A dry curing agent coated sand mold and a method for manufacturing the same

Abstract

The application belongs to a preparation method of a casting sand mold, and aims at the technical problems that liquid acidic curing agent is easy to volatilize, sensitive to environmental humidity, and insufficient in uniform mixing with sand particles and resin in the existing furan resin sand mold preparation process, and that the content of free formaldehyde and odor of traditional furan resin are relatively high, resulting in insufficient curing uniformity and insufficient stability of the forming strength of the sand mold, and provides a dry-state curing agent coated casting sand mold and a preparation method thereof, which comprises the following steps: preparing an environmentally-friendly modified furan resin; compounding calcium hydrogen phosphate, ammonium p-toluenesulfonate and ammonium oxalate into an acidic dry-state powdery curing agent with a free acid content of 0; adding the curing agent into refractory aggregate or raw sand for high-speed dry-state mixing and coating to obtain dry-state curing agent coated aggregate; and then adding the environmentally-friendly modified furan resin, stirring and mixing, molding and naturally hardening to form a casting sand mold. The method can improve the forming stability and compressive strength of the casting sand mold, and reduce the influence of free formaldehyde, free acid and odor.

Description

Technical Field

[0001] This application relates to a method for preparing casting sand molds, specifically a dry-curing agent coated casting sand mold and its preparation method. Background Technology

[0002] Furan resins, due to their good heat resistance, corrosion resistance, and molding strength, have been widely used in foundry sand molds and refractory material molding. Current furan resin sand mold preparation processes typically involve mixing a liquid acidic curing agent with furan resin, raw sand, or refractory aggregate, followed by molding and curing. While liquid acidic curing agents can promote the curing of furan resin, they still have certain shortcomings in actual production processes.

[0003] On the one hand, liquid acidic curing agents are prone to volatilization and irritating odors during sand mixing and molding processes. Free acid can also corrode sand mixing, conveying, and molding equipment, affecting the working environment. On the other hand, the uniformity of mixing between liquid acidic curing agents, resin, and sand particles is significantly affected by the feeding method, mixing time, and ambient humidity. In high-humidity environments, problems such as unstable curing speed, inconsistent hardness, and fluctuations in sand mold strength can easily occur. Furthermore, traditional furan resins themselves have drawbacks such as high free formaldehyde content and strong odor, making it difficult to meet the foundry industry's requirements for low odor, low emissions, and stable molding.

[0004] Therefore, it is necessary to provide a casting sand mold preparation process that can reduce the influence of resin odor and free formaldehyde, reduce the volatilization and humidity sensitivity problems caused by liquid acid curing agents, and improve the uniformity of sand mold curing and the stability of molding strength. Summary of the Invention

[0005] This application addresses the technical problems in existing furan resin sand mold preparation processes, such as the easy volatility of liquid acid curing agents, sensitivity to environmental humidity, insufficient uniformity of mixing with sand particles and resin, and the high free formaldehyde content and odor of traditional furan resins leading to insufficient uniformity of sand mold curing and stability of molding strength. It provides a dry curing agent coated casting sand mold and its preparation method.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application proposes a method for preparing a dry-curing agent-coated casting sand mold, comprising: Cashew phenol and 2,5-dibromofuran were subjected to a nucleophilic substitution reaction under the action of a catalyst, and then sugar alcohol was added to the reaction system for graft polymerization to obtain an environmentally friendly modified furan resin. A dry powder curing agent with zero free acid content is formed by compounding dicalcium phosphate, ammonium p-toluenesulfonate and ammonium oxalate. The acidic dry powder curing agent is added to refractory aggregate or raw sand for high-speed dry mixing and coating to obtain curing agent dry coated aggregate; The environmentally friendly modified furan resin is added to the dry-coated aggregate of the curing agent and stirred and mixed. After mixing, the mixture is shaped and naturally hardened to obtain a casting sand mold.

