Non-riser casting process for ductile iron

Abstract

The invention discloses a ductile iron dead-head-free casting process which comprises the following steps: S1, a casting mold modeling step: filling cavities of an upper half casting mold and a lower half casting mold with dry mold sand before casting, and arranging a pouring system in the cavities of the upper half casting mold and the lower half casting mold; s2, nodular cast iron smelting, wherein raw materials of nodular cast iron are put into a cupola furnace to be smelted; step S3, spheroidizing and in-ladle inoculation treatment: performing spheroidizing by adopting a dam type flushing method, putting a spheroidizing agent into a ladle pit, tamping, covering the spheroidizing agent with a thin layer of silicon iron and cast iron scraps, performing in-ladle inoculation through an inoculant, and removing scum on the surface of the molten iron after the molten iron reacts stably; s4, pouring is conducted, specifically, the molten iron is poured into a sprue, and stream inoculation is conducted by adding an inoculant in the pouring process; and S5, cooling forming is conducted, specifically, after the casting is cooled and solidified, the casting is taken out, and a sand layer on the surface of the casting is taken out.

Description

Technical Field

[0001] The invention relates to the technical field of ductile iron casting, in particular to a riser-free casting process of ductile iron. Background Art

[0002] With the development of science and technology, ductile iron, a high-strength metal material, has been used more and more widely in industrial production. In order to reduce costs, reduce equipment weight, and achieve the structural strength of parts, many castings have become thin-shell ductile iron castings, such as the base and central shaft of photovoltaic solar tracking reducers. However, the thickness of these castings is not uniform, but there are many places with thicker walls. These thick places form hot nodes and are prone to shrinkage defects. To solve the shrinkage problem, the usual way is to add risers to compensate for the shrinkage. Multiple hot nodes require multiple risers. This design not only wastes a lot of time for modeling and cutting, but also wastes a lot of metal materials and energy. At the same time, there are often holes or shrinkage at the root of the riser, causing the casting to be scrapped. Even if some units use edge-pressing risers, shrinkage holes or shrinkage often appear at the root or near the riser due to improper design of the edge-pressing riser, and the process yield of the casting is also low. Therefore, the implementation of riser-free casting process in the production of ductile iron parts is undoubtedly an important way to reduce casting costs, improve casting quality and process yield, and reduce materials and energy. A solution to the above problems is proposed below. Summary of the invention

[0003] The purpose of the present invention is to provide a riser-free casting process for ductile iron, which solves the problems raised by the above-mentioned background technology.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions:

[0005] A ductile iron riser-free casting process comprises the following steps:

[0006] Step S1, casting mold modeling step: the existing casting model is divided into an upper mold and a lower mold, and the upper mold and the lower mold are both provided with a matching mold cavity. Before casting, the mold cavity of the upper mold and the lower mold is filled with dry mold sand, and a 5-8mm sand layer is formed in the mold cavity by dry film sand, and then a layer of alcohol-based paint is painted on the outside of the sand layer. The upper mold and the lower mold with sand are assembled and fixed by screws. A pouring system is provided in the mold cavity of the upper mold and the lower mold, and the pouring system consists of a sprue and an ingend, and the sprue is connected to each ingend, and one end of the ingend is connected to the mold cavity;

[0007] Step S2, ductile iron smelting step: the raw material of ductile iron is put into a medium frequency electric furnace for smelting to obtain molten iron, the smelting temperature is 1500° C., and the mass percentages of the components in the raw material are: carbon C: 3.80%-3.9%, silicon Si: 1.0%-1.5%, manganese Mu: 0.3%-0.5%, phosphorus P≤0.05%, sulfur S<0.03%, and the rest are iron Fe;

[0008] After smelting, the molten iron is sampled for spectral inspection. The treated molten iron is tempered by adding carburizer and desulfurized to achieve the target composition of the original molten iron. The carbon equivalent CE in the molten iron is controlled between 4.30% and 4.50%.

