A casting method of a cast state QT700-3 gear hub

Abstract

The application discloses a casting method of a cast-state QT700-3 gear hub, and comprises the following steps: step one, determining the placing state of the gear hub in the sand mold as a placing mode with a small opening downward and a large opening upward; step two, determining that one gear hub is placed in the sand mold of each sand box; step three, determining a riser structure, the riser is designed to be integrated with the gear hub, the cross section of the riser extends along the large opening direction of the gear hub, and the cross section is Y-shaped; step four, determining that the parting mode of the gear hub during casting is horizontal parting along the top of the riser of the gear hub, and the sand mold is divided into two parts; and step five, determining a gating system structure, the sprue gate and the runner are located on the upper sand mold, and the position, at which the top of the sprue gate is connected with the outside of the mold, is a funnel-shaped top structure of the sprue gate. The casting method of the cast-state QT700-3 gear hub can reduce casting defects such as inclusions, pores and loose in the gear hub during the casting process, improves the internal quality of the gear hub, and meets the performance requirements of the QT700-3 material in the cast state.

Description

Technical Field

[0001] This invention relates to the field of casting technology, specifically to a casting method for a QT700-3 gear hub in the as-cast state. Background Technology

[0002] Gear hubs are important components in transmission machinery. The material is QT700-3. The inner circle of the gear hub is all toothed. It is subjected to large forces during use. Its performance meets the requirements of QT700-3 material. The hardness of the body meets 250~300HBW. At the same time, it is required that its internal structure be dense and free from defects such as shrinkage porosity, shrinkage cavities, slag inclusions and air holes.

[0003] The existing Chinese patent title is "A Riser-less Casting Structure for Ductile Iron Wheel Hubs for Automobiles" (Publication No. CN214290715U). This patent has the following defects: (1) In this patent, the chills are placed inside the sand core, and the thickness of the sand core outside the chills is 5-10mm. The disadvantage is that it is difficult to place the chills during the core making process, and it is not easy to operate. The chills do not directly contact the casting, and the chill effect is weak for thick wheel hubs. There is a risk that the casting defects inside the wheel hub cannot be effectively eliminated during the casting process; (2) The gating system designed in this patent has no slag filter structure. The disadvantage is that the gating system designed by it, such as the horizontal gating channel, cannot effectively filter the slag in the molten metal, which can easily cause slag inclusion defects in the casting; (3) The structure designed by this patent does not have an exhaust hole or a similar exhaust structure. The disadvantage is that the exhaust will be poor during the pouring process, which can easily cause defects such as insufficient pouring and porosity in the casting; (4) The structure designed by this patent does not have a sand core exhaust structure. The disadvantage is that most of the sand core is wrapped by the molten iron during the pouring process. Under the action of high temperature, a large amount of gas will be generated in the sand core. Without an exhaust structure, the casting is prone to porosity defects. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a casting method for QT700-3 gear hub in the as-cast state. This method can reduce casting defects such as inclusions, porosity and looseness in the gear hub during the casting process, improve its internal quality, and effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a casting method for a QT700-3 gear hub in the as-cast state, comprising the following steps:

[0006] Step 1: Determine the placement of the gear hub within the sand mold with the smaller opening facing down and the larger opening facing up;

[0007] Step 2: Determine that there is one gear hub per sand mold in each sand box;

[0008] Step 3: Determine the riser structure. The riser is designed to be integrated with the gear hub. The riser cross-section extends along the cross-section of the gear hub in the direction of the large opening, and the cross-section is Y-shaped.

[0009] Step 4: Determine the parting method for gear hub casting as horizontal parting along the top of the gear hub riser, dividing it into upper and lower types;

[0010] Step 5: Determine the gating system structure. The sprue and runner are located in the upper sand mold. The top of the sprue, where it connects to the outside of the mold, has a funnel-shaped structure. On the parting surface, it forms an open ring along the outer circle of the gear hub. The center of the annular runner is concentric with the center of the gear hub, divided into left and right parts. The sprue is located at the midpoint where the extended lines of the two runner parts intersect. The sprue and runner are not directly connected. A corresponding sprue recess is designed in the lower sand mold. The ingate is located on the lower sand mold, arranged in a ring along the outer circle of the riser on the parting surface, evenly distributed within a 360° range. The ingate connects the runner and riser. A semi-closed gating system is selected, with a gating system ratio of ΣF. 直 :ΣF 横 :ΣF 内 =1.2:1.4:1, with circular vents arranged in a ring at the top of the riser. The other end of the vents is connected to the outside to expel air from the cavity during the pouring process.

