Process for casting grinding balls through horizontal stack box precoated sand shell mold

Abstract

The invention discloses a process for casting grinding balls through horizontal stack box precoated sand shell molds, and relates to the technical field of precoated sand shell mold casting. According to the process, precoated sand shell molds are stacked layer by layer to achieve horizontal pouring, scrap steel, ferrochrome, ferromanganese and a carburant are added into a smelting furnace according to the proportion and smelted to the temperature larger than or equal to 1520 DEG C, 0.4-0.7 Kg of aluminum ingots are added for deoxidation two minutes before discharging after detection is qualified, and the aluminum ingots are added into the smelting furnace to be smelted to the temperature larger than or equal to 1520 DEG C; after slagging-off of the transfer ladle, pouring at 1420-1520 DEG C; by optimizing the shell mold arrangement, the raw material ratio and key process parameters, the product yield is increased to 73.8%-74.2%, the error rate is reduced to 0.18%-0.2%, the mechanical property and the production efficiency are remarkably improved, the process is stable, the application range is wide, and the method is suitable for batch production of various wear-resistant grinding balls.

Description

Technical Field

[0001] This invention relates to the field of coated sand shell casting technology, and more particularly to a process for casting grinding balls using a horizontal stacked coated sand shell casting method. Background Technology

[0002] Grinding balls are key wear-resistant components in the material grinding process of industries such as mining, cement, and metallurgy. They are in high demand and have stringent performance requirements, needing not only high hardness, wear resistance, and impact toughness, but also stability and economy in mass production. Coated sand shell casting has become one of the mainstream processes for grinding ball casting due to its advantages such as high dimensional accuracy, good surface quality, and high production efficiency.

[0003] Currently, the traditional coated sand shell casting process for grinding balls in the industry mostly adopts a vertical pouring method, where the shell mold is arranged vertically and the molten metal is poured into the cavity from top to bottom. However, this traditional process has many insurmountable defects in actual production: On the one hand, the flow path of the molten metal in the cavity is relatively long during vertical pouring, and it is prone to uneven filling and insufficient feeding due to gravity, resulting in defects such as shrinkage cavities and porosity inside the casting. At the same time, the proportion of molten metal occupied by the gating system is relatively high, resulting in a low product yield. Taking the widely used Φ25mm grinding ball as an example, its yield is only 70%, and the low utilization rate of raw materials leads to a waste of production costs. On the other hand, the vertically stacked shell molds are easily affected by the impact force of molten metal, temperature stress, and assembly errors during the pouring process. Misalignment is prone to occur at the shell mold joints, leading to frequent misalignment defects. Again, taking the Φ25mm grinding ball as an example, the misalignment rate is as high as 3%, which seriously affects the dimensional accuracy and appearance quality of the grinding ball, increases the scrap rate, and increases subsequent processing costs.

[0004] Furthermore, the production capacity of traditional vertical casting processes is limited by the shell arrangement, resulting in a small number of products cast per batch. Additionally, the higher defect rate necessitates greater investment of manpower and resources for screening and rework, further hindering production efficiency. With downstream industries demanding increasingly higher quality grinding balls and market competition intensifying, optimizing the coated sand shell casting process to improve product yield, reduce miscasting rates, and simultaneously enhance the internal mechanical properties and production efficiency of grinding balls has become a pressing technical challenge for the industry. Summary of the Invention

[0005] To address the technical problems existing in the background art, this invention proposes a process for casting grinding balls using a horizontally stacked, coated sand shell.

[0006] The present invention proposes a process for casting grinding balls using horizontally stacked coated sand shell molds, comprising the following steps: arranging the coated sand shell molds in a layered manner to achieve horizontal casting; adding scrap steel, ferrochrome, ferromanganese, and carbon raiser in a melting furnace in a specific ratio; melting to ≥1520℃; after the pre-furnace chemical composition test is qualified; adding 0.4-0.7Kg of aluminum ingot for deoxidation two minutes before tapping; transferring to a transfer ladle for slag removal; and casting at a casting temperature of 1420℃-1520℃.

[0007] Furthermore, the number of layers of the coated sand shell is 3-8, and a sealing and heat insulation pad is provided between two adjacent shell layers. The thickness of the sealing and heat insulation pad is 2-5mm, and the material is ceramic fiber.

