A casting sand based on the carbonization of waste rice straw and its preparation method

Abstract

This invention relates to the field of casting molding sand preparation technology, and more particularly to a casting molding sand based on the carbonization of waste rice straw and its preparation method. The molding sand is composed of the following raw materials: quartz sand, rice straw carbon powder, molding sand binder, and water; its mass ratio is: quartz sand: rice straw carbon powder: molding sand binder: water = 100: (1~3): (7~9): (3~5). This invention utilizes the multi-level porous structure of the carbon powder obtained from the carbonization of waste rice straw, providing channels for gas discharge during the casting process, preventing gas from being entrained in the molten metal and forming pores, thus reducing the porosity defect rate of the casting. This invention uses carbon powder obtained from the carbonization of waste rice straw to replace coal powder / wood chips, reducing the cost of molding sand raw materials, while simultaneously solving the problem of agricultural waste disposal, achieving "waste treatment with waste."

Description

Technical Field

[0001] This invention relates to the field of molding sand preparation technology, and more particularly to a molding sand based on the carbonization of waste rice straw and its preparation method. Background Technology

[0002] In the foundry industry, molding sand, as the core material for casting, needs to possess sufficient strength, good venting properties, and ease of cleaning. Currently, the mainstream molding sand additives are mostly coal powder, sawdust, or resin-based materials, which have the following significant drawbacks: 1. Cost and resource issues: Coal powder is a non-renewable fossil resource, costing 800-1200 yuan per ton, leading to persistently high casting production costs in the long term; sawdust relies on forestry resources and is easily affected by seasonal and regional limitations, resulting in poor supply stability. 2. Conflict between environmental protection and performance: Coal powder combustion during casting produces harmful gases such as SO2 and tar, polluting the environment, and castings require acid washing to remove carbon; traditional sawdust has poor high-temperature resistance (easily carbonizes and fails at >600℃), leading to porosity and sand adhesion defects in large, thick-walled castings. 3. Waste of agricultural waste: my country produces more than 100 million tons of rice straw every year. The current treatment method is mainly incineration, which not only wastes resources but also causes air pollution. Although the cellulose fiber structure of rice straw has the potential to strengthen molding sand, its direct application has problems such as poor high-temperature stability, insufficient compatibility with binders, and poor dispersibility, making it difficult to meet the requirements of casting process.

[0003] In summary, existing technologies lack a molding sand technology solution that can achieve synergistic effects of "resource utilization of agricultural waste - cost reduction in casting - environmental protection and emission reduction". There is an urgent need to optimize the characteristics of rice straw charcoal powder through process optimization to make it suitable for the performance requirements of casting molding sand. Summary of the Invention

[0004] The purpose of this invention is to provide a foundry sand based on waste rice straw and its preparation method, so as to overcome the defects of existing additives such as coal powder and wood chips, such as high cost, limited resources, high pollution, and mismatched performance, thereby achieving the synergistic goal of agricultural waste resource utilization, cost reduction and efficiency improvement in the casting process, and environmental protection and emission reduction.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a casting molding sand based on the carbonization of waste rice straw, which is composed of the following raw materials: quartz sand, rice straw carbon powder, molding sand binder, and water;

[0007] Its mass ratio is: quartz sand: rice straw charcoal powder: molding sand binder: water = 100: (1~3): (7~9): (3~5);

[0008] The method for preparing rice straw charcoal powder includes the following steps: pretreated rice straw is placed in a carbonization furnace and heated at 100-200℃ for 2-3 hours under a nitrogen atmosphere to remove moisture, followed by heating at 300-400℃ for 2-3 hours to remove lignin, hemicellulose and plant polysaccharides from the fiber surface, and finally kept at 550-650℃ for 2 hours. After naturally cooling to room temperature, the charcoal powder is pulverized and passed through a 200-mesh sieve.

[0009] The quartz sand has a particle size of 50-140 mesh and a SiO2 content of ≥98%.

[0010] The method for pre-treating rice straw is as follows: waste rice straw is mechanically screened to remove soil, rice husks and roots, and then cut to a length of 30-40mm.

[0011] The molding sand binder is artificial sodium bentonite.

