Casting method that can reduce casting weight

Abstract

To provide a casting method that can significantly reduce the amount of molten metal in the casting of molten spheroidal graphite cast iron. [Solution] A new feeder reduction technology that obtains sound casting products by combining the right chemical components, pouring at a lower temperature than usual, and using an appropriate feeder with a lower solidification modulus than conventional feeders allows for a significant reduction in the pouring weight. Furthermore, by combining this with technology that can also reduce the number of gates and runners, an even greater reduction in the amount of molten metal is possible.

Description

[Technical Field]

[0001] The present invention is a casting method for pouring molten spheroidal graphite cast iron into a sand mold, and provides a new technology that eliminates the need for feeders, thereby achieving a significant reduction in the amount of molten metal. It also aims to provide a casting method that drastically reduces CO2 emissions in foundries by combining this technology with a technology that eliminates gates and runners, thereby enabling an even greater reduction in the amount of molten metal. [Background technology]

[0002] In the casting of spheroidal graphite iron castings using sand molds, the mold cavity typically consists of the following components: product, feeder, runner, and gate. While the average proportion of each component varies depending on the material and product size, it is typically 50% product, 30% feeder, 10% runner, and 10% gate. Therefore, the casting yield (product weight / total casting weight) is low at approximately 50%. This situation has remained virtually unchanged for the past 50 years. In other words, to obtain a sound casting, twice the weight of the molten metal is melted. Furthermore, among the components, the feeder accounts for 30% of the total casting weight, making it a major cause of low casting yields. The feeder, runner, and gate are ultimately separated from the product as unnecessary parts and are remelted as returned material.

[0003] Regarding the reduction of the large proportion of feeders, a characteristic phenomenon in cast iron castings is that graphite crystallizes during the solidification process, causing volume expansion. This compensates for part of the solidification shrinkage of the molten metal in the product, so it is known that a sound casting can be obtained with a smaller feeder than in cast steel castings.

[0004] Although attempts have been made to reduce the number of feeders in the spheroidal graphite cast iron castings that are the subject of the present application, the casting yield has remained low as described above without any clear standards. In other words, no method has been disclosed for spheroidal graphite cast iron that can achieve a significant reduction in the number of feeders while maintaining the soundness of the casting. [Prior art documents]

[0005] As a result of searching patent documents using keywords such as feeder removal, no feeder, feeder reduction, and molten metal reduction, the following prior art documents were obtained. [Patent documents]

[0006] [Patent Document 1] Patent 5458295 [Patent Document 2] Patent application 2009-123998 [Patent Document 2] Patent application 2005-305977 [Patent Document 2] Patent application 2005-268163 [Patent Document 2] Patent application 2006-531397 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above, this application provides a new casting method for spheroidal graphite iron casting, which obtains sound casting products by using an appropriate combination of chemical components, pouring at a lower temperature than usual, and using a feeder with a lower solidification modulus than conventional feeders, thereby significantly reducing the weight of the cast product. Furthermore, by combining this feeder reduction technology with a technology that can also significantly reduce the number of gates and runners, an even greater reduction in molten metal can be achieved. As a result, the power required for melting is reduced, and the effect of reducing the generation of greenhouse gases such as CO2, which has become a problem in recent years, is sought. Means for solving the problem (Means 1)

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

[0009] This method provides a casting method that can stably reduce the number of feeders by taking advantage of the characteristics of molten spheroidal graphite cast iron during solidification. The elemental technologies used for this purpose are explained below. An essential condition for reducing the number of feeders is maintaining the soundness of the casting. Important evaluation items used for this purpose are maintaining a graphite spheroidization rate that does not result in a decrease in strength, and specifying clear conditions that do not cause or increase shrinkage cavities.

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

[0011] In this application, the CE value of 4.4 to 4.7 is defined as CE value = C% + 1 / 3Si%. If the CE value is lower than 4.4, the amount of graphite crystallized during solidification decreases, resulting in a decrease in volume expansion due to graphite. On the other hand, if the CE value is higher than 4.7, the amount of graphite crystallized increases, but the amount of floating graphite increases, resulting in a decrease in volume expansion due to graphite. Therefore, in either case, the shrinkage tendency of the molten metal increases, shrinkage cavities become more likely to occur, and it becomes difficult to reduce the size of the feeder head. Therefore, a range of 4.4 to 4.7 is appropriate. Details of this numerical value definition will be explained in the examples.

[0012] Generally, the relationship between the spheroidization rate and strength of spheroidal graphite cast iron castings and the tendency for shrinkage cavities to occur are evaluated based on the residual magnesium content after spheroidizing treatment. According to this, the practically appropriate range for magnesium is 0.030% to 0.060%. However, the inventors' research has shown that even within this range of residual magnesium, the target properties may not be achieved, resulting in reduced strength or shrinkage cavities. Therefore, by using the Mg / S ratio, which takes into account the interaction between residual magnesium and residual sulfur as a factor that takes into account the previously neglected influence of sulfur, we found that strength and the tendency for shrinkage cavities to occur can be predicted more accurately than by evaluating magnesium alone. Therefore, we applied the Mg / S ratio as a new factor.

