Casting methods that can reduce casting weight

Abstract

This invention provides a casting method that enables a significant reduction in molten metal in the casting of spheroidal graphite cast iron. [Solution] By using an appropriate combination of chemical components, pouring at a lower temperature than usual, and using a suitable riser with a lower solidification modulus than conventional risers, a novel riser reduction technology is employed to obtain sound cast products, thereby significantly reducing the casting weight. Furthermore, by combining this with a technology that can also reduce the sprue and runner, even greater reductions in molten metal are possible.

Description

Detailed Description of the Invention

Technical Field

[0001] The present invention is a casting method for pouring a molten spheroidal graphite cast iron into a sand mold, providing a novel technique for reducing the riser to obtain a significant reduction in molten metal, and enabling a further substantial reduction in molten metal in combination with the technique for reducing the sprue and runner, thereby providing a casting method for drastically reducing CO2 generated in a casting factory.

Background Art

[0002] Generally, in the casting of spheroidal graphite cast iron castings using a sand mold, the mold cavity is generally composed of the product part, riser, runner, and sprue elements. The average ratio of each part varies slightly depending on the material, product size, etc., but it is 50% for the product part, 30% for the riser, 10% for the runner, and 10% for the sprue. Therefore, the casting yield = product weight / total poured weight is as low as about 50%. This situation has hardly changed in the past 50 years. That is, in order to obtain a sound casting, molten metal with a weight twice that of the product weight is melted. Also, among the design elements, the riser occupies 30% of the total poured weight, which is a major cause of the low casting yield. The riser, runner, and sprue excluding the product part are finally separated from the product part as unnecessary parts and are reused as return materials for remelting.

[0003] Regarding the reduction of the large - ratio riser among these, in cast iron castings, as a characteristic phenomenon, graphite crystallizes during the solidification process and volume expansion occurs, so a part of the solidification shrinkage of the molten metal in the product part is compensated. Thus, it has been found that sound castings can be obtained with a smaller riser compared to steel castings.

[0004] In the spheroidal graphite cast iron castings targeted by the present application, attempts have been made to reduce the riser conventionally, but they have remained at the low casting yield as described above without clear criteria. That is, in spheroidal graphite cast iron, a method for obtaining a significant reduction in the riser while maintaining the soundness of the casting has not been disclosed.

Prior Art Documents

[0005] A search of patent documents using keywords such as riser removal, no riser, riser reduction, and molten metal reduction yielded the following prior art documents. [Patent Documents]

[0006] [Patent Document 1] Patent No. 5458295 [Patent Document 2] Japanese Patent Application No. 2009-123998 [Patent Document 2] Japanese Patent Application No. 2005-305977 [Patent Document 2] Japanese Patent Application No. 2005-268163 [Patent Document 2] Japanese Patent Application No. 2006-531397 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In view of the above points, this invention provides a novel casting method for spheroidal graphite cast iron castings that obtains sound cast products by using an appropriate combination of chemical components, pouring at a lower temperature than usual, and using risers with a lower solidification modulus than conventional risers, thereby significantly reducing the casting weight. Furthermore, by combining this riser reduction technology with a technology that can significantly reduce the number of sprues and runners, an even greater reduction in molten metal is achieved. As a result, the electricity required for melting is reduced, and the invention aims to reduce the generation of greenhouse gases such as CO2, which have become a problem in recent years. Means for solving the problem (Method 1)

[0008] This casting method involves pouring molten spheroidal graphite cast iron into a sand mold, characterized in that the CE value of the molten metal after spheroidization treatment is 4.4 to 4.7, the ratio of residual Mg to residual S (Mg / S) is 2.7 to 5.6, Mc is the solidification modulus of the product part and Mf is the solidification modulus of the riser, a riser with an Mf value of Mf ≤ 0.9 Mc is used, and the molten metal temperature PT is in the range of 1350°C > PT > 1300°C when pouring.

[0009] This method provides a casting method that can stably achieve a significant reduction in risers by utilizing the solidification characteristics of molten spheroidal graphite cast iron. The elemental technologies for this purpose are described below. An essential condition for reducing risers is maintaining the integrity of the casting. The important evaluation items used for this purpose are maintaining a graphite spheroidization rate that does not cause a decrease in strength, and defining clear conditions that do not cause or increase shrinkage cavities.

[0010] (Element 1) The chemical composition of the molten metal to be poured shall be such that the CE value after spheroidization treatment using a Mg alloy or pure Mg, which is commonly used for spheroidization, is 4.4 to 4.7, and the ratio of residual Mg to residual S (Mg / S) shall be 2.7 to 5.6. The effects of these molten metal conditions will be explained below.

[0011] For CE values ​​between 4.4 and 4.7, this application defines CE value as C% + 1 / 3Si%. When the CE value is lower than 4.4, the amount of graphite crystallized during solidification decreases, reducing volume expansion due to graphite. When the CE value is higher than 4.7, the amount of graphite crystallized increases, but the amount of floating graphite also increases, reducing volume expansion due to graphite. Therefore, in either case, the shrinkage of the molten metal increases, making it easier for shrinkage cavities to occur and making it difficult to reduce the size of the riser. Accordingly, the range of 4.4 to 4.7 is appropriate. Details of this numerical specification will be explained in the examples.

