Rail transit brake disc horizontal line production process and brake disc

Abstract

The application discloses a production process of a horizontal line of a brake disc for rail transit, and comprises the following steps: S1, a central top pouring system is adopted, a sprue and an ingate are arranged at a center position of a casting, a ring-shaped water storage block is arranged in a parting surface disc, synchronous mold filling of molten iron from the center to the periphery is realized, all thin-wall radiating fin structures are arranged on a lower mold surface, overflow risers and gravity column feeding units are arranged at thick and large boss positions; S2, a compactness CB value of molding sand is controlled to be 30-35%; after molding, alcohol-based refractory paint is sprayed at the radiating fin position of the lower mold; compared with the prior art, the central ring-shaped water storage block pouring system of the application realizes synchronous mold filling of molten iron from the center to the periphery, shortens a mold filling process, disperses heat, and solves the contradiction between filling difficulty of the thin-wall radiating fin and local overheating and sand sticking; the gravity column and the overflow riser cooperatively feed, respectively solve feeding requirements and exhaust and deslagging requirements of thick and large positions, and effectively eliminate the shrinkage defect near the mounting hole.

Description

Technical Field

[0001] This invention relates to the field of metal material casting technology, specifically to a production process for a horizontal line of a brake disc for rail transit and the brake disc itself. Background Technology

[0002] The brake disc in rail transit is a core safety component of the train braking system, and its working conditions are extremely harsh—the disc surface temperature can instantly reach 600~800℃ during braking, while simultaneously bearing enormous frictional forces and thermal shock loads. Therefore, brake discs not only require high tensile strength (≥200N / mm²) and suitable hardness (190~240HB), but also good thermal conductivity, resistance to thermal cracking, and wear resistance, and the heat dissipation tooth area must not contain brittle phases such as carbides (white iron).

[0003] The structural characteristics of brake disc castings determine their extremely high casting difficulty: the disc diameter is usually 500~800mm, belonging to the category of large-diameter thin-walled disc castings; the heat sink wall thickness is only about 4~6mm, and the height reaches 50~60mm, with a height-to-width ratio of more than 10:1, which is a typical thin-walled deep cavity structure; while the wall thickness of the wheel hub mounting boss can reach 40~60mm, and the wall thickness ratio between the thin-walled area and the thick-walled area is close to 1:10, resulting in a huge difference in the temperature field and shrinkage behavior during the solidification process.

[0004] The existing horizontal sand casting process for producing this type of brake disc mainly has the following technical problems:

[0005] 1. Due to the extremely thin wall thickness of the heat sink fins (≤6mm), the cooling rate after molten iron filling is extremely fast, resulting in a large degree of supercooling. Carbon atoms do not have time to precipitate in the form of graphite, but instead combine with iron atoms to form cementite (Fe3C), i.e., casting white iron structure. White iron structure has high hardness (up to HV600 and above) and high brittleness, which severely aggravates tool wear during machining. It is also prone to crack initiation and propagation during braking, causing the heat sink teeth to break and fail. Although existing processes attempt to suppress white iron by increasing the pouring temperature or increasing the inoculation amount, the effect is unstable due to the limitations of the horizontal line cycle and the thin-walled structure, especially with the high rate of excessive carbides at the ends and roots of the heat sink fins.

[0006] 2. The heat sink is located in the deep cavity of the lower mold, making it difficult to ensure the compactness of the molding sand in the vertical direction, resulting in insufficient strength of the sand mold in some areas. At the same time, the deep cavity is subjected to high static pressure from molten iron during pouring, and the high temperature of molten iron (above 1380℃) easily seeps into the gaps between sand particles, forming mechanical sand adhesion. If the anti-adhesion materials such as coal powder in the molding sand fail, chemical sintering will also occur, and the sand adhesion layer will be firmly bonded to the surface of the casting. Conventional shot blasting is difficult to remove, requiring a lot of grinding and rework, and in severe cases, the casting will be scrapped directly.

[0007] 3. Thick sections such as wheel hub mounting bosses solidify slowly, forming isolated hot spots. Insufficient molten iron replenishment during the later stages of solidification makes them highly susceptible to shrinkage cavities and porosity defects. Shrinkage porosity not only reduces the effective load-bearing cross-sectional area at the mounting hole but also becomes a stress concentration source, accelerating fatigue failure under alternating loads. Existing processes typically use larger risers, but this is limited by the size of the sand box at the horizontal level and molding efficiency, limiting the increase in riser size. Furthermore, larger risers increase the hot spot effect, exacerbating localized overheating.

[0008] 4. The horizontal molding line has a fast production pace (approximately 60-90 boxes per hour), and the properties of the molding sand fluctuate frequently due to factors such as ambient temperature, old sand recycling rate, and mixing time. If only the compaction rate (CB value) is controlled as a single indicator, it is impossible to effectively guarantee the hot and wet strength, permeability, and toughness of the molding sand, resulting in large quality variations between different batches, and even between different box numbers within the same batch.

[0009] 5. Conventional gating systems are mostly peripheral entry or bottom pouring systems. Molten iron enters the mold cavity from the edge of the casting. The process is long and the temperature drop is large. The molten iron that enters first solidifies prematurely at the thin wall, forming cold shuts or white iron. At the same time, the liquid level rises unevenly during the filling process, which easily causes air entrapment and porosity defects in the heat sink area.

[0010] To address the aforementioned issues, existing technologies offer several improvements, such as increasing the carbon equivalent to suppress white iron formation and applying coatings to the cavity surface. However, these are mostly localized optimizations using single methods, failing to provide a systematic integration across multiple dimensions, including mold structure, filling method, inoculation system, molding sand control, and shrinkage compensation system. In particular, a comprehensive process solution is lacking that can simultaneously address white iron formation suppression for thin-walled heat sinks, prevention of sand adhesion in deep cavities, and shrinkage compensation for thicker areas. Summary of the Invention

[0011] The purpose of this invention is to propose a horizontal manufacturing process for brake discs used in rail transit and a brake disc in general; to solve the problem in the prior art of lacking a comprehensive process that can simultaneously address the issues of white cast iron suppression for thin-walled heat sinks, prevention of sand adhesion in deep cavities, and shrinkage compensation for thick parts.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A manufacturing process for the horizontal line of a brake disc for rail transit includes the following steps:

[0014] S1. A center-top pouring gating system is adopted, with a vertical sprue and an inner gate set at the center of the casting, and an annular water storage block set in the parting plate to realize the synchronous filling of molten iron from the center to the outer periphery; the thin-walled heat sink structure with a wall thickness of 4-6mm and a height of 50-60mm is placed on the lower mold surface; overflow risers and gravity column feeding units are set at the thick boss position;

[0015] S2. Control the compaction rate (CB value) of molding sand to 30-35%, moisture content to 2.8-4.0%, wet compressive strength to ≥1.5MPa, and air permeability to ≥80; after molding, spray alcohol-based refractory coating on the heat sink position of the lower mold.