[0009] Step S3, spheroidization, ladle inoculation treatment: spheroidization treatment is carried out by a dam-type flushing method, and generally two inoculation treatments are carried out, wherein a FeSiMg8Rt3 spheroidizer is placed in a ladle pit, compacted, a thin layer of ferrosilicon and cast iron chips is covered on the spheroidizer, and ladle inoculation is carried out by an inoculant, and the dissolved molten iron is poured into the ladle pit to carry out spheroidization and ladle inoculation treatment, and after the molten iron reacts stably, the scum on the surface of the molten iron is scraped off, and the mass percentages of the components in the molten iron after spheroidization are carbon C: 3.70%-3.8%, silicon Si: 2.1%-2.3%, manganese Mu: 0.3%-0.5%, phosphorus P≤0.05%, sulfur S<0.02%, magnesium Mg: 0.04%-0.06%, rare earth element Re: 0.02%-0.04%, copper Cu: 0.4%-0.6%, and the rest are iron Fe;

[0010] Step S4, pouring: pouring the molten iron treated in step S3 into the sprue in step S1, adding an inoculant during the pouring process to perform flow inoculation, and controlling the pouring temperature of the molten iron to be 1390-1420° C. during the pouring;

[0011] Step S5, cooling and molding: after the casting is cooled and solidified, the fixing parts on the upper and lower molds are removed, the upper and lower molds are separated, the casting is taken out, and the sand layer on the surface of the casting is removed.

[0012] Preferably, in step S1, the ingates are provided with a plurality of runners, and the ingates connecting the ingates and the cavity are of a flat structure.

[0013] Preferably, in step S1, external chillers are installed on the upper half of the mold and the lower half of the mold. The external chillers are located at the hot spots of the casting, i.e., the parts of the casting where the wall thickness is larger or the heat is concentrated. The external chillers are made of graphite chillers, and the thickness of the external chillers is 0.6-0.7 times the wall thickness of the casting.

[0014] Preferably, in step S1, a vent hole communicating with the mold cavity is provided on the top of the upper half of the casting mold.

[0015] Preferably, in step S2, the iron raw material is a combination of pig iron and scrap steel, and the carbon content in the molten iron is controlled by adding a carburizer to the molten iron, and the silicon content in the molten iron is controlled by adding 75SiFe to the molten iron.

[0016] Preferably, in step S3, the inoculant is ferrosilicon inoculant, and in step S4, the inoculant is rare earth calcium barium inoculant.

[0017] Beneficial effects: By designing a riser-free casting process, material waste can be reduced because no additional riser material is needed to compensate for the shrinkage of the casting during cooling; by precisely controlling the chemical composition and casting process, self-shrinkage of the casting can be achieved, reducing or eliminating internal shrinkage cavities and shrinkage defects, thereby improving the internal quality and mechanical properties of the casting; the riser production and removal process is eliminated, and auxiliary work in production is reduced, thereby reducing production costs; the riser-free casting technology improves the process yield and reduces the scrap rate by optimizing the pouring system and casting process. DETAILED DESCRIPTION

[0018] A ductile iron riser-free casting process comprises the following steps:

[0019] Step S1, casting mold modeling step: the existing casting model is divided into an upper mold and a lower mold, and the upper mold and the lower mold are both provided with a matching mold cavity. The sand mold compactness of the upper mold and the lower mold is uniform during molding, and the hardness is controlled to be above 90, so that the upper mold and the lower mold can have sufficient rigidity and strength. Before casting, the mold cavity of the upper mold and the lower mold is filled with dry mold sand, and a 7mm sand layer is formed in the mold cavity by dry film sand, and then a layer of alcohol-based paint is applied to the outside of the sand layer. After using the alcohol-based paint, the painted mold or core does not need to be dried and can be used directly, which is conducive to improving production efficiency and saving energy. The upper mold and the lower mold with sand attached are assembled and fixed by screws, and the upper mold and the lower mold are fixed by bolts to prevent the volume expansion of the casting during the solidification process from causing box lifting, box expansion, and the like.