[0012] Generally, the relationship between the spheroidization rate and strength of spheroidal graphite cast iron castings, as well as the tendency for shrinkage cavities to occur, is evaluated using the residual Mg after spheroidization treatment. According to this method, the practically appropriate range for Mg is considered to be 0.030% to 0.060%. However, in the inventors' studies, even when the residual Mg is within the above range, the strength may decrease or shrinkage cavities may occur, deviating from the desired characteristics. Therefore, by considering the interaction between residual Mg and residual S as a factor that takes into account the influence of S, which has been previously neglected, it was found that the strength and the tendency for shrinkage cavities to occur could be predicted with greater accuracy than by evaluating Mg alone. Thus, Mg / S was applied as a new factor.

[0013] As a result of the evaluation and study, it was found that Mg / S = 2.7 to 5.6 is appropriate. In other words, the smaller the Mg / S value, the less likely shrinkage cavities are to occur, and the easier it is to reduce risers. However, if the Mg / S value is less than 2.7, there is a risk that it will fall below 80%, which is the limit value for graphite spheroidization that does not cause a decrease in strength. Also, if it is greater than 5.6, the shrinkage of the molten metal increases, making it easier for unacceptable shrinkage cavities to occur, making it difficult to significantly reduce risers. Therefore, in this application, the appropriate Mg / S value is set to 2.7 to 5.6. Details of these numerical specifications will be explained in the examples. In actual mass production casting, if there is an influence from elements that inhibit graphite spheroidization or elements that increase the shrinkage of the molten metal in addition to Mg and S, then 3.0 to 5.0 is preferable.

[0014] Furthermore, both residual Mg and residual S fluctuate due to MgS, MgO, and various other chemical reactions, so careful control is necessary. Since residual Mg is largely determined by the amount of S before the spheroidization treatment, the amount of S is generally kept low from the standpoint of the yield of added Mg. Therefore, the amount of residual S tends to be low. As a result, the Mg / S ratio becomes large and may exceed the upper limit of 5.6 targeted by this application. In such cases, in order to reliably implement this application, it is recommended to adjust the residual S by adding an appropriate amount of S source such as FeS after the spheroidization treatment as needed, thereby bringing the Mg / S value within an appropriate range.

[0015] (Element 2) The molten metal temperature PT is between 1300°C and 1350°C. The average temperature is 1325°C. This pouring temperature range does not necessarily mean that the molten metal must be poured within this range, but rather that the molten metal should be poured within an appropriate predetermined temperature range within this range depending on the casting conditions.

[0016] The typical pouring temperature is between 1450°C and 1350°C, depending on the size, wall thickness, and complexity of the casting process, with an average pouring temperature of 1400°C. Even in this case, actual pouring is often performed using a single ladle for casting multiple frames, and the temperature is adjusted within a suitable range within this range. Therefore, the present invention uses a pouring temperature that is approximately 75°C lower on average compared to the usual pouring temperature. The reason for using such a low pouring temperature is to reduce the amount of liquid shrinkage of the molten metal before solidification begins.

[0017] With spheroidal graphite cast iron molten metal, sound castings can be obtained with smaller risers than with general metal molten metals (such as cast steel). This is because, during the solidification process, the carbon content of the metal crystallizes as graphite, causing volume expansion. This self-feeding effect compensates for any shortage of molten metal due to solidification shrinkage of the product. This expansion effect due to graphite crystallization is an extremely rare and distinctive effect among metals. This method also makes effective use of this effect.

[0018] The factors contributing to the expansion and contraction during the solidification process of molten spheroidal graphite cast iron are the amount of contraction due to liquid shrinkage as the temperature decreases (-), the amount of expansion due to primary graphite (+), the amount of contraction due to austenite in eutectic solidification (-), and the amount of expansion due to eutectic graphite (+). At normal pouring temperatures, the sum of these factors (hereinafter referred to as the total expansion / contraction Q) is negative, meaning that contraction is greater. Therefore, it is necessary to supply the molten metal shortage in the product section from risers.

[0019] The numerical values of expansion and contraction during the above-mentioned solidification process are as follows. Generally, the amount of contraction accompanying liquid shrinkage is -1.5% per 100 °C, which is determined by the temperature difference from the pouring temperature to the solidification temperature. If the pouring temperature is PT (°C), the liquid shrinkage can be expressed as =(PT - 1150)×(-1.5) / 100 (%). 1150 is the solidification temperature. That is, when the pouring temperature is 1400 °C, the liquid shrinkage is -3.75%, and when it is 1350 °C, it is -3.0%. Also, for primary graphite and eutectic graphite, there are differences depending on the CE value (=C + 1 / 3Si). Considering the CE value = 4.4 - 4.7 proposed in this application, the expansion amount due to primary graphite is +0.46% - +1.51%, the expansion amount due to eutectic graphite is approximately +6.2% - +6.0%, and the shrinkage amount due to austenite in eutectic solidification is approximately constant at about -3.3%.