[0007] Furthermore, the molar ratio of cashew phenol to 2,5-dibromofuran is 1:(1.0~1.2), the reaction temperature of the nucleophilic substitution reaction is 80~100℃, and the reaction time is 2~3h.

[0008] Furthermore, the molar ratio of cashew phenol to sugar alcohol is 1:(0.8~1.0), the reaction temperature of the graft polymerization reaction is 110~130℃, and the reaction time is 3~4h.

[0009] Furthermore, the catalyst is tetrabutylammonium bromide, and the amount of catalyst added is 0.5% to 1.0% of the mass of cashew phenol.

[0010] Furthermore, the mass ratio of the dicalcium phosphate, the ammonium p-toluenesulfonate, and the ammonium oxalate is (2~3):(1~2):1.

[0011] Furthermore, the amount of the acidic dry powder curing agent added is 1.5% to 3.0% of the mass of the refractory aggregate or raw sand; And / or, the rotation speed of the high-speed dry mixing coating is 1500~2000 r / min, and the coating time is 10~15 min.

[0012] Furthermore, the amount of the environmentally friendly modified furan resin added is 2.0% to 4.0% of the mass of the dry-state coated aggregate of the curing agent.

[0013] Furthermore, the mixing time after adding the environmentally friendly modified furan resin is 1-2 minutes.

[0014] Furthermore, the ambient temperature for natural curing is 15~35℃, the relative humidity is 30%~85%, and the curing time is 24~48h.

[0015] Secondly, this application proposes a casting sand mold prepared by the above-mentioned dry curing agent coated casting sand mold preparation method.

[0016] Compared with the prior art, this application has the following beneficial effects: A dry-curing agent-coated casting sand mold and its preparation method are disclosed. The method involves a nucleophilic substitution reaction between cashew phenol and 2,5-dibromofuran, followed by graft polymerization with sugar alcohols to obtain an environmentally friendly modified furan resin. This resin system possesses low free formaldehyde, low odor, and good adhesion to refractory aggregates or raw sand. Simultaneously, a dry-state powdered curing agent with zero free acid content is formed by compounding dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate. This acidic dry-state powdered curing agent is first added to the refractory aggregate or raw sand for high-speed dry mixing and coating to form a dry-state coated aggregate. Then, the environmentally friendly modified furan resin is added, followed by stirring, molding, and natural hardening. This avoids the problems of traditional liquid acidic curing agents, such as easy volatilization, equipment corrosion, significant susceptibility to environmental humidity, and uneven mixing during sand mixing. Because the acidic dry powder curing agent is pre-distributed on the surface of the refractory aggregate or raw sand, the environmentally friendly modified furan resin comes into contact with it during the subsequent mixing process and initiates the curing reaction. This allows the casting sand mold to form a more uniform cured structure during the natural hardening process, thereby improving the hardening uniformity, molding stability and compressive strength of the casting sand mold, and reducing the risk of harmful defects such as acid seepage and sulfur seepage caused by free acid. At the same time, it helps to reduce the odor and environmental impact during the sand mold preparation process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the reaction principle of the environmentally friendly modified furan resin in this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] This application proposes a dry curing agent coated casting sand mold and its preparation method. The following is a detailed description of this application with reference to the embodiments and accompanying drawings.

[0022] The dry curing agent coated casting sand mold preparation method of this application may include the preparation of environmentally friendly modified furan resin, the preparation of acidic dry powder curing agent, the preparation of curing agent dry coated aggregate, and the molding and natural hardening of casting sand mold.

[0023] Specifically, cashew phenol and 2,5-dibromofuran undergo a nucleophilic substitution reaction under the action of a catalyst, allowing 2,5-dibromofuran to participate in the modification of the resin system. After the nucleophilic substitution reaction is completed, a sugar alcohol is added to the reaction system for graft polymerization to obtain an environmentally friendly modified furan resin. This environmentally friendly modified furan resin is subsequently used for mixing with dry-coated aggregates with a curing agent, and participates in the natural hardening and molding of foundry sand molds after molding.

