A foundry inorganic binder for warm core box process having high strength, moisture resistance and easy disintegration and a method of using the same

Abstract

The application discloses a casting warm core box method inorganic binder with high strength, moisture resistance and easy collapse performance, and belongs to the technical field of casting molding materials. The binder contains siloxane modified graphene oxide. The siloxane is short-chain siloxane containing active groups and / or cage polysiloxane containing active groups. The active groups are selected from one or more than two combinations of amino groups, mercapto groups, hydroxyl groups, epoxy groups and carboxyl groups. The sand core and / or sand mold prepared from the binder has the advantages of good mechanical strength, good yield, strong moisture resistance, good collapse performance, easy sand cleaning and the like.

Description

Technical Field

[0001] This invention belongs to the field of casting molding materials technology, specifically relating to an inorganic binder for casting using the warm core box method with high strength, resistance to moisture absorption and easy collapse, and its application method. The binder system meets the technical requirements for casting molding materials and has excellent performance. Background Technology

[0002] Casting is a method of producing blanks for parts in the machinery manufacturing industry. Among them, sand casting is a major casting process due to its low material cost and high productivity. First, sand molds and / or sand cores are made using molding sand. The cavity formed by the combination of sand molds and sand cores has the same shape and similar size as the target part. Then, the selected metal is melted into liquid and poured into the cavity. After the molten metal cools and solidifies, the product casting is obtained.

[0003] In molding sand casting, casting binder is essential. Its function is to bind sand grains into various desired shapes, namely sand molds or sand cores, and to ensure that the strength of the sand molds or sand cores is not damaged or deformed during forming, handling, core assembly, and pouring of molten metal. At the same time, after the molten metal cools and solidifies into the desired shape, the casting binder can be decomposed by heat, and the sand molds or sand cores disintegrate into "loose sand".

[0004] Currently, the binders commonly used in the foundry industry fall into two main categories: organic binders and inorganic binders. Organic binders are mostly resin polymers, with furan resins, basic phenolic resins, and triethylamine cold box resins being the most widely used. While organic binders offer excellent performance, they cause significant pollution during casting applications, releasing irritating gases during molding and pouring, posing health risks to operators and causing severe environmental pollution. Against this backdrop, inorganic binders are receiving increasing attention from foundry professionals both domestically and internationally.

[0005] Water glass is a commonly used inorganic binder. While it does not produce toxic or harmful gases that pollute the environment or human health during use, its poor collapsibility remains a difficult problem to solve. This is because cores made with water glass have low strength. To improve the strength of the sand mold, technicians often increase the amount of water glass added, resulting in high residual strength in the sand mold after casting. This makes it difficult to separate the casting from the molding sand, leading to difficulties in subsequent sand cleaning. Furthermore, water glass binders have poor fluidity during sand mixing and sand injection, and also exhibit poor moisture resistance.

[0006] In order to implement the concept of "green casting" that is efficient, energy-saving and environmentally friendly, this invention provides an inorganic binder for casting using the warm core box method with high strength, resistance to moisture absorption and easy collapse. The binder can significantly improve the sand collapse performance and moisture resistance while ensuring the strength of the sand mold. Summary of the Invention

[0007] The applicant's invention patent application No. 202211268973.4, filed on October 17, 2022, discloses a two-component water-soluble binder for casting using a warm core box method. The binder includes component A and component B, wherein component B is a powder comprising silica fume, zircon powder, corundum powder, graphite powder, polyvinyl alcohol, and sodium tripolyphosphate, used to improve the binder's bonding performance and moisture resistance. During subsequent research and development, the technicians discovered that the mechanical properties, collapsibility, and moisture resistance of the binder could be further improved. Based on this, the present invention improves the binder based on the prior application, providing an inorganic binder with better tensile strength and improved collapsibility and moisture resistance.

[0008] This invention includes the following technical solutions:

[0009] In a first aspect, the present invention provides the use of siloxane-modified graphene oxide in the preparation of a high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method, characterized in that the siloxane is a short-chain siloxane containing active groups and / or a cage-type silsesquioxane containing active groups, wherein the active groups are selected from one or more combinations of amino, mercapto, hydroxyl, epoxy, and carboxyl groups.

[0010] Preferably, the active group is selected from amino, thiol or hydroxyl groups.

[0011] In a specific embodiment of the present invention, the short-chain siloxane containing an active group is selected from γ-aminopropyltriethoxysilane or γ-mercaptopropyltrimethoxysilane.

[0012] Preferably, the siloxane is selected from cage-like silsesquioxanes containing active groups; further, the cage-like silsesquioxane-modified graphene oxide has a structure as shown in Formula I:

[0013]

[0014] n is an even number ≥ 8. In specific embodiments of the present invention, n is selected from 8, 10 or 12.

