Thin-walled high-strength 40Cr cast steel planet carrier for mine car transmission and preparation method thereof

Abstract

This invention discloses a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method, relating to the field of mining machinery. The thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method include a planetary carrier. The core load-bearing area of ​​the planetary carrier is designed with an ultra-thin-walled main structure. The planetary carrier is equipped with spokes, and the spokes are equipped with biomimetic reinforcing ribs to improve the radial stiffness and bending strength of the spokes. The non-critical load-bearing end faces of the planetary carrier are provided with weight-reduction zones to reduce the rotational inertia of the components. This thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method fully unleash the performance potential of 40Cr material through stress-relief annealing, segmented heating quenching, and double-stage tempering processes. The yield strength and impact toughness are increased by more than 20% compared to traditional processes, ensuring the reliability of the thin-walled structure under harsh working conditions from a material perspective, and extending the service life to over 16,000 hours.

Description

Technical Field

[0001] This invention relates to the field of mining machinery technology, specifically to a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its preparation method. Background Technology

[0002] As the core load-bearing component in the wheel-side reducer of a mining dump truck, the planetary carrier's structural design, material properties, and manufacturing precision directly affect the reliability, operating efficiency, and service life of the entire transmission system. Currently, these planetary carriers are generally made of 40Cr cast steel and heat-treated using conventional quenching and tempering processes. However, in actual service, the existing design and manufacturing process have revealed the following three significant defects:

[0003] 1. The structure is bulky and the transmission efficiency is low.

[0004] To meet the high stress requirements of mining dump trucks under extreme conditions such as heavy loads, impacts, and mud, traditional planetary carriers generally adopt a conservative thick-walled structure design, with wall thicknesses typically reaching 28–38 mm. While this design can meet static strength requirements, it results in a single component weight of 50–70 kg and a significant increase in rotational inertia. During high-speed operation, the excessive inertial load not only exacerbates system vibration but also causes significant torque transmission losses, with measured transmission efficiency losses reaching 9%–13%, directly increasing the overall vehicle energy consumption and contradicting the current development trend of energy conservation and emission reduction in mining equipment.

[0005] II. The material's strength and toughness potential has not been fully realized.

[0006] Although 40Cr alloy structural steel possesses good hardenability and comprehensive mechanical properties, current heat treatment processes (such as oil quenching at 830℃ + high-temperature tempering at 550℃) only maintain its yield strength at 800–850 MPa, far below the potential of over 1000 MPa that this material can achieve after optimized treatment. This results in insufficient fatigue resistance of the planetary carrier under long-term exposure to frequent start-stop cycles, heavy impacts, and alternating loads from mine cars, leading to a high risk of early crack initiation. Its actual service life is generally only 7500–9500 hours, failing to meet the requirements of modern large-scale mining equipment for long service life and high reliability of key components.

[0007] III. Insufficient precision in casting and machining

[0008] Due to the limitations of the water glass sand casting process, thick-walled planetary carrier castings are prone to internal shrinkage cavities and other metallurgical defects during solidification due to insufficient feeding. This results in insufficient density of the casting body, with an overall pass rate of only 72%–78%. Furthermore, the coaxiality control accuracy of the planetary gear mounting holes during subsequent machining is poor, with measured errors often reaching 0.12–0.20 mm. This geometric deviation can induce additional radial forces during operation, leading to uneven loading of the planetary gear train, abnormal bearing wear, and even gear meshing instability, further shortening the transmission system's lifespan and increasing maintenance costs.

[0009] To address the shortcomings of existing technologies, this invention provides a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method, thereby solving the aforementioned problems. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method. This solves the problem of traditional planetary carriers typically employing conservative, thick-walled designs, with wall thicknesses usually reaching 28–38 mm. However, this results in a single-piece weight of 50–70 kg and a significant increase in rotational inertia. During high-speed operation, this excessive inertial load not only exacerbates system vibration but also causes significant torque transmission losses, with measured transmission efficiency losses reaching 9%–13%, directly increasing the overall vehicle energy consumption and contradicting the current trend of energy conservation and emission reduction in mining equipment.