[0024] Then, dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate are compounded to form an acidic dry powder curing agent with zero free acid content. This acidic dry powder curing agent is a powder solid and is not added in the form of a liquid acidic curing agent, which can reduce the volatilization, corrosion, and uneven distribution problems caused by liquid acidic curing agents during sand mixing and molding.

[0025] Next, the acidic dry powder curing agent is added to the refractory aggregate or raw sand for high-speed dry mixing and coating, so that the acidic dry powder curing agent is distributed on the surface of the refractory aggregate or raw sand, resulting in curing agent-coated aggregate. Subsequently, environmentally friendly modified furan resin is added to the curing agent-coated aggregate and stirred and mixed. After mixing, it is molded and naturally hardened to obtain casting sand mold.

[0026] This application improves the hardening uniformity and molding stability of casting sand molds by first coating the surface of refractory aggregates or raw sand with an acidic dry powder curing agent and then adding environmentally friendly modified furan resin.

[0027] like Figure 1 The diagram illustrates the reaction principle of environmentally friendly modified furan resin. It shows the process of resin structure formation through the reaction of cashew phenol with 2,5-dibromofuran followed by grafting of hydroxyl-containing components. In some embodiments of this application, the environmentally friendly modified furan resin is first prepared. Using cashew phenol as the base material, cashew phenol and 2,5-dibromofuran are added to the reaction system at a molar ratio of 1:(1.0~1.2), and a nucleophilic substitution reaction is carried out under the action of a catalyst. The reaction temperature of the nucleophilic substitution reaction is 80~100℃, and the reaction time is 2~3h. Optionally, the catalyst is tetrabutylammonium bromide, and the amount of tetrabutylammonium bromide added is 0.5%~1.0% of the mass of cashew phenol.

[0028] The molar ratio of cashew phenol to 2,5-dibromofuran, the nucleophilic substitution reaction temperature, and the reaction time all influence the extent to which the furan ring structure is introduced into the resin system. Controlling the molar ratio of cashew phenol to 2,5-dibromofuran at 1:(1.0~1.2), and controlling the nucleophilic substitution reaction temperature at 80~100℃ and the reaction time at 2~3h, allows 2,5-dibromofuran to participate in the modification reaction of the cashew phenol system, introducing the furan ring structure into the resin system. After the furan ring structure participates in the resin system construction, it is beneficial to improve the heat resistance and crosslinking density of the environmentally friendly modified furan resin, providing a foundation for maintaining the strength of the casting sand mold under natural hardening and high-temperature use conditions.

[0029] After the nucleophilic substitution reaction is completed, a sugar alcohol is added to the reaction system to carry out a graft polymerization reaction. The molar ratio of cashew phenol to sugar alcohol is 1:(0.8~1.0), the reaction temperature of the graft polymerization reaction is 110~130℃, and the reaction time is 3~4h. Optionally, the sugar alcohol includes at least one of mannitol, sorbitol, and xylitol.

[0030] The molar ratio of cashew phenol to sugar alcohol, the graft polymerization temperature, and the reaction time all influence the degree to which the polyhydroxyl structure of the sugar alcohol participates in the construction of the resin molecular structure. By controlling the molar ratio of cashew phenol to sugar alcohol at 1:(0.8~1.0), and the graft polymerization temperature at 110~130℃ and the reaction time at 3~4h, the hydroxyl groups of the sugar alcohol can be grafted onto the active groups in the resin molecules, forming an environmentally friendly modified furan resin with a three-dimensional network structure. This graft polymerization process can reduce the free formaldehyde content in the resin system and improve the adhesion of the environmentally friendly modified furan resin to the surface of refractory aggregates or raw sand, resulting in an environmentally friendly modified furan resin that combines low free formaldehyde, low odor, and strong sand mold bonding. In some embodiments, the free formaldehyde content of the obtained environmentally friendly modified furan resin is ≤0.1%, and the odor level is ≤2.

