A method for manufacturing lost foam iron castings using a novel coating

Abstract

The invention relates to a method for manufacturing a lost foam cast iron part using a novel coating. The method comprises the steps of preparing a foam block, preparing a mold bundle, preparing a first coating layer, drying for the first time, preparing a second coating layer, drying for the second time, preparing a third coating layer, drying for the third time, filling sand and vibrating, negative pressure pouring, and opening and dropping sand; preparing a coating layer on the surface of the mold bundle and dividing it into three layers, namely, a first coating layer, a second coating layer and a third coating layer; arranging the coating layer into three layers, so that the coating layer meets the premise of strength and stability, improving the surface finish and air permeability of the coating layer, improving the surface quality of the cast iron part (such as improving the surface finish and flatness, avoiding excess flesh or burrs, etc.), reducing or avoiding the formation of casting defects (such as: not pouring, pores, air pockets, etc.); while improving the mechanical properties of the cast iron part, reducing or preventing the cast iron part from being scrapped due to casting defects caused by the coating.

Description

Technical Field

[0001] The invention belongs to the technical field of lost foam casting, and in particular relates to a method for manufacturing lost foam iron castings using a novel coating. Background Art

[0002] Lost foam casting, also known as "full mold casting", is a method of bonding a foam model and a pouring system model that are similar in size and shape to the cast iron part into an integral foam model. After the surface of the integral foam model is coated with refractory material and dried, it is buried in dry sand particles and vibrated to form a compact. Pouring under negative pressure conditions, during the pouring process, the high temperature of the molten metal causes the integral foam model to gasify, and the molten metal fills the model position, and the molten metal solidifies and cools to form a cast iron part. In the process of producing cast iron parts using the lost foam casting method, the sand particles are adhered and compacted by negative pressure, avoiding the use of binders and allowing the sand particles to be reused continuously. Reducing the generation of waste sand is beneficial to environmental protection.

[0003] The structure of the lost foam model is as described in the Chinese utility model patent with the authorization announcement number CN205020741U, "A lost foam casting model". The lost foam casting model includes a lost foam model, and the surface of the foam model has three layers of coating, which are, from the inside to the outside, a coating layer, a bonded casting sand layer, and a coating layer, so that a coating composed of two layers of coating and one layer of sand is formed on the surface of the foam model. In the lost foam casting production, the coating layer of the foam model plays a very important role in the formation of cast iron parts. The quality of the coating layer will directly affect the surface quality of the cast iron parts (such as surface finish, flatness, fleshiness or burrs, etc.) and the formation of casting defects of the cast iron parts (such as: inability to pour, pores, slag inclusions, gas pockets, etc.); therefore, the quality of the lost foam casting model will directly affect the generation of casting defects and the surface quality of the cast iron parts. Summary of the invention

[0004] In order to improve the quality of high-strength and high-toughness cast iron parts and prevent or reduce the occurrence of casting defects, the present invention provides a method for manufacturing lost foam cast iron parts using a new coating; in order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for manufacturing lost foam iron castings using a novel coating, characterized in that the steps are as follows:

[0006] (1) preparing a foam block by foaming the foam particles to form a square foam block;

[0007] (2) preparing a mold bundle, according to the casting process requirements, using a wire cutting method to prepare the cast iron foam and the pouring system foam, and using a foam adhesive to glue the casting foam and the pouring system foam to form a mold bundle;

[0008] (3) preparing a first coating layer, mixing the first coating powder and the water base in a ratio of 0.8 to 1.2:1 and stirring them evenly to form a first coating suspension; dipping the mold bundle in the first coating suspension, the dipping time is controlled to be 3 to 5 seconds, taking it out and draining it, and forming a first coating layer on the surface of the mold bundle; the first coating powder mainly comprises: by weight percentage, quartz powder 12 to 15, magnesia powder 13 to 15, bauxite powder 40 to 45, sodium bentonite powder 5 to 8, water glass 15 to 20, iron oxide powder 1 to 2, graphite powder 2 to 3, chromium nitride iron powder 2 to 4, starch 0.5 to 1, ferrosilicon powder 1 to 2 and defoaming agent 0.02 to 0.03;

[0009] (4) First drying: the drained mold bundle is placed in the first drying chamber for drying. The temperature in the drying chamber is controlled at 40-50° C. and the drying time is 48-72 hours.

[0010] (5) preparing a second coating layer, dipping the mold beam into a binder for 1 to 2 seconds, taking it out, and attaching a second coating on the surface; the binder is mainly water glass, and the main components of the second coating include: by weight percentage, 97 to 99.5 of pearl sand particles and 0.1 to 0.5 of starch.