[0020] As an example of the numerical values of expansion and contraction during the solidification process, the following table shows the results obtained for pouring temperatures of 1400 °C, 1350 °C, and 1300 °C when CE = 4.4 and 4.7. TIFF2026088990000002.tif54137

[0021] For example, when the CE value = 4.4 and the normal average pouring temperature is 1400 °C, the total expansion and contraction Q = -0.44%. The shrinkage in the product part cannot be compensated by self-feeding due to graphite crystallization. That is, additional pouring is required to compensate for this. Next, for example, when the upper limit pouring temperature guideline according to this application is 1350 °C, the total expansion and contraction Q = +0.32%, and when the lower limit pouring temperature guideline is 1300 °C, the total expansion and contraction Q = +1.10%. The shrinkage in the product part can be compensated by self-feeding due to graphite crystallization at any pouring temperature. That is, the product part can be soundly manufactured without internal defects such as shrinkage cavities without melt supply from additional pouring. Therefore, there is a possibility of removing or significantly reducing additional pouring.

[0022] When the CE value = 4.7, calculating in the same way, when the pouring temperature is 1400°C, the total expansion and contraction Q = +0.46%. When the reference upper limit pouring temperature according to the present application is 1350°C, the total expansion and contraction Q = +1.23%. When the reference lower limit pouring temperature is 1300°C, the total expansion and contraction Q = +2.00%. In any case, graphite crystallization can supply the shrinkage of the product part by self-feeding. However, in the cases of the reference upper and lower limit pouring temperatures of 1350°C and 1300°C of the present application, sound castings can be obtained by more safely removing or significantly reducing the riser head.

[0023] However, in actual casting, when the primary graphite is excessive, a part of it may float to the upper part of the molten metal and cannot serve for self-feeding, and the total expansion and contraction Q may decrease. Also, when the product part is filled with the molten metal, the mold cavity expands due to its heat, resulting in a shortage of molten metal. Considering these factors, apparently, the total expansion and contraction Q will decrease. Therefore, it is expected that the possibility of removing or significantly reducing the riser head is smaller than the above calculation, so it is necessary to compensate for the decrease in the total expansion and contraction Q by some means. Thus, the following element 3 is used.

[0024] (Element 3) When the solidification modulus of the product part is Mc and the solidification modulus of the riser head is Mf, use a riser head with an appropriate Mf value within the range of Mf ≦ 0.9Mc.

[0025] Element 1 of this method stabilizes the spheroidization rate with appropriate chemical components and reduces the shrinkage of the molten metal, and Element 2 makes the sum of expansion and contraction Q during solidification positive, allowing the product part to self-supply itself, and conditions are met for internal defects such as shrinkage cavities to occur in a method that eliminates or significantly reduces risers. However, a decrease in the sum of expansion and contraction Q occurs due to unforeseen factors such as the floating of primary graphite and mold expansion as described above. To compensate for this and further ensure the integrity of the product part, a riser with a smaller solidification modulus (= volume / surface area) (= smaller volume) than conventional risers is used to supply some of the solidification shrinkage of the product part. When the solidification modulus of the product part is Mc and the solidification modulus of the riser of this application is Mf, an appropriate value in the range of Mf ≤ 0.9 Mc is used depending on the casting conditions. As a result, the solidification time is shorter and the supply action is smaller than with conventional risers, but molten metal can be supplied to the product part for an appropriate amount of time. Furthermore, using a suitable Mf value within the range of Mf ≤ 0.9 Mc includes the case where Mf = 0, i.e., no pressing water is used.

[0026] For the solidification modulus Mr of a typical riser, Mr = (1.0~1.2)Mc has traditionally been considered the appropriate value. However, this is a recommended value obtained from experiments with simple-shaped products more than 50 years ago. In actual manufacturing today, due to the size and complexity of the product shape, isolated thick-walled areas prone to shrinkage cavities are often far from the riser, making it difficult to supply molten metal with a riser of this size. For this reason, in most cases, a value larger than this recommended value, i.e., a larger riser, is used. The conventional approach to risers is to completely supply molten metal to compensate for the negative (shrinkage) portion of the total expansion and contraction Q of the product caused by pouring molten metal at a higher temperature than that of the present invention. This is the cause of the low casting yield.

[0027] In contrast, in this application, element 1 provides an appropriate chemical composition, and element 2 uses low-temperature pouring to make the sum of expansion and contraction S during solidification as large as possible (expansion). Therefore, even if isolated thick sections are far from the riser, and even if there is some mold expansion, the self-pouring action due to the positive sum of expansion and contraction Q associated with the solidification of the product itself suppresses the occurrence of shrinkage cavities. A sound casting can be obtained by pouring molten metal for an appropriate amount of time using a riser with a small solidification modulus (= small volume). Accordingly, the range of solidification modulus Mf ≤ 0.9 Mc and the concept of pouring time for the riser in this application are based on a novel idea that is clearly different from the conventional concept of risers.

[0028] The range Mf ≤ 0.9 Mc should be adjusted according to the casting conditions, i.e., the molten metal material, mold type, product shape and size, pouring temperature, etc. For the material, if the CE value is low, use the value closer to 0.9 Mc; if it is high, use the smaller value. For the mold type, it depends on the strength of the mold, with shell molds being the strongest, followed by self-hardening molds and then green sand molds. The higher the mold strength, the less likely shrinkage cavities are to occur. Considering these characteristics of the mold, for shell molds and self-hardening molds, use the smaller value closer to Mf = 0 (no riser), and for green sand molds, use the value closer to 0.9 Mc.