[0031] Subsequently, an acidic dry powder curing agent is prepared. Dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate are compounded to obtain an acidic dry powder curing agent with zero free acid content. Optionally, the mass ratio of dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate is (2~3):(1~2):1. As an example, the mass ratio of dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate can be 2:1:1, 3:2:1, or 2.5:1.5:1.

[0032] The mass ratio of dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate is used to adjust the curing compatibility between the acidic dry powder curing agent and the environmentally friendly modified furan resin. Controlling the mass ratio of the three to (2~3):(1~2):1 allows the acidic dry powder curing agent to maintain its powder form while meeting the curing conditions required for the subsequent natural curing of the environmentally friendly modified furan resin. Since the free acid content of this acidic dry powder curing agent is zero, it does not participate in sand mixing as liquid free acid during use, reducing problems such as acid mist volatilization, equipment corrosion, and uneven curing caused by localized accumulation of acidic liquid, and lowering the risk of harmful defects such as acid seepage and sulfur seepage.

[0033] Then, high-speed dry mixing and coating are performed. The acidic dry powder curing agent is added to the refractory aggregate or raw sand, and high-speed dry mixing and coating are carried out to obtain curing agent-coated aggregate. The amount of acidic dry powder curing agent added is 1.5%~3.0% of the mass of the refractory aggregate or raw sand; the high-speed dry mixing and coating speed is 1500~2000 r / min, and the coating time is 10~15 min.

[0034] The amount of acidic dry powder curing agent added, the coating speed, and the coating time all affect the distribution of the acidic dry powder curing agent on the surface of refractory aggregates or raw sand. Controlling the amount of acidic dry powder curing agent added to 1.5%–3.0% of the mass of the refractory aggregates or raw sand, and performing high-speed dry mixing and coating at 1500–2000 r / min for 10–15 min, allows the acidic dry powder curing agent to distribute on the surface of the refractory aggregates or raw sand, forming a dry-coated aggregate with the curing agent. This dry coating state ensures that the curing agent is pre-positioned on the aggregate surface, rather than being pre-mixed with the environmentally friendly modified furan resin in liquid form, thereby reducing the risk of localized premature curing and uneven curing.

[0035] In some embodiments of this application, the refractory aggregate includes at least one of quartz sand, zircon sand, and corundum sand. The raw sand can be washed quartz sand, and the particle size of the washed quartz sand can be 50-100 mesh. Depending on the requirements of the casting sand mold, quartz sand can be selected as the raw sand for conventional casting sand molds, or zircon sand or corundum sand can be selected as the refractory aggregate. Among them, zircon sand can be used for refractory brick casting in glass kilns, while corundum sand can be used for casting sand mold printing in scenarios where high refractory performance is required.

[0036] Finally, the mixture is molded and allowed to harden naturally. Environmentally friendly modified furan resin is added to the dry-coated aggregate and stirred. The amount of environmentally friendly modified furan resin added is 2.0%~4.0% of the mass of the dry-coated aggregate, and the stirring time after adding the environmentally friendly modified furan resin is 1~2 minutes. After mixing, the mixture is molded and allowed to harden naturally. The ambient temperature for natural hardening is 15~35℃, the relative humidity is 30%~85%, and the hardening time is 24~48 hours, resulting in a foundry sand mold.

[0037] The amount of environmentally modified furan resin added and the mixing time both affect the contact state between the environmentally modified furan resin and the dry-coated aggregate with curing agent. Controlling the amount of environmentally modified furan resin added to 2.0%~4.0% of the mass of the dry-coated aggregate with curing agent, and controlling the mixing time to 1~2 minutes, allows the environmentally modified furan resin to contact the dry-coated aggregate with curing agent and initiate the curing reaction. Since the acidic dry-powdered curing agent is pre-distributed on the aggregate surface, the added environmentally modified furan resin can undergo a cross-linking curing reaction around the aggregate surface, resulting in a more uniform cured structure in the casting sand mold during natural hardening, thereby improving the hardening uniformity, molding accuracy, and compressive strength of the casting sand mold.

