A foundry sand binder and a method for preparing the same

Abstract

The application provides a foundry bonded sand and a preparation method thereof, and comprises the following components: phosphoric acid, aluminum hydroxide, magnesium hydroxide, organic acid, bimetallic biomass charcoal and water, wherein after the aluminum phosphate is formed by the phosphoric acid and the aluminum hydroxide, the aluminum phosphate is modified by the bimetallic biomass charcoal and the organic acid respectively, and then a spatial network with strength is formed, so that the wet resistance of the binder is improved; compared with the existing inorganic foundry bonded sand, the foundry bonded sand has better wet resistance and strength, also has excellent collapsibility, and no toxic gas is generated in the pouring link of the prepared sand.

Description

Technical Field

[0001] The present invention relates to the field of casting auxiliary materials, in particular to a casting sand binder and a preparation method thereof. Background Art

[0002] Casting, a fundamental process in the modern machinery manufacturing industry, enables the efficient and cost-effective formation of complex metal workpieces. It is essential for the manufacture of high-end equipment and major projects in emerging industries such as aviation, satellites, and new energy vehicles. Common casting auxiliary materials, such as sand binders, are used to bind loose foundry sand into molding sand or core sand. The binder is mixed with sand particles and coated with a film of binder, providing sufficient strength for the molding and core sand, improving their performance and preventing deformation and breakage during assembly, handling, and pouring.

[0003] Currently, foundry sand binders are divided into two categories: organic and inorganic. Organic binders, primarily resin polymers, offer high bonding strength and a dust-free sand mixing process, facilitating automated production. However, the pouring process of these binders produces toxic and harmful gases such as sulfur dioxide, dioxins, and ammonia, which seriously pollute the environment. Furthermore, resin polymers are non-renewable resources, increasing production costs and limiting their application. Inorganic binders are less likely to produce toxic and harmful gases and have low raw material costs, making them a popular research area. Common inorganic binders, such as water glass and clay, are widely used. However, molding sand using water glass as a binder exhibits low bonding strength, is prone to aging, and has poor moisture resistance. Molding sand using clay as a binder requires drying, which consumes a lot of energy and produces a lot of dust.

[0004] Although the molding sand prepared by inorganic binders has high strength or moisture resistance, the problems such as high high-temperature residual strength, difficulty in peeling and cleaning after casting have always been the bottleneck of the development of inorganic sand binders. To solve the above problems, the patent with publication number CN110640078 discloses a molding sand binder for casting. Although it has good bonding strength, its high-temperature residual strength is relatively general, and its moisture resistance and collapsibility are not ideal; the patent with publication number CN114472796A discloses a modified inorganic binder with collapsibility and a preparation method. Although it improves the problem of collapsibility, it introduces organic powders such as epoxy resin powder, phenolic resin powder and sodium benzenesulfonate powder into the powder disintegrator. In the later stage of molding sand preparation and pouring, toxic and harmful gases such as formaldehyde and sulfide will be released, which has a great impact on the processing environment and processing personnel. Summary of the Invention

[0005] In view of this, the present invention proposes a foundry sand binder and a preparation method thereof, which improves the moisture resistance and strength of the inorganic phosphate binder by introducing bimetallic biochar and organic acid, and has better disintegration properties.

[0006] The technical solution of the present invention is achieved as follows:

[0007] The invention provides a foundry sand binder and a preparation method thereof. The binder comprises the following components: phosphoric acid, aluminum hydroxide, magnesium hydroxide, organic acid, bimetallic biochar and water.

[0008] Preferably, the raw materials include the following parts by weight: 80-100 parts of phosphoric acid, 20-30 parts of aluminum hydroxide, 3-8 parts of magnesium hydroxide, 60-80 parts of organic acid, 15-30 parts of bimetallic biochar and 300-500 parts of water.

[0009] Preferably, the mass concentration of phosphoric acid is 80-90%.

