A casting process for a cast steel ring with CO2 hardening resin sand stack type string casting
By employing composite modified molding sand, graded blowing hardening, controlled pouring, and old sand regeneration processes, the problems of molding sand compatibility and uneven hardening in the existing CO2 hardened resin sand stack casting process have been solved, achieving efficient and stable production of cast steel gear rings with a low defect rate, and improving the consistency of casting quality and environmental friendliness.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QUANZHOU HUAMAO MACHINERY EQUIP
- Filing Date
- 2026-05-12
- Publication Date
- 2026-06-09
AI Technical Summary
The existing CO2 hardened resin sand stack casting process has problems such as poor sand performance compatibility, uneven hardening, unstable pouring and filling leading to high casting defect rate and poor quality consistency, as well as poor old sand recycling effect, high production cost and insufficient environmental protection.
The casting process of the cast steel gear ring is optimized by using composite raw sand made from a mixture of quartz sand and abrasive sand, combined with modified alkaline phenolic resin and composite additives, three-stage graded CO2 blowing hardening, low-temperature drying pretreatment, three-stage controllable casting and combined old sand recycling process, and precise tempering heat treatment.
It has enabled efficient, stable, and low-defect mass production of cast steel gear rings, reduced the probability of hot cracking, porosity, and sand adhesion defects in castings, improved the consistency of casting quality and the reuse rate of old sand, and reduced production costs and solid waste emissions.
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal casting technology, specifically to a CO2-hardened resin sand stack casting process for cast steel gear rings. Background Technology
[0002] Currently, the industrial mass production of small and medium-sized cast steel gear rings mainly adopts three mainstream processes: lost-wax precision casting, ordinary sand mold horizontal parting casting, and vertical cascade casting. Among them, lost-wax precision casting can achieve high dimensional accuracy and surface quality of castings, but it has inherent defects such as numerous production steps, long production cycle, large consumption of wax and mold materials, high production cost, serious pollution in the dewaxing and baking process, and high labor intensity for workers, making it difficult to adapt to the needs of low-cost, large-scale production. Ordinary sand mold horizontal parting casting mostly adopts a production mode of two, four, or eight pieces per mold, which has low single-mold casting yield, large investment in sand mold and positioning tooling equipment, and the possibility of excessive temperature drop of molten steel due to multiple pouring times, which can lead to casting defects such as cold shut, incomplete pouring, and watermarks. Moreover, it is difficult to control the dimensional accuracy of castings due to mold assembly errors and sand mold positioning gaps, resulting in poor quality consistency of products in the same batch.
[0003] Vertical casting, with its core technical features of multi-layer vertical sand mold stacking, multiple parts per mold, and shared central sprue, can significantly increase the number of castings produced per casting cycle, reduce the proportion of molten steel consumed at risers and gating points, and decrease the investment in tooling and production steps, thereby significantly improving production efficiency and reducing production costs. For example, Chinese Patent Publication No. CN106964756A discloses a vertical casting mold and corresponding casting method for steel castings. This scheme forms a casting cavity by bolting a base plate and a cover plate. The casting cavity is equipped with a casting module composed of a bottom mold block, multiple layers of middle mold blocks, and an upper mold block stacked sequentially. By stacking and stringing multiple sand molds vertically, multiple steel castings can be cast simultaneously, which simplifies the production process, improves production efficiency, and reduces the fixed investment cost of tooling and equipment to a certain extent.
[0004] However, the current mainstream CO2-cured resin sand stack casting process still has the following drawbacks: The existing string casting process only designs the stacking structure of sand molds, without specifically optimizing the raw material formula and mixing process of molding sand. Most existing CO2 hardened resin sand uses single quartz sand as raw sand. In order to ensure the overall rigidity of the stacked mold string, a high proportion of resin binder needs to be added to improve the room temperature strength of the sand mold. This directly leads to a sharp increase in gas generation during molding sand pouring, which greatly increases the probability of invasive porosity and blasting defects in the casting. Existing processes mostly employ single-point surface blowing and constant-pressure one-time blowing hardening methods, which cannot achieve uniform penetration of CO2 gas inside the sand mold, and are very likely to cause uneven hardening problems of "hard surface and soft interior" in thick sand molds. The existing cascade casting process does not have an optimized gating system and process to suit the filling flow and solidification characteristics of multi-layer stacked molds. The rapid casting method it adopts is prone to unstable filling of molten steel, which can lead to defects such as air entrapment and slag inclusion. Existing string casting processes mostly use a single mechanical regeneration method to process the fallen sand, which cannot completely remove the resin film and organic impurities remaining on the surface of the sand particles. This leads to a rapid decline in the performance of the regenerated sand, a high proportion of new sand added during the production process, high raw material costs, and a large amount of waste sand discharge causing serious solid waste pollution. Summary of the Invention
[0005] Therefore, in view of the above problems, the present invention provides a CO2 hardened resin sand stack casting process for cast steel gear rings, which solves the problems of poor sand performance adaptability, uneven sand mold hardening, unstable pouring and filling leading to high casting defect rate and poor quality consistency, as well as poor old sand recycling effect, high production cost and insufficient environmental protection in the existing process.