[0038] The ambient temperature, relative humidity, and curing time all influence the strength formation process of naturally hardened sand molds. Controlling the ambient temperature to 15–35℃, the relative humidity to 30%–85%, and the curing time to 24–48 hours allows the environmentally friendly modified furan resin and the acidic dry powder curing agent to complete the cross-linking and curing reaction, resulting in stable molding strength for the sand mold. Especially under high relative humidity conditions, because the acidic dry powder curing agent is pre-distributed on the aggregate surface in a dry coating manner, it reduces the problem of inconsistent hardening caused by humidity, which is a common issue with traditional liquid curing agents. This allows the sand mold to maintain a relatively stable hardening effect even in high-humidity environments.

[0039] Optionally, the high-speed dry mixing and coating can be carried out in a mixing device that combines high-speed dispersion and granulation functions; during the mixing, molding, and natural hardening processes, the dry-coated aggregate with curing agent can be conveyed to the upper sand hopper of a traditional continuous sand mixer for casting, and environmentally friendly modified furan resin can be added to the dry-coated aggregate with curing agent for stirring and mixing. The above-mentioned equipment configuration is used to realize the dry coating and mixing molding processes and does not constitute a limitation on the preparation method of this application.

[0040] In practical applications, the resulting casting sand molds can be used for printing and molding casting sand molds, as well as for casting refractory bricks in glass kilns. After use, the formed casting sand molds can be recycled and reused through mechanical crushing, screening, and other methods.

[0041] Example 1 Preparation of environmentally friendly modified furan resin: 1 mol of cashew nut shellac was added to the reaction system, along with 0.007 mol of tetrabutylammonium bromide as a catalyst. The amount of tetrabutylammonium bromide added was 0.7% of the cashew nut shellac mass. The temperature was raised to 90℃, and 1.1 mol of 2,5-dibromofuran was slowly added dropwise to the reaction system. After the addition was complete, the reaction was maintained at this temperature for 2.5 h. Subsequently, 0.9 mol of mannitol was added to the reaction system, the temperature was raised to 120℃, and the reaction was maintained at this temperature for 3.5 h. After cooling to room temperature, the product was discharged to obtain the environmentally friendly modified furan resin. Testing showed that the free formaldehyde content of this environmentally friendly modified furan resin was 0.08%, and the odor level was grade 2.

[0042] Acidic dry-state powdered curing agent was prepared and subjected to high-speed dry mixing and coating: Calcium hydrogen phosphate, ammonium p-toluenesulfonate, and ammonium oxalate were weighed at a mass ratio of 2:1:1, mixed, and ground to obtain the acidic dry-state powdered curing agent. The free acid content of this acidic dry-state powdered curing agent was 0. 100 kg of 70-mesh washed quartz sand was taken, and 2.0 kg of the above-mentioned acidic dry-state powdered curing agent was added. High-speed dry mixing and coating was carried out at a rotation speed of 1800 r / min for 12 min to obtain curing agent-coated dry-state quartz sand, which is the curing agent-coated dry-state aggregate.

[0043] Mixed molding and natural hardening: 3.0% of the dry-coated quartz sand containing the curing agent was added to the environmentally friendly modified furan resin prepared in this embodiment. After stirring and mixing for 1.5 minutes, molding was performed, and the mixture was naturally hardened for 36 hours at 25°C and 60% relative humidity to obtain the casting sand mold. Testing showed that the room temperature compressive strength of the casting sand mold was 9.2 MPa, and the residual strength at 1000°C was 3.5 MPa. No sulfur penetration defects were observed. The casting sand mold can be 100% recycled and reused after crushing and sieving.