[0012] Another aspect of the present invention provides a method for preparing the above-mentioned casting sand based on the carbonization of waste rice straw, the method comprising the following steps:

[0013] 1) Raw material premixing: Add quartz sand, rice straw charcoal powder and molding sand binder into a twin-shaft mixing mixer and mix at a speed of 150~200 r / min for 5~8 min;

[0014] 2) Moisture adjustment: Add water and stir for 3-5 minutes.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. This invention utilizes carbon powder obtained from the carbonization of waste rice straw, which maintains structural stability at high temperatures and is less prone to secondary combustion or structural collapse. This makes it suitable for the pouring temperature range of cast iron and cast steel, reducing defects such as porosity and sand erosion caused by high-temperature failure of molding sand. Simultaneously, the multi-level porous structure of the rice straw carbon powder provides channels for gas discharge during the pouring process, preventing gas from being trapped in the molten metal and forming pores, thus reducing the porosity defect rate of the casting. Furthermore, the rice straw carbon powder contains silicon (mainly in the form of amorphous SiO2), which has low thermal conductivity and high-temperature micro-expansion characteristics. This slows down the heat dissipation rate of the mold, prolongs the filling time of the molten metal, and compensates for the high-temperature shrinkage of the mold, effectively inhibiting excessive shrinkage during pouring, slowing down the heat dissipation rate of the mold, prolonging the flow time of the molten metal, and thus reducing casting defects such as cold shuts and incomplete pouring.

[0017] 2. This invention uses carbon powder obtained from the carbonization of waste rice straw to replace coal powder / wood chips, reducing the cost of molding sand raw materials by 12%~18% and the total cost of castings by 10%~15%, while solving the problem of agricultural waste treatment and realizing "waste treatment".

[0018] 3. After traditional coal powder molding sand casting, the carbon layer remaining on the surface of the casting needs to be removed by acid washing. The acid washing wastewater contains heavy metal ions and acidic substances, which is costly to treat and easily causes water pollution. In contrast, the rice straw combustion of the present invention only produces CO2 and H2O, with no harmful gas emissions. The casting cleaning does not require acid washing, reducing wastewater pollution. Attached Figure Description

[0019] Figure 1 The images shown are scanning electron microscope images of rice straw charcoal powder in the specific implementation method. a is magnified 2000 times, and b is magnified 1000 times.

[0020] Figure 2 X-ray energy dispersive spectroscopy analysis of rice straw charcoal powder in a specific embodiment, where a represents the microstructure and b represents the microstructure. Figure 2 EDS energy dispersive spectral analysis results for the region corresponding to spectrum 4 in figure a;

[0021] Figure 3 The metallographic structure of the castings after pouring molten metal into the sand molds made by molding in Example 2 and Comparative Example 2 is shown in Figure a. Example 2 is shown in Figure b. Comparative Example 2 is shown in Figure b. Detailed Implementation

[0022] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0023] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0024] The method for preparing rice straw charcoal powder in the following embodiments includes the following steps:

[0025] (1) Rice straw pretreatment: The waste rice straw is mechanically screened to remove soil, rice husks and roots, and cut to a length of 30~40mm;

[0026] (2) Carbonization treatment: The cut rice straw is placed in a carbonization furnace and heated at 100°C for 3 hours under a nitrogen atmosphere to remove moisture. Then it is heated at 300°C for 3 hours to remove lignin, hemicellulose and plant polysaccharides on the fiber surface. Finally, it is kept at 600°C for 2 hours, cooled naturally to room temperature, crushed, passed through a 200-mesh sieve and stored.

[0027] The composition of the rice straw charcoal powder is shown in Table 1.

[0028] Table 1

[0029]

[0030] Example 1

[0031] The molding sand components in this embodiment include: quartz sand (50~140 mesh), rice straw charcoal powder, artificial sodium bentonite (200 mesh, purchased from Jianping Weike Te Bentonite Mining Co., Ltd.), and water in a mass ratio of 100:1:9:3.5.

[0032] The above-mentioned method for preparing molding sand includes the following steps:

[0033] 1) Raw material premixing: Add 600g of quartz sand, 6g of rice straw charcoal powder and 54g of artificial sodium bentonite to a twin-shaft mixing sand mixer and mix for 6 minutes at a speed of 150r / min;

[0034] 2) Moisture adjustment: Add 21g of water and stir for 4 minutes.

[0035] The performance test results of the molding sand in this embodiment are shown in Table 2.

[0036] Example 2

[0037] The molding sand components in this embodiment include: quartz sand (50~140 mesh), rice straw charcoal powder, artificial sodium bentonite (200 mesh, purchased from Jianping Weike Te Bentonite Mining Co., Ltd.), and water in a mass ratio of 100:2:8:3.5.

[0038] The above-mentioned method for preparing molding sand includes the following steps:

[0039] 1) Raw material premixing: Add 600g of quartz sand, 12g of rice straw charcoal powder and 48g of artificial sodium bentonite to a twin-shaft mixing sand mixer and mix for 6 minutes at a speed of 150r / min;

[0040] 2) Moisture adjustment: Add 21g of water and stir for 4 minutes.

[0041] The performance test results of the molding sand in this embodiment are shown in Table 2.

[0042] Example 3

[0043] The molding sand components in this embodiment include: quartz sand (50~140 mesh), rice straw charcoal powder, artificial sodium bentonite (200 mesh, purchased from Jianping Weike Te Bentonite Mining Co., Ltd.), and water in a mass ratio of 100:3:7:3.5.

