Casting method of isothermal quenching nodular cast iron subway wheel

Abstract

The invention relates to a casting method of an isothermal quenching nodular cast iron subway wheel, and belongs to the technical field of casting. Comprising the steps of manufacturing a subway wheel casting mold; the method comprises the following steps: firstly, manufacturing a subway wheel metal mold comprising a pouring system, and placing a graphite block and a heating and insulating riser at a mold position corresponding to a large-thickness part of a subway wheel casting or a high-structure-compactness part of the wheel casting; then, an iron mold, graphite and precoated sand composite subway wheel pouring mold is manufactured through a core making machine; proportioning the components of the casting liquid and smelting the components; the smelted pouring liquid is subjected to a spheroidizing inoculation reaction, after the spheroidizing inoculation reaction is completed, the temperature is controlled, pouring is conducted on the manufactured pouring mold, and stream inoculation is adopted in the pouring process; and after pouring is completed, isothermal quenching post-treatment is conducted on the subway wheel casting. According to the casting technology, the solidification process of the casting is controlled to be sequential solidification, it is guaranteed that no isolated hot spot exists in the solidification process of the casting, and the quality of the casting with high internal density is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of casting, in particular to a casting method for an isothermal quenching ductile iron subway wheel. Background Art

[0002] The manufacturing technology of high-speed wheels is an important factor affecting the development of my country's railways. At present, rail transit vehicle wheels are mainly divided into cast steel wheels and rolled steel wheels. Among them, domestic freight cars mainly use cast steel wheels, which are cast by graphite sand coating process; subways mainly use rolled steel wheels, which are formed by hot rolling.

[0003] The integral train rolled steel wheel is formed by rolling or casting a steel wheel blank, which has many processes and high energy consumption. In the prior art, when producing lightweight austempered ductile iron subway wheels, this type of subway wheel is different from the traditional single-web rolled steel wheel. It adopts a double-spoke hollow design with a number of spoke holes on each side; the hub and rim structure are basically the same as the traditional single-spoke rolled steel wheel, but due to the double-spoke hollow design, the plate wall thickness is thin, but the density of the casting is high, and the integral rolling forming process cannot produce a ductile iron subway wheel that meets the design requirements. The technical requirements for lightweight austempered ductile iron subway wheels refer to "GB / T 24733-2009 Austempered Ductile Iron Castings", lightweight austempered ductile iron subway wheel material QTD 900-8, in the as-cast, partially machined or final machined conditions, the casting surface is subjected to magnetic particle inspection according to ISO 4986, and meets the level 1 requirements specified in the standard. The lightweight austempered ductile iron subway wheel has a complex structure, the spoke wheel profile size is φ840*178mm, the theoretical weight is 290Kg, the local thickness of the wheel casting is large, resulting in a large heat node, and the graphite mold sand coating process is used for casting, which is difficult to compensate for shrinkage and is prone to shrinkage defects. In order to prevent the subway wheel from failing under the impact of load, excellent comprehensive mechanical properties are required, which not only requires high strength but also high plasticity, resulting in the existing lightweight austempered ductile iron subway wheel castings being difficult to produce, with low yield and high cost. Therefore, a casting method for austempered ductile iron subway wheels is needed to solve the problems of difficulty in production, low yield and high production cost in the production of austempered ductile iron subway wheels in the prior art. Summary of the invention

[0004] The object of the present invention is to provide a method for casting an austempered ductile iron subway wheel to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a casting method for an isothermal quenching ductile iron subway wheel, comprising the following casting steps: S1. Making a subway wheel casting mold; first, making a subway wheel metal mold including a casting system, placing graphite blocks and heat-generating and heat-insulating risers at the mold positions corresponding to the parts of the subway wheel casting with large thickness or the parts of the wheel casting with high density; then making a composite subway wheel casting mold of iron mold + graphite + coated sand by a core making machine; S2, proportioning the casting liquid components and melting the components; S3, subjecting the smelted pouring liquid in S2 to a spheroidizing inoculation reaction, and after the spheroidizing inoculation reaction is completed, the pouring liquid is poured into the pouring mold made in S1 under temperature control, and flow inoculation is adopted during the pouring process; S4. After the pouring is completed, the subway wheel casting is subjected to isothermal quenching post-treatment.

[0006] Preferably, in S1, a subway wheel casting mold is manufactured; first, a subway wheel metal mold including a casting system is manufactured, and graphite blocks and heat-generating and heat-insulating risers are placed at mold positions corresponding to locations where the subway wheel casting has a large thickness or a location where the wheel casting has a high density; then, a composite subway wheel casting mold of iron mold + graphite + coated sand is manufactured by a core making machine, specifically: S10, firstly designing a combined subway wheel mold including a casting system according to the subway wheel structure and casting requirements, wherein the combined subway wheel mold includes a metal outer mold and a mud core mold; and using the mud core mold to form a subway wheel casting mud core using a core making machine; S11. According to the casting process, a pouring system, a gas outlet rod, a graphite block and a heating and heat-insulating riser are placed on the metal outer mold, and a layer of coated sand tire layer is formed in the mold cavity of the metal outer mold by a hot core machine to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; S12, flow coating the subway wheel casting core obtained in S10 and the casting molding parts of the composite subway wheel casting outer mold of iron mold + graphite + coated sand obtained in S11; S13. After the coating is dried, the subway wheel casting mud core and the composite subway wheel casting outer mold of iron mold + graphite + coated sand are assembled, and the mud core positioning is detected to form a subway wheel casting mold assembly; the molding cavity of the subway wheel casting mold assembly is a subway wheel rim downward structure, then the molding cavity is cleaned, a filter assembly is placed in the pouring channel of the pouring system, and the pouring system is connected to the subway wheel casting mold assembly cavity, and a pouring cup is attached to the pouring gate of the pouring system, and finally a heat-generating and heat-insulating riser is installed, and an overflow exhaust sand mold is attached to the upper side of the heat-generating and heat-insulating riser to form a composite subway wheel casting mold of iron mold + graphite + coated sand.

