Inorganic composite casting binder for cold core machine and manual molding and preparation method of inorganic composite casting binder

Abstract

The invention discloses an inorganic composite casting binder for a cold core machine and manual molding and a preparation method of the inorganic composite casting binder, and belongs to the technical field of binders. The preparation method comprises the following steps: 1) pretreating raw materials; 2) preparing a main binder; and 3) vacuum defoaming and aging. According to the binder, hydrophobization of internal components is catalyzed and a gradient hydrophobic structure from inside to outside is constructed through an in-situ catalytic moisture-proof agent and a surface gradient treatment process, so that the problem that an inorganic binder sand core is prone to getting damp is solved, the strength retention rate of a casting obtained by using the binder exceeds 85% within 48 h in a 90% RH high-humidity environment, and the casting quality is improved. Meanwhile, the environment-friendly characteristics of no formaldehyde and low VOCs are achieved; meanwhile, used waste sand can be regenerated through simple winnowing, the recovery rate exceeds 90%, green closed-loop circulation of casting production is achieved, and the comprehensive performance is remarkably superior to that of a traditional product.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and more particularly to inorganic composite casting adhesives for cold core machines and manual molding, and their preparation methods. Background Technology

[0002] Currently, cold-core casting production mainly uses the triethylamine cold box process with organic phenolic resin. Toxic gases are generated during core making and casting. Triethylamine is highly corrosive and irritating to the eyes, skin, and respiratory mucous membranes. Although it is blown into a closed core box, triethylamine and unreacted phenolic resin vapors inevitably escape into the workshop air during sand injection, air blowing, mold opening, core removal, and subsequent sand core storage and handling, posing a continuous threat to the health of operators.

[0003] Costs associated with waste gas and waste sand regeneration: Amine-containing waste gas generated during production cannot be directly discharged and requires a highly efficient waste gas treatment system (such as acid washing towers, activated carbon adsorption, catalytic combustion, etc.), which increases equipment investment and operation and maintenance costs. Waste sand, cleaned dust, and waste liquid / used activated carbon generated in the waste gas treatment system may be contaminated with triethylamine or phenolic resin residues, requiring treatment as hazardous waste, which incurs high disposal costs.

[0004] Casting Defects: Porosity is a common casting defect in this process. Phenolic resin decomposes under high-temperature molten iron, producing large amounts of hydrogen and gaseous hydrocarbons. If the gas generation rate of the sand core is too fast and the gas escape channels are not smooth, subcutaneous or internal porosity can easily form in the casting.

[0005] Currently, the main inorganic environmentally friendly material used in production is modified glass, which is inexpensive, non-toxic and odorless, and relatively environmentally friendly in the molding, core making and casting processes. However, its sand mold has poor collapsibility, low waste sand reuse rate, and increases the cost and difficulty of post-processing of blank castings, resulting in a lower yield.

[0006] To address the above challenges, this invention provides an inorganic, environmentally friendly composite adhesive that releases no free formaldehyde or VOCs during material production and use, suitable for use in cold core machines and for self-curing adhesives in hand-shaped molding. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing an inorganic composite casting binder for cold core machines and manual molding, and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention first proposes an inorganic composite casting binder for cold core machines and manual molding, comprising the following components by weight:

[0010] Sodium silicate solution: 35-45 parts;

[0011] Basic silica sol: 15-25 parts;

[0012] Sodium carbonate: 12-18 parts;

[0013] Xylitol: 15-25 parts;

[0014] Surfactant OP-10: 0.3 parts;

[0015] Preservative parabens: 0.03 parts;

[0016] Plasticizer triacetin: 3 parts;

[0017] Dispersant polyvinylpyrrolidone K30: 8-12 parts;

[0018] Small-leaf sandalwood powder: 0.8-1.2 parts;

[0019] In-situ catalytic moisture-proofing agent: 1.0-1.5 parts;

[0020] Silane coupling agent KH560: 0.6 parts;

[0021] Reaction enhancer: 2-5 parts;

[0022] Defoamer: 0.05-0.1 parts;

[0023] Leveling agent: 0.05 parts;

[0024] The in-situ catalytic moisture-proofing agent is prepared by mixing boric acid and ethanolamine in a molar ratio of 1:2.

[0025] Preferably, the basic silica sol contains 25-30% SiO2 and has a particle size of 10-15 nm; the small-leaf sandalwood powder has a particle size of 200-300 mesh; the reaction enhancer is silica micro powder with a particle size of 350-450 mesh; and the defoamer is an organosilicon defoamer.

