A coating used in the production of cast iron parts

Abstract

The invention relates to a coating for producing iron castings. The coating mainly comprises, by weight percentage, 12-15 parts of quartz powder, 13-15 parts of magnesia powder, 40-45 parts of bauxite powder, 5-8 parts of sodium bentonite powder, 15-20 parts of water glass, 1-2 parts of ferric oxide powder, 2-3 parts of graphite powder, 2-4 parts of chromium ferronitride powder, 0.5-1 part of starch, 1-2 parts of ferrosilicon powder and 0.02-0.03 part of a defoamer. The coating is prepared by rationally designing the components and content of the coating to improve the air permeability of a coating layer formed on the surfaces of a mold bundle, a sand core and a mold, facilitate the coating layer to fall off easily from the surface of a casting and reduce the occurrence of casting defects caused by the coating.

Description

Technical Field

[0001] The invention belongs to the technical field of casting auxiliary materials, and in particular relates to a coating used in the production of cast iron parts. Background Art

[0002] Cast iron includes gray cast iron, ductile iron, and vermicular cast iron. High-strength and high-toughness cast iron, a key development area for ductile iron, generally refers to high-strength and high-toughness ductile iron. This type of ductile iron, characterized by its high strength and toughness, is widely used in mining machinery, wind turbine equipment, and transportation vehicles such as heavy trucks. High-strength and high-toughness ductile iron castings are primarily produced by sand casting and lost foam casting. When producing high-strength and high-toughness ductile iron using sand casting, a coating is applied to the inner surface of the sand mold and the sand core. This coating comes into direct contact with the molten metal during pouring, and the quality of the coating directly affects the occurrence of casting defects during the casting process. When producing high-strength and high-toughness ductile iron using lost foam casting, a coating is applied to the mold bundle. During the pouring process, the high temperature of the molten metal vaporizes the mold bundle, filling it with molten metal and occupying the mold space. This direct contact between the coating and the molten metal results in a significant impact on the occurrence of casting defects during the casting process. Therefore, the performance of the coating directly affects the yield of high-strength and high-toughness ductile iron.

[0003] A Chinese invention patent with authorization publication number CN103586407B discloses a "casting coating" comprising raw sand, a binder, a curing agent, and a lubricant. The raw sand is composed of 5% to 10% iron mud and 90% to 95% quartz sand, with the binder comprising 30% to 40% of the raw sand by weight, the curing agent comprising 18% to 22% of the binder by weight, and the lubricant comprising 5% to 9% of the binder by weight. The coating also includes an activated modifier, comprising 10% to 20% of the raw sand by weight; the modifier is selected from activated carbon, diatomaceous earth, or bentonite. This modifier imparts excellent adsorption properties to the coating, ensuring the quality of the casting. The coating layer applied to the mold bundle, sand core, and pattern has poor air permeability, making it difficult to fall off the surface of the high-strength, high-toughness cast iron after it is formed. Summary of the Invention

[0004] In order to improve the air permeability of the coating layer formed on the surface of the mold bundle, sand core and pattern, and facilitate the coating layer to fall off the surface of the casting, the present invention provides a coating for the production of iron castings. To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows:

[0005] A coating for producing iron castings mainly comprises, by weight percentage, 12-15 parts of quartz powder, 13-15 parts of magnesia powder, 40-45 parts of bauxite powder, 5-8 parts of sodium bentonite powder, 15-20 parts of water glass, 1-2 parts of ferric oxide powder, 2-3 parts of graphite powder, 2-4 parts of chromium nitride powder, 0.5-1 part of starch, 1-2 parts of ferrosilicon powder and 0.02-0.03 parts of a defoaming agent.