[0007] Preferably, in S10, the metal outer mold includes an upper outer mold, a lower outer mold and a locking mechanism, and after the upper outer mold and the lower outer mold are molded together, they are connected as a whole through the locking mechanism; the upper outer mold and the lower outer mold are made of ductile iron, and are integrally cast and processed by a metal outer mold mold; the upper outer mold and the lower outer mold are made into a casting upper outer mold and a casting lower outer mold of a composite subway wheel casting outer mold of iron mold + graphite + coated sand by a core making machine in a one-mold-one-piece manner, and the parting surfaces between the two are respectively provided with positioning components; The cement core mold comprises a wheel spoke plate hole mold and a wheel axle hole sand-insulated cold iron mold; a first cement core is made by the wheel spoke plate hole mold using a core making machine, and a wheel axle hole sand-insulated cold iron second cement core is made by the wheel axle hole sand-insulated cold iron mold; the first cement core and the second cement core with sand-insulated cold iron constitute the subway wheel casting cement core; a first anti-mistake positioning component is provided on the cement core surface of the first cement core facing the casting upper outer mold and the casting lower outer mold, and a second anti-mistake positioning component is respectively provided on the casting upper outer mold and the casting lower outer mold at the position of the first anti-mistake positioning component, so as to be used for positioning and installing the first cement core with the casting upper outer mold and the casting lower outer mold.

[0008] Preferably, in S10, when the subway wheel casting core is made by the core mold using the core making machine, the core mold includes an upper core mold and a lower core mold, and the two molds are combined to form a sand shooting cavity with a wheel spoke plate horizontal surface facing upward and an inclined surface facing downward; the sand shooting nozzle on the core mold is located in the middle of the elliptical core head on the upper side of the casting core; the movable mold ejector rod located on the lower side of the core is located in the middle of the lower core head; The cast clay core is made by a cold core machine. The SiO2 content of the raw sand is ≥92%, the particle size is 50 / 100 mesh, the three-sieve concentration rate is ≥85%, and the pH value is 6.5~7.2; the resin binder uses a two-component resin, model XLI-318 and XLII-618; the resin binder is added in an amount of 1.3~1.5% of the sand weight, and the two components are proportioned as XLI-318: XLI-618=55%:45%; in the sand mixing process, the stirring time is 90S~120S in summer and 150S~180S in winter; when the core is made by the cold core machine, the core making parameters are: sand shooting once, sand shooting time 8~10S; sand shooting pressure 0.55~0.65MPa; amine addition time 10~20S.

[0009] Preferably, in S11, according to the casting process, a pouring system, an air outlet rod, a graphite block and a heating and heat-insulating riser are placed on the metal outer mold, and a layer of coated sand tire layer is formed in the mold cavity of the metal outer mold by a hot core machine to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand. When making the metal outer mold, a graphite block and a heating and heat-insulating riser installation groove are reserved at the location of the metal outer mold where the thickness of the subway wheel casting is large or the location where the wheel casting has a high density of tissue, and a plurality of heating pipes are pre-embedded in the metal outer mold; the heating and heat-insulating riser is formed by a riser mold, and after the metal outer mold is formed, the graphite block and the heating and heat-insulating riser are assembled into one with the metal outer mold, and then sand is shot by a hot core machine to form a coated sand tire layer in the metal outer mold cavity to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; When the coated sand tire layer is made in the metal outer mold cavity, the coated sand particle size is 70 / 140 mesh, the temperature is 180~200℃, the insulation time is 5~5.5 min, and the strength of the coated sand at room temperature is 3.5~5.0MPa; the thickness of the coated sand tire layer is: the thickness of the sand layer at the wheel spoke position is 8mm, the thickness of the sand layer at the casting system position is 20mm, and the thickness of the sand layer in the heating and insulation riser area is 25mm.

[0010] Preferably, in S13, after the coating is dried, when the subway wheel casting mud core and the composite subway wheel casting outer mold of iron mold + graphite + coated sand are assembled, the first anti-mistake positioning component is four columnar protrusions; the four columnar protrusions are arranged in a cross shape on the surface of the first mud core, and the cross-sections of three of the columnar protrusions are circular structures, and the other columnar protrusion is a square structure; the second anti-mistake positioning component is a positioning hole on the casting upper outer mold and the casting lower outer mold that is compatible with the columnar protrusions, and the positioning hole that is compatible with the circular columnar protrusion is an elliptical structure in cross section, and the positioning hole that is compatible with the square columnar protrusion is a rectangular structure in cross section; the present invention arranges four columnar protrusions distributed in a cross shape on the first mud core and the positioning holes that are compatible with the upper outer mold and the lower outer mold as the positioning installation of the first mud core and the upper outer mold and the lower outer mold. One of the four columnar protrusions is set to have a square cross-section structure to achieve positioning and error prevention purposes, so as to ensure the rapid positioning and installation of the first mud core. In addition, in order to avoid excessive positioning caused by setting four columnar protrusions, the present invention sets the positioning hole adapted to the circular columnar protrusion to have an elliptical cross-section structure, and sets the positioning hole adapted to the square columnar protrusion to have a rectangular cross-section structure, so as to avoid excessive positioning.

[0011] When closing the box, firstly, the first mud core and the lower casting outer mold are positioned and assembled, and the positioning and matching accuracy of the first mud core and the lower casting outer mold is checked by a conformal inspection fixture, and then the second mud core is positioned and assembled with the lower casting outer mold through the cylindrical hole position, and then the upper casting outer mold and the lower casting outer mold are assembled by the positioning component of the parting surface, and locked by the locking mechanism to form a subway wheel casting mold combination; before closing the mold, graphite blocks are embedded in the upper casting outer mold and the lower casting outer mold, and then the heating and heat-insulating riser is installed in the reserved riser installation groove, and the overflow insulation sand sleeve is pasted on the top of the riser; the overflow insulation sand sleeve is provided with an exhaust hole in the middle that is aligned with the exhaust hole on the top of the heating and heat-insulating riser, and a molten iron retaining ring is installed on the top of the overflow insulation sand sleeve.

