Process for casting gearbox by using iron mold coated sand

Abstract

The invention discloses a process for casting a gearbox by applying iron mold sand coating, which comprises the following steps of: S1, adopting an iron mold with the same shape as the gearbox; s2; the center of the iron mold coincides with the center of a sand shooting cylinder of the double-station hot core sand shooting main machine; s3, a pressing mechanism of the double-station hot core sand shooting main machine is controlled to ascend, and a sand shooting plate is driven to press downwards and make close contact with the upper surface of the outer mold body; s4, the outer mold body and the iron mold are heated through an electric heating pipe; s5, sand shooting; s6, opening the mold; s7, spraying a coating; s8, filter pieces are arranged at the bottom and the top of the sprue, and mold closing is conducted; and S9, pouring is conducted, and after 13-16 min, box opening and shakeout are conducted in an auxiliary vibration mode. According to the design, the sand consumption filled in the iron mold is greatly reduced, the material loss is reduced, and the cost is saved. And inclusions of molten iron in the pouring process are filtered out through the foamed ceramic filter and the straight-hole ceramic filter, so that the quality of a casting is improved, air holes are prevented from being formed in the casting, and the smoothness and compactness are improved.

Description

Technical Field

[0001] This invention relates to the field of gearbox casting technology, and in particular to a process for casting gearboxes using iron molds covered with sand. Background Technology

[0002] Currently, the production of gearbox iron castings typically employs either sand casting or lost foam casting. Sand casting suffers from drawbacks such as a high sand-to-iron ratio, high molding costs, dimensional instability, and poor surface finish. Lost foam casting, on the other hand, is prone to dimensional deformation, affecting the precise dimensions of the casting.

[0003] Iron mold sand casting technology is a semi-precision casting method distinct from sand casting, lost foam casting, V-process casting, metal mold casting, shell casting, paraffin casting, ceramic casting, and steel shot casting. This method uses a metal model—a cast iron model (also known as an iron mold with sand coating)—and a cast iron cavity with a shape similar to the casting as the sand mold. A 6-10mm layer of coated sand is applied to the mold to form the casting. The gearbox has a basic wall thickness of 8mm, with outline dimensions of 970mm × 500mm × 240mm. The casting material is GG25, and the deepest part of the cavity reaches 200mm, making it a complex structure with a deep cavity and thin walls. In existing technologies, when using resin sand or silica sand molding processes, the sand-to-iron ratio is usually high (6:1 or higher), resulting in large deformation of the blank size, non-dense internal structure, poor surface finish, high manufacturing cost, and a tendency to crack during the casting process. Summary of the Invention

[0004] This invention addresses the technical problems in the process of casting gearboxes using iron molds with sand coating, such as excessively high sand-to-iron ratio leading to dimensional deformation, low surface finish, poor density, high cost, and large differences in gearbox wall thickness. It provides a process for casting gearboxes using iron molds with sand coating, comprising the following steps: Step S1: Using an iron mold of the same shape as the gearbox, and cleaning the working surface of the iron mold and residual sand in the sand injection channel; Step S2: Select a dual-station hot core sandblasting machine, attach the outer mold body and the iron mold together, and transport them to the molding station of the dual-station hot core sandblasting machine so that the center of the iron mold coincides with the center of the sandblasting cylinder of the dual-station hot core sandblasting machine. Step S3: Securely install the sand-shooting plate on the dual-station hot core sand-shooting host, align the sand-shooting nozzle of the sand-shooting plate with the sand-shooting hole of the iron mold, control the pressing mechanism of the dual-station hot core sand-shooting host to rise, drive the sand-shooting plate to press down and make close contact with the upper surface of the outer mold body. Step S4: Use electric heating tubes to heat the outer mold body and the iron mold respectively; Step S5: Spray the release agent 4-6 times on the surface of the outer mold body, align the positioning pin hole of the iron mold with the positioning pin hole of the outer mold body, plug the ejection hole of the upper layer of the iron mold with the plug, and then start the dual-station hot core sand shooting host to perform sand shooting. Step S6: After sand shooting is completed, control the sand shooting cylinder of the dual-station hot core sand shooting host to retract. After the iron mold is covered with sand and solidified, the mold is opened to obtain the upper mold and the lower mold respectively. Step S7: Move the upper and lower molds to the turning station, clean the loose sand in the inner cavity, spray paint on the working surfaces of the upper and lower molds, and spray water-based paint locally in the inner cavity; Step S8: Move the upper and lower molds to the mold closing machine, install filter plates at the bottom and top of the sprue, and close the upper and lower molds by controlling the mold closing machine and lock the upper and lower molds. Step S9: Add a mixture of 3.15-3.25 parts by mass of C, 1.7-1.9 parts by mass of Si, 0.6-0.8 parts by mass of Mn, 0.3-0.4 parts by mass of Cu, 0.4-0.6 parts by mass of ferrosilicon inoculant, <0.1 parts by mass of S, <0.15 parts by mass of P, and the balance being Fe into a smelting furnace and melt it into molten iron. Then pour the mixture from the flange face to obtain a casting. The pouring temperature is 1420-1430℃, and the pouring time is controlled at 27-30 seconds. After pouring, 13-16 minutes later, the casting is removed from the mold by auxiliary vibration.

