Method for relieving shrinkage porosity of spheroidal graphite cast iron based on improvement of liquid inlet amount in casting

Abstract

The invention provides a method for relieving the shrinkage porosity of a nodular cast iron shrinkage cavity based on improving the liquid inlet amount in casting, the method is used for relieving the shrinkage porosity of the nodular cast iron by improving the shrinkage amount of molten metal when a flow gate is not closed yet, and the method specifically comprises the following steps: S1, reducing the liquid shrinkage volume when the nodular cast iron is solidified; s2, the eutectic expansion volume of the nodular cast iron in the paste solidification period is reduced when the nodular cast iron is solidified; s3, selecting a corresponding chill specification according to the size of a casting to be cast, calculating a shrinkage cavity and shrinkage porosity position generated in the pouring process of the nodular cast iron by using analog simulation software, and then placing the chill at the shrinkage cavity and shrinkage porosity position or prolonging the pouring time; the method can solve the problem that the casting is easy to be scrapped due to the defects of shrinkage cavity and shrinkage porosity, and meanwhile, quantitative analysis can be realized aiming at the large complex iron casting so as to implement a scheme for promoting the simultaneous solidification of each part of the casting.

Description

Technical Field

[0001] The invention relates to the technical field of cast iron, in particular to a method for alleviating shrinkage cavities and porosity of ductile iron based on increasing the amount of liquid inflow during casting. Background Art

[0002] With the increasing development of computer technology, a large number of numerical simulation technologies have been applied to casting research and have proven their scientificity. Numerical simulation of the entire casting process provides a high fault tolerance rate for the research and development of castings, transforms heuristic techniques and experimental methods into more scientific simulations, presents the dynamic behavior of the entire casting process and the casting system under corresponding working conditions, visualizes the distribution of casting flow field, temperature field, and stress field, reasonably predicts the type, distribution, and size of casting defects, and guides production practice, which has positive significance for the optimization of casting process, the improvement of casting product quality and production efficiency, and the reduction of production costs. Solidification simulation is mainly based on the calculation of casting temperature field, supplemented by stress and strain calculation, so as to predict defects such as shrinkage and shrinkage of castings, which is the core content of simulation technology in casting production applications. JMatPro has fast and correct calculation capabilities. With powerful and stable thermodynamic models and thermodynamic data as the core technology and calculation basis, the establishment of all physical models has been widely verified to ensure the accuracy of material performance calculations. By calculating the properties of metal materials through JMatPro, we can better analyze the influence of material composition on the material itself during the solidification process.

[0003] Since its introduction in 1947, ductile iron has developed rapidly due to its high strength, good toughness and low production cost. However, ductile iron has the characteristics of paste solidification and graphitization expansion, which makes castings prone to defects such as shrinkage and shrinkage, leading to scrapping. Especially for large and complex cast iron parts, the modulus of the casting itself varies greatly in different parts. If there is a lack of quantitative analysis and the process is designed only by experience, it is difficult to achieve simultaneous solidification. Summary of the invention

[0004] The present invention proposes a method for alleviating shrinkage cavities and porosity of ductile iron based on increasing the amount of liquid inlet during casting, which can solve the problem that castings are easily scrapped due to defects mainly caused by shrinkage cavities and porosity. At the same time, quantitative analysis can be achieved for large and complex iron castings to implement a solution to promote simultaneous solidification of various parts of the casting.

[0005] The present invention adopts the following technical solutions.

[0006] A method for alleviating shrinkage cavities and porosity of ductile iron based on increasing the amount of liquid inflow during casting, wherein the method alleviates shrinkage cavities and porosity of ductile iron by increasing the amount of molten metal shrinkage when the inner gate is not yet closed, and specifically comprises the following steps:

[0007] Step S1, reducing the liquid shrinkage volume of ductile iron during solidification;

[0008] Step S2, reducing the eutectic expansion volume during the mushy solidification period when the ductile iron solidifies;

[0009] Step S3, according to the size of the casting to be cast, select the corresponding chill specifications, use simulation software to calculate the shrinkage cavities and shrinkage positions generated by ductile iron during the pouring process, and then place chills at the shrinkage cavities and shrinkage positions or extend the pouring time.