[0013] As a result of evaluation and investigation, it was found that a Mg / S ratio of 2.7 to 5.6 is appropriate. That is, the smaller the Mg / S ratio, the less likely shrinkage cavities are to occur, making it easier to reduce the number of feeders. However, at Mg / S values ​​below 2.7, the graphite spheroidization rate may fall below 80%, the limit at which strength is not reduced. Furthermore, at Mg / S values ​​above 5.6, the shrinkage of the molten metal increases, making it more likely that unacceptable shrinkage cavities will occur, making it difficult to significantly reduce the number of feeders. Therefore, in this application, the appropriate Mg / S ratio is set to 2.7 to 5.6. Details of these numerical specifications will be explained in the Examples. In actual mass-production casting, when there is a possibility that elements other than Mg and S that inhibit graphite spheroidization or increase the shrinkage of the molten metal may have an effect, a ratio of 3.0 to 5.0 is appropriate.

[0014] Furthermore, both the residual Mg and residual S vary due to various chemical reactions with MgS, MgO, and other compounds, so careful management is required. Since the residual Mg is largely determined by the amount of S before the spheroidizing process, the amount of S is generally kept low to maximize the yield of added Mg. Therefore, the amount of residual S tends to be low. As a result, the Mg / S ratio increases, and may exceed the upper limit of 5.6 targeted by this application. In such cases, to ensure the implementation of this application, it is recommended to adjust the residual S by adding an appropriate amount of an S source, such as FeS, after the spheroidizing process, as needed, to bring the Mg / S ratio into the appropriate range.

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

[0016] Typical pouring temperatures are between 1450°C and 1350°C, depending on the size and thickness of the product, the complexity of the design, and other factors, with the average pouring temperature being 1400°C. In many cases, actual pouring is performed using a single ladle for multiple flask casting, and is carried out at an appropriate temperature range within this range. Therefore, the pouring temperature in this application is approximately 75°C lower on average than the usual pouring temperature. The reason for using such a low pouring temperature is to minimize the amount of liquid contraction of the molten metal before solidification begins.

[0017] With molten spheroidal graphite cast iron, sound castings can be obtained with smaller feeders than with ordinary molten metal (such as cast steel). This is because the carbon in the cast iron crystallizes as graphite during the solidification process, causing the volume to expand, creating a self-supply effect where the molten metal itself compensates for the shortage of molten metal that occurs as the product solidifies and shrinks. This expansion caused by graphite crystallization is an extremely rare and unique effect among metals. This method also makes effective use of this effect.

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

[0019] The expansion and contraction values ​​during the solidification process are as follows: Generally, the amount of shrinkage associated with liquid contraction is -1.5% per 100°C and is determined by the temperature difference between the pouring temperature and the solidification temperature. If the pouring temperature is PT (°C), the liquid contraction can be expressed as (PT - 1150) x (-1.5) / 100 (%), where 1150 is the solidification temperature. In other words, the liquid contraction is -3.75% when the pouring temperature is 1400°C and -3.0% when the pouring temperature is 1350°C. Furthermore, while primary and eutectic graphite differ depending on the CE value (= C + 1 / 3Si), considering the CE value of 4.4 to 4.7 proposed in this application, the expansion due to primary graphite is +0.46% to +1.51%, the expansion due to eutectic graphite is approximately +6.2% to +6.0%, and the contraction due to eutectic solidification austenite is approximately constant at -3.3%.

[0020] The table below shows an example of the expansion and contraction values ​​during the solidification process when CE is 4.4 and 4.7 and the pouring temperatures are 1400°C, 1350°C, and 1300°C. TIFF0007737593000002.tif54137

[0021] For example, when the CE value is 4.4 and the average pouring temperature is 1400°C, the total expansion and contraction Q is -0.44%, meaning that the shrinkage of the product cannot be compensated for by self-supplying the product through graphite crystallization. Therefore, a feeder is required to compensate for this. Next, for example, if the upper limit pouring temperature is 1350°C, the total expansion and contraction Q is +0.32%, and if the lower limit pouring temperature is 1300°C, the total expansion and contraction Q is +1.10%, meaning that the shrinkage of the product can be compensated for by self-supplying the product through graphite crystallization at either pouring temperature. In other words, the product can be manufactured soundly without internal defects such as shrinkage cavities without the need for replenishment of molten metal from a feeder. This offers the potential to eliminate or significantly reduce the use of feeders.