[0010] Preferably, the bimetallic biochar is magnesium-aluminum bimetallic oxide biochar, and its preparation process comprises the following steps:

[0011] S1. Crush the straw, soak it in an alkaline solution, stir it at 90-120°C for 2-4 hours, remove impurities, wash it with water, add sodium chlorite solution to decolorize it until the pH value is 4.2-5.0, and then wash it with water to obtain straw fiber;

[0012] S2. Soaking the straw fiber obtained in step S1 in an aluminum nitrate nonahydrate solution for 10-20 hours, filtering, drying, and calcining for 2-8 hours to obtain modified straw fiber;

[0013] S3. Dissolve magnesium nitrate hexahydrate, hexamethylenetetramine and the modified straw fiber obtained in step S2 in water, stir, react at 90-120° C. for 12-18 hours, filter, wash, dry, and calcine for 2-8 hours to obtain bimetallic biochar.

[0014] Preferably, the alkaline solution in step S1 comprises sodium hydroxide or potassium hydroxide with a concentration of 0.15-0.25M.

[0015] Preferably, the mass concentration of the sodium chlorite solution in step S1 is 8%-10%.

[0016] Preferably, the mass concentration of the aluminum nitrate nonahydrate solution in step S2 is 15-25%.

[0017] Preferably, the calcination conditions in steps S2 and S3 are inert gas protection and a temperature of 400-900°C.

[0018] Preferably, in step S3, the mass ratio of magnesium nitrate hexahydrate, hexamethylenetetramine and modified straw fiber is (0.2-1.5): (66.5-266): (0.08-0.8).

[0019] Preferably, the organic acid comprises one or more of boric acid, citric acid or silicic acid.

[0020] On the other hand, the present invention also provides a method for preparing a foundry sand binder, comprising the following steps:

[0021] A1. Weigh phosphoric acid, aluminum hydroxide, and magnesium hydroxide by weight, add half water, mix well, and stir at 90-140°C for 2-4 hours. Cool to 70-120°C, add the organic acid, and continue stirring for 1-2 hours.

[0022] A2. Add bimetallic biochar and the remaining half of the water, mix well, and stir for 2-4 hours;

[0023] A3. After cooling to 20-40° C., forming, hardening, and discharging, the foundry sand binder is obtained.

[0024] Further preferably, the hardening includes CO2 hardening or mold heating hardening.

[0025] The foundry sand binder and preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0026] (1) Although the current phosphate binder is environmentally friendly, its moisture resistance and strength still have many problems. The foundry sand binder of the present invention first forms phosphate with aluminum hydroxide and phosphoric acid, and then the bimetallic biochar has a structure of bimetallic cations and interlayer anions, which can fix the free phosphate between the metal sheets. After the phosphate enters the interlayer, it can achieve the fixation of the phosphate, thereby forming a strong spatial network and improving the moisture resistance of the binder.

[0027] (2) Currently, phosphate binders improve moisture resistance and increase the bonding strength of phosphates by introducing oxides, but the effect is not good and it also causes difficulties in recycling old sand. The aluminum phosphate formed in the foundry sand binder of the present invention is also modified with organic acid to form an amorphous phase, and magnesium hydroxide can avoid the condensation of aluminum phosphate and maintain stability, and has good strength and disintegration properties, and the recycling effect of old sand is good.

[0028] (3) In addition, the foundry sand binder of the present invention does not require the introduction of resin as a disintegrating agent, and the casting process of the sand casting will not produce toxic and harmful gases, which not only saves the cost of raw material preparation, but also ensures the green and environmental protection of the preparation process. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0030] Embodiment 1

[0031] A foundry sand binder comprises the following components by weight:

[0032] Phosphoric acid 80 parts, aluminum hydroxide 20 parts, magnesium hydroxide 3 parts, boric acid 60 parts, double-metal biomass charcoal 15 parts and water 300 parts

[0033] The preparation process of the double-metal biomass charcoal comprises the following steps:

[0034] S1, the straw is crushed, soaked in 0.15M sodium hydroxide solution, stirred at 90℃ for 4h, impurities are removed, washed with water, and decolorized by adding 8% sodium chlorite solution until the pH value is 4.2, and then washed with water to obtain straw fibers;

[0035] S2, the straw fibers obtained in step S1 are soaked in 15% aluminum nitrate nine-water solution, soaked for 10h, filtered, dried, and then calcined at 400℃ for 8h under helium protection to obtain modified straw fibers;

[0036] S3, magnesium nitrate hexahydrate, hexamethylenetetramine and the modified straw fibers obtained in step S2 are added in a mass ratio of 0.2:66.5:0.08, dissolved with water, stirred, reacted at 90℃ for 18h, filtered, washed, dried, and then calcined at 400℃ for 8h under helium protection to obtain the double-metal biomass charcoal.