[0010] The volume change curve of ductile iron solidification period in the casting process is divided into liquid shrinkage period (corresponding to Figure 2 The position to the right of the line on the right), the solidification period of the solid-liquid mixture (corresponding to Figure 2 The middle position of the two lines above), solid contraction period (corresponding to Figure 2 to the left of the upper left line).

[0011] In step S1, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

[0012] In step S1, the time period corresponding to the liquid shrinkage period is located according to the volume change curve. This time period is the time period when the molten iron has good fluidity and the internal gate and the shrinkage feeding channel inside the casting are not closed. Then, the shrinkage speed in this time period is accelerated to create a volume vacancy in the casting as early as possible, so as to increase the material content in the mold by increasing the inflow of molten iron during the casting process.

[0013] In step S2, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

[0014] In step S2, the time period corresponding to the liquid solidification period is located according to the volume change curve, and the ductile iron alloy component with smaller shrinkage in the liquid period and smaller expansion in the eutectic reaction period is set by comparing the curves of ductile iron with different component proportions, so as to reduce the tendency of ductile iron to produce shrinkage cavities and shrinkage under a reasonable casting system.

[0015] In step S2, the content ratio of silicon in the ductile iron component is increased to reduce the shrinkage of the ductile iron in the liquid state and the expansion of the ductile iron when the graphite expands.

[0016] In step S1 and step S2, the expansion amount of liquid shrinkage and eutectic expansion of ductile iron is reduced by increasing the content ratio of silicon in the ductile iron alloy component, so as to promote the liquid inflow during the pouring process, thereby facilitating the alleviation of shrinkage cavities and shrinkage of the casting, specifically:

[0017] When the ingates are in the paste solidification period, the blockage of the ingates is reduced by reducing the eutectic expansion of the ductile iron, so that the mold has more liquid shrinkage to alleviate the shrinkage cavities and porosity in the ductile iron.

[0018] When the ingates are completely sealed and there is no liquid compensation, the gap caused by insufficient self-compensation of ductile iron is alleviated by reducing liquid shrinkage, so as to alleviate the shrinkage cavities and shrinkage of ductile iron, and enable ductile iron to achieve compensation by relying on its self-compensation mechanism.

[0019] In step S3, ProCast is used to simulate the shrinkage cavities and shrinkage positions of ductile iron during the pouring process, and chillers are placed at the shrinkage cavities and shrinkage positions to increase the liquid shrinkage of the ductile iron. The corresponding pouring time is set to increase the shrinkage of the molten metal before the inner gate is closed, forming more vacancies so that more molten metal can enter the mold to form liquid shrinkage compensation, that is, the shrinkage cavities and shrinkage of ductile iron are alleviated by promoting the amount of liquid inflow during the pouring process.

[0020] In step S3, the ductile iron casting is a thick-walled complex ductile iron gear part with a main wall thickness of 166 mm and a height of 98 mm. The straight runner of the pouring system is cylindrical, and the cross runner is a shape composed of rectangles and circular rings. The ingrown runner is a combination of multiple rectangles, specifically: the straight runner of the pouring system is a cylinder with a length of 176 mm and a radius of 16 mm, and the cross runner is composed of a rectangle with a length of 480 mm, a width of 46 mm, and a height of 24 mm and a circular ring of the same height with an inner radius of 437 mm and an outer radius of 503 mm. The ingrown runner is 10 rectangles with a length of 50 mm, a width of 50 mm, and a height of 23 mm.

