Method of manufacturing pump impeller

Abstract

To provide a method of manufacturing a pump impeller allowing for accurately forming a part of a core corresponding in shape to a vane part.SOLUTION: A method of manufacturing a pump impeller 100 comprises the process to make a core 10 including the steps of: charging a sand material 13 containing resin in a for-core die 1 including a one-body type core-body die 11 to form an outside shape of the core 10 and a core-vane die 12 attached in the core-body die 11 and having a twisted shape corresponding in shape to a vane part 101; and removing the core-vane die 12 from the core-body die 11 in a semi-solidified state in a duration from a start of setting of resin to a completion of setting.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a pump impeller, and more particularly to a method for manufacturing a pump impeller including a step of manufacturing a core. [Background technology]

[0002] BACKGROUND ART Conventionally, a method for manufacturing a pump impeller that includes a step of manufacturing a core is known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a method for manufacturing an impeller (pump impeller) including the steps of: placing a vane model having a twisted shape corresponding to the shape of the impeller vanes between a first core molding die and a second core molding die; filling the space between the first and second core molding dies with core sand to manufacture a core; removing the vane model from the manufactured core; and placing the manufactured core between the first and second molds and pouring molten metal into it. In Patent Document 1, the vane model is removed from the manufactured core to form a portion on the core corresponding to the shape of the impeller vanes. Furthermore, in Patent Document 1, the core molding die is one-piece, and the core vane model is made of deformable rubber to make it easy to remove the twisted vane model after the sand material has solidified. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-16157 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as disclosed in the above Patent Document 1, when the core vane mold (vane plate model) is formed from a deformable material (rubber), the core vane mold deforms when sand is filled, causing the parts corresponding to the shape of the vane portion of the core to deform, which may make it difficult to accurately form the parts corresponding to the shape of the vane portion of the core.

[0006] Furthermore, although not disclosed in Patent Document 1, if a twisted-shaped core vane mold is formed from a material that is difficult to deform, it is difficult to remove the core vane mold after the sand has hardened in an integrated mold that requires the core vane mold to be removed. Therefore, it is considered to use a separable core mold (core molding mold) in which the portion corresponding to the shape of the vane portion is composed of multiple parts. However, with a separable core mold, the portion of the core corresponding to the shape of the vane portion may deform due to misalignment between the parts that make up the portion corresponding to the shape of the vane portion, making it difficult to accurately form the portion of the core corresponding to the shape of the vane portion. Therefore, there is a need for a manufacturing method for a pump impeller that can accurately form the portion of the core corresponding to the shape of the vane portion.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a method for manufacturing a pump impeller that is capable of forming a portion that corresponds to the shape of the blade portion of a core with high precision. [Means for solving the problem]

[0008] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by utilizing the properties of a resin contained in sand. That is, in one aspect of the present invention, a method of manufacturing a pump impeller includes the steps of: manufacturing a core, which is a mold for forming blade portions having twisted shapes with different inclination angles when viewed from the direction of the rotation axis of the pump impeller; and manufacturing a pump impeller by placing the core in a main mold, which is a mold for forming at least a main plate portion located on one side of the blade portions in the direction of the rotation axis, wherein the core manufacturing step includes the steps of filling a core mold with sand containing resin, the core mold including an integrated core body mold for forming the external shape of the core, and a core blade mold attached within the core body mold and having a twisted shape corresponding to the blade portions; and removing the core blade mold from the core body mold in a semi-hardened state, which is between the start of hardening and the complete hardening of the resin.

[0009] In one aspect of the present invention, the method for manufacturing a pump impeller includes the steps of filling a core mold with sand containing resin into the core mold, the core mold including an integrated core body mold that forms the external shape of the core and a core vane mold that is attached to the core body mold and has a twisted shape corresponding to the vane portion, and removing the core vane mold from the core body mold in a semi-cured state between when the resin begins to harden and when it is completely hardened. By including the step of removing the core vane mold from the core body mold in a semi-cured state, the core vane mold can be removed before the resin is completely hardened, allowing for the use of a core vane mold that is less likely to deform when filled with sand. This prevents a decrease in the precision of the portion of the core that corresponds to the vane portion. Furthermore, by including a step of filling a core mold with sand material containing resin, which includes an integrated core body mold that forms the external shape of the core, and a core vane mold that is attached within the core body mold and has a twisted shape that corresponds to the shape of the vanes, there is no misalignment between the components that make up the parts that correspond to the shape of the vanes, unlike when a separable core mold is used. This makes it possible to suppress a decrease in the accuracy of the parts of the core that correspond to the shape of the vanes. As a result, the parts of the core that correspond to the shape of the vanes can be formed with high accuracy.

[0010] In the method for manufacturing a pump impeller according to the above aspect, the core vane mold preferably has a hardness in a semi-cured state greater than that of the resin in the semi-cured state. With this configuration, the core vane mold has a hardness greater than that of the resin in the semi-cured state, which makes it possible to suppress deformation of the core vane mold when filling with sand, thereby enabling the portion of the core corresponding to the shape of the vane portion to be formed with greater precision.

