Preparation method of green sand mixed binder for pulverized coal-free casting

Abstract

The invention discloses a preparation method of a green sand mixed binder for pulverized coal-free casting, particularly relates to the technical field of materials, and relates to a preparation method of a green sand mixed binder for pulverized coal-free casting. The preparation raw materials comprise the following components in parts by weight: 115 to 125 parts of montmorillonite, 115 to 125 parts of kaolin, 10 to 14 parts of nanoscale silica sol, 5 to 10 parts of bamboo charcoal powder, 10 to 15 parts of calcium carbonate, 5 to 10 parts of rice hull ash, 4.2 to 5.8 parts of lactic acid bacteria fermentation liquor, 2 to 5 parts of sodium lignin sulfonate and 11 to 16 parts of deionized water. According to the method, pulverized coal is completely abandoned, minerals such as montmorillonite and kaolin and bio-based materials of bamboo charcoal powder and rice hull ash are adopted as raw materials, and non-combustion processes such as silica sol coating and biological fermentation are combined, so that SO2 emission and dust pollution are completely eradicated from the source, and the workshop environment is clean; the problems of atmospheric pollution and occupational health caused by dependence on pulverized coal in the traditional technology are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, and more particularly to a preparation method of a wet sand mixing binder for coal-free casting. BACKGROUND

[0002] In the casting industry, wet sand molding is widely used due to its low cost and simple operation. Traditional wet sand usually uses coal powder as an auxiliary material to improve the surface quality of castings and prevent defects such as sand sticking.

[0003] The sand mixing binder in the related art includes coal powder, bentonite, and water. The coal powder burns to form a reducing gas film, which isolates the metal liquid from the sand mold and prevents sand sticking. The bentonite swells to form a colloid after absorbing water, which wraps the sand particles to achieve wet-state bonding. The water activates the colloid properties of bentonite to adjust the plasticity and fluidity of the sand.

[0004] However, there are still some drawbacks in actual use, such as environmental performance defects. The sand mixing binder in the related art relies on coal powder, which releases SO2 and dust upon combustion, and the casting defect control is insufficient. The coal powder particles in the sand mixing binder in the related art are unevenly distributed, which easily forms a local carbon-rich area, leading to sand inclusion and peeling defects. The stability is low. The sand mixing binder in the related art relies on a single bonding mechanism of bentonite, and the strength of the wet sand fluctuates greatly, with a sharp drop at high temperatures. SUMMARY

[0005] To improve the above problems and reduce the environmental performance defects, insufficient casting defect control, and low stability of the wet sand mixing binder for coal-free casting in the related art, the present application provides a preparation method of a wet sand mixing binder for coal-free casting to solve the problems raised in the background art.

[0006] To achieve the above-mentioned purposes, the present application provides the following technical solutions: A wet sand mixing binder for coal-free casting, comprising the following steps: S1, weigh the montmorillonite and kaolin, and crush them in an air flow pulverizer to a particle size of ≤5 μm. Transfer them to a vacuum drying oven and dry them at 100-120°C for 2-3h to remove surface adsorbed water. Then add the dried mineral powder to a silica sol and ultrasonically disperse it at a frequency of 40 kHz and a power of 200 W for 30 min. Then centrifuge it at a speed of 5000 r / min for 10 min. Collect the precipitate and vacuum dry it at 60°C to a water content of ≤1% to obtain silica sol-coated mineral particles. S2, the bamboo charcoal powder is placed in a tube furnace, calcined at 800-900℃ for 1-2h under nitrogen atmosphere, after removing the volatile components, cooled, and crushed to a particle size of ≤20μm, to obtain a high-purity bio-carbon source with a carbon content of ≥85% and an ash content of ≤5%; the calcium carbonate, rice husk ash and lactic acid bacteria fermentation broth are mixed, the pH of the system is adjusted to 5.5-6.5, and then transferred into a fermentation tank, and fermented at 30-35℃ for 12-24h, during which the material is stirred at a speed of 100r / min every 2h, and after the fermentation is completed, the material is dried at 60℃ until the moisture content is ≤3%, to obtain a bio-fermentation activated material; S3, the silica sol coated mineral particles prepared in S1, the bio-fermentation activated material prepared in S2 and the auxiliary modifier sodium lignosulfonate are put into a three-dimensional high-speed mixer, mixed at a speed of 800-1000r / min for 10-15min, and then subjected to three-stage gradient heating treatment, first heated to 60-80℃, kept for 30min, then heated to 100-120℃, kept for 20min, and finally heated to 150-180℃, kept for 10min, to obtain a glassy bonding film; S4, the glassy bonding film obtained in S3 is cooled to room temperature, deionized water is added, and then transferred into a sand mill, ground at a shearing rate of 2000-3000r / min for 30-40min, so that the particle size is uniformly distributed in the range of 1-5μm, to form a stable colloidal dispersion system; the slurry is dried through a spray drying tower, then dried into a powder, sieved through a 200 mesh screen, and then packaged in an aluminum foil bag under vacuum sealing, to obtain a wet sand mixing and bonding agent for coal-free foundry with a water content of ≤0.5%, thereby obtaining a coal-free wet sand mixing and bonding agent for foundry.