[0026] Preferably, the preparation process of the in-situ catalytic moisture-proof agent includes the following steps:

[0027] Boric acid and ethanolamine were stirred and reacted in a 50°C water bath for 30±2 min. Deionized water was added to dilute the mixture and prepare a solution with a solid content of 45-55% for later use.

[0028] This invention also proposes a method for preparing the aforementioned inorganic composite casting binder for cold core machines and manual molding, comprising the following steps:

[0029] S1. Raw material pretreatment:

[0030] Xylitol was dissolved in deionized water at 45±2℃ with stirring, and then cooled to 30±2℃ to obtain an aqueous solution of xylitol for later use.

[0031] Xylitol pre-dissolution involves breaking down the xylitol crystal structure in advance, dispersing it in water in a molecular state.

[0032] Surfactant OP-10, 1 / 3 of silane coupling agent KH560, and triacetin were emulsified by high-speed shearing, and then deionized water at 40±2℃ was added to prepare a functional additive mixed emulsion.

[0033] OP-10, KH560, and triacetin were used to form an oil-in-water (O / W) microemulsion through high-speed shearing. The hydrophilic head of the surfactant OP-10 faced the aqueous phase, and the hydrophobic tail was inserted into the oil phase droplet to reduce the interfacial tension and form a thermodynamically metastable system.

[0034] S2. Preparation of the main adhesive:

[0035] Add basic silica sol, sodium silicate solution, xylitol aqueous solution and sodium carbonate sequentially to the reaction vessel. Heat to 35±2℃ while stirring at 150±20 rpm. Add in-situ catalytic moisture-proofing agent and react at a constant temperature for 180±2 min.

[0036] The in-situ catalytic desiccant dissociates into borate ions (B(OH)4) under alkaline conditions. - Boron atoms, being electron-deficient centers, can undergo "boron-silicate ester" crosslinking with the silanol groups (Si-OH) produced by the hydrolysis of sodium silicate and basic silica sol, forming Si-OB bonds.

[0037]

[0038] Heat to 42±1℃, add functional additives to the emulsion mixture, add polyvinylpyrrolidone K30 while stirring at 400±50 rpm, and disperse for 40±2 min;

[0039] Add small-leaf sandalwood powder and 1 / 3 of KH560, and continue to disperse for 60±2 min;

[0040] Cool to 38±1℃, add parabens and reaction enhancer, stir at 350±30 rpm for 70±2 min, adjust pH to 10.8-11.2 with citric acid to obtain crude binder;

[0041] Polyvinylpyrrolidone (PVP), as a water-soluble polymer, has lactam groups (C=O) on its molecular chain that are strong hydrogen bond acceptors. These groups can simultaneously bind to the silanol groups, xylitol hydroxyl groups, and phenolic hydroxyl groups on the surface of the inorganic network through hydrogen bonds. This physically crosslinks and entangles the dispersed inorganic particles, small organic molecules, and subsequently added wood flour together, forming a preliminary interpenetrating network structure. This greatly improves the uniformity and stability of the system and prevents phase separation.

[0042] The main components of small-leaf sandalwood powder are cellulose and lignin. When KH560 is added, it hydrolyzes in an alkaline aqueous solution to generate silanols. These silanols react with hydroxyl groups on the surface of the wood powder on the one hand, and with silanol groups in the inorganic network on the other hand, thereby anchoring the wood powder to the inorganic framework through chemical bonds. At the same time, under the catalyst of boric acid and at a suitable temperature, the lignin and activated xylitol in the wood powder begin to undergo preliminary dehydration etherification / esterification reactions, consuming some hydrophilic hydroxyl groups and generating hydrophobic ether bonds.

[0043]

[0044] The crude product obtained at the end of step S2 has PVP molecular chains and silica sol particles oriented due to shearing, and the network structure is temporarily straightened. Under vacuum low-speed stirring (50-100 rpm), the shear rate decreases, and the above-mentioned polymers and colloidal particles return to a random coiled and entangled state. At the same time, after the air bubbles are removed, the material becomes more compact, thus the apparent viscosity decreases significantly. This is a typical shear-thinning non-Newtonian fluid behavior, which also indicates that a strong and reversible physical cross-linked network has been formed inside.

[0045] S3, Vacuum Degassing and Aging

[0046] Reduce the pressure inside the vessel to -0.09 MPa, add defoamer and defoam for 20-30 minutes while stirring at a low speed of 50-100 rpm;

[0047] The remaining KH560 and anhydrous ethanol were mixed at a mass ratio of 1:1, a leveling agent was added, and the mixture was stirred evenly to obtain a surface treatment agent.

[0048] The vacuum was slowly broken, and the surface treatment agent was atomized by an ultrasonic atomizer and added to the reaction vessel. The mixture was stirred at 25±5 rpm for 10±2 min, and then allowed to stand and age at 38±1℃ for 15-20 min. The mixture was then passed through a 100μm bag filter to obtain an environmentally friendly inorganic composite binder for cold core machines and manual casting.