[0021] The invention belongs to the technical field of cast iron, and discloses a method for alleviating shrinkage cavities and shrinkage of ductile iron based on increasing the amount of liquid inflow during a casting process. The method is theoretically applicable to all ductile iron castings, and comprises the following steps: step S1, reducing the liquid shrinkage volume of the ductile iron during solidification, step S2, reducing the eutectic expansion volume during the mushy solidification period of the ductile iron during solidification, and step S3, if necessary, by selecting corresponding chiller specifications according to the size of the casting to be cast, placing chillers at shrinkage cavities and shrinkage positions, appropriately extending the pouring time, and other methods to increase the shrinkage of the molten metal before the inner gate is closed; the method of the invention is different from the traditional method of increasing the eutectic expansion of the ductile iron to make it self-supplementing to offset the shrinkage cavities and shrinkage, and this method can effectively increase the content of the material of the molten metal entering the casting during the pouring process, thereby alleviating or even eliminating the shrinkage cavities and shrinkage of the ductile iron, and also has obvious effects on complex ductile iron castings.

[0022] The present invention can increase the silicon content in the ductile iron, thereby reducing the liquid shrinkage and eutectic expansion of the ductile iron, thereby promoting the liquid inflow during the pouring process, and can achieve the purpose of significantly alleviating the shrinkage and porosity of the ductile iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Attached Figure 1 It is a schematic diagram of the simulated pouring results of the pouring system of thick and thin wall complex ductile iron gear parts under different grades;

[0025] Attached Figure 2 It is a schematic diagram of the volume change curve of ductile iron with different compositions;

[0026] Attached Figure 3 It is a schematic diagram of the volume change curve of QT500-7 with different silicon contents;

[0027] Attached Figure 4 It is a schematic diagram of the volume change curve of QT500-14 with different silicon contents;

[0028] Attached Figure 5 It is a schematic diagram of the simulated pouring results of the pouring system of thick and thin wall complex ductile iron gear parts under different specimens;

[0029] Attached Figure 6 Schematic diagram of chill size required for example castings in the case of QT500-7 ductile iron with a silicon content of 2.8;

[0030] Attached Figure 7 Schematic diagram of the position of the chiller in the case of QT500-7 ductile iron with a silicon content of 2.8 for the casting of the embodiment (the left part of the figure is a top view schematic diagram of the casting shape shown in three dimensions by the right part);

[0031] Attached Figure 8 This is a schematic diagram of the simulated pouring results of the casting in this article after placing chilled iron in the case of QT500-7 ductile iron with a silicon content of 2.8. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] As shown in the figure, a method for alleviating shrinkage cavities and shrinkage of ductile iron based on increasing the amount of liquid inflow during casting, the method alleviates shrinkage cavities and shrinkage of ductile iron by increasing the shrinkage of molten metal when the inner gate is not yet closed, and specifically includes the following steps:

[0034] Step S1, reducing the liquid shrinkage volume of ductile iron during solidification;

[0035] Step S2, reducing the eutectic expansion volume during the mushy solidification period when the ductile iron solidifies;

[0036] Step S3, according to the size of the casting to be cast, select the corresponding chill specifications, use simulation software to calculate the shrinkage cavities and shrinkage positions generated by ductile iron during the pouring process, and then place chills at the shrinkage cavities and shrinkage positions or extend the pouring time.

[0037] The volume change curve of ductile iron solidification period in the casting process is divided into liquid shrinkage period (corresponding to Figure 2 The position to the right of the line on the right), the solidification period of the solid-liquid mixture (corresponding to Figure 2 The middle position of the two lines above), solid contraction period (corresponding to Figure 2 to the left of the upper left line).

[0038] In step S1, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

[0039] In step S1, the time period corresponding to the liquid shrinkage period is located according to the volume change curve. This time period is the time period when the molten iron has good fluidity and the internal gate and the shrinkage feeding channel inside the casting are not closed. Then, the shrinkage speed in this time period is accelerated to create a volume vacancy in the casting as early as possible, so as to increase the material content in the mold by increasing the inflow of molten iron during the casting process.

