Improved self-hardening furan resin sand mold and preparation method thereof

Abstract

The invention discloses an improved self-hardening furan resin sand mold and a preparation method thereof, and belongs to the technical field of casting molding materials. According to the method, a surfactant lauryl sodium sulfate is introduced in the preparation process of a furan resin curing agent, the curing agent is composed of a benzenesulfonic acid substance, concentrated sulfuric acid, an alcohol-water solution and lauryl sodium sulfate, and the modified curing agent is prepared through a reaction after premixing; and sequentially mixing silica sand with the modified curing agent and furan resin, and molding and hardening to obtain the sand mold. The dispersity and permeability of the curing agent on the surface of sand are improved through the lauryl sodium sulfate, so that acidity distribution is uniform, the room-temperature tensile strength of a sand mold is remarkably improved, and the sand inclusion defect rate of a casting is reduced. The used surfactant is environment-friendly, the process is simple, complex equipment is not needed, and the method has important industrial application value.

Description

Technical Field

[0001] This invention relates to the field of casting molding materials technology, specifically to a self-hardening furan resin sand mold and its preparation method. Background Technology

[0002] Furan resin is one of the most widely used organic binders in sand casting, especially in the cast iron and cast aluminum industries. When mixed with a suitable curing agent, it can self-harden at room temperature, offering advantages such as high production efficiency and good molding sand performance. The performance of the curing agent is a key factor determining the final properties of self-hardening furan resin sand. Currently commonly used curing agents include sulfonic acids (such as benzenesulfonic acid and p-toluenesulfonic acid), phosphoric acids, and sulfate esters. To reduce sulfur content and improve performance, modified sulfonic acid curing agents have emerged in existing technologies, typically composed of mixtures of inorganic acids (such as concentrated sulfuric acid), alcohols (such as ethylene glycol), and benzenesulfonic acids.

[0003] However, these modified curing agents still suffer from poor dispersibility and penetration during application. This leads to uneven distribution of the curing agent on the sand grain surface, resulting in differences in acidity across different sand grain surfaces. Acidity not only directly affects the curing strength of furan resin but is also closely related to the curing rate. Uneven acidity distribution can cause localized curing to be too fast or too slow, generating residual stress within the sand mold, weakening the integrity of the resin bond film between sand grains, and ultimately leading to a decrease in the overall strength of the sand mold. Sand molds with insufficient strength are prone to surface sand shedding and erosion during handling and pouring, resulting in defects such as sand inclusions and sand holes in the castings.

[0004] To improve the dispersibility of curing agents, existing technologies have attempted to add various surfactants, such as alkylphenol polyoxyethylene ethers, sodium dodecylbenzenesulfonate, or fatty alcohol polyoxyethylene ethers. However, alkylphenol polyoxyethylene ethers and sodium dodecylbenzenesulfonate suffer from poor biodegradability and environmental unfriendliness. While fatty alcohol polyoxyethylene ethers offer some environmental improvements, their ability to reduce liquid surface tension (approximately 33.46 mN / m) and contact angle (approximately 32.3°) is limited, resulting in unsatisfactory improvements in the dispersibility and penetration of curing agents. In contrast, sodium dodecyl sulfate has lower surface tension (approximately 29.64 mN / m) and contact angle (approximately 16.7°), theoretically offering superior wetting, dispersion, and penetration properties, and is more environmentally friendly. However, its application in self-hardening furan resin curing agent systems is currently rarely reported.

[0005] Therefore, it is of great significance to develop an environmentally friendly preparation method that can significantly improve the dispersion and penetration of the curing agent, thereby enhancing the strength of the sand mold. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of existing self-hardening furan resin sand molds, which are prone to casting defects due to uneven dispersion of curing agent. The present invention provides an improved self-hardening furan resin sand mold and its preparation method that can significantly improve the room temperature strength of the sand mold and reduce casting defects.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An improved self-hardening furan resin sand mold is made from the following raw materials in parts by weight: 97-99 parts silica sand, 0.05-0.2 parts p-toluenesulfonic acid, 0.1-0.3 parts concentrated sulfuric acid, 0.1-0.3 parts alcohol solution, 0.005-0.05 parts sodium dodecyl sulfate, and 0.5-2 parts furan resin.