[0022] When the CE value is 4.7, if the pouring temperature is 1400°C, the total expansion and contraction Q = +0.46%, if the pouring temperature is 1350°C, the upper limit of the pouring temperature guideline in this application, the total expansion and contraction Q = +1.23%, and if the pouring temperature is 1300°C, the lower limit of the pouring temperature guideline in this application, the total expansion and contraction Q = +2.00%. In either case, the shrinkage in the product can be compensated for by graphite crystallization. However, if the pouring temperature guideline in this application is 1350°C or 1300°C, the upper and lower limits, a sound casting can be obtained more safely by removing or significantly reducing the feeder.

[0023] However, in actual casting, if there is an excess of primary graphite, some of it will rise to the top of the molten metal and will not be useful for self-feeding, resulting in a decrease in the total sum of expansion and contraction Q. Also, when the molten metal is filled into the product section, the heat causes the mold cavity to expand, resulting in a shortage of molten metal, and when these factors are taken into consideration, the total sum of expansion and contraction Q appears to decrease. Therefore, it is expected that the possibility of eliminating or significantly reducing the number of feeders will be smaller than in the above calculation, so it is necessary to compensate for this decrease in the total sum of expansion and contraction Q in some way. Therefore, 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 feeder head is Mf, a feeder head with an appropriate Mf value in the range of Mf≦0.9Mc is used.

[0025] In this method, element 1 stabilizes the spheroidization rate with appropriate chemical composition and reduces shrinkage of the molten metal. Element 2 ensures a positive sum of expansion and shrinkage Q during solidification, allowing the product to self-feed. The elimination or significant reduction of the feeder creates conditions for preventing internal defects such as shrinkage cavities. However, a decrease in the sum of expansion and shrinkage Q occurs due to unforeseen factors such as the floating of primary graphite and mold expansion. To compensate for this and further ensure the integrity of the product, a feeder with a smaller solidification modulus (= volume / surface area) than conventional feeders is used to partially compensate for the solidification shrinkage of the product. If the solidification modulus of the product is Mc and the solidification modulus of the feeder of the present invention is Mf, an appropriate value in the range of Mf≦0.9Mc is used depending on the casting conditions. This results in a shorter solidification time and a smaller feeding action than conventional feeders, but allows the product to continue to receive molten metal for an appropriate period of time. The use of a feeder with an appropriate Mf value in the range of Mf≦0.9Mc also includes the case where Mf=0, i.e., no feeder.

[0026] The optimum value for the solidification modulus Mr of a typical feeder head has traditionally been Mr = (1.0-1.2) Mc. However, this is a recommended value derived from experiments on simple-shaped products conducted over 50 years ago. In today's actual manufacturing, due to the size and complexity of the product shape, isolated thick-walled areas prone to shrinkage cavities are often far from the feeder head, making it difficult for a feeder head of this size to reach them. For this reason, a value larger than this recommended value, i.e., a large feeder head, is often used. The conventional concept of a feeder head is to completely supply the minus (shrinkage) portion of the total expansion and contraction Q of the product, which occurs when pouring at a higher temperature than the intended temperature, through the feeder head. This is the cause of low casting yields.

[0027] In contrast, in the present application, the appropriate chemical composition is used in element 1, and the sum of expansion and contraction S during solidification is made as large a positive value (expansion) as possible by low-temperature pouring in element 2, so even if the isolated thick portion is located far from the feeder head, or even if there is a certain degree of mold expansion, the sum of expansion and contraction Q associated with the solidification of the product portion itself is positive, which allows for self-feeding to suppress the occurrence of shrinkage cavities, and a sound casting can be obtained by feeding molten metal for an appropriate time using a feeder head with a small solidification modulus (=small volume). Therefore, the range of solidification modulus Mf≦0.9Mc of the feeder head and the concept of the feeding time in the present application are based on a novel concept that is clearly different from conventional feeder head concepts.

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

[0029] Next, with regard to the product shape and size, 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, prism, or similar shape, shrinkage cavities are unlikely to occur, so a smaller value closer to Mf = 0 is applied. Also, when the solidification modulus Mc of the product part is 2.5 cm or less, or when the product is a plate, ring, cylinder, or complex shape, shrinkage cavities are likely to occur, so a value closer to 0.9 Mc is applied. Since the shape and size of general product parts are somewhere between these, an appropriate value in the range of Mf ≦ 0.9 Mc is applied.

[0030] Regarding the pouring temperature, since the lower the pouring temperature, the less likely shrinkage cavities are to occur, the closer to 1300°C the target pouring temperature of the present invention is to use a value closer to Mf=0, and the closer to 1350°C the target pouring temperature is to use a value closer to 0.9Mc.

[0031] An appropriate Mf value is determined by combining several of the above-mentioned casting conditions. The means for determining this value is to some extent empirical, but more specifically, it is desirable to determine it by solidification simulation or the like.