[0049] Ethanol, acting as a co-solvent, instantly reduces the water activity of the binder surface, promoting rapid hydrolysis and condensation of KH560 on the surface, rather than diffusing into the interior for dilution. Due to atomized addition and low-speed stirring (25 rpm), the treatment agent is mainly concentrated on the material surface. KH560 rapidly reacts with the inorganic binder and sand particle surface on the surface, forming a high-density hydrophobic siloxane film. The KH560 concentration inside the material is lower, and the degree of hydrophobic modification is also lower. This naturally creates a chemical gradient from "moderately hydrophobic" in the core to "highly hydrophobic" on the surface. This structure ensures both the necessary air permeability and mechanical integrity of the core, while giving the sand core surface extremely strong hydrophobicity, directly blocking the intrusion of environmental moisture.

[0050] Preferably, the solid content of the xylitol aqueous solution is 55-60%; the solid content of the functional additive mixed emulsion is 25-26%.

[0051] Preferably, the viscosity of the crude adhesive at 25°C is 1500-2500 mPa·s.

[0052] Preferably, the viscosity of the cold core machine and the environmentally friendly inorganic composite binder for manual casting is 150-400 mPa·s at 25°C; and the solid content is 45±2%.

[0053] This invention also proposes the application of inorganic composite casting binders for cold core machines and manual molding. Sand cores and sand molds using cold core machines and environmentally friendly inorganic composite casting binders for manual molding achieve a recycling rate of over 90%. The specific recycling process includes the following steps:

[0054] Step 1: Crushing and preliminary screening:

[0055] After the sand blocks have cooled, they are fed evenly into the crusher by a vibrating feeder. After crushing, a mixture of sand particles is obtained. The mixture is then passed through a coarse screen with a pore size of 3.0-5.0 mm to separate large sand clumps that have not been completely broken up and mechanical impurities from the casting. The large sand clumps are returned to the crusher, while the impurities are discharged.

[0056] Step Two: Air Classification and Fine Separation

[0057] The sand and grain mixture after crushing and coarse screening enters the air classifier. The binder residue powder and fine dust with extremely low density are drawn away by the rising airflow and enter the dust collection system; the clean quartz sand particles with higher specific gravity fall down due to gravity and become the main body of recycled sand.

[0058] Step 3: Multi-stage screening and particle size control:

[0059] The recycled sand enters a multi-layer vibrating screen and is classified by the grading screen.

[0060] Step 4: Cooling and Reuse

[0061] After being screened, the recycled sand is cooled and then transported to a sand mixer to be mixed with a cold core machine and a hand-casting environmentally friendly inorganic composite binder. This mixture is then used directly to manufacture new sand cores and sand molds, forming a closed-loop cycle.

[0062] Preferably, the grading screen in step two is divided into an upper screen of 20-40 mesh, a core screen of 50-100 mesh, and a bottom screen of 140 mesh or more.

[0063] This binder achieves this through boron-silicon crosslinking and the formation of a denser Si-OB crosslinking network, within the hydrophilic Na... + The surrounding steric hindrance restricts its hydration migration and reduces the hygroscopic force. Under the action of in-situ catalytic desiccant, a large number of hydrophilic hydroxyl groups (-OH) in xylitol and lignin undergo intramolecular or intermolecular dehydration, transforming into hydrophobic ether bonds (-COC-) or ester bonds;

[0064] PVP, hydrophobically modified xylitol / lignin, and a dense inorganic silica network are intertwined and interconnected. The hydrophobic organic phase is dispersed in the continuous phase at the nano / micro scale, effectively interrupting the continuous permeation channels of water molecules. KH560 transforms the interface between sand particles, inorganic binders, and organic additives from primarily physical adsorption to chemical bonding (Si-O-Si, Si-OC), constructing a rich, highly cross-linked silane protective layer on the outermost layer of the sand core, which can effectively prevent the adsorption and capillary condensation of liquid and gaseous water in the initial contact stage.

[0065] The aforementioned moisture-proof structure is primarily based on thermally reversible or thermally decomposable chemical bonds (BO, organic ether bonds, ester bonds) and physical entanglement. During high-temperature casting (>700℃), these organic and borate ester structures completely decompose, burn, or vaporize, leaving only a brittle inorganic silicate skeleton. Therefore, the residue on the surface of the used waste sand remains a brittle, low-density, non-sticky inorganic powder, characterized by "no sticky coking residue on the surface, only a low-density dust-like inorganic film adhering to it," thus ensuring that it can be efficiently removed by simple air classification, achieving closed-loop recycling.