[0009] The self-hardening furan resin sand mold is made from the following raw materials in parts by weight: 98 parts silica sand, 1.4 parts furan resin, 0.15 parts p-toluenesulfonic acid, 0.23 parts concentrated sulfuric acid, 0.2 parts ethylene glycol aqueous solution, and 0.025 parts sodium dodecyl sulfate.

[0010] The self-hardening furan resin sand mold is made from the following raw materials in parts by weight: 98.5 parts silica sand, 0.99 parts furan resin, 0.1 parts p-toluenesulfonic acid, 0.21 parts concentrated sulfuric acid, 0.19 parts ethylene glycol aqueous solution, and 0.025 parts sodium dodecyl sulfate.

[0011] The self-hardening furan resin sand mold is made from the following raw materials in parts by weight: 98.9 parts silica sand, 0.7 parts furan resin, 0.09 parts p-toluenesulfonic acid, 0.19 parts concentrated sulfuric acid, 0.17 parts ethylene glycol aqueous solution, and 0.025 parts sodium dodecyl sulfate.

[0012] The concentrated sulfuric acid has a mass concentration of ≥98wt%; the alcohol solution is prepared by mixing ethylene glycol and water in a volume ratio of 1:1.

[0013] The silica sand has a SiO2 content >92.0 wt%, a mud content <1 wt%, a water content <0.3 wt%, and a particle size of 30-70 mesh; the furan resin has a density of 1.0-1.3 g / mL, a viscosity of 30-40 mPa·s, and a water content <11 wt%.

[0014] A method for preparing an improved self-hardening furan resin sand mold includes the following steps:

[0015] (1) Ingredients: The raw materials are composed of the following by weight: 97-99 parts silica sand, 0.05-0.2 parts p-toluenesulfonic acid, 0.1-0.3 parts concentrated sulfuric acid, 0.1-0.3 parts alcohol solution, 0.005-0.05 parts sodium dodecyl sulfate, and 0.5-2 parts furan resin. Weigh each raw material according to the composition.

[0016] (2) Preparation of curing agent: Mix p-toluenesulfonic acid, sodium dodecyl sulfate and alcohol solution, stir and dissolve evenly, add concentrated sulfuric acid, stir and react at 30-50 ℃ for 50-70 min, cool to room temperature to obtain modified curing agent;

[0017] (3) Mixing: Mix the silica sand with the modified curing agent to make the curing agent evenly cover the surface of the sand particles, then add furan resin and mix evenly to obtain a molding sand mixture;

[0018] (4) Molding and hardening: The molding sand mixture is filled into the mold and hardened at room temperature. After demolding, a furan resin sand mold is obtained.

[0019] In the preparation method described above, step (3) mixing is carried out under the conditions of ambient temperature of 0-40 ℃ and relative humidity of 40%-70%.

[0020] In step (3), the curing agent and silica sand are mixed for 1 to 5 minutes, and furan resin is added and mixed for another 1 to 5 minutes.

[0021] In step (4), the mixed molding sand mixture is filled into the mold within 10 minutes, self-hardened at room temperature, and demolded after 20 minutes.

[0022] Beneficial effects of the present invention

[0023] (1) Significantly improved strength: By adding sodium dodecyl sulfate as a surfactant, the wettability, dispersibility, and penetration of the curing agent on the silica sand surface are greatly improved, ensuring that the acid catalyst is more evenly distributed on the surface of each sand grain with small acidity differences. This makes the curing reaction of furan resin more synchronous and complete, reducing the cracking of the adhesive film caused by local stress concentration, and significantly improving the room temperature tensile strength of the self-hardening sand. Experiments show that the sand mold prepared by the method of the present invention has a tensile strength that is about 4-5% higher than that of the traditional method using fatty alcohol polyoxyethylene ether.

