Environment-friendly casting sand binder and preparation method thereof

Abstract

The present application relates to the technical field of self-hardening binder for casting, and particularly relates to an environment-friendly sand mold binder for casting and a preparation method thereof, which comprises 100-400 parts of bio-based phenolic compound, 100-400 parts of phenol, 1100-1500 parts of furfuryl alcohol, 800-1000 parts of furfuryl alcohol, 1-10 parts of catalyst and 3-5 parts of silane coupling agent; wherein, in the amount of the furfuryl alcohol, the part used for the synthesis of the main chain of furan resin is 800-1000 parts, and the part used for the viscosity adjustment in the post-processing is 300-500 parts. The present application solves the problem that the strength, collapsibility and process stability of the zero-formaldehyde binder in the prior art cannot be considered simultaneously, thereby failing to meet the casting requirements.

Description

Technical Field

[0001] This invention relates to the field of self-hardening binders for casting, and more particularly to an environmentally friendly sand mold binder for casting and its preparation method. Background Technology

[0002] Casting is a core foundational process in the equipment manufacturing industry. Key components of strategic emerging industries such as aerospace, rail transportation, and new energy vehicles all rely on precision casting technology for their formation. As the skeleton of the sand mold / core, the performance of the binder directly determines the quality of the castings and the level of environmental protection in production.

[0003] Furan resins have become the mainstream binder for precision casting due to their high strength, excellent heat resistance, and good compatibility with silica sand. However, traditional furan resins face three major technical bottlenecks: Formaldehyde pollution is serious. The synthesis relies on formaldehyde raw materials, and large amounts are released during sand mixing and casting, which endangers the health of operators. It has poor collapsibility, and the cross-linked network is dense and stable after curing. The residual strength after casting is greater than or equal to 0.2MPa. Strong vibration is required for sand removal and cleaning, which can easily cause damage to the surface of the casting. The post-treatment cost accounts for more than 15% of the total cost of the casting. Existing modification technologies mostly use biomass materials to dilute furan resin. Although this can improve the collapsibility to a certain extent, it reduces the tensile strength of molding sand by 10% to 15% and cannot solve the problem of formaldehyde residue at the root, making it difficult to balance environmental protection and performance.

[0004] Chinese Patent Application Publication No. CN116622044A discloses a phenol-modified furan resin for casting with low free phenol content and its preparation method, comprising: reacting phenol and formaldehyde A with phenol-formaldehyde at a reaction temperature of 50℃~70℃ for 1.5h~2h; adding urea and formaldehyde B to the phenol-formaldehyde reaction product and reacting with urea-formaldehyde at 80℃~100℃ for 0.5h~2h; adding furfuryl alcohol A to the urea-formaldehyde reaction product, adjusting the pH of the solution to 3~4, and reacting with formic acid as a catalyst at 110℃~130℃ for 0.5h~1.5h to condense phenol, urea-formaldehyde, and furfuryl alcohol into chains; and adding furfuryl alcohol B to the reaction system after the condensation reaction is terminated. However, this invention relies on phenol, formaldehyde, and urea, and only pursues low free phenol, without solving the problems of formaldehyde and biotoxicity. As a hydroxymethylation agent, formaldehyde is an essential raw material for traditional phenolic resins, which inevitably leads to the presence of free formaldehyde and phenolic structures in the finished product, making it impossible to meet the increasingly stringent requirements for formaldehyde-free casting. Summary of the Invention

[0005] Therefore, this invention provides an environmentally friendly sand mold binder for casting and its preparation method, in order to overcome the problem that the strength, collapsibility and process stability of the existing zero-formaldehyde binder cannot be simultaneously achieved, thus failing to meet the casting requirements.

[0006] To achieve the above objectives, on the one hand, the present invention provides an environmentally friendly sand mold binder for casting, wherein the raw materials for preparing the sand mold binder, by weight, consist of the following components: 100-400 parts of bio-based phenolic compounds, 100-400 parts of phenol, 1100-1500 parts of furfuryl alcohol, 800-1000 parts of furfural, 1-10 parts of catalyst, and 3-5 parts of silane coupling agent; Of the amount of furfuryl alcohol used, 800 to 1000 parts are used for the synthesis of the furan resin backbone, and 300 to 500 parts are used for post-treatment to adjust viscosity.

[0007] Furthermore, the bio-based phenolic compound is selected from one or more of dehydrorosinol, piperol, lignin depolymerized long-chain phenol, tallol, and cashew phenol.

[0008] Furthermore, the catalyst is selected from one or more of CuBr2, FeCl3, CuCl2, CuI, FeBr3, CoCl2, and NiCl2.