[0044] Example 2 Preparation of environmentally friendly modified furan resin: 1 mol of cashew nut shellac was added to the reaction system, along with 0.005 mol of tetrabutylammonium bromide as a catalyst. The amount of tetrabutylammonium bromide added was 0.5% of the cashew nut shellac mass. The temperature was raised to 80℃, and 1.0 mol of 2,5-dibromofuran was added dropwise to the reaction system. After the addition was complete, the reaction was maintained at this temperature for 2 hours. Subsequently, 0.8 mol of sorbitol was added to the reaction system, the temperature was raised to 110℃, and the reaction was maintained at this temperature for 3 hours to obtain the environmentally friendly modified furan resin. Testing showed that the free formaldehyde content of this environmentally friendly modified furan resin was 0.09%, and the odor level was grade 2.

[0045] Acidic dry-state powdered curing agent was prepared and subjected to high-speed dry mixing and coating: Calcium hydrogen phosphate, ammonium p-toluenesulfonate, and ammonium oxalate were weighed at a mass ratio of 3:2:1, mixed, and ground to obtain the acidic dry-state powdered curing agent. The free acid content of this acidic dry-state powdered curing agent was 0. 100 kg of zircon sand was taken, and 1.5 kg of the above-mentioned acidic dry-state powdered curing agent was added. High-speed dry mixing and coating was carried out at a rotation speed of 1500 r / min for 10 min to obtain curing agent-coated zircon sand, which is the curing agent-coated aggregate.

[0046] Mixed molding and natural curing: 2.0% of the mass of the dry-coated zircon sand with curing agent was added to the environmentally friendly modified furan resin prepared in this embodiment. After stirring and mixing for 1 minute, molding was performed, and the mixture was naturally cured for 48 hours at 15℃ and 85% relative humidity to obtain the casting sand mold. Testing showed that the room temperature compressive strength of this casting sand mold was 8.1 MPa, and the high-temperature residual strength at 1000℃ was 3.1 MPa. It can be used for casting refractory bricks in glass kilns, and the solid waste from the casting sand mold is 100% recyclable.

[0047] Example 3 Preparation of environmentally friendly modified furan resin: 1 mol of cashew nut shellac was weighed and added to the reaction system, along with 0.01 mol of tetrabutylammonium bromide as a catalyst. The amount of tetrabutylammonium bromide added was 1.0% of the cashew nut shellac mass. The temperature was raised to 100℃, and 1.2 mol of 2,5-dibromofuran was added dropwise to the reaction system. After the addition was complete, the reaction was maintained at this temperature for 3 hours. Subsequently, 1.0 mol of xylitol was added to the reaction system, the temperature was raised to 130℃, and the reaction was maintained at this temperature for 4 hours to obtain the environmentally friendly modified furan resin. Testing showed that the free formaldehyde content of this environmentally friendly modified furan resin was 0.07%, and the odor rating was Grade 1.

[0048] Acidic dry-state powdered curing agent was prepared and subjected to high-speed dry mixing and coating: Calcium hydrogen phosphate, ammonium p-toluenesulfonate, and ammonium oxalate were weighed at a mass ratio of 2:2:1, mixed, and ground to obtain the acidic dry-state powdered curing agent. The free acid content of this acidic dry-state powdered curing agent was 0. 100 kg of corundum sand was taken, and 3.0 kg of the above-mentioned acidic dry-state powdered curing agent was added. High-speed dry mixing and coating was carried out at a rotation speed of 2000 r / min for 15 min to obtain curing agent-coated corundum sand, which is the curing agent-coated aggregate.

[0049] Hybrid molding and natural curing: 4.0% of the dry-coated corundum sand containing the curing agent was added to the environmentally friendly modified furan resin prepared in this embodiment. After stirring and mixing for 2 minutes, the mixture was printed into a casting sand mold and naturally cured for 24 hours at 35°C and 30% relative humidity to obtain the casting sand mold. Testing showed that the room temperature compressive strength of this casting sand mold was 9.5 MPa, and the residual strength at 1000°C was 3.7 MPa. No sulfur penetration defects were observed.