[0032] Here, we will compare the volumes of the feeder head of the present application and a conventional feeder head. As an example, we will compare the solidification modulus Mr of a conventionally used feeder head, which is the minimum value of the conventional feeder recommended, Mr = 1.0 Mc, with the maximum value of the present application, Mf = 0.9 Mc. Assuming that the shape of the feeder head is a typical cylindrical shape (for example, diameter D, height H = 1.75D), and assuming that the feeder head of the present application is also cylindrical, we will convert this into a volume ratio. The solidification modulus M is linearly proportional (directly proportional) to the characteristic dimension of the shape, and the volume V is proportional to the cube of the characteristic dimension. Therefore, when the volume of the conventional feeder is Vr and the volume of the feeder head of the present application is Vf, Vf / Vr = (Mf / Mr) 3 This becomes:

[0033] Therefore, Vf / Vr=(0.9 / 1.0) 3 = 0.73. In other words, the minimum reduction rate for feeders according to this application is 27%. Since feeders account for approximately 30% of the total pouring weight, the reduction rate for the total pouring weight is 8.1%. This reduction reduces the required melt volume by 8.1%, and in the case of multiple flask pouring with one ladle, the number of pouring flasks increases by one or two, improving productivity in both respects.

[0034] The above results are the results of considering the minimum value of the effect of this invention, but when Mf = 0.8Mc, the reduction rate of the feeder is 49%, and the reduction rate of the total pouring amount is 14.6%. As a result, the required melt volume is reduced by 14.6%, and in the case of multi-flask pouring, the number of pouring flasks increases by two or three. As mentioned above, in reality, Mr = 1.0Mc is rarely used, and Mr = 1.2Mc or more is used, so even greater reductions can be expected with this feeder.

[0035] Under optimal conditions, such as the molten metal material, mold type, product shape and size, and pouring temperature, Mf = 0 (no feeder), resulting in a maximum 100% reduction in feeder use and a 30% reduction in the total pouring volume. As a result, the required melt volume is reduced by 30%, and in the case of multi-flask pouring, the number of pouring flasks increases. The most optimal mold conditions include applying the pouring temperature of this application to a shell mold or a self-hardening mold. Even in the case of green sand, where feeder reduction is the most difficult, significant feeder reduction is possible by adding additional conditions such as using as strong a mold as possible and suppressing mold deformation after pouring.

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

[0037] In this method, since it has become possible to obtain sound castings by using a small-volume feeder instead of the conventional feeder by Method 1, and a significant reduction in the amount of molten metal has been achieved, a method is provided in which, in addition to this, the number of gates and runners can be reduced. That is, when pouring, a volume of molten metal approximately equal to the volume of the desired cavity portion (for example, the product portion and feeder) to be filled with the molten metal, which is a portion of the entire cavity, is poured, and compressed gas is supplied from the gate immediately after pouring, or compressed gas is supplied and refractory granules are fed, so that the poured molten metal fills the desired cavity portion.

[0038] In this method, the volume of the poured molten metal is smaller than the volume of the entire cavity. Naturally, the poured molten metal does not fill the desired cavity portion, but spreads throughout the entire cavity and temporarily stagnates. However, one method of this method is to supply compressed gas through the sprue immediately after pouring, thereby filling the desired cavity portion with the poured molten metal. In this case, the supply of compressed gas is continued until the tail end of the poured molten metal solidifies to a certain extent and the molten metal filling the desired cavity portion no longer flows into the other cavity portions. This results in a casting in which the molten metal is filled only in the desired cavity portion. Compressed air is the simplest and least expensive compressed gas. Using other gases, such as inert nitrogen gas, is also effective in preventing oxidation of the molten metal.

[0039] Alternatively, the molten metal can be filled into the desired cavity by pouring a volume of molten metal approximately equal to the volume of the desired cavity portion, and then immediately feeding compressed gas and refractory granules into the desired cavity portion after pouring. In this case, the refractory granules are sequentially filled into at least a portion of the other cavity portions, starting from the end of the molten metal filled into the desired cavity portion. The refractory granules do not necessarily have to fill the entire other cavity portions.

[0040] The molten metal filled in the desired cavity portion is prevented from flowing back by friction between the refractory granules filled in the other cavity portions and the mold, so there is no need to wait for the tail end of the filled molten metal to solidify. In other words, filling the molten metal by supplying compressed gas and refractory granules significantly shortens the casting cycle compared to filling using compressed gas. However, both methods result in a casting in which the molten metal is filled only in the desired cavity portion.

[0041] The refractory granules can be fluidly dispersed within the cavity, and it is preferable to use the same type of refractory granules (such as sand) as the mold, without changing the mold characteristics. The refractory granules can be supplied by providing a refractory granule tank or by scraping the mold near the gate. Alternatively, refractory granules different from the mold can be supplied by a different method. Details will be explained in the examples.