[0066] Compared with the prior art, the beneficial effects of the present invention are:

[0067] 1. Systematic solution to the problem of moisture and efflorescence: The borate ions derived from the catalyst not only cross-link with silicate ions to form a dense network, but their electron-deficient properties also allow them to react with sodium ions (Na+) in the system. + This catalyst exhibits strong interactions, effectively "locking in" the main hygroscopic ions and significantly reducing their hydration activity and migration ability. Simultaneously, under the same alkaline environment, the catalyst drives the dehydration reaction of xylitol and lignin, converting their hydrophilic hydroxyl groups into hydrophobic ether / ester bonds. This process eliminates two core hygroscopic hazards (Na₂O₃, Na ... +Simultaneously with free -OH groups, they are converted into structurally stable hydrophobic or fixed components, thereby weakening the hydrophilicity of the system from the root.

[0068] As an amphiphilic polymer, PVP forms an extensive hydrogen bond network with the carbonyl groups (C=O) of the inorganic phase and the hydroxyl groups of the organic phase. This network uniformly weaves and anchors the in-situ generated hydrophobic organic phase (modified xylitol oligomers and lignin fragments) within a rigid inorganic silica network framework, forming a stable organic-inorganic interpenetrating network (IPN). The hydrophobic organic phase dispersed within acts like countless "nanohydrophobic islands," effectively interrupting and prolonging the penetration path of water molecules within the material, significantly improving its impermeability.

[0069] The KH560 added in the early stage participates uniformly in the overall network construction to achieve bulk modification. In the later stage, the remaining KH560 is diluted with ethanol and sprayed in atomized form. Utilizing the "dehydration" effect and surface enrichment principle of ethanol, a dense cross-linked siloxane hydrophobic film is constructed in situ on the surface of the sand core / mold. The moderate hydrophobicity inside ensures the core strength and air permeability. The high-density hydrophobic layer on the outside constitutes a protective system against environmental moisture. This hydrophobic gradient structure from the inside out achieves the optimal balance between moisture-proof effect and mechanical and process performance.

[0070] 2. Enhanced Comprehensive Mechanical and Processing Properties: Nanoscale silica powder fills the network pores, achieving a "nano-reinforcement" effect. The long-chain structure of PVP acts as a "tough skeleton," absorbing and dispersing stress through hydrogen bonds and physical entanglement. KH560 strengthens the heterogeneous interfaces, including the chemical bonding between sand particles and binder, and between inorganic and organic phases. The synergy of these three elements allows the cured bond bridge to possess both the high rigidity and heat resistance of inorganic materials and the toughness and crack resistance similar to polymers, thus exhibiting excellent instantaneous strength, final strength, and thermal strength.

[0071] Because it contains no nitrogen and does not produce a large amount of hydrogen at high temperatures, it fundamentally eliminates defects such as subcutaneous porosity and nitrogen porosity in castings caused by binders. It is particularly suitable for complex thin-walled castings with extremely high airtightness requirements. After the sand core is cured, it has high strength and dimensional stability. During the casting process, it can effectively resist the erosion of molten metal, prevent surface defects such as sand adhesion and burrs, significantly improve the surface quality of castings, and reduce the amount of cleaning work.

[0072] 3. Meets Green Recycling Requirements: The moisture-proof and reinforced structure constructed in this invention allows its basic chemical bonds (organic ether / ester bonds, BO bonds, physical hydrogen bonds) to predictably and completely undergo pyrolysis, oxidation, and gasification under the thermal action of molten metal at temperatures >700℃, without producing viscous tar or residual carbon. The final residue consists only of brittle, low-density, pure inorganic silicates and a small amount of oxide powder. This residue is easily carried away by airflow; through air classification, the purity and recovery rate of the recycled sand can be ensured, achieving closed-loop production with outstanding environmental and economic value. Attached Figure Description

[0073] Figure 1 This is a flowchart illustrating the preparation, use of the binder, and recycling of sand particles according to the present invention. Detailed Implementation

[0074] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0075] Example 1: A method for preparing an inorganic composite casting binder for cold core machines and manual molding, comprising the following steps:

[0076] S1. Raw material pretreatment:

[0077] 25 kg of xylitol was dissolved in deionized water at 45 °C with stirring, and then cooled to 30 °C to obtain an aqueous solution of xylitol with a solid content of 60% for later use.

[0078] 0.3 kg of surfactant OP-10, 0.2 kg of silane coupling agent KH560, and 3 kg of triacetin were emulsified by high-speed shearing, and then deionized water at 40°C was added to prepare a functional additive mixed emulsion with a solid content of 26%.