[0011] Step Six: Determine the structure and placement of the chills. Place a bottom chill at the bottom of the gear hub. Place inner chills arranged in a 360° ring around the circumference of the gear hub where the teeth are machined. The surface of the inner chills that contacts the inner wall of the gear hub is arc-shaped, with the radius of the arc matching that of the inner wall of the gear hub. The casting solidifies in a bottom-up sequence.

[0012] Step 7: Determine the sand core venting structure. A hollow sand core venting hole is designed at the center of the sand core, with the side closest to the upper sand mold open. At the position of the upper sand mold corresponding to the sand core venting hole, a hollow structure with a cross-sectional dimension larger than that of the sand core venting hole is designed, so that the sand core venting hole is directly connected to the outside.

[0013] Step 8: Mold and tooling fabrication; each sand box is made from a single integral casting.

[0014] Step Nine: Production of sand cores, upper sand molds, and lower sand molds, all made of furan resin self-hardening sand;

[0015] Step 10: During the loading and unloading process, after the sand core is loaded into the lower sand mold, the upper sand mold is closed. Dry sand without resin and hardener is filled into the open position of the upper sand mold corresponding to the air outlet of the sand core. After the box is closed, a pressure iron is placed on top of the upper sand mold.

[0016] Step 11: Smelting. Use a medium-frequency induction furnace to smelt the molten iron at a temperature of 1500–1530℃. The raw materials include pig iron, scrap steel, recycled materials, and ferromanganese. Control the chemical composition of the molten iron in the furnace as follows: C: 3.6%–3.7%, Si: 1.4%–1.5%, Mn: 0.4%–0.6%, Cu: 0.6%–0.7%, Mo: 0.15%–0.2%, P < 0.04%, S < 0.02%.

[0017] Step 12: Tapping and Pouring of Molten Iron. After the molten iron has melted, tap it from the furnace to the ladle at 1470–1500℃. Add 1.1%–1.5% of rare earth magnesium-silicon-iron alloy spheroidizing agent, 0.4%–0.8% of high-calcium barium inoculant, and a covering agent by weight of the tapped molten iron to the bottom of the ladle beforehand. The pouring temperature is 1350±10℃, and the pouring time is 10–15 seconds. During the pouring process, use rare earth silicon inoculant with a particle size of 0.2–0.7 mm for in-flow inoculation. The amount of in-flow inoculant added is 0.07%–0.1% of the weight of the poured molten iron.

[0018] Step 13: Sand removal. 30 minutes after pouring, start removing the casting from the mold. After removing the casting from the mold, spray water mist to cool it. Spray water mist until the casting turns dark red. Then, air cool the casting.

[0019] Step Fourteen: Cleaning. Clean the casting structure thoroughly, including the gating system, risers, and vents.

[0020] Step 15: Check the hardness of the gear hub. When the hardness is 310HBW, temper it using process parameters of 500-520℃ and holding for 2-4 hours.

[0021] When the hardness is 310-330 HBW, tempering is performed using process parameters of 550-560℃ and holding for 2-4 hours.

[0022] When the hardness is greater than 330HBW, tempering is performed using process parameters of 580-600℃ and holding for 2-4 hours.

[0023] Step Sixteen: Shot blasting and inspection.

[0024] As a preferred embodiment of the present invention, in step two, the center of the gear hub is located on the center line of the sand mold in the length direction and the center line of the gear hub, and is located 43mm to one side of the center line of the sand mold in the width direction.

[0025] In a preferred embodiment of the present invention, the height of the riser in step three is one-third of the height of the gear hub.