[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: A CO2-hardened resin sand stack casting process for cast steel gear rings includes the following steps: S1. Preparation of Composite Modified Molding Sand: A composite raw sand made of quartz sand and granulated sand is mixed with a CO2-hardening modified alkaline phenolic resin binder and composite additives to prepare molding sand. The mass ratio of granulated sand in the composite raw sand is 30%~50%, the SiO2 content of quartz sand is ≥96%, and the mud content is ≤0.2%. The modified alkaline phenolic resin is a nitrogen-free, low-sulfur, and low-phosphorus modified alkaline phenolic resin, and the amount added is 1.2%~2.0% of the total mass of the composite raw sand. The composite additives include a high-temperature disintegrating agent and a moisture-resistant hardening agent, and the amounts added are 0.1%~0.3% and 0.2%~0.4% of the total mass of the composite raw sand, respectively. During mixing, the composite raw sand, composite additives, and modified alkaline phenolic resin are added to the sand mixer in the following order. The mixing time is 1.5~3 minutes to obtain uniform molding sand with a usable time of ≥40 minutes. S2. Single-piece sand mold graded hardening and low gas generation pretreatment: A special template for stacked sand molds with toothed rings is used for sand filling and compaction. Through the multi-point distributed air blowing channels preset on the template, a three-stage graded CO2 blowing hardening process is performed on the sand mold. The three-stage graded CO2 blowing hardening process is as follows: low-pressure penetration stage, blowing pressure 0.15~0.25MPa, blowing time 20~40s; medium-pressure hardening stage, blowing pressure 0.3~0.4MPa, blowing time 30~80s; pressure holding and shaping stage, blowing pressure 0.2~0.3MPa, blowing time 10~30s; after hardening, the mold is removed and the shape is repaired. A zircon powder-based refractory coating for cast steel is coated on the surface of the sand mold cavity. The dry film thickness of the coating is 0.15~0.3mm. After drying, it is placed in a low-temperature drying kiln at 80~120℃ for 2~4h to obtain a single-piece stacked sand mold. S3. Assembly of stacked casting mold: Each single stacked sand mold is stacked vertically layer by layer. After the stacking is completed, a rigid reinforcing steel sleeve is fitted on the outside of the casting mold. The gap between the steel sleeve and the casting mold is filled and tightened with self-hardening resin sand. A pouring cup is set on the top layer of the casting mold to obtain the stacked casting mold. S4. Steel Melting and Casting: The steel for the cast steel gear ring is melted in a medium-frequency induction furnace. After composite deoxidation, refining, degassing, and impurity removal, the S content in the molten steel is controlled to be ≤0.025%, P content ≤0.03%, and oxygen content ≤20ppm. A bottom-pouring-step composite casting system is used, with an automatic casting machine executing a three-stage controllable casting process. The casting temperature is controlled at 1550~1580℃. The three-stage controllable casting process is as follows: Initial slow pouring stage, filling the mold at 20%~30% of the rated total flow until the pouring cup and the bottom of the sprue are completely filled; Rapid and stable filling stage, filling the mold at a uniform rate of 70%~90% of the rated total flow, keeping the sprue fully filled; Feeding slow pouring stage, filling the mold at 15%~25% of the rated total flow until the riser is completely filled, then holding pressure for feeding; After casting, the casting is allowed to cool naturally in the mold to 620~680℃ before being unpacked. S5. Shaking and Old Sand Regeneration: After the castings are unpacked, they are shaken to separate the molding sand from the castings. After removing the risers and gating gates, they are shot blasted and then heat-treated to adjust the metallographic structure and mechanical properties. The old sand generated by the shaking is subjected to a combination of magnetic separation, sieving, mechanical regeneration and roasting regeneration to remove the residual resin film and micro powder on the surface of the sand particles. The regenerated sand is recycled after meeting the performance standards.
[0007] Further, in step S1, the particle size of the composite raw sand is 40 / 70 mesh or 50 / 100 mesh, and the particle shape coefficient is ≤1.2.
[0008] Further, in step S1, the modified alkaline phenolic resin has a free phenol content ≤0.5%, a solid content ≥75%, and a viscosity of 100~300 mPa·s at 25°C.
[0009] Furthermore, in step S2, the purity of the CO2 gas is ≥99.5%, the multi-point distributed blowing channels are uniformly arranged along the circumference of the sand mold cavity, the number of blowing ports is ≥4, and the depth of the blowing into the sand mold is 1 / 2 to 2 / 3 of the total thickness of the sand mold.