[0007] Preferably, the preparation raw materials of the wet sand mixing and bonding agent for coal-free foundry are as follows: montmorillonite 15-25 parts, kaolin 15-25 parts, nano-silica sol 100-144 parts, bamboo charcoal powder 5-10 parts, calcium carbonate 10-15 parts, rice husk ash 5-10 parts, lactic acid bacteria fermentation broth 4.2-5.8 parts, sodium lignosulfonate 2-5 parts, and deionized water 11-16 parts.

[0008] Preferably, the silica sol is a silica sol with a SiO2 content of 15% and a particle size of 15nm.

[0009] Preferably, the lactic acid bacteria fermentation broth is a lactic acid bacteria fermentation broth with a viable bacterial concentration of ≥1×10 8 CFU / mL.

[0010] Preferably, the spray drying tower drying conditions in S4 are as follows: inlet air temperature 180-200℃, outlet air temperature 80-90℃, and atomization pressure 0.3-0.5MPa.

[0011] 1. The present application completely abandons pulverized coal and uses minerals such as montmorillonite and kaolin, and bio-based materials such as bamboo charcoal powder and rice husk ash as raw materials, combined with silicon sol coating, biological fermentation and other non-combustion processes, to completely eliminate SO2 emissions and dust pollution from the source, achieve clean workshop environment, and solve the problems of air pollution and occupational health caused by the dependence of traditional technology on pulverized coal. 2. The present application modifies the surface of the mineral raw material, activates it by biological fermentation, and processes it by gradient thermochemical treatment, to enhance the uniformity of the sand mold interface bonding, improve the harmful gas adsorption capacity, and optimize the gas evolution process, thereby effectively inhibiting casting defects such as pores, sand eyes, and sand inclusion, and significantly improving the quality and reliability of the castings. 3. The present application uses interface modification, multi-temperature zone gradient control, and precise particle size control processes to enhance the wet sand bonding strength at room temperature and high temperature, stabilize the moisture content of the sand, and improve the moisture absorption and desorption resistance, thereby adapting to different casting process conditions and environmental humidity, ensuring consistent sand performance stability, and solving the process fluctuation problem caused by the environmental sensitivity of traditional binders. DETAILED DESCRIPTION

[0012] The present application will be further described in detail below in conjunction with the examples of the present application. The raw materials used in the examples and embodiments of the present application are all common commercially available materials, except for the special descriptions below. Preparation Examples 1-5 A coal-free wet sand mixing binder for casting is prepared from the following components and their corresponding ratios as shown in the table below, and is prepared by the following method: S1, montmorillonite and kaolin are weighed and ground in an air flow grinder to a particle size of ≤5 μm, then transferred to a vacuum drying oven and dried at 100°C for 2h to remove surface adsorbed water, then the dried mineral powder is added to the silicon sol and ultrasonically dispersed at a frequency of 40 kHz and a power of 200 W for 30 min, then centrifuged at a speed of 5000 r / min for 10 min, the precipitate is collected and vacuum dried at 60°C to a moisture content of ≤1%, to obtain silicon sol coated mineral particles; The silicon sol is a silicon sol with a SiO2 content of 15% and a particle size of 15 nm.

[0013] S2, the bamboo charcoal powder is placed in a tube furnace and calcined at 800°C for 1h under a nitrogen atmosphere to remove volatile matter, then cooled and ground to a particle size of ≤20 μm to obtain a high-purity biological carbon source with a carbon content of ≥85% and an ash content of ≤5%; calcium carbonate, rice husk ash and lactic acid bacteria fermentation broth are mixed, the pH of the system is adjusted to 5.5, and then transferred to a fermentation tank, and fermented at 30°C for 12h, with stirring at a speed of 100 r / min every 2h during the fermentation, and then the material is dried at 60°C to a moisture content of ≤3% after fermentation to obtain a biological fermentation activated material. The lactic acid bacteria fermentation liquor has a viable bacteria concentration of ≥1×10 8 CFU / mL.

[0014] S3, the silicon sol coated mineral particles prepared in S1, the bio-fermentation activated material prepared in S2, and the auxiliary modifier sodium lignin sulfonate are put into a three-dimensional high-speed mixer, mixed at a speed of 800 r / min for 10 min, and then subjected to three-stage gradient heating treatment, first heated to 60°C, kept for 30 min, then heated to 100°C, kept for 20 min, and finally heated to 150°C, kept for 10 min, to obtain a glassy bonding film; S4, the glassy bonding film obtained in S3 is cooled to room temperature, deionized water is added, and transferred into a sand mill, ground at a shearing rate of 2000 r / min for 30 min, so that the particle size is uniformly distributed in 1-5 μm, forming a stable colloidal dispersion system; the slurry is dried into a powder by a spray drying tower at an inlet air temperature of 180°C, an outlet air temperature of 80°C, and an atomization pressure of 0.3 MPa, sieved through a 200-mesh screen, vacuum sealed with aluminum foil bags, and prepared into a wet sand mixing and binding agent for coal-free casting with a water content of ≤0.5%, to obtain a coal-free casting wet sand mixing and binding agent.