[0026] As a preferred embodiment of the present invention, in step five, the sprue is a cylindrical structure with an incline. The cross-sectional dimension of the small end of the sprue is φ56mm. The lower sand mold is designed with a lower sand mold horizontal runner for connecting the sprue and the sprue socket. The end of the lower sand mold horizontal runner is designed with a lower sand mold overlapping structure. The end of the horizontal runner near the sprue is designed with an upper sand mold overlapping structure. The cross-sectional dimensions of the upper sand mold overlapping structure and the lower sand mold overlapping structure are larger than the cross-sectional dimensions of the lower sand mold horizontal runner and the horizontal runner. The gating system in the upper sand mold and the lower sand mold is axially symmetrical with respect to the line connecting the center of the sprue and the center of the gear hub. The number of ingates is four, arranged in a ring at 90° intervals.

[0027] As a preferred technical solution of the present invention, in step five, the sprue is divided into upper and lower parts. The upper part is a funnel-shaped open structure for injecting molten iron, and the lower part is conical with a smaller cross section on the side closer to the parting surface and a larger cross section on the side farther from the parting surface. A filter is provided at the lower sand mold position where the lower sand mold overlapping structure intersects with the upper sand mold overlapping structure, and the cross section at the intersection of the lower sand mold overlapping structure and the upper sand mold overlapping structure is larger than the cross section of the sprue at other positions.

[0028] As a preferred embodiment of the present invention, in step six, four bottom chills are placed, which are evenly arranged at 360° on the bottom, with a gap of 20-30mm between them and a thickness of 40mm. Ten inner cavity chills are placed, which are evenly distributed on the circumference of the gear hub's machined tooth profile, with a gap of 20-40mm between them.

[0029] As a preferred technical solution of the present invention, in step seven, after the gear hub is fitted with the upper sand mold, a pressure iron is placed on top of the upper sand mold.

[0030] As a preferred technical solution of the present invention, the tooling used in step eight during the production of the upper and lower sand molds is an integral casting sand box.

[0031] As a preferred technical solution of the present invention, in step nine, furan resin sand is used to fill the space between the sand box and the mold. After the furan resin hardens from the hard sand, it forms the upper and lower shapes with the sand box on the outside.

[0032] In a preferred embodiment of the present invention, in step ten, the surface of the dry sand is not higher than the surface of the upper sand mold.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: The casting method of QT700-3 gear hub in the as-cast state (1) placing one gear hub in the same sand mold, compared with placing multiple pieces in one sand mold, can avoid the thermal influence between each gear hub during the pouring and cooling process, and reduce the internal defects of the gear hub caused by this; ceramic filter plates or filter screens are horizontally placed at the lower sand mold position where the lower sand mold overlapping structure intersects with the upper sand mold transverse runner, effectively filtering impurities in the molten iron and preventing the gear hub from having inclusion defects due to impurity of the molten iron; (2) the top of the riser is designed with vent holes arranged in a ring, which can smoothly discharge the air in the cavity during the pouring process, and avoid the gear hub from having insufficient pouring or porosity defects due to poor venting; the center position of the sand core is designed as the sand core vent hole, which is a hollow structure, open on the side close to the upper sand mold, and a hollow structure is designed at the upper sand mold position corresponding to the hollow structure of the sand core. , so that the hollow structure of the sand core vent hole is directly connected to the outside, ensuring that the gas generated by the resin and curing agent in the sand core under high temperature during the iron pouring process can be smoothly discharged to the outside, avoiding gas intrusion into the iron and causing porosity defects in the gear hub; (3) The inner gate is arranged in a ring along the outer circle of the gear hub and is evenly distributed within a 360° range, making the iron filling more stable, avoiding local heat concentration, and reducing its impact on the casting; A ring chill is placed at the bottom of the gear hub, and the ring chill is evenly distributed within a 360° range at the bottom, which can effectively cool the gear hub after pouring. When used in conjunction with the riser, it realizes the sequential solidification method of the gear hub from bottom to top, ensuring the internal quality of the gear hub; (4) The upper and lower sand boxes adopt integral casting sand boxes. The sand boxes and the mold use high-hardness furan resin sand, which improves the rigidity of the mold and thus improves the internal density of the gear hub, further ensuring the internal quality of the gear hub. Attached Figure Description

[0034] Figure 1 This is a top view of the present invention;

[0035] Figure 2 for Figure 1 Sectional view at point AA;

[0036] Figure 3 for Figure 1 Sectional view at point BB.

