Casting method

Abstract

To provide a casting method for manufacturing a casting improved in hardness of a hard part by smoothly dipping molten metal between hard particles and increased in degree of integration of the hard part with the other casing part, and a casting using the same.SOLUTION: A casting is manufactured by pouring molten metal after setting of a particle molding 6 composed of hard particles and a binder in a mold 1 and integrating a hard part formed by dipping molten metal between the hard particles with the other casing part. A heating molding 7 composed of a heating agent and a binder is set in the mold 1 in contact with the particle molding 6 of a part equivalent to the surface of the hard part. A sub-runner 10 different from a main runner 9 for pouring molten metal is formed for the heating molding 7. The heating agent is caused to generate heat by pouring molten heat through the sub-runner 10 separately from pouring of molten heat through the main runner.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a casting method, and more particularly to a casting method in which a grain compact made of hard grains and a binder is set in a mold, and then molten metal is poured into the mold to impregnate the spaces between the hard grains, forming a hard portion that is integrated with other cast portions to produce a casting. [Background technology]

[0002] One known method for improving the wear resistance, hardness, etc. of specific parts of a casting involves applying a mixture of hard particles and a binder to specific parts of a mold and combining the coating with the cast metal (see, for example, Patent Document 1). However, this method has the problem that because the surface modifying layer is directly bonded to the base steel of the casting, large residual stress occurs at the interface between them, making them prone to peeling and cracking. Patent Document 2 solves this problem by inserting a backing layer for welding.

[0003] However, with the technology of Patent Document 2, as the thickness of the lining layer increases, the amount of heat required to melt the carbonyl iron powder in the lining layer increases, the temperature of the mixed metal of carbonyl iron powder and molten metal decreases, making it difficult to raise the temperature of the surface layer for modification and making it difficult for the molten metal to fully penetrate to the edge. This becomes more pronounced as the particle size of the hard particles in the surface layer for modification decreases. Furthermore, because the mixed metal of carbonyl iron powder and molten metal penetrates the surface layer for modification, the hardness decreases dramatically. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3061332 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-220462 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above-mentioned conventional situation, the present invention aims to provide a casting method for producing a casting in which the hardness of the hard portion is improved by more smoothly impregnating the molten metal between the hard particles, and the degree of integration between the hard portion and other cast portions is improved. [Means for solving the problem]

[0006] To achieve this object, the casting method of the present invention is characterized in that a grain compact made of hard grains and a binder is set in a mold, and then molten metal is poured into the mold, and the molten metal is impregnated between the hard grains to form hard portions that are integrated with other cast portions, to produce a casting. In this method, the hard grains are WC (tungsten carbide), the molten metal is any of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, and grains with an average grain size of 26 μm or more are large grains, and the large grains and the large grains are interspersed. At least two types of large particles and medium particles having a particle size 1 / 10 to 1 / 4 of the average particle size are mixed, and the volume ratio is 50 to 88% of the large particles and 12 to 50% of the medium particles. A heat-generating molded body made of a heat-generating agent for casting and a binder is set in a mold in contact with the particle molded body at a position corresponding to the surface of the hard portion, and a side runner separate from a main runner for pouring the molten metal is formed in the heat-generating molded body, and the heat-generating agent is heated by pouring the molten metal into the side runner separately from the main runner.

[0007] According to this method, the exothermic agent for casting is heated by pouring the molten metal into the side runner separately from pouring it into the main runner, so that the exothermic agent is ignited and heated before pouring it into the main runner. Because the exothermic molded body is in contact with the grain compact, the molten metal poured from the main runner comes into contact with the grain compact while the grain compact is in a preheated state, and the molten metal easily penetrates between the grains of the grain compact. Even if the grain compact is located beyond other intricate parts of the casting, heat is supplied by the separate heating caused by the ignition of the exothermic molded body. This prevents poor impregnation or poor adhesion between the grain compact and other parts of the casting due to a drop in the molten metal temperature caused by the intricate parts, and can improve the quality of the casting. The hard particles are WC (tungsten carbide), the molten metal is any of FC100-FC350, FCD350-FCD800, and high-Cr cast iron, and the large particles have an average particle size of 26 μm or more. The large particles are mixed with at least two types of medium particles, with the large particles having an average particle size of 1 / 10 to 1 / 4 of the large particles' average particle size, and the mixture is composed of 50-88% of the large particles and 12-50% of the medium particles by volume. This configuration allows smaller hard particles to be placed between the hard particles, improving the packing density of the hard particles and increasing the hardness of the hard portion. Furthermore, it was found that the preheating using the exothermic molding body sufficiently maintains impregnation between the hard particles.