[0016] S3. Using scrap steel, gray iron recycled material and new iron as furnace charge, the smelting temperature is 1520℃-1550℃, high temperature standing for 5min-8min, and the tapping temperature is 1480℃-1520℃.

[0017] S4. Inoculation is carried out before tapping the iron, and the amount of inoculant added before tapping the iron is 0.15%-0.25% of the total mass of the molten iron; in-mold forming inoculant blocks are placed in the mold cavity; in-flow inoculation is carried out during the casting process, and the in-flow inoculant addition rate is 8g / s-14g / s.

[0018] S5, pouring temperature 1380℃-1420℃, full filling time 12s-18s, molten iron rising speed controlled at 15mm / s-25mm / s; sequential solidification is achieved under the synergistic effect of gravity column and overflow riser;

[0019] S6. The finished product is obtained after machining and testing.

[0020] As a further preferred embodiment of the present invention, in S1,

[0021] Four to six anti-collision pillars are installed at the inner runner 2 of the gating system to support the contact between the heat sink and the trolley after the casting is shaken off the sand, and to prevent the heat sink from being damaged or broken during the unloading process.

[0022] The annular water storage block is connected to the central casting system, enabling simultaneous water intake and filling of the mold through the six inner gates, dispersing the heat of the molten iron, and avoiding local overheating that could lead to sand adhesion and sintering of the teeth.

[0023] Overflow risers of φ25×100mm are installed at six thick boss positions to discharge slag and gas from the top of the molten iron during filling; the gravity column is made of ZG40Cr25Ni20 cast steel, which is resistant to high temperature and corrosion, and its modulus is 1.2 times greater than that of the part being fed, so as to provide stable feeding pressure in the high temperature casting environment and ensure that there are no shrinkage cavities or coarse graphite in the connecting hole after machining.

[0024] As a further preferred embodiment of the present invention, in step S1, a foam ceramic filter sheet is provided below the vertical gating channel, and a circular inoculation groove is provided below the filter sheet for placing the in-mold inoculation block; a slag-gathering block structure is added between the annular in-gating channel and the mold cavity to intercept slag particles carried in during the filling process and prevent slag hole defects.

[0025] As a further preferred embodiment of the present invention, in S2, the compaction rate (CB) of the molding sand during mixing is 32±2%, the moisture content is 3.0%-3.8%, the wet compressive strength is ≥1.8MPa, and the air permeability is ≥90; the alcohol-based refractory coating is an alcohol-based zircon powder coating with a ZrO2 content ≥65%, a Baume degree of 65°-75°Bé, and a spraying thickness of 0.2-0.4mm; after molding, the entire surface of the lower mold is sprayed with FOSECO XY-SY-102 coating.

[0026] As a further preferred embodiment of the present invention, in step S4, the inoculant is a barium-containing high-efficiency inoculant with the following chemical composition by mass fraction: Si≥60%, Ca:1.0-3.0%, Ba:0.5-1.5%, Al≤2.5%, with the remainder being Fe and impurities. The amount added is 0.20% of the total mass of molten iron, and the particle size is 1-3 mm.

[0027] As a further preferred embodiment of the present invention, in step S4, the in-mold inoculation block is placed in a circular inoculation tank below the lower mold filter plate. The weight of the inoculation block is 90±5g, and its chemical composition by mass fraction is: Si: 65-75%, Ba: 2-4%, Zr: 1-3%, Al≤1.5%, with the remainder being Fe and impurities.

[0028] As a further preferred embodiment of the present invention, in step S4, the chemical composition of the inoculant has the following mass fractions: Si: 73-78%, Ca≤0.10%, Ba: 0.5-1.5%, Al≤0.50%, Sr: 0.80-1.40%, Zr: 1.00-1.50%, with the balance being Fe and impurities, and the addition rate is 10-12 g / s.

[0029] As a further preferred embodiment of the present invention, the final chemical composition of the prepared brake disc casting is as follows: C: 3.20-3.40%, Si: 1.80-2.10%, Mn: 0.60-0.90%, P≤0.060%, S: 0.06-0.09%, Cr≤0.15%, with the balance being Fe and unavoidable impurities; the carbon equivalent CE is controlled at 3.80%-4.10%.

[0030] As a further preferred embodiment of the present invention, the step S1 is preceded by a MAGMA mold flow software simulation verification step: predicting the filling process, solidification temperature field, and shrinkage porosity of the gating system and the feeding system, confirming the overall solidification directionality, optimizing the gate size and feeding channel layout, and ensuring that the metallographic structure and mechanical properties of key areas meet the design requirements; the simulation verification results are compared with the first piece verification results of mass production to ensure consistency.

[0031] A brake disc for rail transit is made of FC250 gray cast iron with a hardness of 190-240HB and a tensile strength of 200-300N / mm². The metallographic structure is dominated by type A graphite with a graphite length of 3-5 grades and type D+E graphite ≤20%. After machining, there is no shrinkage porosity or coarse graphite in the mounting holes, and the heat dissipation teeth are free from sintering, sand adhesion, and fracture. There are no carbides at the top and root of the teeth. The circular runout tolerance is ≤0.1mm, the roughness Rz is ≤16μm, and the dynamic balance weight deviation is ≤±200g.