[0005] Preferably, in the above technical solution, the heating temperature in step S4 is 180~190℃.

[0006] Preferably, in the above technical solution, in step S7, the coatings sprayed on the working surfaces of the upper and lower casting molds are prepared by mixing water-based coatings and alcohol-based coatings in a volume ratio of 1:1.

[0007] Preferably, in the above technical solution, the bottom filter in step S8 is a foam ceramic filter with a size of 100×100×20mm and a pore size of 10ppi, and the top filter is a straight-pore ceramic filter with a pore size of 2.5~3.0mm.

[0008] Preferably, in the above technical solution, when the upper and lower molds are closed in step S8, a gap of 0.15~0.25mm needs to be reserved between their parting surfaces.

[0009] Preferably, in the above technical solution, in step S9, a ferrosilicon inoculant of 0.1% of the mass of molten iron is added again with water during the casting process.

[0010] Preferably, in the above technical solution, in step S9, before casting, a transition top plate with 7 push rods is installed on the iron mold, so that the 7 push rods are inserted into the holes at the top of the iron mold.

[0011] Preferably, in the above technical solution, 4-5 minutes after pouring, the residue around the sprue is cleaned, the mold is moved to the mold opener, the mold is held in place by a cylinder, the transition top plate is pushed down, and the casting is ejected from the mold; the process of pushing the transition top plate down and ejecting is achieved by a vibrating motor driving a vibrating push rod in the top hole of the iron mold to achieve assisted vibration mold opening.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the conformal iron mold and the outer mold body to control the thickness of the sand-coated surface to 6-10mm, which significantly reduces the amount of sand used to fill the iron mold in the process of casting gearboxes with iron mold sand coating, making the sand-to-iron ratio less than 1, reducing material loss when casting gearboxes with iron mold sand coating, and thus saving the cost of molding materials.

[0013] This invention improves casting quality by installing foamed ceramic filters and perforated ceramic filters at the top and bottom of the sprue between the upper and lower molds to remove inclusions in the molten iron during pouring. Furthermore, the rapid passage of molten iron through the perforated ceramic filters fills the sprue, reducing turbulence during pouring and preventing porosity caused by air pockets. The pre-reserved gap between the upper and lower molds during mold closing effectively increases the rate of internal venting, further preventing porosity within the casting and ensuring the quality of the blank, thus improving surface finish and density.

[0014] In this invention, a vibrating motor drives a vibrating ejector rod, and auxiliary vibration is used to accelerate the demolding process of the casting. This invention provides a more labor-saving and time-saving solution and method for structural parts that are relatively difficult to eject. 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] The present invention discloses a process for casting a gearbox using a sand-coated iron mold, comprising the following steps: Step S1: Use an iron mold of the same shape as the gearbox and clean the working surface of the iron mold and the residual sand in the sand-shooting channel. The sand-covered surface of the iron mold should be made to conform to the shape of the outer mold body, leaving a space for a sand layer. Control the thickness of the sand layer to be about 6-10mm. Use a steel chisel and electric pick to clean the working surface of the iron mold and the residual sand in the sand-shooting channel, avoiding bumping the parting surface of the iron mold during the cleaning process, which could cause "sand leakage" in subsequent operations.

[0018] Traditional resin sand casting processes require a large amount of coated sand, with a sand-to-iron ratio of 6.2. Each sand casting process necessitates the mixing of 45-75 mesh silica sand, furan resin, and a curing agent. The furan resin comprises 1.0-1.3% of the sand weight, and the curing agent accounts for 40-60% of the furan resin. While some of the coated sand and silica sand can be recycled, the remaining materials are disposable, resulting in relatively high costs for sand casting. This new process utilizes coated sand to complete the sand casting process. Compared to traditional resin sand casting, the cost of iron mold sand casting is significantly reduced, cutting casting costs and achieving cost reduction and efficiency improvement.