[0010] Furthermore, in step S2, the zircon powder-based refractory coating has a zircon powder content of ≥85%, a refractoriness of ≥1700℃, is coated using an dip coating process, and is then ignited and allowed to dry naturally or dried at a low temperature of 50~80℃.
[0011] Furthermore, in step S3, the number of stacked layers in the stacked group is 5 to 12.
[0012] Furthermore, in step S4, the composite deoxidation adopts a process of pre-deoxidation with silicon-manganese alloy, final deoxidation with aluminum, and dispersion deoxidation with silicon-calcium-barium alloy. The amount of final deoxidized aluminum added is 0.04%~0.06% of the total mass of the molten steel. The refining process adopts argon bottom blowing and stirring, and the stirring time is ≥5min.
[0013] Furthermore, after the preparation of the stacked casting mold in step S3 and before the pouring of molten steel in step S4, the mold is subjected to an overall anti-moisture pretreatment. The pretreatment temperature is controlled at 60~100℃ and the holding time is 1~3h. During the holding process, dry and clean compressed air is continuously circulated into the central sprue and exhaust channel of the mold to remove the free moisture, dust and volatiles remaining inside the mold. The pouring operation is completed within 30 minutes after the pretreatment is completed.
[0014] Furthermore, in step S5, the mechanical regeneration adopts a centrifugal rubbing regeneration machine, and the number of rubbing times is ≥3 times; the temperature of the calcination regeneration is 550~650℃, the holding time is 1~2h, and the loss on ignition of the sand particles after calcination is ≤0.3%.
[0015] Further, in step S5, the heat treatment adopts a quenching and tempering process of normalizing and high-temperature tempering, specifically: the casting is heated to 850-880℃ at a heating rate of 80-120℃ / h, held for 2-4h, then air-cooled for normalizing, and then heated to 580-650℃ at a heating rate of 60-100℃ / h, held for 3-6h, and then cooled in the furnace to below 200℃ before being taken out of the furnace. The metallographic structure of the casting is adjusted to be uniform tempered sorbite, and the hardness is controlled at 220-280HBW.
[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention systematically solves the problems of high molding sand gas generation, poor hardening uniformity, frequent hot cracking / porosity / sand adhesion defects in castings, poor quality consistency in multi-layer casting, and low reuse rate of old sand in existing processes, and achieves efficient, stable, and low-defect mass production of cast steel gear rings. Through the synergistic system of composite raw sand of quartz sand and alumina sand, modified alkaline phenolic resin and composite additives, the amount of resin added is reduced while the room temperature strength, moisture resistance and high temperature collapse resistance of molding sand are improved. This ensures the overall rigidity of the stacked molding assembly and greatly reduces the risk of hot cracking of castings and the difficulty of cleaning up fallen sand, thereby reducing the amount of molding sand gas generation from the source.
[0017] 2. This invention solves the problems of uneven hardening and surface hardening in traditional air-blowing processes by combining a three-stage CO2 blowing hardening process with low-temperature drying pretreatment. This ensures uniform and stable sand mold strength while thoroughly removing residual moisture and volatiles from the sand mold, significantly reducing the probability of invasive porosity defects. The invention also employs a three-stage controllable casting process to balance the filling temperature and static pressure of the molten steel in multi-layer cascade casting, achieving stable filling and sequential solidification throughout the entire cascade. This solves the problems of uneven quality, insufficient filling, and shrinkage porosity in traditional cascade casting, significantly improving the dimensional and performance consistency of castings in the same batch.
[0018] 3. This invention regenerates old sand through a combination of mechanical and roasting processes, which significantly improves the reuse rate of old sand, reduces the consumption of new sand and solid waste emissions, meets the requirements of green casting, and ensures the stable performance of recycled molding sand. Detailed Implementation
[0019] The following will describe in detail the implementation of the present invention with reference to specific embodiments, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.
[0020] Both the examples and comparative examples use the same experimental subjects to ensure the uniqueness of variables and the verifiability of the comparison results: Basic casting information: 42CrMo cast steel gear ring for engineering machinery transmission, nominal outer diameter 280mm, inner diameter 180mm, axial tooth width 40mm, module m=8, number of teeth 32, single casting weight approximately 12kg; Technical requirements: dimensional tolerance CT8 grade, surface roughness Ra≤25μm, Brinell hardness 220~280HBW, internal quality meets GB / T7233.1-2009 grade 2 requirements, free from defects such as cracks, shrinkage cavities, porosity, and sand holes.
[0021] General equipment: S14 series rotor sand mixer, fully automatic core shooter, medium frequency induction melting furnace, automatic casting machine, centrifugal rubbing regeneration machine, trolley heat treatment kiln, low temperature drying kiln.
