Sand mold casting coating for preventing nitrogen porosity of gray cast iron and method for preparing the same

Abstract

This invention provides a sand casting coating for preventing nitrogen porosity in gray cast iron and its preparation method. The coating comprises a base material and additives. The additives include the following components by mass percentage: 15%–35% basalt fiber, 1%–10% zirconia microspheres, 40%–50% alumina powder, and 0.5%–1.5% rare earth element powder. The sand casting coating of this invention exhibits strong high-temperature stability, strength, toughness, and density. It can form a dense protective film on the surface of the sand mold, effectively preventing gas from penetrating into the molten iron.

Description

Technical Field

[0001] This invention relates to the field of casting coating technology, specifically to a sand casting coating for preventing nitrogen porosity in gray cast iron and its preparation method. Background Technology

[0002] Currently, there are two main sources of nitrogen in molten iron: one is the nitrogen contained in the molten metal itself before casting; the other is the decomposition of nitrogen-containing resin into NH2 when heated, and the NH2 dissociates on the surface of the molten metal, NH2-[N]+3 / 2H2, and a considerable portion of the [N] atoms enter the surface layer of the metal in the mold cross section which is still in a molten state, and diffuse from the surface inward.

[0003] Nitrogen porosity is a common defect in the production of gray cast iron parts. It is mainly caused by the fact that the solubility of nitrogen in molten iron generally decreases during the solidification process. When the nitrogen content in molten iron exceeds its maximum solubility, it will precipitate in the form of nitrogen gas, thus forming pores in the casting. This has a certain impact on the material of the casting and reduces the stability of the casting in later use.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] The main objective of this invention is to propose a sand casting coating for preventing nitrogen porosity in gray cast iron and its preparation method. The sand casting coating of this invention has strong high-temperature stability, strength, toughness and density, and can form a dense protective film on the surface of the sand mold, effectively preventing gas in the sand mold from penetrating into the molten iron.

[0006] To achieve the above objectives, the present invention provides the following technical solutions.

[0007] A first aspect of the present invention provides a sand casting coating for preventing nitrogen porosity in gray cast iron, comprising a base material and an additive, said additive comprising the following components in weight percentage:

[0008] The composition includes 15%–35% basalt fiber, 1%–10% zirconia microspheres, 40%–50% alumina powder, and 0.5%–1.5% rare earth element powder.

[0009] Basalt fiber is a novel inorganic fiber with excellent heat resistance and toughness. It maintains its properties at high temperatures, resisting deformation or decomposition, thus improving the high-temperature stability of coatings. Adding basalt fiber to coatings can also increase their strength and toughness, enhancing their tensile and impact resistance.

[0010] Adding zirconia microspheres to coatings has two advantages. First, they can be used in conjunction with basalt fibers, resulting in a denser and more dispersed coating after the reaction during high-temperature production. This makes the overall coating denser and more complete, reducing the risk of gas intrusion and improving the protective effect. Second, zirconia can promote the conversion of nitrogen. Even if nitrogen is produced by the decomposition of NH2, the gas generated under these catalytic conditions is generally insoluble in molten iron and does not form subcutaneous pores.

[0011] Alumina can improve the fluidity of coatings, making them easier to apply and evenly cover the surface of castings, thus improving the smoothness and density of the coating. Furthermore, the microporous structure of alumina helps gases escape more easily from the coating, reducing the formation of nitrogen pores.

[0012] In embodiments of the present invention, the rare earth element powder includes one of cerium oxide powder and lanthanum oxide powder.

[0013] In an embodiment of the present invention, the mass ratio of the additive to the base material is (2-3):10.

[0014] In embodiments of the present invention, the base material comprises the following components by mass percentage: 30-50% filler, 1%-8% binder, 2%-10% suspending agent, 0.5%-1.5% thickener, and the balance being solvent.

[0015] In embodiments of the present invention, the filler includes one or more of alumina and silicon dioxide.

[0016] In an embodiment of the present invention, the mass ratio of alumina to silicon dioxide is (2-3):(1-2).