[0044] The above-mentioned method for preparing molding sand includes the following steps:

[0045] 1) Raw material premixing: Add 600g of quartz sand, 18g of rice straw charcoal powder and 42g of artificial sodium bentonite to a twin-shaft mixing sand mixer and mix for 6 minutes at a speed of 150r / min;

[0046] 2) Moisture adjustment: Add 21g of water and stir for 4 minutes.

[0047] The performance test results of the molding sand in this embodiment are shown in Table 2.

[0048] Comparative Example 1

[0049] The difference from Example 1 is that rice straw charcoal powder was replaced with coal powder, while the other conditions were the same as in Example 1. The performance test results of the molding sand are shown in Table 2.

[0050] Comparative Example 2

[0051] The difference from Example 2 is that rice straw charcoal powder was replaced with coal powder, while the other conditions were the same as in Example 2. The performance test results of the molding sand are shown in Table 2.

[0052] Comparative Example 3

[0053] The difference from Example 3 is that rice straw charcoal powder was replaced with coal powder, and the other conditions were the same as in Example 3. The performance test results of the molding sand are shown in Table 2.

[0054] Table 2

[0055]

[0056] Results analysis:

[0057] Figure 1 The images show scanning electron microscopy (SEM) characterization of the rice straw charcoal powder used in Examples 1-3. As can be seen from the images, the 200-mesh rice straw charcoal powder used in this application exhibits a typical cylindrical porous structure. Although the overall pore distribution is uneven, the secondary micropore structure derived from the pore wall surface provides an effective channel for the discharge of gas within the system during the casting process, effectively reducing casting defects caused by gas retention and significantly improving the stability of the casting process.

[0058] Furthermore, such as Figure 2 As shown, the elemental composition of the rice straw charcoal powder was characterized by X-ray energy dispersive spectroscopy (EDS), confirming that the rice straw charcoal powder contains silicon (Si), and that the Si exists in the form of amorphous SiO2. Since amorphous SiO2 possesses significant heat-insulating properties, it can meet the technical requirements for heat preservation in the casting process. Therefore, the 200-mesh rice straw charcoal powder used in this invention has excellent applicability in the casting process.

[0059] The molding sands obtained in Example 2 and Comparative Example 2 were filled into molds and compacted under a pressure of 20 MPa to obtain sand molds. The sand molds obtained in Example 2 and Comparative Example 2 were then used for casting. Taking ductile iron as an example, the comparison results of key casting properties (spheroidization rate) are as follows. Figure 3 As shown. By Figure 3 As can be seen from 'a' in Example 2, most of the graphite in the carbon powder sand casting is regular 'near-spherical' with smooth contours and no obvious deformation; while Figure 3 In Comparative Example 2, the coal powder sand casting exhibits more irregularly shaped graphite, with some graphite appearing as irregular blocks or nodules (such as the graphite in the central area), and the proportion of spheroidal graphite is lower than in Example 2. According to the spheroidization rate determination rules in GB / T 9441-2021 "Metallographic Examination of Ductile Iron" (with graphite roundness and spheroidal proportion as core indicators), the spheroidization rate of the casting prepared by the carbon powder sand mold in Example 2 is significantly higher than that of the casting corresponding to the coal powder sand mold in Comparative Example 2.

[0060] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A foundry molding sand based on carbonization of discarded rice straw, characterized by, Composed of quartz sand, rice straw carbon powder, molding sand binder, water; The mass ratio is: quartz sand: rice straw carbon powder: molding sand binder: water = 100: (1-3): (7-9): (3-5); The particle size of the quartz sand is 50-140 mesh, and the SiO2 content in the quartz sand is ≥98%; The molding sand binder is artificial sodium bentonite; The preparation method of the rice straw carbon powder comprises the following steps: putting the pretreated rice straw into a carbonization furnace, heating at 100-200℃ for 2-3h under nitrogen atmosphere, then heating at 300-400℃ for 2-3h, and finally heating at 550-650℃ for 2h, and then crushing after natural cooling to room temperature, and sieving through a 200 mesh sieve.

2. The foundry molding sand based on carbonization of discarded rice straw according to claim 1, characterized by, The pretreatment method of the rice straw is: removing soil, rice husk and roots by mechanical screening, and shearing to a length of 30-40mm.

3. A method for preparing the foundry molding sand based on carbonization of waste rice straw according to any one of claims 1-2, characterized by, The method comprises the following steps: 1) raw material premixing: adding quartz sand, rice straw carbon powder and molding sand binder into a double-shaft stirring sand mixer, and stirring at a rotating speed of 150-200r / min for 5-8min; 2) water content adjustment: adding water, and stirring for 3-5min.

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