[0050] In another specific embodiment, dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate can be compounded in a mass ratio of 2.5:1.5:1 to form an acidic dry powder curing agent, the free acid content of which is 0. This acidic dry powder curing agent is added to 70-mesh washed quartz sand at 2.0% of the mass of the refractory aggregate or raw sand, and subjected to high-speed dry mixing and coating at 1800 r / min for 12 min to obtain curing agent-coated quartz sand. Then, environmentally friendly modified furan resin is added at 3.0% of the mass of the curing agent-coated quartz sand, stirred and mixed for 1.5 min, molded, and naturally hardened at 25°C and 60% relative humidity for 36 h to obtain a casting sand mold. This specific embodiment is used to illustrate the values ​​of dicalcium phosphate, ammonium p-toluenesulfonate, and ammonium oxalate within the mass ratio range of (2~3):(1~2):1).

[0051] Comparative Example 1 Comparative Example 1 uses a traditional furan resin sand mold preparation process. The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not use cashew phenol, 2,5-dibromofuran and sugar alcohol to prepare environmentally friendly modified furan resin, nor does it use dicalcium phosphate, ammonium p-toluenesulfonate and ammonium oxalate to form an acidic dry powder curing agent with a free acid content of 0. Furthermore, it does not add the acidic dry powder curing agent to refractory aggregate or raw sand for high-speed dry mixing and coating. Instead, it uses commercially available conventional furan resin and liquid acid curing agent to directly mix sand for molding.

[0052] Specifically, commercially available conventional furan resin was purchased, with a free formaldehyde content of 0.85% and an odor rating of level 5. A 65% concentration of p-toluenesulfonic acid aqueous solution was used as the liquid curing agent, and 70-mesh washed quartz sand of the same specifications as in Example 1 was selected. 100 kg of washed quartz sand was taken, 3 kg of commercially available conventional furan resin was added, and then 1.5 kg of p-toluenesulfonic acid aqueous solution curing agent was added. After stirring for 2 minutes, it was naturally cured for 36 hours at a temperature of 25°C and a relative humidity of 60% to obtain a traditional casting sand mold.

[0053] The samples obtained in Examples 1-3 and Comparative Example 1 were tested. The test items included the room temperature compressive strength of the casting sand mold, the free formaldehyde content of the environmentally friendly modified furan resin or commercially available conventional furan resin, the free acid content of the curing agent, the resin odor level, and the solid waste recycling rate. The resin odor level was evaluated with level 1 being the best and level 5 being the worst. The test results are shown in Table 1 below: Table 1 Test Performance Table

[0054] As shown in Table 1, the room temperature compressive strength of the casting sand molds obtained in Examples 1-3 is 8.1-9.5 MPa, which is higher than that of Comparative Example 1 (6.3 MPa). The free formaldehyde content of the environmentally friendly modified furan resin used in Examples 1-3 is 0.07%-0.09%, which is lower than that of the commercially available conventional furan resin in Comparative Example 1 (0.85%). The free acid content of the acidic dry powder curing agent used in Examples 1-3 is 0%, while the free acid content of the liquid acidic curing agent in Comparative Example 1 is 12%. The odor level of the resin in Examples 1-3 is 1-2, which is better than that of Comparative Example 1 (5). The solid waste recycling rate of Examples 1-3 is 100%, which is higher than that of Comparative Example 1 (25%).

[0055] Based on the high-temperature residual strength test results of Examples 1-3, the high-temperature residual strength of the casting sand mold obtained in Example 1 at 1000℃ is 3.5 MPa, that of the casting sand mold obtained in Example 2 at 1000℃ is 3.1 MPa, and that of the casting sand mold obtained in Example 3 at 1000℃ is 3.7 MPa, all exceeding 3 MPa. These results indicate that the environmentally friendly modified furan resin obtained by reacting cashew phenol with 2,5-dibromofuran and sugar alcohol, when used in conjunction with an acidic dry powder curing agent with zero free acid content, can enable the casting sand mold to simultaneously possess both room-temperature molding strength and high-temperature residual strength.