[0012] Preferably, the pouring system is a bottom pouring pouring system with a semi-closed structure and several levels of filtering components are arranged inside; the pouring system is provided with a straight runner, a cross runner and an ingrown runner, and the number of the ingrowns is several, and the several ingrowns are evenly spaced along the circumference of the casting cavity, and the ingrowns on both sides are arranged at an opposite angle to the cross runners to control the molten iron initially entering the cavity to converge on the runner side, and then flow together away from the runner side to ensure the continuity of the molten iron; the straight runner and the ingrown runner are connected by cross runners on both sides; the ratio of the cross-sectional areas of the straight runner, the cross runner and the ingrown runner is 1:1.5:0.8.

[0013] Preferably, in S2, when the proportioning of the pouring liquid components is carried out and the components are smelted, the charge for smelting the pouring liquid includes pig iron, scrap steel, recycled materials, ferromolybdenum, ferromanganese, ferrosilicon, nickel plates and copper plates; an electric furnace is used for charge smelting, and after melting, a sample in front of the furnace is taken for component element analysis, and then the element content is adjusted according to the analysis results; the temperature in the smelting furnace is 1520~1550℃; the molten iron is poured into a spheroidizing bag for spheroidization and inoculation treatment, and after the treatment is completed, it is transferred to a casting bag for pouring, and the casting temperature is controlled at 1350~1370℃.

[0014] Preferably, before pouring in S3, the smelted casting liquid is poured into a spheroidizing bag, and a punching spheroidizing process is adopted. The spheroidizing bag is a pit-type structure, and a spheroidizing agent, an inoculant, a covering agent and a pressing plate are added into the pit; the spheroidizing agent adopts a yttrium-based heavy rare earth-magnesium alloy spheroidizing agent, the addition ratio is 1.1%~1.3%, the particle size is 5~25mm, and the composition is: Si: 40~50%, Mg: 5.5~7.5%, RE: 1.0~2.5%, Ca: 2.0~3.0%, and the rest is Fe; when inoculating the casting liquid, a three-time inoculation method is adopted, and a composite inoculant is used, and the composition of the composite inoculant is: Si: 70~75%, Ca: 1~1.5%, Al≤1%, the rest is Fe; this can retain the advantages of the two spheroidizing elements, rare earth and magnesium, which complement each other. Due to the purification and anti-interference effect of rare earth, a lower residual magnesium content can obtain spherical graphite with better roundness; during inoculation, 0.4% to 0.6% of the mass of the molten iron is placed on the spheroidizing agent for one inoculation; after the spheroidization reaction is completed, the molten iron in the spheroidizing ladle is transferred to the pouring ladle, and 0.4% to 0.6% of the mass of the molten iron is added to the molten iron during the pouring process for a second inoculation; during the pouring process, the inoculation is carried out with the flow, and the content of the inoculant is 0.05% to 0.1% of the mass of the molten iron, and the inoculation is carried out three times. Through the three-time inoculation method, graphitization is promoted, and graphite balls with fine and high roundness are obtained, while free cementite is eliminated and the eutectic group is refined.

[0015] Preferably, in S4, after pouring is completed, the casting is kept warm in the mold for more than 12 hours, unpacked, the residual coated sand in the mold is cleaned, the pouring system and the riser are cut and removed, and a shot blasting is performed and then an isothermal quenching heat treatment is performed; When the casting is subjected to isothermal quenching heat treatment, the casting is subjected to rough grinding, stress relief annealing heat treatment, fine grinding, fine polishing, rough machining, isothermal quenching heat treatment and fine machining; when the stress relief annealing heat treatment is performed, the casting is heated to 610±20℃, kept warm for 2~3 hours, and then air-cooled to room temperature; when the casting is subjected to rough machining, a 2mm fine machining allowance is reserved for isothermal quenching heat treatment. When the isothermal quenching heat treatment is performed, the component is heated to 900±20℃, kept warm for 2~3 hours, and then cooled to 360±10℃, kept warm for 2~3 hours, and then air-cooled to room temperature. Beneficial Effects

[0016] The present invention adopts the casting process of "iron mold + graphite + coated sand" to control the solidification process of the casting to sequential solidification, ensuring that there is no isolated heat node in the solidification process of the casting, and obtaining the casting quality with high internal density. This solves the problem that the prior art uses the graphite mold coated sand casting process, which has the problem of difficulty in process shrinkage compensation and easy formation of shrinkage and shrinkage defects.

[0017] The present invention adopts a bottom pouring type semi-enclosed structure pouring system, and designs a reasonable cross-sectional area ratio of the sprue, runner and entgate. The entgate and the runner form a reverse angle to control the molten iron initially entering the mold cavity to merge on the runner side, and then flow together to the side away from the runner, ensuring the continuity of the molten iron and effectively avoiding cold shut casting defects away from the runner side; the molten iron can be filled in sequence from top to bottom, and after the filling is completed, a temperature gradient is formed from near to far and from top to bottom, and the temperature gradually decreases, and the upper plane of the casting is not prone to cold shut defects. The pouring system is arranged with a multi-stage filtration system to improve the purity of the molten iron and minimize the slag inclusion defects in the casting, thereby meeting the magnetic particle flaw detection of the casting and meeting the Level 1 requirements specified in the standard.

[0018] When making a subway wheel casting mold, the present invention first makes a subway wheel metal mold including a casting system, and the metal mold includes a metal outer mold and a mud core mold, and places a heating and heat-insulating riser and a graphite block at the mold position corresponding to the part of the subway wheel casting with large thickness or the part of the wheel casting with high density, such as the wheel rim part, to improve the density of the wheel rim part. In addition, the mud core mold of the present invention is provided with a sand-insulating chiller to form a wheel hub, which improves the cooling rate of the casting at the wheel hub, improves the density of the casting, and meets the magnetic particle flaw detection requirements of the molded casting.