[0040] In step S2, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

[0041] In step S2, the time period corresponding to the liquid solidification period is located according to the volume change curve, and the ductile iron alloy component with smaller shrinkage in the liquid period and smaller expansion in the eutectic reaction period is set by comparing the curves of ductile iron with different component proportions, so as to reduce the tendency of ductile iron to produce shrinkage cavities and shrinkage under a reasonable casting system.

[0042] In step S2, the content ratio of silicon in the ductile iron component is increased to reduce the shrinkage of the ductile iron in the liquid state and the expansion of the ductile iron when the graphite expands.

[0043] In step S1 and step S2, the expansion amount of liquid shrinkage and eutectic expansion of ductile iron is reduced by increasing the content ratio of silicon in the ductile iron alloy component, so as to promote the liquid inflow during the pouring process, thereby facilitating the alleviation of shrinkage cavities and shrinkage of the casting, specifically:

[0044] When the ingates are in the paste solidification period, the blockage of the ingates is reduced by reducing the eutectic expansion of the ductile iron, so that the mold has more liquid shrinkage to alleviate the shrinkage cavities and porosity in the ductile iron.

[0045] When the ingates are completely sealed and there is no liquid compensation, the gap caused by insufficient self-compensation of ductile iron is alleviated by reducing liquid shrinkage, so as to alleviate the shrinkage cavities and shrinkage of ductile iron, and enable ductile iron to achieve compensation by relying on its self-compensation mechanism.

[0046] In step S3, ProCast is used to simulate the shrinkage cavities and shrinkage positions of ductile iron during the pouring process, and chillers are placed at the shrinkage cavities and shrinkage positions to increase the liquid shrinkage of the ductile iron. The corresponding pouring time is set to increase the shrinkage of the molten metal before the inner gate is closed, forming more vacancies so that more molten metal can enter the mold to form liquid shrinkage compensation, that is, the shrinkage cavities and shrinkage of ductile iron are alleviated by promoting the amount of liquid inflow during the pouring process.

[0047] In step S3, the ductile iron casting is a thick-walled complex ductile iron gear part with a main wall thickness of 166 mm and a height of 98 mm. The straight runner of the pouring system is cylindrical, and the cross runner is a shape composed of rectangles and circular rings. The ingrown runner is a combination of multiple rectangles, specifically: the straight runner of the pouring system is a cylinder with a length of 176 mm and a radius of 16 mm, and the cross runner is composed of a rectangle with a length of 480 mm, a width of 46 mm, and a height of 24 mm and a circular ring of the same height with an inner radius of 437 mm and an outer radius of 503 mm. The ingrown runner is 10 rectangles with a length of 50 mm, a width of 50 mm, and a height of 23 mm.

[0048] Example:

[0049] The casting mold in this example is theoretically suitable for all ductile iron castings. The ductile iron casting used in this example is a thick-thin-wall complex ductile iron gear part with a main wall thickness of 166mm and a height of 98mm. The straight runner of the pouring system is a cylinder with a length of 176mm and a radius of 16mm. The cross runner is composed of a rectangle with a length of 480mm, a width of 46mm, and a height of 24mm and a circular ring with the same height and an inner radius of 437mm and an outer radius of 503mm. The inner runner is 10 rectangles with a length of 50mm, a width of 50mm, and a height of 23mm.