[0029] Next, regarding the shape and size of the product, when the solidification modulus Mc of the product part is 2.5 cm or more, or when the shape of the product part is a cube, sphere, cylinder, prismatic shape, or a shape close to these, shrinkage cavities are less likely to occur, so the smaller value closer to Mf=0 is applied. On the other hand, when the solidification modulus Mc of the product part is 2.5 cm or less, or when the product is a plate-like body, ring-like body, cylindrical body, or a complex-shaped product, shrinkage cavities are more likely to occur, so the value closer to 0.9 Mc is applied. The shape and size of the product part in general will be somewhere in between these, so an appropriate value in the range Mf≦0.9Mc is applied.

[0030] Furthermore, regarding the pouring temperature, shrinkage cavities are less likely to occur at lower pouring temperatures. Therefore, the closer the target pouring temperature is to 1300°C, the closer the value of Mf is to 0 should be used, and the closer the target pouring temperature is to 1350°C, the closer the value of 0.9 Mc should be used.

[0031] The appropriate Mf value is determined by a combination of several casting conditions as described above. While this can be determined to some extent through empirical observation, it is preferable to determine it more precisely through solidification simulations or similar methods.

[0032] Here, let's compare the volume of the riser in this application with that of a conventional riser. We will compare the solidification modulus Mr of a conventionally used riser, using Mr = 1.0 Mc as an example, and the maximum value Mf = 0.9 Mc in this application. Assuming the shape of the riser is a typical cylindrical shape (for example, diameter D, height H = 1.75D), and assuming the riser in this application is also cylindrical, we will convert this to a volume ratio. Since the solidification modulus M is linearly proportional to the representative dimension of the shape, and the volume V is proportional to the cube of the representative dimension, if the volume of the conventional riser is Vr and the volume of the riser in this application is Vf, then Vf / Vr = (Mf / Mr) 3 This is the result.

[0033] Therefore, Vf / Vr = (0.9 / 1.0) 3 This results in a value of 0.73. In other words, the minimum reduction rate of risers according to this invention is 27%. Since risers account for approximately 30% of the total casting weight, the reduction rate relative to the total casting weight is 8.1%. This reduction reduces the amount of melting required by 8.1%, and in the case of pouring multiple ladles in one pot, it increases the number of pouring slots by one or two, resulting in improved productivity on both sides.

[0034] The above is the result of examining the minimum effect of the present invention. When Mf = 0.8 Mc, the reduction rate of risers is 49%, and the reduction rate of the total casting volume is 14.6%. As a result, the required amount of melting is reduced by 14.6%, and in the case of multi-frame pouring, the number of pouring frames increases by 2 or 3. As mentioned earlier, in reality, Mr = 1.0 Mc is rarely used, and Mr = 1.2 Mc or higher is used, so an even greater reduction can be expected with the risers of the present invention.

[0035] Under optimal casting conditions, including molten metal material, mold type, product shape and size, and pouring temperature, Mf=0 (no risers) is achieved, resulting in a riser reduction of up to 100% and a total casting volume reduction of 30%. As a result, the required amount of molten metal is reduced by 30%, and in the case of multi-frame pouring, the number of pouring frames increases significantly. The most optimal mold conditions include applying the pouring temperature of this invention to shell molds or self-hardening molds. Even in the case of green sand molds, where riser reduction is most difficult, significant riser reduction is possible by adding additional conditions such as using the strongest possible mold and minimizing mold deformation after pouring.

[0036] (Measure 2) The casting method described in Means 1 is characterized in that the amount of molten metal poured is approximately equal to the volume of the desired cavity portion to be filled with molten metal, which is a part of the entire mold cavity, and compressed gas is supplied from the sprue immediately after pouring, or compressed gas is supplied and refractory granular material is introduced, thereby filling the poured molten metal into the desired cavity portion.

[0037] In this method, by means 1, it is possible to obtain a sound casting using a small volume of riser instead of a conventional riser, and a significant reduction in molten metal is achieved. In addition, a method is provided that can further reduce the sprue and runner. Specifically, when pouring, a volume of molten metal approximately equal to the volume of the desired cavity portion (for example, the product portion and the riser) to be filled with molten metal is poured, and compressed gas is supplied from the sprue immediately after pouring, or compressed gas is supplied and refractory granules are introduced to fill the poured molten metal into the desired cavity portion.

[0038] In this method, since the volume of the poured molten metal is smaller than the total volume of the cavity, the poured molten metal naturally cannot fill the desired cavity portion and spreads throughout the cavity, temporarily accumulating there. However, one method of this method is to supply compressed gas from the sprue immediately after pouring, thereby filling the poured molten metal into the desired cavity portion. In this case, the supply of compressed gas is continued until the last part of the filled molten metal has solidified to some extent and the molten metal filling the desired cavity portion no longer flows into other cavity portions. As a result, a casting is obtained in which molten metal is filled only into the desired cavity portion. Compressed air is the simplest and cheapest compressed gas to use. Using other gases, such as inert nitrogen gas, is also effective as it has the effect of preventing oxidation of the molten metal.

[0039] Another method of this process involves pouring molten metal in a volume approximately equal to the volume of the desired cavity portion to be filled, and then immediately after pouring, supplying compressed gas and refractory granules through the sprue to fill the desired cavity portion. In this case, the refractory granules are sequentially filled into at least a portion of the other cavity portions, starting from the rear of the molten metal that has filled the desired cavity portion. The refractory granules do not necessarily need to fill the entirety of the other cavity portions.