[0019] The present invention adopts a yttrium-based heavy rare earth-magnesium alloy spheroidizing agent and a three-time inoculation spheroidizing inoculation treatment process when proportioning the casting liquid components and performing component smelting, thereby solving the problems of low roundness and small number of graphite balls at thick wall portions of subway wheel castings and poor comprehensive mechanical properties of strength and plasticity after heat treatment.

[0020] When making the casting clay core of the present invention, an integral molding process is adopted, and a cold core machine is used to make the core, thereby improving the compactness of the sand mold and improving the consistency of the roughness of the wheel surface; anti-mistake positioning components are provided on both sides of the first clay core to perform anti-mistake positioning, thereby ensuring the positioning accuracy of the clay core and the metal outer mold, ensuring the accuracy of the wheel casting, and reducing the dynamic imbalance of the casting.

[0021] After the casting of the present invention is formed, it undergoes stress relief annealing and isothermal quenching heat treatment to improve the mechanical properties of the wheel casting. Compared with carbon steel and low alloy steel, it has good fatigue resistance and better wear resistance than steel with the same hardness. In addition, the isothermal quenched ductile iron has excellent comprehensive mechanical properties, light weight, good wear resistance, good fatigue resistance, good noise reduction and vibration reduction, and is an ideal choice for rail vehicle wheel materials. It is expected to alleviate the current problem of wheel out-of-roundness and extend the service life of the wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic structural diagram of an austempered ductile iron subway wheel according to an embodiment; Figure 2is a schematic structural diagram of a first clay core of an embodiment; Figure 3 Schematic diagram of sand shooting of the first clay core of the embodiment; Figure 4 It is a structural schematic diagram of the upper outer mold of the embodiment; Figure 5 A schematic diagram of the structure of the upper outer mold of the embodiment for making a coated sand tire layer; Figure 6 It is a structural schematic diagram of the lower outer mold of the embodiment; Figure 7 A schematic diagram of the structure of the lower outer mold of the embodiment for making a coated sand tire layer; Figure 8 It is a schematic diagram of positioning detection of the casting mud core and the lower outer mold of the embodiment; Fig. 9 It is a structural schematic diagram of a subway wheel casting mold assembly according to an embodiment; Fig.10 A process diagram of stress relief annealing heat treatment of a casting in an embodiment; Fig.11 The figure is a process diagram of isothermal quenching heat treatment of a casting in an embodiment. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments.

[0024] The schematic diagram of the structure of the isothermal quenching ductile iron subway wheel casting of the present invention is as follows Figure 1As shown, structure 1 in the figure is the wheel rim. Structure 2 is the wheel rim part, which is the key part where the wheel directly contacts the vehicle track. In order to ensure the safety of vehicle operation, the microstructure density here is extremely high, and magnetic traces are not allowed to appear during magnetic particle flaw detection. During ultrasonic flaw detection, defects exceeding level 1 are not allowed. The heat node here is large and difficult to compensate for shrinkage. The wall thickness here is large, which is prone to problems such as poor spheroidization and incubation decline. Structure 3 is a double-sided spoke plate, which is a thin-walled area. It solidifies preferentially during the solidification process here, and is prone to forming isolated heat nodes, which are difficult to compensate for shrinkage. This embodiment improves the quality of the casting by using a heating and heat-insulating method with a graphite block on the mold corresponding to the rim part. Structure 5 is the hub part, which is directly connected to the axle. In order to ensure the matching accuracy with the axle, the microstructure density here is extremely high, and magnetic traces are not allowed to appear during magnetic particle flaw detection. During ultrasonic flaw detection, defects exceeding level 1 are not allowed. In order to improve the casting quality at the wheel hub, this embodiment sets a sand-insulating chilled iron as the second mud core on the mold at the wheel hub position, and sets a heating riser and a graphite block casting method. Structure 4 is a spoke hole on the spoke. Since it is opened on the spoke, the spoke between the spoke holes is a thin-walled area, which solidifies first during the solidification process and is easy to form an isolated heat node. In addition, the spoke holes are set at intervals. The technical requirements are that the overall density of the spoke is consistent, but the riser cannot be placed here, and the process shrinkage compensation is more difficult. Placing a chilled iron is easy to produce carbides and form hard points, resulting in inconsistent roughness of the spoke surface, causing the spoke to fail. This embodiment uses a first mud core to increase the compactness of the sand mold by setting the first mud core at the spoke position, which can improve the consistency of the roughness of the wheel surface.