[0006] The coating used in the production of iron castings of the present invention has the following beneficial effects: by rationally designing the composition and content of the coating, the air permeability of the coating layer formed on the surface of the mold bundle, sand core and pattern is improved, and the coating layer is easily detached from the surface of the casting;

[0007] (1) Quartz powder, magnesia powder and bauxite powder serve as the skeleton structure of the coating. Through multiple tests, the ratio of quartz powder, magnesia powder and bauxite powder is determined to ensure that the skeleton structure can form a stable support. At the same time, the silicon dioxide in the quartz powder combines with the sodium ions in the sodium-based bentonite to form sodium silicate. The sodium silicate has a certain viscosity, which makes the magnesia powder and bauxite powder adhere to each other as a whole, which is beneficial to improving the stability of the skeleton. The use of magnesia powder is reasonably controlled to reduce costs. At the same time, the magnesium element in the magnesia powder diffuses into the metal liquid through metallurgy, which is beneficial to the spheroidization of graphite in high-strength and high-toughness cast iron. The sodium-based bentonite powder provides sodium ions while increasing the viscosity of the coating suspension, which is beneficial to the viscosity of the material suspension and the suspension of the coating suspension on the mold bundle, sand core and model surface. The content of water glass is controlled between 15 and 20, which makes the coating suspension have a certain viscosity while preventing excessive addition from damaging other properties of the coating.

[0008] When this coating is used in lost foam casting, during the vaporization of the mold bundle, iron oxide powder reacts with carbon or iron in the molten metal to produce carbon monoxide gas and iron oxide, reducing carbon deposits after the mold bundle vaporizes. The iron oxide facilitates the peeling of the coating from the casting surface after cooling. During the contact between the coating and the molten metal, some graphite powder and ferrosilicon powder undergo metallurgical diffusion into the molten metal, providing graphite nuclei and promoting the graphitization of carbon in the high-strength and high-toughness cast iron. However, excessive levels of graphite powder and ferrosilicon powder in the coating can reduce its performance.

[0009] 0.5-1% starch is added to the coating. During the pouring of molten metal, the starch is carbonized and gasified at high temperature. Under the premise of not affecting the strength, tiny pores are formed in the coating layer, which is beneficial to improving the air permeability of the coating, facilitating the discharge of gas, and reducing the occurrence of casting defects such as air pockets.

[0010] 2 to 4 ferrochromium nitrides are set in the coating. During the pouring of the molten metal, the ferrochromium nitride decomposes, and part of the nitrogen and chromium metallurgically diffuse into the molten metal, increasing the nitrogen content in the molten metal, which is beneficial to the formation of austenite in the cast iron, improving the quenching permeability of the cast iron and the matrix toughness of the cast iron. This changes the traditional process of adding nitrogen during the smelting process. Under atmospheric pressure, the solubility of nitrogen in the molten metal is certain, and a large amount of nitrogen overflows the molten metal, making it difficult to add nitrogen and the addition amount is insufficient; chromium metallurgically expands into the molten metal. Due to the large radius of chromium and the limited metallurgical diffusion distance, chromium mainly accumulates on the surface or below the surface of the casting and forms carbides with carbon, which is beneficial to improving the surface hardness and strength of the casting.

[0011] Furthermore, the main components of the coating used in the production of cast iron parts also include copper oxide powder and boric acid powder. In terms of weight percentage, the copper oxide powder content is 0.3-0.5, and the boric acid powder content is 0.05-0.1.

[0012] Beneficial Effects: By adding a certain amount of copper oxide powder and boric acid powder to the coating powder, without affecting the coating's basic properties, the coating layer comes into contact with molten metal. The oxygen in the copper oxide reacts with carbon or iron to produce carbon monoxide and iron oxide. The iron oxide facilitates the peeling of the coating from the casting surface after cooling. The metallurgical diffusion of copper ions into the molten metal promotes surface graphitization and pearlite formation due to the limited diffusion distance of copper ions, which helps improve the hardness and strength of the high-strength and high-toughness cast iron surface layer. The skeletal structure of the boric acid powder, silicon dioxide, and iron compound enhances the strength, stability, and plasticity of the coating layer, reducing cracking during the casting process.