[0032] The present invention provides a manufacturing process for a horizontal line of a brake disc for rail transit and a brake disc thereof, which, compared with the prior art, has the following advantages:

[0033] 1. The central annular water storage block casting system enables molten iron to be filled from the center to the surrounding area simultaneously, shortening the filling process, dispersing heat, and solving the contradiction between the difficulty of filling thin-walled heat sinks and the local overheating and sand adhesion; the gravity column and overflow riser work together to feed the feed, respectively solving the feeding and venting and slag removal needs of thick parts, effectively eliminating shrinkage defects near the mounting holes.

[0034] 2. Pre-furnace inoculation (Si-Ba-Ca) provides the initial graphite core, in-mold inoculation (Si-Ba-Zr) supplements the core before filling, and in-flow inoculation (Si-Sr-Zr) strengthens inoculation at the end of casting. The triple protection completely suppresses the formation of carbides at the thin-walled heat sink and obtains the ideal A-type graphite structure in the whole cross section.

[0035] 3. Multiple measures are used, such as spraying high-refractory alcohol-based zircon powder coating on the lower mold heat sink, spraying special coating on the entire lower mold, systematically improving the strength of molding sand, and setting anti-collision columns in the inner gating system, to prevent sand adhesion, sintering and damage defects throughout the entire process from molding, pouring to post-treatment.

[0036] 4. Strict numerical limits were imposed on multiple parameters such as molding sand CB value, moisture content, wet compressive strength, and permeability, as well as key process points such as inoculant composition, addition amount, pouring temperature window, and filling time. This ensured a high degree of consistency in casting quality during mass production, significantly reduced the defect rate, and met the high reliability requirements of rail transit for braking components. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the interior of the upper mold of the present invention;

[0038] Figure 2 This is a schematic diagram of the interior of the lower mold of the present invention.

[0039] The meanings of the labels in the attached diagram are as follows: 1. Brake disc casting, 2. Vertical runner, 3. Ingate, 4. Slag block, 5. Gravity column, 6. Inoculation tank, 7. Filter plate, 8. Anti-collision column, 9. Heat sink. Detailed Implementation

[0040] The present invention will be described in detail below with reference to specific embodiments.

[0041] This invention relates to a production process and a brake disc for rail transit with a horizontal line. By comprehensively applying innovative mold structure, optimized gating system, three-level composite inoculation technology, precise control of molding sand, and synergistic feeding system, it solves three major casting problems: white iron in thin-walled heat sinks, sand adhesion sintering in deep cavities, and shrinkage porosity in thick parts. It can stably produce high-quality brake disc castings with excellent metallographic structure, qualified mechanical properties, and qualified dimensional accuracy in batches.

[0042] Example 1: A horizontal casting production process for brake discs used in rail transit, comprising the following steps:

[0043] (1) Mold process design

[0044] A central top-pouring gating system is adopted, with the vertical sprue 2 and the ingate positioned at the center of the brake disc casting 1. An annular water storage block is installed within the parting plate, connected to the central gating system, enabling simultaneous water intake and filling of the mold through the six ingates. This allows the molten iron to advance radially and synchronously from the center outwards, dispersing the heat of the molten iron and preventing localized overheating that could lead to sand adhesion and sintering at the teeth.

[0045] The thin-walled heat sink 9 structure with a wall thickness of 4~6mm and a height of 50~60mm is placed on the lower mold surface. The cooling effect of the lower mold accelerates the graphite nucleation rate, while the direction of gravity facilitates the extrusion and filling of the thin-walled area by molten iron.

[0046] Four to six anti-collision pillars 8 are installed at the inner runner 2 of the gating system to support the contact between the heat sink 9 and the trolley after the casting is shaken off the sand, and to prevent the heat sink 9 from being damaged or broken during the unloading process.

[0047] Overflow risers 5, φ25×100mm, are installed at six thick, large boss locations to discharge slag and gas from the top of the molten iron during filling, while also providing heat capacity for the thick sections. Gravity columns 5 (concealed risers) are installed at the thick, hot sections to provide feeding units. The gravity columns 5 are made of high-temperature and corrosion-resistant ZG40Cr25Ni20 cast steel, and their modulus is more than 1.2 times that of the feeding section, to provide stable feeding pressure in high-temperature casting environments.

[0048] A foam ceramic filter sheet 7 is installed below the sprue, and a circular inoculation groove 6 is installed below the filter sheet 7 to place the in-mold inoculation block; a slag-gathering block 4 structure is added between the annular ingate 2 and the cavity to intercept slag particles carried in during the filling process.

[0049] (2) Sand treatment and molding

[0050] When mixing molding sand, control the compaction rate (CB) to be 32±2%, moisture content to be 3.0~3.8%, wet compressive strength to be ≥1.8MPa, and air permeability to be ≥90. Increase clay, blending powder, and graphite powder in proportion during sand mixing to improve the hot and wet strength of the molding sand.

[0051] After the molding is completed, an alcohol-based zircon powder coating with a ZrO2 content ≥65%, a Baumé degree of 65~75°Bé, and a coating thickness of 0.2~0.4mm is sprayed onto the heat sink 9 position of the lower mold. After spraying, it is ignited and dried. Subsequently, FOSECO XY-SY-102 coating or similar high-performance alcohol-based casting coating is sprayed onto the entire surface of the lower mold to further reduce sand adhesion defects.

[0052] (3) Smelting and batching

[0053] The composition of the feed per ton of molten iron is as follows: 300-500 kg of scrap steel (carbon steel), 400-600 kg of gray iron remelting material (same material), 100-200 kg of new iron (Z14 / Z18), appropriate amount of carbon raiser, and 25-50 kg of silicon carbide.

[0054] The smelting process is carried out using a medium-frequency induction furnace at a smelting temperature of 1520~1550℃. After the furnace charge has completely melted and been thoroughly stirred and slag removed, it is allowed to stand at a high temperature for 5~8 minutes, with the standing temperature controlled at 1550~1500℃, to promote the flotation of inclusions and the escape of gases. The tapping temperature is 1480~1520℃.

[0055] The final chemical composition of the prepared brake disc casting is controlled as follows: C: 3.20~3.40%, Si: 1.80~2.10%, Mn: 0.60~0.90%, P≤0.060%, S: 0.06~0.09%, Cr≤0.15%, with the balance being Fe and unavoidable impurities; the carbon equivalent CE is controlled at 3.80~4.10%.