[0011] Current heat treatment processes only maintain the yield strength at 800–850 MPa, far below the potential of over 1000 MPa that the material can achieve after optimization. As a result, the planetary carriers have insufficient fatigue resistance under the long-term effects of frequent start-stop operations of mining cars, heavy impacts, and alternating loads, leading to a high risk of early crack initiation. Their actual service life is generally only 7500–9500 hours, which is insufficient to meet the requirements of modern large-scale mining equipment for long service life and high reliability of key components.

[0012] Thick-walled planetary carrier castings are prone to internal shrinkage cavities and other metallurgical defects during solidification due to insufficient feeding, resulting in insufficient density of the casting body and an overall pass rate of only 72%–78%. Furthermore, the coaxiality control accuracy of the planetary gear mounting holes during subsequent machining is poor, with measured errors often reaching 0.12–0.20 mm. This geometric deviation can induce additional radial forces during operation, leading to uneven loading of the planetary gear train, abnormal bearing wear, and even gear meshing instability, further shortening the transmission system's lifespan and increasing maintenance costs.

[0013] To achieve the above objectives, the present invention provides the following technical solution: a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its preparation method, comprising:

[0014] The planetary carrier, whose core load-bearing area is designed with an ultra-thin-walled main structure;

[0015] The planetary frame is equipped with spokes;

[0016] A biomimetic reinforcing rib assembly is installed on the spokes to improve the radial stiffness and bending strength of the spokes.

[0017] The weight reduction zone is located on the non-critical load-bearing end face of the planetary carrier to reduce the rotational inertia of the components.

[0018] Preferably, the wall thickness of the core bearing area of ​​the planetary carrier is 14-20 mm.

[0019] Preferably, the biomimetic reinforcing rib assembly includes a first reinforcing rib disposed on the spoke plate and an annular reinforcing rib disposed on the spoke plate. The first reinforcing rib is radially disposed on the spoke plate and forms a composite reinforcing structure with the annular reinforcing rib.

[0020] Preferably, the number of the first reinforcing ribs is at least 6, and the cross-section of the first reinforcing rib on the spoke is inverted T-shaped. The number of ring reinforcing ribs is at least 2, and the cross-section of the ring reinforcing rib on the spoke is rectangular. Through the T-shaped and rectangular design, the structural strength of the spoke is significantly improved without significantly increasing its weight.

[0021] Preferably, the weight reduction zone includes waist-shaped weight reduction holes, which are opened on the non-critical load-bearing end face of the planetary carrier, and the number of waist-shaped weight reduction holes is 4-5.

[0022] Preferably, the planetary carrier is provided with four mounting holes, which are machined to IT5 level precision through a composite process of rough boring, fine reaming and honing, and the coaxiality error of the four mounting holes is controlled within 0.04mm.

[0023] Preferably, a method for preparing a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission includes the following steps:

[0024] Step 1: Perform stress-relief annealing on the cast planetary carrier at 650-680℃ for at least 4 hours;

[0025] Step 2, Segmented heating and quenching treatment: The cast planetary carrier is first heated to 650℃ and held, then heated to the austenitizing temperature of 860-880℃ and held, and then transferred to a nitrate bath for isothermal quenching treatment.

[0026] Step 3: Perform a two-stage tempering treatment on the warm-quenched cast planetary carrier: first temper at 320-340℃, then temper at 520-540℃.

[0027] Preferably, in step two, the temperature is increased to 650℃ at a rate of 5℃ / min and held for 2 hours, then increased to 860-880℃ and held for 3 hours.

[0028] Preferably, in step two, the nitrate bath is heated to 200-220°C, and the isothermal quenching treatment in the nitrate bath is carried out for 30-40 minutes.

[0029] Preferably, in step three, the tempering is carried out at 320-340℃ for 2.5 hours, and then tempered at 520-540℃ for 3 hours.