[0008] Furthermore, the mass ratio of the scrap steel, ferrochrome, ferromanganese, and carbon raiser is (60-75):(10-18):(3-8):(2-5), and the carbon content of the scrap steel is ≤0.2%, sulfur content is ≤0.05%, and phosphorus content is ≤0.05%.

[0009] Furthermore, a medium-frequency induction furnace is used for smelting during the smelting process. The heating rate during smelting is 8-12℃ / min, and the first slag removal is carried out when the smelting temperature reaches 1400℃. The amount of slag removed is 0.5-1.2% of the total mass of the furnace charge.

[0010] Furthermore, the aluminum ingot is an industrial pure aluminum ingot with a purity of ≥99.7%. When adding it, a special feeding device is used to uniformly add it from the top of the smelting furnace for a period of 30-60 seconds.

[0011] Furthermore, the slag removal of the transshipment container adopts a combination of mechanical slag removal and manual slag removal. The mechanical slag removal time is 3-5 minutes, and the manual slag removal removes the residual slag. After slag removal, the residual slag in the transshipment container is ≤0.3%.

[0012] Furthermore, a bottom-pouring system is used during pouring, with the pouring speed controlled at 0.8-1.5 kg / s. The pouring temperature is monitored in real time during the pouring process, and the temperature fluctuation range is controlled within ±5℃.

[0013] Furthermore, the coated sand shell is made by pressing phenolic resin coated sand. The amount of phenolic resin added to the coated sand is 2.5-4.0% of the sand mass. The melting point of the coated sand is ≥130℃ and the compressive strength at room temperature is ≥25MPa.

[0014] Furthermore, after the casting is completed, the stacked boxes are kept warm and cooled at a temperature of 800-900℃ for 2-4 hours, and then allowed to cool naturally to room temperature before being opened.

[0015] Furthermore, the chemical composition detection before the furnace is carried out using a direct-reading spectrometer. The detection items include the content of C, Si, Mn, Cr, S and P. Among them, the mass fraction of Si is controlled at 0.8-1.5%, the mass fraction of Mn is controlled at 1.0-2.0%, the mass fraction of Cr is controlled at 5.0-10.0%, the mass fraction of S is ≤0.03%, and the mass fraction of P is ≤0.03%.

[0016] The beneficial effects of this invention are: 1. By adopting a horizontal stacked shell arrangement, the utilization rate of molten metal in the casting system is optimized, the waste of molten metal during the casting process is reduced, the product yield is increased from 70% in the traditional process to 73.8%-74.2%, the raw material utilization rate is significantly improved, and the raw material cost and overall production cost of grinding balls are effectively reduced. 2. The horizontal stacked box structure, combined with the sealing and heat insulation pad design between adjacent shells, effectively offsets the impact of molten metal impact and temperature stress on the shells, reduces the risk of misalignment at the shell joints, and reduces the misalignment rate from 3% in the traditional process to 0.18%-0.2%, which greatly improves the dimensional accuracy and appearance quality of the grinding balls, and reduces the scrap rate and the workload of subsequent processing and finishing. 3. This process effectively reduces defects such as shrinkage cavities, porosity, and slag inclusions in castings by precisely controlling the raw material ratio, melting temperature (≥1520℃), pouring temperature (1420℃-1520℃), and key processes such as deoxidation and slag removal. Simultaneously, reasonable alloy composition control (precise ratio of elements such as Si, Mn, and Cr) and heat preservation and cooling processes increase the Rockwell hardness of the grinding balls to 64-68 HRC and the impact toughness to 16.2-18.3 J / cm², improving wear resistance by more than 40% compared to traditional products. This significantly enhances the wear-resistant service life of the grinding balls in industries such as mining and cement. 4. The horizontal stacking box design allows for simultaneous casting of 3-8 shell layers, significantly increasing the production quantity per batch. At the same time, the optimized process reduces rework and screening time caused by product defects. The production time for a single batch (1000 pieces) is shortened from 8.5 hours in the traditional process to 5.8-6.5 hours, improving production efficiency by 23.5%-31.8%, effectively expanding the production capacity of grinding balls and meeting the needs of mass production. Detailed Implementation

[0017] Example 1

[0018] The present invention proposes a process for casting grinding balls using a horizontally stacked, coated sand shell type, with the following specific steps: 1. Preparation of coated sand shell: The shell is made of phenolic resin coated sand, wherein the amount of phenolic resin added is 2.5% of the sand mass. The melting point of the coated sand is 132℃ and the compressive strength at room temperature is 26MPa.