[0009] Furthermore, the silane coupling agent is selected from one or more of KH540, A-1110, A-1120, KH551, A-1126, and KH792.

[0010] On the other hand, the present invention also provides a method for preparing an environmentally friendly casting sand mold binder, comprising: Step S1: Add bio-based phenolic compounds, phenol, and catalyst to the first reaction vessel, heat to 80℃~100℃ at a rate of less than 1℃ / min, and hold at that temperature for 60min~120min to obtain a mixture; Step S2: Adjust the pH of the mixture to 6.5-8.0 using a 30% sodium hydroxide solution, and obtain the prepolymer after cooling; Step S3: Add furfuryl alcohol and furfural used for the synthesis of furan resin main chain to the second reactor, adjust the pH of the system in the second reactor to 3.8-4.6 with 10% hydrochloric acid, raise the temperature to 70℃-80℃, and keep it at that temperature for 60min-120min to obtain furan resin. Step S4: Add the prepolymer to the furan resin, adjust the pH of the furan resin to 3.8-4.6 with 10% hydrochloric acid, heat to 60℃-70℃, and hold for 30-60 minutes to obtain modified furan resin; Step S5: Cool the modified furan resin to below 60℃, add some furfuryl alcohol for post-treatment viscosity adjustment to adjust the viscosity to the preset target viscosity; Step S6: Cool the modified furan resin, which has reached the preset target viscosity, to below 40°C, add silane coupling agent, stir at 150 r / min to 200 r / min for 10 min to 15 min, mix evenly, and then discharge to obtain sand mold binder. The component weight ratios and process parameters in steps S1 to S5 are dynamically determined based on the target performance parameters of the sand-type binder.

[0011] Furthermore, the specific component weight ratio, heating temperature, and holding time of the sand mold binder are determined based on the target performance parameters. The target performance parameters include target tensile strength, hardening strength at room temperature for 24 hours, and target working viscosity.

[0012] Furthermore, the total amount of bio-based phenolic compounds and phenol is determined based on the target tensile strength, the weight percentage of bio-based phenolic compounds in the total amount of phenols is determined based on the target free phenol content in the finished sand-type adhesive, and the total amount of furfuryl alcohol used is calculated based on the total amount of phenols and the weight percentage of bio-based phenolic compounds in the total amount of phenols. The mass percentage of the bio-based phenolic compounds in the total phenolic content is negatively correlated with the target free phenol content.

[0013] Furthermore, the amount of furfural used for the synthesis of the furan resin backbone is determined based on the amount of bio-based phenolic compounds, and the specific amount of furfuryl alcohol used for post-treatment viscosity adjustment is determined based on the target working viscosity. The amount of furfural used in the synthesis of the furan resin backbone is negatively correlated with the amount of the bio-based phenolic compound, and the amount of furfuryl alcohol used for post-treatment viscosity adjustment is negatively correlated with the target working viscosity.

[0014] Furthermore, the heating rate and holding time are determined based on the total amount of phenols, and the heating rate and holding time are positively correlated with the total amount of phenols.

[0015] Further, in step S5, adjusting the viscosity to a preset target viscosity includes: Add furfuryl alcohol for post-processing viscosity adjustment, and measure the actual viscosity under stirring conditions of 200 r / min. Compare and analyze the measured viscosity with the preset target viscosity. The difference between the measured viscosity and the preset target viscosity determines the amount of furfuryl alcohol to be added. After adding furfuryl alcohol, stir for 30 min and measure the actual viscosity again until the measured viscosity is greater than the preset target viscosity.

[0016] Compared with existing technologies, the beneficial effects of this invention are that it designs a brand-new formulation system, uses bio-based phenolic compounds and phenol in combination, and completely replaces formaldehyde with furfural. At the same time, it clarifies the specific weight range of each component, significantly reducing the product's dependence on fossil resources and conforming to the trend of green manufacturing. It also eliminates the residue and release of free formaldehyde in the finished product from the source, greatly improving the production environment and worker health in the foundry workshop.

[0017] Furthermore, this invention specifically defines bio-based phenols, all of which contain reactive phenolic hydroxyl groups and / or unsaturated long chains, ensuring their copolymerization reactivity with phenol and furfural. In particular, the long chains or rigid structures inherent in dehydrorosinol, cashew phenol, etc., can effectively toughen furan resin networks, reduce their brittleness, and improve the impact resistance of sand molds. These phenols come from multiple sources, including plant extracts, papermaking by-products, and agricultural and forestry waste conversion, which is beneficial for reducing costs and achieving resource utilization.

[0018] Furthermore, this invention defines a catalyst that exhibits high selectivity and efficiency in the initial polycondensation reaction of bio-based phenols and phenols, without affecting the subsequent synthesis of furan resins; its catalytic properties do not conflict with the subsequent acid-catalyzed furan resin synthesis stage, and some metal ions have the potential to contribute to the heat resistance of the final resin.