[0017] In embodiments of the present invention, the adhesive includes at least one of phenolic resin, furan resin, isocyanate, and urea resin.

[0018] In embodiments of the present invention, the suspending agent includes at least one of organic bentonite, sodium carboxymethyl cellulose, and polyvinyl butyral.

[0019] In embodiments of the present invention, the thickener includes at least one of ethyl cellulose and propyl cellulose.

[0020] In embodiments of the present invention, the solvent includes at least one of ethanol and isopropanol.

[0021] The second aspect of the present invention provides a method for preparing the sand casting coating described in the first aspect of the present invention, comprising the following steps: preparing a base material; preparing an additive: mixing and grinding basalt fiber, zirconia microspheres, alumina powder and rare earth element powder to obtain the additive; the particle size of the additive is 10μm to 15μm; and, under stirring conditions, mechanically mixing the base material and the additive and ultrasonically mixing them sequentially to obtain the sand casting coating.

[0022] In an embodiment of the present invention, basalt fiber, zirconia microspheres, alumina powder and rare earth element powder are mixed in a mixer for 30 min to 90 min, and then ground in a three-roll mill at a frequency of 100 r / min to 200 r / min for 10 min to 30 min to ensure that the particle size of the additives is 10 μm to 15 μm.

[0023] In an embodiment of the present invention, the preparation of the base material includes the following steps: mixing filler, binder, suspending agent, thickener and solvent together and stirring evenly to obtain the base material.

[0024] In an embodiment of the present invention, the stirring speed of the mechanical mixing of the base material and the additive is 300 r / min to 700 r / min, and the stirring time is 10 min to 30 min.

[0025] In an embodiment of the present invention, the ultrasonic temperature of the ultrasonic mixture is 5°C to 15°C, the ultrasonic frequency is 20kHz to 30kHz, and the ultrasonic time is 0.5h to 3h.

[0026] Under the ultrasonic process of this invention, the coating becomes more densely dispersed, making the overall coating denser and more complete, reducing the risk of gas intrusion, and improving the protective effect. It has strong high-temperature stability, strength, toughness and density, and can form a dense protective film on the surface of the sand mold, effectively preventing gas in the sand mold from penetrating into the molten iron.

[0027] Compared with the prior art, the present invention achieves the following technical effects:

[0028] 1. The sand casting coating of the present invention increases the strength and toughness of the coating by adding basalt fiber material, thereby improving its tensile and impact resistance.

[0029] 2. The zirconium oxide microspheres and rare earth powder added to the sand casting coating of the present invention can also promote the thermal decomposition of nitrogen-containing resins. The gas produced under these catalytic conditions is usually insoluble in molten iron and forms subcutaneous pores.

[0030] 3. In the sand casting coating of the present invention, alumina can improve the fluidity of the coating, making it easier to apply and evenly cover the casting surface, thus improving the smoothness and density of the coating. Furthermore, the microporous structure of alumina helps gases escape more easily from the coating, reducing the formation of nitrogen pores.

[0031] 4. In the sand casting coating of the present invention, basalt fiber, zirconia microspheres and rare earth element powder are used in combination. Under the action of ultrasonic process, they are more densely dispersed, making the overall coating more dense and complete, reducing the risk of gas intrusion and improving the protective effect. It has strong high temperature stability, strength, toughness and density, and can form a dense protective film on the surface of the sand mold, effectively preventing gas in the sand mold from penetrating into the molten iron.

[0032] 5. The preparation method in this invention does not involve any additional steps and requires no special equipment, making it highly applicable.

[0033] 6. The preparation method in this invention has low production cost and unchanged production efficiency.