[0019] 2. Shell stacking arrangement: The prepared coated sand shell is stacked in 4 layers to achieve horizontal casting. A sealing and heat insulation pad with a thickness of 3mm and made of ceramic fiber is placed between adjacent shell layers.

[0020] 3. Raw material proportioning and smelting: Scrap steel, ferrochrome, ferromanganese, and carbon raiser are selected according to a mass ratio of 65:12:5:3, where the scrap steel has a carbon content of 0.18%, a sulfur content of 0.04%, and a phosphorus content of 0.04%. The above raw materials are added sequentially to a medium-frequency induction furnace for smelting. The heating rate during smelting is 10℃ / min. When the smelting temperature reaches 1400℃, the first slag removal is performed, with the amount of slag removed being 0.8% of the total mass of the furnace charge. Smelting continues until the temperature reaches 1530℃.

[0021] 4. Pre-furnace inspection and deoxidation: The chemical composition of the molten metal in the furnace is detected using a direct-reading spectrometer. The test items include the content of C, Si, Mn, Cr, S, and P. After the test is qualified (where the mass fraction of Si is 1.0%, the mass fraction of Mn is 1.2%, the mass fraction of Cr is 6.5%, the mass fraction of S is 0.025%, and the mass fraction of P is 0.025%), 0.5 kg of industrial pure aluminum ingot with a purity of 99.8% is added for deoxidation two minutes before tapping. The ingot is added uniformly from the top of the smelting furnace using a special feeding device, and the addition time is 40 seconds.

[0022] 5. Slag Removal from Transfer Ladle: The deoxidized molten metal is transferred to the transfer ladle. Slag removal is carried out by a combination of mechanical and manual slag removal. The mechanical slag removal time is 4 minutes, and the manual slag removal removes the residual slag. After slag removal, the residual slag in the transfer ladle is 0.25%.

[0023] 6. Casting: The stacked shell molds are cast at a casting temperature of 1450℃ using a bottom-pouring casting system. The casting speed is controlled at 1.0 kg / s. The casting temperature is monitored in real time during the casting process, and the temperature fluctuation range is controlled within ±5℃.

[0024] 7. Cooling and Unpacking: After casting, the entire stack of boxes is kept at 850℃ for 3 hours, then allowed to cool naturally to room temperature before unpacking to obtain the grinding balls. Testing showed that the yield of this grinding ball product was 74%, and the mispacking rate was 0.2%.

[0025] Example 2 The present invention proposes a process for casting grinding balls using a horizontally stacked, coated sand shell type, with the following specific steps: 1. Preparation of coated sand shell: The shell is made of phenolic resin coated sand, with the amount of phenolic resin added being 3.2% of the sand mass. The melting point of the coated sand is 135℃ and the compressive strength at room temperature is 28MPa.

[0026] 2. Shell stacking arrangement: The prepared coated sand shell is stacked in 6 layers to achieve horizontal casting. A sealing and heat insulation pad with a thickness of 4mm and made of ceramic fiber is set between adjacent shell layers.

[0027] 3. Raw material proportioning and smelting: Select scrap steel, ferrochrome, ferromanganese, and carbon raiser according to a mass ratio of 70:15:6:4. The scrap steel has a carbon content of 0.15%, a sulfur content of 0.03%, and a phosphorus content of 0.03%. Add the raw materials to the medium-frequency induction furnace, with a heating rate of 9℃ / min. At 1400℃, remove 0.6% of the slag for the first time, and continue smelting to 1550℃.

[0028] 4. Pre-furnace inspection and deoxidation: The chemical composition is qualified by direct reading spectrometer (Si mass fraction 1.2%, Mn 1.5%, Cr 8.0%, S 0.02%, P 0.02%). Two minutes before tapping out of the furnace, 0.6Kg of industrial pure aluminum ingot with a purity of 99.7% is added for deoxidation. The ingot is fed into the furnace at a uniform speed from the top of the special feeding device for 50 seconds.

[0029] 5. Slag removal in transit: Mechanical slag removal for 3.5 minutes + manual slag removal, with 0.2% molten slag residue.

