36 recycling cycles, 15.8% remains. Using the same cylinder foam mold, with 15x25mm oil passage holes in the cylinder cavity, and filling with silica sand and ceramsite sand, the lost foam casting test and ceramsite sand process test showed no sintering or sand adhesion defects in the oil passage holes, indicating that ceramsite sand has better flowability and compactness.

[0034] This embodiment illustrates that the recycling rate of ceramsite sand is as high as 98%, which is more environmentally friendly than abrasive sand. This reduces the amount of new sand needed for subsequent lost foam casting, thereby reducing production costs and improving the production efficiency of castings.

[0035] Example 3

[0036] In this embodiment, an HT200 (gray cast iron) casting will be used as an example. The casting process described in Example 1 will be employed, and the property values ​​will be compared with those of an HT200 (gray cast iron) casting produced by a conventional process through experimental measurement. Table 1: Comparison of the effects of HT200 (gray cast iron) castings produced using the first example process with castings produced using common processes.

[0037] In this embodiment, an experimental comparison was conducted between HT200 (gray cast iron) cast using the process of Example 1 and HT200 (gray cast iron) cast using conventional casting methods. As can be seen from the table, both the HT200 (gray cast iron) cast using the casting process of Example 1 and the conventional casting method meet the standards for use and strength in all data aspects. Therefore, it is evident that the process flow in Example 1, after using ceramsite sand, satisfies and meets the requirements for lost foam casting with ceramsite sand.

[0038] In addition, the use of ceramsite sand significantly reduces the weight of sand used in the sand box, lowers the cost of sand per ton of casting, and significantly reduces overall economic costs. Furthermore, based on the characteristics of ceramsite sand, the recycling rate is increased, thereby reducing the amount of new sand needed for subsequent lost foam casting, further reducing production costs and improving the production efficiency of castings.

[0039] 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 process for casting a transmission case casting using a ceramic sand lost foam, characterized in that, The method comprises the following steps: Step S1: Pre-expansion, the expandable polystyrene beads are heated by steam to spherical beads; Step S2: Bead curing, the spherical beads are put into a curing bin for curing, wherein the control point of volatile matter is 7%~8%; Step S3: Molding, the cured beads are molded under the environment with a steam pressure of 0.5~0.7 MPa to obtain a mold piece; Step S4: Mold piece drying, the molded mold piece is placed in a drying room for drying, and the residual volatile matter in the mold piece is controlled at 2.3%~3%; Step S5: Bonding and molding, the mold pieces are bonded in sequence, and hot glue is used for bonding the riser and the runner; Step S6: Coating, dry powder paint is mixed with water and then coated four times, wherein the first layer has a Baume degree of 85±1°Be, the second and third layers have a Baume degree of 81±1°Be, and the fourth layer has a Baume degree of 100±5°Be; Step S7: sand filling in the box, the model is put into the sand box containing the sand bottom sand of ceramic sand, the particle size of the ceramic sand is 20-30 mesh, and the bulk specific gravity is 1.35-1.45 g / cm 3 , and the rain shower type sand filling and vibration are sequentially performed until the height of the ceramic sand is flush with the upper surface of the sand sleeve, and the distance between the model and the side edge of the sand box is 100-150 mm during the sand filling. Step S8: Pouring, pouring is performed under the environment with a negative pressure of 0.04~0.06 MPa, and the pressure is maintained for 8~10 minutes after pouring.

2. The process of claim 1, wherein the ceramic sand is used for casting the transmission case casting using the lost foam process. The density of the spherical beads in step S1 is 19~20 g / L.

3. The process of claim 1, wherein the ceramic sand is used for casting the transmission case casting using the lost foam process. The curing time of the spherical beads in step S2 is 12~48 hours.

4. The process of claim 1, wherein the ceramic sand is used for casting the transmission case casting using the lost foam process. The mixing weight ratio of the dry powder paint to water in step S6 ranges from 1:0.65 to 1:0.

7.

5. The process of claim 4, wherein the ceramic sand is used for casting the transmission case casting in the lost foam process. After the first coating in step S6, heating and drying are performed after 1.5 hours of placement under ventilation, and drying is performed after each coating, and the drying time is 8~12 hours.

6. The process of claim 1, wherein the process is characterized by: The thickness of the bottom sand in step S7 is ≥180 mm, and the bottom sand is vibrated and tamped flat.

7. The process of claim 6, wherein the ceramic sand is a ceramic sand of the type sold under the name "Ceramsite" by the company "Ceramsite" of the city of "Bucharest" in Romania. In the rain shower type sand filling in step S7, the height of each sand filling is 100~300 mm, and the sand filling is performed again after vibration for 15~30 seconds after each sand filling.

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