[0024] (2) Effective reduction of casting defects: The increased strength of the sand mold directly enhances its resistance to erosion and wear. In actual casting production, the method of this invention can significantly reduce casting defects caused by sand loss on the sand mold surface and sand erosion during pouring. Batch production verification shows that the casting defect rate of sand inclusion can be reduced from about 5% to about 1%.

[0025] (3) Environmentally Friendly: This invention uses sodium dodecyl sulfate to replace traditional surfactants such as alkylphenol polyoxyethylene ether or sodium dodecylbenzene sulfonate. Sodium dodecyl sulfate has good biodegradability and is more environmentally friendly, which is in line with the development trend of green casting. Compared with fatty alcohol polyoxyethylene ether, sodium dodecyl sulfate has lower surface tension and contact angle, which has both theoretical and practical advantages in improving liquid dispersion and permeability, providing a scientific basis for the strength improvement brought about by this invention.

[0026] (4) Simple process and easy to implement: This invention only requires adding sodium dodecyl sulfate to the existing curing agent preparation process and carrying out a conventional mixing reaction. It does not require complex equipment or significant changes to the existing process, and is easy to promote and apply. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the parts mentioned in the embodiments refer to parts by mass, and the percentages refer to percentages by mass.

[0028] The performance indicators of each raw material in the examples are as follows: Silica sand: SiO2 content > 92.0 wt%, particle size 30-70 mesh, mud content < 1 wt%, water content < 0.3 wt%; Furan resin: density 1.0-1.3 g / mL, viscosity 30-40 mPa·s, water content < 11 wt%; p-Toluenesulfonic acid: purity ≥ 98.5%; Concentrated sulfuric acid: concentration 98 wt%; Sodium dodecyl sulfate: purity ≥ 99%; Fatty alcohol polyoxyethylene ether: pH 5-7, moisture content < 1% (wt), ash content < 0.5%.

[0029] Example 1: Improved preparation of self-hardening furan resin sand molds

[0030] 1. Ingredients: Weigh the raw materials as follows: 98.0 kg silica sand, 1.40 kg furan resin, 0.15 kg p-toluenesulfonic acid, 0.23 L 98wt% concentrated sulfuric acid, 0.20 kg ethylene glycol aqueous solution (ethylene glycol to water volume ratio 1:1), and 0.025 kg sodium dodecyl sulfate.

[0031] 2. Preparation of curing agent: p-Toluenesulfonic acid, sodium dodecyl sulfate, and ethylene glycol aqueous solution are added to a sealed container in sequence and stirred for 10 min until completely dissolved and mixed evenly; then concentrated sulfuric acid is added, and the temperature of the liquid is controlled not to exceed 40 ℃. After stirring for another 60 min, the mixture is finally cooled to room temperature to obtain the modified curing agent.

[0032] 3. Mixing: Under the conditions of ambient temperature of 25 ℃ and relative humidity of 55%, pour the silica sand into the sand mixer, add the above-mentioned modified curing agent, stir for 3 minutes, then add furan resin and stir until the materials are evenly mixed.

[0033] 4. Molding and hardening: Fill the mold with the mixed molding sand mixture within 10 minutes, allow it to harden at room temperature, and demold after 20 minutes to obtain furan resin sand mold.

[0034] Product performance test: The room temperature tensile strength of the sand mold was tested 24 hours after demolding, and the result was 2.01 MPa.

[0035] Example 2: Improved preparation of self-hardening furan resin sand molds

[0036] 1. Ingredients: Weigh the raw materials as follows: 98.5 kg silica sand, 0.99 kg furan resin, 0.10 kg p-toluenesulfonic acid, 0.21 L 98wt% concentrated sulfuric acid, 0.19 kg ethylene glycol aqueous solution (ethylene glycol to water mass ratio 1:1), and 0.025 kg sodium dodecyl sulfate (purity ≥99%).