[0008] Another feature of the casting method according to the present invention, which is intended to achieve the above object, is that a grain compact made of hard grains and a binder is set in a mold, and then molten metal is poured into the mold, and the molten metal is impregnated between the hard grains to form hard portions that are integrated with other cast portions, to produce a casting, in which the hard grains are WC (tungsten carbide), the molten metal is any of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, and particles with an average grain size of 26 μm or more are large grains, and the large grains and medium grains having an average grain size of 1 / 10 to 1 / 4 of the average grain size of the large grains are mixed. The method is characterized in that at least three types of particles are mixed: large particles, medium particles, and small particles having an average particle size 1 / 10 to 1 / 4 of the medium particles, and the mixture is composed of 50 to 88% of the large particles, 8 to 46% of the medium particles, and 4 to 25% of the small particles, in volume ratios of 50 to 88% of the large particles, 8 to 46% of the medium particles, and 4 to 25% of the small particles; an exothermic molded body made of an exothermic agent for casting and a binder is set in a mold in contact with the grain molded body in a portion corresponding to the surface of the hard portion; and a side runner separate from a main runner for pouring the molten metal is formed in the exothermic molded body, and the exothermic agent is heated by pouring the molten metal into the side runner separately from the main runner. The reason is the same as the previous feature.

[0010] In order to achieve the above object, yet another feature of the casting method of the present invention is that a grain compact comprising hard particles and a binder is set in a mold, and then molten metal is poured into the mold to produce a casting in which the molten metal is impregnated between the hard particles to form a hard portion that is integrated with other cast portions, wherein the hard particles are tungsten carbide (WC) particles having an average particle size of 26 μm or more, the molten metal is any of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, and a heat-generating molded body comprising a heat-generating agent for casting and a binder is set in the mold in contact with the grain compact in a portion corresponding to the surface of the hard portion, and a side runner separate from a main runner for pouring the molten metal is formed in the heat-generating molded body, and the heat-generating agent is heated by pouring the molten metal into the side runner separately from the main runner.

[0011] In the above configuration, it is desirable to pour the molten metal into the side runner before pouring it into the main runner, because in this method the exothermic molded body will already be heated by pouring the molten metal into the side runner before pouring it into the main runner, which tends to improve the degree of impregnation.

[0012] Furthermore, it is preferable to add Te to the grain compact.

[0016] In practice, the present invention is applied to a full mold casting method, and a mold is formed by stacking the grain compact and the exothermic compact on a part of a lost pattern. Also, the hard part formed by impregnating molten metal between the hard particles is preferably disposed on a cutting blade or bending blade of a press die, a sliding part of a machine tool, or an abrasion-resistant pipe. [Effects of the Invention]

[0017] As described above, according to the features of the present invention, it is possible to provide a casting method for producing a casting in which the hardness of the hard portion is improved by more smoothly impregnating the molten metal between the hard particles, and the degree of integration between the hard portion and other cast portions is improved.

[0018] Other objects, configurations and effects of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view of a mold during molding (before pouring molten metal). [Figure 2] 1 shows the appearance of the particle compact and the foam pattern. [Figure 3] 1 shows the external appearance of the composite material produced in Experimental Example 1, where (a) uses a heat-generating molded body and (b) does not use a heat-generating molded body. [Figure 4] 1 is a graph showing hardness in Experimental Examples 2 to 8. [Figure 5] 10 is a photograph of the structure of a composite part manufactured in Experimental Example 4. [Figure 6] 1 is a graph showing hardness in Experimental Examples 2 to 9. [Figure 7] 1 is a graph showing hardness in Experimental Examples 4, and 9 to 12. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will now be described in more detail with reference to the accompanying drawings as appropriate. Figure 1 shows a schematic diagram of a mold 1 in an example in which the present invention is applied to full mold casting. A lost model 5 is provided within a mold flask 2, in which a grain compact 6, formed by bonding grains with a binder, is set in a notched corner 5a. Meanwhile, another surface of the grain compact 6 is placed in contact with a notched corner 7a of a heat-generating molded body 7, formed by bonding a heat-generating agent with a binder. A casting heat-generating agent is used as the heat-generating agent.