[0040] The molten metal filling the desired cavity is prevented from flowing back due to friction between the mold and the refractory granules filling the other cavities, so there is no need to wait for the last portion of the molten metal to solidify. In other words, filling the molten metal by supplying compressed gas and feeding in refractory granules significantly shortens the casting cycle compared to filling with compressed gas. However, in either method, a casting is obtained in which only the desired cavity is filled with molten metal.

[0041] The above-mentioned refractory granules can be fluidly dispersed within the cavity, and it is preferable to use refractory granules of the same type as the mold (such as sand grains) without altering the mold properties. The refractory granules may be supplied by providing a refractory granule tank or by scraping the mold near the sprue. In addition, refractory granules different from those of the mold may be supplied by other methods. Details will be explained in the examples.

[0042] Furthermore, the desired cavity portion is not limited to the product section and riser as described above. Depending on the shape characteristics of the product section and the casting method, it can be appropriately determined and poured as part or all of the product section, riser, and runner, or part of the product section, riser, runner, and sprue.

[0043] To calculate the effect of this method, let's assume, for example, that the desired cavity portion consists of the product section and the riser. This reduces the amount of molten metal in the other cavity portions. In this case, the molten metal in the runners and sprues is reduced, and a casting is obtained with only the product section and riser as the desired cavity portion. This method reduces the total amount of molten metal in the runners and sprues by approximately 20%. When this method is used in combination with method 1, under the favorable conditions of method 1, with zero riser, the combined 30% riser reduction and a maximum molten metal reduction of 50% can be achieved. In other words, a casting with only the product section and no sprues, runners, or riser can be obtained, achieving a dream casting method with 100% casting yield. Effect of the Invention

[0044] As described above, the present invention provides the following effects. Means 1 allow for the acquisition of sound castings using smaller volume risers instead of conventional risers, resulting in a reduction of up to 30% in casting weight relative to the total cavity. Means 2 also allow for a reduction of up to 20% in runners and sprues, resulting in a total reduction of up to 50% in casting weight relative to the total cavity. In other words, a casting method with a 100% casting yield can be achieved.

[0045] From the above, if the present invention is applied to the production of cast iron castings, the melting energy, which currently accounts for about 60% of the energy consumed in foundries, can be reduced by up to 50% (up to 30% of the total energy consumption of the factory). This will make a significant contribution to reducing greenhouse gases, especially CO2 gas, which have become a major problem in recent years.

[0046] Incidentally, 1.5 million tons of spheroidal graphite cast iron are produced domestically annually. Since 0.92 tons of CO2 gas are generated to produce 1 ton of cast iron, based on this calculation, 1.38 million tons of CO2 gas are generated annually, and if this invention is applied, it may be possible to reduce this by up to approximately 50%. [Brief explanation of the drawing]

[0047] [Figure 1] This figure shows the relationship between the CE value and the shrinkage cavity area ratio in Example 1 of the casting method using means 1 of the present invention. [Figure 2] This figure shows the relationship between residual Mg / S and graphite spheroidization rate in Example 1. [Figure 3] This figure shows the relationship between residual Mg / S and shrinkage cavity area ratio in Example 1. [Figure 4] This figure shows the relationship between the CE value and the sum of expansion and contraction Q for each pouring temperature in Example 2 of the casting method using means 1 of the present invention. [Figure 5] This figure shows the shape of product A and the riser design used in the study of Example 3 of the casting method using means 1 of the present invention. [Figure 6] This figure shows an example of the molten metal reduction rate obtained by applying the elements of the present invention to product A in Example 3. [Figure 7] This figure shows an example of the casting method using means 2 of the present invention, where molten metal equal in volume to the desired cavity portion to be filled has been poured. [Figure 8] This figure shows the state in Example 4 where compressed gas is supplied from the sprue immediately after the molten metal is poured in, thereby pressurizing and filling the poured molten metal. [Figure 9] This figure shows the state when a normal pouring procedure is performed in Example 4, for comparison with the present invention. [Figure 10] This figure shows an example of a casting method using means 2 of the present invention, in which compressed gas and refractory granules are supplied from the sprue immediately after the molten metal is poured, thereby pressurizing and filling the poured molten metal. [Figure 11] This figure shows an example 6 of the casting method using means 2 of the present invention, in which refractory granular material obtained by cutting the mold material near the sprue while supplying compressed gas after pouring the molten metal is used to pressurize and fill the poured molten metal. [Modes for carrying out the invention]

[0048] The present invention will be described in detail below based on examples, but the present invention is not limited by these examples. [Examples]

[0049] The results of the study regarding the appropriate values ​​of the chemical components in method 1 of the present invention will be explained using Figures 1 to 3. Figure 1 shows the relationship between the CE value and the shrinkage cavity area ratio. The shrinkage cavity is small in the range of CE 4.5 to 4.7. This is near the eutectic point in the phase diagram. In this application, a certain degree of shrinkage cavity is addressed by using a riser that is smaller than in the prior art, so CE 4.4 to 4.7 was adopted.