[0034] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Detailed Implementation

[0035] The following describes embodiments of the present invention. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this invention are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of the present invention, the technical terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0040] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0041] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0042] Currently, the main methods to avoid nitrogen porosity defects are reducing the gas emission from the core and promoting gas expulsion from the core to achieve a gas-proof effect. For example, existing technology discloses a low-gas-emission resin and its preparation method. In the synthesis of furan resin, formaldehyde and urea are not used, and no formaldehyde gas or nitrogen oxides are released during use, which is both environmentally friendly and reduces the gas emission of the resin. Ethyl silicate and polytetrahydrofuran are used to further block the hydroxyl groups of low molecular weight furfuryl alcohol, thereby reducing the volatility of furfuryl alcohol in the resin. In the end, the free furfuryl alcohol accounts for only one-tenth of the total furfuryl alcohol, effectively reducing the volatilization of the resin and the gas emission during casting. For example, a method for manufacturing low-gas-emission casting cores disclosed in the prior art involves baking the silica sand used to make the core at 580-600℃ until it turns red, then removing it. The core is then hollowed out using pre-embedded pipes or venting ropes. After core making, the core is placed in a vacuum device to remove the gas. A layer of casting coating is evenly applied to the core surface. After the coating dries naturally, it is sanded until smooth and uniform, with no residue on the mold surface. Finally, a layer of carbon black is evenly fumigated onto the mold surface using a burning acetylene nozzle. These measures generate a strong reducing atmosphere during molten metal pouring, forming a gas film and carbon film at the interface between the casting and the coating, preventing the molten metal from interacting with the sand mold and creating a gas-proof effect. However, both of these techniques suffer from drawbacks such as complex operation processes, the need for specialized equipment, increased production costs, and reduced production efficiency.

[0043] Of course, there are existing technologies that improve sand casting coatings. For example, by adding iron oxide and active high-temperature oxidizing fluxes, highly active zirconium silicate and high-temperature oxidizing agents are used. At high temperatures, the coating melts upon heating, forming a dense, shielding coating that reduces gas penetration into the molten metal. Furthermore, the use of active coatings increases the coating's sintering ability at high temperatures, forming a liquid coating film that effectively blocks gas from entering the molten metal, improving the stability of the castings in later use. However, while this technology increases the coating's sintering ability at high temperatures to some extent, the resulting liquid coating film has poor density and weak gas shielding.

[0044] To address this issue, the present invention provides a casting sand mold coating to prevent nitrogen porosity in gray cast iron. By co-fusing the base material and additives under ultrasonic processing, the overall high-temperature stability, strength, toughness, and density of the coating are improved, preventing the interaction between the molten metal and the sand mold, thus producing a gas-proof effect. Furthermore, the coating promotes the thermal decomposition of nitrogen-containing resins; the gases generated under these catalytic conditions are generally insoluble in molten iron and do not form subcutaneous pores. Moreover, the coating application process requires no special production equipment, is simple to operate, and is easily applied to production sites.

[0045] The first aspect of this invention provides a sand casting coating for preventing nitrogen porosity in gray cast iron, comprising a base material and additives, wherein the additives comprise the following components by mass percentage:

[0046] The composition includes 15%–35% basalt fiber, 1%–10% zirconia microspheres, 40%–50% alumina powder, and 0.5%–1.5% rare earth element powder.

[0047] In embodiments of the present invention, the mass percentage of basalt fiber in the additive can be one of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%, or any value satisfying the above range.

[0048] In embodiments of the present invention, the mass percentage of zirconia microspheres in the additive can be one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the above range.

[0049] In embodiments of the present invention, the mass percentage of alumina powder in the additive can be one of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any value satisfying the above range.

[0050] In embodiments of the present invention, the mass percentage of rare earth element powder in the additive can be one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, or any value within the above range.

[0051] In embodiments of the present invention, the rare earth element powder can be cerium oxide powder. Of course, other rare earth element powders, such as lanthanum oxide powder, can also be selected as appropriate.

[0052] In embodiments of the present invention, the mass ratio of additive to base material can be (2-3):10. For example, the mass ratio of additive to base material can be one of 2:10 and 3:10 or any value that satisfies the above range.

[0053] In embodiments of the present invention, the base material comprises the following components by weight percentage:

[0054] The composition consists of 30-50% filler, 1%-8% binder, 2%-10% suspending agent, 0.5%-1.5% thickener, and the remainder is solvent.