[0015] R is an active or inactive group of a cage-like silsesquioxane, wherein the active group is selected from amino, thiol, or hydroxyl groups.

[0016] Furthermore, the number of active groups in the cage-like silsesquioxane is an integer greater than or equal to 1, such as 1, 2, 3, 4, 5, 6, 7, or 8.

[0017] m represents the covalent linking unit formed by the reaction of oxygen-containing functional groups on the surface of graphene oxide with cage-like silsesquioxanes, where m is an integer ≥ 1.

[0018] The oxygen-containing functional groups on the surface of the graphene oxide include, but are not limited to, hydroxyl, epoxy, carboxyl, and carbonyl groups.

[0019] In a specific embodiment of the present invention, the cage-like silsesquioxane-modified graphene oxide has a structure as shown in Formula II:

[0020]

[0021] In Formula II, R is independently selected from alkenyl, alkyl, aryl, amino, mercapto, or hydroxyl groups, and at least one R is selected from amino, mercapto, or hydroxyl groups. When R in Formula II is selected from multiple amino, mercapto, or hydroxyl groups, each R can form a covalent linking unit with graphene oxide.

[0022] In a specific embodiment of the present invention, the cage-like silsesquioxane used to prepare the cage-like silsesquioxane-modified graphene oxide is selected from one or more combinations of aminopropyl isobutyl-POSS, octaaminopropyl-POSS, octaaminophenyl-POSS, octahydroxybutyl-POSS, and octamercaptopropyl-POSS.

[0023] Preferably, the cage-like silsesquioxane is selected from aminopropyl isobutyl-POSS (A-POSS), octaaminopropyl-POSS (OAS-POSS), and octaaminophenyl-POSS (OA-POSS).

[0024] In the most preferred embodiment of the present invention, the cage-like silsesquioxane is octaaminopropyl-POSS (OAS-POSS).

[0025] The siloxane-modified graphene oxide was prepared by the following method:

[0026] Graphene oxide was uniformly dispersed in an ethanol solution, and siloxane was slowly added while stirring. The reaction was carried out overnight at 70-100°C. The mixture was filtered, washed with ethanol solution, and dried to obtain siloxane-modified graphene oxide. The mass ratio of siloxane to graphene oxide was 1:(1-10).

[0027] The graphene oxide used in this invention can be purchased commercially or prepared using existing technology. In a specific embodiment of this invention, the graphene oxide is prepared by the following method:

[0028] Sulfuric acid and phosphoric acid are mixed in a volume ratio of 10:1 to obtain a mixed acid. Graphite powder is evenly dispersed in the mixed acid, and sodium nitrate and potassium permanganate are added for oxidation. Then, H2O2 solution and hydrochloric acid solution with a mass fraction of 30-40% are added in sequence. After centrifugation, washing, and drying, graphene oxide is obtained.

[0029] Secondly, the present invention provides an inorganic binder for casting using the warm-box method, characterized in that the warm-box inorganic binder is composed of a water-based binder, powder additives, and an accelerator, wherein the accelerator includes the siloxane-modified graphene oxide described in the present invention. The specific form of the siloxane-modified graphene oxide is as described in the first aspect of the present invention.

[0030] Furthermore, the accelerator also includes a hydraulic component, which is selected from one or more of fly ash, calcium silicate, calcium aluminate, calcium sulfoaluminate, and sodium sulfate.

[0031] In a specific embodiment of the present invention, the hydraulic component is a combination of fly ash, calcium silicate, calcium aluminate, calcium sulfoaluminate, and sodium sulfate, wherein the fly ash is high-calcium fly ash.

[0032] The high-calcium fly ash described in this invention is a type of fly ash produced by burning lignite and bituminous coal in a circulating fluidized bed boiler. Its f-CaO content is greater than 10%, and the high-calcium fly ash contains a certain amount of hydraulic minerals with potential activity.

[0033] Among them, the water-based binder and powder additive are the same as components A and B in the patent application with application number 202211268973.4.

[0034] Specifically, the water-based adhesive material comprises the following components by mass percentage: 50-60% deionized water, 0.05-0.5% sodium polymethacrylate, 0.05-0.4% sodium dodecyl sulfonate, 0.05-0.5% polyacrylamide, 25-35% silicate, 10-15% polyvinyl alcohol, and 0.05-2% sodium tripolyphosphate.

[0035] The powder additive comprises the following components by mass percentage: 30-40% silica fume, 5-10% zircon powder, 5-10% corundum powder, 0.1-2% graphite powder, 30-40% propyl methylcellulose, and 5-10% copolymer of ethylene / vinyl acetate.

[0036] In a preferred embodiment of the present invention, the accelerator comprises the following components in weight percentages: 0.5-5% siloxane-modified graphene oxide, 5-10% fly ash, 30-45% calcium silicate, 30-40% calcium aluminate, 5-10% calcium sulfoaluminate, and 5-10% sodium sulfate.