[0050] In this example, a method for alleviating shrinkage cavities and shrinkage of ductile iron based on increasing the amount of liquid inflow during pouring comprises the following steps: step S1, reducing the liquid shrinkage volume of ductile iron during solidification, step S2, reducing the eutectic expansion volume during the mushy solidification period of ductile iron during solidification, step S3, if necessary, the shrinkage of the molten metal before the inner gate is closed can be increased by, for example, selecting the corresponding chill specifications according to the size of the casting to be cast, placing chills at the shrinkage cavities and shrinkage positions, and appropriately extending the pouring time;

[0051] Step S1: Calculate the volume change curve of ductile iron during liquid solidification period by JMatPro;

[0052] Step S2: Calculate the volume change curve of eutectic expansion of ductile iron during the mushy solidification period by JMatPro;

[0053] Step S3: ProCast is used to simulate the shrinkage cavities and shrinkage positions of ductile iron during the pouring process. The shrinkage cavities and shrinkage of ductile iron can be further alleviated by placing chillers at the shrinkage cavities and shrinkage positions, appropriately extending the pouring time, and other methods.

[0054] The line on the right side of the JMatPro calculation result graph in step S1 corresponds to the position to the right of the liquidus line.

[0055] The step S2 corresponds to the position between the two lines in the JMatPro calculation result graph, that is, the position between the liquidus line and the solidus line.

[0056] In step S3, the shrinkage of the molten metal before the inner gate is closed is increased by placing cold iron at the location of the shrinkage cavity and shrinkage, appropriately extending the pouring time, etc., so as to form more vacancies, so that more molten metal can enter the mold to form liquid shrinkage compensation, thereby alleviating the shrinkage cavity and shrinkage of ductile iron.

[0057] In this example, ProCAST is used to simulate the solidification temperature field of castings of different materials. The shrinkage cavities when they are finally cooled to a solid state are as follows: Figure 1 As shown in the figure, the circled area is the shrinkage cavity and shrinkage porosity existing in the casting. Figure 1 It can be seen that the shrinkage cavities and shrinkage on the casting mainly occur in the thick wall where the thick and thin walls meet, and the main form is a large number of concentrated shrinkage cavities and shrinkage. This is because the thin wall solidifies earlier than the thick wall. The shrinkage cavities and shrinkage produced will be compensated by the unsolidified liquid metal of the thick wall. At the same time, the solidification of the thin wall will block the flow of molten iron inside the casting, resulting in insufficient shrinkage compensation between the thick walls.

[0058] In this example, the volume change curve of the material reflects the change in volume relative to the original volume at different temperatures during the solidification process. During the pouring process, the liquid metal will shrink when it cools and solidifies, which is reflected as a negative value on the volume change curve. If the value of the volume change curve of the material is smaller, the more shrinkage it will produce during the solidification process, which will easily form shrinkage holes. At the same time, there will be an upward mutation on the curve, indicating that ductile iron expands within the temperature range of the mutation. During the casting process, ductile iron liquid metal will expand when it cools and solidifies. The mutation occurs during the graphitization precipitation in the solidification stage. The expansion caused by the precipitation of graphitization is greater than the contraction of the liquid phase, and the volume change curve rises sharply at this time. If the volume change curve rises more at this time, it means that the expansion caused by graphitization precipitation is greater. Generally, the temperature range corresponding to this stage is between 1090 and 1190℃.

[0059] In this example, during the solidification process of ductile iron, it is first in a liquid contraction state, at which time the volume of the ductile iron decreases, corresponding to Figure 2 The position is to the right of the line on the right. After that, the ductile iron will be in a solid-liquid mixed paste solidification state, corresponding to the position between the two lines in the figure. At this time, there will be a sudden change on the curve. This is because the expansion caused by graphitization precipitation is greater than the contraction of the liquid phase, and the volume will increase. The more the volume change curve rises, the greater the expansion caused by graphitization precipitation. Finally, the ductile iron will enter a solid contraction state, corresponding to the left of the line on the left of the figure above, but at this time it is not closely related to the shrinkage and shrinkage problems during the solidification process of ductile iron.