[0030] The technical effects and advantages of this invention are as follows:

[0031] The thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its manufacturing method involve stress-relief annealing of the planetary carrier at 650-680℃ for at least 4 hours, followed by heating the planetary carrier to 650℃ at a rate of 5℃ / min and holding for 2 hours, then heating it to the austenitizing temperature of 860-880℃ and holding for 3 hours. Subsequently, it undergoes isothermal quenching in a nitrate bath at 200-220℃ for 30-40 minutes. After isothermal quenching, the planetary carrier is tempered at 320-340℃ for 2.5 hours, and then tempered again at 520-540℃ for 3 hours. This process of stress-relief annealing, segmented heating and quenching, and double-stage tempering fully unleashes the performance potential of the 40Cr material. The yield strength and impact toughness are improved by more than 20% compared to traditional processes, ensuring the reliability of the thin-walled structure under harsh working conditions and extending its service life to over 16,000 hours.

[0032] This paper presents a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission, along with its manufacturing method. By improving the feeding capacity of the casting and combining it with water glass sand casting process control, the overall product qualification rate has been increased to over 90%. High-precision hole machining ensures smooth transmission and reduces bearing wear. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0035] Figure 2 This is a cross-sectional structural diagram of the present invention;

[0036] Figure 3 This is a flowchart illustrating the fabrication process of the planetary carrier of the present invention.

[0037] In the diagram: 1. Planetary carrier; 2. Spoke plate; 3. Reinforcing rib 1; 4. Circular reinforcing rib; 5. Waist-shaped weight reduction hole; 6. Mounting hole. 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This embodiment discloses a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission and its preparation method, according to the appendix. Figure 1 To be continued Figure 3 As shown, the planet carrier 1 is made of 40Cr cast steel. The core load-bearing area of ​​the planet carrier 1 is designed with an ultra-thin wall structure, and the wall thickness of the core load-bearing area is 14-20mm, which is more than 35% thinner than the traditional design.

[0040] A spoke 2 is mounted on the planetary carrier 1. A biomimetic reinforcing rib assembly is mounted on the spoke 2. The biomimetic reinforcing rib assembly consists of reinforcing rib 3 and annular reinforcing rib 4. There are 6-8 reinforcing ribs 3, which are arranged radially on the spoke 2. The cross-section of the reinforcing rib 3 on the spoke 2 is inverted T-shaped, which is used to imitate the trabecular bone structure to disperse radial tensile stress. There are 2-3 annular reinforcing ribs 4. The cross-section of the annular reinforcing rib 4 on the spoke 2 is rectangular, which is used to resist circumferential shear force. The annular reinforcing rib 4 is also mounted on the spoke 2 and forms a composite reinforcing structure with the reinforcing rib 3. This significantly improves the structural strength of the spoke 2 without significantly increasing its weight, thereby improving the radial stiffness and bending strength of the spoke 2.

[0041] Through the collaborative design of ultra-thin walls and biomimetic rib structures, the planetary carrier 1 is 38-40% lighter (down to 30-42kg), and the moment of inertia is significantly reduced, lowering the torque loss rate of the transmission system to 3.2-4.5%, thus significantly improving the energy efficiency of the mining truck.

[0042] Four waist-shaped weight-reducing holes 5 are evenly opened along the outer periphery on the non-critical load-bearing end face of the planet carrier 1 to form a weight-reducing zone. This design effectively reduces the rotational inertia of the component while ensuring strength.

[0043] Four mounting holes 6 are provided on the planetary carrier 1 body, using a composite machining process of "rough boring-fine reaming-honing". First, rough boring is performed to remove most of the excess material; then fine reaming is performed to transition the hole diameter to φ60H6; finally, honing is used to finally machine the hole diameter to φ60H5, ensuring an ultra-high precision of IT5 level. After testing, the coaxiality error of the four mounting holes 6 is controlled within 0.035mm to ensure the final dimensional accuracy and coaxiality. The connection between the hub and the spoke 2 adopts a large arc smooth transition of R6-R10 to reduce stress concentration.