[0022] Common raw materials: Quartz sand: SiO2 content ≥96%, mud content ≤0.2%; Pearl sand: Al2O3 content ≥75%, refractoriness ≥1800℃; Modified alkaline phenolic resin: nitrogen-free, low sulfur and phosphorus, free phenol ≤0.5%, solid content ≥75%, viscosity at 25℃ 100~300mPa・s; Composite additives: high-temperature disintegrating agent (organic esters), moisture-resistant hardening agent (silicate modified system); Zircon powder-based refractory coatings: Zircon powder content ≥85%, refractoriness ≥1700℃; CO2 gas: purity ≥ 99.5%; 42CrMo steelmaking furnace charge, deoxidizing alloy, argon, etc. all meet industry standards.
[0023] Example 1: S1. Preparation of composite modified molding sand: 50 / 100 mesh composite raw sand with a particle shape coefficient of 1.1 is used, of which 30% is alumina sand and 70% is quartz sand; nitrogen-free, low-sulfur, and phosphorus modified alkaline phenolic resin is added at a rate of 1.2% of the total mass of the composite raw sand; among the composite additives, the amount of high-temperature disintegrating agent is 0.1% and the amount of moisture-resistant hardening agent is 0.2%; during mixing, the composite raw sand, composite additives, and modified alkaline phenolic resin are added to the sand mixer in the following order, and the mixing time is 1.5 minutes to obtain uniform molding sand with a usable time of 45 minutes.
[0024] S2. Single-piece sand mold graded hardening and low gas generation pretreatment: A special template for stacked sand molds with toothed rings is used to fill the sand tightly. The template is pre-set with 6 air blowing ports evenly distributed along the circumference of the mold cavity. The air blowing ports penetrate into the sand mold to a depth of 1 / 2 of the total thickness of the sand mold. A three-stage graded CO2 blowing hardening process is implemented: low-pressure penetration stage, blowing pressure 0.15MPa, blowing time 40s; medium-pressure hardening stage, blowing pressure 0.3MPa, blowing time 80s; pressure holding and shaping stage, blowing pressure 0.2MPa, blowing time 30s. After hardening, the mold is removed and the shape is repaired. A zircon powder-based refractory coating is applied to the surface of the mold cavity using an dip-coating process. The dry film thickness of the coating is 0.15mm. After coating, it is ignited and allowed to dry naturally. Then it is placed in a low-temperature drying kiln at 80℃ for 4 hours to obtain a single-piece stacked sand mold.
[0025] S3. Assembly of stacked casting mold: The single-piece stacked sand molds are stacked vertically layer by layer, with a stacking number of 5 layers; after the stacking is completed, a rigid reinforcing steel sleeve is fitted on the outside of the casting mold, and the gap between the steel sleeve and the casting mold is filled and tightened with self-hardening resin sand. A pouring cup is set on the top layer of the casting mold to obtain the stacked casting mold.
[0026] Pre-treatment to prevent moisture from returning to the mold: After the mold is prepared and before pouring, the mold is subjected to an overall pre-treatment to prevent moisture from returning to the mold. The pre-treatment temperature is 60℃ and the holding time is 3h. During the holding process, dry and clean compressed air is continuously circulated into the central sprue and exhaust channel of the mold to remove residual moisture, dust and volatiles. The pouring operation is completed within 20 minutes after the pre-treatment is completed.
[0027] S4. Steel Melting and Casting: 42CrMo steel is melted in a medium-frequency induction furnace, using a composite deoxidation process of silicon-manganese alloy pre-deoxidation + aluminum final deoxidation + silicon-calcium-barium alloy dispersion deoxidation. The final deoxidation aluminum addition is 0.04% of the total steel mass. Argon bottom blowing stirring is used during the refining process for 5 minutes. After refining, the S content of the steel is controlled at 0.022%, P content at 0.028%, and oxygen content at 18 ppm. A bottom-pouring-step composite casting system is used, employing an automatic casting machine. A three-stage controllable pouring process is implemented, with the pouring temperature controlled at 1550℃. The three-stage controllable pouring process is as follows: in the initial slow pouring stage, 20% of the rated total flow rate is used to fill the mold until the pouring cup and the bottom of the sprue are completely filled; in the rapid and stable filling stage, 70% of the rated total flow rate is used to fill the mold at a uniform speed, keeping the sprue completely filled; in the feeding slow pouring stage, 15% of the rated total flow rate is used to fill the mold until the riser is completely filled, and then pressure is maintained for feeding; after pouring, the casting is allowed to cool naturally in the mold to 620℃ before being unpacked.