[0037] In a specific embodiment of the present invention, the mass ratio of the water-based adhesive material, powder additive and accelerator that make up the water-soluble adhesive of the warm core box method is (15-20): (8-13): (1-3).

[0038] In the most preferred embodiment of the present invention, the mass ratio of water-based binder, powder additive and accelerator is 20:13:2.

[0039] Thirdly, the present invention provides a method for preparing coated sand for casting, the method comprising the following steps:

[0040] (1) Preparation of water-based adhesive material

[0041] ① Boil deionized water for 5–20 minutes;

[0042] ② Add sodium polymethacrylate, sodium dodecyl sulfonate, and polyacrylamide in proportion and stir to dissolve;

[0043] ③ Add one or more of sodium silicate, potassium silicate, and lithium silicate, stir to dissolve, heat to 200-250℃, and keep warm for 4-7 hours;

[0044] ④ After the temperature drops below 100℃, add sodium tripolyphosphate and polyvinyl alcohol and stir to dissolve, completing the reaction and obtaining a water-based adhesive material;

[0045] (2) Preparation of powder additives

[0046] The silica fume, zircon powder, corundum powder, graphite powder, propyl methylcellulose, and ethylene / vinyl acetate copolymer are stirred and mixed evenly in a certain proportion to obtain a powder additive.

[0047] (3) Preparation of accelerator

[0048] The accelerator is obtained by mixing siloxane-modified graphene oxide, fly ash, calcium silicate, calcium aluminate, calcium sulfoaluminate, and sodium sulfate in a certain proportion.

[0049] (4) Sand mixing

[0050] First, mix the powder additive with the raw sand for 1-2 minutes, then add the accelerator and mix for 1-2 minutes, and finally add the water-based binder and mix for 1-2 minutes to prepare the coated sand. The powder additive is added at 1.0-1.5% of the raw sand mass; the accelerator is added at 0.2-0.4% of the raw sand mass; and the water-based binder is added at 2.0-3.0% of the raw sand mass.

[0051] The foundry raw sand described in this invention is selected from one or a mixture of two of the following: foundry silica sand with a particle size distribution of 50 / 100 and recycled sand with a particle size distribution of 50 / 100.

[0052] In a specific embodiment of the present invention, the foundry raw sand is a composition with the following mass fractions: 90% recycled sand with a particle size distribution of 50 / 100 and 10% foundry silica sand with a particle size distribution of 50 / 100; or 100% recycled sand with a particle size distribution of 50 / 100.

[0053] Fourthly, the present invention provides a coated sand for casting, wherein the coated sand for casting is prepared by the method described in the third aspect of the present invention.

[0054] Fifthly, the present invention provides a method for preparing casting sand cores and / or sand molds, the method comprising: loading the casting coated sand prepared by the present invention into the core-making mold of a core-making box, shooting the core, blowing in a mixture of hot CO2 and air, and preparing sand cores and / or sand molds.

[0055] Preferably, the volume ratio of CO2 to air is (55-60):10, the heating temperature of the core-making mold is 120-160℃, and the core-shooting pressure is 0.5-0.6MPa.

[0056] In a sixth aspect, the present invention provides a casting sand core and / or sand mold, wherein the casting sand core and / or sand mold is prepared by the method described in the fifth aspect of the present invention.

[0057] In a seventh aspect, the present invention provides the use of the coated sand in the manufacture of sand cores and / or sand molds for casting metal parts.

[0058] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method provided by this invention has the following technical advantages:

[0059] In sand casting, the coated sand material used to prepare sand cores and / or sand molds is particularly important. High-quality coated sand produces sand cores and / or sand molds with good mechanical strength, good collapsibility, strong moisture resistance, good collapsibility, and easy sand removal. This invention is an improvement based on previous research. By adding an accelerator to the inorganic binder used to prepare the coated sand, the tensile strength, moisture resistance, and collapsibility of the sand cores and / or sand molds are further enhanced.

[0060] Unexpectedly, those skilled in the art discovered that adding siloxane-modified graphene oxide to the early-stage binder improves tensile strength and collapse performance. The cage-like silsesquioxane (POSS) described in this invention is a nanomaterial containing an organic-inorganic hybrid core-shell structure. Its internal inorganic framework, as a core, is a hexahedral cage structure composed of Si-O-Si or Si-O bonds, with one Si atom at each corner and each face composed of Si-O-Si eight-membered rings, exhibiting strong structural symmetry. Therefore, the cage-like silsesquioxane framework structure can significantly improve the mechanical strength of sand cores. Simultaneously, those skilled in the art also found that while POSS as a promoter can significantly increase the mechanical properties of sand cores or molds prepared with binders, the high strength of the POSS carbon skeleton leads to poor collapse performance of the coated sand. Based on this, those skilled in the art introduced graphene oxide into POSS.