[0011] (6) Second drying: placing the mold bundle in step 5 in a second drying chamber for drying; the temperature in the drying chamber is controlled at 60 to 70° C. and the drying time is 6 to 8 hours;

[0012] (7) preparing a third coating layer, mixing the third coating powder and alcohol at a ratio of 1.1 to 1.3:1 to form a third coating suspension, dipping the mold bundle in step 6 in the third coating suspension for a dipping time of 2s to 4s, taking out and draining, and forming a third coating layer on the surface of the mold bundle in step 6; the third coating powder mainly comprises: quartz powder 75 to 80, sodium bentonite powder 5 to 8, water glass 10 to 20, starch 0.5 to 1, and defoaming agent 0.02 to 0.03 by weight;

[0013] (8) drying for the third time, placing the mold bundle drained in step 7 in a third drying chamber for drying, wherein the temperature in the drying chamber is controlled at 40 to 50° C., and the drying time is 24 to 36 hours;

[0014] (9) Filling sand and vibrating, placing the mold bundle in step 8 in a sand box, filling the sand box with pearl sand, vibrating it and sealing it;

[0015] (10) Negative pressure pouring: vacuum equipment is used to evacuate the sand box, and the negative pressure is controlled at 0.02-0.03Mpa during pouring; during the pouring process, the foam is gasified and filled with molten metal;

[0016] (11) Unpack and remove sand, clean the surface paint, remove the pouring system, and complete the production of cast iron parts.

[0017] The beneficial effects of the method for making lost foam iron castings using the novel coating of the present invention are as follows:

[0018] (1) When using lost foam cast iron parts to produce high-strength and high-toughness cast iron parts, the coating layer prepared on the surface of the mold bundle is divided into three layers, namely, the first coating layer, the second coating layer and the third coating layer. The first coating layer is the surface layer, which is directly in contact with the molten metal after the mold bundle is gasified. The second coating layer is the skeleton layer, which provides stable support for the coating layer; the third coating layer is the back layer, which is used to contact with the precious sand particles in the sand box; the coating layer is set into three layers, so that the coating layer meets the premise of strength and stability, and the surface finish and air permeability of the coating layer are improved, the surface quality of the cast iron parts is improved (such as: improving the surface finish and flatness, avoiding excess flesh or burrs, etc.), and reducing or avoiding the formation of casting defects (such as: inability to pour, air holes, air pockets, etc.).

[0019] (2) When preparing the mold bundle, wire cutting is used to prepare the cast iron part foam and the pouring system foam, so as to improve the dimensional accuracy of the cast iron part foam and the pouring system foam and avoid defects such as burrs formed on the foam surface during processing, thereby improving the dimensional accuracy of the mold bundle formed by gluing, making the mold bundle surface smooth, and improving the surface quality of the lost foam cast iron part.

[0020] (3) After many tests, it was determined that the mixing ratio between the first coating powder and the water base was 0.8 to 1.2:1, so that the viscosity of the mixed first coating suspension met the wall hanging requirements, and the first coating suspension was stably attached to the mold beam surface during the dipping process; the dipping time was controlled at 3 to 5 seconds, so that the first coating suspension was fully attached to the surface of the mold beam.

[0021] (4) By rationally designing the composition and content of each component of the first powder, quartz powder, magnesia powder and bauxite powder are used as the skeleton structure of the first coating. Through multiple tests, the ratio of quartz powder, magnesia powder and bauxite powder is determined so 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, so that the magnesia powder and the bauxite powder are adhered to each other as a whole, which is beneficial to improving the stability of the skeleton; the use of magnesia powder is rationally controlled to reduce the cost. 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 first coating suspension, which is beneficial to the suspension of the first coating suspension on the surface of the mold beam. The content of water glass is controlled between 15 and 20, so that the first coating suspension has a certain viscosity while preventing excessive addition and damaging other properties of the first coating powder.

[0022] (5) During the mold beam gasification process, the iron oxide powder reacts with the carbon or iron in the molten metal to produce carbon monoxide gas and iron oxide, which reduces the amount of carbon deposits after the mold beam gasification. The iron oxide is conducive to the peeling of the coating from the surface of the cast iron after the cast iron is cooled. During the contact between the coating and the molten metal, part of the graphite powder and ferrosilicon powder undergo metallurgical diffusion and diffuse into the molten metal to provide graphite nuclei, which is conducive to the graphitization of carbon in the high-strength and high-toughness cast iron; however, when the content of graphite powder and ferrosilicon powder in the first coating powder is too high, the performance of the coating is reduced.