[0056] (4) Multi-stage incubation treatment

[0057] First stage: Furnace inoculation. During tapping, a barium-containing high-efficiency inoculant, FOUNDRIBAR or a similar Si-Ba-Ca inoculant, is added using a flushing method. The addition amount is 0.20% of the total mass of the molten iron, with a particle size of 1~3mm. Its chemical composition by mass fraction is: Si≥60%, Ca: 1.0~3.0%, Ba: 0.5~1.5%, Al≤2.5%, with the balance being Fe and impurities.

[0058] Second stage: In-mold inoculation. After placing the filter slag sheet 7 in the lower mold, an in-mold forming inoculation block is placed in the circular inoculation tank 6. The inoculation block weighs 90±5g. Its chemical composition by mass fraction is: Si: 65~75%, Ba: 2~4%, Zr: 1~3%, Al≤1.5%, with the balance being Fe and impurities. When the molten iron enters the mold cavity and flows through the inoculation tank 6, it dissolves the inoculation block, achieving secondary inoculation before solidification.

[0059] Third stage: In-flow inoculation: During the casting process, a dedicated in-flow inoculation device is used to continuously add the in-flow inoculation agent at a rate of 10~12 g / s. Its chemical composition by mass fraction is: Si: 73~78%, Ca≤0.10%, Ba: 0.5~1.5%, Al≤0.50%, Sr: 0.80~1.40%, Zr: 1.00~1.50%, with the balance being Fe and impurities.

[0060] (5) Casting and shrinkage compensation

[0061] The pouring temperature is controlled at 1380~1420℃, the full filling time is 12~18 seconds, and the molten iron rising speed is controlled at 15~25mm / s. An open pouring system is adopted, with water entering and filling the mold simultaneously through six inner gates via a central annular water storage block. During the pouring process, sequential solidification is achieved under the synergistic action of gravity column 5 and overflow riser 5, ensuring a continuous supply of molten iron to thick sections during solidification shrinkage.

[0062] (6) Simulation verification

[0063] During the mold design phase, MAGMA mold flow analysis software was used to predict the filling process, solidification temperature field, and shrinkage cavities of the gating and feeding systems. This confirmed the overall solidification directionality, optimized the gate size and feeding channel layout, and ensured that the metallographic structure and mechanical properties of key areas met the design requirements. Before mass production, the optimized design was used for first-piece verification to ensure consistency between the physical quality and the simulation results.

[0064] (7) Post-processing and testing

[0065] After the casting cools, the sand is removed, and shot blasting is performed to remove surface sand and oxide scale. Roughing and finishing are then carried out according to process requirements to the finished dimensions. The finished product undergoes a dynamic balancing test to ensure a weight deviation of ≤±200g. Each piece undergoes non-destructive testing, with random checks of metallographic structure, hardness, and tensile strength.

[0066] Example 2: The main equipment used in this example is: KGPS-2000kW medium-frequency induction furnace (capacity 2t), horizontal molding line (sand box size 1200×1000×350mm, molding speed 80 boxes / hour), automatic casting machine, MAGMA5.3 mold flow analysis software, SPECTRO spectrometer, HB-3000 Brinell hardness tester, WDW-300 universal testing machine, metallographic microscope (Zeiss Axio Imager), dynamic balancing tester, etc.

[0067] Set up experimental examples 1, 2, 3 (3A, 3B) and comparative examples 1, 2, 3, respectively.

[0068] Experimental Example 1: A batch (15 pieces) was produced using the process of this invention; the specific steps are as follows: Before mold manufacturing, the gating system and the feeding system were modeled and numerically simulated using MAGMA software. The casting model is a certain type of rail transit brake disc with an outer diameter of φ620mm, 9 heat sinks with a wall thickness of 5mm and a height of 55mm, a total of 24 pieces evenly distributed along the circumference, and 6 mounting bosses with a maximum wall thickness of 52mm.

[0069] Simulated boundary conditions: pouring temperature 1400℃, mold material is wet molding sand, initial temperature 25℃, molten iron density 7.2g / cm³, and heat transfer coefficient is set based on actual sand mold measurements. Simulation results show that when using the center-top-pouring annular water storage block scheme, the filling time is 15.2 seconds, and the molten iron front temperature at the end of heat sink 9 is still ≥1370℃, with no significant risk of cold shut-off. Solidification simulation shows that the heat sink 9 area completes solidification within 15~25 seconds after filling, during which time the three-stage inoculation has been fully effective. The thick boss area still has liquid phase channels in the later solidification stage (180~250 seconds after filling), and the gravity column modulus is 1.35 times that of the shrinkage-compensating area, providing effective shrinkage compensation. The predicted shrinkage porosity volume is ≤0.15cm³, within the machining allowance range. Based on the simulation results, the final mold gate size and shrinkage compensation channel scheme are determined.

[0070] Based on a batch size of 2500kg, 1820kg of recycled sand and 680kg of new sand (to compensate for burn-off) are added. The following parameters are controlled during the sand mixing process: compaction rate (CB value) 33%, moisture content 3.4%, wet compressive strength 2.0MPa, permeability 95%, and mud content 9.5%. Compared to the conventional mix, an additional 3kg of clay, 5kg of blending powder, and 3kg of graphite powder are added. The molding sand performance is tested every 30 minutes to ensure stability during continuous production.

[0071] The shape was completed along the horizontal molding line, with the lower mold cavity facing upwards. Using an automatic spray gun, alcohol-based zircon powder coating was evenly sprayed onto all 24 heat sinks of the lower mold at 9 locations. The coating, tested to have a ZrO2 content of 67.8% and a Baumé degree of 72°Bé, was sprayed to a thickness of 0.30~0.35mm. Immediately after spraying, the coating was ignited, allowing the alcohol to evaporate and adhere densely. Subsequently, FOSECO XY-SY-102 coating was sprayed onto the entire surface of the lower mold to a thickness of 0.15mm, and then ignited for drying.