[0030] 6. Pouring: Pouring temperature 1480℃, bottom pouring system, pouring speed 1.2kg / s, real-time temperature control, fluctuation ±5℃.

[0031] 7. Cooling and Unpacking: Insulate at 880℃ for 2.5 hours, then allow to cool naturally to room temperature before unpacking. Product yield is 74.2%, and the mispacking rate is 0.18%.

[0032] Example 3 The present invention proposes a process for casting grinding balls using a horizontally stacked, coated sand shell type, with the following specific steps: 1. Preparation of coated sand shell: Phenolic resin coated sand is pressed into a shell shape, with phenolic resin addition of 3.8%, the melting point of the coated sand is 138℃, and the compressive strength at room temperature is 30MPa.

[0033] 2. Shell-shaped stacking arrangement: 3 shell-shaped stacking horizontal casting, with 2.5mm thick ceramic fiber sealing and heat insulation pads installed between adjacent layers.

[0034] 3. Raw material ratio and smelting: Mass ratio 62:11:4:2.5, scrap steel 0.19% carbon, 0.045% sulfur, 0.045% phosphorus. Smelting in a medium frequency induction furnace, heating rate 11℃ / min, first slag removal at 1400℃, slag removal amount 1.0%, smelting to 1540℃.

[0035] 4. Pre-furnace inspection and deoxidation: The spectral analysis results are qualified (Si 0.9%, Mn 1.1%, Cr 5.8%, S 0.028%, P 0.028%). Two minutes before tapping out of the furnace, add 0.45 kg of 99.9% pure aluminum ingot for deoxidation, and add it at a uniform speed over 35 seconds.

[0036] 5. Slag removal in transit: Mechanical slag removal for 4.5 minutes + manual slag cleaning, with 0.28% molten slag remaining.

[0037] 6. Pouring: Pouring temperature 1430℃, bottom pouring, speed 0.9kg / s, temperature fluctuation ±5℃.

[0038] 7. Cooling and Unpacking: Keep warm at 820℃ for 3.5 hours, then allow to cool naturally before unpacking. Product yield is 73.8%, and the mispacking rate is 0.19%.

[0039] Experimental Section I. Experimental Objective The advantages of the three embodiments in terms of yield, mis-boxing rate, product mechanical properties and production efficiency are verified. By comparing with the traditional vertical casting process, the beneficial effects of the technical solution are quantified.

[0040] II. Experimental Subjects 1. Experimental Group: Φ25mm grinding balls were produced using the process schemes of the three embodiments, which were respectively designated as Experimental Group 1 (Process of Embodiment 1), Experimental Group 2 (Process of Embodiment 2), and Experimental Group 3 (Process of Embodiment 3).

[0041] 2. Comparative Example: Φ25mm grinding balls were produced using the traditional vertical casting process (disclosed in the technical background: yield rate 70%, miscast rate 3%), and are referred to as Comparative Example 1.

[0042] III. Control of Experimental Conditions 1. All experimental groups and control groups used the same raw material base: the basic components of scrap steel, ferrochrome, ferromanganese and carbon raiser were the same (only the experimental groups were adjusted according to their respective proportions).

[0043] 2. Uniform production batch: 1000 grinding balls were produced for each group of experiments, and a total of 3 parallel experiments were conducted, with the average value taken.

[0044] 3. Standardized testing equipment: The same direct-reading spectrometer is used to test chemical composition, the same universal testing machine is used to test mechanical properties, and the same set of measuring tools with an accuracy of 0.01mm is used to test dimensional deviations.

[0045] IV. Detection Indicators 1. Yield: The percentage of qualified products out of the total number of cast products.

[0046] 2. Mis-boxing rate: The percentage of products with mis-boxing defects (mis-boxing amount ≥ 0.3mm) out of the total number of products.

[0047] 3. Mechanical properties: Rockwell hardness (HRC), impact toughness (αk, unit: J / cm²), wear resistance (wear amount, unit: g / 100h, tested using ML-100 wear testing machine).

[0048] 4. Production efficiency: Total time from raw material melting to unpacking for a single batch (1000 pieces) of products (unit: h).

[0049] V. Experimental Results and Data Statistics

[0050] VI. Experimental Conclusions 1. Yield: The yield of the three experimental groups (73.8%-74.2%) was significantly higher than that of the control group (70.0%), with an increase of 5.4%-6.0%, which verified the optimization effect of the horizontal stacking process on raw material utilization.