[0025] See also Figure 2-Figure 11 In order to cast an austempered ductile iron subway wheel that meets the requirements, this embodiment provides an austempered ductile iron subway wheel casting method, comprising the following casting steps: S1. Making a subway wheel casting mold; first, making a subway wheel metal mold including a casting system, placing graphite blocks and heat-generating and heat-insulating risers at the mold positions corresponding to the parts of the subway wheel casting with large thickness or the parts of the wheel casting with high density; then making a composite subway wheel casting mold of iron mold + graphite + coated sand by a core making machine; S2, proportioning the components of the casting liquid and smelting the components; the charge for smelting the casting liquid in this embodiment includes pig iron, scrap steel, recycled materials, ferromolybdenum, ferromanganese, ferrosilicon, nickel plate and copper plate; weigh the charge according to the batching list and use a medium frequency induction furnace for smelting; add pig iron, scrap steel, recycled materials and other alloys to the medium frequency induction furnace in turn for smelting, and after melting, take the sample in front of the furnace, use a spectrometer and a carbon-sulfur analyzer to analyze the content of elements such as C, Si, Mn, P, S, Cu, Ni, and Mo in the molten iron, and adjust the content of each element in the molten iron in the furnace within the designed composition range according to the results; control the temperature in the furnace at 1520~1550℃, prepare to go out of the furnace and enter the spheroidization and inoculation process; pour the molten iron into the spheroidizing bag for spheroidization and inoculation treatment, and after the treatment is completed, transfer it to the casting bag for pouring, and the pouring temperature is controlled at 1350~1370℃; S3, pour the smelted pouring liquid in S2 into the spheroidizing bag, adopt the flushing spheroidizing process, the spheroidizing bag is a pit-type structure, add the spheroidizing agent, inoculant, covering agent and pressing plate into the pit at one time, so that the molten iron covers the spheroidizing agent to a certain height, and then the spheroidizing agent starts to react with the molten iron to spheroidize, which increases the uniformity of the reaction between the spheroidizing agent and the molten iron and improves the absorption rate of the spheroidizing agent; the spheroidizing agent uses yttrium-based heavy rare earth-magnesium alloy spheroidizing agent, the addition ratio is 1.1%~1.3%, the particle size is 5~25mm, and the composition is: Si: 40~50%, Mg: 5.5~7.5%, RE: 1.0~2.5%, Ca: 2.0~3.0% , the rest is Fe; when inoculating the pouring liquid, a three-time inoculation method is adopted, and a composite inoculant is used, the composition of the composite inoculant is: Si: 70-75%, Ca: 1-1.5%, Al≤1%, and the rest is Fe; when inoculating, 0.4%-0.6% of the mass of the molten iron out of the furnace is placed on the spheroidizing agent for one inoculation; immediately after the spheroidizing reaction is completed, the molten iron in the spheroidizing ladle is transferred to the pouring ladle, and 0.4%-0.6% of the mass of the molten iron out of the furnace is added to the molten iron during the pouring process, and a second inoculation is carried out; in the pouring process, the inoculant content is 0.05%-0.1% of the mass of the molten iron out of the furnace, and three inoculations are carried out; S4. After pouring, keep the casting in the mold for more than 12 hours, unpack it, clean the residual coated sand in the mold, cut and remove the pouring system and riser, and perform isothermal quenching heat treatment after shot blasting; When the casting is subjected to isothermal quenching heat treatment, the casting is subjected to rough grinding, stress relief annealing heat treatment, fine grinding, fine polishing, rough machining, isothermal quenching heat treatment and fine machining; when the stress relief annealing heat treatment is performed, the casting is heated to 610±20℃, kept warm for 2~3 hours, and then air-cooled to room temperature; when the casting is subjected to rough machining, a 2mm fine machining allowance is reserved for isothermal quenching heat treatment. When the isothermal quenching heat treatment is performed, the component is heated to 900±20℃, kept warm for 2~3 hours, and then cooled to 360±10℃, kept warm for 2~3 hours, and then air-cooled to room temperature.

[0026] In this embodiment, in S1, a subway wheel casting mold is manufactured; first, a subway wheel metal mold including a casting system is manufactured, and graphite blocks and heat-generating and heat-insulating risers are placed at mold positions corresponding to the thickest parts of the subway wheel casting or the parts with high structural density of the wheel casting; then, a composite subway wheel casting mold of iron mold + graphite + coated sand is manufactured by a core making machine, specifically: S10. First, a combined subway wheel mold including a casting system is designed according to the subway wheel structure and casting requirements. The combined subway wheel mold includes a metal outer mold and a mud core mold 8. The subway wheel casting mud core is made by using the mud core mold using a core making machine. The metal outer mold includes an upper outer mold, a lower outer mold and a locking mechanism (not shown) for locking the upper outer mold and the lower outer mold. The upper outer mold and the lower outer mold are made of QT500-7. In order to ensure the accuracy of the mold, a metal outer mold mold is used for integral casting and processing, and the metal outer mold mold includes an upper outer mold mold 60 and a lower outer mold mold 70. The upper outer mold and the lower outer mold are made into a casting upper outer mold 6 and a casting lower outer mold 7 of an iron mold sand-coated subway wheel casting outer mold by a hot core machine in a one-mold-one-piece manner, and the parting surface of the casting upper outer mold is provided with three cylindrical positioning pins 61, and the parting surface of the casting lower outer mold is provided with positioning pin holes 71 at positions corresponding to the positioning pins, so as to quickly position the casting upper outer mold and the casting lower outer mold when the mold is closed. The cement core mold of this embodiment includes a wheel spoke plate hole mold 80 and a wheel axle hole sand-insulated cold iron mold 81; a first cement core 82 is made by a triethylamine cold core machine through the wheel spoke plate hole mold, and a wheel axle hole sand-insulated cold iron second cement core 83 is made by a wheel axle hole sand-insulated cold iron mold; the first cement core and the sand-insulated cold iron second cement core constitute the subway wheel casting cement core; the first cement core is provided with four cross-distributed columnar protrusions on the cement core surface facing the casting upper outer mold and the casting lower outer mold, of which three columnar protrusions are The cross-section of one columnar protrusion is a columnar protrusion 820 with a circular structure, and the cross-section of the other columnar protrusion is a columnar protrusion 821 with a square structure. The square columnar protrusion is used to prevent wrong positioning, and the four columnar protrusions are respectively provided with positioning holes matched with the columnar protrusions on the casting upper outer mold and the casting lower outer mold. The positioning holes matched with the circular columnar protrusions have an elliptical structure in cross-section, and the positioning holes matched with the square columnar protrusions have a rectangular structure in cross-section, which are used for positioning and installing the first mud core with the casting upper outer mold and the casting lower outer mold.

[0027] In addition, when the subway wheel casting core is made by using the core mold of the present embodiment using the triethylamine cold core machine, the wheel spoke plate hole mold 80 includes an upper core mold 800 and a lower core mold 801, and after the two molds are combined, a sand shooting cavity with a wheel spoke plate horizontal surface facing upward and an inclined surface facing downward is formed between them. Figure 3 The sand-shooting nozzle 802 on the wheel spoke hole mold is located in the middle of the elliptical core head on the upper side of the first core to avoid the sand-shooting nozzle affecting the appearance quality of the core; the movable mold ejector rod 803 located on the lower side of the core is located in the middle of the lower side of the first core head to avoid damage to the core when the core is ejected from the movable mold, thereby improving the appearance quality of the core.