[0021] A ceramic pipe 9a and an elbow member 9b are provided to form a main runner 9 through which the molten metal poured into the overflow weir 8 flows to the expendable pattern 5. Meanwhile, a ceramic pipe 10a and an elbow member 10b are provided to form a sub-runner 10 for ignition, separate from the main runner 9 for pouring the molten metal, from the top of the mold to the exothermic formed body 7. The outer surfaces of these elements are filled with molding sand 3. A layer of mold wash 11 is provided around the expendable pattern 5, except for the aforementioned cutout portion 5a, the main runner 9, and the sub-runner 10.

[0022] After the mold 1 is formed, molten metal is poured into the sub-runner 10 for igniting the exothermic agent, which ignites the exothermic agent and preheats it. The molten metal is then poured into the dam 8 and poured into the evaporative pattern 5 through the main runner 9. The exothermic mold 7 preheats the grain compact 6 by ignition, and the molten metal infiltrates between the grains of the grain compact, resulting in a casting product in which the metal and the grain compact are combined.

[0023] The full mold casting method is suitable for the production of non-mass products and large castings. This method involves creating a lost pattern 5 using polystyrene foam, then replacing the foam with molten cast iron to create a casting. Spaces for placing a powder compact at any location on the casting, such as the corner cutouts 5a described above, can be created, facilitating the design of the casting, making the present invention easy to apply. Furthermore, unlike the wooden mold method, powder compact 6 can be placed on foam pattern 5, for example, via cutout 5a, before the molding process, and then a heat-generating molded body 7 with cutout 7a can be placed, resulting in high manufacturing efficiency.

[0024] WC is used as the hard particles, but SiC (silicon carbide) or alumina can also be used. This makes it possible to manufacture a composite part that is harder than the poured metal, improving the wear resistance of specified product areas.

[0025] According to the experimental examples described below, it is desirable that the hard particles be a mixture of two or more types with different average particle sizes. This is because, with this configuration, hard particles with smaller particle sizes are arranged between the hard particles, improving the packing density of the hard particles and thereby improving the hardness of the hard portion. Furthermore, it was found that the impregnation between the hard particles is sufficiently maintained by preheating using the heat-generating molded body. Furthermore, according to the experimental examples described below, it is desirable that the hard particles be a mixture of three or more types with different average particle sizes. The reason is the same when two or more types are mixed.

[0026] By the way, a mixture of two or more types of particles with different average particle diameters is desirable, more specifically, the hard particles are composed of 50 to 88% large particles and 12 to 50% medium particles, which have an average particle diameter of 1 / 10 to 1 / 4 of the average particle diameter of the large particles (hereinafter, "particle diameter" means "average particle diameter") by weight. The same applies to a mixture of three or more types, but even if the ratio does not fall within this range, the degree of solidity of the hard particles can be improved, which of course can contribute to enhancing the effects of the present invention.

[0027] When hard particles are made of the same material, the specific gravity itself does not change even if the particle size is different. Therefore, in this specification, weight ratio and volume ratio are interpreted as having the same meaning, and further, measurements are made based on weight ratio.

[0028] The particle size of the medium particles is preferably 1 / 10 to 1 / 4 of the particle size of the large particles, and even more preferably 1 / 7. When the particle size of the medium particles is 1 / 7 of the particle size of the large particles, the particles can penetrate into the gaps between the large particles when the large particles are closely packed, improving the filling rate. When the average particle size of the medium particles is larger than 1 / 4 of the large particle size, the medium particles are too large to penetrate into the gaps between the large particles, making it difficult to expect an improvement in the filling rate. When the average particle size is smaller than 1 / 10, the particles will penetrate into the gaps between the large particles, but the amount of binder required to bond the particles will increase unnecessarily, resulting in increased binder residue in the hard particle compact after molten metal impregnation.