[0042] The desired cavity portion is not limited to the product portion and the feeder head as described above, but can be determined as appropriate to pour molten metal into the product portion, the feeder head, and part or all of the runner, or the product portion, the feeder head, the runner, and part of the gate, depending on the shape characteristics of the product portion and the casting method.

[0043] To calculate the effect of this method, let us assume that the product portion and the feeder are specified as the desired cavity portion. This reduces the amount of molten metal in the other cavity portions. In this case, the molten metal in the runner and gate is reduced, and a casting with only the product portion and feeder as the desired cavity portion is obtained. This method reduces the gate and runner by a total of approximately 20% of the total cavity. When this method is used in conjunction with Method 1, in the case of Method 1 under favorable conditions with no feeder, a 30% reduction in feeder reduces the amount of molten metal, resulting in a maximum reduction of 50%. In other words, a casting with only the product portion without the gate, runner or feeder can be obtained, achieving the dream casting method with a 100% casting yield. Effects of the invention

[0044] As described above, the present invention provides the following advantages. Measure 1 allows sound castings to be obtained using a smaller-volume feeder instead of the conventional feeder, resulting in a reduction in casting weight of up to 30% for all cavities. Measure 2 also allows for a reduction in the number of runners and gates by up to 20%, resulting in a total reduction in casting weight of up to 50% for all cavities. In other words, a casting method with a 100% casting yield can be achieved.

[0045] From the above, if this invention is applied to the production of cast iron castings, the melting energy, which accounts for approximately 60% of the energy consumed in current foundries, can be reduced by up to 50% (up to 30% in terms of the energy consumed by the entire factory). This will make a significant contribution to reducing greenhouse gases, especially CO2 gas, which has become an increasingly serious problem in recent years.

[0046] Incidentally, 1.5 million tons of spheroidal graphite iron castings are produced in Japan annually. Producing one ton of casting product generates 0.92 tons of CO2 gas, so based on this calculation, 1.38 million tons of CO2 gas is generated annually, and if this invention is applied, it could potentially reduce that by up to approximately 50%. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 is a diagram showing 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 application. [Figure 2] FIG. 2 is a graph showing the relationship between residual Mg / S and the graphite spheroidization rate in Example 1. [Figure 3] FIG. 2 is a graph showing the relationship between residual Mg / S and shrinkage cavity area ratio in Example 1. [Figure 4] FIG. 10 is a diagram showing 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 application. [Figure 5] FIG. 10 is a diagram showing the shape of product A and a feeder design used in the study of Example 3 of the casting method using Means 1 of the present application. [Figure 6] FIG. 10 is a diagram showing an example of a molten metal reduction rate obtained by applying the elements of the present invention to product A in Example 3. [Figure 7] FIG. 10 is a diagram showing a state in which molten metal of a volume equal to the desired cavity portion to be filled with the molten metal has been poured in Example 4 of the casting method using Means 2 of the present application. [Figure 8] FIG. 10 is a diagram showing a state in Example 4 where compressed gas is sent from a sprue immediately after the molten metal is poured to pressurize and fill the poured molten metal. [Figure 9] FIG. 10 is a diagram showing the state when normal pouring is performed in Example 4 for comparison with the present application. [Figure 10] FIG. 10 is a diagram showing a state in which compressed gas and refractory granules are supplied from the sprue immediately after pouring the molten metal, thereby pressurizing and filling the poured molten metal in a casting process according to Example 5 of the casting method using Means 2 of the present invention. [Figure 11] FIG. 10 is a diagram showing a state in which the poured molten metal is pressurized and filled by feeding refractory granules obtained by cutting the mold material near the gate while supplying compressed gas after pouring in Example 6 of the casting method using Means 2 of the present application. DETAILED DESCRIPTION OF THE INVENTION

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

[0049] The results of the investigation into the appropriate values ​​of the chemical components in Means 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 cavities are small in the range of CE 4.5 to 4.7, which is near the eutectic point on the phase diagram. In this application, a certain degree of shrinkage cavities can be addressed by using a smaller feeder than in the prior art, so a CE of 4.4 to 4.7 was adopted.

[0050] Figure 2 shows the relationship between residual Mg / S and spheroidization rate. To achieve a spheroidization rate of 80% or more, the limit at which mechanical properties do not deteriorate, an Mg / S ratio of 2.7 or more is required, and to achieve a spheroidization rate of 80% or more stably, an Mg / S ratio of 3.0 or more is preferable.