[0015] Table: the components and mass ratio (g) of the raw materials in preparation examples 1-5

[0016]

[0017] Preparation example 6 A wet sand mixing and binding agent for coal-free casting, which is different from preparation example 1 in that the preparation method is as follows: S1, montmorillonite and kaolin are weighed, put into an air flow pulverizer, and pulverized to a particle size of ≤5 μm, transferred to a vacuum drying oven, dried at 110°C for 2.5 h to remove surface adsorbed water, and then the dried mineral powder is added to a silicon sol, ultrasonically dispersed at a frequency of 40 kHz and a power of 200 W for 30 min, and then centrifuged at a speed of 5000 r / min for 10 min, the precipitate is collected and vacuum dried at 60°C to a water content of ≤1%, to obtain silicon sol coated mineral particles; S2, the bamboo charcoal powder is placed in a tube furnace, calcined at 850°C for 1.5 h under a nitrogen protective atmosphere, cooled after removing the volatile matter, and pulverized to a particle size of ≤20 μm, to obtain a high-purity biological carbon source with a carbon content of ≥85% and an ash content of ≤5%; the calcium carbonate, rice husk ash, and lactic acid bacteria fermentation liquor with a viable bacteria concentration of ≥1×10 8The lactic acid bacteria fermentation liquor with CFU / mL is mixed, the pH of the system is adjusted to 5.5, and then the mixture is transferred into a fermentation tank, and then fermentation is carried out at 32.5°C for 18 hours, during which the mixture is stirred at a speed of 100 r / min every 2 hours; after the fermentation is completed, the material is dried at 60°C until the water content is less than or equal to 3%, and then a bio-fermentation activated material is obtained; S3, the silicasol-coated mineral particles prepared in S1, the bio-fermentation activated material prepared in S2, and the auxiliary modifier sodium lignosulfonate are put into a three-dimensional high-speed mixer, mixed at a speed of 900 r / min for 13 minutes, and then subjected to three-stage gradient heating, first heated to 70°C, kept for 30 minutes, then heated to 110°C, kept for 20 minutes, and finally heated to 165°C, kept for 10 minutes, to obtain a glassy bonding film; S4, the glassy bonding film obtained in S3 is cooled to room temperature, deionized water is added, and then the mixture is transferred into a sand mill and ground at a shearing rate of 2500 r / min for 35 minutes, so that the particle size is uniformly distributed in the range of 1-5 μm, to form a stable colloidal dispersion system; the slurry is dried into a powder by a spray drying tower at an inlet air temperature of 190°C, an outlet air temperature of 85°C, and an atomization pressure of 0.4 MPa, and then sieved through a 200-mesh screen, and then packaged in an aluminum foil bag under vacuum sealing, to obtain a wet sand mixing and bonding agent for coal-dust-free foundry use, with a water content of less than or equal to 0.5%.

[0018] Preparation Example 7 A wet sand mixing and bonding agent for coal-dust-free foundry use, which is different from that of Preparation Example 1 in the preparation method as follows: S1, montmorillonite and kaolin are weighed and put into an air flow pulverizer to be pulverized to a particle size of less than or equal to 5 μm, and then transferred into a vacuum drying oven and dried at 120°C for 3 hours to remove the surface adsorbed water, and then the dried mineral powder is added into a silicasol, ultrasonically dispersed at a frequency of 40 kHz and a power of 200 W for 30 minutes, and then centrifuged at a speed of 5000 r / min for 10 minutes, and then the precipitate is collected and vacuum dried at 60°C until the water content is less than or equal to 1%, to obtain silicasol-coated mineral particles; S2, bamboo charcoal powder is put into a tube furnace and calcined at 900°C for 1 hour under a nitrogen protective atmosphere, cooled after removing the volatile matter, and pulverized to a particle size of less than or equal to 20 μm, to obtain a high-purity biological carbon source with a carbon content of more than or equal to 85% and an ash content of less than or equal to 5%; calcium carbonate, rice husk ash, and lactic acid bacteria fermentation liquor with a viable bacterial concentration of more than or equal to 1×10 8 The lactic acid bacteria fermentation liquor with CFU / mL is mixed, the pH of the system is adjusted to 5.5, and then the mixture is transferred into a fermentation tank, and then fermentation is carried out at 32.5°C for 18 hours, during which the mixture is stirred at a speed of 100 r / min every 2 hours; after the fermentation is completed, the material is dried at 60°C until the water content is less than or equal to 3%, and then a bio-fermentation activated material is obtained; S3, the silicasol coated mineral particles prepared in S1, the bio-fermentation activated material prepared in S2 and the auxiliary modifier sodium ligninsulfonate are put into a three-dimensional high-speed mixer, mixed at a speed of 1000 r / min for 15 min, and then subjected to three-stage gradient heating treatment, first heated to 80°C, kept for 30 min, then heated to 120°C, kept for 20 min, and finally heated to 180°C, kept for 10 min, to obtain a glassy bonding film; S4, the glassy bonding film obtained in S3 is cooled to room temperature, deionized water is added, and then transferred into a sand mill, ground at a shearing rate of 3000 r / min for 40 min, so that the particle size is uniformly distributed in 1-5 μm, to form a stable colloidal dispersion system; the slurry is dried into a powder by a spray drying tower at an inlet temperature of 200°C, an outlet temperature of 90°C and an atomization pressure of 0.5 MPa, sieved through a 200-mesh screen, and then vacuum sealed with an aluminum foil bag to obtain a wet sand mixing and bonding agent for coal-free casting with a water content of ≤0.5%.