[0028] When making the core of the cast mud core of the present embodiment, the raw sand is selected from Dalin sand with SiO2 content ≥ 92%, and its parameters are: particle size is 50 / 100 mesh, fineness is 40-46, three-sieve concentration rate is ≥ 85%, pH value is 6.5-7.2, mud content is ≤ 0.25%, water content is ≤ 0.2%, loss on ignition is ≤ 0.2% and acid consumption is ≤ 5ml / 50g; and the resin binder adopts a two-component resin, model XLI-318 and XLII-618; the resin density of model XLI-318 is 1.05-1.15 g / cm3.25℃, and the resin density of XLII-618 is 1.05-1.20 g / cm3.25℃; the resin binder is added in a proportion of 1.3-1.5% of the sand weight, and the two resin components are divided into XLI-318: XLI-618=55%:45%; in the sand mixing process, the stirring time is 90S~120S in summer and 150S~180S in winter; when making cores through the cold core machine, the core making parameters are: sand shooting times once, sand shooting time 8~10S; sand shooting pressure 0.55~0.65MPa; amine (triethylamine) adding time 10~20S.

[0029] S11. According to the casting process, a pouring system, an air outlet rod, a graphite block and a heating and heat-insulating riser are placed on the metal outer mold, and a layer of coated sand tire layer is formed in the mold cavity of the metal outer mold by a hot core machine to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; in this embodiment, when making the metal outer mold, i.e., making the upper outer mold and the lower outer mold, a graphite block and a heating and heat-insulating riser installation groove 600 are reserved at the location of the metal outer mold where the thickness of the subway wheel casting is large or the location where the wheel casting has a high density of tissue, and a plurality of heating pipes are pre-embedded in the metal outer mold; the heating and heat-insulating riser 601 is formed by a riser mold, and after the metal outer mold is formed, the graphite block and the heating and heat-insulating riser are assembled with the metal outer mold as a whole, and then sand is shot by a hot core machine to form a coated sand tire layer in the metal outer mold cavity to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; When forming the coated sand tire layer in the metal outer mold cavity, the coated sand particle size is 70 / 140 mesh, the temperature is 180-200° C., the insulation time is 5-5.5 min, and the strength of the coated sand at room temperature is 3.5-5.0 MPa; the thickness of the coated sand tire layer is 8 mm at the wheel spoke position, 20 mm at the pouring system position, and 25 mm at the heating and insulation riser area; S12, flow coating is performed on the subway wheel casting mud core obtained in S10 and the casting molding parts of the iron mold covered sand type subway wheel casting outer mold obtained in S11, and the coating material is alcohol-based Al2O3 coating.

[0030] S13. After the coating is dried, the subway wheel casting mud core and the subway wheel casting outer mold are assembled. Specifically, the first mud core 82 is positioned and installed with the positioning holes of the casting lower outer mold through three circular columnar protrusions and one square columnar protrusion, and then the sand-insulated cold iron second mud core 83 is positioned and assembled with the casting lower outer mold through the cylindrical hole position, and then the positioning accuracy of the lower core of the first mud core is checked by the follow-up inspection fixture 9, and then the positioning is performed by the positioning pins and positioning holes on the parting surfaces of the casting upper outer mold 6 and the casting lower outer mold 7, and the subway wheel casting mud core and the subway wheel casting outer mold are assembled and locked by the locking mechanism. Then, the heating and insulating riser 601 is installed into the riser installation groove reserved in the metal outer mold, and the overflow insulating sand sleeve 602 is installed on the top of the riser; an exhaust hole aligned with the exhaust hole on the top of the heating and insulating riser is opened in the middle of the overflow insulating sand sleeve, and a molten iron retaining ring is installed on the top of the overflow insulating sand sleeve; a graphite block 603 is provided in the cavity where the wheel rim and the hub of the casting upper outer mold 6 and the casting lower outer mold 7 are located to form a subway wheel casting mold assembly.

[0031] The molding cavity of the subway wheel casting mold assembly of this embodiment is a subway wheel rim downward structure. Then the molding cavity is cleaned, a filter component is placed in the pouring channel of the pouring system, and the pouring system is connected to the subway wheel casting mold assembly cavity. Finally, a pouring cup is pasted at the pouring gate of the pouring system to form a composite subway wheel casting mold of iron mold + graphite + coated sand.

[0032] In S12 of this embodiment, according to the casting process, the pouring system of this embodiment is a bottom pouring pouring system, which adopts a semi-closed structure and is provided with several stages of filtering components inside; the pouring system is provided with a straight runner, a cross runner and an ingode, and the number of ingodes is six. The six ingodes are evenly spaced along the circumference of the casting cavity, and the ingodes on both sides are arranged at an opposite angle to the cross runner to control the molten iron initially entering the cavity to converge on the runner side, and then flow together away from the runner side to ensure the continuity of the molten iron; the straight runner and the ingode are connected by cross runners on both sides; the ratio of the cross-sectional areas of the straight runner, the cross runner and the ingode is 1:1.5:0.8.

[0033] This embodiment adopts a composite molding process of iron mold + graphite + coated sand. The amount of sand used in the lower outer mold is 16.5 kg, and the amount of sand used in the upper outer mold is 42 kg, totaling 58.5 kg. The upper and lower outer molds use iron molds + coated sand to form a coated sand tire layer in the casting cavity to improve the surface quality of the wheel, especially the reinforcing ribs. At the same time, the first mud core and the sand-insulating cold iron are used as the casting sand cores of the wheel spokes and hubs to increase the cooling rate of the wheel's bilateral spokes and the thin-walled parts of the wheel hub, and improve the density of the casting; the upper and lower outer molds are embedded with graphite blocks to increase the local cooling rate of the wheel rim, and the riser method is combined to improve the density of the wheel rim. The surface of the casting is subjected to magnetic particle inspection according to ISO 4986, meeting the level 1 requirements specified in the standard. Refer to ASTM E94, ASTM E446, and ASTM E186 standards to conduct radiographic inspection on the detectable parts of key areas of the product to meet the Level 1 requirements specified in the standards.