[0020] A pouring system is provided in the cavity of the upper mold and the lower mold of the casting mold. The pouring system consists of a straight runner and an ingates. The straight runner is connected to each ingates. The ingates are provided with multiple runners. One end of the ingates is connected to the cavity. The ingates adopt a smaller flat and thin structure. By arranging multiple ingates, the molten metal can fill the cavity more quickly and evenly, so as to complete solidification as soon as possible, establish internal pressure, and avoid defects in local areas due to uneven filling. The dispersed ingates can also help to make the temperature of different parts of the cavity more balanced, reduce the shrinkage stress caused by excessive temperature difference, and thus reduce the risk of cracks and deformation. Multiple ingates can avoid local overheating of the sand mold by the molten metal at a single inlet, reduce the possibility of damage to the sand mold, and by reasonably designing the number and position of the ingates, the mechanical properties and internal quality of the casting can be significantly improved, and defects such as pores and shrinkage cavities can be reduced.

[0021] The ingates connecting the ingates to the cavity adopt a flat structure. The flat ingates can solidify earlier than the casting, prevent the molten iron of the casting from flowing back, and give full play to the self-compensation effect of the graphitization expansion of the casting.

[0022] External chillers are installed on the upper and lower molds of the casting. The external chillers are located in the hot spots of the casting, i.e., the areas where the wall thickness is thicker or the heat is concentrated. The external chillers are made of graphite, and the thickness of the external chillers is 0.6-0.7 times the wall thickness of the casting. The installation of external chillers can accelerate the cooling rate of these areas and help achieve sequential solidification. The use of external chillers can also reduce the tendency of chilling and shrinkage cavities, while strengthening the nucleation conditions of graphite.

[0023] Step S2, smelting step of ductile iron: putting the raw material of ductile iron into a medium frequency electric furnace for smelting to obtain molten iron, the smelting temperature is 1500° C., and the mass percentages of the components in the raw material are: carbon C: 3.8%, silicon Si: 1.3%, manganese Mu: 0.4%, phosphorus P: 0.03%, sulfur S: 0.05%, and the rest are iron Fe;

[0024] The raw material iron is a combination of pig iron and scrap steel. The carbon content in the molten iron is controlled by adding a carburizer, and the silicon content in the molten iron is controlled by adding 75SiFe.

[0025] After smelting, the molten iron is sampled for spectrum inspection. By adding carburizer to temper and desulfurize, the treated molten iron reaches the target composition of the original molten iron, and the carbon equivalent CE in the molten iron is controlled between 4.50%;

[0026] Step S3, spheroidization, inoculation in a ladle: a dam-type flushing method is used for spheroidization, wherein a FeSiMg8Rt3 spheroidizer is placed in a ladle pit, compacted, a thin layer of ferrosilicon and cast iron chips is covered on the spheroidizer, inoculation in a ladle is performed using a ferrosilicon inoculant, and the dissolved molten iron is poured into the ladle pit to perform spheroidization and inoculation in a ladle, and after the molten iron reacts stably, the scum on the surface of the molten iron is scraped off, and filtering the molten iron helps to enhance the microscopic fluidity of the molten iron and reduce the probability of generating microscopic shrinkage cavities. The mass percentages of the components in the molten iron after spheroidization are carbon C: 3.70%, silicon Si: 2.2%, manganese Mu: 0.4%, phosphorus P: 0.04%, sulfur S: 0.01%, magnesium Mg: 0.05%, rare earth element Re: 0.03%, copper Cu: 0.5%, and the rest are iron Fe;

[0027] Step S4, pouring: pouring the molten iron treated in step S3 into the sprue in step S1, adding rare earth calcium barium inoculant for flow inoculation during the pouring process, the particle size of the inoculant is 60 mesh, the pouring temperature of the molten iron is controlled at 1400°C during pouring, and appropriately lowering the pouring temperature can reduce liquid shrinkage, and rapid pouring is adopted during pouring, and the rising speed of the molten iron in the casting mold is controlled at 9 mm / s, so that the inner gate can solidify as soon as possible after the pouring is completed, so as to prevent the molten iron in the mold cavity from being squeezed into the gate when the eutectic expands, and the top of the upper half of the casting mold is also provided with an air outlet connected to the mold cavity, and a plurality of air outlets are provided and evenly distributed, so as to minimize the resistance when the molten iron liquid level rises, so as to avoid reducing the punching speed of the molten iron;

[0028] Step S5, cooling and molding: after the casting is cooled and solidified, the fixing parts on the upper and lower molds are removed, the upper and lower molds are separated, the casting is taken out, and the sand layer on the surface of the casting is removed.