[0013] Furthermore, the main components of the coating used in the production of cast iron parts also include rare earth powder and magnesium powder. In terms of weight percentage, the content of the rare earth powder is 0.1-0.2, and the content of the magnesium powder is 0.05-0.1.

[0014] Beneficial effects: The contact between the molten metal and the coating layer keeps the coating layer in a high temperature state, allowing the rare earth and magnesium powder to metallurgically diffuse into the molten metal, supplementing and promoting the spheroidization of graphite in high-strength and high-toughness cast iron, and improving the spheroidization effect of graphite; supplementing the addition of spheroidizing agents in the flushing method and wire feeding method.

[0015] Furthermore, the particle sizes of the quartz powder, magnesia powder and bauxite powder are respectively 200-400 mesh, the particle sizes of the sodium bentonite powder and ferric oxide powder are 600-800 mesh; the particle sizes of the graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder and magnesium powder are greater than 1000 mesh.

[0016] Beneficial effects: Controlling the particle size of quartz powder, magnesia powder and bauxite powder within 200-400 meshes is beneficial to the formation of the skeleton, while improving the contact surface between the coating layer and the mold bundle or the smooth surface of the coating layer, which is beneficial to improving the surface quality of the casting; the particle size of graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder and magnesium powder is greater than 1000 meshes, making the particle size more refined, which is beneficial to diffusion into the metal liquid.

[0017] Furthermore, the defoaming agent is specifically n-octanol or n-butanol.

[0018] Beneficial effects: n-Octanol or n-Butanol has good defoaming effect and stable performance.

[0019] A method for preparing a coating used in the production of cast iron parts, the preparation steps comprising:

[0020] S1: preparing raw materials, crushing, grinding and screening the raw materials used to prepare the coating to obtain quartz powder, magnesia powder, bauxite powder, ferric oxide powder, graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder and copper oxide powder that meet the particle size requirements; directly selecting sodium bentonite, water glass, defoaming agent, boric acid powder, rare earth powder and magnesium powder that meet the requirements;

[0021] S2: Sprinkle and preliminarily mix the quartz powder, magnesia powder, bauxite powder, ferric oxide powder, graphite powder, ferrochromium nitride powder, ferrosilicon powder and copper oxide powder according to the proportion, add them into the mixing machine, and stir and mix for 0.5 to 1 hour to obtain a preliminary mixture;

[0022] S3: heating and stirring, introducing the preliminary mixture into a heating mixer, and adding water glass, defoaming agent and boric acid powder in sequence while stirring, heating the materials during stirring, controlling the heating temperature at 70-80°C and the stirring time at 2-3h to obtain an intermediate mixture;

[0023] S4: low-temperature stirring: add the obtained intermediate mixture into a blender, and while stirring, add starch, rare earth powder and magnesium powder in sequence and at intervals, and stir to mix evenly. During stirring, the temperature is controlled below 45°C and the stirring time is controlled within 6 to 8 hours. After stirring, the coating is obtained;

[0024] S5: Bag and seal: put the coating into bags according to the amount and seal them.

[0025] The beneficial effects of the method for preparing a coating used in the production of cast iron parts of the present invention are as follows: the coating is prepared by selecting suitable raw materials and stirring and mixing them evenly; the stirring process is divided into preliminary mixing, heating stirring and low-temperature stirring, so that the mixing is more uniform, the segregation of the various components in the coating is reduced, and the overall performance of the coating is improved; during the heating and stirring process, the temperature is controlled at 70-80°C through multiple experiments, which is conducive to the loss of water in water glass, defoaming agent and boric acid powder while avoiding excessive temperature and oxidation of the materials; during the low-temperature stirring process, the temperature is controlled at below 45°C, and during the stirring process, excessive temperature is prevented from causing oxidation of starch, rare earth powder and magnesium powder; and the coating composition is changed.