[0019] Furthermore, it enhances the chemical bonding force between the organic resin and the surface of the inorganic sand particles, thereby significantly improving the bonding strength, especially the moisture resistance and long-term strength; it also improves the instantaneous tensile strength and 24-hour hardening strength of the sand mold, and reduces the strength decay caused by environmental humidity, resulting in more accurate casting dimensions and fewer defects.

[0020] Furthermore, the present invention employs a stepwise synthesis process, first preparing a bio-based phenol-phenol prepolymer, then synthesizing a furan backbone with furfuryl alcohol and furfural, and finally incorporating the prepolymer into the backbone for modification, and fine-tuning by adding furfuryl alcohol and silane coupling agent to ensure that the bio-based phenols can be uniformly incorporated into the resin macromolecular chain by chemical bonding. Furthermore, this invention innovatively replaces formaldehyde entirely with furfural. Due to the fundamental differences between furfural and formaldehyde in terms of reactivity, toxicity, and impact on resin network structure, the entire synthesis system was redesigned. Based on the chemical structural characteristics of bio-based phenolic compounds, it is compounded with phenol to balance rigidity and toughness. The introduction of bio-based phenols reduces dependence on fossil resources, while their long-chain flexible structure can toughen furan resin networks, improve collapsibility and impact resistance, which is fundamentally different from the traditional method of simply using phenol or diluting with simple biomass.

[0021] Furthermore, the preparation method of the present invention employs a multi-step reaction, including first synthesizing a bio-based phenol-phenol prepolymer, then synthesizing a furan resin backbone, and finally incorporating the prepolymer into the backbone for modification. This stepwise process ensures that the bio-based phenolic compounds are uniformly incorporated into the resin macromolecular chain through chemical bonding rather than physical mixing, thereby improving the uniformity of the structure and the stability of the performance, and overcoming the problem of strength reduction caused by simple blending or dilution in the prior art.

[0022] Furthermore, while achieving zero formaldehyde, the adhesive of this invention exhibits higher tensile strength in molding sand than traditional furan resin, and significantly lower high-temperature residual strength than traditional resin, indicating a substantial improvement in collapsibility. This directly solves the problem in the prior art where zero-formaldehyde adhesives cannot simultaneously achieve strength, collapsibility, and process stability.

[0023] Furthermore, by selecting catalysts, precisely controlling pH, and iteratively adjusting post-treatment viscosity, the controllability of the reaction and the consistency of the finished product are ensured, overcoming the instability or performance fluctuations caused by the addition of biomass in existing modification technologies. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the method for preparing an environmentally friendly casting sand mold binder according to an embodiment of the present invention; Figure 2 This is a schematic flowchart illustrating the calculation of the total amount of furfuryl alcohol in the preparation method of the environmentally friendly casting sand mold binder according to an embodiment of the present invention; Figure 3 This is a logic diagram for determining the heating rate and holding time in the preparation method of the environmentally friendly casting sand mold binder in this embodiment of the invention; Figure 4 This is a logic diagram of viscosity adjustment in the preparation method of environmentally friendly casting sand mold binder according to an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0026] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0027] This invention discloses an environmentally friendly sand mold binder for casting. The raw materials for preparing the sand mold binder, by weight, consist of the following components: 100-400 parts of bio-based phenolic compounds, 100-400 parts of phenol, 1100-1500 parts of furfuryl alcohol, 800-1000 parts of furfural, 1-10 parts of catalyst, and 3-5 parts of silane coupling agent; Of the amount of furfuryl alcohol used, 800 to 1000 parts are used for the synthesis of the furan resin backbone, and 300 to 500 parts are used for post-treatment to adjust viscosity.

[0028] Understandably, bio-based phenolic compounds contain reactive phenolic hydroxyl groups, which can partially replace petroleum-based phenols in reactions, reducing dependence on fossil resources and introducing long-chain flexible structures. When combined with phenol, they can achieve a balance between rigidity and toughness.

[0029] This invention completely replaces formaldehyde with furfural, eliminating this toxic and harmful raw material from the source, so that the final product has zero free formaldehyde, solving the core environmental and health issues. The main chain of furan resin is formed by the reaction of furfural and furfuryl alcohol.

[0030] Furfuryl alcohol is used in two parts. One part is used to synthesize the main chain of furan resin with furfural, which is the basic reaction for forming the resin skeleton. The other part is reserved for the post-processing stage to adjust the viscosity of the finished product. This design achieves decoupling of reaction and performance adjustment, so that the final viscosity is controllable without affecting the degree of the main synthesis reaction.