[0050] Figure 2 shows the relationship between residual Mg / S and spheroidization rate. To obtain a spheroidization rate of 80% or higher, which is the limit without a decrease in mechanical properties, an Mg / S ratio of 2.7 or higher is required, and to stably obtain a spheroidization rate of 80% or higher, a ratio of 3.0 or higher is preferable.

[0051] Figure 3 shows the relationship between residual Mg / S and the shrinkage cavity area ratio, where the shrinkage cavity area ratio increases with increasing Mg / S. No shrinkage cavities are obtained when Mg / S = 2.7 or less, the shrinkage cavity area ratio is 2% or less when Mg / S = 5.0 or less, and 3% or less when Mg / S = 5.6 or less. In this application, a shrinkage cavity area ratio of 3% or less is addressed by using a smaller riser than in the conventional technology, and Mg / S = 5.6 was set as the upper limit. Therefore, from Figures 2 and 3, the appropriate value for Mg / S is determined to be 2.7 to 5.6, preferably 3.0 to 5.0.

[0052] Based on the above, the appropriate values ​​for the chemical composition of element 1 of this application were adopted as CE = 4.4 to 4.7 and residual Mg / S = 2.7 to 5.6. [Examples]

[0053] Element 2 of Means 1 of this application specifically demonstrates the basis for pouring molten metal at a guideline temperature PT of 1350°C to 1300°C. Figure 4 shows the relationship between the CE value and the sum of expansion and contraction Q for each pouring temperature. In the range of CE = 4.4 to 4.7, as explained in Figure 1 of Example 1, and in the range of the guideline pouring temperature of 1350°C to 1300°C proposed in this application, the sum of expansion and contraction Q is stably positive (expansion), indicating that the product part has the conditions to self-heat as a molten metal property, and that there is a high possibility of achieving the riser removal or significant reduction targeted in this application.

[0054] When the CE value falls below 4.4, the sum of expansion and contraction Q becomes negative (contraction), and shrinkage cavities increase rapidly, as shown in Figure 1. When the CE value exceeds 4.7, the sum of expansion and contraction Q becomes numerically even larger and positive (expansion), but in this case, excess carbon in the components rises to the surface, reducing the amount of crystallized graphite, and thus the effective sum of expansion and contraction Q decreases, increasing the shrinkage property.

[0055] Regarding the pouring temperature, when the temperature exceeds 1350°C, the sum of expansion and contraction Q decreases by 0.15% for every 10°C increase, reducing the possibility of self-pouring in the product and decreasing the possibility of removing or significantly reducing risers. Therefore, in this application, the upper limit of the guideline pouring temperature is set at 1350°C. Furthermore, when the temperature is lower than 1300°C, the sum of expansion and contraction Q is even larger, increasing the possibility of self-pouring in terms of shrinkage, but the risk of casting defects such as inconsistencies and molten metal boundaries during pouring increases significantly. For this reason, the lower limit of the guideline temperature in this application is set at 1300°C. [Examples]

[0056] When the solidification modulus of the product part, as explained in element 3 of means 1, is Mc, and the solidification modulus of the riser is Mf, the use of a riser with an appropriate Mf value in the range of Mf ≤ 0.9 Mc, depending on the casting conditions, will be explained using specific product shapes and examples of applied casting conditions with reference to Figures 5 and 6.

[0057] Figure 5 shows an example of the product shape used in the study. Product A in this figure consists of a disc-shaped flange and a central perforated boss, with a solidification modulus of Mc = 0.82 cm. The mold used for casting was a green sand mold. Since shrinkage cavities occur at the intersection of the flange 29 and the boss 30, the plan is to supply molten metal from the riser through the flange. However, because the flange 29 is thin and solidifies quickly, it is difficult to supply sufficient molten metal from the riser 31, and under conventional casting conditions, it was not possible to eliminate shrinkage cavities using the conventionally recommended minimum riser solidification modulus Mr = 1.0 Mc. Therefore, to delay the solidification of the flange 29, an excess material pad 32 was attached to the upper part of the flange 29 on the riser 31 side to increase the wall thickness and delay solidification, thereby enabling molten metal supply from the riser 31, and only then was a product without shrinkage cavities obtained. However, this excess material pad 32 required machining removal after casting, resulting in extra finishing work.

[0058] Figure 6 shows an example of the results of a study on riser reduction when applying the proposed chemical composition, pouring temperature, and riser solidification modulus to green sand molds, shell molds, and self-hardening molds using product A. In the proposed solution, the conventionally added excess pad 32 was removed, and risers with several riser solidification modulos were used to investigate the conditions for eliminating shrinkage cavities and the riser reduction rate at that time.

[0059] First, with green sand molds, the riser reduction rate was somewhat low at 49-100% due to the weakness of the mold, but it was definitely possible to obtain products without shrinkage cavities with smaller risers than before. With shell molds, the mold strength is more than 10 times stronger than that of green sand molds, so a high riser reduction rate of 79-100% was achieved. Furthermore, with self-hardening molds, the mold strength is slightly lower than that of shell molds, so a riser reduction rate of 66-100% was obtained.