[0037] 2. Preparation of curing agent: p-Toluenesulfonic acid, sodium dodecyl sulfate, and ethylene glycol aqueous solution are added to a mixing tank in sequence and stirred until the materials are completely dissolved and mixed evenly; then concentrated sulfuric acid is added, and the temperature of the liquid is controlled not to exceed 35°C. The mixture is stirred and reacted for 55 min, and then cooled to room temperature to obtain the modified curing agent.

[0038] 3. Mixing: At 15 ℃ and 45% relative humidity, pour the silica sand into the sand mixer, add the above modified curing agent and stir for 2 min, then add furan resin and continue mixing for 2.5 min until the material is evenly mixed.

[0039] 4. Molding and hardening: Fill the mold with the mixed molding sand mixture within 8 minutes, allow it to harden at room temperature, and then demold to obtain a furan resin sand mold.

[0040] The room temperature tensile strength of the product was tested 24 hours after demolding, and the result was 1.93 MPa.

[0041] Example 3: Improved preparation of self-hardening furan resin sand molds

[0042] 1. Ingredients: Weigh the raw materials by mass: 98.9 kg silica sand, 0.7 kg furan resin, 0.09 kg p-toluenesulfonic acid, 0.19 L 98wt% concentrated sulfuric acid, 0.17 kg ethylene glycol aqueous solution (ethylene glycol to water mass ratio 1:1), and 0.025 kg sodium dodecyl sulfate (purity ≥99%).

[0043] 2. Preparation of curing agent: p-Toluenesulfonic acid, sodium dodecyl sulfate, and ethylene glycol aqueous solution are added to a mixing tank in sequence and stirred until completely dissolved and mixed evenly; then concentrated sulfuric acid is added, and the temperature of the liquid is controlled not to exceed 45 ℃. The reaction is continued to be stirred for 65 min, and then cooled to room temperature to obtain the modified curing agent.

[0044] 3. Mixing: At 35 ℃ and 65% relative humidity, pour the silica sand into the sand mixer, add the above-mentioned modified curing agent and stir for 5 minutes, then add furan resin and continue mixing until the materials are evenly mixed.

[0045] 4. Molding and hardening: Fill the mixed molding sand mixture into the figure-eight mold within 8 minutes, allow it to harden at room temperature, and demold after 18 minutes to obtain the furan resin sand mold.

[0046] The room temperature tensile strength of the sand mold was tested 24 h after demolding, and the result was 1.90 MPa.

[0047] Example 4 (Comparative Example): Performance Comparison of Self-Hardening Furan Resin Sands Prepared with Fatty Alcohol Polyoxyethylene Ether and Sodium Dodecyl Sulfate as Surfactants

[0048] Using the same raw material ratios, preparation processes, and testing conditions as Examples 1-3, except that the surfactant was replaced with an equal mass of fatty alcohol polyoxyethylene ether, three groups of samples were prepared as comparative examples. Five parallel samples were prepared for each group, and their room temperature tensile strength was tested. The results are as follows:

[0049] Comparative Example 1 (corresponding to Example 1): 1.92 MPa, Comparative Example 2 (corresponding to Example 2): 1.84 MPa, Comparative Example 3 (corresponding to Example 3): 1.82 MPa, see Table 1.

[0050] Table 1. Tensile strength of self-hardening furan resin sand in different treatment groups

[0051]

[0052] Results analysis: The room temperature tensile strength of the self-hardening furan resin sand molds prepared by using sodium dodecyl sulfate as a surfactant in Examples 1-3 was higher than that of the comparative examples 1-3 using fatty alcohol polyoxyethylene ether, with a strength increase of 0.08-0.09 MPa and a relative increase rate of about 4.3%-4.9%.

[0053] It is evident that the sodium dodecyl sulfate used in this invention is superior to traditional surfactants in improving the overall strength of sand molds, and also has a good effect in improving the dispersion and penetration of curing agents and balancing acid catalysis.