[0055] In embodiments of the present invention, the sand casting coating is composed of base materials such as fillers, binders, suspending agents, thickeners, and solvents, as well as additives such as basalt fibers, zirconia microspheres, alumina powder, and rare earth element powders.

[0056] In embodiments of the present invention, the mass percentage of filler in the base material can be one of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%, or any value satisfying the above range.

[0057] In embodiments of the present invention, the filler includes one or more of alumina and silicon dioxide, for example, the filler is composed of alumina and silicon dioxide.

[0058] In embodiments of the present invention, the mass ratio of alumina to silicon dioxide is (2-3):(1-2). Exemplarily, the mass ratio of alumina to silicon dioxide can be one of 2:1, 2:2, 3:1, 3:2, or any value satisfying the above range.

[0059] In embodiments of the present invention, the mass percentage of the binder in the base material can be one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value that satisfies the above range.

[0060] In embodiments of the present invention, the binder may be phenolic resin. Of course, other materials may also be selected as binders in embodiments of the present invention, such as furan resin, isocyanate, urea resin, etc., depending on the circumstances.

[0061] In embodiments of the present invention, the mass percentage of the suspending agent in the base material can be one of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value that satisfies the above range.

[0062] In embodiments of the present invention, the suspending agent may be organobentonite. Of course, other materials may also be selected as suspending agents in the embodiments of the present invention, such as sodium carboxymethyl cellulose or polyvinyl butyral.

[0063] In embodiments of the present invention, the mass percentage of the thickener in the base material can be one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, or any value satisfying the above range.

[0064] In embodiments of the present invention, the thickener may be an ethyl cellulose solution. Of course, other solutions, such as propyl cellulose, may also be selected as the thickener in these embodiments, depending on the circumstances.

[0065] In embodiments of the present invention, the solvent can be ethanol. Of course, other solvents, such as isopropanol, can also be selected as appropriate.

[0066] The second aspect of the present invention provides a method for preparing the sand casting coating for preventing nitrogen porosity in gray cast iron as described in the first aspect of the present invention, which is specifically carried out according to the following steps.

[0067] (1) Preparation of base material.

[0068] The filler, binder, suspending agent, thickener, and solvent are mixed and stirred evenly to obtain the base material.

[0069] In an embodiment of the present invention, powdered alumina and silica are added to a mixer and mixed for 30 to 90 minutes. Then, phenolic resin, organobentonite, ethyl cellulose and ethanol are added to the resulting mixed filler and mixed for 30 to 90 minutes. The mixture is then introduced into a high-speed disperser at a frequency of 100 to 200 r / min for 10 to 30 minutes until homogeneous.

[0070] In embodiments of the present invention, the mixing or blending time can be any one of 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, and 90 min, or any value satisfying the above range. The disperser frequency can be any one of 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, and 200 r / min, or any value satisfying the above range. The dispersion time can be any one of 10 min, 15 min, 20 min, 25 min, and 30 min, or any value satisfying the above range.

[0071] (2) Preparation of additives.

[0072] The additive is obtained by mixing and grinding basalt fiber, zirconium oxide microspheres, alumina and rare earth element powder.

[0073] In an embodiment of the present invention, basalt fiber, zirconia microspheres, alumina and rare earth element powder are added to a mixing mill and mixed for a period of time, such as 30 min to 90 min, and then ground for a period of time, such as 10 min to 30 min, using a three-roll mill.

[0074] In embodiments of the present invention, the grinding frequency of the grinding mill can be from 100 r / min to 200 r / min, for example, the grinding frequency can be one of 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min or any value satisfying the above range. The grinding time can be one of 10 min, 15 min, 20 min, 25 min, 30 min or any value satisfying the above range. The mixing time in the mixing mill can be one of 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min or any value satisfying the above range.

[0075] (3) Under stirring conditions, the base material and the additives are mechanically mixed and ultrasonically mixed in sequence to obtain sand casting coating.

[0076] In an embodiment of the present invention, the base material and additives are introduced into a high-speed mixer according to the required ratio, and after being mixed evenly, they are placed in an ultrasonic processor, and the ultrasonic processor is started to perform ultrasonic mixing.