[0028] S5. Shaking and Old Sand Regeneration: After unpacking, the castings are shaken off by vibration to separate the molding sand from the castings. After removing the gating gates and risers by gas cutting, they are shot blasted. Then, they undergo a tempering heat treatment of normalizing and high-temperature tempering. Specifically, the castings are heated to 850℃ at a heating rate of 80℃ / h, held for 4 hours, and then air-cooled for normalizing. They are then heated to 580℃ at a heating rate of 60℃ / h, held for 6 hours, and then cooled to 180℃ in the furnace before being removed from the furnace. The old sand generated from the shaking is magnetically separated and sieved. It is then rubbed three times by a centrifugal rubbing regeneration machine and then roasted at 550℃ for 2 hours. After roasting, the sand particles lose 0.25% of their weight on ignition. After meeting the performance standards, it is recycled.
[0029] Example 2: S1. Preparation of composite modified molding sand: 40 / 70 mesh composite raw sand with a particle shape coefficient of 1.0 is used, of which 40% is alumina sand and 60% is quartz sand; nitrogen-free, low-sulfur, and phosphorus modified alkaline phenolic resin is added at a rate of 1.6% of the total mass of the composite raw sand; among the composite additives, the amount of high-temperature disintegrating agent is 0.2% and the amount of moisture-resistant hardening agent is 0.3%; during mixing, the composite raw sand, composite additives, and modified alkaline phenolic resin are added to the sand mixer in the following order, and the mixing time is 2 minutes to obtain uniform molding sand with a usable time of 50 minutes.
[0030] S2. Single-piece sand mold graded hardening and low gas generation pretreatment: A special template for stacked sand molds with toothed rings is used to fill the sand tightly. The template has 8 air blowing ports evenly distributed around the circumference of the mold cavity. The air blowing ports penetrate into the sand mold to a depth of 2 / 3 of the total thickness of the sand mold. A three-stage graded CO2 blowing hardening process is implemented: low-pressure penetration stage, blowing pressure 0.2MPa, blowing time 30s; medium-pressure hardening stage, blowing pressure 0.35MPa, blowing time 50s; pressure holding and shaping stage, blowing pressure 0.25MPa, blowing time 20s. After hardening, the mold is removed and the shape is repaired. A zircon powder-based refractory coating is applied to the surface of the mold cavity using an dip-coating process. The dry film thickness of the coating is 0.2mm. After coating, it is dried at a low temperature of 60℃ and then placed in a low-temperature drying kiln at 100℃ for 3 hours to obtain a single-piece stacked sand mold.
[0031] S3. Assembly of stacked casting mold: The single-piece stacked sand molds are stacked vertically layer by layer, with a stacking number of 8 layers; after the stacking is completed, a rigid reinforcing steel sleeve is fitted on the outside of the mold, and the gap between the steel sleeve and the mold is filled and tightened with self-hardening resin sand. A pouring cup is set on the top layer of the mold to obtain the stacked casting mold.
[0032] Pre-treatment to prevent moisture in the mold: After the mold is prepared and before pouring, the mold is subjected to an overall pre-treatment to prevent moisture in the mold. The pre-treatment temperature is 80℃ and the holding time is 2h. During the holding process, dry and clean compressed air is continuously circulated into the central sprue and exhaust channel of the mold to remove residual moisture, dust and volatiles. The pouring operation is completed within 15 minutes after the pre-treatment is completed.
[0033] S4. The molten steel (42CrMo) is smelted in a medium-frequency induction furnace, undergoing a composite deoxidation process involving pre-deoxidation with silicon-manganese alloy, final deoxidation with aluminum, and dispersion deoxidation with silicon-calcium-barium alloy. The final deoxidation aluminum addition is 0.05% of the total steel mass. The refining process uses argon bottom-blowing stirring for 6 minutes. After refining, the S content of the molten steel is controlled at 0.018%, P content at 0.025%, and oxygen content at 15 ppm. A bottom-pouring / stepped composite casting system is used, executed by an automatic casting machine. The casting process employs a three-stage controllable pouring method, with the pouring temperature controlled at 1565℃. The three-stage controllable pouring process consists of: an initial slow pouring stage, where 25% of the rated total flow rate is used to fill the mold until the pouring cup and the bottom of the sprue are completely filled; a rapid and stable filling stage, where 80% of the rated total flow rate is used to fill the mold at a uniform speed, keeping the sprue completely filled; and a feeding slow pouring stage, where 20% of the rated total flow rate is used to fill the mold until the riser is completely filled, followed by pressure holding and feeding. After pouring, the casting is allowed to cool naturally in the mold to 650℃ before being unpacked.
[0034] S5. After the castings are unpacked, they are subjected to vibration-assisted sand removal to separate the molding sand from the castings. After the risers and gates are removed by gas cutting, they are shot-blasted. Then they undergo a tempering heat treatment of normalizing and high-temperature tempering. Specifically, the castings are heated to 865°C at a heating rate of 100°C / h, held for 3 hours, and then air-cooled for normalizing. They are then heated to 620°C at a heating rate of 80°C / h, held for 4.5 hours, and then cooled to 150°C in the furnace before being unpacked. The old sand generated from the sand removal is magnetically separated and sieved. It is then rubbed four times by a centrifugal rubbing regeneration machine and then roasted at 600°C for 1.5 hours. After roasting, the sand particles lose 0.2% of their weight on ignition. After meeting the performance standards, the sand is recycled.