[0060] Moreover, in all studies, the results were obtained with the conventionally provided excess material pad 32 removed, so in addition to the reduction in riser volume, the effect of reducing extra finishing work was also obtained. Note that in the conventional technology, if the excess material pad 32 is omitted, the riser solidification modulus required to obtain a product without shrinkage cavities is Mr=1.2Mc. In this case, the riser volume becomes 1.7 times that of a riser with Mr=1.0Mc, resulting in a significant decrease in casting yield and a substantial increase in production costs. If the casting conditions of the present invention are compared with the method without the excess material pad 32, an even greater reduction in molten metal can be obtained.

[0061] Based on the above, in this example, by using means 1 of the present invention, a riser reduction of 49-100% is possible by using risers with an appropriate solidification modulus according to the casting conditions and by pouring at a lower temperature than the conventional technique. In this example, the possible reduction rate was examined for product A as an example, but for other product shapes with different sizes, wall thicknesses, and complexities, although there will be some variation in the reduction rate, it is possible to reliably obtain a sound product with less riser or no riser at all than conventional methods, and the riser can be reduced by up to 100%.

[0062] This section explains how to determine the casting conditions and the applicable riser solidification modulus. The appropriate riser solidification modulus for a single product varies depending on the mold type, molten metal material, product shape, pouring temperature, etc. Therefore, a basic table like this is created based on some empirical values, and the solidification modulus of the riser for the initial test casting is determined based on this table. Then, the value is adjusted according to the test results to determine the appropriate solidification modulus for production.

[0063] Generally, in a single factory, the type of mold is fixed, and the appropriate values ​​for the molten metal material are largely determined; therefore, the main factors that vary are the product shape and the pouring temperature. Consequently, while referring to the appropriate solidification modulus of risers based on the experience of each factory, solidification simulations and other methods are used to determine the most appropriate solidification modulus of risers by considering both experience and calculated values. [Examples]

[0064] An example of a casting method using means 2 of the present invention will be described with reference to Figures 7 to 9. Specifically, this example shows a casting method characterized by making the amount of molten metal poured approximately equal to the volume of the desired cavity portion to be filled with molten metal, which is a part of the entire mold cavity, and filling the poured molten metal into the desired cavity portion by rapidly supplying compressed gas from the sprue after pouring.

[0065] Let's explain the configuration of Figure 7. Mold 1 is a green sand mold and consists of a product section 2, a riser 3, a runner 4, and a sprue 5. In this example, the product section 2 and riser 3, which are part of the total cavity 6, are designated as the desired cavity section 7, and molten metal of approximately the same volume as this section is poured from the ladle 9. Since the poured molten metal 10 does not have enough volume to fill the total cavity 6, it spreads out within the total cavity 6 and temporarily remains there, as shown in Figure 7.

[0066] As shown in Figure 8, after pouring the molten metal, the pressurized mouthpiece 11 is quickly and airtightly placed on top of the sprue 5, and compressed gas 12 from the compression pump 14 is sent into the cavity 6, thereby filling the desired cavity portion 7 with molten metal 10. The supply of compressed gas 12 is then continued until the last portion 13 of the filled molten metal solidifies and the filled molten metal 10 stops flowing back. As a result, a casting is obtained that does not have a runner 4 or sprue 5, and consists only of the product portion 2 and riser 3.

[0067] Comparing this state with Figure 9, which shows the state when pouring is done normally, a significant difference can be seen. In this application, although the same design is used, the runner 4 and spout 5 are eliminated. Generally, the runner 4 and spout 5 account for about 20% of the total cavity, and this is almost completely eliminated. Furthermore, if method 1 is used in conjunction with this embodiment 4, the riser 3 is also reduced by about 50-100% compared to conventional risers. Since the riser 3 accounts for about 30% of the total cavity, the riser 3 represents a 15-30% reduction in the total cavity, and when combined with the reduction of the runner 4 and spout 5, the total cavity 6 is reduced by 35-50%.

[0068] In this example, the product section and riser were selected as the desired cavity section. However, the desired cavity section is not limited to the product section and riser as described above. Depending on the shape characteristics of the product section and the casting method, it can be appropriately determined and poured as part or all of the product section, riser, and runner, or part of the product section, riser, runner, and sprue. In other words, the desired cavity section can be arbitrarily selected. The same applies to Examples 5 and 6 shown below. [Examples]

[0069] Example 5 of the casting method using means 2 of the present invention will be described with reference to Figures 7 and 10. That is, as shown in Figure 7, the amount of molten metal poured is approximately equal to the volume of the desired cavity portion 7 to be filled with molten metal, which is a part of the total cavity 6, as in Example 4. Since the poured molten metal 10 does not have a volume to fill the entire cavity, it spreads throughout the entire cavity 6 and temporarily remains there. In this example, as shown in Figure 10, an example of a casting method is shown in which the poured molten metal is filled into the desired cavity portion by supplying compressed gas and refractory granules from the sprue immediately after pouring.

[0070] The configuration shown in Figure 10 will now be explained. Immediately after pouring the molten metal, the pressurized mouth 11 of the refractory granular material injection device 15 is airtightly placed on top of the spout 5. The refractory granular material injection device 15 has a refractory granular material tank 16 on top, in which refractory granular material 17 (such as sand grains) is stored. After the refractory granular material injection device 15 is airtightly placed on top of the spout 5, the shutter 18 is opened to drop the refractory granular material 17, and the valve 21 of the compressed gas supply pipe 20 connected to the refractory granular material supply pipe 19 is opened to supply compressed gas 12.