[0054] In practical applications: Following the process described in Example 1 of this invention, sand molds were mass-produced at a foundry. A total of 1000 similar castings were continuously analyzed and compared with products obtained using fatty alcohol polyoxyethylene ether curing agents under the same process conditions. The results showed that, for the same casting type, the original process resulted in a sand inclusion defect rate of approximately 5% due to sand mold issues, while the product of this invention had a sand inclusion defect rate of approximately 1%, demonstrating better application performance.

Claims

1. An improved self-curing furan resin sand mold, characterized by, The following weight parts of raw materials are used: silica sand 97-99 parts, p-toluenesulfonic acid 0.05-0.2 parts, concentrated sulfuric acid 0.1-0.3 parts, alcohol solution 0.1-0.3 parts, sodium dodecyl sulfate 0.005-0.05 parts, furan resin 0.5-2 parts.

2. The self-curing furan resin sand mold according to claim 1, characterized by The following weight parts of raw materials are used: silica sand 98 parts, furan resin 1.4 parts, p-toluenesulfonic acid 0.15 parts, concentrated sulfuric acid 0.23 parts, ethylene glycol aqueous solution 0.2 parts, sodium dodecyl sulfate 0.025 parts.

3. The self-curing furan resin sand mold according to claim 1, wherein, The following weight parts of raw materials are used: silica sand 98.5 parts, furan resin 0.99 parts, p-toluenesulfonic acid 0.1 parts, concentrated sulfuric acid 0.21 parts, ethylene glycol aqueous solution 0.19 parts, sodium dodecyl sulfate 0.025 parts.

4. The self-curing furan resin sand mold according to claim 1, wherein The following weight parts of raw materials are used: silica sand 98.9 parts, furan resin 0.7 parts, p-toluenesulfonic acid 0.09 parts, concentrated sulfuric acid 0.19 parts, ethylene glycol aqueous solution 0.17 parts, sodium dodecyl sulfate 0.025 parts.

5. The self-curing furan resin sand mold according to claim 1, wherein, The mass concentration of the concentrated sulfuric acid is ≥98wt%; the alcohol solution is prepared by mixing ethylene glycol and water in a volume ratio of 1:

1.

6. The self-curing furan resin sand mold according to claim 1, wherein The silica sand has a SiO2 mass content of >92.0wt%, a clay content of <1wt%, a water content of <0.3wt%, and a particle size of 30-70 mesh; the furan resin has a density of 1.0-1.3 g / mL, a viscosity of 30-40 mPa·s, and a water content of <11wt%.

7. A process for improving the production of self-curing furan resin sand molds according to any one of claims 1 to 6, characterized in that, The following steps are included: (1) batching: the raw materials are composed of, by weight parts: silica sand 97-99 parts, p-toluenesulfonic acid 0.05-0.2 parts, concentrated sulfuric acid 0.1-0.3 parts, alcohol solution 0.1-0.3 parts, sodium dodecyl sulfate 0.005-0.05 parts, furan resin 0.5-2 parts, each raw material is weighed according to the composition; (2) preparation of curing agent: mix p-toluenesulfonic acid, sodium dodecyl sulfate, and alcohol solution, stir to dissolve uniformly, then add concentrated sulfuric acid, stir at 30-50 ℃ for 50-70 min, cool to room temperature to obtain a modified curing agent; (3) mixing: mix silica sand with the modified curing agent to uniformly cover the surface of the sand particles, then add furan resin and mix uniformly to obtain a molding sand mixture; (4) molding and hardening: fill the molding sand mixture into a mold, self-hardening at room temperature, and then demold to obtain a furan resin sand mold.

8. The preparation method according to claim 7, characterized in that, The mixing in step (3) is carried out at an ambient temperature of 0-40 ℃ and a relative humidity of 40%-70%.

9. The preparation method according to claim 7, characterized in that, The mixing time of the curing agent and silica sand in step (3) is 1-5 min, and the furan resin is added and mixed for another 1-5 min.

10. The preparation method according to claim 7, characterized in that, In step (4), the mixed molding sand mixture is filled into a mold within 10 min, self-hardening at room temperature, and then demolded after 20 min.

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