[0035] Example 3: S1. The composite modified molding sand is prepared using 50 / 100 mesh composite raw sand with a particle shape coefficient of 1.15, of which 50% is alumina sand and 50% is quartz sand; it is mixed with nitrogen-free, low-sulfur, and phosphorus modified alkaline phenolic resin, with an addition amount of 2.0% of the total mass of composite raw sand; among the composite additives, the addition amount of high-temperature disintegrating agent is 0.3% and the addition amount of moisture-resistant hardening agent is 0.4%; during mixing, the composite raw sand → composite additives → modified alkaline phenolic resin are added to the sand mixer in the following order, and the mixing time is 3 minutes, to obtain uniform molding sand with a usable time of 55 minutes.
[0036] S2. Single-piece sand mold graded hardening and low gas generation pretreatment: A special template for stacked sand molds with toothed rings is used to fill the sand tightly. The template is pre-set with 10 air blowing ports evenly distributed around the circumference of the mold cavity. The air blowing ports penetrate into the sand mold to a depth of 2 / 3 of the total thickness of the sand mold. A three-stage graded CO2 blowing hardening process is implemented: low-pressure penetration stage, blowing pressure 0.25MPa, blowing time 20s; medium-pressure hardening stage, blowing pressure 0.4MPa, blowing time 30s; pressure holding and shaping stage, blowing pressure 0.3MPa, blowing time 10s. After hardening, the mold is removed and the shape is repaired. A zircon powder-based refractory coating is applied to the surface of the mold cavity using an dip coating process. The dry film thickness of the coating is 0.3mm. After coating, it is dried at a low temperature of 80℃ and then placed in a low-temperature drying kiln at 120℃ for 2 hours to obtain a single-piece stacked sand mold.
[0037] S3. Assembly of stacked casting mold: The single-piece stacked sand molds are stacked vertically layer by layer, with a stacking number of 12 layers; after the stacking is completed, a rigid reinforcing steel sleeve is fitted on the outside of the casting mold, and the gap between the steel sleeve and the casting mold is filled and tightened with self-hardening resin sand. A pouring cup is set on the top layer of the casting mold to obtain the stacked casting mold.
[0038] Pre-treatment to prevent moisture from returning to the mold: After the mold is prepared and before pouring, the mold is subjected to an overall pre-treatment to prevent moisture from returning to the mold. The pre-treatment temperature is 100℃ and the holding time is 1 hour. During the holding process, dry and clean compressed air is continuously circulated into the central sprue and exhaust channel of the mold to remove residual moisture, dust and volatiles. The pouring operation is completed within 10 minutes after the pre-treatment is completed.
[0039] S4. Steel Melting and Casting: 42CrMo steel is melted in a medium-frequency induction furnace, using a composite deoxidation process of silicon-manganese alloy pre-deoxidation + aluminum final deoxidation + silicon-calcium-barium alloy dispersion deoxidation. The final deoxidation aluminum addition is 0.06% of the total steel mass. Argon bottom blowing stirring is used during the refining process for 8 minutes. After refining, the S content of the steel is controlled at 0.015%, P content at 0.022%, and oxygen content at 12 ppm. A bottom-pouring-step composite casting system is used, employing an automatic casting machine. A three-stage controllable pouring process is implemented, with the pouring temperature controlled at 1580℃. The three-stage controllable pouring process is as follows: In the initial slow pouring stage, the mold is filled with 30% of the rated total flow rate until the pouring cup and the bottom of the sprue are completely filled; in the rapid and stable filling stage, the mold is filled at a uniform speed of 90% of the rated total flow rate to keep the sprue completely filled; in the feeding slow pouring stage, the mold is filled with 25% of the rated total flow rate until the riser is completely filled, and then pressure is maintained for feeding; after pouring, the casting is allowed to cool naturally in the mold to 680℃ before being unpacked.
[0040] S5. Shaking and Old Sand Recycling: After unpacking, the castings are shaken off by vibration to separate the molding sand from the castings. After removing the gating gates and risers by gas cutting, they are shot blasted. Then, they undergo quenching and tempering heat treatment of normalizing and high-temperature tempering. Specifically, the castings are heated to 880℃ at a heating rate of 120℃ / h, held for 2 hours, and then air-cooled for normalizing. They are then heated to 650℃ at a heating rate of 100℃ / h, held for 3 hours, and then cooled to 180℃ in the furnace before being removed from the furnace. The old sand generated from the shaking is magnetically separated and sieved. It is then rubbed 5 times by a centrifugal rubbing regeneration machine and then roasted at 650℃ for 1 hour. After roasting, the sand particles lose 0.18% of their weight on ignition. After meeting the performance standards, it is recycled.