[0061] Graphene oxide (GO) is an oxide of graphene. The surface of GO is covered with oxygen-containing groups such as hydroxyl, epoxy, carboxyl, and carbonyl groups. This invention creatively couples POSS with GO to obtain POSS-modified GO. GO exhibits excellent dispersibility, increasing the flowability of binders. Furthermore, GO is amphiphilic, acting as a surfactant at the interface, reducing interfacial energy and improving the collapsibility of the core. In addition, GO possesses good thermal conductivity, promoting the thermal decomposition of the resin's residual carbon skeleton during casting, reducing the residual strength of the coated sand, and further improving its collapsibility.

[0062] Secondly, this invention also adds hydraulic components to the accelerator, which only improves the moisture resistance of the sand core and / or sand mold and enhances its strength after moisture absorption. However, technicians have found that the hydraulic components reduce the collapsibility of the sand core, resulting in sand adhesion or inclusion. Based on this, the inventors unexpectedly discovered that fly ash, especially high-calcium fly ash, as a hydraulic component not only improves the moisture resistance of the sand core but also has a positive auxiliary effect on its collapsibility. The inventors believe that the reason why high-calcium fly ash has this effect is because it inherently possesses volume instability. Although this is a defect in the reuse of high-calcium fly ash, it can significantly improve the collapsibility problem in sand core preparation.

[0063] Based on the above analysis, the sand cores and / or sand molds prepared using the water-soluble binder provided by the present invention have advantages such as better mechanical properties, better moisture resistance, and better collapse resistance compared to the original methods. Attached Figure Description

[0064] Figure 1 Transmission electron microscopy image of the graphene oxide prepared in this invention.

[0065] Figure 2 Transmission electron microscopy image of the octaaminopropyl-POSS modified graphene oxide prepared in this invention.

[0066] Figure 3 Diagram of the tensile property testing process.

[0067] Figure 4 Tensile property testing process diagram

[0068] Figure 5 Diagram showing the process of testing the collapsibility of coated sand.

[0069] Figure 6 The diagram shows the process of testing the collapsibility of the coated sand. Detailed Implementation

[0070] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0071] Unless otherwise specified, the raw materials and reagents used in the specific embodiments of this invention are all purchased through commercial channels.

[0072] Preparation of graphene oxide

[0073] At 4℃, 200 mL of sulfuric acid and 20 mL of phosphoric acid were mixed to obtain a mixed acid. 10 g of graphite powder was weighed and placed in an Erlenmeyer flask, and the mixed acid was added. 5 g of NaNO3 and 25 g of KMnO4 were added slowly with stirring in an ice-water bath. The mixture was stirred for 30 min, and the temperature was gradually increased to 35℃ and maintained for 3 days. 300 mL of deionized water was slowly added dropwise with stirring, followed by 1 L of deionized water. The mixture was stirred for 20 min, and then 50 mL of 30% H2O2 and 600 mL of 1 mol / L dilute hydrochloric acid were slowly added. The mixture was stirred for 1 h, allowed to stand, centrifuged, and the lower precipitate was collected and dried to obtain graphene oxide. The transmission electron microscopy results of the graphene oxide prepared by the above method are as follows: Figure 1 As shown.

[0074] Preparation of siloxane-modified graphene oxide

[0075] I. Short-chain siloxane-modified graphene oxide

[0076] 1. γ-aminopropyltriethoxysilane-modified graphene oxide

[0077] 10g of the graphene oxide prepared in this invention was mixed with a 70% ethanol solution and sonicated for 2 hours to form a uniform dispersion. Under magnetic stirring, 4g of γ-aminopropyltriethoxysilane was slowly added and reacted overnight at 100°C. After filtration, the product was washed three times with anhydrous ethanol and then three times with deionized water and dried to obtain γ-aminopropyltriethoxysilane-modified graphene oxide.

[0078] 2. γ-Mercaptopropyltrimethoxysilane-modified graphene oxide

[0079] The preparation method is the same as above, with 10g of graphene oxide and 4g of γ-mercaptopropyltrimethoxysilane added. γ-mercaptopropyltrimethoxysilane-modified graphene oxide is prepared according to the above method and dried for later use.

[0080] II. Cage-type silsesquioxane-modified graphene oxide

[0081] 1. Aminopropyl isobutyl-POSS modified graphene oxide

[0082] The preparation method is the same as above, with 10g of graphene oxide and 4g of aminopropyl isobutyl-POSS added. The aminopropyl isobutyl-POSS modified graphene oxide is prepared according to the above method and dried for later use.