[0044] The preparation method of thin-walled high-strength 40Cr cast steel planetary carrier for mine car transmission includes the following processes:

[0045] The planetary carrier 1 is subjected to stress-relief annealing at 650-680℃ for a holding time of not less than 4 hours.

[0046] Segmented heating and quenching treatment: The planetary carrier 1 is first heated to 650℃ at a rate of 5℃ / min and held for 2 hours, then heated to the austenitizing temperature of 860-880℃ and held for 3 hours, and then transferred to a nitrate bath heated to 200-220℃ for isothermal quenching treatment for 30-40 minutes.

[0047] The planetary carrier 1 after warm quenching is subjected to a two-stage tempering treatment: first tempering at 320-340℃ for 2.5 hours, and then tempering at 520-540℃ for 3 hours.

[0048] The process of stress-relief annealing, segmented heating quenching, and double-stage tempering fully stimulates the performance potential of 40Cr material. The yield strength and impact toughness are improved by more than 20% compared with the traditional process. From the material level, the reliability of thin-walled structure under harsh working conditions is guaranteed, and the service life is extended to more than 16,000 hours.

[0049] Example 1: The preparation steps of the planetary carrier 1 suitable for a 150-ton mining dump truck are as follows:

[0050] A. Preparation of water glass sand molds:

[0051] The mixture consists of 100-140 mesh quartz sand (96%), water glass with a modulus of 2.6-2.8 (3.2%), and an organic ester curing agent (0.8%) composed of ethylene glycol diacetate and propylene glycol diacetate.

[0052] Add the dry quartz sand to the S114 sand mixer, start the equipment to perform dry mixing for 2 minutes to break up the sand clumps and make the sand particles fully loose and evenly distributed. Add a certain amount of water glass into the machine and continue mixing for 3 minutes to ensure that the binder evenly coats the surface of each sand particle. Then add the specified amount of curing agent and perform final rapid mixing for 1.5 minutes.

[0053] Immediately after mixing, open the discharge door to discharge the sand and send it into the Z148 molding machine. Set the compressed air pressure to 0.45MPa for high-pressure compaction molding to ensure uniform sand mold density. Control the temperature at 20-25℃. After mixing, let the sand stand for 35 minutes until the sand mold has sufficient strength before demolding. After demolding, continue to let it stand for 5 hours until the sand mold reaches its final strength. Take a sample to test the wet compressive strength, which should be ≥0.35MPa. Apply two coats of ZrO2-based coating to the fully cured cavity surface using a robotic arm. The coating viscosity is 32s, and the total dry film thickness after coating is approximately 0.25mm. Then, send the coated sand mold into the drying oven. The drying temperature is set to 70℃, and hot air drying is carried out for 2 hours.

[0054] B. Melting and Casting

[0055] A 10-ton medium-frequency induction furnace was used. The furnace charge was proportioned and loaded according to the chemical composition of 40Cr national standard. The medium-frequency furnace was started for smelting. The temperature of the molten steel was controlled to rise to 1550℃. Before tapping, 0.1% silicon-calcium alloy (Si-Ca) was added to the furnace for preliminary deoxidation and inclusion modification treatment. The molten steel was then discharged from the furnace to the ladle. During the tapping process, 0.05% aluminum wire was added to the ladle for final deep deoxidation to ensure the purity of the molten steel.

[0056] The bottom-pouring ingate design of the bottom-pouring gating system enables the molten steel to rise steadily, avoids splashing and oxidation, controls the temperature of the molten steel within 1550℃-1510℃, and controls the single pouring time to about 10 seconds to ensure rapid filling and reduce temperature drop. A stepped gating and riser system is set up to establish sequential solidification conditions by using height difference to ensure effective feeding of thick parts of the casting.