[0029] To confirm the effect of two types of particles with an ideal particle size ratio of 1 / 7, the inventors calculated the packing ratio when large particles with a particle size of 70 μm and medium particles with a particle size of 10 μm were mixed. It was found that for a particle compact with a two-peak particle size distribution, a good packing ratio of over 69% was achieved when the weight (volume) ratio of medium particles in the weight (volume) ratio of the two particles was 12 to 50%. It was also confirmed that the best packing ratio was achieved when the weight (volume) ratio of large particles to medium particles was 3:1 (i.e., a medium particle ratio of 25%). This is thought to be because the medium particles penetrated into the gaps between the large particles, reducing the porosity of the particle compact.

[0030] In this case, if the weight (volume) ratio of large particles is below 50%, the gaps between the large particles will be reduced, and the number of medium particles filling the gaps will increase, resulting in a stagnant filling rate. If it exceeds 88%, fewer medium particles will enter the gaps between the large particles, resulting in more voids inside the compact. Also, as mentioned above, if the weight (volume) ratio of medium particles is increased above 50%, the amount of binder used will unnecessarily increase.

[0031] Furthermore, it is desirable to use a mixture of three or more types of particles with different average particle sizes, more specifically, the hard particles are composed of 50 to 88% large particles, 8 to 46% medium particles that are 1 / 10 to 1 / 4 the average particle size of the large particles, and 4 to 25% small particles that are 1 / 10 to 1 / 4 the average particle size of the medium particles, in weight ratio.

[0032] The purpose of using three particle sizes is to further improve particle packing by applying the same geometric similarity relationship between the medium and small particles as described above, since the packing density is improved by using large and medium particles. Therefore, medium particles with an average particle size of 1 / 10 to 1 / 4 the large particle size and small particles with an average particle size of 1 / 10 to 1 / 4 the medium particle size are also used. Similarly, it is more preferable that the particle sizes of the medium and small particles are 1 / 7 of the large and medium particle sizes, respectively. The disadvantages of exceeding these ranges are also as described above.

[0033] The inventors calculated the packing ratio when mixing three types of particles with different particle sizes. The large particles were set to 70 μm, the medium particles to 10 μm, and the small particles to 1.4 μm, so that the particle sizes of the large particles were approximately 1 / 7 of each other.

[0034] The calculation results for the above two types of particle blends show that the filling rate is highest when the weight (volume) ratio of medium particles is 25%, and it is thought that the filling rate can be further improved by filling the voids under these conditions with small particles. Therefore, calculations were carried out by fixing the weight (volume) ratio of medium particles at 25% and varying the ratio of large particles to small particles. The calculation results showed that a good filling rate of over 80% was achieved when the weight (volume) ratio of small particles was set to 4-31%.

[0035] In this case, if the weight (volume) ratio of small particles is below 4%, fewer particles will enter the gaps, making it difficult to expect an improvement in the filling rate, while if it exceeds 25%, the amount of binder used will unnecessarily increase.Since small particles complement the relationship between large and medium particles through a geometric similarity relationship, it is desirable to use a weight (volume) ratio of large particles of 50 to 88%, as adopted in a two-peak particle size distribution.Furthermore, if the weight (volume) ratio of small particles is 4 to 25%, the weight (volume) ratio of medium particles will be 8 to 46%.

[0036] Te may be added to the particle compact, the particles themselves, or the particle binder, but the former is more preferable. The addition of Te causes chill in the impregnated metal of the composite, as described below, and improves hardness.

[0037] The pouring metal may be spheroidal graphite cast iron, flake graphite cast iron, high Cr cast iron, etc. By changing the pouring metal, the hardness of the composite part can be selected in various ways. [Example]

[0038] EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples as experimental examples, but the present invention is not limited to the following examples.

[0039] The present inventors first conducted experiments to efficiently impregnate the molten metal into the grain compact.