[0060] Traditional technology believes that the self-compensation ability of ductile iron can solve the shrinkage and porosity defects of ductile iron, but simply improving the expansion ability of ductile iron cannot effectively alleviate the shrinkage and porosity problems of ductile iron. Expansion that occurs too early and too much will not only cause the outflow of molten iron, but also because the number of graphite balls and eutectic groups increases significantly, the solid-liquid zone expands rapidly, and the tendency of "paste solidification" becomes more obvious, making the liquid channel easy to clog, resulting in the obstruction of shrinkage of the molten metal, thereby increasing the tendency of shrinkage and porosity. In fact, before ensuring good fluidity of the molten iron and the closing of the inner gate and the internal shrinkage channel of the casting, the expansion generated in the casting should be minimized, and the shrinkage should even be accelerated as much as possible, so as to create volume vacancies as early as possible, so that more molten iron can flow in and the material content in the mold can be increased. Increasing the graphite expansion of ductile iron in the early stage will prevent the feeding molten iron from entering the cavity. For complex castings, it may also cause the thin-walled part to block the flow of molten iron in the thick-walled part, so that the thick walls cannot be fully fed. These will hinder self-feeding and molten metal feeding, resulting in insufficient expansion to offset shrinkage after the gate and the feeding channel are closed, and eventually shrinkage cavities and shrinkage porosity will form.

[0061] In this case, in order to reduce the tendency of ductile iron to produce shrinkage cavities and shrinkage under a reasonable pouring system, ductile iron with smaller shrinkage during the liquid period and smaller expansion during the eutectic reaction period is selected. If necessary, methods such as chilling iron can also be used to accelerate the shrinkage of the molten metal before the inner gate is closed, forming more vacancies, allowing more molten metal to enter the mold and form liquid shrinkage compensation.

[0062] By comparison Figure 2 , QT400-18, which has the largest shrinkage volume, has the largest liquid shrinkage, close to -2.5%, while QT500-14 and QT500-7, which have the smallest shrinkage volume and the second largest shrinkage volume, have the same change of -2.08%, which indicates that when the inner gate of the gating system solidifies, the liquid shrinkage in the mold is smaller, which is more conducive to the offset of self-compensation, thereby better alleviating or even solving the shrinkage problem. QT500-14, which has the same liquid shrinkage, performs better than QT500-7 in shrinkage and shrinkage, because the precipitation of graphite balls in the eutectic stage will cause expansion. The volume change curve of QT500-14 in the eutectic stage increases by 0.29%, which is less than the volume change curve of QT500-7 in the eutectic stage. The increase of 0.6%, that is, the expansion of QT500-14 is less than that of QT500-7. The ingates in the pouring system are one of the first parts to solidify. If the expansion is too large, it will block or even block the ingates, and cause the molten iron in the mold to flow out, resulting in insufficient shrinkage in the mold, thus increasing the tendency of shrinkage cavities and shrinkage. Figure 2 It can be seen that the volume change curve of QT500-14 in the eutectic stage rises the smallest, only 0.29%, which is less than half of QT500-7. The eutectic expansion is the smallest, so more molten iron enters the pouring and the material content of the casting increases. At the same time, the liquid shrinkage of QT500-14 is not large, so the smaller self-compensation shrinkage is enough to offset the shrinkage generated during the solidification process.

[0063] By comparison Figure 2 As shown in Table 1, the ductile iron that shrinks less during the liquid phase and expands less during the eutectic reaction phase has a higher silicon content.

[0064] Table 1 Composition of ductile iron

[0065]

[0066] In this case, by comparing the effects of ductile iron materials with different silicon contents on shrinkage cavities and shrinkage, it is concluded that silicon plays a vital role in the shrinkage compensation of ductile iron. The research in this case shows that carbon and silicon are the two main elements in ductile iron. The binding force between silicon and iron atoms is greater than that between carbon and iron atoms. When silicon is dissolved in molten iron and iron solid solution, it weakens the binding force between iron and carbon atoms, thereby promoting graphitization; at the same time, the increase in silicon content will lead to an increase in the eutectic temperature range of the stable system and the metastable system, that is, the eutectic temperature range of austenite plus graphite will be higher than the eutectic temperature range of austenite plus cementite, which is more conducive to the acquisition of graphite. Therefore, high-silicon ferrite ductile iron contains a higher silicon content, which makes the graphite nodules small and uniform, and the number increases, thereby improving the self-compensation ability of ductile iron.