[0051] Figure 3 shows the relationship between residual Mg / S and shrinkage cavity area ratio, with the shrinkage cavity area ratio increasing as the Mg / S ratio increases. When Mg / S is 2.7 or less, no shrinkage cavities are observed. When Mg / S is 5.0 or less, the shrinkage cavity area ratio is 2% or less. When Mg / S is 5.6 or less, the shrinkage cavity area ratio is 3% or less. In this application, a shrinkage cavity area ratio of 3% or less can be achieved by using a smaller feeder than in the prior art, and an upper limit of Mg / S is set at 5.6. Therefore, based on Figures 2 and 3, the appropriate value for Mg / S is determined to be 2.7 to 5.6. Preferably, it is 3.0 to 5.0.

[0052] From the above, the appropriate values ​​for the chemical composition of element 1 of the present invention are CE=4.4 to 4.7 and residual Mg / S=2.7 to 5.6. [Example]

[0053] The basis for pouring the molten metal at a temperature lower than 1350°C and higher than 1300°C, as proposed in Element 2 of Means 1 of the present application, is specifically shown below. Figure 4 is a diagram showing the relationship between the CE value and the sum of expansion and contraction Q for each pouring temperature. When the CE value adopted in Figure 1 of Example 1 is in the range of 4.4 to 4.7, and when the pouring temperature is in the range of 1350°C to 1300°C, as proposed in the present application, the sum of expansion and contraction Q is stably positive (expanded), and it can be seen that the molten metal properties provide the product with the conditions to be self-feeding, and there is a high possibility that the removal or significant reduction of feeders, which is the objective of the present application, can be achieved.

[0054] When the CE value is less than 4.4, the sum of expansion and shrinkage Q becomes negative (shrinkage), and shrinkage cavities increase rapidly as shown in Figure 1. When the CE value exceeds 4.7, the sum of expansion and shrinkage Q becomes even larger and positive (expansion) numerically, but in this case, excess C in the components rises to the surface, reducing the amount of crystallized graphite, and the actual sum of expansion and shrinkage Q decreases, so shrinkage increases.

[0055] Regarding the pouring temperature, when the temperature exceeds 1350°C and the total expansion and contraction Q decreases by 0.15% per 10°C, the possibility of self-feeding in the product decreases, and the possibility of removing or significantly reducing the feeder becomes smaller. Therefore, in this application, the upper limit of the pouring temperature guideline is set to 1350°C. Furthermore, when the temperature is lower than 1300°C, the total expansion and contraction Q becomes even more positive, increasing the possibility of self-feeding in terms of shrinkage, but greatly increasing the risk of casting defects such as poor pouring and cold shuts. For this reason, the lower limit of the pouring temperature guideline in this application is set to 1300°C. [Example]

[0056] As explained in Element 3 of Means 1, when the solidification modulus of the product is Mc and the solidification modulus of the feeder is Mf, the use of a feeder with an appropriate Mf value in the range of Mf≦0.9Mc depending on the casting conditions will be explained using Figures 5 and 6 for specific product shapes and examples of applied casting conditions.

[0057] Figure 5 shows an example of the product shape used in this study. Product A in this figure consists of a disc-shaped flange and a central boss with a hole. Its solidification modulus is Mc = 0.82 cm. The casting was performed using a green sand mold. Shrinkage cavities tend to occur at the intersection of the flange 29 and the boss 30, so a method of supplying molten metal from the feeder head through the flange was used. However, because the flange 29 is thin and solidifies quickly, sufficient molten metal is difficult to supply from the feeder head 31. Using the previously recommended minimum feeder solidification modulus of Mr = 1.0 Mc, shrinkage cavities could not be eliminated under conventional casting conditions. Therefore, to delay the solidification of the flange 29, an extra pad 32 was attached to the top of the flange 29 near the feeder head 31, increasing its thickness and delaying solidification, allowing molten metal to be supplied from the feeder head 31. Finally, a shrinkage cavity-free product was finally obtained. However, this extra pad 32 required machining and removal after casting, requiring additional finishing work.

[0058] An example of the results of examining the feeder reduction rate when the proposed chemical components, pouring temperature, and feeder solidification modulus of this application are applied to green sand, shell molds, and self-hardening molds using this product A is shown in Figure 6. In this proposal, the excess pad 32 that was previously added was removed, and feeders with several feeder solidification moduli were used to examine the conditions under which shrinkage cavities are eliminated and the resulting feeder reduction rate.

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

[0060] Moreover, in both studies, the results were obtained with the conventional pad 32 removed, so in addition to the reduction in feeder volume, there was also the effect of reducing unnecessary finishing work. Furthermore, if the pad 32 were not used with the conventional technology, the feeder solidification modulus required to obtain a product without shrinkage cavities would be Mr = 1.2 Mc. In this case, the feeder volume would be 1.7 times that of a feeder with Mr = 1.0 Mc, significantly reducing the casting yield and resulting in a significant increase in production costs. If the casting conditions of the present invention are compared with the plan without the pad 32, an even greater reduction in molten metal can be achieved.