[0079] S2. Preparation of the main adhesive:

[0080] Add 25 kg of basic silica sol, 35 kg of sodium silicate solution, xylitol aqueous solution, and 12 kg of sodium carbonate to the reactor in sequence. Heat to 35°C while stirring at 150 rpm, add 1.0 kg of in-situ catalytic moisture-proofing agent, and react at a constant temperature for 180 min.

[0081] Heat to 42℃, add functional additives to the emulsion, add 8kg of polyvinylpyrrolidone K30 while stirring at 400rpm, and disperse for 40min;

[0082] Add 1.2 kg of small-leaf sandalwood powder and 0.2 kg of KH560, and continue to disperse for 60 min;

[0083] Cool to 38℃, add 0.03kg paraben and 2kg reaction enhancer, stir at 350rpm for 70min, adjust pH to 11 with citric acid to obtain crude binder;

[0084] S3, Vacuum Degassing and Aging

[0085] Reduce the pressure inside the vessel to -0.09 MPa, add 0.05 kg of defoamer and defoam for 25 min while stirring at a low speed of 100 rpm;

[0086] 0.2 kg of KH560 and anhydrous ethanol were mixed at a mass ratio of 1:1, and 0.05 kg of leveling agent was added. The mixture was stirred evenly to obtain a surface treatment agent.

[0087] The vacuum was slowly broken, and the surface treatment agent was atomized by an ultrasonic atomizer and added to the reaction vessel. The mixture was stirred at 25 rpm for 10 min, allowed to stand and age at 38°C for 15 min, and then passed through a 100 μm bag filter to obtain an environmentally friendly inorganic composite binder for cold core machines and manual casting.

[0088] The crude binder has a viscosity of 1500-2500 mPa·s at 25°C.

[0089] The viscosity of the environmentally friendly inorganic composite binder for cold core machines and manual casting is 150-400 mPa·s at 25℃; the solid content is 45±2%.

[0090] Example 2:

[0091] Sodium silicate solution: 40 kg;

[0092] Basic silica sol: 20kg;

[0093] Sodium carbonate: 16 kg;

[0094] Xylitol: 20kg;

[0095] Surfactant OP-10: 0.3 kg;

[0096] Preservative parabens: 0.03 kg;

[0097] Plasticizer triacetin: 3 kg;

[0098] Dispersant polyvinylpyrrolidone K30: 10 kg;

[0099] Small-leaf sandalwood powder: 1kg;

[0100] In-situ catalytic desiccant: 1.25 kg;

[0101] Silane coupling agent KH560: 0.6 kg;

[0102] Reaction enhancer: 3.5 kg;

[0103] Defoamer: 0.075 kg;

[0104] Leveling agent: 0.05 kg;

[0105] The solid content of the xylitol aqueous solution is 55%; the solid content of the functional additive mixed emulsion is 26%.

[0106] The crude binder has a viscosity of 1500-2500 mPa·s at 25°C.

[0107] The viscosity of the environmentally friendly inorganic composite binder for cold core machines and manual casting is 150-400 mPa·s at 25℃; the solid content is 45±2%.

[0108] Example 3:

[0109] Sodium silicate solution: 45 kg;

[0110] Basic silica sol: 15kg;

[0111] Sodium carbonate: 18 kg;

[0112] Xylitol: 15kg;

[0113] Surfactant OP-10: 0.3 kg;

[0114] Preservative parabens: 0.03 kg;

[0115] Plasticizer triacetin: 3 kg;

[0116] Dispersant polyvinylpyrrolidone K30: 12 kg;

[0117] Small-leaf sandalwood powder: 0.8kg;

[0118] In-situ catalytic desiccant: 1.5 kg;

[0119] Silane coupling agent KH560: 0.6 kg;

[0120] Reaction enhancer: 2 kg;

[0121] Defoamer: 0.1 kg;

[0122] Leveling agent: 0.05 kg;

[0123] The solid content of the xylitol aqueous solution is 55%; the solid content of the functional additive mixed emulsion is 25%.

[0124] The crude binder has a viscosity of 1500-2500 mPa·s at 25°C.

[0125] The viscosity of the environmentally friendly inorganic composite binder for cold core machines and manual casting is 150-400 mPa·s at 25℃; the solid content is 45±2%.

[0126] Comparative Example 1: Based on Example 2, the difference is that the in-situ catalytic desiccant was prepared by boric acid and ethanolamine in a molar ratio of 2:1, and the rest was the same as in Example 2.

[0127] Comparative Example 2: Based on Example 2, the difference is that no in-situ catalytic moisture-proof agent is added, otherwise it is the same as Example 2.