[0072] A foamed ceramic filter sheet 7 (1.5 mm pore size, 85% porosity) was placed below the lower mold sprue. An in-mold inoculation block, weighing 92.3 g, was placed in the circular inoculation tank 6 below the filter sheet 7. The chemical composition of the inoculation block, determined by XRF analysis, was: Si: 71.2%, Ba: 3.1%, Zr: 1.8%, Al: 1.2%, with the balance being Fe.

[0073] Ingredients (per ton of molten iron): 420 kg scrap steel (Q235), 520 kg gray iron remelting material (same material scrap and risers), 60 kg new pig iron (Z18), carbon raiser (graphitized petroleum coke, C≥98%) added according to the carbon equivalent target, and 35 kg silicon carbide.

[0074] Melting process: The medium-frequency furnace was energized for melting. When the melting temperature reached 1535℃, a sample was taken for spectral analysis. The composition was determined to be: C: 3.52%, Si: 1.62%, Mn: 0.78%, P: 0.045%, S: 0.072%, Cr: 0.12%. Based on the test results, 2.5 kg of carburizing agent and 1.8 kg of ferrosilicon were added to adjust the composition. The final furnace composition after adjustment was: C: 3.48%, Si: 1.75%, Mn: 0.77%, P: 0.046%, S: 0.071%, Cr: 0.12%.

[0075] The furnace temperature was raised to 1540℃ and allowed to stand for 6.5 minutes, during which time the slag was continuously skimmed off, a total of 3 times. After the standing period, the temperature was lowered to 1515℃, ready for tapping.

[0076] During the process from tapping to casting (capacity 1.5t), the furnace inoculation is carried out by the pouring method: 2.0kg of FOUNDRIBAR inoculant (i.e., 0.20% of the total mass of 1000kg of molten iron) with a particle size of 2~3mm is placed at the bottom of the casting ladle, and the molten iron is poured into the ladle and thoroughly stirred and dissolved. The tapping end temperature is 1495℃.

[0077] The ladle is transported to the automatic pouring machine station. During the pouring process, the temperature inside the ladle is monitored in real time. The pouring temperature of the first batch is 1408℃, and the pouring temperature of the last batch is 1395℃, both within the target range of 1380~1420℃.

[0078] After the casting machine is started, the molten iron enters the annular water storage block through the direct pouring channel and enters the cavity simultaneously through the 6 ingates. The total filling time is recorded as 14.8 seconds by high-speed camera, and the rising speed of the molten iron is calculated to be 22.5 mm / s.

[0079] During the pouring process, the in-flow inoculant device is started simultaneously. The device is installed directly above the pouring cup. The in-flow inoculant feeding speed is calibrated to 11.2 g / s. The measured chemical composition of the in-flow inoculant is: Si: 75.4%, Ca: 0.06%, Ba: 1.1%, Al: 0.32%, Sr: 1.15%, Zr: 1.28%, with the balance being Fe.

[0080] After the casting was kept in the mold for 75 minutes to cool, it was removed from the mold and the sand was removed. At this time, the surface temperature of the casting was approximately 320℃ according to infrared thermography. After sand removal, it was shot blasted in a drum shot blasting machine (steel shot diameter φ0.8mm, shot blasting time 8 minutes) to remove surface loose sand and slight oxide scale.

[0081] After shot blasting, rough machining (turning the outer diameter, end face, and boring the mounting holes) is performed, followed by finish machining to the finished product dimensions.

[0082] A full inspection was conducted on 15 brake discs produced in this batch, and the results are as follows:

[0083] Chemical composition: C: 3.35%, Si: 1.98%, Mn: 0.76%, P: 0.047%, S: 0.070%, Cr: 0.13%, CE = 3.35 + 1.98 / 3 = 4.01%, which meets the target requirements.

[0084] Hardness: Brinell hardness tester, load 3000kg, cemented carbide ball φ10mm, 6 points were evenly sampled on the surface of the disc for testing. The hardness values ​​were 212, 218, 215, 221, 209, and 216HB, with an average value of 215HB. The range was 209~221HB, which meets the requirement of 190~240HB.

[0085] Tensile strength: Samples were cut from the nine ends of the heat sink body and processed into φ14mm standard tensile test bars; three test bars were tested, and the tensile strengths were 258, 264 and 261 N / mm², respectively, with an average of 261 N / mm², which meets the requirement of 200~300 N / mm².

[0086] Metallographic structure: Observations were taken at the base, middle, and near the mounting holes of heat sink 9 under a 100x metallographic microscope. The graphite morphology was mainly type A, with a graphite length of 4 grades. The area proportions of type D and type E graphite were 5%, 4%, and 6%, respectively, averaging 5%, which is far below the control requirement of ≤20%. No carbide (cementite) structures were found at the base, top, and middle of heat sink 9. The matrix structure consisted of approximately 95% pearlite and approximately 5% ferrite, with finely spaced pearlite lamellars.

[0087] Dimensional accuracy: The circular runout tolerance measured by the coordinate measuring machine is 0.045~0.072mm (average of 0.058mm for 15 pieces), and the surface roughness Rz measured by the roughness tester is 12.5~14.8μm, both of which meet the requirements of circular runout ≤0.1mm and Rz≤16μm.

[0088] Dynamic balancing: The weight deviation corresponding to the unbalance measured by the dynamic balancing test machine is -115~+128g, and all 15 pieces are ≤±150g, which meets the requirement of ≤±200g.

[0089] Appearance and non-destructive testing: Visual inspection and dye penetrant testing (PT) showed that all heat dissipation tooth surfaces were free of adhering sand, sintering, cracks, and fractures, and the tooth tops and roots were smooth; the mounting holes showed no shrinkage cavities, coarse graphite, or cracks.

[0090] Finished product yield: 14 out of 15 pieces were qualified, and 1 piece was scrapped due to out-of-tolerance inner hole dimensions during machining (not due to casting reasons). The casting-related finished product yield was 100%, and the overall finished product yield was 93.3%. Batch statistics (5 consecutive production batches, 15 pieces per batch, totaling 75 pieces): 2 casting defects (1 due to fire in the gating system, 1 due to sand holes). The casting finished product yield was 97.3%, and the overall finished product yield (including machining) was 94.7%.