[0037] In the diagram: 1. Centerline of sand mold width direction; 2. Centerline of gear hub; 3. Horizontal runner; 4. Ingate; 5. Centerline of sand mold length direction; 6. Gear hub; 7. Riser; 8. Vent hole; 9. Sand core; 10. Sand core vent hole; 11. Internal chill; 12. Bottom chill; 13. Top structure of sprue; 14. Sprue; 15. Upper sand mold overlap structure; 16. Filter plate; 17. Lower sand mold overlap structure; 18. Lower sand mold horizontal runner; 19. Sprue recess. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments (for ease of description and understanding, hereinafter referred to as...). Figure 2 (The above is described above). Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0039] Please see Figure 1-3 This invention provides a technical solution: a casting method for a QT700-3 gear hub in the as-cast state, comprising the following steps:

[0040] Step 1: Determine the placement of gear hub 6 within the sand mold with the smaller opening facing down and the larger opening facing up;

[0041] Step 2: Determine one gear hub 6 per pattern, that is, place one gear hub 6 in the sand mold of each sand box. The center of the gear hub 6 is on the center line 5 of the sand mold length direction and the center line 2 of the gear hub, and is located 43mm to one side of the center line 1 of the sand mold width direction.

[0042] Step 3: Determine the structure of riser 7. The riser 7 is designed to be integrated with the gear hub. The cross-section of riser 7 extends along the cross-section of the gear hub 6 in the direction of the large opening. The cross-section is Y-shaped. The slope of riser 7 is 5°. The height of riser 7 is one-third of the height of gear hub 6.

[0043] Step 4: Determine the parting method for casting gear hub 6 as horizontal parting along the top of the gear hub riser, dividing it into upper and lower types;

[0044] Step 5: Determine the gating system structure. The sprue 14 and gating runner 3 are located in the upper sand mold. To facilitate molten iron injection, a funnel-shaped top structure 13 is installed at the top of the sprue where it connects to the outside of the mold. The sprue 14 is divided into upper and lower parts. The upper part is a funnel-shaped open structure for injecting molten iron, and the lower part is conical, with a smaller cross-section near the parting line and a larger cross-section away from the parting line. The lower sand mold gating runner 18 has a lower sand mold overlapping structure 17 at its end. The end of the gating runner 3 near the sprue 14 has an upper sand mold overlapping structure 15. The cross-sectional dimensions of the upper sand mold overlapping structure 15 and the lower sand mold overlapping structure 17 are larger than the cross-sectional dimensions of the lower sand mold horizontal runner 18 and horizontal runner 3. Their cross-sectional area is more than twice that of the horizontal runner 3 to ensure that the flow rate of the molten iron does not affect the subsequent pouring system after passing through the filter plate 16. The pouring systems in the upper and lower sand molds are axially symmetrical with respect to the line connecting the center of the sprue and the center of the gear hub 6. There are four ingates 4, arranged in a ring at 90° intervals, forming an open ring design along the outer circle of the gear hub 6 on the parting surface. The center of the ring-shaped horizontal runner 3 is concentric with the center of the gear hub, and is divided into left and right sides. The two parts on the right are connected by a sprue 14 located at the midpoint where the extended lines of the two horizontal runners 14 intersect. The sprue 14 is not directly connected to the horizontal runner 3. A sprue recess 19 is designed at the corresponding position of the lower sand mold to buffer the molten iron scouring during the pouring process and stabilize the flow of molten iron. A filter 16 is installed at the lower sand mold position where the lower sand mold overlapping structure 17 intersects with the upper sand mold overlapping structure 15. The cross-section at the intersection of the lower sand mold overlapping structure 17 and the upper sand mold overlapping structure 15 is larger than the cross-section of the horizontal runner 3 at other positions. The sprue 14 is a cylindrical structure with an incline. The sprue 14 is small. The end cross-section is φ56mm. The lower sand mold is designed with a lower sand mold horizontal sprue 18 to connect the sprue 14 and the sprue socket 19. The ingate 4 is located on the lower sand mold and is arranged in a ring along the outer circle of the riser on the parting surface, evenly distributed within a 360° range. The ingate cross-section is trapezoidal, with a cross-section size of 40 / 45×12mm, which makes the molten iron filling more stable, avoids local heat concentration, and reduces its impact on the casting. The horizontal sprue 3 has a cross-section size of 32 / 40×40mm. The ingate 4 connects the horizontal sprue 3 and the riser 7. The gating system is semi-closed, and the gating system ratio is ΣF. 直 :ΣF 横 :ΣF 内 =1.2:1.4:1, with circular vent holes 8 arranged in a ring at the top of riser 7. The other end of the vent holes 8 is connected to the outside, which is used to discharge the air in the cavity during the pouring process. The pouring system in the upper sand mold and the lower sand mold is axially symmetrical with respect to the line connecting the center of the sprue 14 and the center of the gear hub 6.