[0061] As described above, in this example, by using a feeder with an appropriate solidification modulus according to the casting conditions and pouring the melt at a lower temperature than conventional techniques, it is possible to reduce the number of feeders by 49 to 100% using Means 1 of the present invention. Note that in this example, the possible reduction rate was examined for Product A as an example, but for other product shapes with different sizes, thicknesses, complexity, etc., although there will be some variation in the reduction rate, it is certainly possible to obtain a sound product with a smaller feeder than conventionally or no feeder at all, and the number of feeders can be reduced by up to 100%.

[0062] The following explains how to determine the solidification modulus of the feeder head to be applied under these casting conditions. The appropriate solidification modulus of the feeder head for a product varies depending on the type of mold, the molten metal material, the product shape, the pouring temperature, etc. Therefore, a basic list like this is created based on empirical values ​​to some extent, and the solidification modulus of the feeder head for the initial test casting is determined based on this, and the value is then adjusted according to the test results to determine the appropriate solidification modulus for production.

[0063] Generally, the type of mold used in a factory is fixed, and the optimum value for the molten metal material is also largely determined, so the main factors that change are the product shape and pouring temperature. Therefore, while referring to the optimum feeder head solidification modulus based on the experience of each factory, a more optimum feeder head solidification modulus is determined by using a solidification simulation, etc., taking into consideration both the experience and the calculated value. [Example]

[0064] Example 4 of the casting method using Means 2 of the present invention will be described with reference to Figures 7 to 9. That is, this example shows an example of a casting method characterized in that the amount of molten metal poured is approximately equal to the volume of the desired cavity portion, which is a portion of the entire mold cavity, to be filled with the molten metal, and compressed gas is sent from the sprue immediately after pouring to fill the poured molten metal into the desired cavity portion.

[0065] The configuration of Figure 7 will be explained. Mold 1 is a green sand mold, and is composed of a product section 2, a feeder head 3, a runner 4, and a gate 5. In this example, the product section 2 and feeder head 3, which are part of the entire cavity 6, are set as the desired cavity section 7, and molten metal of a volume approximately equal to this volume is poured from a ladle 9. The poured molten metal 10 does not have enough volume to fill the entire cavity 6, so it spreads throughout the entire cavity 6 and temporarily remains there, as shown in Figure 7.

[0066] Therefore, as shown in Figure 8, after pouring, a pressurized mouth 11 is quickly placed airtight above the gate 5 and compressed gas 12 from a compression pump 14 is sent into the cavity 6, filling the molten metal 10 into the desired cavity portion 7. The supply of compressed gas 12 is then continued until the tail end 13 of the filled molten metal solidifies and the filled molten metal 10 no longer flows back. This results in a casting that has only the product portion 2 and riser 3, without the runner 4 and gate 5.

[0067] A significant difference can be seen when comparing this state with Figure 9, which shows the state when pouring normally. In this application, the same design is used, but the runner 4 and gate 5 have been eliminated. Generally, the runner 4 and gate 5 occupy approximately 20% of the total cavity, and this amount has been reduced almost entirely. Furthermore, if Method 1 is used in conjunction with Example 4, the feeder 3 can be reduced by approximately 50 to 100% compared to the conventional feeder. Since the feeder 3 occupies approximately 30% of the total cavity, the feeder 3 is reduced by 15 to 30% of the total cavity, and together with the reduction of the runner 4 and gate 5, the total cavity 6 is reduced by 35 to 50%.

[0068] In this example, the product portion and the feeder head were selected as the desired cavity portion, but the desired cavity portion is not limited to the product portion and the feeder head as described above. Depending on the shape characteristics of the product portion and the casting design, the desired cavity portion can be determined as appropriate to pour the molten metal into the product portion, feeder head, and part or all of the runner, or the product portion, feeder head, runner, and part of the gate. In other words, the desired cavity portion can be selected arbitrarily. The same applies to Examples 5 and 6 shown below. [Example]

[0069] A fifth embodiment of the casting method using the second aspect of the present invention will be described with reference to Figures 7 and 10. As shown in Figure 7, the amount of molten metal poured is set to be approximately equal to the volume of the desired cavity portion 7, which is a portion of the entire cavity 6, as in the fourth embodiment. The poured molten metal 10 does not have enough volume to fill the entire cavity 6, so it spreads throughout the entire cavity 6 and temporarily remains there. This example shows an example of a casting method in which, as shown in Figure 10, compressed gas and refractory granules are fed from a sprue immediately after pouring to fill the desired cavity portion with the poured molten metal.