[0083] 2. Octaaminopropyl-POSS modified graphene oxide

[0084] The preparation method is the same as above, using 10g of graphene oxide and 4g of octaaminopropyl-POSS. Octaaminopropyl-POSS-modified graphene oxide was prepared according to the above method and dried for later use. The transmission electron microscopy results of the prepared octaaminopropyl-POSS-modified graphene oxide are as follows. Figure 2 As shown, technicians found that modifying graphene oxide with siloxanes did not significantly alter its morphology.

[0085] 3. Octaaminophenyl-POSS modified graphene oxide

[0086] The preparation method is the same as above, with 10g of graphene oxide and 4g of octaaminophenyl-POSS added. Octaaminophenyl-POSS modified graphene oxide is prepared according to the above method and dried for later use.

[0087] 4. Octahydroxybutyl-POSS modified graphene oxide

[0088] The preparation method is the same as above, with 10g of graphene oxide and 4g of octahydroxybutyl-POSS added. Octahydroxybutyl-POSS modified graphene oxide is prepared according to the above method and dried for later use.

[0089] 5. Octadectopropyl-POSS modified graphene oxide

[0090] The preparation method is the same as above, with 10g of graphene oxide and 4g of octamercaptopropyl-POSS added. Octamercaptopropyl-POSS modified graphene oxide is prepared according to the above method and dried for later use.

[0091] Preparation of high-strength, moisture-resistant, and easily collapsible inorganic binders for casting using the warm core box method.

[0092] Example 1

[0093] Water-based adhesives consist of the following components by mass fraction:

[0094] Sodium polymethacrylate 0.3％ Sodium dodecyl sulfonate 0.2％ Polyacrylamide 0.3％ Sodium silicate 20％ Potassium silicate 10％ Polyvinyl alcohol 13％ Sodium tripolyphosphate 1.2％

[0095] The powder additive consists of the following components by mass fraction:

[0096] Zircon powder 5％ Corundum powder 10％ Graphite powder 1％ Propyl methylcellulose 40％ Ethylene / vinyl acetate copolymer 10％

[0097] The accelerator consists of the following components by mass fraction:

[0098] fly ash 10％ Calcium silicate 35％ Calcium aluminate 30％ Calcium sulfoaluminate 10％ Sodium sulfate 10％

[0099] The fly ash used in this embodiment is high-calcium fly ash, sourced from a coal-fired power plant in Guangxi. This high-calcium fly ash is the fly ash discharged after the combustion and washing of residual high-calcium coal gangue in a low-temperature circulating fluidized bed boiler. Its chemical composition is shown in the table below:

[0100] Table 1. Chemical composition (%) of high-calcium fly ash

[0101]

[0102] Example 2

[0103] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of γ-mercaptopropyltrimethoxysilane-modified graphene oxide.

[0104] Example 3

[0105] The high-strength, moisture-resistant, and easily collapsible casting core box method inorganic binder consists of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane modified graphene oxide in the accelerator is replaced with the same mass fraction of aminopropylisobutyl-POSS modified graphene oxide.

[0106] Example 4

[0107] The high-strength, moisture-resistant, and easily collapsible casting core box method inorganic binder consists of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane modified graphene oxide in the accelerator is replaced with the same mass fraction of octaaminopropyl-POSS modified graphene oxide.

[0108] Example 5

[0109] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of octaaminophenyl-POSS-modified graphene oxide.

[0110] Example 6

[0111] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of octahydroxybutyl-POSS-modified graphene oxide.

[0112] Example 7

[0113] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of octamercaptopropyl-POSS-modified graphene oxide.

[0114] Comparative Example 1

[0115] The high-strength, moisture-resistant, and easily collapsible casting core box method inorganic binder consists of a water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of uncoupled graphene oxide octaaminopropyl-POSS.

[0116] Comparative Example 2

[0117] The high-strength, moisture-resistant, and easily collapsible casting core box method inorganic binder consists of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the γ-aminopropyltriethoxysilane-modified graphene oxide in the accelerator is replaced with the same mass fraction of uncoupled graphene oxide octaaminophenyl-POSS.

[0118] Comparative Example 3

[0119] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the accelerator does not contain γ-aminopropyltriethoxysilane-modified graphene oxide, and the calcium silicate content is changed to 40%.

[0120] Comparative Example 4

[0121] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method is composed of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the high-calcium fly ash in the accelerator is replaced with the same mass fraction of low-calcium fly ash. The low-calcium fly ash is conventional circulating fluidized bed fly ash, and its chemical composition is shown in the table below.

[0122] Table 2 Chemical composition (%) of low-calcium fly ash

[0123]

[0124] Comparative Example 5

[0125] The high-strength, moisture-resistant, and easily collapsible inorganic binder for casting using the warm core box method consists of water-based binder, powder additives, and accelerators. The components are the same as in Example 1, except that the accelerator does not contain high-calcium fly ash, and the calcium silicate content is changed to 45%.