[0091] Experimental Example 2: To verify the adaptability of the process parameter window of the present invention, a batch (15 pieces) was produced again after adjusting some key parameters to examine the process stability.

[0092] Change the following parameters:

[0093] The CB value of the molding sand was adjusted to 31% (lower limit), moisture content to 3.8% (upper limit), and wet compressive strength to 1.9 MPa.

[0094] The pouring temperature should be set at a relatively low value, controlled between 1385 and 1395℃;

[0095] The full filling time is extended to 17.5 seconds (molten iron rising speed 16.8 mm / s).

[0096] The amount of inoculant added before the furnace was 0.18%, the weight of the inoculant block inside the mold was 86.5g, and the in-flow inoculant rate was 10.5g / second.

[0097] Test results: The measured hardness values are 198~223HB, with an average value of 208HB; the tensile strength is 235~252N / mm², with an average value of 243N / mm²; the metallographic structure is dominated by type A graphite, the average proportion of type D+E graphite is 7%, no carbides are present in all parts of the heat sink 9; the circular runout tolerance is 0.048~0.085mm; the dynamic balance weight deviation is ≤±165g; no sand adhesion or sintering is present on the surface. 14 out of 15 pieces are qualified, and 1 piece is scrapped due to slight porosity at the end of heat sink 9 (analyzed to be caused by low molten iron temperature and poor exhaust at the final stage of pouring), with a finished product rate of 93.3%.

[0098] The results of Example 2 show that, with appropriate fluctuations within the process parameter window of the present invention, qualified castings that meet the requirements of technical indicators can still be obtained, indicating that the process of the present invention has good robustness and adaptability.

[0099] Experimental Example 3: In order to verify the irreplaceability of each stage of inoculation in the three-stage composite inoculation system, single-factor comparative tests were carried out by canceling in-mold inoculation and stream inoculation respectively.

[0100] Example 3A: Retain furnace inoculation and stream inoculation, cancel in-mold inoculation, the rest of the conditions are the same as in Example 1, and the in-mold inoculation block is removed. 15 pieces were produced. Metallographic inspection showed that the average proportion of type D+E graphite at the root of heat sink 9 reached 22%, exceeding the control requirement of ≤20%. Among them, carbides (cementite) with an area proportion of about 3% were detected at the end of heat sink 9 in 2 pieces, and the average hardness value rose to 232HB, which was still within the range of 190~240HB but close to the upper limit, and the tool wear during processing was significantly accelerated. The finished product rate of this batch is 80% (3 pieces are scrapped due to excessive carbides).

[0101] Example 3B: Retain furnace inoculation and place the formed in-mold inoculation block in the mold, cancel stream inoculation: the rest of the conditions are the same as in Example 1, and stream inoculation is canceled. 15 pieces were produced. Metallographic inspection of the end of the filling (heat sink 9 farthest from the ingate) showed that the graphite morphology deteriorated, a large amount of type D graphite appeared, the average proportion of type D+E graphite was 18%, slight carbides appeared in one piece (6.7%) at the top of heat sink 9, the hardness distribution had great discreteness (189~236HB), and the minimum tensile strength was only 201N / mm². The finished product rate of this batch is 86.7%.

[0102] The results of Example 3A and 3B illustrate that in-mold inoculation and stream inoculation each undertake irreplaceable functions in the three-stage composite system: in-mold inoculation supplements nuclei before molten iron enters the mold cavity, especially ensuring that the region of heat sink 9 far from the ingate obtains sufficient graphite nuclei; stream inoculation provides the final strong inoculation effect at the end of filling, preventing graphite fading of the molten iron at the end due to long flow path and large temperature drop. The absence of any stage will lead to degradation of the metallographic structure and even carbide precipitation.

[0103] Comparative Example 1: To highlight the superiority of the central annular water storage block casting system of the present invention, a conventional peripheral cutting-in casting system was adopted, that is, molten iron enters from the outer edge of the casting, not from the center top, and there is no annular water storage block. The other process parameters, including molding sand, inoculation, smelting, and casting temperature, are exactly the same as those in Example 1, and a batch of 15 pieces was produced.

[0104] Test results:

[0105] (1) High-speed camera footage shows that after the molten iron enters the cavity from one side of the periphery, it flows along the circumference of the plate and fills the entire cavity in 23.5 seconds, which is about 59% longer than the 14.8 seconds in Example 1. When the leading edge of the molten iron reaches the end of the heat sink 9 on the opposite side, the temperature has dropped to below 1350°C (below the lower limit of 1380°C of this invention).

[0106] (2) Metallographic examination showed that the structure of the heat sink 9 near the ingate was normal (Type A graphite grade 4, D+E accounted for 6%), but the proportion of D+E type graphite in the heat sink 9 on the opposite side away from the ingate (i.e. the last filling area) was as high as 28~35%, and obvious ledeburite carbides appeared on the top of the heat sink 9 (carbides accounted for 5~8%), with hardness values ​​reaching 238~248HB, and some measuring points exceeding the upper limit of 240HB.

[0107] (3) Due to the low filling temperature of the heat sink 9 on the opposite side, two pieces had cold insulation defects (not fully fused) at the end of the heat sink 9 and were scrapped directly.

[0108] (4) Sand adhesion: Due to the long flow path of molten iron and severe erosion of the mold cavity, multiple mechanical sand adhesions occurred in the eroded parts of the molding sand (near the ingate). After cleaning, the surface was rough and the Ra value reached 25~32μm, exceeding the requirement of Rz≤16μm (equivalent to Ra≤5μm).

[0109] (5) Overall yield rate: Only 8 out of 15 pieces were qualified, with a yield rate of 53.3%.

[0110] Comparative Example 1 illustrates that conventional peripheral casting systems suffer from long filling paths and significant temperature drops, resulting in severe undercooling of the molten iron at the ends of the thin-walled heat sink 9 and the precipitation of large amounts of carbides. Simultaneously, the long flow path exacerbates the tendency for sand adhesion. In contrast, the central annular water storage block scheme of this invention significantly shortens the filling distance, achieving synchronous filling and effectively solving the aforementioned problems.