[0031] The weight ranges of each component were optimized through numerous experiments to ensure that a resin network with sufficient strength and collapsibility can be formed under the environmentally friendly system. Less than the lower limit may result in insufficient strength, while more than the upper limit may result in increased brittleness, runaway reaction, or excessive cost.

[0032] Specifically, the bio-based phenolic compounds are selected from one or more of dehydrorosinol, piperol, lignin depolymerized long-chain phenol, tallol, and cashew phenol.

[0033] Understandably, the selected dehydrorosinol, piperol, lignin depolymerization long-chain phenols, tall oil phenol, and cashew phenol all contain reactive phenolic hydroxyl groups, ensuring their reactivity in copolymerization with phenol and furfural. More importantly, these bio-based phenols typically possess rigid structures or long aliphatic chains. Introducing rigid structures into the resin network enhances heat resistance; introducing long flexible chains acts like an internal plasticizer, toughening the originally brittle furan resin network and improving the impact resistance and collapse resistance of the sand mold. Their diversified sources also contribute to cost reduction and resource utilization.

[0034] Specifically, the catalyst is selected from one or more of CuBr2, FeCl3, CuCl2, CuI, FeBr3, CoCl2, and NiCl2.

[0035] Understandably, the selected catalysts are all Lewis acid catalysts, whose core role is to efficiently catalyze the polycondensation reaction between bio-based phenols and phenols in the prepolymer synthesis stage of step S1, forming the prepolymer. These metal ion catalysts have high selectivity for phenol polycondensation, and their catalytic characteristics do not conflict with the acidic catalytic furan resin synthesis and co-condensation stages in subsequent steps S3 and S4; some metal ions may remain in the resin, potentially enhancing the heat resistance of the final cured product.

[0036] Specifically, the silane coupling agent is selected from one or more of KH540, A-1110, A-1120, KH551, A-1126, and KH792.

[0037] Understandably, the silane coupling agent molecule has a hydrolyzable alkoxy group at one end and an organic functional group at the other. Its mechanism of action is as follows: after addition in step S6, the alkoxy group hydrolyzes to generate silanol groups, which undergo a condensation reaction with the hydroxyl groups on the surface of the inorganic sand particles, forming a strong -Si-O-Si- chemical bond. Simultaneously, its organic functional group interacts or chemically reacts with the active groups in the resin, enhancing the interfacial bonding force. This directly improves the immediate and long-term strength of the molding sand and reduces casting defects caused by interfacial damage.

[0038] Please see Figure 1 As shown, a method for preparing an environmentally friendly casting sand mold binder includes: Step S1: Add bio-based phenolic compounds, phenol, and catalyst to the first reaction vessel, heat to 80℃~100℃ at a rate of less than 1℃ / min, and hold at that temperature for 60min~120min to obtain a mixture; Step S2: Adjust the pH of the mixture to 6.5-8.0 using a 30% sodium hydroxide solution, and obtain the prepolymer after cooling; Step S3: Add furfuryl alcohol and furfural used for the synthesis of furan resin main chain to the second reactor, adjust the pH of the system in the second reactor to 3.8-4.6 with 10% hydrochloric acid, raise the temperature to 70℃-80℃, and keep it at that temperature for 60min-120min to obtain furan resin. Step S4: Add the prepolymer to the furan resin, adjust the pH of the furan resin to 3.8-4.6 with 10% hydrochloric acid, heat to 60℃-70℃, and keep warm for 30-60 minutes to obtain the modified furan resin. Step S5: Cool the modified furan resin to below 60°C, and add some furfuryl alcohol for post-treatment viscosity adjustment to adjust the viscosity to the preset target viscosity; Step S6: Cool the modified furan resin, which has reached the preset target viscosity, to below 40°C, add silane coupling agent, stir at 150r / min to 200r / min for 10min to 15min, mix evenly, and then discharge to obtain sand mold binder.

[0039] Specifically, the specific component weight ratio, heating temperature, and holding time of the sand-type binder are determined based on the target performance parameters. The target performance parameters include target tensile strength, hardening strength at room temperature for 24 hours, and target working viscosity.

[0040] Understandably, the target tensile strength corresponds to the mechanical strength and crosslinking density of the resin matrix; the target free phenol content is a core indicator for environmental protection and toxicology; and the target working viscosity directly affects the sand mixing process and the flowability of the sand mold.