[0077] In embodiments of the present invention, the stirring speed of the mechanical mixing in the high-speed mixer is 300 r / min to 700 r / min, and the stirring time is 10 min to 30 min. Exemplarily, the stirring speed can be one of 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, or 700 r / min, or any value satisfying the above range. The stirring time can be one of 10 min, 10 min, 15 min, 20 min, 25 min, or 30 min, or any value satisfying the above range.

[0078] In embodiments of the present invention, the ultrasonic temperature for ultrasonic mixing can be one of 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, or 15°C, or any value satisfying the above range. The ultrasonic frequency can be one of 20kHz, 21kHz, 22kHz, 23kHz, 24kHz, 25kHz, 26kHz, 27kHz, 28kHz, 29kHz, or 30kHz, or any value satisfying the above range. The ultrasonic duration can be one of 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h, or any value satisfying the above range.

[0079] In the embodiments of the present invention, the density between particles is higher under the action of ultrasound, which is a key technology to enhance the density of coating materials. In addition, the high thermal conductivity of basalt fiber itself can quickly evaporate the flux in the coating to reduce the generation of fine cracks and voids, thus obtaining a sand casting coating that prevents nitrogen porosity in gray cast iron.

[0080] The following will describe in detail, with reference to specific embodiments, the sand casting coating for preventing nitrogen porosity in gray cast iron and its preparation method.

[0081] Unless otherwise specified, the techniques or conditions described in the examples shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. Unless otherwise specified, the experimental methods in the following examples are conventional methods. Unless otherwise specified, the experimental materials used in the following examples are all commercially available products.

[0082] Example 1

[0083] S1: Add 20% powdered alumina and 20% powdered silica to a mixer and mix for 30 minutes; add 1% phenolic resin, 10% organic bentonite, 1.5% ethyl cellulose and ethanol to the mixed base material, mix and then transfer to a high-speed disperser and stir evenly. The disperser frequency is 150 r / min.

[0084] S2: Add 15% basalt fiber, 10% zirconia microspheres, 50% alumina powder and 1.5% cerium oxide powder to a mixer and mix for 30 minutes. Then grind the mixture in a three-roll mill for 1 hour before use.

[0085] S3: 100% of the base material and 20% of the additives are introduced into a high-speed mixer and stirred at a speed of 300 r / min. After stirring evenly, the mixture is placed in an ultrasonic processor, which is then started to begin ultrasonic mixing at a temperature of 10℃, a frequency of 25 kHz, and a time of 2 h to obtain a sand casting coating that prevents nitrogen porosity in gray cast iron.

[0086] Example 2

[0087] S1: Add 30% powdered alumina and 10% silicon dioxide to a mixer and mix for 60 minutes; add 8% phenolic resin, 2% organic bentonite, 0.5% ethyl cellulose and ethanol to the mixed base material, mix and then transfer to a high-speed disperser and stir evenly. The disperser frequency is 200 r / min and the time is 10 minutes.

[0088] S2: Add 35% basalt fiber, 1% zirconia microspheres, 40% alumina powder and 0.5% cerium oxide powder to a mixer and mix for 30 minutes. Then grind the mixture in a three-roll mill for 1 hour before use.

[0089] S3: 100% of the base material and 30% of the additives are introduced into a high-speed mixer and stirred at a speed of 600 r / min for 20 min. After stirring evenly, the mixture is placed in an ultrasonic processor, which is then started to begin ultrasonic mixing at a temperature of 15℃ and a frequency of 20 kHz for 1 h. This produces a sand casting coating that prevents nitrogen porosity in gray cast iron.

[0090] Example 3

[0091] S1: Add 25% powdered alumina and 15% powdered silica to a mixer and mix for 90 minutes; add 5% phenolic resin, 6% organobentonite, 1.0% ethyl cellulose and ethanol to the mixed base material, mix and then transfer to a high-speed disperser and stir evenly. The disperser frequency is 150 r / min and the time is 10 minutes.