[0111] Comparative Example 2: To verify the key role of alcohol-based zircon powder coating in preventing sand adhesion of deep cavity heat sink 9, except that alcohol-based zircon powder coating was not sprayed, coal powder and bentonite anti-adhesion sand were added to the molding sand according to conventional methods, and the other process conditions were the same as in Example 1, producing a batch of 15 pieces.

[0112] Test results:

[0113] (1) Upon opening the box and removing the sand, it was found that the molding sand in the deep cavity of the lower mold heat sink 9 was sintered into a large area of ​​grayish-white hard block, which was firmly bonded to the surface of the casting heat sink 9 and could not be removed by ordinary shot blasting (8 minutes).

[0114] (2) After increasing the shot blasting time to 20 minutes and assisting with manual grinding, 11 pieces (73%) of the heat sink 9 still had varying degrees of sintered sand residue on their surface. The gaps between the teeth of some heat sink 9 were blocked by sintered material, and each piece needed to be ground with a diamond grinding wheel. Each piece required an additional grinding time of about 45 minutes.

[0115] (3) The wall thickness of the heat sink 9 after removing the sand layer was measured. Six pieces (40%) had their wall thickness reduced to less than 4.2 mm due to excessive polishing (design wall thickness 5 mm, minimum allowable 4.5 mm). Three of these pieces were scrapped due to excessive thinning.

[0116] (4) The surface roughness Rz of heat sink 9 is 21~38μm, which is much higher than the requirement of ≤16μm in this invention, seriously affecting heat dissipation efficiency and braking performance.

[0117] (5) The overall yield (excluding 3 scrapped pieces due to sand adhesion during sintering, plus 1 scrapped piece due to grinding damage) was 73.3%.

[0118] Comparative Example 2 illustrates that conventional anti-sticking methods such as adding coal powder to molding sand are insufficient to resist the static pressure and high-temperature penetration of molten iron in the thin walls of deep cavities. The alcohol-based zircon powder coating used in this invention effectively blocks the occurrence of sticking sand from the perspective of physical isolation due to its ultra-high refractoriness and dense coating.

[0119] Comparative Example 3: To verify the effect of the gravity column feeding unit on eliminating shrinkage at the thick mounting boss, the gravity column feeding unit was removed, and only 6 φ25×100mm overflow risers 5 (the same size as in Example 1) were retained. The other process conditions remained unchanged, and a batch of 15 pieces was produced.

[0120] Test results:

[0121] (1) After rough machining, visual inspection revealed that 5 out of 15 pieces (33%) had obvious dark shrinkage spots on the machined surface of the mounting hole, and the surface finish was uneven.

[0122] (2) All 15 samples were dissected (samples were taken from non-installation surfaces) and observed under a metallographic microscope. Among the samples without gravity columns, 8 samples (53%) showed obvious interdendritic shrinkage porosity, with a shrinkage porosity area of ​​0.5-2.8%. Among them, 4 samples (27%) had a shrinkage porosity area of ​​more than 1.5%. According to the internal quality judgment standard of rail transit brake disc (shrinkage porosity area ≤1.0% is qualified), these 4 samples were judged as unqualified.

[0123] (3) Tensile strength tests were conducted on the four pieces that failed the shrinkage porosity test (taken from the side of the mounting hole). The tensile strength was only 182~195 N / mm², which is lower than the minimum requirement of 200 N / mm². The shrinkage porosity area appeared as a gray loose area in the tensile fracture surface, and the effective load-bearing area was significantly reduced.

[0124] (4) Among the remaining 11 pieces without shrinkage porosity, the tensile strength is 215~245 N / mm², with an average of 228 N / mm². Although it meets the requirements, it is lower than the average of 261 N / mm² in Example 1. This indicates that even if no shrinkage porosity is found in the casting, its feeding effect is still not as good as the scheme with gravity columns.

[0125] (5) The overall yield of this batch (shrinkage porosity and excessive strength) was 73.3%.

[0126] Comparative Example 3 illustrates that the main functions of the φ25×100mm overflow riser are slag removal, venting, and heat collection. Its feeding capacity is limited and insufficient to completely eliminate shrinkage porosity at the hot joint of the thick, large boss with a large modulus. The ZG40Cr25Ni20 gravity column added in this invention, due to its large modulus (≥1.2 times the modulus of the feeding part) and high-temperature resistant material properties, can continuously supply molten iron to the hot joint during the later stages of solidification, thereby ensuring the density and mechanical properties of the mounting hole area.

[0127] A comprehensive comparison is shown in Table 1.

[0128] Table 1 Comparison of key performance indicators of each embodiment and comparative example.

[0129]

[0130] From this, we can see that:

[0131] 1. The process involved in this invention performs excellently in all key indicators, especially achieving the goal of zero carbide, zero sand adhesion, and zero shrinkage of the mounting holes in the heat sink. The yield rate is stable at over 93%, which is much higher than that of other pairs.

[0132] 2. As shown in Comparative Example 1, the gating system has a decisive influence on the quality of the thin-walled heat sink 9. Peripheral gating leads to severe white iron and cold shut at the ends, and insufficient filling temperature is the primary cause of carbide formation.

[0133] 3. As can be seen from Comparative Example 2, coating protection is an irreplaceable means of preventing sand from sticking to the deep cavity, and the sintering problem cannot be solved by adjusting the molding sand alone.

[0134] 4. As can be seen from Comparative Example 3, gravity column feeding is a key measure to ensure the tightness of thick parts, and overflow risers cannot replace its feeding function.

[0135] 5. As can be seen from Experiments 3A and 3B, the absence of any one of the three-level composite inoculation stages will significantly increase the risk of carbide precipitation, and the three levels work together to form a complete graphite nucleation guarantee system.

[0136] Example 3: A 6-month trial production run verified the production of approximately 4800 rail transit brake disc castings, achieving an average yield of 95.2%, an increase of 11.6 percentage points compared to the previous process (83.6% using conventional methods), resulting in annual savings of approximately 1.2 million yuan in casting waste losses. Simultaneously, the grinding and repair time caused by sand adhesion and sintering of the heat sink 9 was reduced from an average of 32 minutes per piece to 3 minutes, significantly improving processing efficiency. Bench braking tests verified that the brake disc prepared by this invention, under continuous emergency braking conditions (initial braking speed 200 km / h, braking deceleration 1.2 m / s², 20 consecutive braking cycles), showed no breakage or crack propagation of the heat sink 9, and the braking friction coefficient remained stable between 0.35 and 0.40, meeting all requirements of the TB / T 2980-2014 "Technical Conditions for Locomotive and Rolling Stock Brake Discs" standard.