[0019] Preparation Example 8 A wet sand mixing and bonding agent for coal-free casting, which is different from that of Preparation Example 1, is prepared by the following method: S1, montmorillonite and kaolin are weighed and put into an airflow pulverizer to be pulverized to a particle size of ≤5 μm, and then transferred into a vacuum drying oven to be dried at 100°C for 2 h to remove the surface adsorbed water, and then the dried mineral powder is added into a silicasol, ultrasonically dispersed at a frequency of 40 kHz and a power of 200 W for 30 min, and then centrifuged at a speed of 5000 r / min for 10 min, and the precipitate is collected and vacuum dried at 60°C to a water content of ≤1%, to obtain silicasol coated mineral particles; S2, bamboo charcoal powder is put into a tube furnace, calcined at 800°C for 1 h under a nitrogen protective atmosphere, cooled after removing the volatile matter, and pulverized to a particle size of ≤20 μm, to obtain a high-purity biological carbon source with a carbon content of ≥85% and an ash content of ≤5%; calcium carbonate, rice husk ash and lactic acid bacteria fermentation liquid are mixed, the pH of the system is adjusted to 6, and then transferred into a fermentation tank, and fermented at 30°C for 12 h, with stirring at a speed of 100 r / min every 2 h during the fermentation, and then the material is dried at 60°C to a water content of ≤3% after the fermentation, to obtain a bio-fermentation activated material; S3, the silicasol coated mineral particles prepared in S1, the bio-fermentation activated material prepared in S2 and the auxiliary modifier sodium ligninsulfonate are put into a three-dimensional high-speed mixer, mixed at a speed of 800 r / min for 10 min, and then subjected to three-stage gradient heating treatment, first heated to 60°C, kept for 30 min, then heated to 100°C, kept for 20 min, and finally heated to 150°C, kept for 10 min, to obtain a glassy bonding film; S4, cooling the glassy adhesive film obtained in S3 to room temperature, adding deionized water, and transferring into a sand mill to grind for 30 min at a shearing rate of 2000 r / min, so that the particle size is uniformly distributed in 1-5 μm to form a stable colloidal dispersion system; the slurry is dried into a powder by a spray drying tower at an inlet air temperature of 180 ℃, an outlet air temperature of 80 ℃, and an atomization pressure of 0.3 MPa, and after sieving through a 200 mesh screen, vacuum sealing packaging is performed with an aluminum foil bag to prepare a wet sand mixing and binding agent for coal-dust-free foundry use with a water content of ≤0.5%, thereby obtaining the wet sand mixing and binding agent for coal-dust-free foundry use.

[0020] Preparation Example 9 A wet sand mixing and binding agent for coal-dust-free foundry use, which is different from that of Preparation Example 1, is prepared by the following method: S1, weighing the montmorillonite and kaolin, and pulverizing in an airflow pulverizer to a particle size of ≤5 μm, and then transferring into a vacuum drying oven to dry at 100 ℃ for 2 h to remove surface adsorbed water, and then adding the dried mineral powder into a silica sol, and ultrasonic dispersing at a frequency of 40 kHz and a power of 200 W for 30 min, and then centrifuging at a speed of 5000 r / min for 10 min, and collecting the precipitate and vacuum drying at 60 ℃ to a water content of ≤1% to obtain silica sol coated mineral particles; wherein the silica sol is a silica sol with a SiO2 content of 15% and a particle size of 15 nm.

[0021] S2, calcining the bamboo charcoal powder in a tube furnace under a nitrogen protective atmosphere at 800 ℃ for 1 h to remove volatile matter, and then cooling and pulverizing to a particle size of ≤20 μm to prepare a high-purity biological carbon source with a carbon content of ≥85% and an ash content of ≤5%; mixing calcium carbonate, rice husk ash, and lactic acid bacteria fermentation liquor, and adjusting the pH of the system to 6.5, and then transferring into a fermentation tank, and constant temperature fermentation at 30 ℃ for 12 h, and stirring once every 2 h at a speed of 100 r / min during the period, and then drying the material at 60 ℃ to a water content of ≤3% after the fermentation is completed to obtain a biological fermentation activated material; wherein the lactic acid bacteria fermentation liquor is a lactic acid bacteria fermentation liquor with a viable bacterial concentration of ≥1×10 8 CFU / mL.