[0045] Step Six: Determine the chill structure and placement. Place four bottom chills 12 at the bottom of the gear hub, evenly spaced at 360°. The gap between the bottom chills 12 is 20-30mm, and the thickness of each chill 12 is 40mm. Ten inner cavity chills 11 are placed evenly on the circumference of the machined tooth profile within the gear hub 6, with a gap of 20-40mm between them. In this invention, the thickness of the inner cavity chills is 35mm. The circumferential position of the machined tooth profile within the gear hub 6... The inner cavity chills 11 are evenly distributed in a 360° ring on the top. The surface of the inner cavity chills 11 that contacts the inner cavity sidewall of the gear hub 6 is arc-shaped, and the radius of the arc is the same as that of the inner cavity sidewall of the gear hub 6. They are directly attached to the inner cavity sidewall of the gear hub 6. The bottom of the inner cavity chills 11 is 15-25mm away from the bottom surface of the inner cavity of the gear hub 6. In this invention, the distance is 20mm. The top of the inner cavity chills 11 is flush with or slightly higher than the final machining height of the gear hub 6. The thickness of the inner cavity chills 11 is close to or the same as the wall thickness of the gear hub 6. In this invention, the thickness of the inner cavity chills 11 is 35mm. The solidification method of the casting is solidification in a bottom-up sequence.

[0046] Step 7: Determine the sand core venting structure. A hollow sand core venting hole 10 is designed at the center of the sand core 9, open on the side near the upper sand mold. The cross-sectional shape of the hollow structure can be circular, square, or elliptical, etc. The cross-sectional shape used in this invention is circular. The height of the hollow structure has an inclination, and the height dimension is related to the height of the gear hub 6 and the riser. In order to maximize the discharge of gas in the sand core, the size can be as large as possible without affecting the sand core structure. In this invention, the bottom of the hollow structure is 50mm away from the bottom of the inner cavity of the gear hub 6. At the position of the upper sand mold corresponding to the sand core venting hole 10, a hollow structure with a cross-sectional dimension larger than that of the sand core venting hole 10 is designed so that the sand core venting hole 10 is directly connected to the outside. After the gear hub 6 is closed with the upper sand mold, a pressure iron is placed on the top of the upper sand mold to prevent the mold from lifting and the fire from escaping during the casting process.

[0047] Step 8: Mold and tooling fabrication. One integral casting sand box is used for both the upper and lower sand boxes. The tooling used during the production of the upper and lower sand molds is also an integral casting sand box.

[0048] Step Nine: Production of sand cores, upper sand molds, and lower sand molds. All materials are furan resin self-hardening sand. The space between the sand box and the mold is filled with furan resin sand. After the furan resin self-hardening sand hardens, the sand box is removed, forming the upper and lower shapes with the sand box on the outside.

[0049] Step 10: During the loading and unloading process, after the sand core is loaded into the lower sand mold, the upper sand mold is closed. Dry sand without resin and hardener is filled from the open position of the upper sand mold corresponding to the air outlet 10 of the sand core. The upper surface of the dry sand is flush with or slightly lower than the surface of the upper sand mold to prevent molten iron from entering the hollow structure in the middle of the sand core during the pouring process. After the box is closed, a pressure iron is placed on top of the upper sand mold.

[0050] Step 11: Smelting. Use a medium-frequency induction furnace to smelt the molten iron at a temperature of 1500–1530℃. The raw materials include pig iron, scrap steel, recycled materials, and ferromanganese. Control the chemical composition of the molten iron in the furnace as follows: C: 3.6%–3.7%, Si: 1.4%–1.5%, Mn: 0.4%–0.6%, Cu: 0.6%–0.7%, Mo: 0.15%–0.2%, P < 0.04%, S < 0.02%.