[0023] (6) 0.5-1% starch is set in the first coating powder. During the pouring of molten metal, the starch is carbonized and gasified at high temperature. Under the premise of not affecting the strength, fine pores are formed in the first coating layer, which is beneficial to improve the air permeability of the first coating layer, facilitate the discharge of gas, and reduce the occurrence of casting defects such as air pockets.

[0024] (7) 2 to 4 layers of ferrochromium nitride are arranged in the first coating body. During the pouring of the molten metal, the ferrochromium nitride decomposes, and part of the nitrogen and chromium metallurgically diffuse into the molten metal, thereby 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, thereby changing the traditional process of adding nitrogen during the smelting process. Under atmospheric pressure, the solubility of nitrogen in the molten metal is constant, and a large amount of nitrogen overflows from the molten metal, making it difficult to add nitrogen and the amount of nitrogen added insufficient. Chromium metallurgically expands into the molten metal. Due to the large radius of chromium and the limited metallurgical diffusion distance, chromium is mainly concentrated on the surface or below the surface of the cast iron part, and forms carbides with carbon, which is beneficial to improving the surface hardness and strength of the cast iron part.

[0025] (8) The mold bundle with the first coating layer is dried in the first drying chamber, and the temperature is controlled at 40-50°C to prevent the heating temperature from being too high, which will cause the water in the first coating layer to dissipate too quickly, causing the first coating layer to crack and reduce the performance of the first coating layer; the drying time is 48-72 hours to allow it to dry fully and avoid water residue in the first coating layer.

[0026] (9) The second coating is mainly composed of abrasive particles. The high roundness of the abrasive particles is conducive to the formation of pores between the abrasive particles. Under the premise of ensuring strength, the air permeability of the coating layer is improved. During the pouring of molten metal, the starch is gasified and carbonized to form pores, which further improves the air permeability. The dipping time is controlled at 1 to 2, so that under the premise of sufficient dipping, the dipping time is prevented from damaging the first coating layer.

[0027] (10) The main components of the third coating powder are quartz powder, sodium bentonite powder, water glass and starch. By rationally designing the ratio between the components, the third coating layer is made to have a lower working stability under the heat insulation effect of the first coating layer and the second coating layer. Quartz powder is selected. During the pouring process, the performance of the quartz powder is stable, which is beneficial to reducing production costs.

[0028] (11) The third drying temperature is controlled at 40-50°C and the drying time is 24-36 hours, which is conducive to the full volatilization of alcohol, prevents cracking of the coating layer after drying, and improves the performance of the coating layer.

[0029] (12) Use jelly sand as the sand box filler. The high roundness of jelly sand is conducive to the formation of vacuum negative pressure. The negative pressure is controlled at 0.02-0.03Mpa so that the gas generated by the gasification of the mold bundle can be sucked away.

[0030] Furthermore, the main components of the first coating powder also include copper oxide powder and boric acid powder. In terms of weight percentage, the copper oxide powder is 0.3-0.5, and the boric acid powder content is 0.05-0.1.

[0031] Beneficial effects: When a certain amount of copper oxide powder and boric acid powder are added to the first coating powder, and the first coating layer contacts the molten metal without affecting the basic properties of the coating, the oxygen in the copper oxide reacts with carbon or iron to produce carbon monoxide and iron oxide, reducing carbon deposition. Iron oxide is conducive to the peeling of the coating from the surface of the cast iron after the cast iron is cooled; copper ions metallurgically diffuse into the molten metal, and due to the limited diffusion distance of copper ions, the surface graphitization and the formation of pearlite are promoted, which is conducive to improving the hardness and strength of the surface layer of high-strength and high-toughness cast iron. The skeleton structure of the boric acid powder, silicon dioxide and iron compound improves the strength, stability and plasticity of the first coating layer and reduces the cracking of the coating during the pouring process.

[0032] Furthermore, the main components of the first coating powder 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.

[0033] Beneficial effects: After the mold beam is gasified, the molten metal contacts the first coating layer, making the first 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 agent in the punching method and wire feeding method.

[0034] Furthermore, the particle sizes of the quartz powder, magnesia powder and bauxite powder are respectively 200-400 meshes, the particle sizes of the sodium bentonite powder and ferric oxide powder are 600-800 meshes; 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 meshes.

[0035] Beneficial effects: The particle size of quartz powder, magnesia powder and bauxite powder is controlled within 200-400 meshes, which is beneficial to the formation of the skeleton and improves 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 cast iron parts. 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.