[0022] S3, adding the silica sol coated mineral particles prepared in S1, the biological fermentation activated material prepared in S2, and the auxiliary modifier sodium lignosulfonate into a three-dimensional high-speed mixer, and mixing at a speed of 800 r / min for 10 min, and then sequentially performing three-stage gradient heating treatment, first heating to 60 ℃, and holding for 30 min, then heating to 100 ℃, and holding for 20 min, and finally heating to 150 ℃, and holding for 10 min, to obtain a glassy adhesive film. S4, cooling the glassy adhesive film obtained in S3 to room temperature, adding deionized water, and transferring into a sand mill to grind for 30 min at a shearing rate of 2000 r / min, so that the particle size is uniformly distributed in 1-5 μm to form a stable colloidal dispersion system; the slurry is dried into powder by a spray drying tower at an inlet temperature of 180 ℃, an outlet temperature of 80 ℃, and an atomization pressure of 0.3 MPa, and after sieving through a 200 mesh screen, vacuum sealing packaging is performed by using an aluminum foil bag to obtain a wet sand mixing binder for coal-dust-free foundry use with a water content of ≤0.5%, thereby obtaining the wet sand mixing binder for coal-dust-free foundry use.

[0023] Performance detection test The wet sand mixing binder for coal-dust-free foundry use prepared in each example is selected for testing, and the test objects are 90 portions of the wet sand mixing binder for coal-dust-free foundry use, 10 portions in each group; the strength and permeability resistance are detected, and the specific detection steps are as follows: Environmental performance: First, the wet sand mixing binder for coal-dust-free foundry use prepared in the example is sampled, the method for determining and sampling gaseous pollutants in exhaust gas from stationary sources is used, waste gas is collected during the casting pouring process, and the concentration of SO2 is determined by using the ultraviolet fluorescence method to characterize the environmental performance of the wet sand mixing binder for coal-dust-free foundry use; the detection results and evaluation criteria are as follows: The emission concentration of SO2 is <10 mg / m 3 (considered as good environmental performance); The emission concentration of SO2 is >10 mg / m 3 (considered as poor environmental performance).

[0024] Defect control ability: First, the wet sand mixing binder for coal-dust-free foundry use prepared in the example is sampled, visual inspection, X-ray flaw detection or ultrasonic detection is used, the number of defects such as pores, sand eyes, sand inclusions and sand sticking is counted, and then the average value is taken to characterize the defect control ability of the wet sand mixing binder for coal-dust-free foundry use; the detection results and evaluation criteria are as follows: The defect rate of the casting is <10% (considered as strong defect control ability); The defect rate of the casting is >10% (considered as weak defect control ability).

[0025] Stability: First, the wet sand mixing binder for coal-dust-free foundry use prepared in the example is sampled, and the bending strength is determined after heating to 500 ℃ to characterize the stability of the wet sand mixing binder for coal-dust-free foundry use; the detection results and evaluation criteria are as follows: The high-temperature bending strength is >0.3 MPa (considered as strong stability); The high-temperature bending strength is <0.3 MPa (considered as weak stability).

[0026] It is necessary to specify that the above-mentioned prepared coal-powder-free casting wet sand mixed binder is the coal-powder-free casting wet sand mixed binder produced in normal production mode, the coal-powder-free casting wet sand mixed binder with defects, and the data of the coal-powder-free casting wet sand mixed binder is discarded.

[0027] Examples 1-5 A coal-powder-free casting wet sand mixed binder, and the corresponding relationship of the preparation method thereof is shown in the following table.

[0028] Table: Comparison table of use of coal-powder-free casting wet sand mixed binder in examples 1-5

[0029] The coal-powder-free casting wet sand mixed binder in the above-mentioned examples 1-5 is extracted, and its SO2 emission concentration, casting defect rate, and high-temperature bending strength are tested according to the above-mentioned measurement steps and measurement standards, and the test results are averaged and recorded in the following table.

[0030] Table: Performance test results of SO2 emission concentration, casting defect rate, and high-temperature bending strength of examples 1-5