[0128] Comparative Example 3: Based on Example 2, the difference is that the surface treatment agent is not added in an atomized manner, and the rest is the same as Example 2.

[0129] Comparative Example 4: Based on Example 2, the difference is that the amount of KH-560 is increased to 5 times the original amount, and the rest is the same as Example 2.

[0130] The preparation of binders and the process of crushing and recycling castings are as follows: Figure 1 As shown, the binder produced by this invention was used in cold-core casting to produce 5cm*5cm*5cm square castings as standard sand core samples. The standard sand core samples were placed in a constant temperature and humidity chamber at 40℃ and 90%RH, and weighed periodically to test their 48-hour moisture resistance – moisture absorption weight gain rate. After treating the standard sand core samples in a high-humidity environment at 40℃ and 90%RH for 48 hours, their tensile strength was immediately measured to obtain their moisture resistance – high-humidity strength retention rate. The loss on ignition of the waste sand was determined using the muffle furnace ignition method (GB / T2684) to obtain its recyclability. Simultaneously, the loss on ignition, heavy metal content, and VOCs content were tested. The results are shown in Table 1.

[0131] Table 1. Performance Test Table for Standard Sand Core Samples

[0132]

[0133] Data Analysis:

[0134] Comparative Example 2, without the catalyst, showed a significantly lower high-wet strength retention rate (58%) compared to all other examples (86%-90%), and also had the highest moisture absorption weight gain rate (4.8%). This difference directly confirms the core role of the "in-situ catalytic moisture-proofing agent." The lack of a catalyst means that two key reactions failed to initiate:

[0135] Boron-silicon crosslinking deficiency: The inorganic silicon-oxygen network failed to be strengthened and densified through BO bonds, resulting in larger network pores and reduced susceptibility to sodium ions (Na+). + The weak fixation effect of the molecule provides a channel for water molecules to penetrate.

[0136] The xylitol / lignin hydrophobication reaction is missing: xylitol and lignin in wood flour retain a large number of hydrophilic hydroxyl groups (-OH), which become water absorption points within the system. In humid environments, these components absorb a large amount of moisture, severely weakening the mechanical strength of the bonding bridge.

[0137] The data from Comparative Example 2 serves as a baseline control, demonstrating the indispensability of the catalyst in the examples. It transforms hydrophilic xylitol and lignin into hydrophobic components while strengthening the inorganic network, thereby improving the bulk's moisture resistance at both the "molecular" and "structural" levels.

[0138] Comparative Example 3, which did not undergo surface treatment, showed an improved high-wet strength retention rate (62%) compared to Comparative Example 2, but it was still significantly lower than that of the Example (approximately 90%). However, its moisture absorption weight gain rate (3.9%) was significantly better than Comparative Example 2, and even better than Comparative Example 1. This reflects the unique function of surface gradient treatment:

[0139] Low retention rate: This indicates that in a long-term high-humidity environment, sand cores lacking a high-strength surface hydrophobic layer for protection will still be gradually penetrated and destroyed by water vapor, even though their internal network has undergone catalytic modification (therefore the moisture absorption rate is lower than that of control sample 2), resulting in a significant loss of strength.

[0140] The moisture absorption rate is acceptable, indicating that the internal catalytic modification has indeed played a role, reducing the overall moisture absorption rate and total amount. However, due to the lack of an outermost hydrophobic layer, water vapor can still continuously penetrate.

[0141] Synergistic Effect: This data illustrates the concept of "gradient" moisture protection. The example, through atomization treatment, forms a highly cross-linked KH560 siloxane film (large hydrophobic angle, strong water resistance) on the surface, like putting a "raincoat" on the sand core. In contrast, Comparative Example 3 only has a "sweater with low hygroscopicity," unable to withstand continuous "rain" (high humidity environment). Surface treatment and internal modification form a synergistic defense of "shield" and "armor."

[0142] Comparative Example 1, which had an improper catalyst ratio, had moisture-proof performance (72% retention rate and 3.5% moisture absorption rate) between that of Example 1 and Comparative Example 2.

[0143] An incorrect molar ratio of boric acid to ethanolamine (1:2) (2:1) may result in:

[0144] Changes in system pH or complex morphology can affect catalytic activity.

[0145] Excessive boric acid may self-condense or react too quickly with silicates, affecting network uniformity.

[0146] Insufficient ethanolamine may affect the stability of the catalytic system and the efficiency of xylitol activation.

[0147] The effectiveness of a catalyst is not simply a matter of its existence; its specific stoichiometry is key to achieving optimal catalytic efficiency and network construction, reflecting the precision of the formulation.

[0148] One of the major advantages of this invention is that it enables the efficient recycling of waste sand, and the data indirectly confirms the "environmentally friendly" characteristics of its chemical design.