[0026] Furthermore, in step S3, water glass, defoaming agent and boric acid powder are dispersed and added into the heating mixer, and the interval time between the addition of the two is controlled to be 0.3 to 0.5 hours.

[0027] Beneficial effect: During the heating and stirring process, the water glass, defoaming agent and boric acid powder are added at intervals of 0.3 to 0.5 hours, so that the upper raw material is added and dried before adding the next raw material to dry. This is beneficial to the drying of the materials while reducing the mutual influence between the water glass, defoaming agent and boric acid powder.

[0028] Furthermore, the mixer used in steps S2, S3 and S4 is an integrated mixer, which includes a heating device, a cooling device and a temperature detection device.

[0029] Beneficial effects: Preliminary mixing, heating stirring and low-temperature stirring are completed in the integrated mixer, shortening the production process and helping to improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is one of the metallographic microstructure photos of high-strength and high-toughness ductile iron produced using the coating used in the production of iron castings of the present invention (100 times uncorroded);

[0031] Figure 2 This is the second metallographic structure photo of high-strength and high-toughness ductile iron produced by using the coating used in the production of iron castings of the present invention (200 times without corrosion). DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0033] Example 1 of the coating used for producing iron castings of the present invention comprises, by weight percentage, 12-15% quartz powder, 13-15% magnesia powder, 40-45% bauxite powder, 5-8% sodium bentonite powder, 15-20% water glass, 1-2% ferric oxide powder, 2-3% graphite powder, 2-4% chromium nitride powder, 0.5-1% starch, 1-2% ferrosilicon powder, and 0.02-0.03% defoaming agent. Quartz powder 12-15, magnesia powder 13-15, bauxite powder 40-45, sodium bentonite powder 5-8, water glass 15-20, ferric oxide powder 1-2, graphite powder 2-3, chromium ferronitride powder 2-4, starch 0.5-1, ferrosilicon powder 1-2, defoaming agent 0.02-0.03, copper oxide powder 0.3-0.5, boric acid powder content 0.05-0.1, rare earth powder 0.1-0.2 and magnesium powder 0.05-0.1.

[0034] In the actual production of this embodiment 1, the specific ingredients of the coating are quartz powder 12, magnesia powder 14, bauxite powder 42, sodium bentonite powder 6, water glass 17, ferric oxide powder 1.5, graphite powder 2.5, chromium ferronitride powder 2.5, starch 0.6, ferrosilicon powder 1.2, defoamer 0.025, copper oxide powder 0.35, boric acid powder 0.08, rare earth powder 0.15, and magnesium powder 0.08, with the remainder being impurities. The defoamer is specifically n-octanol.

[0035] The specific ingredients of the coating are quartz powder 15, magnesia powder 13, bauxite powder 40, sodium bentonite powder 5, water glass 15, ferric oxide powder 2, graphite powder 2, chromium ferronitride powder 4, starch 1, ferrosilicon powder 2, defoaming agent 0.03, copper oxide powder 0.5, boric acid powder 0.1, rare earth powder 0.2 and magnesium powder 0.1, and the rest are impurities. The defoaming agent is specifically n-octanol.

[0036] The specific ingredients of the coating are 12.9% quartz powder, 15% magnesia powder, 40% bauxite powder, 8% sodium bentonite powder, 16% water glass, 1% ferric oxide powder, 3% graphite powder, 2% chromium ferronitride powder, 0.5% starch, 1% ferrosilicon powder, 0.02% defoaming agent, 0.3% copper oxide powder, 0.05% boric acid powder, 0.1% rare earth powder and 0.05% magnesium powder. The rest are impurities. The defoaming agent is specifically n-octanol.