[0031] From the above table, the production of the coal-free casting wet sand mixed binder in examples 1-5 has good effect of improving the production effect of the coal-free casting wet sand mixed binder, montmorillonite as the main wet state binder, builds the initial bonding force between sand particles, the layered silicate structure expands after absorbing water to form a colloid, forms hydrogen bonds with the Si-O bonds on the surface of the sand particles through the hydroxyl groups, realizes the physical-chemical bonding in wet state, after coated with silica sol, the surface forms a SiO2 nano protective layer, improves the high temperature resistance, avoids the strength drop caused by the loss of interlayer water of traditional bentonite at high temperature, kaolin has the effect of high temperature bonding enhancement and defect inhibition, dehydration at medium temperature generates metakaolin, forms a mesoporous adsorption structure, chemically adsorbs harmful gas of metal liquid, high temperature and silica sol melt to generate low melting point glass phase, forms a covalent bond bonding film on the surface of the sand particles, replaces the mechanical bonding of traditional coal powder residual carbon, nano silica sol is used for mineral surface coating and bonding film strengthening, increases the surface hydroxyl group density to improve the hydrogen bond binding energy of the sand particles, generates glassy bonding film by melting with minerals at high temperature, enhances the high temperature strength and moisture resistance of the sand mold, bamboo charcoal powder pyrolysis generates nano carbon crystal nucleus, reacts with SiO2 in the silica sol coating layer to generate SiC-C composite protective layer, physically isolates the metal liquid and the sand mold; calcium carbonate is used for gas regulation and mesoporous structure construction, low temperature decomposition produces CO2 micro-bubbles, forms an initial exhaust channel, improves the sand mold permeability; after fermentation by lactic acid bacteria, the surface generates an active layer of calcium carboxylate, reduces the gas hole defects, rice husk ash is used as a silicon source supplement and collapsibility regulator, provides silicon source to participate in glass phase formation and enhance the high temperature strength of the sand mold; thereby achieving the purpose of improving the production effect of the coal-free casting wet sand mixed binder. The emission concentration of SO2 is 0 mg / m 3 , which is considered to have good environmental performance; the casting defect rate is 3.4-4.5%, which is considered to have strong defect control ability; the high temperature bending strength is 0.38-0.48 MPa, which is considered to have strong stability.

[0032] It can be seen that under the condition of certain production raw materials, the production effect of the wet sand mixed binder for coal-free foundry can be increased by adjusting the preparation raw material ratio. It is not difficult to see from the above table data that when the wet sand mixed binder for coal-free foundry is prepared, the wet sand mixed binder for coal-free foundry prepared by using 120 parts of montmorillonite, 125 parts of kaolin, 13.5 parts of nano-silica sol, 5 parts of bamboo charcoal powder, 15 parts of calcium carbonate, 5 parts of rice husk ash, 5.8 parts of lactic acid bacteria fermentation liquor, 2 parts of sodium lignosulfonate and 11 parts of deionized water has the strongest defect control ability and stability. The reason is that the content of kaolin reaches the upper limit, the amount of meta-kaolin generated by medium temperature dehydration is maximized, the mesoporous adsorption structure is formed, the chemical adsorption capacity of the pore-forming gas is improved, the high-temperature and 13.5 parts of silica sol are fused to generate a high-thickness glass phase binder film, the sand mold high-temperature bending strength is improved, and the sand inclusion defect caused by metal liquid erosion is effectively resisted. In this proportion, 125 parts of kaolin and 13.5 parts of high-concentration silica sol cooperate to generate a large amount of mesoporous structure to adsorb gas at medium temperature, form a thick glass phase binder film at high temperature to improve the anti-erosion ability; 11 parts of deionized water strictly controls the moisture content of the wet sand, and 5 parts of low bamboo charcoal powder makes the gas generation amount decrease and the gas generation rate stable; 15 parts of calcium carbonate is treated by 5.8 parts of lactic acid bacteria fermentation liquor, the surface active carboxyl group increases, and H2 adsorption is strengthened; at the same time, silica sol coating improves the surface hydroxyl group density and uniform coverage rate of the mineral particle, and cooperates from three aspects of gas adsorption, high-temperature strength and interface uniformity to inhibit defects such as gas hole, sand inclusion and sand sticking, especially suitable for the high gas sensitivity and high structural precision requirement of thin-walled cast steel parts, so the defect control ability is the strongest; the use of 25 parts of kaolin and 135 parts of high-concentration silica sol forms a “mineral-silica sol” composite system, the mesoporous structure generated by medium temperature dehydration cooperates with the high-temperature glass phase binder film, significantly improves the wet-state hydrogen bond bonding force and high-temperature covalent bond strength, and the wet sand normal temperature shear strength and high-temperature strength retention rate reach the peak value; the 15% deionized water forms a low moisture system, cooperates with the activation treatment of lactic acid bacteria fermentation liquor on calcium carbonate, accurately controls the moisture content of the wet sand and enhances the surface activity of the mineral, and reduces the influence of water content fluctuation on the strength of the sand mold; low bamboo charcoal powder and high silica sol coating ensure the uniform dispersion of the binder in the sand mold, reduce the stability risk caused by particle agglomeration or cracking in the process of moisture absorption and moisture removal, and obtain examples 1-5.

[0033] Examples 6-9 A wet sand mixed binder for coal-free foundry, the corresponding relationship of the preparation method used is shown in the following table.

[0034] Table: Wet sand mixed binder for coal-free foundry use situation comparison table in examples 6-9

[0035] The wet sand binder for coal-dust-free casting in the above-mentioned examples 6-9 was extracted, and its SO2 emission concentration, casting defect rate, and high-temperature bending strength were tested according to the above-mentioned measurement steps and measurement standards, and the test results were averaged and recorded in the following table.