[0149] The LOI was extremely low in all examples (0.32%-0.41%), and slightly higher in comparative examples 2 and 4 (0.65%).

[0150] LOI directly reflects the amount of decomposable organic residues at high temperatures. The low LOI of the example benefits from:

[0151] Thoroughness of catalytic conversion: Xylitol and other substances are catalytically converted into ether / ester structures that are relatively less thermally stable or more easily combusted, and are more easily decomposed and vaporized at high casting temperatures.

[0152] The dominance of inorganic networks: The system uses inorganic silicates as the framework, with organic components acting as modifiers rather than the main components, and the total amount is controllable.

[0153] Comparative Example 2 with high LOI: Due to the lack of catalysis, xylitol and other substances may exist in their original form, resulting in different pyrolysis behavior and potentially producing more solid carbon residue.

[0154] Potential problems with Comparative Example 4: Excess KH560, as an organosilane, can increase the organic content, which may lead to an increase in LOI, consistent with its VOCs surge.

[0155] A low LOI (Lower Oxygen Intake) means that the residue on the surface of the waste sand is mainly inorganic, brittle silicate powder, which is the material basis for the efficient separation (large density difference) of the air classification process. The VOC content in the example was low (12-18 g / L), while in Comparative Example 4 it soared to 48 g / L.

[0156] VOCs mainly originate from volatile small-molecule organic compounds. The examples demonstrate how a chemical reaction converts small-molecule xylitol into oligomers or part of a network, thus immobilizing the carbon source.

[0157] The outlier in Comparative Example 4 was primarily due to the use of 5 times the normal amount of KH560. Excessive silane coupling agent cannot fully participate in the effective reaction within the system; some remains in a free state or as oligomers. These substances are highly volatile, leading to severely excessive VOCs. This is not only an environmental defect but also indicates process instability and cost waste. This data, conversely, demonstrates the scientific validity and optimization of the KH560 dosage in the original formula.

[0158] The examples have moderate viscosity (190-260 mPa·s) and long usable time (6-7 h). Comparative Example 4 has abnormally high viscosity (850 mPa·s) and short usable time (4 h).

[0159] Example: The moderate viscosity benefits from the reversible physical network (shear thinning) formed by PVP and silica sol, resulting in good rheological properties. Long service life demonstrates that, with optimized pH and catalyst, the condensation reaction rate at room temperature is effectively suppressed, and the system remains stable.

[0160] Comparative Example 4: Excessive KH560 will undergo large-scale and rapid hydrolysis and condensation, forming a large amount of silanols, which may self-polymerize. This leads to an abnormal increase in the crosslinking density of the system during storage, manifested as a sharp increase in viscosity and a drastic reduction in usable time. This compromises the process suitability of the binder.

[0161] The 24-hour tensile strength (2.5-2.8 MPa) and gas generation (9.8-11.2 mL / g) of the examples were both at excellent levels.

[0162] Strength: Thanks to the toughening effect of PVP, the reinforcement of silica powder, the interface strengthening of KH560, and the dense boron-silicon network, a composite structure with both rigidity and toughness is formed.

[0163] Gas Emission: The low gas emission indicates that the decomposition of organic components (modified xylitol, lignin, a small amount of PVP, etc.) during casting is relatively gradual and thorough, without violent gas bursts. This is due to their well-organized and fixed presence in the network, rather than existing in a free state.

[0164] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An inorganic composite casting binder for cold core machines and manual molding, characterized in that, Includes the following components by weight: Sodium silicate solution: 35-45 parts; Basic silica sol: 15-25 parts; Sodium carbonate: 12-18 parts; Xylitol: 15-25 parts; Surfactant OP-10: 0.3 parts; Preservative parabens: 0.03 parts; Plasticizer triacetin: 3 parts; Dispersant polyvinylpyrrolidone K30: 8-12 parts; Small-leaf sandalwood powder: 0.8-1.2 parts; In-situ catalytic moisture-proofing agent: 1.0-1.5 parts; Silane coupling agent KH560: 0.6 parts; Reaction enhancer: 2-5 parts; Defoamer: 0.05-0.1 parts; Leveling agent: 0.05 parts; The in-situ catalytic moisture-proofing agent is prepared by mixing boric acid and ethanolamine in a molar ratio of 1:

2.

2. The inorganic composite casting binder for cold core machines and manual molding as described in claim 1, characterized in that, The basic silica sol contains 25-30% SiO2 and has a particle size of 10-15 nm; the small-leaf sandalwood powder has a particle size of 200-300 mesh; the reaction enhancer is silica micro powder with a particle size of 350-450 mesh; and the defoamer is an organosilicon defoamer.