[0036] Furthermore, the defoamer in the first coating powder has the same component as the defoamer in the third coating powder, and is uniformly n-octanol or n-butanol.

[0037] Beneficial effect: the defoaming agent in the first coating powder and the third coating powder is selected as n-octanol or n-butanol, which reduces the production components and has the characteristics of good defoaming effect and stable performance.

[0038] Furthermore, the main component of the second coating also includes sodium bentonite, and the content of the sodium bentonite is 1 to 1.5 in weight percentage.

[0039] Beneficial effect: sodium bentonite is added to the second coating. During the pouring of molten metal, the second coating layer is in a high temperature state. The sodium ions in the sodium bentonite combine with the silicate ions in the water glass to form sodium silicate. The sodium silicate is sticky and adheres to the pearl sand particles, which is beneficial to improve the stability of the second coating.

[0040] Furthermore, the particle size of the pearl sand is between 50 and 100 meshes, and the particle size of the sodium bentonite and starch is between 600 and 800 meshes.

[0041] Beneficial effects: The roundness of the beads is high, and the selection of 50-100 mesh is conducive to the formation of gaps between the beads. After the starch is gasified or carbonized, it is conducive to the starch particle size of 600-800 mesh, so that the formed pores are small and uniform, which reduces the influence on the strength of the second coating layer and improves the air permeability of the second coating layer.

[0042] Furthermore, in step 5, during the process of preparing the second coating layer, the second coating is attached to the surface of the mold bundle in step 4 by pouring; the second coating flows from above, and the mold bundle is located directly below and rotates continuously, so that the second coating is poured on the surface of the mold bundle in step 4.

[0043] Beneficial effect: The second coating is dripped on the surface of the mold bundle by the dripping method, so that the second coating layer is dripped evenly, which is beneficial to improving the stability of the second coating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1This is one of the metallographic structure photos of high-strength and high-toughness ductile iron produced by the method for making lost foam cast iron parts using the new coating of the present invention (100 times without corrosion);

[0045] Figure 2 This is the second metallographic structure photo of high-strength and high-toughness ductile iron produced by the method for making lost foam cast iron parts using the new coating of the present invention (200 times without corrosion). DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0047] The specific steps of Example 1 of the method for making lost foam iron castings using the new coating of the present invention are as follows:

[0048] (1) Prepare foam blocks by foaming plastic particles to form square foam blocks.

[0049] (2) Prepare the mold bundle. According to the casting process requirements, prepare the cast iron foam and the pouring system foam by wire cutting, and use the foam adhesive to glue the casting foam and the pouring system foam to form a mold bundle. When preparing the mold bundle, the cast iron foam and the pouring system foam are prepared by wire cutting to improve the dimensional accuracy of the cast iron foam and the pouring system foam, avoid the formation of burrs and other defects on the foam surface during the processing, thereby improving the dimensional accuracy of the mold bundle formed by gluing, making the mold bundle surface smooth, and improving the surface quality of the lost foam cast iron parts.

[0050] (3) Prepare the first coating layer, mix the first coating powder and the water base in a ratio of 0.8 to 1.2:1 and stir evenly to form a first coating suspension; dip the mold bundle in the first coating suspension, the dipping time is controlled to be 3 to 5 seconds, take it out and drain it, and form the first coating layer on the surface of the mold bundle. After many tests, it is determined that the mixing ratio between the first coating powder and the water base is 0.8 to 1.2:1, so that the viscosity of the mixed first coating suspension meets the requirements of wall hanging, and the dipping process is conducive to the stable attachment of the first coating suspension to the surface of the mold bundle; the dipping time is controlled to 3 to 5 seconds, so that the first coating suspension is fully attached to the surface of the mold bundle. In this embodiment, the mixing ratio of the first coating powder and the water base is specifically 1:1, and the dipping time is controlled to 4 seconds; the mixing ratio between the first coating powder and the water base can be adjusted to change the consistency of the first coating suspension. In other embodiments, in order to increase the thickness of the first coating layer, the mixing ratio of the first coating powder and the water base is adjusted to 1.2:1, the dipping time is controlled at 5s, the consistency of the first coating suspension is increased, and the dipping time is extended, thereby thickening the thickness of the first coating layer; when the thickness of the first coating layer needs to be reduced, the mixing ratio of the first coating powder and the water base is adjusted to 0.8:1, the dipping time is controlled at 3s, the consistency of the first coating suspension is reduced, the dipping time is shortened, and the thickness of the first coating layer is reduced.