[0057] C. Heat treatment and machining of castings

[0058] The casting was stress-relief annealed at 650℃ for at least 4 hours, and then cooled in the furnace or under controlled cooling to room temperature to eliminate residual stress from casting and machining. A segmented heating method was used to heat the austenitizing temperature to 870℃ and hold it for 3 hours to ensure complete austenitization and uniform composition. Then, it was transferred to a nitrate bath at 210℃ for isothermal quenching for 35 minutes, and then tempered at 330℃ for 2.5 hours for the first tempering treatment, and then tempered at 530℃ for 3 hours for the second tempering treatment. After tempering, the surface hardness of planetary carrier 1 was tested, and the standard value was 30HRC.

[0059] First, rough machining is performed using a CNC lathe, with a machining allowance of 1.8mm intentionally left to completely remove the surface decarburized layer and oxide scale that may be generated during the heat treatment process, and to correct the deformation of the substrate.

[0060] Secondly, the mounting hole 6 of planetary carrier 1 is machined using a three-stage progressive machining process of "rough boring - fine reaming - honing" on a machining center. Starting with rough boring of φ59.8mm, transitioning through fine reaming of φ60H6, and finally achieving an IT5 level of ultra-high precision of φ60 H5, while strictly ensuring that the coaxiality of the hole system is ≤0.035mm, in order to meet the dynamic balance and fit requirements at high speeds;

[0061] For the features of radial / annular reinforcing ribs 4 and waist-shaped weight-reducing holes 5 on the casting, wire cutting technology is used for machining, which avoids stress concentration and tool interference problems caused by traditional milling and ensures the accuracy of the contour.

[0062] Finally, the process is finished with sandblasting to uniformly control the surface roughness to Ra≤3.2μm, which not only improves the appearance and texture, but also introduces beneficial residual compressive stress through the surface shot peening effect, thereby improving the fatigue resistance of the workpiece and completing the preparation of planetary carrier 1.

[0063] The planetary carrier 1 was installed on a 150-ton mining car for real-world testing. After a total of 8,400 hours of operation, the components showed no cracks or deformation, the bearings showed normal wear, and the car ran smoothly, fully meeting the usage requirements.

[0064] In this embodiment, the weight of the planetary carrier 1 is reduced to 30-42kg, the moment of inertia is reduced, the torque loss is reduced to 3.2-4.5%, and the coaxiality of the mounting holes is extremely high, ensuring smooth transmission.

[0065] By improving the feeding capacity of castings and combining it with the water glass sand casting process control, the overall product qualification rate has been increased to over 90%. High-precision hole machining ensures smooth transmission and reduces bearing wear.

[0066] The above solution can be implemented directly using existing water glass sand casting production lines without modifying other parts of the mine car, making it easy to promote and apply in the mining industry and yielding significant economic value.

[0067] Example 2: The manufacturing steps of a compact planetary carrier suitable for 80-ton mining cars are as follows:

[0068] Based on the above-mentioned thin-walled high-strength structure, the core load-bearing area wall thickness is set to 14mm to adapt to the compact box space. Six radial inverted T-shaped reinforcing ribs 3 are set on the radial plate 2, and two ring reinforcing ribs 4 are set. Four waist-shaped weight reduction holes 5 are opened on the key stress end face.

[0069] Casting and shaping:

[0070] The water glass sand casting process is adopted. The mixed molding sand is filled into the mold, compacted, and then dried.

[0071] Melting and casting: Control the casting temperature and time, pour the qualified 40Cr steel into the ladle preheated to 200℃, control the casting temperature at 1520℃ and the casting time at 12 seconds to ensure that the steel fills the mold smoothly and avoid air entrapment due to casting too fast or cold shut due to casting too slow.

[0072] Customized heat treatment:

[0073] Stress-relief annealing: The cast blank is placed in a heat treatment furnace, heated to 660℃, held for 4.5 hours, and then cooled in the furnace to below 200℃ to remove it from the furnace to eliminate residual casting stress.