[0011] In the method for manufacturing a pump impeller according to the above aspect, the sand preferably contains a resin whose surface and interior are cured substantially simultaneously. With this configuration, the surface and interior have approximately the same hardness in the semi-cured state. Therefore, unlike a case in which the interior hardness is lower than the surface hardness, the sand can be prevented from deforming inward when pressed from the surface side. As a result, even if the sand is pressed from the surface side when removing the core vane mold, deformation of the sand can be effectively prevented. Therefore, deformation of the sand before and after removing the core vane mold can be effectively prevented.

[0012] In this case, the sand material preferably contains either a self-hardening resin that hardens at room temperature or a gas-hardening resin that hardens when exposed to gas. By using a self-hardening resin, the sand hardens when exposed to room temperature, eliminating the need for special hardening procedures. Furthermore, by using a gas-hardening resin, the sand material can be adjusted to a semi-hardened state by adjusting the amount of gas injected.

[0013] In a configuration in which the sand material contains either a self-hardening resin that hardens at room temperature or a gas-hardening resin that hardens with gas, the sand material preferably further contains the self-hardening resin and a hardener, and the ratio of the hardener to the total of the self-hardening resin and the hardener is smaller than the ratio of the self-hardening resin. The present inventors have found in the examples (experimental examples) described below that with this configuration, the viscosity of the self-hardening resin in a semi-hardened state increases due to the small ratio of the hardener, making it easier to remove the core vane mold.

[0014] In this case, the ratio of the curing agent to the total of the self-hardening resin and the curing agent is preferably 20% or more and 40% or less. With this configuration, the ratio of the curing agent is 40% or less, so that the viscosity of the self-hardening resin in a semi-hardened state is increased, and the core vane mold can be easily removed. Furthermore, the ratio of the curing agent is 20% or more, so that the self-hardening resin can be sufficiently hardened.

[0015] In a configuration in which the sand material contains either a self-hardening resin that hardens at room temperature or a gas-hardening resin that hardens when exposed to gas, the sand material preferably further contains a catalyst, and the proportion of catalyst added to the sand material is smaller than the proportion of self-hardening resin added to the sand material. With this configuration, the low proportion of catalyst means that it takes longer for the self-hardening resin to completely harden, and the inventors of the present application have found in the examples (experimental examples) described below that this makes it easier to remove the core vane mold by extending the semi-hardened state.

[0016] In this case, the proportion of catalyst added to the sand is preferably 1% or more and 10% or less of the self-hardening resin added to the sand. With this configuration, since the proportion of catalyst is 10% or less of the self-hardening resin, it takes time for the self-hardening resin to completely harden, so the semi-hardened state is extended and the core vane mold can be easily removed. Furthermore, the inventors of this application have found in the examples (experimental examples) described below that by having the proportion of catalyst be 1% or more of the self-hardening resin, it is possible to prevent the time until complete hardening from becoming excessively long and to easily remove the core vane mold.

[0017] In the above-described sand material containing the self-hardening resin and the curing agent, the self-hardening resin is preferably one of furan resin, urethane resin, and alkaline phenol resin. This configuration allows cores to be easily and accurately manufactured using sand material containing furan resin, urethane resin, or alkaline phenol resin. [Effects of the Invention]

[0018] According to the present invention, as described above, it is possible to provide a method for manufacturing a pump impeller that is capable of accurately forming portions of a core that correspond to the shape of the blade portions. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a pump impeller according to an embodiment. [Figure 2]FIG. 10 is a cross-sectional view showing a state in which a core is placed in a main mold. [Figure 3] FIG. 2 is a schematic diagram of a core body mold according to an embodiment. [Figure 4] FIG. 1 is a schematic diagram of a core body mold to which a core vane mold is attached according to an embodiment. [Figure 5] This is a diagram showing the state in which sand material has been filled into the lower core body mold. [Figure 6] This is a diagram showing the state in which sand has been moved from the lower core body mold to the upper core body mold. [Figure 7] FIG. 10 is a view showing the state in which the core is being removed from the upper core main body mold. [Figure 8] FIG. 2 is a schematic diagram of a core according to an embodiment. [Figure 9] 1 is a graph showing changes in hardness of a resin. [Figure 10] 1 is a flowchart showing the flow of a method for manufacturing a pump impeller. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment will be described with reference to the drawings.

[0021] (Embodiment) A method for manufacturing a pump impeller 100 according to an embodiment will be described with reference to FIGS.

[0022] The pump impeller 100 shown in FIG. 1 is used in a pump. The pump is configured to suck in a fluid through a suction port and discharge the fluid through a discharge port. As an example, the pump is placed underwater and used to pump water. The pump impeller 100 is configured to be rotated by a motor to create a flow that sucks in a fluid through the suction port and discharges the fluid through the discharge port. Here, in this embodiment, the rotational axis direction, which is the direction in which the rotational axis of the pump impeller 100 extends, is defined as the Z direction. The pump impeller 100 has a circular shape when viewed from the Z direction.

