A molding sand auxiliary material containing rare earth oxides, a preparation method thereof, and molding sand

Abstract

The present application discloses a molding sand auxiliary material containing rare earth oxides, a preparation method thereof and molding sand, and belongs to the technical field of casting molding materials. It is prepared from the following components: 50-90 parts of sodium bentonite, 2-15 parts of α-starch, 5-15 parts of husk powder, 1-5 parts of rare earth oxide powder, 1-5 parts of potassium acetate and 1-10 parts of ethyl silicate. The molding sand mixed with the auxiliary material can eliminate the flaky graphite layer on the surface of small and medium-sized ductile iron castings during the casting process, improve the mechanical properties of the castings, and the auxiliary material does not produce toxic and polluting gases during the casting process. After casting, there is no need to add new sand and coal powder. The auxiliary material can be directly added to the old sand to carry out the next batch of casting, ensuring that the molding sand has excellent performance while reducing waste sand emissions, improving the reuse rate of old sand, saving costs and achieving environmental protection.

Description

Technical Field

[0001] The present application relates to a molding sand auxiliary material containing rare earth oxides, a preparation method thereof and molding sand, and belongs to the technical field of casting molding materials. Background Art

[0002] my country's casting output accounts for more than 50% of the world's casting output. The output of ductile iron has basically increased year by year, currently accounting for 30% of the casting output, of which most small and medium-sized parts are cast using wet clay sand. At present, coal powder clay sand casting is widely used. Adding coal powder to the sand can prevent mechanical sand sticking to the casting and make the casting surface smooth and beautiful.

[0003] However, coal powder will seriously deteriorate working conditions and environmental hygiene, and will also emit unpleasant odors and a lot of thick smoke during pouring. The smoke contains a lot of harmful gases such as dioxins, which are very harmful to the human body. The amount of new sand, bentonite and coal powder added to coal powder clay sand is large, the reuse rate of old sand is low, and the amount of waste sand discharged is large.

[0004] Ductile iron parts made of green clay sand casting often have a flaky graphite surface layer. Since the mechanical properties of ductile iron mainly depend on the shape of graphite, the presence of flaky graphite defects on the surface layer of ductile iron parts will lead to deterioration of mechanical properties.

[0005] Therefore, a casting material which is both environmentally friendly and can eliminate the flaky graphite on the surface of ductile iron castings is needed. Summary of the invention

[0006] Based on the above problems, the present invention provides a molding sand auxiliary material containing rare earth oxides, a preparation method thereof, and molding sand. No coal powder is added, no new sand needs to be added, and no toxic and polluting gases are generated during the casting process. The excellent performance of the molding sand is ensured while reducing the discharge of waste sand and increasing the recycling rate of old sand. When producing ductile iron castings, no flaky graphite layer is generated on the surface of the castings, and the performance of the castings is improved.

[0007] The technical solution adopted by the present invention is:

[0008] A molding sand auxiliary material containing rare earth oxide is prepared from the following components: 50-90 parts of sodium bentonite, 2-15 parts of alpha-starch, 5-15 parts of rice husk powder, 1-5 parts of rare earth oxide powder, 1-5 parts of potassium acetate and 1-10 parts of ethyl silicate.

[0009] α-starch can not only improve the hot wet tensile strength of the molding sand, but also produce gaps on the surface of the mold after burning, which can buffer the thermal expansion of silica sand and greatly improve the ability of the molding sand to resist sand inclusion. At the same time, α-starch can also reduce the friction between the molding sand and the mold, and improve the mold release of the molding sand; it can significantly reduce the sensitivity of wet molding sand to moisture, reduce the water content of molding sand and increase the compaction rate of molding sand, improve the ability of molding sand to resist wind drying, and reduce sand erosion defects in castings.

[0010] Husk powder is rich in cellulose, lignin, and silica, and has good toughness and porosity. It can improve the hot and wet tensile strength of the molding sand. After burning, the husk powder produces reducing gas, which can prevent the casting from sticking sand. Husk powder has good water retention and porosity, and can filter and absorb the smoke generated during pouring. It can also buffer the thermal expansion of silica sand, greatly improving the ability of the molding sand to resist sand inclusion.