[0041] Comparative Example: This comparative example uses the conventional CO2-cured resin sand stack casting process, which is a common industry practice, and does not employ the core technology improvements of this invention. The specific steps are as follows: Molding sand preparation: Single 50 / 100 mesh quartz sand, without abrasive sand and composite additives, 3.0% of ordinary CO2-cured alkaline phenolic resin was added, and the mixing time was 3 minutes to obtain molding sand.
[0042] Sand mold hardening: Single-point surface air blowing is used, with a constant pressure of 0.4MPa for 60 seconds. After hardening, the mold is removed and the shape is repaired. Ordinary quartz powder-based coating is brushed on and air-dried naturally for 24 hours. There is no low-temperature drying process.
[0043] Stringing and casting: 8 layers are stacked. There is no pre-treatment to prevent moisture from returning after stringing. A common top-pouring casting system is used. The casting is done manually and quickly at a temperature of 1580℃. The mold is cooled to 600℃ before unpacking.
[0044] Smelting and post-treatment: Single aluminum final deoxidation is used, without argon refining; after sand removal, the old sand is only mechanically rubbed and regenerated once, without baking process; castings are treated with conventional normalizing, without high-temperature tempering process.
[0045] Comparison of performance test results between the examples and the comparative examples: Testing items Example 1 Example 2 Example 3 Comparative Example Finished casting pass rate (same batch) 98.2% 99.5% 98.7% 82.5% Major defect rates (porosity / cracks / sand holes / sand adhesion) 1.8% 0.5% 1.3% 17.5% Consistency of dimensional tolerances in the same batch of castings CT8 grade, tolerance ≤0.15mm CT8 grade, tolerance ≤0.1mm CT8 grade, range ≤0.12mm CT10 grade, range ≤0.4mm Surface roughness Ra of casting 20μm 16μm 18μm 50μm Old sand recycling rate 91% 94% 95% 65% Hardness range after heat treatment 230~260HBW 240~265HBW 245~270HBW 190~280 HBW, poor uniformity Metallographic structure Uniform tempered sorbite Uniform tempered sorbite Uniform tempered sorbite Pearlite + ferrite, coarse grains The present invention, in its first, second, and third embodiments, achieves a comprehensive optimization of the entire process through a composite modified molding sand system, a three-stage graded air-blowing hardening process, anti-moisture pretreatment, three-stage controllable casting, combined old sand regeneration, and precise tempering heat treatment. This addresses the core defects of existing processes in the background technology, resulting in a finished casting qualification rate of over 98% and a major defect rate reduced to less than 2%, which is far superior to the existing technical solutions in the comparative examples.
[0046] Compared to conventional processes, this invention reduces the amount of resin added by more than 30% through a composite raw sand and modified resin system, significantly reducing the gas generation of molding sand and decreasing the porosity defect rate by more than 90%. The three-stage hardening process completely solves the problem of the sand mold being hard on the surface and soft on the inside, improving the uniformity of sand mold strength by more than 80%. The combined old sand recycling process increases the old sand reuse rate from 65% to more than 90%, greatly reducing production costs.
[0047] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.
Claims
1. A CO2-hardened resin sand stack casting process for cast steel gear rings, characterized in that, Includes the following steps: S1. Preparation of Composite Modified Molding Sand: A composite raw sand made of quartz sand and granulated sand is mixed with a CO2-hardening modified alkaline phenolic resin binder and composite additives to prepare molding sand. The mass ratio of granulated sand in the composite raw sand is 30%~50%, the SiO2 content of quartz sand is ≥96%, and the mud content is ≤0.2%. The modified alkaline phenolic resin is a nitrogen-free, low-sulfur, and low-phosphorus modified alkaline phenolic resin, and the amount added is 1.2%~2.0% of the total mass of the composite raw sand. The composite additives include a high-temperature disintegrating agent and a moisture-resistant hardening agent, and the amounts added are 0.1%~0.3% and 0.2%~0.4% of the total mass of the composite raw sand, respectively. During mixing, the composite raw sand, composite additives, and modified alkaline phenolic resin are added to the sand mixer in the following order. The mixing time is 1.5~3 minutes to obtain uniform molding sand with a usable time of ≥40 minutes. S2. Single-piece sand mold graded hardening and low gas generation pretreatment: A special template for stacked sand molds with toothed rings is used for sand filling and compaction. Through the multi-point distributed air blowing channels preset on the template, a three-stage graded CO2 blowing hardening process is performed on the sand mold. The three-stage graded CO2 blowing hardening process is as follows: low-pressure penetration stage, blowing pressure 0.15~0.25MPa, blowing time 20~40s; medium-pressure hardening stage, blowing pressure 0.3~0.4MPa, blowing time 30~80s; pressure holding and shaping stage, blowing pressure 0.2~0.3MPa, blowing time 10~30s; after hardening, the mold is removed and the shape is repaired. A zircon powder-based refractory coating for cast steel is coated on the surface of the sand