[0126] Coated sand is prepared using a high-strength, moisture-resistant, and easily collapsible foundry core box method inorganic binder.

[0127] Coated Sand 1

[0128] (1) Preparation of water-based adhesive material

[0129] Heat deionized water to boiling for 15 minutes, add sodium polymethacrylate, sodium dodecyl sulfonate and polyacrylamide according to the mass ratio disclosed in Example 1, stir until dissolved, add sodium silicate and potassium silicate and stir until dissolved, heat to 220°C and keep warm for 6 hours, and when the temperature drops to below 100°C, add sodium tripolyphosphate and polyvinyl alcohol, stir until dissolved, and obtain water-based adhesive material.

[0130] (2) Preparation of powder additives

[0131] The silica fume, zircon powder, corundum powder, graphite powder, propyl methylcellulose, and ethylene / vinyl acetate copolymer were stirred and mixed evenly according to the mass ratio disclosed in Example 1 to obtain a powder additive.

[0132] (3) Preparation of accelerator

[0133] The accelerator was obtained by mixing siloxane-modified graphene oxide, high-calcium fly ash, calcium silicate, calcium aluminate, calcium sulfoaluminate, and sodium sulfate evenly according to the mass ratio disclosed in Example 1.

[0134] (4) Sand mixing

[0135] The foundry raw sand is recycled sand with a particle size distribution of 50 / 100. 1.3% of the raw sand mass of powder additive is mixed with the raw sand for 2 minutes, then an accelerator is added and mixed for 2 minutes. The accelerator is 0.2% of the raw sand mass. Finally, 2.0% of the raw sand mass of water-based binder is added and mixed for 2 minutes to prepare coated sand 1.

[0136] Coated Sand 2

[0137] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 2. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 2 was prepared.

[0138] Coated Sand 3

[0139] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 3. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 3 was prepared.

[0140] Coated Sand 4

[0141] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 4. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 4 was prepared.

[0142] Coated Sand 5

[0143] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 5. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 5 was prepared.

[0144] Coated Sand 6

[0145] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 6. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 6 was prepared.

[0146] Coated Sand 7

[0147] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Example 7. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, and coated sand 7 was prepared.

[0148] Comparison with coated sand 1

[0149] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Comparative Example 1. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, so as to prepare control coated sand 1.

[0150] Comparison with coated sand 2

[0151] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Comparative Example 2. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, so as to prepare control coated sand 2.

[0152] Comparison with coated sand 3

[0153] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Comparative Example 3. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, so as to prepare control coated sand 3.

[0154] Comparison with coated sand 4

[0155] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Comparative Example 4. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, thus preparing control coated sand 4.

[0156] Comparison with coated sand 5

[0157] Water-based binder, powder additives and accelerators were prepared according to the mass ratio of each component disclosed in Comparative Example 5. The sand mixing process was the same as above, and the amount of water-based binder, powder additives and accelerators added was the same as above, thus preparing control coated sand 5.

[0158] Use coated sand to prepare sand cores and / or sand molds

[0159] Sand cores and / or sand molds were prepared using the coated sand 1-7 prepared according to the present invention and the control coated sand 1-5. The preparation method of the sand cores and / or sand molds is as follows: the coated sand is loaded into the core-making mold of the core-making box, the mold is heated to 150°C, the core is shot, the core-shooting pressure is 0.5MPa, and a mixture of hot CO2 and air is blown in, with a CO2 to air volume ratio of 55:10, to obtain the sand cores and / or sand molds.

[0160] Effect test of sand core and / or sand mold

[0161] Experimental objective: To test the tensile strength, collapsibility, and moisture resistance of coated sand prepared by the water-soluble binder provided in the warm core box method according to the present invention in the preparation of casting sand cores and / or sand molds.

[0162] Test methods: The test methods for tensile strength, collapse resistance, and moisture absorption resistance are as follows:

[0163] I. Tensile Strength

[0164] The coated sand mixture prepared in the embodiments of the present invention was made into figure-eight specimens by a core-making machine. The size of the figure-eight specimens was in accordance with GB2684 "Test Methods for Raw Sand and Mixtures for Foundry". The instantaneous tensile strength and 24-hour tensile strength were tested.

[0165] II. Collapse Performance

[0166] The coated sand mixture prepared in this embodiment of the invention was used to form cylindrical samples with a diameter of 30 mm and a height of 50 mm using a core-making machine. The molding sand was compacted, ensuring that the weight of the sand core was approximately 160 g. The sample dimensions were in accordance with GB2684 "Test Methods for Raw Sand and Mixtures for Foundry". After standing for 24 hours, the samples were weighed, wrapped in tin foil, and calcined in a muffle furnace at a constant temperature of 400°C for 15 min. After cooling to room temperature, the calcined samples were placed in a 70-mesh vibrating sieve and vibrated for 2 min. The remaining sample weight was then weighed. The collapsibility was expressed as a percentage. A higher collapsibility value indicates a lower high-temperature residual strength of the molding sand and better collapsibility performance.