[0011] The compounding of ethyl silicate and bentonite can improve the expansion of bentonite, thereby reducing the amount of bentonite added to the molding sand; ethyl silicate optimization can also optimize the performance of starch and improve the stability of the molding sand; ethyl silicate attached to husk powder can not only improve the bonding ability of husk powder with other molding materials, but also improve the fluidity of the molding sand; ethyl silicate can absorb fine powder in the molding sand and reduce dust in the workshop.

[0012] Rare earth oxides can introduce a certain amount of rare earth oxides on the surface or between layers of bentonite. On the one hand, it can weaken the interlayer bond energy of montmorillonite in bentonite, increase the interlayer distance, and make the structure loose, which is beneficial to the dispersion of bentonite and improves its bonding ability; on the other hand, it can also help to compound bentonite with starch, improve the stability of bentonite and starch, and reduce the production of dead clay and the burning loss of starch; in addition, rare earth oxides can greatly reduce the amount of CO produced by the combustion of organic matter.

[0013] Preferably, the auxiliary material is prepared from the following components: 60-80 parts of sodium bentonite, 5-12 parts of α-starch, 7-12 parts of rice husk powder, 2-4 parts of rare earth oxide powder, 2-4 parts of potassium acetate and 4-8 parts of ethyl silicate.

[0014] Preferably, more than 95wt% of the mass of the rare earth oxide powder passes through a 200-mesh sieve. The rare earth oxide powder is La2O3 and / or CeO2. Compared with other rare earth oxides, the mixed rare earth oxide of La2O3 and CeO2 has a lower market price and a significant effect, which can reduce production costs and achieve cost reduction and efficiency improvement.

[0015] Preferably, the rare earth oxide powder is La2O3 and CeO2, and the weight ratio of La2O3 to CeO2 is 1:0.2-5.

[0016] Preferably, more than 95wt% of the mass of the sodium bentonite passes through a 200-mesh sieve, and the colloid value is greater than 99mL / 15g; the higher colloid value makes the colloid particles of the sodium bentonite have a higher concentration and a larger particle size when the sodium bentonite absorbs water to form a colloidal solution, so that the molding sand has stronger adhesion.

[0017] Preferably, more than 95 wt% of the potassium acetate passes through a 100-mesh sieve, and the purity of the potassium acetate is greater than 95%.

[0018] Preferably, more than 95wt% of the mass of the α-starch passes through a 140-mesh sieve, and the degree of gelatinization is greater than 96%; a higher degree of gelatinization can significantly reduce the sensitivity of the molding sand to moisture, reduce the moisture content of the molding sand, and increase the firmness of the molding sand.

[0019] Preferably, more than 95 wt% of the husk powder passes through a 140-mesh sieve, and the organic matter in the husk powder is greater than 80 wt%.

[0020] Preferably, the purity of the ethyl silicate is greater than 99%, and the ethyl silicate may be one or more of ethyl silicate 28, ethyl silicate 32 or ethyl silicate 40.

[0021] According to another aspect of the present application, a method for preparing a molding sand auxiliary material containing rare earth oxides is provided, comprising the following steps:

[0022] (1) Crush and grind the husk powder and pass it through a 140-mesh sieve;

[0023] (2) Sodium bentonite and potassium acetate powder are first mixed, and then active α-starch, rice husk powder, and rare earth oxide powder are added and mixed, and the mixture is stirred evenly, and ethyl silicate is sprayed into the mixture to obtain a formula material;

[0024] (3) The mixed material obtained in step (2) is dried and then ground into powder, and then passed through a 140-mesh sieve to obtain a molding sand auxiliary material containing rare earth oxides.

[0025] According to another aspect of the present application, there is provided a molding sand containing rare earth oxides, comprising a main material and auxiliary materials, wherein the main material comprises, by weight percentage: 5-7% bentonite, 2.6-3.8% water, and the rest is silica sand;

[0026] The addition amount of the auxiliary material accounts for 0.5-1.5wt% of the main material, and the auxiliary material is any of the above-mentioned molding sand auxiliary materials containing rare earth oxides or any of the molding sand auxiliary materials containing rare earth oxides prepared by the above-mentioned preparation methods.