[0051] (4) First drying: Place the drained mold bundle in the first drying chamber for drying. The temperature in the drying chamber is controlled at 40-50°C and the drying time is 48-72 hours. The temperature is controlled at 40-50°C to prevent the heating temperature from being too high, causing the water in the first coating layer to lose too quickly, causing the first coating layer to crack and reduce the performance of the first coating layer. The drying time is 48-72 hours to fully dry it and avoid water residue in the first coating layer. In this embodiment, the temperature in the drying chamber is specifically controlled at 45°C and the drying time is controlled at 60 hours. In other embodiments, the temperature in the drying chamber is specifically controlled at 40°C and the drying time is controlled at 72 hours; or the temperature in the drying chamber is specifically controlled at 50°C and the drying time is controlled at 48 hours.

[0052] (5) Prepare the second coating layer, dip the mold bundle into the binder, the dipping time is controlled to be 1 to 2 seconds, take it out, and attach the second coating to the surface of the mold bundle; the binder is mainly water glass; the dipping time is controlled to be 1 to 2 seconds, so that under the premise of sufficient dipping, the dipping time process is prevented from damaging the first coating layer. In this embodiment, during the preparation of the second coating layer, the time for dipping the mold bundle in water glass is controlled to be 1.5 seconds, and the second coating is attached to the surface of the mold bundle in step 4 by pouring; the second coating flows from the top, the mold bundle is located directly below, and it is continuously rotated so that the second coating is poured on the surface of the mold bundle in step 4; the second coating is poured on the surface of the mold bundle by pouring, so that the second coating layer is poured evenly, which is beneficial to improve the stability of the second coating layer. In other embodiments, during the preparation of the second coating layer, the time for dipping the mold bundle in water glass is controlled to be 1 second or 2 seconds, and the second coating is attached to the surface of the mold bundle specifically by rolling and sticking in the second coating directly after the mold bundle is dipped in water glass.

[0053] (6) Second drying: Place the mold bundle in step 5 in a second drying chamber for drying. The temperature in the drying chamber is controlled at 60-70°C for 6-8 hours. This allows the water in the water glass to fully dissipate and improves the stability of the second coating layer. In this embodiment, the temperature is specifically controlled at 65°C and the drying time is 7 hours. In other embodiments, the temperature is controlled at 60°C and the drying time is 8 hours; or the temperature is controlled at 70°C and the drying time is 6 hours.

[0054] (7) Prepare a third coating layer, mix the third coating powder and alcohol at a ratio of 1.1 to 1.3:1, and stir evenly to form a third coating suspension, dip the mold bundle in step 6 into the third coating suspension, and control the dipping time to be 2s to 4s, take it out and drain it, and form a third coating layer on the surface of the mold bundle in step 6. In this embodiment, the mixing ratio of the third coating powder and alcohol is specifically 1.2:1, and the dipping time is 3s. In other embodiments, the mixing ratio of the third coating powder and alcohol is specifically 1.1:1, and the dipping time is 4s; or the mixing ratio of the third coating powder and alcohol is specifically 1.3:1, and the dipping time is 2s.

[0055] (8) Third drying: the mold bundle drained in step 7 is placed in a third drying chamber for drying. The temperature in the drying chamber is controlled at 40-50°C and the drying time is 24-36 hours. This is conducive to the full volatilization of the alcohol, preventing the coating layer from cracking after drying, and improving the performance of the coating layer. In this embodiment, the temperature in the third drying chamber is controlled at 45°C and the drying time is 30 hours. In other embodiments, the temperature in the third drying chamber is controlled at 40°C and the drying time is 36 hours, or the temperature in the third drying chamber is controlled at 50°C and the drying time is 24 hours.

[0056] (9) Filling sand and vibrating it: Place the mold bundle in step 8 in a sand box, fill the sand box with gemstone sand, vibrate it and seal it; gemstone sand is used as the sand box filling material. The gemstone sand has high roundness and the gaps between the particles are conducive to forming negative pressure in the sand box.

[0057] (10) Negative pressure pouring: vacuum equipment is used to evacuate the sand box, and the negative pressure is controlled at 0.02-0.03Mpa during pouring; during the pouring process, the foam is gasified and filled with molten metal; negative pressure is formed in the sand core, which is conducive to the suction of the gas generated after the foam is gasified. In this embodiment, the negative pressure is controlled at 0.025Mpa during pouring. In other embodiments, the negative pressure is controlled at 0.02Mpa or 0.03Mpa instead of 0.025Mpa.