[0070] The configuration of Figure 10 will be explained. After pouring the molten metal, the pressure mouth 11 of the refractory granular material injection device 15 is immediately placed airtight above the gate 5. The refractory granular material injection device 15 has a refractory granular material tank 16 at its top, in which refractory granular material 17 (such as sand grains) is stored. After the refractory granular material injection device 15 is placed airtight above the gate 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 accumulated throughout the entire cavity 6 is filled into the desired cavity portion 7 (product portion and riser). The refractory granules 17 are sequentially filled into parts of the other cavity portions 8 starting from the rearmost portion 13 of the filled molten metal 10. The refractory granules 17 do not necessarily have to fill the entire other cavity portions 8.

[0072] If the refractory granules 17 filled in the other cavity portions 8 have a certain filling length, the frictional force with the mold can stop the backflow of the molten metal 10 filled in the desired cavity portion 7. Therefore, in this example, there is no need to wait for the tail end 13 of the filled molten metal to solidify as in Example 4, and the supply of compressed gas 12 and refractory granules 17 can be stopped as soon as filling of the refractory granules 17 is complete. This makes it possible to obtain a cast product consisting of only the product portion 2 and feeder head 3, which are the desired cavity portion 7, in a short casting cycle. The molten metal reduction effect is the same as in Example 4. [Example]

[0073] Example 6, which is a casting method different from Example 5 using Means 2 of the present invention, will be described with reference to Figure 11. In this example, compressed gas is also supplied to feed refractory granules into the mold, and the poured molten metal fills the desired cavity portion. The difference is that the refractory granules are supplied by scraping the mold near the top of the gate.

[0074] First, a brief description of the configuration of the refractory granule filling device 22 used will be given in Figure 11. The refractory granule filling device 22 is composed of a rotary electric motor 25 that rotates a mold cutter 23 and a turning tool 24 attached to the tip of the mold, a vertical lifting device 26 that raises and lowers the refractory granule filling device 22 to press the entire device against and separate it from the mold, a pressure mouth 11 that creates an airtight chamber, and piping 20 that supplies compressed gas 12 for feeding the refractory granules 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 be described using the above-described equipment configuration. The pouring method is the same as that shown in FIG. 7 for Example 4. Next, as shown in FIG. 11, immediately after pouring, the pressure mouth 11 of the refractory granule filling device 22 is airtightly placed above the gate 28 of the mold. The mold is then scraped near the gate 28 with a mold scraper 23 to produce fillable granular molding material particles 17, which are then forced into the mold through the gate 5 by compressed gas 12 supplied to the pressure mouth 11. Molten metal 10 fills the desired cavity 7. The refractory granules 17 are then gradually filled into at least a portion of the remaining cavities 8, starting at the tail 13 of the molten metal filled in the desired cavity 7. This example also produces a final casting state identical to that of Examples 4 and 5.

[0076] As shown in Examples 4, 5, and 6 using Method 2 of the present invention, after pouring the molten metal only into the desired cavity volume, compressed gas or compressed gas and refractory granules are injected to produce a casting with only the desired cavity volume, resulting in a significant reduction in molten metal. In addition to the reduction in feeder heads achieved by Method 1, Method 2, which pours the molten metal only into the desired cavity, also reduces the need for runners and gates. By using both methods in combination, a significant reduction in molten metal of approximately 35 to 50% can be achieved for the entire cavity. Note that these molten metal reduction effects can be achieved by simply changing the size of the feeder head in Method 1, while Method 2 can be achieved using the current pattern design. [Explanation of symbols]

[0077] 1 Mold 2 Product part 3 Riser 4 Runner 5 Sprue 6 Whole cavity 7 Desired cavity Partial cavity 8 Other cavity parts 9 Ladle 10 Molten metal 11 Pressure mouse 12 compressed gas 13 end of filled molten metal 14 compression pump 15 Refractory granule blowing device 16 Refractory granule tank 17 Refractory granule 18 Shutter 19 Fire-resistant granular material supply pipe 20 Compressed gas supply pipe 21 Valve 22 Refractory granule filling device 23 Mold scraping machine 24 Turning tool 25 Rotating electric motor 26 Up / down lifting device 27 Gas for driving the mold scraper up and down 28 Upper part of the gate 29 Flange 30 Boss 31 Riser 32 Excess pad

Claims

1. A casting method for pouring molten spheroidal graphite cast iron into a sand mold, characterized in that, when the CE value of the molten metal after spheroidizing treatment is 4.4 to 4.7, the ratio of the amount of residual Mg to the amount of residual S is Mg / S is 2.7 to 5.6, the solidification modulus of the product part is Mc, and the solidification modulus of the feeder head is Mf, a feeder head with an appropriate Mf value in the range of Mf≦0.9Mc depending on the casting conditions is used, and the molten metal temperature PT is in the range of 1350°C > PT > 1300°C is used for pouring.

2. 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, which is a portion of the entire mold cavity, to be filled with the molten metal, and the poured molten metal is filled into the desired cavity portion by immediately supplying compressed gas from the sprue after pouring, or by supplying compressed gas and refractory granules.

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