3. The inorganic composite casting binder for cold core machines and manual molding as described in claim 1, characterized in that, The preparation process of the in-situ catalytic moisture-proof agent includes the following steps: Boric acid and ethanolamine were stirred and reacted in a 50°C water bath for 30±2 min. Deionized water was added to dilute the mixture and prepare a solution with a solid content of 45-55% for later use.

4. A method for preparing an inorganic composite casting binder for cold core machines and manual molding as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Raw material pretreatment: Xylitol was dissolved in deionized water at 45±2℃ with stirring, and then cooled to 30±2℃ to obtain an aqueous solution of xylitol for later use. Surfactant OP-10, 1 / 3 of silane coupling agent KH560, and triacetin were emulsified by high-speed shearing, and then deionized water at 40±2℃ was added to prepare a functional additive mixed emulsion. S2. Preparation of the main adhesive: Add basic silica sol, sodium silicate solution, xylitol aqueous solution and sodium carbonate sequentially to the reaction vessel. Heat to 35±2℃ while stirring at 150±20 rpm. Add in-situ catalytic moisture-proofing agent and react at a constant temperature for 180±2 min. Heat to 42±1℃, add functional additives to the emulsion mixture, add polyvinylpyrrolidone K30 while stirring at 400±50 rpm, and disperse for 40±2 min; Add small-leaf sandalwood powder and 1 / 3 of KH560, and continue to disperse for 60±2 min; Cool to 38±1℃, add parabens and reaction enhancer, stir at 350±30 rpm for 70±2 min, adjust pH to 10.8-11.2 with citric acid to obtain crude binder; S3, Vacuum Degassing and Aging Reduce the pressure inside the vessel to -0.09 MPa, add defoamer and defoam for 20-30 minutes while stirring at a low speed of 50-100 rpm; The remaining KH560 and anhydrous ethanol were mixed at a mass ratio of 1:1, a leveling agent was added, and the mixture was stirred evenly to obtain a surface treatment agent. The vacuum was slowly broken, and the surface treatment agent was atomized by an ultrasonic atomizer and added to the reaction vessel. The mixture was stirred at 25±5 rpm for 10±2 min, and then allowed to stand and age at 38±1℃ for 15-20 min. The mixture was then passed through a 100μm bag filter to obtain an environmentally friendly inorganic composite binder for cold core machines and manual casting.

5. The preparation method of the inorganic composite casting binder for cold core machine and manual molding according to claim 4, characterized in that, The solid content of the xylitol aqueous solution is 55-60%; the solid content of the functional additive mixed emulsion is 25-26%.

6. The method for preparing the inorganic composite casting binder for cold core machines and manual molding according to claim 4, characterized in that, The crude binder has a viscosity of 1500-2500 mPa·s at 25°C.

7. The method for preparing the inorganic composite casting binder for cold core machines and manual molding according to claim 4, characterized in that, The viscosity of the environmentally friendly inorganic composite binder for cold core machines and manual casting is 150-400 mPa·s at 25℃; the solid content is 45±2%.

8. The application of an inorganic composite casting binder for cold core machines and manual molding as described in any one of claims 1-3, characterized in that, Sand cores and sand molds using cold core machines and manual casting with environmentally friendly inorganic composite binders achieve a recycling rate of over 90%. The specific recycling process includes the following steps: Step 1: Crushing and preliminary screening: After the sand blocks have cooled, they are fed evenly into the crusher by a vibrating feeder. After crushing, a mixture of sand particles is obtained. The mixture is then passed through a coarse screen with a pore size of 3.0-5.0 mm to separate large sand clumps that have not been completely broken up and mechanical impurities from the casting. The large sand clumps are returned to the crusher, while the impurities are discharged. Step Two: Air Classification and Fine Separation The sand and grain mixture after crushing and coarse screening enters the air classifier. The binder residue powder and fine dust with extremely low density are drawn away by the rising airflow and enter the dust collection system; the clean quartz sand particles with higher specific gravity fall down due to gravity and become the main body of recycled sand. Step 3: Multi-stage screening and particle size control: The recycled sand enters a multi-layer vibrating screen and is classified by the grading screen. Step 4: Cooling and Reuse After being screened, the recycled sand is cooled and then transported to a sand mixer to be mixed with a cold core machine and a hand-casting environmentally friendly inorganic composite binder. This mixture is then used directly to manufacture new sand cores and sand molds, forming a closed-loop cycle.

9. The application of the inorganic composite casting binder for cold core machines and manual molding as described in claim 8, characterized in that, The graded screens are divided into an upper screen of 20-40 mesh, a core screen of 50-100 mesh, and a bottom screen of 140 mesh or more.

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