[0040] (Experimental Example 1) A particle compact was created using tungsten carbide (WC) with an average particle size of 81 μm as the hard particles, with 3 wt% water glass added as a binder for the hard particles. Figure 2 shows the particle compact and the lost mold used in the experiment. The particle compact was manufactured to a size of 20 mm square and 120 mm long. After placing the resulting particle compact in the foam pattern, a heat-generating agent made with 10 wt% water glass was placed around one half of the particle compact, while the other half was placed in a flask without any attachment. Next, runners for igniting the heat-generating agent and pouring the molten metal were created, and sand was filled into the flask. A breaker was installed above the pouring runner to create a mold. Molten metal was poured into the ignition runner of the mold, igniting the heat-generating agent. One of the particle compacts was heated, and then poured into the breaker, impregnating the particle compact with the molten metal.

[0041] Figure 3 shows the product shape after pouring; (a) shows the case using an exothermic compact, and (b) shows the case without an exothermic compact. In the example using an exothermic agent (Figure 3(a)), the base casting (other cast parts) 25 and the hard particle compact composite (hard part) 26 were each beautifully formed, and it was confirmed that the molten metal had penetrated the particle compact to its edges. In contrast, in Figure 3(b), the corners of the hard particle compact composite (hard part) 26 are rounded, indicating that the molten metal had not penetrated all the way to the edges. When there is a temperature difference, WC and molten metal lose their wettability. Furthermore, the heat of the molten metal impregnating the particle voids is transferred to the particles, gradually lowering their temperature, solidifying them and preventing impregnation. When an exothermic agent is used, the particle compact can be sufficiently heated before pouring, reducing the temperature difference between the molten metal and the particle compact while also minimizing the temperature drop of the impregnating molten metal, improving impregnation efficiency.

[0042] Next, the inventors conducted various experiments to improve the hardness of the composite portion.

[0043] (Experimental Example 2) WC with an average particle size of 81 μm was used as the hard particles, and 0.3 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as the exothermic agent and molding was performed. FCD700 was used as the pouring material.

[0044] (Experimental Example 3) WC with an average particle size of 26 μm was used as the hard particles, and 0.3 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as the exothermic agent and molding was performed. FCD700 was used as the pouring material.

[0045] (Experimental Example 4) WC with an average particle size of 8 μm was used as the hard particles. When making a compact using only particles with an average particle size of 8 μm, it is difficult to make a compact if the amount of water glass is small, so 1.2 wt% water glass was added to make a particle compact. The exothermic agent was 10 wt% water glass, and molding was carried out. The pouring material was FCD700.

[0046] (Experimental Example 5) The hard particles used were WC with an average particle size of 81 μm and WC with an average particle size of 8 μm mixed in a volume ratio of 70:30, with a particle size distribution with at least two peaks. 0.6 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as a heat generating agent and molding was performed. FCD700 was used as the pouring material.

[0047] (Experimental Example 6) The hard particles used were WC with an average particle size of 26 μm and WC with an average particle size of 3.17 μm mixed in a volume ratio of 70:30, with a particle size distribution with at least two peaks. 1.2 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as a heat generating agent and molding was performed. FCD700 was used as the pouring material.

[0048] (Experimental Example 7) The hard particles used were WC with an average particle size of 81 μm, WC with an average particle size of 8 μm, and WC with an average particle size of 1.50 μm, mixed in a volume ratio of 65:25:10, with a particle size distribution with at least three peaks. 0.9 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as a heat generating agent and molding was performed. FCD700 was used as the pouring material.

[0049] (Experimental Example 8) The hard particles used were WC with an average particle size of 26 μm, WC with an average particle size of 3.17 μm, and WC with an average particle size of 0.72 μm, mixed in a volume ratio of 65:25:10, with a particle size distribution with at least three peaks. 1.5 wt% water glass was added as a binder for the hard particles to create a particle compact. 10 wt% water glass was added as a heat generating agent and molding was performed. FCD700 was used as the pouring material.

[0050] In the above experimental examples, a particle compact and lost mold of the same size as in Figure 2 were used. In these experiments, after manufacturing the composite under the above conditions, the composite portion of the particle compact and base material was cut out to create a test piece, and the structure was observed to confirm cracks in the particle compact within the composite portion. Table 1 shows the test conditions and the presence or absence of cracks for each experimental example. Rockwell hardness tests were also conducted, measuring the hardness at nine points on the particle compact and calculating the average value. A graph showing the average value, maximum hardness, and minimum hardness is shown in Figure 4.