[0041] Please see Figure 2 The diagram shows a flowchart illustrating the process of calculating the total amount of furfuryl alcohol in the preparation method of the environmentally friendly casting sand mold binder according to an embodiment of the present invention. Specifically, the total amount of bio-based phenolic compounds and phenol is determined based on the target tensile strength, the weight percentage of bio-based phenolic compounds in the total amount of phenols is determined based on the target free phenol content in the finished sand mold binder, and the total amount of furfuryl alcohol used is calculated based on the total amount of phenols and the weight percentage of bio-based phenolic compounds in the total amount of phenols. The mass percentage of the bio-based phenolic compounds in the total phenolic content is negatively correlated with the target free phenol content.

[0042] The specific calculation method for the total amount of bio-based phenolic compounds and phenol is as follows: M = M0 + M1 × (P - P0) / P0; Where M is the total amount of phenols, M0 is the minimum total amount of phenols, M1 is the adjustment value of the total amount of phenols, preferably 2250 parts, P is the target tensile strength, and P0 is the tensile strength threshold, preferably 2.5 MPa.

[0043] In the formula for calculating the total phenol content based on the target tensile strength, the total phenol content adjustment value is an adjustment coefficient that determines the magnitude of adjustment of the total phenol content when the target tensile strength changes relative to a threshold. This value is based on regression analysis of a large amount of experimental data. When the target strength P varies within the typical range of 2.0 MPa to 3.0 MPa, the calculated total phenol content falls within a reasonable range, and the trend of change is positively correlated with the strength requirement. This value ensures the practicality of the calculation model and the operability of the results.

[0044] In the foundry industry, the tensile strength of sand molds is a core performance indicator. The value of 2.5 MPa comes from the previous process verification. Setting this value as a benchmark allows the formula design model to be adjusted around a clear high-performance target.

[0045] Table 1 shows the relationship between the mass percentage of bio-based phenolic compounds in the total phenolic content and the target free phenol content: Table 1. Comparison of the mass percentage of bio-based phenolic compounds and the content of target free phenol.

[0046] Of these, bio-based phenols account for less than or equal to 80% to ensure reaction stability.

[0047] The specific calculation method for the total amount of furfuryl alcohol used is as follows: N = N0 + N1 × (t - t0) / t0; Where N is the total amount of furfuryl alcohol used, N0 is the minimum amount of furfuryl alcohol used, N1 is the preset furfuryl alcohol adjustment amount, preferably 10 parts, t is the preset target viscosity, and t0 is the preset target viscosity threshold, preferably 25 mPa·s.

[0048] The working viscosity of the resin binder used in casting directly affects the uniformity of sand mixing, the flowability of the sand mold, and its coatability. The preset target viscosity threshold is the optimal process viscosity determined through a large number of process experiments. Using this value as the threshold, the formula calculates the corresponding change in furfuryl alcohol dosage when the target viscosity changes, ensuring that the viscosity of the final product accurately meets the process requirements for sand mixing and molding.

[0049] It is understandable that phenolic compounds are the main providers of rigid segments and crosslinking points in the resin network. Increasing their total amount means increasing the crosslinking density and rigid components of the resin network, thereby directly contributing to higher tensile strength of molding sand.

[0050] Bio-based phenols typically have greater steric hindrance and different reactivity than phenols. In a cocondensation system, appropriately increasing their proportion can reduce the absolute amount of small-molecule, highly volatile free phenols in the system when a similar degree of reaction is achieved, thereby reducing the free phenol content in the finished product.

[0051] Furfuryl alcohol is both a reactant and a regulator. Its total amount must be matched with the total amount of phenols to ensure the sufficiency of the reaction and the appropriate molecular weight.

[0052] Specifically, the amount of furfural used for the synthesis of furan resin backbone is determined based on the amount of bio-based phenolic compounds, and the amount of furfuryl alcohol used for post-treatment viscosity adjustment is determined based on the target working viscosity. The amount of furfural used in the synthesis of the furan resin backbone is negatively correlated with the amount of the bio-based phenolic compound, and the amount of furfuryl alcohol used for post-treatment viscosity adjustment is negatively correlated with the target working viscosity.

[0053] It is understandable that bio-based phenols have complex structures, and their long chains or rigid structures may affect the steric hindrance and effective cross-linking points of the network when they participate in network formation. Reducing the amount of furfural can moderately reduce the cross-linking density of furan segments, thereby balancing performance to accommodate the introduction of bio-based phenols and prevent the network from becoming too dense, which would lead to a surge in brittleness.

[0054] The furfuryl alcohol added in the post-treatment mainly serves as a physical diluent and end-capping agent. The lower the target viscosity, the more free furfuryl alcohol molecules are needed to reduce the internal frictional resistance of the resin system. Therefore, more post-treatment furfuryl alcohol needs to be added.