[0019] Step S2: Select a dual-station hot-core sand-shooting machine. After attaching the outer mold body and the iron mold, transport them to the molding station of the dual-station hot-core sand-shooting machine, ensuring that the center of the iron mold coincides with the center of the sand-shooting cylinder of the dual-station hot-core sand-shooting machine. The dual-station hot-core sand-shooting machine can simultaneously process and manufacture the upper and lower molds to improve production efficiency. Fasteners can be used to secure and lock the iron mold and outer mold body. The iron mold and outer mold assembly are transported to the molding station of the machine via a power-driven roller. The mold is installed and fixed on the base of the sand-shooting machine. After installation, the mold closing and opening strokes need to be adjusted.

[0020] Step S3: Securely install the sand-shooting plate onto the dual-station hot-core sand-shooting main unit, aligning the sand-shooting nozzle of the sand-shooting plate with the sand-shooting hole of the iron mold. Control the pressing mechanism of the dual-station hot-core sand-shooting main unit to rise, causing the sand-shooting plate to press down and make tight contact with the upper surface of the outer mold body. Raise the base of the dual-station hot-core sand-shooting main unit, raising the base and the outer mold body until they contact the iron mold. Before the base reaches its highest position, the upper surface of the iron mold should engage with the sand-shooting plate of the mold already securely installed on the main unit, ensuring smooth mold closing and positioning. After the main unit descends to its lowest position, the outer mold body should be at least 50mm away from the upper surface of the iron mold to ensure normal operation of the iron mold on the roller conveyor.

[0021] Step S4: Use electric heating tubes to heat the outer mold body and the iron mold separately, with a heating temperature of 180~190℃. Ensure that the outer mold body has a uniform temperature after heating and that the temperature meets the process setting requirements. It should be able to completely cure within 5~8 minutes after sandblasting, and the mold should open smoothly after curing. The iron mold should also have a good sandblasting curing effect.

[0022] Step S5: Spray release agent 4-6 times onto the surface of the outer mold body. Align the positioning pin holes of the iron mold with the positioning pin holes of the outer mold body. After plugging the ejector hole on the upper layer of the iron mold with a plug, start the dual-station hot core sand shooting machine for sand shooting. Before sand shooting, check the parting surface to ensure there are no gaps or visible light. Plug the ejector hole on the upper layer of the iron mold with a plug to prevent sand from "running out" during the sand shooting process.

[0023] The base of the dual-station hot core sand-shooting host is raised so that the outer mold body contacts the iron mold and continues to rise. The upper surface of the iron mold contacts the sand-shooting plate and presses it tightly before the sand-shooting operation can be performed. At this time, the sand-shooting nozzle has entered the sand-shooting hole of the iron mold to prevent sand from running out due to gaps between the iron mold and the outer mold body.

[0024] Step S6: After sand injection is complete, control the sand injection cylinder of the dual-station hot-core sand injection host to retract. After the iron mold is coated with sand and cured, open the mold to obtain the upper and lower molds. After sand injection is complete, control the iron mold to descend appropriately and observe that the iron mold is no longer in contact with the rollers of the dual-station hot-core sand injection host. When the iron mold is out of contact with the rollers, the sand injection cylinder withdraws from the sand injection hole of the iron mold. Observe whether the mold is filled with sand; if not, add sand. The release agent helps to facilitate demolding after curing. The iron mold should be demolded after 5-8 minutes of sand curing time for better shell curing effect.

[0025] Step S7: Move the upper and lower molds to the turning station, clean the loose sand in the inner cavity, and spray paint on the working surfaces of the upper and lower molds. The paint is prepared by mixing water-based paint and alcohol-based paint in a 1:1 volume ratio. Apply water-based paint locally to the inner cavity to improve the mold surface's resistance to sand inclusions and vein patterns. After demolding, move the molds to the turning station, turn them over, and check the inner surfaces of both molds to ensure there are no flashes on the sprue and ingate, the inner cavity surface is intact, and there are no protrusions at the vent plug. After cleaning the loose sand from the inner cavity, apply adhesive to the core head and correctly extend the core into the lower mold.