[0092] S2: Add 25% basalt fiber, 6% zirconia microspheres, 45% alumina powder and 1.0% cerium oxide powder to a mixer and mix for 30 minutes. Then grind the mixture in a three-roll mill for 1 hour before use.

[0093] S3: 100% of the base material and 30% of the additives are introduced into a high-speed mixer and stirred until uniform. The mixture is then placed in an ultrasonic processor, which is started to begin ultrasonic mixing. The ultrasonic mixing temperature is 5℃, the frequency is 30kHz, and the time is 3h to obtain a sand casting coating that prevents nitrogen porosity in gray cast iron.

[0094] In this invention, the base material and additives are fused together under ultrasonic processing, which improves the overall high-temperature stability, strength, toughness and density of the coating, prevents the interaction between the molten metal and the sand mold, and produces an anti-gas effect.

[0095] In addition, the coating can promote the thermal decomposition of nitrogen-containing resins. The gas produced under these catalytic conditions is usually insoluble in molten iron and forms subcutaneous pores, effectively shielding the gas from entering the molten metal, improving the material of the casting, and thus improving the stability of the casting in later use.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sand casting coating for preventing nitrogen porosity in gray cast iron, characterized in that, The additives include a base material and an additive, wherein the mass ratio of the additives to the base material is (2~3):10; the additives are obtained by mixing and grinding 15%~35% basalt fiber, 1%~10% zirconium oxide microspheres, 40%~50% alumina powder and 0.5%~1.5% rare earth element powder.

2. The sand casting coating as described in claim 1, characterized in that, The rare earth element powder includes one of cerium oxide powder and lanthanum oxide powder.

3. The sand casting coating as described in claim 1, characterized in that, The base material comprises the following components by weight percentage: The composition consists of 30% to 50% filler, 1% to 8% binder, 2% to 10% suspending agent, 0.5% to 1.5% thickener, and the remainder is solvent.

4. The sand casting coating as described in claim 3, characterized in that, The filler includes one or more of alumina and silicon dioxide.

5. The sand casting coating as described in claim 4, characterized in that, The mass ratio of the alumina to the silicon dioxide is (2~3):(1~2).

6. The sand casting coating as described in claim 3, characterized in that, The adhesive includes at least one of phenolic resin, furan resin, isocyanate, and urea resin.

7. The sand casting coating as described in claim 3, characterized in that, The suspending agent includes at least one of organic bentonite, sodium carboxymethyl cellulose, and polyvinyl butyral.

8. The sand casting coating as described in claim 3, characterized in that, The thickener includes at least one of ethyl cellulose and propyl cellulose.

9. The sand casting coating as described in claim 3, characterized in that, The solvent includes at least one of ethanol and isopropanol.

10. A method for preparing a sand casting coating according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: Preparation of base material; Preparation of additives: Basalt fibers, zirconia microspheres, alumina powder and rare earth element powder are mixed and ground to obtain the additives; the particle size of the additives is 10 μm~15 μm; Under stirring conditions, the base material and the additives are mechanically mixed and ultrasonically mixed in sequence to obtain the sand casting coating.

11. The preparation method according to claim 10, characterized in that, Basalt fiber, zirconia microspheres, alumina powder and rare earth element powder are mixed in a mixer for 30 min to 90 min, and then ground in a three-roll mill at a frequency of 100 r / min to 200 r / min for 10 min to 30 min.

12. The preparation method according to claim 10, characterized in that, The preparation of the base material includes the following steps: The filler, binder, suspending agent, thickener, and solvent are mixed and stirred evenly to obtain the base material.

13. The preparation method according to claim 10, characterized in that, The mixing speed of the base material and the additive is 300 r / min to 700 r / min, and the mixing time is 10 min to 30 min.

14. The preparation method according to claim 10, characterized in that, The ultrasonic mixing process involves an ultrasonic temperature of 5℃ to 15℃, an ultrasonic frequency of 20 kHz to 30 kHz, and an ultrasonic duration of 0.5 h to 3 h.