[0058] (11) Unpack and remove sand, clean the surface paint, remove the pouring system, and complete the production of cast iron parts; when unpacking and removing sand, the temperature of the cast iron parts should be lower than 500℃; prevent the unpacking process from being too early, which may cause the cast iron parts to be insufficient in strength and cause deformation, or cool too quickly and cause stress concentration.

[0059] The main components of the first coating powder include: by weight percentage, quartz powder 12-15, magnesia powder 13-15, bauxite powder 40-45, sodium bentonite powder 5-8, water glass 15-20, iron oxide powder 1-2, graphite powder 2-3, chromium ferronitride powder 2-4, starch 0.5-1, ferrosilicon powder 1-2 and defoamer 0.02-0.03; by reasonably designing the composition and content of each component of the first powder, quartz powder, magnesia powder and bauxite powder are used as the skeleton structure of the first coating, and it is determined through multiple tests that the quartz powder, magnesia powder and bauxite powder are The ratio of quartz powder to sodium ions in sodium-based bentonite allows the skeleton structure to 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 the cost. 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 first coating suspension, which is beneficial to the suspension of the first coating suspension on the surface of the mold bundle.

[0060] During the gasification of the mold bundle, the iron oxide powder reacts with the carbon or iron in the molten metal to produce carbon monoxide gas and iron oxide, which reduces the amount of carbon deposits after the mold bundle is gasified. The iron oxide is conducive to the peeling of the coating from the surface of the cast iron after the cast iron is cooled. During the contact between the coating and the molten metal, part of the graphite powder and ferrosilicon powder undergo metallurgical diffusion and diffuse into the molten metal to provide graphite nuclei, which is conducive to the graphitization of carbon in the high-strength and high-toughness cast iron; however, when the content of graphite powder and ferrosilicon powder in the first coating powder is too high, the performance of the coating is reduced.

[0061] 0.5-1% starch is set in the first coating powder. 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 first coating layer, which is beneficial to improve the air permeability of the first coating layer, facilitate the discharge of gas, and reduce the occurrence of casting defects such as air pockets.

[0062] 2 to 4 ferrochromium nitrides are arranged in the first coating body. During the pouring of the molten metal, the ferrochromium nitride decomposes, and part of the nitrogen and chromium metallurgically diffuse into the molten metal, thereby 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, and changing 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 from the molten metal, making it difficult to add nitrogen and the amount of nitrogen added insufficient; chromium metallurgically expands into the molten metal, and due to the large radius of chromium and the limited metallurgical diffusion distance, it is mainly concentrated on the surface or below the surface of the cast iron part, and forms carbides with carbon, which is beneficial to improving the surface hardness and strength of the cast iron part.

[0063] In this embodiment, the main components of the first coating powder also include copper oxide powder, boric acid powder, rare earth powder and magnesium powder. According to the weight percentage, the copper oxide powder is 0.3-0.5, the boric acid powder content is 0.05-0.1; the rare earth powder content is 0.1-0.2, and the magnesium powder content is 0.05-0.1. A certain amount of copper oxide powder and boric acid powder are added to the first coating powder. Under the premise that the basic properties of the coating are not affected, the first coating layer contacts the molten metal, and the oxygen in the copper oxide reacts with carbon or iron to produce carbon monoxide and iron oxide, reducing carbon deposition. Iron oxide is conducive to the peeling of the coating from the surface of the cast iron after the cast iron is cooled; copper ions metallurgically diffuse into the molten metal. Due to the limited diffusion distance of copper ions, the surface graphitization and the formation of pearlite are promoted, which is conducive to improving the hardness and strength of the surface layer of high-strength and high-toughness cast iron. The skeleton structure of the compound of boric acid powder, silicon dioxide and iron improves the strength, stability and plasticity of the first coating layer and reduces the cracking of the coating during the casting process. After the mold beam is gasified, the molten metal contacts the first coating layer, making the first 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 agent in the punching method and wire feeding method.

[0064] In this embodiment, the components of the first coating powder are specifically 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, defoaming agent 0.025, copper oxide powder 0.35, boric acid powder 0.08, rare earth powder 0.15 and magnesium powder 0.08, and the rest are impurities.

[0065] The components of the first coating powder in Example 2 of the method for making lost foam cast iron parts using a new coating of the present invention are specifically 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.

[0066] The first coating powder in Example 3 of the method for making lost foam cast iron parts using the new coating of the present invention comprises 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, and the rest are impurities.