[0056] In Example 2, after natural curing for 48 hours at 15°C and 85% relative humidity, the room temperature compressive strength of the casting sand mold still reached 8.1 MPa, and the high-temperature residual strength at 1000°C reached 3.1 MPa. This result indicates that, in environments with high relative humidity, pre-distributing the acidic dry powder curing agent onto the surface of the refractory aggregate through high-speed dry mixing and coating, followed by contact curing with environmentally friendly modified furan resin, can reduce the risk of uneven curing caused by humidity affecting the liquid acidic curing agent, allowing the casting sand mold to still achieve the strength required for molding.

[0057] The comparison results between Examples 1-3 and Comparative Example 1 also show that using environmentally friendly modified furan resin can reduce the free formaldehyde content and odor level of the resin; using acidic dry powder curing agent with 0% free acid content can reduce the influence of free acid; and using a process sequence of high-speed dry mixing and coating followed by adding environmentally friendly modified furan resin can improve the uniformity of contact between acidic dry powder curing agent and environmentally friendly modified furan resin on the aggregate surface, thereby improving the room temperature compressive strength of the foundry sand mold and the solid waste recycling rate.

[0058] In industrial applications, environmentally friendly modified furan resin can be synthesized on a large scale, and acidic dry powder curing agents can be prepared using conventional powder mixing methods. High-speed dry mixing and coating processes, as well as subsequent mixing and molding processes, can be adapted to existing casting production lines. Therefore, the preparation method of this application does not require additional large-scale specialized equipment, is suitable for scenarios such as casting sand mold printing and molding, and refractory brick casting in glass kilns, and facilitates the recycling and reuse of casting sand mold solid waste after molding.

[0059] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing casting sand molds coated with a dry curing agent, characterized in that, include: Cashew phenol and 2,5-dibromofuran were subjected to a nucleophilic substitution reaction under the action of a catalyst, and then sugar alcohol was added to the reaction system for graft polymerization to obtain an environmentally friendly modified furan resin. A dry powder curing agent with zero free acid content is formed by compounding dicalcium phosphate, ammonium p-toluenesulfonate and ammonium oxalate. The acidic dry powder curing agent is added to refractory aggregate or raw sand for high-speed dry mixing and coating to obtain curing agent dry coated aggregate; The environmentally friendly modified furan resin is added to the dry-coated aggregate of the curing agent and stirred and mixed. After mixing, the mixture is shaped and naturally hardened to obtain a casting sand mold.

2. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The molar ratio of cashew phenol to 2,5-dibromofuran is 1:(1.0~1.2), the nucleophilic substitution reaction is carried out at a temperature of 80~100℃ and a reaction time of 2~3h.

3. The method for preparing dry-curing agent coated casting sand molds according to claim 1 or 2, characterized in that, The molar ratio of cashew phenol to sugar alcohol is 1:(0.8~1.0), the reaction temperature of the graft polymerization reaction is 110~130℃, and the reaction time is 3~4h.

4. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The catalyst is tetrabutylammonium bromide, and the amount of catalyst added is 0.5% to 1.0% of the mass of cashew phenol.

5. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The mass ratio of the dicalcium phosphate, the ammonium p-toluenesulfonate, and the ammonium oxalate is (2~3):(1~2):

1.

6. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The amount of the acidic dry powder curing agent added is 1.5% to 3.0% of the mass of the refractory aggregate or raw sand; And / or, the rotation speed of the high-speed dry mixing coating is 1500~2000 r / min, and the coating time is 10~15 min.

7. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The amount of the environmentally friendly modified furan resin added is 2.0% to 4.0% of the mass of the dry coated aggregate of the curing agent.

8. The method for preparing dry-curing agent coated casting sand molds according to claim 7, characterized in that, The mixing time after adding the environmentally friendly modified furan resin is 1-2 minutes.

9. The method for preparing dry-curing agent coated casting sand molds according to claim 1, characterized in that, The ambient temperature for natural curing is 15~35℃, the relative humidity is 30%~85%, and the curing time is 24~48h.

10. A casting sand mold prepared by the dry curing agent coating casting sand mold preparation method according to any one of claims 1 to 9.

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