[0037] The preparation method of the foundry sand binder comprises the following steps:

[0038] A1, 80 parts of phosphoric acid, 20 parts of aluminum hydroxide and 3 parts of magnesium hydroxide are weighed by weight, mixed with 150 parts of water, and stirred at 90℃ for 4h; after cooling to 70℃, 60 parts of boric acid is added and stirred for 1h;

[0039] A2, 15 parts of double-metal biomass charcoal and the remaining half of water are added and mixed, and stirred for 2h;

[0040] A3, after cooling to 20℃, molding, hardening, and discharging, the foundry sand binder is obtained.

[0041] Embodiment 2

[0042] A foundry sand binder comprising the following components by weight:

[0043] 100 parts of phosphoric acid, 30 parts of aluminum hydroxide, 8 parts of magnesium hydroxide, 40 parts of citric acid, 40 parts of boric acid, 30 parts of bimetallic biochar and 500 parts of water

[0044] The preparation process of bimetallic biochar includes the following steps:

[0045] S1. Crush the straw, soak it in a 0.25M potassium hydroxide solution, stir it at 120°C for 2h, remove impurities, wash it with water, add a 10% sodium chlorite solution to decolorize it until the pH value is 5, and then wash it with water to obtain straw fiber;

[0046] S2, soaking the straw fiber obtained in step S1 in a 25% by mass concentration of aluminum nitrate nonahydrate solution for 20 hours, filtering, drying, and then calcining at 900° C. for 2 hours under argon protection to obtain modified straw fiber;

[0047] S3. Magnesium nitrate hexahydrate, hexamethylenetetramine and the modified straw fiber obtained in step S2 are added in a mass ratio of 1.5:266:0.8, dissolved in water, stirred, reacted at 120°C for 12 hours, filtered, washed, dried, and then calcined at 900°C for 2 hours under argon protection to obtain bimetallic biochar.

[0048] The preparation method of the foundry sand binder comprises the following steps:

[0049] A1. Weigh 100 parts of phosphoric acid, 30 parts of aluminum hydroxide, and 8 parts of magnesium hydroxide by weight, add 250 parts of water, mix well, and stir at 140°C for 2 hours; cool to 120°C, add 40 parts of citric acid and 40 parts of boric acid, and continue stirring for 2 hours;

[0050] A2, add 30 parts of bimetallic biochar and the remaining half of the water, mix well, and stir for 4 hours;

[0051] A3. After cooling to 40° C., forming, hardening, and discharging, the foundry sand binder is obtained.

[0052] Example 3

[0053] A foundry sand binder comprising the following components by weight:

[0054] 90 parts of phosphoric acid, 25 parts of aluminum hydroxide, 6 parts of magnesium hydroxide, 35 parts of silicic acid, 35 parts of boric acid, 20 parts of bimetallic biochar and 400 parts of water

[0055] The preparation process of bimetallic biochar includes the following steps:

[0056] S1. Crush the straw, soak it in 0.2M sodium hydroxide solution, stir it at 100°C for 3h, remove impurities, wash it with water, add 9% sodium chlorite solution for decolorization until the pH value is 4.5, and then wash it with water to obtain straw fiber;

[0057] S2, soaking the straw fiber obtained in step S1 in a 20% aluminum nitrate nonahydrate solution for 15 hours, filtering, drying, and then calcining at 600° C. for 5 hours under helium protection to obtain modified straw fiber;

[0058] S3. Magnesium nitrate hexahydrate, hexamethylenetetramine and the modified straw fiber obtained in step S2 are added in a mass ratio of 0.8:133:0.6, dissolved in water, stirred, reacted at 100°C for 15 hours, filtered, washed, dried, and then calcined at 600°C for 5 hours under helium protection to obtain bimetallic biochar.