[0167] Collapse rate = (AB) / A × 100%

[0168] Where: A—weight of the sample before calcination

[0169] B—Weight of the sample after calcination

[0170] III. Moisture absorption resistance

[0171] The coated sand mixture prepared in the embodiments of the present invention was made into cylindrical samples with a diameter of 30 mm and a height of 50 mm by a core-making machine. After being stored in a workshop with a humidity of 65% ± 5 and a temperature of 25 ± 5°C for 24 hours, the percentage decrease in tensile strength was tested. A small percentage decrease in tensile strength indicates good moisture resistance.

[0172] The results of the above experiments are shown in the table below:

[0173] Table 3. Performance test results of samples prepared from coated sand.

[0174] Coated Sand 1 0.87 2.37 96.4 11.2 Coated Sand 2 0.84 2.31 96.1 11.5 Coated Sand 3 0.91 2.43 96.0 11.0 Coated Sand 4 0.93 2.57 97.8 11.2 Coated Sand 5 0.92 2.69 95.6 11.2 Coated Sand 6 0.90 2.33 96.4 11.4 Coated Sand 7 0.91 2.51 96.3 11.1 Comparison with coated sand 1 0.91 2.78 83.6 11.4 Comparison with coated sand 2 0.92 2.84 80.1 11.5 Comparison with coated sand 3 0.87 1.99 91.6 11.1 Comparison with coated sand 4 0.90 2.20 93.0 15.3 Comparison with coated sand 5 0.90 2.26 90.8 17.6

[0175] As can be seen from the mechanical property data in the table above, the instantaneous tensile strength of the sand cores prepared using the coated sand prepared in the embodiments of the present invention did not show significant differences. However, after 24 hours, the tensile strength of the sand cores changed due to the different binders used. The binder preparation methods for coated sands 1-7 were the same, with the only difference being the siloxane used to modify graphene oxide in the raw materials. Coated sands 1 and 2 used short-chain siloxanes, while coated sands 3-7 used cage-like silsesquioxanes. From the overall trend, it can be seen that the tensile strength of graphene oxide modified with cage-like silsesquioxanes as an additive was superior to that of graphene oxide modified with short-chain siloxanes. This is because, compared with short-chain siloxanes, cage-like silsesquioxanes have a three-dimensional structural framework with good structural stability, resulting in superior mechanical properties of the prepared sand cores.

[0176] Among specific cage-like silsesquioxane compounds, technicians have found that siloxanes with amino and mercapto groups as active groups have a better effect on improving the mechanical properties of sand cores, with the amino group being the optimal active group. Technicians believe that the amino groups on the cage-like silsesquioxane structure have better bonding properties with the oxygen-containing groups in the graphene oxide structure.

[0177] Specifically, in the binder used for coated sand 4, the siloxane in the siloxane-modified graphene oxide is octaaminopropyl-POSS, while in coated sand 5 it is octaaminophenyl-POSS. From their mechanical properties, it can be seen that the addition of octaaminophenyl-POSS-modified graphene oxide significantly improves tensile strength; however, due to its structure, its collapsibility performance decreases slightly. Control coated sand 1 and control coated sand 2 show the same trend. The binder used to prepare control coated sand 3 does not contain POSS-modified graphene oxide, so its mechanical properties are very poor. Control coated sand 4 uses low-calcium fly ash on top of coated sand 1, which affects the collapsibility performance of the core and is worse than that of coated sand 1. Control coated sand 5 is based on coated sand 1, but without fly ash and replaced with calcium silicate. Although the hydraulic components are increased, the collapsibility performance is even worse.

[0178] Technicians have discovered that adding high-calcium fly ash to the binder significantly improves the moisture resistance of sand cores. This is because the dissolution process of high-calcium fly ash involves the reaction of f-CaO with water to form Ca(OH)₂, which significantly enhances the moisture resistance of the sand mold or core. Furthermore, technicians have also found that high-calcium fly ash improves the collapse performance of the sand core. While high-calcium fly ash itself exhibits some volume instability compared to other hydraulic components, which is a drawback in other applications, this volume instability contributes to increasing the collapse performance of the sand mold or core. Therefore, this invention utilizes high-calcium fly ash to positively assist the sand mold or core collapse performance while simultaneously improving moisture resistance.