[0051] [Table 1]

[0052] First, the experimental results of Experimental Examples 2 to 4 are compared. It can be seen that the hardness increases in the order Experimental Example 4 > Experimental Example 3 > Experimental Example 2. This suggests that by reducing the particle size, the voids within the particle compact narrow, increasing the density of the particle compact, and therefore increasing the hardness. However, when using only particles with a particle size of 8 μm and adding a small amount of water glass, it is more difficult to produce a particle compact than with the other examples.

[0053] In addition, as shown in Figure 4, when the particle diameter is 8 μm, the hardness measurement results vary widely, indicating that the hardness of the composite is not stable. This is thought to be because particles with a small average particle size have a high frictional resistance during kneading, which prevents the water glass from dispersing evenly within the compact, causing particles to gather around the water glass, creating gaps within the particle compact and resulting in areas with a high concentration of impregnated metal and residue and few particles.

[0054] Another problem was that the binder did not adhere uniformly to the particles, making the particle compact susceptible to cracking due to the impact of pouring. Figure 5 shows a photograph of a composite manufactured under experimental condition 3. A crack indicated by the symbol C can be seen inside the hard particle compact composite section (hard section) 26, compared to the base casting (other casting sections) 25. While increasing the amount of water glass added could solve this problem, this is not recommended because it would increase the amount of water glass residue, which would reduce hardness. Generally, burning water glass produces residue composed primarily of Si, Na, and O. Because the hardness of the residue is significantly lower than that of WC or the pouring metal, increasing the amount of residue inside the particle compact reduces hardness.

[0055] Next, we compare the experimental results of Experimental Examples 2, 3, 5, and 6. Composites made with particle compacts that have at least two peaks in particle size distribution have higher hardness. This shows that when medium particles are blended with large particles, the medium particles fill the gaps between the large particles, increasing the packing rate of the particle compact and resulting in a composite with improved hardness. We also confirmed that increasing the packing rate reduces the gaps between particles, minimizing residue and improving hardness.

[0056] Next, the experimental results of Experimental Examples 4, 5, and 6 are compared. As shown in Figure 4, Experimental Examples 5 and 6 were found to have higher hardness than Experimental Example 4. Because the amount of water glass added in Experimental Example 5 was less than in Experimental Example 4, it is thought that the hardness would be slightly lower when the same amount was added, but even taking this into account, Experimental Example 5 is thought to have a hardness similar to that of Experimental Example 4. Furthermore, in Experimental Examples 5 and 6, no cracking of the particle compact observed in Experimental Example 4 was observed. In addition, it was found that the variation in hardness was small in Experimental Examples 5 and 6, preventing localized reductions in hardness in the composite area.

[0057] Finally, we compare the experimental results of Experimental Examples 5 to 8. As shown in Figure 4, the composite made with a particle compact having a particle size distribution with at least three peaks had higher hardness. This indicates that when small particles are added, the small particles penetrate into the gaps between the large and medium particles, increasing the filling rate of the particle compact and resulting in a composite with improved hardness. Although the hardness variation is greater than in Experimental Examples 5 and 6, the minimum values ​​of the hardness measurement results for Experimental Examples 7 and 8 all exceed the average hardness of Experimental Examples 2 to 6, indicating an increase in the hardness of the entire composite. These results indicate that a composite with improved hardness can be obtained when a particle compact with a particle size distribution with at least three peaks is used.

[0058] The present inventors conducted experiments to further improve the hardness of the composite portion.

[0059] (Experimental Example 9) 450g of WC with an average particle size of 8μm was used as hard particles. 5.3g of Te was used to generate chill in the metal to be impregnated into the WC. After mixing the WC particles and Te, 1.2wt% of water glass was added to create a particle compact. 10wt% of water glass was added as the exothermic agent and molding was carried out. FCD700 was used as the pouring material.

[0060] In Experimental Example 9, a grain compact and a lost die of the same size as those in Figure 2 were used. The test conditions are shown in Table 2. A Rockwell hardness test was also conducted to measure the hardness at three points on the grain compact, and the average value was calculated. A graph showing the average values ​​for Experimental Examples 2 to 9 is shown in Figure 6.