[0037] By rationally designing the composition and content of the coating, it is beneficial to improve the air permeability of the coating layer formed on the mold bundle, sand core and model surface, making it easier for the coating layer to fall off from the casting surface;

[0038] Quartz powder, magnesia powder, and bauxite powder serve as the coating's skeleton. Through numerous tests, the ratio of quartz powder, magnesia powder, and bauxite powder was determined to provide a stable support structure. The silica in the quartz powder combines with the sodium ions in the sodium bentonite to form sodium silicate, which has a certain viscosity. This allows the magnesia powder and bauxite powder to adhere to each other, improving the stability of the skeleton. Properly controlling the use of magnesia powder reduces costs, while the magnesium in the magnesia powder diffuses into the molten metal through metallurgical diffusion, promoting the spheroidization of graphite in high-strength and high-toughness cast iron. The sodium bentonite powder provides sodium ions, increasing the viscosity of the coating suspension, which improves the viscosity and facilitates the suspension's adhesion to the mold bundle, sand core, and mold surface. The water glass content is controlled between 15 and 20%, ensuring a certain viscosity while preventing excessive addition that could damage other coating properties.

[0039] When this coating is used in lost foam casting, during the vaporization of the mold bundle, iron oxide powder reacts with carbon or iron in the molten metal to produce carbon monoxide gas and iron oxide, reducing carbon deposits after the mold bundle vaporizes. The iron oxide facilitates the peeling of the coating from the casting surface after cooling. During the contact between the coating and the molten metal, some graphite powder and ferrosilicon powder undergo metallurgical diffusion into the molten metal, providing graphite nuclei and promoting the graphitization of carbon in the high-strength and high-toughness cast iron. However, excessive levels of graphite powder and ferrosilicon powder in the coating can reduce its performance.

[0040] 0.5-1% starch is added to the coating. During the pouring of molten metal, the starch is carbonized and gasified at high temperature. Under the premise of not affecting the strength, tiny pores are formed in the coating layer, which is beneficial to improving the air permeability of the coating, facilitating the discharge of gas, and reducing the occurrence of casting defects such as air pockets.

[0041] 2 to 4 ferrochromium nitrides are set in the coating. During the pouring of the molten metal, the ferrochromium nitride decomposes, and part of the nitrogen and chromium metallurgically diffuse into the molten metal, increasing the nitrogen content in the molten metal, which is beneficial to the formation of austenite in the cast iron, improving the quenching permeability of the cast iron and the matrix toughness of the cast iron. This changes the traditional process of adding nitrogen during the smelting process. Under atmospheric pressure, the solubility of nitrogen in the molten metal is certain, and a large amount of nitrogen overflows the molten metal, making it difficult to add nitrogen and the addition amount is insufficient; chromium metallurgically expands into the molten metal. Due to the large radius of chromium and the limited metallurgical diffusion distance, chromium mainly accumulates on the surface or below the surface of the casting and forms carbides with carbon, which is beneficial to improving the surface hardness and strength of the casting.

[0042] By adding a certain amount of copper oxide powder and boric acid powder to the coating powder, without affecting the coating's basic properties, the coating layer comes into contact with molten metal. The oxygen in the copper oxide reacts with carbon or iron to produce carbon monoxide and iron oxide. The iron oxide facilitates the peeling of the coating from the casting surface after cooling. The copper ions metallurgically diffuse into the molten metal. Due to their limited diffusion distance, they promote surface graphitization and the formation of pearlite, which helps improve the hardness and strength of the high-strength and high-toughness cast iron surface layer. The skeletal structure of the boric acid powder, silica, and iron compound enhances the strength, stability, and plasticity of the coating layer, reducing cracking during the casting process.

[0043] The contact between the molten metal and the coating layer keeps the coating layer in a high temperature state, causing the rare earth and magnesium powder to metallurgically diffuse into the molten metal, supplementing and promoting the spheroidization of graphite in high-strength and high-toughness cast iron, and improving the spheroidization effect of graphite; supplementing the addition of spheroidizing agents in the flushing method and wire feeding method.