[0036] Table: Performance test results of SO2 emission concentration, casting defect rate, and high-temperature bending strength of examples 1, 6-9

[0037] As can be seen from the above table, the wet sand binder for coal-dust-free casting in examples 6-9 has good effect on improving the production effect of the wet sand binder for coal-dust-free casting. Montmorillonite is used as the main wet binder to build the initial bonding force between sand particles. The layered silicate structure expands after absorbing water to form a colloid. Hydroxyl groups form hydrogen bonds with the Si-O bonds on the surface of the sand particles to achieve physical-chemical bonding in the wet state. After being coated with silica sol, a SiO2 nano protective layer is formed on the surface to improve the high-temperature resistance and avoid the sudden drop in strength caused by the loss of interlayer water in traditional bentonite at high temperatures. Kaolin has the functions of high-temperature bonding enhancement and defect inhibition. Dehydration at medium temperature generates metakaolin, which forms a mesoporous adsorption structure to chemically adsorb harmful gases from the metal liquid. At high temperatures, the silica sol melts to form a low-melting-point glass phase, which forms a covalent bond film on the surface of the sand particles to replace the mechanical bonding of traditional coal dust residual carbon. Nano-silica sol is used for mineral surface coating and bonding film strengthening to increase the surface hydroxyl group density and improve the hydrogen bond binding energy with sand particles. At high temperatures, the mineral melts to form a glassy bonding film, which enhances the high-temperature strength and moisture resistance of the sand mold. Bamboo charcoal powder is pyrolyzed to form a nano-sized carbon crystal nucleus, which reacts with SiO2 in the silica sol coating layer to form a SiC-C composite protective layer, which physically isolates the metal liquid from the sand mold. Calcium carbonate is used for gas regulation and mesoporous structure construction. Low-temperature decomposition produces CO2 micro-bubbles to form an initial exhaust channel and improve the permeability of the sand mold. After fermentation by lactic acid bacteria, an active layer of calcium carboxylate is formed on the surface to reduce gas hole defects. Rice hull ash is used as a silicon source supplement and dispersibility regulator to provide silicon for glass phase formation and enhance the high-temperature strength of the sand mold. Thus, the purpose of improving the production effect of the wet sand binder for coal-dust-free casting is achieved. The SO2 emission concentration of each of them is 0 mg / m 3 , which is considered to have good environmental performance. The casting defect rate is 3.6-4.2%, which is considered to have strong defect control ability. The high-temperature bending strength is 0.42-0.47 MPa, which is considered to have strong stability.

[0038] It can be seen that when the production raw materials are certain, the production effect of the wet sand mixed binder for coal-free foundry can be increased by adjusting the preparation conditions. It is not difficult to see from the above table data that when the wet sand mixed binder for coal-free foundry is prepared, the defect control ability and stability of the wet sand mixed binder for coal-free foundry prepared are also improved by increasing the temperature time of vacuum drying process, the temperature time of calcination process, the temperature time of fermentation process, the temperature time of mixing process, the temperature of three-stage gradient heating, the shear rate time of sand grinding process. The reason is that increasing the vacuum drying temperature time can fully remove the water on the surface of the mineral, enhance the silica sol coating effect, and improve the hydroxyl group density and bonding activity on the surface of the mineral; increasing the calcination temperature time makes the biological carbon source generate more nano-sized carbon crystal nucleus, promotes the uniform formation of SiC-C composite protective layer at high temperature, and strengthens the anti-sticking sand ability; prolonging the fermentation temperature time improves the activity of lactic acid bacteria, increases the content of carboxylic acid group on the surface of the mineral, and enhances the chemical adsorption of H2 and other gases; optimizing the mixing temperature time ensures uniform dispersion of raw materials and avoids local defects; three-stage gradient heating precisely controls the mesoporous structure and glass phase generation, balances gas release and high temperature strength; increasing the sand grinding shear rate time makes the particle size more uniform, the dispersibility of the binder in the sand mold is improved, and the uniform coverage rate of the bonding film is increased, thereby reducing the defects such as pores, sand inclusion and sand sticking from the aspects of gas adsorption, interface protection and structural stability, so the defect control ability is improved. Increasing the vacuum drying temperature time can more fully remove the water on the surface of the mineral, enhance the silica sol coating effect, and improve the interface bonding activity of the mineral and sand particles, and reduce the influence of moisture fluctuation on the strength; prolonging the calcination temperature time makes the biological carbon source structure more dense, promotes the formation of uniform protective layer with the mineral at high temperature, and improves the high temperature strength stability of the sand mold; increasing the fermentation temperature time can strengthen the activation of lactic acid bacteria on the mineral, generate more active groups to enhance the sand particle bonding strength and water retention capacity; optimizing the mixing temperature time ensures uniform dispersion of raw materials and avoids strength differences caused by local uneven composition; three-stage gradient heating precisely controls the formation of stable mesoporous and glass phase structure of the mineral, balances the plasticity of the sand mold at room temperature and the crack resistance at high temperature; increasing the sand grinding shear rate time makes the binder particles finer and more uniformly distributed, forms a continuous and dense bonding film, and enhances the moisture absorption and desorption resistance of the sand mold. These adjustments of preparation conditions synergistically act from the aspects of interface bonding, structural stability, moisture regulation, etc., reduce the interference of environmental factors on the performance of the sand mold, and therefore significantly improve the comprehensive stability of the binder, as obtained from Examples 1, 6-7.