[0061] [Table 2]

[0062] As shown in Figure 6, the hardness of the composite with added Te was higher than that of the other experimental examples. Microstructural observation revealed that only the metal infiltrating the hard particle compact turned into white pig iron. Te is a chill-promoting element, and it is known that adding approximately 0.01 wt% of Te to the FC molten metal causes chill in the entire molten metal. Because the amount of Te between the base metal and the particle surface is very small, it bonds with the Mg contained in the molten metal, preventing chill from forming in the base metal. Te in the particle compact gasifies when the molten metal infiltrates it, but because the mold has better permeability than the molten metal, most of it is released from the mold to the outside. Some of the gasified Te and the oxygen contained in the water glass react with the Mg in the molten metal, causing poor spheroidization. Subsequently, the unreacted Te reacts with the infiltrated molten metal, causing chill. Based on the above, when Te is added to the hard particle compact, only the infiltrating metal in the particle compact turns into white pig iron. When chill occurs in the entire base metal, residual stress during solidification and shrinkage can easily cause cracks on the surface of the product. This problem becomes more pronounced as the product size increases. Furthermore, it is not desirable to generate chills in the entire product, as this results in extremely high hardness and requires significant processing costs. However, the present invention can generate chills only in the metal of the composite portion, thereby improving the hardness of specified areas of the product without causing the above problems.

[0063] Next, the inventors conducted an experiment to change the hardness of the composite part by using different pouring metals.

[0064] (Experimental Example 10) WC with an average particle size of 8 μm was used as the hard particles. 1.2 wt% water glass was added to create a particle compact. 10 wt% water glass was added as the exothermic agent and molding was performed. FC300 was used as the pouring material.

[0065] (Experimental Example 11) WC with an average particle size of 8 μm was used as the hard particles. 1.2 wt% water glass was added to create a particle compact. 10 wt% water glass was added as the exothermic agent and molding was performed. FCD400 was used as the pouring material.

[0066] (Experimental Example 12) WC with an average particle size of 8 μm was used as the hard particles. 1.2 wt% water glass was added to create a particle compact. 10 wt% water glass was added as the exothermic agent and molding was performed. High Cr cast iron was used as the pouring material.

[0067] The particle compacts and evaporative patterns used were of the same size as those shown in Figure 2. The test conditions for Experimental Examples 4 and 9 to 12 are summarized in Table 3. Hardness tests were also conducted in the same manner as for Experimental Example 9, and the average values ​​were calculated. A graph showing the average values ​​for Experimental Examples 4 and 9 to 12 is shown in Figure 7.

[0068] [Table 3]

[0069] The hardness of cast iron varies primarily depending on the proportion of ferrite, pearlite, and cementite. The metals used in this study were ranked in order of hardness: high-Cr cast iron > white pig iron > FCD700 > FCD400 > FC300. Comparing the results of Experiments 4, 9, and 12, the order of hardness was found to be: Experiment 12 > Experiment 9 > Experiment 10 > Experiment 4 > Experiment 11. The poured material in Experiment 10 was FC300, which was lower in hardness than the poured material in Experiment 4 (FCD700) and the poured material in Example 11 (FCD400). However, the hardness of the composite portion was confirmed to be higher in Experiment 10. When pouring FCD700 or FCD400, the oxygen in the water glass (WC binder) reacted with the magnesium in the molten metal, producing magnesium oxide (MgO), resulting in poor spheroidization. Only the metal in the impregnated portion became flake graphite cast iron. The C value was also higher than in FC300, resulting in coarsening of the flake graphite. Additionally, the high proportion of ferrite in the matrix structure resulted in a decrease in hardness. When FCD400 was used as the pouring material, the hardness was lower than in any of the other experimental examples, but a composite with sufficient hardness for practical use was obtained. Furthermore, when high-Cr cast iron was used as the pouring material, the hardness was improved compared to Experimental Example 9, resulting in a composite that can be used in products requiring greater wear resistance. This demonstrates that by changing the pouring material, it is possible to vary the hardness of the composite, making it suitable for use in a variety of products with different mechanical properties. [Industrial Applicability]