[0179] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A casting-grade inorganic binder using the warm core box method, characterized in that, it possesses high strength, resistance to moisture absorption and easy collapse, and is characterized in that, The inorganic binder for the core box method is composed of water-based binder, powder additives, and accelerators. The accelerators include the following components by mass percentage: 0.5-5% siloxane-modified graphene oxide, 5-10% fly ash, 30-45% calcium silicate, 30-40% calcium aluminate, 5-10% calcium sulfoaluminate, and 5-10% sodium sulfate. The fly ash is high-calcium fly ash, and the f-CaO content in the high-calcium fly ash is greater than 10%. The siloxane is a cage-type silsesquioxane containing active groups, and the active groups are selected from amino, mercapto, or hydroxyl groups. The siloxane-modified graphene oxide was prepared by the following method: graphene oxide was uniformly dispersed in an ethanol solution, siloxane was slowly added under stirring, the reaction was carried out overnight at 70-100℃, filtered, washed with ethanol solution, and dried to obtain siloxane-modified graphene oxide; the mass ratio of siloxane to graphene oxide was 1:(1-10). The water-based adhesive material comprises the following components by mass percentage: 50-60% deionized water, 0.05-0.5% sodium polymethacrylate, 0.05-0.4% sodium dodecyl sulfonate, 0.05-0.5% polyacrylamide, 25-35% silicate, 10-15% polyvinyl alcohol, and 0.05-2% sodium tripolyphosphate; The powder additive comprises the following components by mass percentage: 30-40% silica fume, 5-10% zircon powder, 5-10% corundum powder, 0.1-2% graphite powder, 30-40% propyl methylcellulose, and 5-10% copolymer of ethylene / vinyl acetate; The mass ratio of the water-based binder, powder additive and accelerator is (15-20):(8-13):(1-3).

2. The inorganic binder using the temperature-controlled box method according to claim 1, characterized in that, The siloxane-modified graphene oxide has the structure shown in Formula I: （Ⅰ）； n is an even number ≥ 8, R is an active or inactive group of the cage-like silsesquioxane, wherein the active group is selected from amino, mercapto or hydroxyl; the number of active groups in the cage-like silsesquioxane is an integer ≥ 1, and m represents the covalent linking unit formed by the reaction of oxygen-containing functional groups on the surface of graphene oxide with the cage-like silsesquioxane, where m is an integer ≥ 1.

3. The inorganic binder using the temperature-controlled box method according to claim 2, characterized in that, The cage-like silsesquioxane used to prepare the siloxane-modified graphene oxide is selected from one or more combinations of aminopropyl isobutyl-POSS, octaaminopropyl-POSS, octaaminophenyl-POSS, octahydroxybutyl-POSS, and octamercaptopropyl-POSS.

4. A method for preparing coated sand for casting using the inorganic binder of the warm core box method according to any one of claims 1-3, the method comprising the following steps: (1) Preparation of water-based adhesive material ① Boil deionized water for 5–20 minutes; ② Add sodium polymethacrylate, sodium dodecyl sulfonate, and polyacrylamide in proportion and stir to dissolve; ③ Add one or more of sodium silicate, potassium silicate, and lithium silicate, stir to dissolve, heat to 200-250℃, and keep warm for 4-7 hours; ④ After the temperature drops below 100℃, add sodium tripolyphosphate and polyvinyl alcohol and stir to dissolve, completing the reaction and obtaining a water-based adhesive material; (2) Preparation of powder additives The silica fume, zircon powder, corundum powder, graphite powder, propyl methylcellulose, and ethylene / vinyl acetate copolymer are stirred and mixed evenly in a certain proportion to obtain a powder additive. (3) Preparation of accelerator The accelerator is obtained by mixing siloxane-modified graphene oxide, high-calcium fly ash, calcium silicate, calcium aluminate, calcium sulfoaluminate, and sodium sulfate in a certain proportion. (4) Sand mixing First, mix the powder additive with the raw sand for 1-2 minutes, then add the accelerator and mix for 1-2 minutes, and finally add the water-based binder and mix for 1-2 minutes to prepare the coated sand. The amount of powder additives added is 1.0 to 1.5% of the original sand mass; the amount of accelerator added is 0.2 to 0.4% of the original sand mass; and the amount of water-based binder added is 2.0 to 3.0% of the original sand mass.

5. A method for preparing a sand core or sand mold for casting, the method comprising: The casting coated sand prepared according to the method of claim 4 is loaded into the core-making mold of the core-making box, the core is shot, and a mixture of hot CO2 and air is blown in to prepare a sand core or sand mold; the volume ratio of CO2 to air is (55-60):10, the heating temperature of the core-making mold is 120-160℃, and the core-shooting pressure is 0.5-0.6MPa.

6. The use of a casting coated sand prepared by the method of claim 4 in the manufacture of sand cores or sand molds for casting metal parts.

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