[0074] Segmented heating and quenching: To prevent warping deformation of the thin-walled planetary carrier 1 during heating, a slower heating rate of 3℃ / min is adopted. First, the temperature is raised to 650℃ and held for 2.5 hours for preheating, and then the temperature is raised to 860℃ and held for 4 hours to ensure that the austenitization of the thin-walled section is sufficient and uniform.

[0075] Isothermal quenching: After the heat treatment is completed, the workpiece is quickly transferred to a 220℃ salt bath for 40 minutes of isothermal quenching to obtain a lower bainite structure and ensure a balance between strength and toughness.

[0076] Two-stage tempering: Tempering is performed immediately after quenching. First, tempering is carried out at 320℃ for 3 hours to eliminate some stress; then the temperature is raised to 520℃ for 3.5 hours to finally obtain tempered sorbite structure and stabilize the dimensions.

[0077] The mounting hole 6 of planetary carrier 1 (designed size φ55H5) is rough-bored to remove most of the excess material, then semi-finished to control the dimensional tolerance within ±0.02mm, and finally finished-ground to the final size φ55H5.

[0078] Performance verification results:

[0079] The planetary carrier 1 was manufactured and weighed 30.5 kg.

[0080] Mechanical property testing: yield strength 965MPa, tensile strength 1105MPa, impact energy at -40℃ 52J;

[0081] Installation test: A 10,000-kilometer road simulation test was conducted on an 80-ton mining truck. The planetary carrier 1 showed no abnormal deformation, and the transmission torque loss rate was 3.5%.

[0082] Compared to the planetary carrier of the same structure prepared by the traditional 830℃ quenching + 550℃ tempering process, the yield strength of this embodiment is 965MPa, which has a yield strength of 820MPa and an impact energy of 35J. This ensures the reliability of the thin-walled structure under harsh working conditions from the material level.

[0083] This embodiment employs a slow heating and preheating process of 3℃ / min for thin-walled parts, which effectively prevents warping and deformation during the heat treatment process.

[0084] This embodiment achieves a transmission torque loss rate of only 3.5% through the real-time method described above, meeting the space requirements of a compact housing.

[0085] This embodiment significantly improves the yield strength compared to the traditional process (820MPa), solving the problem of insufficient strength in thin-walled parts. The impact energy at -40℃ reaches 52J, ensuring the resistance to brittle fracture under cold conditions. The torque loss during installation testing is only 3.5%, realizing the energy efficiency and advantages brought by lightweighting.

[0086] Example 3:

[0087] This embodiment addresses the problem of planetary carrier surface wear caused by frequent start-stop of mining cars by employing a user-specified specific heat treatment process. By increasing the upper limit of the austenitizing temperature and adjusting the tempering regime, high hardness (32HRC) and excellent wear-resistant microstructure are obtained.

[0088] Casting and Pretreatment:

[0089] The planetary carrier 1 body is made of 40Cr cast steel water glass sand casting to obtain the planetary carrier 1 blank. The core bearing area of ​​the blank has a wall thickness of 16mm. The spokes 2 are provided with inverted T-shaped radial reinforcing ribs 3.

[0090] Clean the sand adhering to the surface of the planetary carrier 1 blank and perform rough machining to remove the excess material from the gating and riser.

[0091] Customized heat treatment:

[0092] Stress-relief annealing: The rough-machined blank is placed in the furnace to eliminate machining stress;

[0093] Segmented heating austenitizing: The billet is placed in a heat treatment furnace, and the heating rate is strictly controlled. The temperature is uniformly increased to 650℃ at a rate of 5℃ / min and held for 2 hours; then the temperature is further increased to 880℃ and held at this high temperature for 3 hours. This high-temperature austenitizing process aims to fully dissolve the carbides in 40Cr steel and make the alloying elements uniformly distributed, in preparation for obtaining a high-strength and high-toughness matrix.

[0094] Isothermal quenching: After the holding time, the blank of planetary carrier 1 is quickly quenched into a nitrate bath at 200℃ and held for 30 minutes. Low-temperature isothermal quenching yields a microstructure dominated by bainite, effectively avoiding the risk of high internal stress cracking in traditional quenching while ensuring hardness;

[0095] Double tempering enhancement:

[0096] First stage tempering: Temper at 340℃ for 2.5 hours. This temperature range is designed to precipitate fine carbides, increase hardness, and eliminate quenching stress.