[0051] 2. Misclassification rate: The misclassification rate of the experimental group (0.18%-0.2%) was much lower than that of the control group (3.0%), with a reduction of 93.3%-94%, proving that the design of horizontal stacking + sealing heat insulation pad effectively solved the problem of prominent misclassification defects in traditional processes.

[0052] 3. Mechanical properties: The Rockwell hardness (64-68HRC) and impact toughness (16.2-18.3J / cm²) of the experimental group grinding balls were better than those of the comparative group (58HRC, 12.5J / cm²), and the wear resistance was improved by 40.7%-44.2%, which reflects the role of the process in improving the intrinsic quality of the product.

[0053] 4. Production efficiency: The production time per batch in the experimental group (5.8-6.5h) was reduced by 23.5%-31.8% compared with the control group (8.5h), which verified the effect of "horizontal stacking + optimized process" on improving production capacity.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for casting grinding balls using a horizontally stacked, coated sand shell mold, characterized in that, Includes the following steps: The coated sand shell molds are arranged in layers to achieve horizontal casting. Scrap steel, ferrochrome, ferromanganese, and carbon raiser are added sequentially in the smelting furnace according to the specified proportions. The furnace is smelted to ≥1520℃. After the chemical composition is tested and found to be qualified before the furnace, 0.4-0.7 kg of aluminum ingots are added two minutes before tapping to deoxidize the molds. After slag removal in the transfer ladle, casting is carried out at a casting temperature of 1420℃-1520℃.

2. The process for casting grinding balls using a horizontally stacked, coated sand shell mold according to claim 1, characterized in that, The number of layers of the coated sand shell is 3-8, and a sealing and heat insulation pad is set between two adjacent shell layers. The thickness of the sealing and heat insulation pad is 2-5mm, and the material is ceramic fiber.

3. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, The mass ratio of scrap steel, ferrochrome, ferromanganese, and carbon raiser is (60-75):(10-18):(3-8):(2-5), and the carbon content of the scrap steel is ≤0.2%, sulfur content is ≤0.05%, and phosphorus content is ≤0.05%.

4. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, The smelting process uses a medium-frequency induction furnace with a heating rate of 8-12℃ / min. The first slag removal is carried out when the smelting temperature reaches 1400℃, and the amount of slag removed is 0.5-1.2% of the total mass of the furnace charge.

5. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, The aluminum ingots are industrial pure aluminum ingots with a purity of ≥99.7%. They are added from the top of the smelting furnace at a uniform speed using a special feeding device, and the feeding time lasts for 30-60 seconds.

6. The process for casting grinding balls using a horizontally stacked, coated sand shell mold according to claim 1, characterized in that, The slag removal of the transshipment container adopts a combination of mechanical slag removal and manual slag removal. The mechanical slag removal time is 3-5 minutes, and the manual slag removal removes the residual slag. After slag removal, the residual slag in the transshipment container is ≤0.3%.

7. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, The bottom-pouring system is used during pouring, with the pouring speed controlled at 0.8-1.5 kg / s. The pouring temperature is monitored in real time during the pouring process, and the temperature fluctuation range is controlled within ±5℃.

8. The process for casting grinding balls using a horizontally stacked, coated sand shell mold according to claim 1, characterized in that, The coated sand shell is made by pressing phenolic resin coated sand. The amount of phenolic resin added to the coated sand is 2.5-4.0% of the sand mass. The melting point of the coated sand is ≥130℃ and the compressive strength at room temperature is ≥25MPa.

9. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, After the casting is completed, the stacked boxes are kept warm and cooled at a temperature of 800-900℃ for 2-4 hours. Then, they are allowed to cool naturally to room temperature before being opened.

10. The process for casting grinding balls using a horizontal stacked, coated sand shell mold according to claim 1, characterized in that, Chemical composition analysis before the furnace is performed using a direct-reading spectrometer. The analysis items include the content of C, Si, Mn, Cr, S, and P. The mass fraction of Si is controlled at 0.8-1.5%, the mass fraction of Mn is controlled at 1.0-2.0%, the mass fraction of Cr is controlled at 5.0-10.0%, the mass fraction of S is ≤0.03%, and the mass fraction of P is ≤0.03%.

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