[0039] It can be seen that when the production raw materials are certain, the production effect of the wet sand mixed binder for coal-free foundry can be increased by adjusting the preparation conditions. It is not difficult to see from the above table data that when the wet sand mixed binder for coal-free foundry is prepared, the defect control ability and stability of the wet sand mixed binder for coal-free foundry prepared are also highest when the system PH is 6.0 in S2 process, as obtained from Examples 1, 8-9.

[0040] The embodiments are only illustrative of the present application, not limit the present application, the skilled in the art can make the modification of the embodiments without the creative contribution according to the need after reading the specification, but as long as in the scope of the claims of the present application are protected by the patent law.

Claims

1. A method for preparing a wet sand binder for non-dust casting, characterized by, It comprises the following steps: S1, take montmorillonite, kaolin, put in airflow pulverizer, crush to particle size ≤5 μm, transfer to vacuum drying oven, dry at 100-120 ℃ for 2-3 h, remove surface adsorbed water, then add the dried mineral powder into silica sol, ultrasonic dispersion at 40 kHz frequency, 200 W power for 30 min, then centrifugal separation at 5000 r / min for 10 min, collect the precipitate and dry at 60 ℃ under vacuum to moisture content ≤1%, obtain silica sol coated mineral particles; S2, put bamboo charcoal powder into a tube furnace, calcine at 800-900 ℃ for 1-2 h under nitrogen protective atmosphere, remove volatile matter and cool, crush to particle size ≤20 μm, prepare high-purity biological carbon source with carbon content ≥85%, ash content ≤5%; mix calcium carbonate, rice husk ash and lactic acid bacteria fermentation liquor, adjust the system pH to 5.5-6.5, transfer into a fermentation tank, constant temperature fermentation at 30-35 ℃ for 12-24 h, stir once every 2 h at 100 r / min during the period, after fermentation, dry the material at 60 ℃ to moisture content ≤3%, obtain biological fermentation activated material; S3, put the silica sol coated mineral particles prepared in S1, the biological fermentation activated material prepared in S2 and the auxiliary modifier sodium lignosulfonate into a three-dimensional high-speed mixer, mix at 800-1000 r / min for 10-15 min, then carry out three-stage gradient heating treatment in turn, first heat to 60-80 ℃, keep for 30 min, then heat to 100-120 ℃, keep for 20 min, finally heat to 150-180 ℃, keep for 10 min, obtain glassy bonding film; S4, cool the glassy bonding film obtained in S3 to room temperature, add deionized water, transfer into a sand mill, grind at 2000-3000 r / min shear rate for 30-40 min, make the particle size uniformly distributed in 1-5 μm, form a stable colloidal dispersion system; pass the slurry through a spray drying tower, then dry into powder, after screening through a 200 mesh screen, vacuum seal packaging with aluminum foil bag, prepare the wet sand mixing and bonding agent for coal-free foundry with moisture content ≤0.5%, obtain the wet sand mixing and bonding agent for coal-free foundry.

2. A process for the preparation of a binder for wet sand mix for non-dusting foundry use according to claim 1, characterized in that: The preparation raw materials of the wet sand mixing and bonding agent for coal-free foundry and the weight fractions are as follows: Montmorillonite 115-125 parts, kaolin 115-125 parts, nano silica sol 10-14 parts, bamboo charcoal powder 5-10 parts, calcium carbonate 10-15 parts, rice husk ash 5-10 parts, lactic acid bacteria fermentation liquor 4.2-5.8 parts, sodium lignosulfonate 2-5 parts, deionized water 11-16 parts.

3. A process for the preparation of a binder for wet sand mix for non-dusting foundry use according to claim 1, characterized in that: The silica sol is a silica sol with SiO2 content 15% and particle size 15 nm.

4. A process for the preparation of a binder for wet sand mix for non-dusting foundry use according to claim 1, characterized in that: The lactic acid bacteria fermentation liquor is a lactic acid bacteria fermentation liquor with a viable cell concentration ≥ 1 × 10 8 CFU / mL.

5. A process for the preparation of a binder for wet sand mix for non-dusting foundry use according to claim 1, characterized in that: The spray drying tower drying conditions in S4 are as follows: inlet air temperature 180-200 ℃, outlet air temperature 80-90 ℃, atomization pressure 0.3-0.5 MPa.

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