[0097] Second stage tempering: The temperature is raised to 540℃ and tempered for 3 hours. This high-temperature tempering ensures that the microstructure is completely transformed into tempered sorbite, achieving a balance between strength and toughness.

[0098] After tempering, remove from the oven and air cool.

[0099] Hardness testing: Tests were conducted at different locations on the planetary carrier 1 hub and spoke 2. The matrix hardness consistently reached 32 HRC, meeting the wear resistance design requirements.

[0100] The planetary carrier 1 prepared in this embodiment showed only 0.05 mm of wear on the inner wall of the planetary gear mounting hole after 1000 hours of operation, which is about 15% better than the wear resistance of components prepared by traditional processes.

[0101] This embodiment achieves a matrix hardness of 32HRC through high-temperature austenitization at 880℃ and a specific tempering process. Low-temperature isothermal quenching effectively avoids the risk of high internal stress cracking, making it suitable for high-wear scenarios caused by frequent start-stop of mining cars.

[0102] Example 4:

[0103] This embodiment focuses on improving the wear resistance of the planetary carrier 1 under extremely high loads. The finishing and surface treatment processes after heat treatment have been strengthened, and the tempering parameters have been adjusted to balance hardness and toughness.

[0104] The planetary carrier 1 body is made of 40Cr cast steel, and the core load-bearing area has a wall thickness of 18mm.

[0105] The height of the annular reinforcing rib on the spoke 2 is increased by 10% to cope with radial shear force.

[0106] Heat treatment:

[0107] The as-cast planetary carrier 1 was subjected to stress-relief annealing at 680℃ for a holding time of not less than 4 hours.

[0108] Strictly control the staged heating: heat up to 650℃ at 5℃ / min and hold for 2 hours, then heat up to 880℃ and hold for 3 hours;

[0109] The isothermal quenching process in a nitrate bath heated to 200°C is 30 minutes.

[0110] Two-stage tempering treatment: The first stage tempering temperature is adjusted to 340℃ and held for 2.5 hours; the second stage tempering temperature is maintained at 540℃ and held for 3 hours. After treatment, the matrix hardness reaches 32 HRC.

[0111] Planetary gear mounting hole machining: Starting with rough boring of φ59.8mm, transitioning through fine reaming of φ60H6, and finally achieving IT5 grade ultra-high precision of φ60H5 through honing;

[0112] After honing, all exposed surfaces of the planetary carrier 1 (especially the transition arc R between the hub and the spokes) are shot peened using cast steel shot with a diameter of 0.6 mm. After strengthening, the surface is subjected to residual compressive stress ≥-800 MPa, and the surface roughness is maintained at Ra3.2 μm.

[0113] Performance verification results:

[0114] The weight of planetary carrier 1 was found to be 39 kg.

[0115] Mechanical property testing: Yield strength 1020MPa (strength slightly increased due to lower tempering temperature), tensile strength 1160MPa, impact energy at -40℃ 48J (still meets the high toughness requirement of ≥47J / cm²).

[0116] Fatigue test: Under the condition of 1.5 times the rated load, 2 million cycles of test were carried out. The surface of planet carrier 1 showed no pitting or cracks, demonstrating excellent fatigue resistance and wear resistance.

[0117] This embodiment boasts a yield strength exceeding 1000MPa and a tensile strength reaching 1160MPa, making it specifically designed for extremely high loads.

[0118] Example 5:

[0119] Based on the structure of Example 2, this embodiment features a topology optimization design for the weight reduction region:

[0120] The original rule "waist-shaped weight reduction hole (5)" is replaced with "bone-like bionic irregular hole". The boundary curve of the irregular hole is smoothed to ensure that the minimum radius of the rounded corner R of the hole edge is greater than 15mm, so as to avoid stress concentration at the sharp corner. The number of irregular holes is optimized to 3, and the area of ​​a single hole is increased by 15% compared with the waist-shaped hole, so as to further reduce the weight.