[0137] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A manufacturing process for the horizontal line of a brake disc for rail transit, characterized in that, Includes the following steps: S1. A center-top pouring gating system is adopted, with a vertical sprue and an inner gate set at the center of the casting, and an annular water storage block set in the parting plate to realize the synchronous filling of molten iron from the center to the outer periphery; the thin-walled heat sink structure with a wall thickness of 4-6mm and a height of 50-60mm is placed on the lower mold surface; overflow risers and gravity column feeding units are set at the thick boss position; S2. Control the compaction rate (CB value) of molding sand to 30-35%, moisture content to 2.8-4.0%, wet compressive strength to ≥1.5MPa, and air permeability to ≥80; after molding, spray alcohol-based refractory coating on the heat sink position of the lower mold. S3. Using scrap steel, gray iron recycled material and new iron as furnace charge, the smelting temperature is 1520℃-1550℃, high temperature standing for 5min-8min, and the tapping temperature is 1480℃-1520℃. S4. Inoculation is carried out before tapping the iron, and the amount of inoculant added before tapping the iron is 0.15%-0.25% of the total mass of the molten iron; in-mold forming inoculant blocks are placed in the mold cavity; in-flow inoculation is carried out during the casting process, and the in-flow inoculant addition rate is 8g / s-14g / s. S5, pouring temperature 1380℃-1420℃, full filling time 12s-18s, molten iron rising speed controlled at 15mm / s-25mm / s; sequential solidification is achieved under the synergistic effect of gravity column and overflow riser; S6. The finished product is obtained after machining and testing.

2. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In S1, Four to six anti-collision pillars are installed at the ingate of the gating system to support the contact between the heat sink and the trolley after the casting is shaken off the sand, and to prevent the heat sink from being damaged or broken during the unloading process. The annular water storage block is connected to the central casting system, enabling simultaneous water intake and filling of the mold through the six inner gates, dispersing the heat of the molten iron, and avoiding local overheating that could lead to sand adhesion and sintering of the teeth. Overflow risers of φ25×100mm are installed at six thick boss positions to discharge slag and gas from the top of the molten iron during filling; the gravity column is made of ZG40Cr25Ni20 cast steel, which is resistant to high temperature and corrosion, and its modulus is 1.2 times greater than that of the part being fed, so as to provide stable feeding pressure in the high temperature casting environment and ensure that there are no shrinkage cavities or coarse graphite in the connecting hole after machining.

3. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In step S1, a foam ceramic filter sheet is set below the vertical gating, and a circular inoculation groove is set below the filter sheet to place the in-mold inoculation block; a slag-gathering block structure is added between the annular ingate and the cavity to intercept slag particles carried in during the filling process and prevent slag hole defects.

4. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In S2, the compaction rate (CB) of the molding sand during mixing is 32±2%, the moisture content is 3.0%-3.8%, the wet compressive strength is ≥1.8MPa, and the air permeability is ≥90. The alcohol-based refractory coating is an alcohol-based zircon powder coating with a ZrO2 content ≥65%, a Baume degree of 65°-75°Bé, and a spraying thickness of 0.2-0.4mm. After molding, the entire surface of the lower mold is sprayed with FOSECO XY-SY-102 coating.

5. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In S4, the furnace inoculant is a barium-containing high-efficiency inoculant with the following chemical composition by mass fraction: Si≥60%, Ca:1.0-3.0%, Ba:0.5-1.5%, Al≤2.5%, with the balance being Fe and impurities. The amount added is 0.20% of the total mass of molten iron, and the particle size is 1-3mm.

6. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In step S4, the in-mold inoculation block is placed in a circular inoculation tank below the lower mold filter plate. The weight of the inoculation block is 90±5g, and its chemical composition by mass fraction is: Si: 65-75%, Ba: 2-4%, Zr: 1-3%, Al≤1.5%, with the remainder being Fe and impurities.

7. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, In S4, the chemical composition of the inoculant has the following mass fractions: Si: 73-78%, Ca≤0.10%, Ba: 0.5-1.5%, Al≤0.50%, Sr: 0.80-1.40%, Zr: 1.00-1.50%, with the balance being Fe and impurities, and the addition rate is 10-12 g / s.

8. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, The final chemical composition of the prepared brake disc casting is as follows (mass fraction): C: 3.20-3.40%, Si: 1.80-2.10%, Mn: 0.60-0.90%, P≤0.060%, S: 0.06-0.09%, Cr≤0.15%, with the balance being Fe and unavoidable impurities; the carbon equivalent (CE) is controlled at 3.80%-4.10%.

9. The manufacturing process for a horizontal line on a brake disc for rail transit according to claim 1, characterized in that, Before step S1, the method also includes a MAGMA mold flow software simulation verification step: predicting the filling process, solidification temperature field, shrinkage porosity and shrinkage cavity of the gating system and the feeding system, confirming the overall solidification directionality, optimizing the gate size and feeding channel layout, and ensuring that the metallographic structure and mechanical properties of key areas meet the design requirements; the simulation verification results are compared with the first piece verification results of mass production to ensure consistency.

10. A brake disc for rail transit manufactured using the horizontal casting process described in any one of claims 1-9, characterized in that: The material is FC250 gray cast iron, with a hardness of 190-240HB and a tensile strength of 200-300N / mm². The metallographic structure is mainly composed of type A graphite with a graphite length of 3-5 grades and type D+E graphite ≤20%. After machining, there is no shrinkage porosity or coarse graphite in the mounting holes, and the heat dissipation teeth are free from sintering, sand adhesion, and fracture. There are no carbides at the top and root of the teeth. The circular runout tolerance is ≤0.1mm, the roughness Rz is ≤16μm, and the dynamic balance weight deviation is ≤±200g.

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