[0044] In Example 2 of the coating for producing iron castings of the present invention, the coating cost, excluding magnesium powder and rare earth powder, specifically comprises 12 grams of quartz powder, 15 grams of magnesia powder, 40 grams of bauxite powder, 6.45 grams of sodium bentonite powder, 20 grams of water glass, 1 gram of ferric oxide powder, 3 grams of graphite powder, 2 grams of ferrochromium nitride powder, 0.5 grams of starch, 1 gram of ferrosilicon powder, 0.02 grams of defoaming agent, 0.3 grams of copper oxide powder, and 0.05 grams of boric acid powder. The remainder is impurities. The defoaming agent is specifically n-butanol.

[0045] In Example 3 of the coating used in the production of iron castings of the present invention, the coating cost excludes magnesium powder, rare earth powder, copper oxide powder, and boric acid powder. Specifically, the coating cost includes 12 grams of quartz powder, 13 grams of magnesia powder, 45 grams of bauxite powder, 5 grams of sodium bentonite powder, 16 grams of water glass, 1 gram of ferric oxide powder, 3 grams of graphite powder, 2.5 grams of ferrochromium nitride powder, 0.9 grams of starch, 1.5 grams of ferrosilicon powder, and 0.02 grams of defoaming agent. The remainder is impurities. The defoaming agent is specifically n-butanol.

[0046] In this embodiment, the particle sizes of quartz powder, magnesia powder, and bauxite powder are respectively 200-400 mesh, and the particle sizes of sodium bentonite powder and ferric oxide powder are 600-800 mesh; the particle sizes of graphite powder, chromium nitride ferroic powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder, and magnesium powder are greater than 1000 mesh; controlling the particle sizes of quartz powder, magnesia powder, and bauxite powder to 200-400 mesh is beneficial to the formation of the skeleton while improving the surface smoothness of the contact surface between the first coating layer and the mold bundle, which is beneficial to improving the surface quality of the casting; setting the particle sizes of graphite powder, chromium nitride ferroic powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder, and magnesium powder to greater than 1000 mesh makes their particle sizes more refined, which is beneficial to diffusion into the molten metal. The particle sizes of quartz powder, magnesia powder and bauxite powder are controlled at about 300 mesh respectively, and the particle sizes of sodium bentonite powder and ferric oxide powder are about 700 mesh; the particle sizes of graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder and magnesium powder are greater than 1000 mesh.

[0047] The preparation method of the coating used in the production of cast iron parts of the present invention:

[0048] S1: preparing raw materials, crushing, grinding and screening the raw materials used to prepare the coating to obtain quartz powder, magnesia powder, bauxite powder, ferric oxide powder, graphite powder, chromium ferronitride powder, starch, ferrosilicon powder and copper oxide powder that meet the particle size requirements; directly selecting sodium bentonite, water glass, defoaming agent, boric acid powder, rare earth powder and magnesium powder that meet the requirements.

[0049] S2: Sprinkling and preliminary mixing: Quartz powder, magnesia powder, bauxite powder, ferric oxide powder, graphite powder, ferrochromium nitride powder, ferrosilicon powder, and copper oxide powder are sprinkled in proportion and added to a mixing machine. The mixture is stirred for 0.5 to 1 hour to obtain a preliminary mixture. The specific stirring and mixing time is 0.8 hours. In other embodiments, the stirring and mixing time is 0.5 hours or 1 hour instead of 0.8 hours.

[0050] S3: Heating and stirring: The preliminary mixture is introduced into a heated mixer. While stirring, water glass, defoamer, and boric acid powder are added in sequence and at intervals. The mixture is heated during stirring, with the heating temperature controlled at 70-80°C and the stirring time controlled at 2-3 hours to obtain an intermediate mixture. This facilitates the loss of moisture from the water glass, defoamer, and boric acid powder while preventing excessive temperature and oxidation. The heating temperature is specifically 75°C, and the stirring time is 2.5 hours. The water glass, defoamer, and boric acid powder are dispersed and added to the heated mixer, with the interval between additions controlled at 0.4 hours. In other embodiments, the heating temperature can be set to 70°C, the stirring time can be set to 3 hours, and the defoamer and boric acid powder can be dispersed and added to the heated mixer, with the interval between additions controlled at 0.5 hours. Alternatively, the heating temperature can be set to 80°C, the stirring time can be set to 2 hours, and the defoamer and boric acid powder can be dispersed and added to the heated mixer, with the interval between additions controlled at 0.3 hours.