[0051] Step 12: Tapping and Pouring of Molten Iron. After the molten iron has melted, tap it from the furnace to the ladle at 1470–1500℃. Add 1.1%–1.5% of rare earth magnesium-silicon-iron alloy spheroidizing agent, 0.4%–0.8% of high-calcium barium inoculant, and a covering agent by weight of the tapped molten iron to the bottom of the ladle beforehand. The pouring temperature is 1350±10℃, and the pouring time is 10–15 seconds. During the pouring process, use rare earth silicon inoculant with a particle size of 0.2–0.7 mm for in-flow inoculation. The amount of in-flow inoculant added is 0.07%–0.1% of the weight of the poured molten iron.

[0052] Step 13: Sand removal. 30 minutes after pouring, start removing the casting from the mold. After removing the casting from the mold, spray water mist to cool it. Spray water mist until the casting turns dark red. Then, air cool the casting.

[0053] Step Fourteen: Cleaning. Clean the casting structure thoroughly, including the gating system, risers, and vents.

[0054] Step 15: Check the hardness of the gear hub. When the hardness is 310HBW, temper it using process parameters of 500-520℃ and holding for 2-4 hours.

[0055] When the hardness is 310-330 HBW, tempering is performed using process parameters of 550-560℃ and holding for 2-4 hours.

[0056] When the hardness is greater than 330HBW, tempering is performed using process parameters of 580-600℃ and holding for 2-4 hours.

[0057] Step Sixteen: Shot blasting and inspection.

[0058] In order to avoid thermal effects between gear hubs during casting and cooling, and to reduce internal defects in the gear hubs caused by this, one gear hub 6 is placed in the same sand mold during use.

[0059] The riser 7 is designed to be integrated with the gear hub 6 and extends along the large opening direction of the gear hub 6. Its cross-section is Y-shaped, which can ensure that the molten iron forms a uniform feeding effect on the entire gear hub 6.

[0060] A filter plate 16 is placed horizontally at the lower sand mold position where the lower sand mold overlapping structure 17 intersects with the horizontal runner 3. This effectively filters impurities in the molten iron and prevents impurities from appearing in the gear hub due to impurities in the molten iron.

[0061] The cross-section of the sprue at the location where the filter plate 16 is placed is larger than the cross-section of the sprue 3 at other locations, ensuring that the flow of molten iron through the filter plate 16 does not affect the flow rate in the subsequent casting system;

[0062] The top of the sprue 14 for injecting molten iron is funnel-shaped, eliminating the need for a pouring cup and facilitating accurate injection of molten iron during the pouring process, thus reducing molten iron spillage.

[0063] The inner sprue 4 is arranged in a ring around the outer circle of the gear hub 6 and is evenly distributed within a 360° range, which makes the filling of the molten iron more stable, avoids local heat concentration, and reduces its impact on the casting.

[0064] The top of the riser 7 is designed with vent holes 8 arranged in a ring, which can smoothly discharge the air in the cavity during the pouring process and avoid incomplete pouring or porosity defects in the gear hub 6 due to poor venting.

[0065] A bottom chill 12 is placed at the bottom of the gear hub 6. The bottom chill 12 is evenly distributed within a 360° range at the bottom, which can effectively cool the gear hub 6 after casting. When used in conjunction with the riser 7, it realizes the sequential solidification method of the gear hub 6 from bottom to top, ensuring the internal quality of the gear hub 6.

[0066] An inner cavity chill 11 is placed on the circumference of the tooth profile machined in the inner cavity of the gear hub 6, and is evenly distributed in a ring within a 360° range. The inner cavity chill 11 is directly attached to the inner cavity sidewall of the gear hub 6, which ensures the internal quality of the tooth profile and avoids casting defects such as shrinkage porosity and shrinkage holes at the tooth profile position.

[0067] The center of the sand core is designed as a sand core vent 10, which has a hollow structure and is open on the side near the upper sand mold. A hollow structure is designed at the position of the upper sand mold corresponding to the hollow structure of the sand core, so that the hollow structure of the sand core vent 10 is directly connected to the outside. This ensures that the gas generated by the resin and curing agent in the sand core under high temperature during the iron pouring process can be smoothly discharged to the outside, and avoids gas from entering the iron and causing porosity defects in the gear hub.