[0026] Step S8: Move the upper and lower molds to the mold assembly machine. Install filter plates at the bottom and top of the sprue. The bottom filter plate is a foam ceramic filter plate with dimensions of 100×100×20mm and a pore size of 10ppi. The top filter plate is a straight-hole ceramic filter plate with a pore size of 2.5~3.0mm. The upper and lower molds are assembled and locked using the mold assembly machine. The foam ceramic filter plate filters inclusions in the molten iron, improving the quality of the casting. The combination of the top straight-hole ceramic filter plate and the bottom foam ceramic filter plate allows the molten iron to quickly fill the sprue during pouring, effectively reducing turbulence and preventing porosity after air accumulation. A gap of 0.15~0.25mm should be left between the parting surfaces of the upper and lower molds during assembly. This gap increases venting and effectively reduces porosity inside the casting.

[0027] In this embodiment, the thickness of the sand-coated surface between the conformally shaped iron mold and the outer mold body is controlled at 6-10mm, which significantly reduces the amount of sand used to fill the inside of the iron mold in the process of casting the gearbox with iron mold sand coating, making the sand-to-iron ratio less than 1, reducing material loss when casting the gearbox with iron mold sand coating, and thus saving the cost of molding materials.

[0028] By installing foamed ceramic filters and perforated ceramic filters at the top and bottom of the sprue between the upper and lower molds, inclusions in the molten iron during pouring are removed, thus improving the quality of the casting. Furthermore, the rapid passage of molten iron through the perforated ceramic filters fills the sprue, reducing turbulence during pouring and preventing porosity caused by air pockets. The pre-reserved gap between the upper and lower molds during mold closing effectively increases the rate of internal venting, further preventing the formation of porosity within the casting and affecting the quality of the casting blank, thereby improving surface finish and density.

[0029] Example 2:

[0030] In this embodiment, the front box of the gearbox, which is cast by sand with iron mold, will be used as an example. The process flow in Embodiment 1 will be used to compare the hardness values ​​of different components after melting and casting, and to scan whether there is any deformation on its flange surface.

[0031] Table 1: Comparison of the effects of different compositions on the sand-coated casting of the gearbox front box under the process of Example 1

[0032] Through comparison of the above experimental data, it was found that using the process flow in Example 1, a mixture of 3.15-3.25 parts by weight of C, 1.7-1.9 parts by weight of Si, 0.6-0.8 parts by weight of Mn, 0.3-0.4 parts by weight of Cu, 0.4-0.6 parts by weight of ferrosilicon inoculant, <0.1 parts by weight of S, <0.15 parts by weight of P, and the balance being Fe, was added to a melting furnace and smelted into molten iron. The molten iron was then poured from the flange face to obtain a casting. The pouring temperature was 1420-1430℃, and the pouring time was controlled at 27-30 seconds. During the pouring process, 0.1% by weight of ferrosilicon inoculant was added again. The addition of inoculant during the pouring process increased the final Si content by 0.3-0.4% compared to the composition before the furnace, ensuring that the hardness of the final casting blank did not exceed 220 HB, meeting the mechanical properties and processing requirements. Since the chromium (Cr) content significantly affects the hardness of gearbox castings, the dimensional deformation is controlled within ±1.5 mm and the hardness is maintained within the range of 185–220 HB by controlling the Cr content in the molten iron and increasing the content of C, Si, and S to reduce the Cu content. This ensures that the surface and internal quality of the blank meet the German GG25 technical standard. A ferrosilicon inoculant at 0.1% of the molten iron mass is added during the pouring process. The casting is then removed from the mold using assisted vibration 13–16 minutes after pouring. Through multiple comparative experiments, controlling the removal time after pouring to 13–16 minutes yields the best results, effectively preventing casting deformation and large thickness variations.

[0033] Example 3: In this embodiment, a transition top plate installed on the iron mold is used to assist the mold opening process before pouring. Four main ejector rods and three auxiliary ejector rods are fixed on the transition top plate. After the top plate is lowered, the seven ejector rods are inserted into the holes at the top of the iron mold. At the pouring station, 4-5 minutes after pouring, a steel chisel is used to clean the residue around the sprue to avoid affecting the subsequent mold opening. The sprue is then separated from the iron mold for demolding. The mold is moved to the mold opening machine, where a cylinder holds the mold in place. The mold opening machine separates the upper and lower molds while simultaneously pushing the transition top plate down, ejecting the casting from the mold.

[0034] For structural components that are difficult to eject smoothly, a vibratory motor drives a vibratory ejector rod to achieve assisted vibration for mold opening. The mold is moved to the mold opening machine, and after the lower mold is secured, the front and rear hooks of the mold opening machine hook the upper mold and lift it up, separating the upper and lower molds. The lower mold moves out of the mold opening station, and simultaneously, the ejector rod is pushed down to 2 / 3 of the depth of the ejector hole. The vibratory motor is then started to drive the ejector rod to vibrate the upper mold. After vibrating for 10 seconds, the ejector rod continues to descend until it successfully ejects the casting from the mold. In this embodiment, vibration can also be used simultaneously during the mold opening and ejection action to eject the casting from the upper mold.