[0055] Please see Figure 3 As shown, this is a logic diagram for determining the heating rate and holding time in the preparation method of the environmentally friendly casting sand mold binder according to an embodiment of the present invention. Specifically, determining the heating rate and holding time based on the total amount of phenols includes: The first preset heating rate and the first preset heat preservation time are determined based on the fact that the total amount of phenols is less than a preset total amount of phenols threshold. The second preset heating rate and the second preset heat preservation time are determined based on the total phenol content being greater than or equal to a preset total phenol content threshold. Preferably, the preset total phenol content threshold is 500 parts. The first preset heating rate is 1.0℃ / min, the first preset holding time is 60min, the second preset heating rate is 0.6℃ / min, and the second preset holding time is 120min.

[0056] The preset threshold for the total amount of phenols is the midpoint of the range of total phenol content. When the total amount of phenolic raw materials is less than 500 parts, the exothermic reaction is relatively mild, and a faster heating rate and a shorter holding time can be used to ensure reaction efficiency. When the total amount reaches or exceeds 500 parts, the number of active sites in the reaction system increases, and the exothermic reaction is more intense. In order to avoid side reactions such as local overheating and explosive polymerization, a milder heating rate and a longer reaction time must be used to ensure that the prepolymerization reaction proceeds smoothly.

[0057] Understandably, a higher total amount of phenols means more reactants are needed in step S1, resulting in greater heat of reaction and increased difficulty in forming a homogeneous prepolymer. Slow heating facilitates the uniform release of heat, preventing localized overheating that could lead to rapid polymerization or side reactions, ensuring a stable and controllable reaction. A longer holding time ensures that all phenolic monomers, especially bio-based phenols with potentially lower reactivity, have sufficient time to react fully, generating a prepolymer with a more uniform molecular weight distribution, laying a good foundation for subsequent co-condensation.

[0058] Please see Figure 4 The diagram shown is a logic diagram of viscosity adjustment in the preparation method of environmentally friendly casting sand mold binder according to an embodiment of the present invention. Specifically, in step S5, adjusting the viscosity to a preset target viscosity includes: Add furfuryl alcohol for post-processing viscosity adjustment, and measure the actual viscosity under stirring conditions of 200 r / min. Compare and analyze the measured viscosity with the preset target viscosity. The difference between the measured viscosity and the preset target viscosity determines the amount of furfuryl alcohol to be added. After adding furfuryl alcohol, stir for 30 min and measure the actual viscosity again until the measured viscosity is less than the preset target viscosity.

[0059] The specific calculation method for the amount of furfuryl alcohol to be added is as follows: N2 = (t1-t) / t × N1; Where N2 is the amount of furfuryl alcohol added, t1 is the measured viscosity, t is the preset target viscosity, and N1 is the preset amount of furfuryl alcohol adjusted.

[0060] Understandably, measuring real-time viscosity under fixed shear conditions, obtaining the deviation from the target viscosity, and calculating the amount of furfuryl alcohol to be added proportionally based on the magnitude of the deviation are based on the assumption that the viscosity deviation and the required dilution dose are linearly related within a certain range. The addition of furfuryl alcohol linearly reduces the viscosity of the system.

[0061] After adding the additional product, stir for 30 minutes to ensure the newly added furfuryl alcohol is fully dispersed and mixed. Then test again, and continue this cycle until the measured viscosity is greater than the target value. This iterative approximation method overcomes the problem of potentially adding too much or too little at once, achieving precise and repeatable control of the key process parameter of finished product viscosity, and ensuring the stability of product quality. Example

[0062] Formula: 100kg dehydrorosinol, 400kg phenol, 11kg CuBr2, 1300kg furfuryl alcohol, 800kg furfural, 3kg KH551 silane coupling agent, of which 1000kg furfuryl alcohol is used for the synthesis of furan resin main chain and 300kg furfuryl alcohol is used for post-treatment viscosity adjustment.

[0063] Preparation steps: Step S1: Add dehydrorosinol, phenol, and CuBr2 to the first reaction vessel, heat to 90℃ at 0.8℃ / min, and hold for 60min; Step S2: Adjust the pH to 7.0 with a 30% NaOH solution to obtain the prepolymer, and cool it for later use. Step S3: Add 1000 kg of furfuryl alcohol and 800 kg of furfural to the second reactor, adjust the pH to 4.2 with 10% hydrochloric acid, heat to 75°C, and keep warm for 60 min to obtain furan resin. Step S4: Add prepolymer to furan resin, adjust pH to 4.0 with 10% hydrochloric acid, heat to 65°C, and keep warm for 30 minutes; Step S5: Cool down to 55℃, add 300kg furfuryl alcohol and stir, continue to cool down to 35℃, add 3kg KH551, stir for 10 minutes and then discharge. Example

[0064] Formula: 400 kg cashew phenol, 150 kg phenol, 35 kg FeCl, 1300 kg furfuryl alcohol, 1000 kg furfural, 3 kg A-1126 silane coupling agent, 2 kg A-1120 silane coupling agent, of which 800 kg furfuryl alcohol is used for the synthesis of furan resin backbone and 500 kg furfuryl alcohol is used for post-treatment viscosity adjustment.