[0068] The upper and lower sand boxes are integrally cast sand boxes. High-hardness furan resin sand is used between the sand box and the mold, which improves the rigidity of the mold and thus improves the internal density of the gear hub, further ensuring the internal quality of the gear hub.

[0069] After the gear hub is assembled, dry sand is filled into the hollow structure of the sand core to prevent molten iron from entering the hollow structure in the middle of the sand core during the casting process. This avoids the gas generated by the sand core from not being able to escape smoothly, which would cause porosity defects in the gear hub 6. It also avoids wasting molten iron and thus saves production energy.

[0070] The sand mold on the gear hub 6 can be filled by placing a pressure iron on top. The pressure iron replaces the box clamps or bolts for fastening, which reduces the workload and labor intensity of the operator. It also prevents the box from being lifted and the fire from escaping during the pouring process.

[0071] This invention provides a gear hub casting method that meets the performance requirements of QT700-3 material in the as-cast state and has a body hardness of 250-300 HBW. This method can effectively filter impurities in molten iron, reduce inclusions and porosity defects in the gear hub 6, and improve the internal quality of the gear hub 6. The gear hub produced using this invention has a simple operation process, stable product quality, and a high pass rate.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A casting method for a QT700-3 gear hub in the as-cast state, characterized in that: Includes the following steps: Step 1: Determine the placement of the gear hub within the sand mold with the smaller opening facing down and the larger opening facing up; Step 2: Determine that there is one gear hub per sand mold in each sand box; Step 3: Determine the riser structure. The riser is designed to be integrated with the gear hub. The riser cross-section extends along the cross-section of the gear hub in the direction of the large opening, and the cross-section is Y-shaped. Step 4: Determine the parting method for gear hub casting as horizontal parting along the top of the gear hub riser, dividing it into upper and lower types; Step 5: Determine the gating system structure. The sprue and runner are located in the upper sand mold. The top of the sprue, where it connects to the outside of the mold, has a funnel-shaped structure. On the parting surface, it forms an open ring along the outer circle of the gear hub. The center of the annular runner is concentric with the center of the gear hub, divided into left and right parts. The sprue is located at the midpoint where the extended lines of the two runner parts intersect. The sprue and runner are not directly connected. A corresponding sprue recess is designed in the lower sand mold. The ingate is located on the lower sand mold, arranged in a ring along the outer circle of the riser on the parting surface, evenly distributed within a 360° range. The ingate connects the runner and riser. A semi-closed gating system is selected, with a gating system ratio of ΣF. 直 :ΣF 横 :ΣF 内 =1.2:1.4:1, with circular vents arranged in a ring at the top of the riser. The other end of the vents is connected to the outside to expel air from the cavity during the pouring process. Step Six: Determine the structure and placement of the chills. Place a bottom chill at the bottom of the gear hub. Place inner chills arranged in a 360° ring around the circumference of the gear hub where the teeth are machined. The surface of the inner chills that contacts the inner wall of the gear hub is arc-shaped, with the radius of the arc matching that of the inner wall of the gear hub. The casting solidifies in a bottom-up sequence. Step 7: Determine the sand core venting structure. A hollow sand core venting hole is designed at the center of the sand core, with the side closest to the upper sand mold open. At the position of the upper sand mold corresponding to the sand core venting hole, a hollow structure with a cross-sectional dimension larger than that of the sand core venting hole is designed, so that the sand core venting hole is directly connected to the outside. Step 8: Mold and tooling fabrication; each sand box is made from a single integral casting. Step Nine: Production of sand cores, upper sand molds, and lower sand molds, all made of furan resin self-hardening sand; Step 10: During the loading and unloading process, after the sand core is loaded into the lower sand mold, the upper sand mold is closed. Dry sand without resin and hardener is filled into the open position of the upper sand mold corresponding to the air outlet of the sand core. After the box is closed, a pressure iron is placed on top of the upper sand mold. Step 11: Smelting. Use a medium-frequency induction furnace to smelt the molten iron at a temperature of 1500–1530℃. The raw materials include pig iron, scrap steel, recycled materials, and ferromanganese. Control the chemical composition of the molten iron in the furnace as follows: C: 3.6%–3.7%, Si: 1.4%–1.5%, Mn: 0.4%–0.6%, Cu: 0.6%–0.7%, Mo: 0.15%–0.2%, P < 0.04%, S < 0.02%. Step 12: Tapping and Pouring of Molten Iron. After the molten iron has melted, tap it from the furnace to the ladle at 1470–1500℃. Add 1.1%–1.5% of rare earth magnesium-silicon-iron alloy spheroidizing agent, 0.4%–0.8% of high-calcium barium inoculant, and a covering agent by weight of the tapped molten iron to the bottom of the ladle beforehand. The pouring temperature is 1350±10℃, and the pouring time is 10–15 seconds. During the pouring process, use rare earth silicon inoculant with a particle size of 0.2–0.7 mm for in-flow inoculation. The amount of in-flow inoculant added is 0.07%–0.1% of the weight of the poured molten iron. Step 13: Sand removal. 30 minutes after pouring, start removing the casting from the mold. After removing the casting from the mold, spray water mist to cool it. Spray water mist until the casting turns dark red. Then, air cool the casting. Step Fourteen: Cleaning. Clean the casting structure thoroughly, including the gating system, risers, and vents. Step 15: Check the hardness of the gear hub. When the hardness is 310HBW, temper it using process parameters of 500-520℃ and holding for 2-4 hours. When the hardness is 310-330 HBW, tempering is performed using process parameters of 550-560℃ and holding for 2-4 hours. When the hardness is greater than 330HBW, tempering is performed using process parameters of 580-600℃ and holding for 2-4 hours. Step Sixteen: Shot blasting and inspection.

2. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step two, the center of the gear hub is located on the center line of the sand mold in the length direction and the center line of the gear hub, and is located 43mm to one side of the center line of the sand mold in the width direction.

3. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step three, the height of the riser is one-third of the height of the gear hub.

4. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step five, the sprue is a cylindrical structure with an incline. The cross-sectional dimension of the small end of the sprue is φ56mm. The lower sand mold is designed with a lower sand mold horizontal runner to connect the sprue and the sprue socket. The end of the lower sand mold horizontal runner is designed with a lower sand mold overlapping structure. The end of the horizontal runner near the sprue is designed with an upper sand mold overlapping structure. The cross-sectional dimensions of the upper sand mold overlapping structure and the lower sand mold overlapping structure are larger than the cross-sectional dimensions of the lower sand mold horizontal runner and the horizontal runner. The gating system in the upper sand mold and the lower sand mold is axially symmetrical with respect to the line connecting the center of the sprue and the center of the gear hub. There are four ingates, arranged in a ring at 90° intervals.

5. The casting method of a QT700-3 gear hub in the as-cast state according to claim 4, characterized in that: In step five, the sprue is divided into upper and lower parts. The upper part is a funnel-shaped open structure for injecting molten iron, and the lower part is conical with a smaller cross section on the side closer to the parting surface and a larger cross section on the side farther from the parting surface. A filter is provided at the lower sand mold position where the lower sand mold overlap structure intersects with the upper sand mold overlap structure, and the cross section at the intersection of the lower sand mold overlap structure and the upper sand mold overlap structure is larger than the cross section of the sprue at other positions.

6. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step six, four bottom chills are placed, evenly arranged at 360° on the bottom, with a gap of 20-30mm between them and a thickness of 40mm. Ten inner cavity chills are placed, evenly distributed on the circumference of the gear hub's machined tooth profile, with a gap of 20-40mm between them.

7. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step seven, after the gear hub is fitted with the upper sand mold, a pressure iron is placed on top of the upper sand mold.

8. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step eight, the tooling used during the production of the upper and lower sand molds is an integral casting sand box.

9. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step nine, furan resin sand is used to fill the space between the sand box and the mold. After the furan resin hardens from the hard sand, it forms the upper and lower shapes with the sand box on the outside.

10. The casting method of a QT700-3 gear hub in the as-cast state according to claim 1, characterized in that: In step ten, the surface of the dry sand should not be higher than the surface of the upper sand mold.

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