[0051] S4: Low-temperature stirring: The intermediate mixture is added to a blender. While stirring, starch, rare earth powder, and magnesium powder are added in sequence and mixed evenly. The temperature is controlled below 45°C during stirring, and the stirring time is controlled between 6 and 8 hours. After stirring, the coating is obtained. The temperature is controlled below 45°C. During the stirring process, the temperature is prevented from being too high, which may cause oxidation of the starch, rare earth powder, and magnesium powder. The coating composition is changed. The heating temperature is specifically 40°C and the stirring time is 7.5 hours. In other embodiments, the heating temperature is 45°C and the stirring time is 6 hours.

[0052] S5: Bag and seal: put the coating into bags according to the amount and seal them.

[0053] In this embodiment, the mixer used in steps S2, S3, and S4 is an integrated mixer, which includes a heating device, a cooling device, and a temperature detection device. By properly controlling the heating and cooling devices, preliminary mixing, heated stirring, and low-temperature stirring of the materials are achieved, shortening the production process and improving production efficiency. In other embodiments, preliminary mixing, heated stirring, and low-temperature stirring can be performed by three mixers separately.

[0054] In the production process of high-strength and high-toughness ductile iron, when the coating of the present invention is applied to lost foam casting or brushed on the inner surface of the sand mold or the outer surface of the sand core, the coating layer improves the surface finish and air permeability, improves the surface quality of the casting (such as: improving the surface finish and flatness, avoiding fleshiness or burrs, etc.), reduces or avoids the formation of casting defects (such as: cannot be poured, air holes, air pockets, etc.), and some components in the coating penetrate into the molten iron, optimize the molten iron, and improve the performance of the casting; the scrap rate of castings caused by casting defects caused by the coating can be controlled within 0.2%. Destructive sampling of high-strength and high-toughness ductile iron castings is carried out for mirror observation. The graphite is spherical, the spheroidization rate is ≥98%, and the spheroidization level is level 1, specifically as follows Figure 1 As shown; the pearlite content is between 45 and 55, as shown in Figure 2 shown.

[0055] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A coating for the production of cast iron parts, characterized in that: The ingredients include, by weight percentage, 12-15 parts of quartz powder, 13-15 parts of magnesia powder, 40-45 parts of bauxite powder, 5-8 parts of sodium bentonite powder, 15-20 parts of water glass, 1-2 parts of ferric oxide powder, 2-3 parts of graphite powder, 2-4 parts of chromium ferronitride powder, 0.5-1 part of starch, 1-2 parts of ferrosilicon powder, 0.02-0.03 parts of defoaming agent, 0.3-0.5 parts of copper oxide powder, 0.05-0.1 parts of boric acid powder, 0.1-0.2 parts of rare earth powder and 0.05-0.1 parts of magnesium powder; the raw materials are stirred and mixed uniformly to prepare the coating; the stirring process is divided into preliminary mixing, heating stirring and low-temperature stirring; the heating stirring temperature is controlled at 70-80°C, and the stirring time is controlled at 2-3 hours; the low-temperature stirring temperature is controlled below 45°C, and the stirring time is controlled at 6-8 hours.

2. The coating for producing iron castings according to claim 1, characterized in that: The particle size of the quartz powder, magnesia powder and bauxite powder is 200-400 mesh, the particle size of the sodium bentonite powder and ferric oxide powder is 600-800 mesh; the particle size of the graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder and magnesium powder is greater than 1000 mesh.

3. The coating for producing iron castings according to claim 2, characterized in that: The defoaming agent is specifically n-octanol or n-butanol.

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