[0027] The beneficial effects of this application include but are not limited to:

[0028] 1. According to the molding sand auxiliary material containing rare earth oxides provided in the present application, by adding sodium bentonite, α-starch, rice husk powder, rare earth oxide powder, potassium acetate, and ethyl silicate, without adding coal powder, the molding sand can have higher strength and toughness, and no toxic and polluting gas will be generated during the casting process; after casting, no new sand needs to be added, and the auxiliary material can be directly added to the old sand to carry out the next batch of casting, thereby ensuring that the molding sand has excellent performance while reducing waste sand discharge, increasing the reuse rate of old sand, making full use of sand resources, and significantly reducing production costs.

[0029] 2. According to the molding sand auxiliary material containing rare earth oxides provided in this application, rice husk powder is added to the components. The rice husk is heated by high-temperature molten iron to form ash containing porous amorphous silicon, which can slow down the inoculation decay of the surface layer of ductile iron parts.

[0030] 3. According to the molding sand auxiliary material containing rare earth oxides provided by the present application, by adding potassium acetate, potassium acetate can react with the sulfur in the surface layer of the molten metal and the auxiliary material, preventing the sulfur from reacting with the magnesium in the molten iron, which is beneficial to reducing or eliminating the flaky graphite layer on the surface of the ductile iron parts.

[0031] 4. According to the molding sand auxiliary material containing rare earth oxides provided in this application, the main components of the rare earth oxide powder are CeO2 and La2O3, both of which can form sulfur oxides with sulfur in molten iron, reduce the sulfur content on the surface of the molten iron, prevent sulfur from reacting with magnesium in the molten iron, and thus prevent the occurrence of spherical decay, reducing or avoiding the appearance of flaky graphite layers on the surface of ductile iron parts. DETAILED DESCRIPTION

[0032] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0033] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in a conventional manner in the art or in accordance with the product instructions. In addition, any method and material similar or equivalent to the described content can be applied to the method of the present invention. The preferred implementation methods and materials described in this patent are for demonstration purposes only.

[0034] Components used in the embodiments and comparative examples:

[0035] Sodium bentonite, red mud, and rare earth oxides all passed through a 200-mesh sieve; rice husk powder passed through a 140-mesh sieve; and α-starch and potassium acetate passed through a 100-mesh sieve.

[0036] Among them, the organic matter content in the husk powder is greater than the colloid value greater than 80wt%; the colloid value of sodium bentonite is greater than 99mL / 15g; more than 95wt% of the mass of α-starch passes through a 100-mesh sieve, and the gelatinization degree is greater than 96%; the purity of potassium acetate is greater than 95wt%; ethyl silicate is ethyl silicate 28, and the SiO2 content is 28-30wt%.

[0037] A method for preparing a molding sand auxiliary material containing rare earth oxides comprises the following steps:

[0038] (1) Crush and grind the husks and pass them through a 140-mesh sieve;

[0039] (2) Mix sodium bentonite and potassium acetate powder first, then add active α-starch, rice husk powder and rare earth oxide powder, mix well, and spray ethyl silicate to mix.

[0040] (3) The mixed material in (2) is dried and then ground into powder, and then passed through a 140-mesh sieve to obtain a molding sand auxiliary material containing rare earth oxides.

[0041] The molding sand auxiliary materials containing rare earth oxides in the following examples and comparative examples are all prepared by the above method.

[0042] The new sand used in the following embodiments and comparative examples includes the following components in percentage by weight: 6.5 wt % sodium bentonite, 0.8 wt % α-starch, 1.0 wt % rice husk powder, 0.25 wt % potassium acetate, 0.15 wt % red mud, 0.3 wt % rare earth oxide powder, 0.5 wt % ethyl silicate, 3 wt % water, and the rest is silica sand.