[0067] In this case, the Figure 2 It can be found that the higher the silicon content, the smaller the shrinkage of ductile iron in the liquid state, and the smaller the expansion when the graphite expands. Through observation, the control group Table 2 and Table 3, which control the components of QT500-7 and QT500-14 and change only the silicon content within the grade range, and their corresponding Figure 3-Figure 5 It can be found that with the increase of silicon content, the expansion of ductile iron liquid shrinkage and eutectic expansion will decrease. When the silicon content reaches QT500-14, the main matrix of ductile iron becomes ferrite, and the expansion of liquid shrinkage and eutectic expansion reaches a very small value. At this time, although increasing the silicon content in ductile iron will also affect the shrinkage in liquid state and the expansion of eutectic expansion, its effect is small. High-silicon ductile iron, with its smaller shrinkage capacity in liquid period and smaller graphite expansion in the early stage, can block the inner gate less during pouring, thereby retaining relatively more molten iron in the casting mold, providing sufficient materials for the later shrinkage compensation, and after the inner gate is closed, the liquid ductile iron shrinks less, so that the self-compensation can better offset the shrinkage and alleviate shrinkage cavities and shrinkage.

[0068] Table 2 Comparative experimental ductile iron composition table

[0069]

[0070] Table 3 Volume changes

[0071]

[0072] In summary, as the silicon content increases, the liquid shrinkage and eutectic expansion of ductile iron will both decrease. The smaller the liquid shrinkage and eutectic expansion, the more conducive to the alleviation of shrinkage and shrinkage. When the ingates are in the paste solidification period, the smaller the eutectic expansion of ductile iron, the smaller the blockage of the ingates, and the more liquid shrinkage for the casting to alleviate the shrinkage and shrinkage in the ductile iron. When the ingates are completely sealed, there is no liquid shrinkage, and the ductile iron can only rely on its self-shrinkage mechanism to compensate for shrinkage. At this time, less liquid shrinkage is needed to alleviate the gap caused by insufficient self-shrinkage, thereby alleviating the shrinkage and shrinkage of the ductile iron.

[0073] In this example, the silicon content in the ductile iron is increased, thereby reducing the liquid shrinkage and eutectic expansion of the ductile iron, and promoting the liquid inflow during the pouring process, which can achieve the purpose of significantly alleviating the shrinkage and porosity of the ductile iron.

[0074] In this example, if chilling iron is required, the chilling iron specifications of the casting need to be determined according to the size of the casting to be cast. Taking QT500-7 ductile iron with a silicon content of 2.8 as an example, by placing chilling iron at the shrinkage cavity and shrinkage porosity, the shrinkage cavity and shrinkage porosity positions can be seen. Figure 1 (b) Marking part, chiller specifications see Figure 6 , cold iron position see Figure 7 , pouring for 90 seconds, simulation results are shown in Figure 8 , through Figure 1 In the present invention, by placing a chiller, the liquid shrinkage of ductile iron is increased to promote the liquid inflow during the pouring process, thereby achieving the purpose of significantly alleviating the shrinkage of ductile iron.

[0075] The implementation cases described in this example, which reduce the liquid shrinkage and eutectic expansion of ductile iron by increasing the silicon content in the ductile iron, and promote the liquid inflow during the pouring process by placing a chill on the casting and appropriately delaying the pouring time, are only preferred implementation cases of the present invention and are not intended to limit the scope of implementation of the present invention. That is, all equivalent changes and modifications made according to the content of the patent application scope of the present invention should be regarded as the technical scope of the present invention.