mold cavity. The dry film thickness of the coating is 0.15~0.3mm. After drying, it is placed in a low-temperature drying kiln at 80~120℃ for 2~4h to obtain a single-piece stacked sand mold. S3. Assembly of stacked casting mold: Each single stacked sand mold is stacked vertically layer by layer. After the stacking is completed, a rigid reinforcing steel sleeve is fitted on the outside of the casting mold. The gap between the steel sleeve and the casting mold is filled and tightened with self-hardening resin sand. A pouring cup is set on the top layer of the casting mold to obtain the stacked casting mold. S4. Steel Melting and Casting: The steel for the cast steel gear ring is melted in a medium-frequency induction furnace. After composite deoxidation, refining, degassing, and impurity removal, the S content in the molten steel is controlled to be ≤0.025%, P content ≤0.03%, and oxygen content ≤20ppm. A bottom-pouring-step composite casting system is used, with an automatic casting machine executing a three-stage controllable casting process. The casting temperature is controlled at 1550~1580℃. The three-stage controllable casting process is as follows: Initial slow pouring stage, filling the mold at 20%~30% of the rated total flow until the pouring cup and the bottom of the sprue are completely filled; Rapid and stable filling stage, filling the mold at a uniform rate of 70%~90% of the rated total flow, keeping the sprue fully filled; Feeding slow pouring stage, filling the mold at 15%~25% of the rated total flow until the riser is completely filled, then holding pressure for feeding; After casting, the casting is allowed to cool naturally in the mold to 620~680℃ before being unpacked. S5. Shaking and Old Sand Regeneration: After the castings are unpacked, they are shaken to separate the molding sand from the castings. After removing the risers and gating gates, they are shot blasted and then heat-treated to adjust the metallographic structure and mechanical properties. The old sand generated by the shaking is subjected to a combination of magnetic separation, sieving, mechanical regeneration and roasting regeneration to remove the residual resin film and micro powder on the surface of the sand particles. The regenerated sand is recycled after meeting the performance standards.
2. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S1, the particle size of the composite raw sand is 40 / 70 mesh or 50 / 100 mesh, and the particle shape coefficient is ≤1.
2.
3. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S1, the modified alkaline phenolic resin has a free phenol content ≤0.5%, a solid content ≥75%, and a viscosity of 100~300 mPa·s at 25°C.
4. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S2, the purity of the CO2 gas is ≥99.5%, the multi-point distributed blowing channels are evenly arranged along the circumference of the sand mold cavity, the number of blowing ports is ≥4, and the depth of the blowing into the sand mold is 1 / 2 to 2 / 3 of the total thickness of the sand mold.
5. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S2, the zircon powder-based refractory coating has a zircon powder content of ≥85%, a refractoriness of ≥1700℃, and is applied using an dip coating process. After coating, it is either ignited and allowed to dry on its own or dried at a low temperature of 50~80℃.
6. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S3, the number of stacked layers in the stacked group is 5 to 12.
7. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S4, the composite deoxidation adopts a process of pre-deoxidation with silicon-manganese alloy, final deoxidation with aluminum, and dispersion deoxidation with silicon-calcium-barium alloy. The amount of final deoxidized aluminum added is 0.04%~0.06% of the total mass of the molten steel. The refining process adopts argon bottom blowing and stirring, and the stirring time is ≥5min.
8. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: After the mold preparation is completed in step S3 and before the molten steel is poured in step S4, the mold is subjected to an overall anti-moisture pretreatment. The pretreatment temperature is controlled at 60~100℃ and the holding time is 1~3h. During the holding process, dry and clean compressed air is continuously circulated into the central sprue and exhaust channel of the mold to remove the free moisture, dust and volatiles remaining inside the mold. The pouring operation is completed within 30 minutes after the pretreatment is completed.
9. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S5, the mechanical regeneration uses a centrifugal rubbing regeneration machine, and the number of rubbing times is ≥3 times; the temperature of the calcination regeneration is 550~650℃, the holding time is 1~2h, and the loss on ignition of the sand particles after calcination is ≤0.3%.
10. The CO2-hardened resin sand stack casting process for cast steel gear rings according to claim 1, characterized in that: In step S5, the heat treatment adopts a quenching and tempering process of normalizing and high-temperature tempering. Specifically, the casting is heated to 850-880℃ at a heating rate of 80-120℃ / h, held for 2-4h, then air-cooled for normalizing, and then heated to 580-650℃ at a heating rate of 60-100℃ / h, held for 3-6h, and then cooled in the furnace to below 200℃ before being taken out of the furnace. The metallographic structure of the casting is adjusted to be uniform tempered sorbite, and the hardness is controlled at 220-280 HBW.