[0059] The preparation method of the foundry sand binder comprises the following steps:

[0060] A1. Weigh 90 parts of phosphoric acid, 25 parts of aluminum hydroxide, and 6 parts of magnesium hydroxide by weight, add 100 parts of water, mix well, and stir at 120°C for 2.5 hours; cool to 100°C, add 35 parts of silicic acid and 35 parts of boric acid, and continue stirring for 1.5 hours;

[0061] A2, add 20 parts of bimetallic biochar and the remaining half of the water, mix well, and stir for 3 hours;

[0062] A3. After cooling to 30° C., forming, hardening, and discharging, the foundry sand binder is obtained.

[0063] Comparative Example 1

[0064] A foundry sand binder is different from Example 1 in that bimetallic biochar is not introduced.

[0065] Comparative Example 2

[0066] A foundry sand binder is different from Example 1 in that no organic acid is introduced.

[0067] Comparative Example 3

[0068] A foundry sand binder, the preparation process of which is based on the patent publication number CN114472796.

[0069] Performance test

[0070] Weigh 3 parts of each binder of Examples 1-3 and Control Examples 1-3, add them to 50 parts of 70-mesh new quartz sand and 50 parts of 70-mesh old quartz sand, mix them evenly, pour them into an 8-shaped mold, compact them, mix them at 120°C for 4 minutes, and harden them with CO2 to obtain molding sand. Take out the molding sand prepared by each method, and test its immediate and one-week tensile strength, collapsibility and moisture resistance with reference to GB2684-81 "Test methods for raw sand and mixtures for casting".

[0071] Table 1 Performance test results

[0072]

[0073] As can be seen from the above, the foundry sand binder of the present invention is used to prepare molding sand, which better improves the moisture resistance of inorganic binders, has good disintegration properties, and also has a certain improvement in tensile strength.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A foundry sand binder, characterized in that: The raw materials include the following parts by weight: 80-100 parts of phosphoric acid, 20-30 parts of aluminum hydroxide, 3-8 parts of magnesium hydroxide, 60-80 parts of boric acid or silicic acid, 15-30 parts of bimetallic biochar and 300-500 parts of water; The preparation process of the bimetallic biochar comprises the following steps: S1. Crush the straw, soak it in an alkaline solution, stir it at 90-120°C for 2-4 hours, remove impurities, wash it with water, add sodium chlorite solution to decolorize it until the pH value is 4.2-5.0, and then wash it with water to obtain straw fiber; S2. Soaking the straw fiber obtained in step S1 in an aluminum nitrate nonahydrate solution for 10-20 hours, filtering, drying, and calcining for 2-8 hours to obtain modified straw fiber; S3. Dissolve magnesium nitrate hexahydrate, hexamethylenetetramine and the modified straw fiber obtained in step S2 in water, stir, react at 90-120° C. for 12-18 hours, filter, wash, dry, and calcine for 2-8 hours to obtain bimetallic biochar.

2. The foundry sand binder according to claim 1, wherein The mass concentration of phosphoric acid is 80-90%.

3. The foundry sand binder according to claim 1, wherein The alkaline solution in step S1 includes 0.15-0.25M sodium hydroxide or potassium hydroxide.

4. The foundry sand binder according to claim 1, wherein The mass concentration of the aluminum nitrate nonahydrate solution in step S2 is 15-25%.

5. The foundry sand binder according to claim 1, wherein The calcination conditions in steps S2 and S3 are inert gas protection and a temperature of 400-900°C.

6. The foundry sand binder according to claim 1, wherein In step S3, the mass ratio of magnesium nitrate hexahydrate, hexamethylenetetramine and modified straw fiber is (0.2-1.5): (66.5-266): (0.08-0.8).

7. The method for preparing a foundry sand binder according to any one of claims 1 to 6, wherein: The following steps are involved: A1. Weigh phosphoric acid, aluminum hydroxide, and magnesium hydroxide by weight, add half water, mix well, and stir at 90-140°C for 2-4 hours. Cool to 70-120°C, then add boric acid or silicic acid and continue stirring for 1-2 hours. A2. Add bimetallic biochar and the remaining half of the water, mix well, and stir for 2-4 hours; A3. After cooling to 20-40° C., forming, hardening, and discharging, the foundry sand binder is obtained.

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