[0067] The first coating powder in Example 4 of the method for making lost foam cast iron parts using a new coating of the present invention comprises quartz powder 12, magnesia powder 15, bauxite powder 40, sodium bentonite powder 6.45, water glass 20, ferric oxide powder 1, graphite powder 3, chromium ferronitride powder 2, starch 0.5, ferrosilicon powder 1, defoaming agent 0.02, copper oxide powder 0.3 and boric acid powder 0.05, and the rest are impurities.

[0068] The first coating powder in Example 5 of the method for making lost foam cast iron parts using a new coating of the present invention comprises quartz powder 12, magnesia powder 13, bauxite powder 45, sodium bentonite powder 5, water glass 16, ferric oxide powder 1, graphite powder 3, chromium ferronitride powder 2.5, starch 0.9, ferrosilicon powder 1.5, defoaming agent 0.02, and the rest are impurities.

[0069] In this embodiment, the particle sizes of quartz powder, magnesia powder and bauxite powder are respectively 200-400 meshes, and the particle sizes of sodium bentonite powder and ferric oxide powder are 600-800 meshes; 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 meshes; controlling the particle sizes of quartz powder, magnesia powder and bauxite powder to 200-400 meshes 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 cast iron part; and setting the particle sizes of graphite powder, ferrochromium nitride powder, starch, ferrosilicon powder, copper oxide powder, boric acid powder, rare earth powder and magnesium powder to greater than 1000 meshes makes the particle size 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.

[0070] The main components of the second coating include: 97-99.5% of jelly sand particles and 0.1-0.5% of starch by weight; the second coating mainly consists of jelly sand particles, which have high roundness, which is conducive to the formation of pores between jelly sand particles, and improves the air permeability of the coating layer under the premise of ensuring strength. During the pouring of molten metal, starch gasifies and carbonizes to form pores, further improving the air permeability. In this embodiment, the main components of the second coating also include sodium bentonite, and the content of sodium bentonite is 1-1.5% by weight; sodium bentonite is added to the second coating, and during the pouring of molten metal, the second coating layer is in a high temperature state, and the sodium ions in the sodium bentonite combine with the silicate ions in the water glass to form sodium silicate. Sodium silicate has viscosity and adheres to jelly sand particles, which is conducive to improving the stability of the second coating. The components of the second coating are specifically 98.5% jelly sand particles, 0.45% starch and 1% sodium bentonite, and the rest are impurities. In Example 2, the second coating specifically includes 98% of quartz sand particles, 0.45% of starch, and 1.5% of sodium bentonite, and the rest are impurities. In Example 3, the second coating specifically includes 99.45% of quartz sand particles and 0.5% of starch, and the rest are impurities.

[0071] In this embodiment, the particle size of the pearl sand is between 50 and 100 meshes, and the particle size of the sodium bentonite and starch is 600 to 800 meshes; the pearl sand has a high roundness, and the selection of 50 to 100 meshes is conducive to the formation of gaps between the pearl sands. After the starch is gasified or carbonized, it is conducive to the starch particle size of 600 to 800 meshes, so that the formed pores are small and uniform, and the air permeability of the second coating layer is improved under the premise of reducing the influence on the strength of the second coating layer. The particle size of the pearl sand is specifically about 80 meshes, and the particle size of the sodium bentonite and starch is about 700 meshes.

[0072] The main components of the third coating powder include: quartz powder 75-80, sodium bentonite powder 5-8, water glass 10-20, starch 0.5-1 and defoamer 0.02-0.03 by weight percentage; the main components of the third coating powder are quartz powder, sodium bentonite powder, water glass and starch; by reasonably designing the ratio between the components, the third coating layer is made to work more stably under the heat insulation effect of the first coating layer and the second coating layer, and quartz powder is selected. During the pouring process, the performance of quartz powder is stable, which is conducive to reducing production costs. The defoamer in the first coating powder is the same as the defoamer in the third coating powder. In this embodiment, the defoamers are all n-octanol. In other embodiments, the defoamers are all n-butanol.

[0073] When producing high-strength and high-toughness spheroidal milled iron castings using the method for making lost foam cast iron parts using the new coating in Examples 1-5 of the present invention, the surface finish and air permeability of the coating layer improve the surface quality of the cast iron parts (such as: improving the surface finish and flatness, avoiding excess flesh or burrs, etc.), and reducing or avoiding the formation of casting defects (such as: not being able to pour, pores, air pockets, etc.). The scrap rate of cast iron parts caused by casting defects caused by the coating is controlled within 0.2%. Destructive sampling is performed on the high-strength and high-toughness spheroidal milled iron castings for mirror observation. The graphite is spherical, the spheroidization rate is ≥98%, and the spheroidization level is level 1. Specifically, Figure 1 As shown; the pearlite content is between 45 and 55, as shown Figure 2 shown.