[0043] The used sand described in the embodiment is the recycled sand after the new sand is cast once with ductile iron.

[0044] Example 1

[0045] A molding sand auxiliary material containing rare earth oxides includes the following components in mass percentage: 50wt% sodium bentonite, 15wt% α-starch, 15wt% rice husk powder, 5wt% rare earth oxide powder (La2O3), 5% potassium acetate and 10wt% ethyl silicate. 1.5wt% of the above auxiliary materials are added to the old sand to obtain molding sand 1#.

[0046] Example 2

[0047] A molding sand auxiliary material containing rare earth oxides includes the following components in mass percentage: 90wt% sodium bentonite, 2wt% α-starch, 5wt% rice husk powder, 1wt% rare earth oxide powder (La2O3:CeO2=1:4), 1wt% potassium acetate and 1wt% ethyl silicate. 0.5wt% of the above auxiliary materials are added to the old sand to obtain molding sand 2#.

[0048] Example 3

[0049] A molding sand auxiliary material containing rare earth oxides includes the following components in mass percentage: 60wt% sodium bentonite, 12wt% α-starch, 12wt% rice husk powder, 4wt% rare earth oxide powder (CeO2), 4wt% potassium acetate and 8wt% ethyl silicate. 1.2wt% of the above auxiliary materials are added to the old sand to obtain molding sand 3#.

[0050] Example 4

[0051] A molding sand auxiliary material containing rare earth oxides includes the following components in mass percentage: 70wt% sodium bentonite, 8wt% α-starch, 10wt% rice husk powder, 3wt% rare earth oxide powder (La2O3:CeO2=1:1), 3% potassium acetate and 6wt% ethyl silicate. 1.0wt% of the above auxiliary materials are added to the old sand to obtain molding sand 4#.

[0052] Example 5

[0053] A molding sand auxiliary material containing rare earth oxides includes the following components in mass percentage: 80wt% sodium bentonite, 5wt% α-starch, 7wt% rice husk powder, 2wt% rare earth oxide powder (La2O3:CeO2=4:1), 2% potassium acetate and 4wt% ethyl silicate. 0.8wt% of the above auxiliary materials are added to the old sand to obtain molding sand 5#.

[0054] Example 6

[0055] The difference between Example 6 and Example 4 is that the rare earth oxide in the auxiliary material added to the molding sand 6# is Nd2O3.

[0056] Comparative Example 1

[0057] 6wt% bentonite and 4wt% coal powder were added to the new sand to obtain comparative molding sand D1#.

[0058] Comparative Example 2

[0059] 6.0wt% new sand, 0.6wt% bentonite and 0.4wt% coal powder were added to the old sand to obtain comparative molding sand D2#.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 4 is that the ethyl silicate in the auxiliary material added to the comparative molding sand D3# is replaced by water glass.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 4 is that the auxiliary materials of comparative molding sand D4# do not include rare earth oxides.

[0064] Comparative Example 5

[0065] The difference between Comparative Example 5 and Example 4 is that potassium acetate is replaced by sodium acetate in comparative molding sand D5#.

[0066] The coal powder clay sand of Examples 1-6 and Comparative Examples 1-5 have the same quality. The properties of molding sands 1#-6# and comparative molding sands D1#-D5# were tested, and the structures are shown in Table 1.

[0067] Table 1

[0068]

[0069] Note: Comparative molding sand D1# becomes old sand after being used once, and the molding sand mixed with the old sand is comparative molding sand D2#.

[0070] As can be seen from Table 1, the strength, toughness and air permeability of molding sands 1#-6# are good, indicating that adding the molding sand auxiliary material containing rare earth oxides of the present application to the old sand is helpful to improve the compaction rate, air permeability, wet compressive strength and hot wet tensile strength of the molding sand.