[0035] 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 gearbox using a sand-coated iron mold, characterized in that, Includes the following steps: Step S1: Use an iron mold of the same shape as the gearbox and clean the working surface of the iron mold and the residual sand in the sand-shooting channel; Step S2: Select a dual-station hot core sandblasting machine, attach the outer mold body and the iron mold together, and transport them to the molding station of the dual-station hot core sandblasting machine so that the center of the iron mold coincides with the center of the sandblasting cylinder of the dual-station hot core sandblasting machine. Step S3: Securely install the sand-shooting plate on the dual-station hot core sand-shooting host, align the sand-shooting nozzle of the sand-shooting plate with the sand-shooting hole of the iron mold, control the pressing mechanism of the dual-station hot core sand-shooting host to rise, drive the sand-shooting plate to press down and make close contact with the upper surface of the outer mold body. Step S4: Use electric heating tubes to heat the outer mold body and the iron mold respectively; Step S5: Spray the release agent 4 to 6 times on the surface of the outer mold body, align the positioning pin hole of the iron mold with the positioning pin hole of the outer mold body, plug the ejection hole of the upper layer of the iron mold with the plug, and start the dual-station hot core sand shooting host to perform sand shooting. Step S6: After sand shooting is completed, control the sand shooting cylinder of the dual-station hot core sand shooting host to retract. After the iron mold is covered with sand and solidified, the mold is opened to obtain the upper mold and the lower mold respectively. Step S7: Move the upper and lower molds to the turning station, clean the loose sand in the inner cavity, spray paint on the working surfaces of the upper and lower molds, and spray water-based paint locally in the inner cavity; Step S8: Move the upper and lower molds to the mold closing machine, install filter plates at the bottom and top of the sprue, and close the upper and lower molds by controlling the mold closing machine and lock the upper and lower molds. Step S9: Add a mixture of 3.15-3.25 parts by mass of C, 1.7-1.9 parts by mass of Si, 0.6-0.8 parts by mass of Mn, 0.3-0.4 parts by mass of Cu, 0.4-0.6 parts by mass of ferrosilicon inoculant, <0.1 parts by mass of S, <0.15 parts by mass of P, and the balance being Fe into a smelting furnace and melt it into molten iron. Then pour the mixture from the flange face to obtain a casting. The pouring temperature is 1420-1430℃, and the pouring time is controlled at 27-30 seconds. After pouring, 13-16 minutes later, the casting is removed from the mold by auxiliary vibration.

2. The process of casting a gearbox using a sand-coated iron mold according to claim 1, characterized in that: The heating temperature in step S4 is 180~190℃.

3. The process of casting a gearbox using an iron mold with sand coating according to claim 1, characterized in that: In step S7, the coatings are sprayed onto the working surfaces of the upper and lower molds, and the water-based coatings and alcohol-based coatings are mixed in a volume ratio of 1:

1.

4. The process of casting a gearbox using an iron mold with sand coating according to claim 1, characterized in that: In step S8, the bottom filter is a foam ceramic filter with dimensions of 100×100×20mm and a pore size of 10ppi, while the top filter is a straight-pore ceramic filter with a pore size of 2.5~3.0mm.

5. The process of casting a gearbox using an iron mold with sand coating according to claim 1, characterized in that: In step S8, when the upper and lower molds are closed, a gap of 0.15~0.25mm should be reserved between their parting surfaces.

6. The process of casting a gearbox using an iron mold with sand coating according to claim 1, characterized in that: In step S9, during the pouring process, 0.1% of ferrosilicon inoculant by mass of molten iron is added again with water.

7. The process for casting a gearbox using a sand-coated iron mold according to claim 1, characterized in that: In step S9, before pouring, a transition plate with 7 ejector pins is installed on the iron mold, so that the 7 ejector pins are inserted into the holes at the top of the iron mold.

8. The process for casting a gearbox using a sand-coated iron mold according to claim 7, characterized in that: 4-5 minutes after pouring, clean the residue around the sprue, move the mold to the mold opener, use a cylinder to hold the mold, push the transition top plate down, and push the casting out of the mold; the process of pushing the transition top plate down and pushing out is driven by a vibrating motor to drive the vibrating push rod in the top hole of the iron mold to achieve assisted vibration mold opening.

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