[0121] Compatibility with irregular hole machining processes:

[0122] Using water jet cutting (high-pressure water jet) technology, irregular hole blanks are cut according to the topology optimization contour, with a 3mm allowance.

[0123] A five-axis CNC machine tool is used to finish mill the hole edges with a ball end mill to ensure that the contour error is ≤0.1mm and the surface roughness Ra is ≤6.3μm.

[0124] Compared to the waist-shaped hole design in Example 2, the weight of the planetary carrier in this example is further reduced to 28.5 kg;

[0125] Under full load conditions, the maximum deformation of the planetary carrier is 0.12mm, which is 18% lower than that of the traditional design;

[0126] The maximum equivalent stress was reduced from 7750MPa to 680MPa, and the stress distribution became more uniform.

[0127] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission, characterized in that, include: Planetary carrier (1), the core load-bearing area of ​​the planetary carrier (1) is designed as an ultra-thin wall main structure; The planetary frame (1) is provided with spokes (2); A biomimetic reinforcing rib assembly is disposed on the spoke (2) to improve the radial stiffness and bending strength of the spoke (2); The weight reduction zone is set on the non-critical force-bearing end face of the planetary carrier (1) to reduce the rotational inertia of the component.

2. The thin-walled high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 1, characterized in that, The core bearing area of ​​the planetary carrier (1) has a wall thickness of 14-20 mm.

3. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 1, characterized in that, The biomimetic reinforcing rib assembly includes a reinforcing rib (3) disposed on the spoke plate (2) and an annular reinforcing rib (4) disposed on the spoke plate (2). The reinforcing rib (3) is radially disposed on the spoke plate (2) and forms a composite reinforcing structure with the annular reinforcing rib (4).

4. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 3, characterized in that, The number of the first reinforcing rib (3) is at least 6, and the cross-section of the spoke (2) where the first reinforcing rib (3) is located is inverted T-shaped. The number of the annular reinforcing rib (4) is at least 2, and the cross-section of the spoke (2) where the annular reinforcing rib (4) is located is rectangular. The design is achieved through the combination of T-shaped and rectangular shapes.

5. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 1, characterized in that, The weight reduction zone includes waist-shaped weight reduction holes (5), which are opened on the non-critical force-bearing end face of the planetary carrier (1), and the number of waist-shaped weight reduction holes (5) is 4-5.

6. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 1, characterized in that, The planetary carrier (1) is provided with four mounting holes (6). The mounting holes (6) are machined to IT5 level precision through a composite process of rough boring, fine reaming and honing. The coaxiality error of the four mounting holes (6) is controlled within 0.04mm.

7. A method for preparing a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission, comprising the thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Perform stress-relief annealing on the cast planetary carrier (1) at 650-680℃ for at least 4 hours; Step 2, segmented heating and quenching treatment: The cast planetary carrier (1) is first heated to 650℃ and held for heat preservation, then heated to the austenitizing temperature of 860-880℃, and then transferred to a nitrate bath for isothermal quenching treatment. Step 3: Perform a two-stage tempering treatment on the cast planetary carrier (1) after warm quenching: first stage tempering at 320-340℃, and then second stage tempering at 520-540℃.

8. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 7, characterized in that, In step two, the temperature is increased to 650℃ at a rate of 5℃ / min and held for 2 hours, then increased to 860-880℃ and held for 3 hours.

9. A thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 7, characterized in that, In step two, the nitrate bath is heated to 200-220°C, and the isothermal quenching treatment in the nitrate bath is carried out for 30-40 minutes.

10. The method for preparing a thin-walled, high-strength 40Cr cast steel planetary carrier for mine car transmission according to claim 7, characterized in that, In step three, the sample is tempered at 320-340℃ for 2.5 hours, and then tempered at 520-540℃ for 3 hours.

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