Claims

1. A riser-free casting process for ductile iron, characterized in that: The steps include: Step S1, casting mold modeling step: the existing casting model is divided into an upper mold and a lower mold, and the upper mold and the lower mold are both provided with a matching mold cavity. Before casting, the mold cavity of the upper mold and the lower mold is filled with dry mold sand, and a 5-8mm sand layer is formed in the mold cavity by dry film sand, and then a layer of alcohol-based paint is painted on the outside of the sand layer. The upper mold and the lower mold with sand are assembled and fixed by screws. A pouring system is provided in the mold cavity of the upper mold and the lower mold, and the pouring system consists of a sprue and an ingend, and the sprue is connected to each ingend, and one end of the ingend is connected to the mold cavity; Step S2, ductile iron smelting step: the raw material of ductile iron is put into a medium frequency electric furnace for smelting to obtain molten iron, the smelting temperature is 1500° C., and the mass percentages of the components in the raw material are: carbon C: 3.80%-3.9%, silicon Si: 1.0%-1.5%, manganese Mu: 0.3%-0.5%, phosphorus P≤0.05%, sulfur S<0.03%, and the rest are iron Fe; After smelting, the molten iron is sampled for spectral inspection. The treated molten iron is tempered by adding carburizer and desulfurized to achieve the target composition of the original molten iron. The carbon equivalent CE in the molten iron is controlled between 4.30% and 4.50%. Step S3, spheroidization, ladle inoculation treatment: spheroidization treatment is carried out by a dam-type flushing method, and generally two inoculation treatments are carried out, wherein a FeSiMg8Rt3 spheroidizer is placed in a ladle pit, compacted, a thin layer of ferrosilicon and cast iron chips is covered on the spheroidizer, and ladle inoculation is carried out by an inoculant, and the dissolved molten iron is poured into the ladle pit to carry out spheroidization and ladle inoculation treatment, and after the molten iron reacts stably, the scum on the surface of the molten iron is scraped off, and the mass percentages of the components in the molten iron after spheroidization are carbon C: 3.70%-3.8%, silicon Si: 2.1%-2.3%, manganese Mu: 0.3%-0.5%, phosphorus P≤0.05%, sulfur S<0.02%, magnesium Mg: 0.04%-0.06%, rare earth element Re: 0.02%-0.04%, copper Cu: 0.4%-0.6%, and the rest are iron Fe; Step S4, pouring: pouring the molten iron treated in step S3 into the sprue in step S1, adding an inoculant during the pouring process to perform flow inoculation, and controlling the pouring temperature of the molten iron to be 1390-1420° C. during the pouring; Step S5, cooling and molding: after the casting is cooled and solidified, the fixing parts on the upper and lower molds are removed, the upper and lower molds are separated, the casting is taken out, and the sand layer on the surface of the casting is removed.

2. A ductile iron riser-free casting process according to claim 1, characterized in that: In step S1, the ingate is provided with a plurality of runners, and the ingate connecting the ingate with the cavity adopts a flat structure.

3. A ductile iron riser-free casting process according to claim 1, characterized in that: In step S1, external chillers are installed on the upper and lower molds of the casting. The external chillers are located at the hot spots of the casting, i.e., the areas of the casting where the wall thickness is thicker or the heat is concentrated. The external chillers are made of graphite chillers, and the thickness of the external chillers is 0.6-0.7 times the wall thickness of the casting.

4. A riser-free casting process for ductile iron according to claim 1, characterized in that: In step S1, a vent hole communicating with the mold cavity is also opened on the top of the upper half of the casting mold.

5. A riser-free casting process for ductile iron according to claim 1, characterized in that: In step S2, the iron raw materials are selected from pig iron and scrap steel in combination, and the carbon content in the molten iron is controlled by adding a carburizer to the molten iron, and the silicon content in the molten iron is controlled by adding 75SiFe to the molten iron.

6. A riser-free casting process for ductile iron according to claim 1, characterized in that: In step S3, the inoculant is ferrosilicon inoculant, and in step S4, the inoculant is rare earth calcium barium inoculant.