[0065] Preparation steps: Step S1: Add cashew phenol, phenol and FeCl3 to the first reaction vessel, heat to 95°C at 0.9°C / min, and hold for 90 min; Step S2: Adjust the pH to 6.8 with a 30% NaOH solution to obtain the prepolymer, and cool it for later use. Step S3: Add 800 kg of furfuryl alcohol and 1000 kg of furfural to the second reactor, adjust the pH to 4.0 with 10% hydrochloric acid, raise the temperature to 78°C, and keep it at that temperature for 90 min to obtain furan resin. Step S4: Add prepolymer to furan resin, adjust pH to 4.1 with 10% hydrochloric acid, heat to 62°C, and keep warm for 60 min; Step S5: Cool down to 58℃, add 500kg furfuryl alcohol and stir, cool down to 38℃, add 5kg mixed silane coupling agent, stir for 12 minutes and then discharge. Example

[0066] Formula: 200 kg of lignin depolymerization long-chain phenol, 200 kg of tall oil phenol, 400 kg of phenol, 2 kg of CuI, 33 kg of FeBr, 1300 kg of furfuryl alcohol, 900 kg of furfural, 3 kg of KH540 silane coupling agent, and 2 kg of KH792 silane coupling agent, of which 900 kg of furfuryl alcohol is used for the synthesis of the furan resin backbone, and 400 kg of furfuryl alcohol is used for post-treatment viscosity adjustment.

[0067] Preparation steps: Step S1: Add lignin-depolymerized long-chain phenol, tall oil phenol, phenol, CuI, and FeBr3 to the first reactor, and heat to 85℃ at 0.7℃ / min, and hold for 90min. Step S2: Adjust the pH to 7.2 with a 30% NaOH solution to obtain the prepolymer, and cool it for later use. Step S3: Add 900 kg of furfuryl alcohol and 900 kg of furfural to the second reactor, adjust the pH to 4.3 with 10% hydrochloric acid, raise the temperature to 72°C, and keep it at that temperature for 120 min. Step S4: Add prepolymer to furan resin, adjust pH to 4.2 with 10% hydrochloric acid, heat to 68°C, and keep warm for 45 minutes; Step S5: Cool down to 56°C, add 400kg furfuryl alcohol and stir; cool down to 36°C, add 5kg mixed silane coupling agent, stir for 15 minutes and then discharge.

[0068] Performance testing and comparison: According to JB / T7526-2008 "Self-hardening furan resins for casting", the test results are as follows: Table 2 Performance Index Test Results

[0069] The environmentally friendly binder of this invention can directly replace traditional furan resin and can be applied to processes such as precision casting and lost foam casting. It is especially suitable for high-end equipment manufacturing fields with high environmental protection requirements and stringent precision requirements for castings.

[0070] The free formaldehyde content in Examples 1-3 is 0%, while that of traditional furan resin is 0.09%. This data directly proves that the present invention not only eliminates the use of formaldehyde, a carcinogen, at the source, but also ensures that the final product is completely free of free formaldehyde. In actual casting production, this means that no formaldehyde gas is released during the entire process of sand mixing, molding, pouring, and sand removal, fundamentally solving the serious health hazards of traditional processes to operators, improving the workshop environment, and fully complying with increasingly stringent environmental regulations and the trend of formaldehyde-free casting.

[0071] The tensile strengths of Examples 1-3 were 2.69 MPa, 2.75 MPa, and 2.94 MPa, respectively, all significantly higher than the 2.12 MPa of traditional furan resin. This invention, through the compounding design of bio-based phenolic compounds and phenol, and a stepwise chemical bonding process, allows the resin network to maintain or even improve crosslinking density and rigidity while introducing flexible long chains to improve toughness. Higher tensile strength means that the sand mold / core is less prone to deformation or damage during handling, assembly, and the impact of pouring molten metal, thereby directly reducing the risk of defects such as sand bulging and sand erosion in the castings, and improving the dimensional accuracy and yield of the castings.

[0072] The high-temperature residual strength of Examples 1-3 is an extremely low 0.02 MPa, while that of traditional resin is as high as 0.22 MPa, proving that the present invention solves the problem of the inability to simultaneously achieve strength and collapsibility. After casting, the sand mold core should easily collapse at high temperatures for easy cleaning. Traditional resin has excessively high residual strength, requiring strong vibration or mechanical means for sand removal, which is energy-intensive, noisy, and easily damages the surface of precision castings. The residual strength of the present invention means that the sand mold almost loses its strength after casting, becoming very loose, and can be cleaned with self-collapse or very slight vibration. This reduces the energy consumption and equipment wear of sand removal, reduces post-processing costs, and avoids surface scratches or dimensional changes in castings caused by strong sand removal, which is beneficial for the production of complex precision castings.