[0071] Application Examples

[0072] Molding sand 4# and comparative molding sand D2# were selected for 10 repeated casting tests (wherein the first casting application of comparative molding sand D2# used molding sand 1#), and 86kg of three-way ductile iron pipe fittings were cast each time. Each time the molding sand 4# was used, 0.8wt% of the auxiliary materials of Example 4 were added to the old sand used last time before the next casting. Each time the comparative molding sand D2# was used, 6.0wt% of new sand, 0.6wt% of bentonite and 0.4wt% of coal powder were added to the old sand used last time, and the next casting was continued. The smoke and waste sand emissions of the 10 casting tests are shown in Table 2. Samples were taken at the wall of the three-way pipe, the metallographic phase was ground, and the surface thickness of the ductile iron part was measured. The measurement results are shown in Table 3.

[0073] Table 2

[0074]

[0075] Table 3

[0076]

[0077] It can be seen from Table 2 that compared with the comparison sand D2#, the emissions of waste gas and waste sand in the repeated casting test of sand 4# were significantly reduced, which saves energy and reduces emissions and meets the requirements of the "Emission Limits of Air Pollutants in the Foundry Industry".

[0078] As can be seen from Table 3, no flake graphite appeared on the surface of the ductile iron castings produced in the repeated casting test of molding sand 4#, and the surface finish and casting yield of the castings were improved; while the ductile iron castings produced in the casting test of comparative molding sand D2# using coal powder clay sand all had a flake graphite layer of about 210μm thick on the surface.

[0079] The above is only the embodiment of the present application, and the protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present application should be included in the protection scope of the present application.

Claims

1. A molding sand auxiliary material containing rare earth oxides, characterized in that: The invention is prepared from the following components: 50-90 parts of sodium bentonite, 2-15 parts of α-starch, 5-15 parts of rice husk powder, 1-5 parts of rare earth oxide powder, 1-5 parts of potassium acetate and 1-10 parts of ethyl silicate.

2. The molding sand auxiliary material containing rare earth oxide according to claim 1, characterized in that: The invention is prepared from the following components: 60-80 parts of sodium bentonite, 5-12 parts of α-starch, 7-12 parts of rice husk powder, 2-4 parts of rare earth oxide powder, 2-4 parts of potassium acetate and 4-8 parts of ethyl silicate.

3. The molding sand auxiliary material containing rare earth oxide according to claim 2, characterized in that: The rare earth oxide powder is La2O3 and / or CeO2.

4. The molding sand auxiliary material containing rare earth oxide according to claim 1, characterized in that: The rare earth oxide powder is La2O3 and CeO2, and the weight ratio of La2O3 to CeO2 is 1:0.2-5.

5. The molding sand auxiliary material containing rare earth oxide according to claim 1, characterized in that: The purity of 95wt% potassium acetate is greater than 95%.

6. The molding sand auxiliary material containing rare earth oxide according to claim 1, characterized in that: The α-starch has a size smaller than 140 meshes and a gelatinization degree greater than 96%.

7. The molding sand auxiliary material containing rare earth oxide according to claim 1, characterized in that: 95wt% of the sodium bentonite has a particle size less than 200 mesh and a colloid value greater than 99mL / 15g.

8. The method for preparing a molding sand auxiliary material containing rare earth oxide according to any one of claims 1 to 7, characterized in that: The steps include: (1) crushing and grinding the husks, and sieving to obtain husk powder; (2) Mix sodium bentonite and potassium acetate powder first, then add α-starch, rice husk powder and rare earth oxide powder, mix well, and spray ethyl silicate to mix; (3) The mixed material is dried and then ground into powder, which is then sieved.

9. The method for preparing a molding sand auxiliary material containing rare earth oxides according to claim 8, characterized in that: The mesh number of the sieve shall not be less than 140.

10. A molding sand containing rare earth oxides, characterized in that: The invention comprises a main material and auxiliary materials, wherein the main material comprises, by weight percentage, 5-7% bentonite, 2.6-3.8% water, and the rest is silica sand; The addition amount of the auxiliary material accounts for 0.5-1.5wt% of the main material, and the auxiliary material is the molding sand auxiliary material containing rare earth oxides as described in any one of claims 1-7 or the molding sand auxiliary material containing rare earth oxides prepared by the preparation method described in any one of claims 8 or 9.

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