[0071] As a result, the refractory granules 17 are sent into the cavity by the compressed gas 12, and the molten metal 10 that has been poured and temporarily spread and remains throughout the entire cavity 6 is filled into the desired cavity portion 7 (product portion and riser portion). The refractory granules 17 are then sequentially filled into parts of the other cavity portions 8, starting from the rearmost part 13 of the filled molten metal 10. The refractory granules 17 do not necessarily need to fill the entire other cavity portions 8.

[0072] The refractory granules 17 filled in the other cavity portions 8 can stop the backflow of the molten metal 10 filled in the desired cavity portion 7 by friction with the mold, provided they are filled to a certain length. Therefore, in this example, there is no need to wait for the solidification of the last 13 of the filled molten metal, as in Example 4, and the supply of compressed gas 12 and the feeding of the refractory granules 17 can be stopped as soon as the filling of the refractory granules 17 is complete. As a result, a casting consisting only of the desired cavity portion 7, which is the product portion 2, and the riser 3 can be obtained in a short casting cycle. The molten metal reduction effect is the same as in Example 4. [Examples]

[0073] Example 6, which uses a different casting method from Example 5 using Means 2 of the present invention, will be explained with reference to Figure 11. In this example as well, compressed gas is supplied to send refractory granules into the mold and the poured molten metal is used to fill the desired cavity. The difference is that the refractory granules sent into the mold are supplied by cutting the mold near the top of the sprue.

[0074] In Figure 11, the configuration of the refractory granular material filling device 22, which is used first, will be briefly explained. The refractory granular material filling device 22 consists of a mold cutting machine 23 and a rotary electric motor 25 that rotates the turning tool 24 attached to its tip, an up and down lifting device 26 that raises and lowers the refractory granular material filling device 22 to press the entire device against and separate it from the mold, a pressurized mouth 11 that creates an airtight chamber, and piping 20 that supplies compressed gas 12 for sending the refractory granular material 17 into the mold and compressed gas 27 for driving the turning tool 24 up and down.

[0075] The casting method of Example 6 will now be described using the above apparatus configuration. The pouring method is the same as shown in Figure 7 of Example 4. Next, as shown in Figure 11, after pouring, the pressurized mouth 11 of the refractory granular material filling device 22 is immediately airtightly placed on the upper part 28 of the mold sprue, and the mold material particles 17, which can be filled, are made into granular form by cutting the mold near the upper part 28 of the sprue using the mold cutting machine 23. Compressed gas 12 supplied to the pressurized mouth 11 is then sent into the mold from the sprue 5. The molten metal 10 is then filled into the desired cavity portion 7, and the refractory granular material 17 is sequentially filled into at least a portion of the other cavity portions 8, starting from where it touches the rearmost part 13 of the molten metal filled in the desired cavity portion 7. In this example as well, the same final casting state as in Examples 4 and 5 can be obtained.

[0076] As shown in Examples 4, 5, and 6 using Means 2 of the present invention, after pouring molten metal to the desired cavity volume, a casting of only the desired cavity volume can be obtained by blowing in compressed gas or by feeding in compressed gas and refractory granules, resulting in a significant reduction in molten metal. This effect is due to the reduction of risers by Means 1, as well as the reduction of runners, sprues, etc., by Means 2's method of pouring molten metal only to the desired cavity volume. By using both means in combination, a substantial reduction of approximately 35-50% of the total cavity volume is possible. These molten metal reduction effects can be achieved by Means 1 simply by changing the size of the riser, and by Means 2 with the current model design. [Explanation of symbols]

[0077] 1. Mold 2. Product section 3. Riser 4. Runner 5. Sprue 6. Full cavity 7. Desired cavity portion 8 Other cavity sections 9 Ladle 10 Molten metal 11 Pressurized mouth 12 Compressed gas 13 Last of the filled molten metal 14 Compression pump 15 Fire-resistant granular material injection device 16 Fire-resistant granular material tank 17 Fire-resistant granular material 18. Shutter 19. Fire-resistant granular material supply pipe 20. Compressed gas supply pipe 21 Valve 22 Refractory granular material filling device 23 Mold cutting machine 24 Turning tool 25 Rotary electric motor 26 Lifting and lowering device 27 Gas for vertical drive of mold cutting machine 28 Top of sprue 29 Flange 30 Boss 31 Pressing Hot Water 32 Excess Fat Pad

Claims

1. A casting method for pouring molten spheroidal graphite cast iron into a sand mold, characterized in that the CE value of the molten metal after spheroidization treatment is 4.4 to 4.7, the ratio of residual Mg to residual S (Mg / S) is 2.7 to 5.6, the solidification modulus of the product is Mc, and the solidification modulus of the riser is Mf, a riser with an Mf value of Mf ≤ 0.9 Mc is used, and the molten metal temperature PT is in the range of 1350°C > PT > 1300°C when pouring.

2. A casting method according to claim 1, characterized in that the amount of molten metal poured is approximately equal to the volume of a desired cavity portion to be filled with molten metal, which is a part of the entire mold cavity, and compressed gas is supplied from the sprue immediately after pouring, or compressed gas is supplied and refractory granules are introduced to fill the poured molten metal into the desired cavity portion.

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