[0034] As above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for casting an isothermal quenching ductile iron subway wheel, characterized in that: The casting steps include: S1. Making a subway wheel casting mold; first, making a subway wheel metal mold including a casting system, placing graphite blocks and heat-generating and heat-insulating risers at the mold positions corresponding to the parts of the subway wheel casting with large thickness or the parts of the wheel casting with high density; then making a composite subway wheel casting mold of iron mold + graphite + coated sand by a core making machine; S2, proportioning the casting liquid components and melting the components; S3, subjecting the smelted pouring liquid in S2 to a spheroidizing inoculation reaction, and after the spheroidizing inoculation reaction is completed, the pouring liquid is poured into the pouring mold made in S1 under temperature control, and flow inoculation is adopted during the pouring process; S4. After the pouring is completed, the subway wheel casting is subjected to isothermal quenching post-treatment.

2. The casting method of austempered ductile iron subway wheel according to claim 1, characterized in that: In S1, a subway wheel casting mold is manufactured; first, a subway wheel metal mold including a casting system is manufactured, and graphite blocks and heat-generating and heat-insulating risers are placed at mold positions corresponding to the thickest parts of the subway wheel casting or the parts with high structural density of the wheel casting; then, a composite subway wheel casting mold of iron mold + graphite + coated sand is manufactured by a core making machine, specifically: S10, firstly designing a combined subway wheel mold including a casting system according to the subway wheel structure and casting requirements, wherein the combined subway wheel mold includes a metal outer mold and a mud core mold; and using the mud core mold to form a subway wheel casting mud core using a core making machine; S11. According to the casting process, a pouring system, a gas outlet rod, a graphite block and a heating and heat-insulating riser are placed on the metal outer mold, and a layer of coated sand tire layer is formed in the mold cavity of the metal outer mold by a hot core machine to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; S12, flow coating the subway wheel casting core obtained in S10 and the casting molding parts of the composite subway wheel casting outer mold of iron mold + graphite + coated sand obtained in S11; S13. After the coating is dried, the subway wheel casting mud core and the composite subway wheel casting outer mold of iron mold + graphite + coated sand are assembled, and the mud core positioning is detected to form a subway wheel casting mold assembly; the molding cavity of the subway wheel casting mold assembly is a subway wheel rim downward structure, then the molding cavity is cleaned, a filter assembly is placed in the pouring channel of the pouring system, and the pouring system is connected to the subway wheel casting mold assembly cavity, and a pouring cup is pasted at the pouring gate of the pouring system, and finally a heat-generating and heat-insulating riser is installed, and an overflow heat-insulating sand sleeve is pasted on the upper side of the heat-generating and heat-insulating riser to form a composite subway wheel casting mold of iron mold + graphite + coated sand.

3. The casting method of austempered ductile iron subway wheel according to claim 2, characterized in that: In S10, the metal outer mold includes an upper outer mold, a lower outer mold and a locking mechanism. After the upper outer mold and the lower outer mold are molded together, they are connected as a whole through the locking mechanism; the upper outer mold and the lower outer mold are made of ductile iron and are integrally cast and processed by a metal outer mold mold; the upper outer mold and the lower outer mold are made into a casting upper outer mold and a casting lower outer mold of a composite subway wheel casting outer mold of iron mold + graphite + coated sand by a core making machine in a one-mold-one-piece manner, and the parting surfaces between the two are respectively provided with positioning components; The cement core mold comprises a wheel spoke plate hole mold and a wheel axle hole sand-insulated cold iron mold; a first cement core is made by the wheel spoke plate hole mold using a core making machine, and a wheel axle hole sand-insulated cold iron second cement core is made by the wheel axle hole sand-insulated cold iron mold; the first cement core and the second cement core with sand-insulated cold iron constitute the subway wheel casting cement core; a first anti-mistake positioning component is provided on the cement core surface of the first cement core facing the casting upper outer mold and the casting lower outer mold, and a second anti-mistake positioning component is respectively provided on the casting upper outer mold and the casting lower outer mold at the position of the first anti-mistake positioning component, so as to be used for positioning and installing the first cement core with the casting upper outer mold and the casting lower outer mold.

4. The casting method of austempered ductile iron subway wheel according to claim 2, characterized in that: In S10, when a subway wheel casting core is made by a core making machine through a core mold, the core mold includes an upper core mold and a lower core mold. After the two molds are closed, a sand shooting cavity with a wheel spoke plate horizontal surface facing upward and an inclined surface facing downward is formed between them; the sand shooting nozzle on the core mold is located in the middle of the elliptical core head on the upper side of the casting core; the movable mold ejector rod located on the lower side of the core is located in the middle of the lower core head; The cast clay core is made by a cold core machine, the SiO2 content of the raw sand is ≥92%, the particle size is 50 / 100 mesh, the three-sieve concentration rate is ≥85%, and the pH value is 6.5-7.2; the resin binder adopts a two-component resin, the model is XLI-318 and XLII-618; the resin binder is added in an amount of 1.3-1.5% of the weight of the sand, and the two components are proportioned as XLI-318: XLI-618=55%:45%; in the sand mixing process, the stirring time is 90S-120S in summer and 150S-180S in winter; when the core is made by the cold core machine, the core making parameters are: sand shooting once, sand shooting time 8-10S; sand shooting pressure 0.55-0.65MPa; amine adding time 10-20S.