[0074] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0075] 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 method for producing lost foam iron castings using a novel coating, characterized in that: Here are the steps: (1) preparing a foam block by foaming the foam particles to form a square foam block; (2) preparing a mold bundle, according to the casting process requirements, using a wire cutting method to prepare the cast iron foam and the pouring system foam, and using a foam adhesive to glue the casting foam box and the pouring system foam to form a mold bundle; (3) preparing a first coating layer, mixing the first coating powder and the water base in a ratio of 0.8 to 1.2:1 to form a first coating suspension; dipping the mold bundle in the first coating suspension for 3 to 5 seconds, taking it out and draining it, thereby forming a first coating layer on the surface of the mold bundle; The first coating powder mainly comprises, by weight percentage, quartz powder 12-15, magnesia powder 13-15, bauxite powder 40-45, sodium bentonite powder 5-8, water glass 15-20, iron oxide powder 1-2, graphite powder 2-3, chromium nitride iron powder 2-4, starch 0.5-1, ferrosilicon powder 1-2 and defoamer 0.02-0.03; (4) First drying: the mold bundle after draining is placed in the first drying chamber for drying. The temperature in the drying chamber is controlled at 40-50° C. and the drying time is 48-72 hours. (5) preparing a second coating layer, dipping the mold beam into a binder, the dipping time is controlled to be 1 to 2 seconds, taking it out, and attaching the second coating on the surface; the binder is mainly water glass, and the main components of the second coating include: by weight percentage, 97 to 99.5 of pearl sand particles and 0.1 to 0.5 of starch; (6) Second drying: placing the mold bundle in step 5 in a second drying chamber for drying; the temperature in the drying chamber is controlled at 60 to 70° C. and the drying time is 6 to 8 hours; (7) preparing a third coating layer, mixing the third coating powder and alcohol at a ratio of 1.1 to 1.3 to form a third coating suspension, dipping the mold bundle in step 6 in the third coating suspension for a dipping time of 2s to 4s, taking out and draining, and forming a third coating layer on the surface of the mold bundle in step 6; the third coating powder mainly comprises: According to the weight percentage, quartz powder 75-80, sodium bentonite powder 5-8, water glass 10-20, starch 0.5-1 and defoamer 0.02-0.03; (8) drying for the third time, placing the mold bundle drained in step 7 in a third drying chamber for drying, wherein the temperature in the drying chamber is controlled at 40 to 50° C., and the drying time is 24 to 36 hours; (9) Filling sand and vibrating, placing the mold bundle in step 8 in a sand box, filling the sand box with pearl sand, vibrating it and sealing it; (10) Negative pressure pouring: vacuum equipment is used to evacuate the sand box, and the negative pressure is controlled at 0.02-0.03Mpa during pouring; during the pouring process, the foam is gasified and filled with molten metal; (11) Unpack and remove sand, clean the surface paint, remove the pouring system, and complete the production of cast iron parts.

2. The method for making lost foam iron castings using a novel coating according to claim 1, characterized in that: The main components of the first coating powder 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.

3. The method for making lost foam iron castings using a novel coating according to claim 2, characterized in that: The main components of the first coating powder 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.

4. The method for making lost foam iron castings using a novel coating according to claim 3, characterized in that: The particle sizes of the quartz powder, magnesia powder and bauxite powder are respectively 200-400 meshes, the particle sizes of the sodium bentonite powder and ferric oxide powder are 600-800 meshes; 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 meshes.

5. The method for making lost foam iron castings using a novel coating according to claim 3 or 4, characterized in that: The defoamer in the first coating powder has the same component as the defoamer in the third coating powder, and is uniformly n-octanol or n-butanol.

6. The method for manufacturing lost foam iron castings using a novel coating according to claim 1, characterized in that: The main component of the second coating also includes sodium bentonite, and the content of the sodium bentonite is 1 to 1.5 by weight.

7. The method for manufacturing lost foam iron castings using a novel coating according to claim 6, characterized in that: The particle size of the pearl sand is between 50 and 100 meshes, and the particle size of the sodium bentonite and starch is between 600 and 800 meshes.

8. The method for manufacturing lost foam iron castings using a novel coating according to claim 7, characterized in that: In step 5, during the process of preparing the second coating layer, the second coating is attached to the surface of the mold bundle in step 4 by pouring; the second coating flows from above, and the mold bundle is located directly below and rotates continuously, so that the second coating is poured on the surface of the mold bundle in step 4.

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