Claims

1. A method for alleviating shrinkage cavities and porosity of ductile iron based on increasing the amount of liquid inlet during casting, characterized in that: The method alleviates shrinkage and porosity of ductile iron by increasing the shrinkage of molten metal when the inner gate is not yet closed, and specifically comprises the following steps: Step S1, reducing the liquid shrinkage volume of ductile iron during solidification; Step S2, reducing the eutectic expansion volume during the mushy solidification period of the ductile iron solidification; Step S3, according to the size of the casting to be cast, select the corresponding chill specifications, use simulation software to calculate the shrinkage cavities and shrinkage positions generated by ductile iron during the pouring process, and then place chills at the shrinkage cavities and shrinkage positions or extend the pouring time.

2. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 1, characterized in that: The volume change curve of ductile iron solidification period in the casting process is divided into liquid contraction period, solid-liquid mixed paste solidification period and solid contraction period in sequence according to the passage of time.

3. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid inlet during casting according to claim 2, characterized in that: In step S1, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

4. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 3, characterized in that: In step S1, the time period corresponding to the liquid shrinkage period is located according to the volume change curve. This time period is the time period when the molten iron has good fluidity and the internal gate and the shrinkage feeding channel inside the casting are not closed. Then, the shrinkage speed in this time period is accelerated to create a volume vacancy in the casting as early as possible, so as to increase the material content in the mold by increasing the inflow of molten iron during the casting process.

5. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 2, characterized in that: In step S2, the volume change curve of ductile iron during liquid solidification is calculated by JMatPro.

6. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 2, characterized in that: In step S2, the time period corresponding to the liquid solidification period is located according to the volume change curve, and the ductile iron alloy component with smaller shrinkage in the liquid period and smaller expansion in the eutectic reaction period is set by comparing the curves of ductile iron with different component proportions, so as to reduce the tendency of ductile iron to produce shrinkage cavities and shrinkage under a reasonable casting system.

7. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 6, characterized in that: In step S2, the content ratio of silicon in the ductile iron component is increased to reduce the shrinkage of the ductile iron in the liquid state and the expansion of the ductile iron when the graphite expands.

8. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 7, characterized in that: In step S1 and step S2, the expansion amount of liquid shrinkage and eutectic expansion of ductile iron is reduced by increasing the content ratio of silicon in the ductile iron alloy component, so as to promote the liquid inflow during the pouring process, thereby facilitating the alleviation of shrinkage cavities and shrinkage of the casting, specifically: When the ingates are in the paste solidification period, the blockage of the ingates is reduced by reducing the eutectic expansion of the ductile iron, so that the mold has more liquid shrinkage to alleviate the shrinkage cavities and porosity in the ductile iron. When the ingates are completely sealed and there is no liquid compensation, the gap caused by insufficient self-compensation of ductile iron is alleviated by reducing liquid shrinkage, so as to alleviate the shrinkage cavities and shrinkage of ductile iron, and enable ductile iron to achieve compensation by relying on its self-compensation mechanism.

9. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 7, characterized in that: In step S3, ProCast is used to simulate the shrinkage cavities and shrinkage positions of ductile iron during the pouring process, and chillers are placed at the shrinkage cavities and shrinkage positions to increase the liquid shrinkage of the ductile iron. The corresponding pouring time is set to increase the shrinkage of the molten metal before the inner gate is closed, forming more vacancies so that more molten metal can enter the mold to form liquid shrinkage compensation, that is, the shrinkage cavities and shrinkage of ductile iron are alleviated by promoting the amount of liquid inflow during the pouring process.

10. The method for alleviating shrinkage cavities and porosity of ductile iron by increasing the amount of liquid fed during casting according to claim 7, characterized in that: In step S3, the ductile iron casting is a thick-thin-walled complex ductile iron gear part, the pouring system sprue is cylindrical, the runner is a shape composed of a rectangle and a ring, and the ingrown is a combination of multiple rectangles.

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