5. The casting method of austempered ductile iron subway wheel according to claim 2, characterized in that: In S11, according to the casting process, a pouring system, an air outlet rod, a graphite block and a heating and heat-insulating riser are placed on the metal outer mold, and a layer of coated sand tire layer is formed in the mold cavity of the metal outer mold by using a hot core machine to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand. When making the metal outer mold, a graphite block and a heating and heat-insulating riser installation groove are reserved at the location of the metal outer mold where the thickness of the subway wheel casting is large or the location where the wheel casting has a high density of tissue, and a plurality of heating pipes are pre-embedded in the metal outer mold; the heating and heat-insulating riser is formed by a riser mold, and after the metal outer mold is formed, the graphite block and the heating and heat-insulating riser are assembled into one with the metal outer mold, and then sand is shot by a hot core machine to form a coated sand tire layer in the metal outer mold cavity to make a composite subway wheel casting outer mold of iron mold + graphite + coated sand; When the coated sand tire layer is made in the metal outer mold cavity, the coated sand particle size is 70 / 140 mesh, the temperature is 180~200℃, the insulation time is 5~5.5 min, and the strength of the coated sand at room temperature is 3.5~5.0MPa; the thickness of the coated sand tire layer is: the thickness of the sand layer at the wheel spoke position is 8mm, the thickness of the sand layer at the casting system position is 20mm, and the thickness of the sand layer in the heating and insulation riser area is 25mm.

6. The casting method of austempered ductile iron subway wheel according to claim 3, characterized in that: In S13, after the coating is dried, when the subway wheel casting mud core and the composite subway wheel casting outer mold of iron mold + graphite + coated sand are assembled, the first anti-mistake positioning component is four columnar protrusions; the four columnar protrusions are arranged in a cross shape on the first mud core surface, and the cross-sections of three of the columnar protrusions are circular structures, and the other columnar protrusion is a square structure; the second anti-mistake positioning component is a positioning hole that is adapted to the columnar protrusion on the casting upper outer mold and the casting lower outer mold, and the positioning hole that is adapted to the circular columnar protrusion is an elliptical structure in cross section, and the positioning hole that is adapted to the square columnar protrusion is a square structure in cross section; When closing the box, firstly, the first mud core and the lower casting outer mold are positioned and assembled, and the positioning and matching accuracy of the first mud core and the lower casting outer mold is checked by a conformal inspection fixture, and then the second mud core is positioned and assembled with the lower casting outer mold through the cylindrical hole position, and then the upper casting outer mold and the lower casting outer mold are assembled by the positioning component of the parting surface, and locked by the locking mechanism to form a subway wheel casting mold combination; before closing the mold, graphite blocks are embedded in the upper casting outer mold and the lower casting outer mold, and then the heating and heat-insulating riser is installed in the reserved riser installation groove, and the overflow insulation sand sleeve is pasted on the top of the riser; the overflow insulation sand sleeve is provided with an exhaust hole in the middle that is aligned with the exhaust hole on the top of the heating and heat-insulating riser, and a molten iron retaining ring is installed on the top of the overflow insulation sand sleeve.

7. The casting method of austempered ductile iron subway wheel according to claim 3, characterized in that: The pouring system is a bottom pouring pouring system with a semi-closed structure and several levels of filtering components are arranged inside; the pouring system is provided with a straight runner, a cross runner and an ingrate, and the number of the ingrates is several, and the several ingrates are evenly spaced along the circumference of the pouring cavity, and the ingrates on both sides are arranged at an opposite angle to the cross runner; the straight runner and the ingrate are connected by cross runners on both sides; the ratio of the cross-sectional areas of the straight runner, the cross runner and the ingrate is 1:1.5:0.

8.

8. The casting method of austempered ductile iron subway wheel according to claim 1, characterized in that: In S2, when the pouring liquid components are proportioned and the components are smelted, the charge for smelting the pouring liquid includes pig iron, scrap steel, recycled materials, ferromolybdenum, ferromanganese, ferrosilicon, nickel plates and copper plates; an electric furnace is used to melt the charge, and after melting, a sample in front of the furnace is taken for component element analysis, and then the element content is adjusted according to the analysis results; the temperature in the smelting furnace is 1520~1550℃; the pouring temperature range is 1350~1370℃.

9. The casting method of austempered ductile iron subway wheel according to claim 1, characterized in that: Before pouring in S3, the smelted casting liquid is poured into the spheroidizing bag, and the punching method spheroidizing process is adopted. The spheroidizing bag is a pit-type structure, and the spheroidizing agent, inoculant, covering agent and pressing plate are added into the pit; the spheroidizing agent adopts yttrium-based heavy rare earth-magnesium alloy spheroidizing agent, the addition ratio is 1.1%~1.3%, the particle size is 5~25mm, and the composition is: Si: 40~50%, Mg: 5.5~7.5%, RE: 1.0~2.5%, Ca: 2.0~3.0%, and the rest is Fe; the three-time inoculation method is adopted when inoculating the casting liquid, and the composite The inoculant comprises the following components: Si: 70-75%, Ca: 1-1.5%, Al≤1%, and the rest is Fe. During inoculation, 0.4%-0.6% of the mass of the molten iron out of the furnace is put on the spheroidizing agent for one inoculation. After the spheroidizing reaction is completed, the molten iron in the spheroidizing ladle is transferred to the pouring ladle, and 0.4%-0.6% of the mass of the molten iron out of the furnace is added to the molten iron during the pouring process for a second inoculation. During the pouring process, the inoculant content is 0.05%-0.1% of the mass of the molten iron out of the furnace, and three inoculations are performed.

10. The casting method of austempered ductile iron subway wheel according to claim 1, characterized in that: In S4, after pouring is completed, the casting is kept warm in the mold for more than 12 hours, unpacked, the residual coated sand in the mold is cleaned, the pouring system and the riser are cut and removed, and a shot blasting is performed and then an isothermal quenching heat treatment is performed; When the casting is subjected to isothermal quenching heat treatment, the casting is subjected to rough grinding, stress relief annealing heat treatment, fine grinding, fine polishing, rough machining, isothermal quenching heat treatment and fine machining; during the stress relief annealing heat treatment, the casting is heated to 610±20°C, kept warm for 2-3 hours, and then air-cooled to room temperature; when the casting is subjected to rough machining, a 2mm fine machining allowance is reserved for isothermal quenching heat treatment, and during the isothermal quenching heat treatment, the component is heated to 900±20°C, kept warm for 2-3 hours, then cooled to 360±10°C, kept warm for 2-3 hours, and then air-cooled to room temperature.

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