[0073] The demolding time in Examples 1-3 ranged from 15 to 21 minutes. Demolding time reflects the resin's curing speed and is a crucial process parameter affecting production efficiency. The environmentally friendly binder of this invention exhibits a curing speed comparable to traditional products, without negative fluctuations due to fundamental changes in formulation and process. This means that foundries using this product do not need to make significant adjustments to their existing molding, demolding, and other production processes, demonstrating excellent process compatibility and ease of replacement.

[0074] Through Examples 1-3, the core advantages of this invention can be verified: All three embodiments achieved zero formaldehyde, eliminating the main source of harmful gases in the foundry workshop; in terms of key mechanical and process properties, they were comprehensively superior to traditional furan resins; by adjusting the type and ratio of bio-based phenols, catalysts, furfuryl alcohol / furfural ratio, and process parameters, different embodiments yielded products with different performance focuses.

[0075] Bio-based components are stably integrated through a stepwise process of bio-based phenol-phenol prepolymerization, furan resin backbone synthesis, and co-condensation modification, thereby achieving greening while maintaining high performance.

[0076] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. An environmentally friendly sand mold binder for casting, characterized in that, The raw materials for preparing the sand mold binder, by weight, consist of the following components: 100-400 parts of bio-based phenolic compounds, 100-400 parts of phenol, 1100-1500 parts of furfuryl alcohol, 800-1000 parts of furfural, 1-10 parts of catalyst, and 3-5 parts of silane coupling agent; Of the amount of furfuryl alcohol used, 800 to 1000 parts are used for the synthesis of the furan resin backbone, and 300 to 500 parts are used for post-treatment to adjust viscosity.

2. The environmentally friendly casting sand mold binder according to claim 1, characterized in that, The bio-based phenolic compounds are selected from one or more of dehydrorosinol, piperol, lignin depolymerization long-chain phenol, tallol, and cashew phenol.

3. The environmentally friendly casting sand mold binder according to claim 2, characterized in that, The catalyst is selected from one or more of CuBr2, FeCl3, CuCl2, CuI, FeBr3, CoCl2, and NiCl2.

4. The environmentally friendly casting sand mold binder according to claim 3, characterized in that, The silane coupling agent is selected from one or more of KH540, A-1110, A-1120, KH551, A-1126 and KH792.

5. A method for preparing the environmentally friendly casting sand mold binder according to any one of claims 1-4, characterized in that, include: Step S1: Add bio-based phenolic compounds, phenol, and catalyst to the first reaction vessel, heat to 80℃~100℃ at a rate of less than 1℃ / min, and hold at that temperature for 60min~120min to obtain a mixture; Step S2: Adjust the pH of the mixture to 6.5-8.0 using a 30% sodium hydroxide solution, and obtain the prepolymer after cooling; Step S3: Add furfuryl alcohol and furfural used for the synthesis of furan resin main chain to the second reactor, adjust the pH of the system in the second reactor to 3.8-4.6 with 10% hydrochloric acid, raise the temperature to 70℃-80℃, and keep it at that temperature for 60min-120min to obtain furan resin. Step S4: Add the prepolymer to the furan resin, adjust the pH of the furan resin to 3.8-4.6 with 10% hydrochloric acid, heat to 60℃-70℃, and keep warm for 30-60 minutes to obtain the modified furan resin. Step S5: Cool the modified furan resin to below 60°C, and add some furfuryl alcohol for post-treatment viscosity adjustment to adjust the viscosity to the preset target viscosity; Step S6: Cool the modified furan resin, which has reached the preset target viscosity, to below 40°C, add silane coupling agent, stir at 150r / min to 200r / min for 10min to 15min, mix evenly, and then discharge to obtain sand mold binder.

6. The method for preparing the environmentally friendly casting sand mold binder according to claim 5, characterized in that, In step S5, adjusting the viscosity to a preset target viscosity further includes: Add furfuryl alcohol for post-treatment viscosity adjustment, and measure the actual viscosity under stirring conditions of 200 r / min. Compare and analyze the measured viscosity with the preset target viscosity. The amount of furfuryl alcohol to be added is determined based on the difference between the measured viscosity and the preset target viscosity. After adding furfuryl alcohol, the mixture is stirred for 30 minutes and the measured viscosity is measured again until the measured viscosity is less than the preset target viscosity.

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