[0070] The casting method and casting of the present invention can be applied to any product that requires increased hardness or wear resistance in a specific location, such as cutting blades and bending blades in press dies, sliding parts in machine tools, and wear-resistant pipes. [Explanation of symbols]

[0071] 1: mold, 2: mold flask, 3: molding sand, 5: lost pattern (foam pattern), 5a: notch, 6: particle compact, 7: exothermic compact, 7a: notch, 8: overhanging weir, 9: main runner, 9a: ceramic pipe, 9b: elbow material, 10: sub-runner, 10a: ceramic pipe, 10b: elbow material, 11: coating material, 25: base casting (other casting parts), 26: hard particle compact composite part (hard part), C: crack

Claims

1. A casting method for manufacturing a casting in which a grain compact comprising hard grains and a binder is set in a mold, and then molten metal is poured into the mold, and the molten metal is impregnated between the hard grains to form a hard portion, which is integrated with other casting portions, the hard particles are tungsten carbide (WC), The molten metal is any one of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, Particles with an average particle size of 26 μm or more are large particles, and at least two types of particles, namely, the large particles and medium particles having an average particle size of 1 / 10 to 1 / 4 of the large particles, are mixed together, and the mixture is composed of 50 to 88% of the large particles and 12 to 50% of the medium particles in terms of volume ratio, a heat-generating molded body made of a heat-generating agent for casting and a binder is set in the mold in a state where it is in contact with the grain compact at a portion corresponding to the surface of the hard portion, and a sub-runner separate from a main runner for pouring the molten metal is formed in the heat-generating molded body; A casting method in which the exothermic agent is heated by pouring molten metal into the sub-runner separately from pouring molten metal into the main runner.

2. A casting method for manufacturing a casting in which a grain compact comprising hard grains and a binder is set in a mold, and then molten metal is poured into the mold, and the molten metal is impregnated between the hard grains to form a hard portion, which is integrated with other casting portions, the hard particles are tungsten carbide (WC), The molten metal is any one of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, Particles with an average particle size of 26 μm or more are large particles, and at least three types of particles are mixed: the large particles, medium particles having an average particle size of 1 / 10 to 1 / 4 of the large particles' average particle size, and small particles having an average particle size of 1 / 10 to 1 / 4 of the medium particles' average particle size, and the mixture is composed of 50 to 88% of the large particles, 8 to 46% of the medium particles, and 4 to 25% of the small particles in terms of volume ratio; a heat-generating molded body made of a heat-generating agent for casting and a binder is set in the mold in a state where it is in contact with the grain compact at a portion corresponding to the surface of the hard portion, and a sub-runner separate from a main runner for pouring the molten metal is formed in the heat-generating molded body; A casting method in which the heat-generating material is heated by pouring molten metal into the sub-runner separately from pouring it into the main runner.

3. A casting method for manufacturing a casting in which a grain compact comprising hard grains and a binder is set in a mold, and then molten metal is poured into the mold, and the molten metal is impregnated between the hard grains to form a hard portion, which is integrated with other casting portions, the hard particles are tungsten carbide (WC) particles having an average particle size of 26 μm or more, The molten metal is any one of FC100 to FC350, FCD350 to FCD800, and high Cr cast iron, a heat-generating molded body made of a heat-generating agent for casting and a binder is set in the mold in a state where it is in contact with the grain compact at a portion corresponding to the surface of the hard portion, and a sub-runner separate from a main runner for pouring the molten metal is formed in the heat-generating molded body; A casting method in which the exothermic agent is heated by pouring molten metal into the sub-runner separately from pouring molten metal into the main runner.

4. A casting method according to any one of claims 1 to 3, wherein the molten metal is poured into the sub-runner before being poured into the main runner.

5. 5. The casting method according to claim 1, wherein the grain compact contains Te.

6. 6. The casting method according to claim 1, which is applied to a full mold casting method, and a mold is formed in a state in which the grain compact and the exothermic compact are stacked on a part of a lost form.

7. The casting method according to any one of claims 1 to 6, wherein the hard part formed by impregnating the molten metal between the hard particles is disposed on a cutting blade or bending blade of a press die, a sliding part of a machine tool, or an abrasion-resistant pipe.

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