[0023] The pump impeller 100 includes a blade portion 101, a main plate portion 102, and a side plate portion 103. The blade portion 101 is configured to generate a vortex flow by rotating. When viewed from the rotation axis direction (Z direction) of the pump impeller 100, the blade portion 101 has a twisted shape with different inclination angles. The blade portion 101 is configured so that the inclination angle with respect to a plane perpendicular to the rotation axis direction of the main plate portion 102 increases from the center toward the outer periphery. A plurality of blade portions 101 are provided around the central axis of rotation. As an example, five blade portions 101 are provided.

[0024] The main plate portion 102 is disposed on one side of the blade portion 101 in the direction of the rotational axis. In this embodiment, the main plate portion 102 is disposed on the Z1 side of the blade portion 101 in the direction of the rotational axis. In addition, the side plate portion 103 is disposed on the other side of the blade portion 101 in the direction of the rotational axis. In this embodiment, the side plate portion 103 is disposed on the Z2 side of the blade portion 101 in the direction of the rotational axis. The main plate portion 102 and the side plate portion 103 are disposed so as to sandwich the blade portion 101 in the direction of the rotational axis. The pump impeller 100 of this embodiment is a closed impeller including the main plate portion 102 and the side plate portion 103.

[0025] As shown in FIGS. 1 and 2 , the pump impeller 100 is manufactured by casting. The pump impeller 100 is made of a metal such as stainless steel. The pump impeller 100 is cast by pouring molten metal into a main mold 20 with a core 10 placed in the main mold 20. The main mold 20 is a mold that forms at least a main plate portion 102. In this embodiment, the main mold 20 is a mold that forms the main plate portion 102 and side plate portions 103. The core 10 is a mold that forms blade portions 101.

[0026] As shown in Figures 3 and 8, core 10 is manufactured using a core mold 1. Core mold 1 includes a core body mold 11 and a core vane mold 12 (see Figure 4). Core 10 is formed from sand material 13 (see Figure 5).

[0027] As shown in Figure 3, the core body mold 11 includes an upper core body mold 11a and a lower core body mold 11b. The upper core body mold 11a and the lower core body mold 11b are each an integral mold made of a single seamless member. The core body mold 11 is, for example, a wooden mold.

[0028] The upper core body mold 11a has an annular shape when viewed in the direction of the rotation axis. Furthermore, the surface of the upper core body mold 11a facing the lower core body mold 11b is recessed on the opposite side to the lower core body mold 11b. The upper core body mold 11a is configured so that it can be filled with sand 13. The upper core body mold 11a has a hole 111a in its center.

[0029] The lower core main body mold 11b is a circular mold with a circular recess 111b formed therein when viewed from the rotation axis direction. The outer diameter of the lower core main body mold 11b is formed to be approximately the same as the outer diameter of the upper core main body mold 11a. The diameter and depth of the recess 111b are also approximately the same as the diameter and depth of the recessed portion on the surface of the upper core main body mold 11a facing the lower core main body mold 11b. The recess 111b of the lower core main body mold 11b is filled with sand material 13 (see Figure 5). The lower core main body mold 11b can be filled with approximately the same amount of sand material 13 as the upper core main body mold 11a. The lower core main body mold 11b has a protrusion 111c formed in its center.

[0030] The protrusions 111c are arranged in positions that overlap with the holes 111a of the upper core main body mold 11a in the direction of the rotation axis. The diameter of the protrusions 111c is smaller than the diameter of the holes 111a of the upper core main body mold 11a. The circular recesses 111b are provided with grooves 111d for attaching the core vane dies 12. More specifically, the ends 12a (see FIG. 6) of the core vane dies 12 are fitted into the grooves 111d, and the core vane dies 12 are attached in a state where they are positioned relative to the grooves 111d. The grooves 111d are provided according to the number of core vane dies 12 to be attached. The grooves 111d are also provided at predetermined intervals to match the positions of the blades 101 of the pump impeller 100.

[0031] As shown in Figures 3 and 4, the core vane mold 12 is attached to the groove 111d of the core main body mold 11. The core vane mold 12 has a twisted shape that corresponds to the vane portion 101. A twisted shape includes a shape with an undercut. The core vane mold 12 is configured so that the angle of inclination with respect to a plane perpendicular to the rotation axis of the lower core main body mold 11b is larger on the outer periphery side than on the center. As an example, the core vane mold 12 is formed from a resin such as urethane resin. A plurality of core vane molds 12 are provided corresponding to the plurality of vane portions 101.

[0032] The core vane mold 12 shown in Fig. 5 has a higher hardness when the resin contained in the sand material 13 is in a semi-cured state than the semi-cured resin contained in the sand material 13. The semi-cured state is a state in which the core vane mold 12 has a degree of elasticity that allows it to return to the shape it had before removal even if it is deformed when removed. When the resin contained in the sand material 13 has cured, the core vane mold 12 may have a hardness equal to or greater than that of the cured resin, or may have a hardness less than that of the fully cured resin.

[0033] The sand material 13 includes, for example, foundry sand, liquid resin, liquid hardener, and liquid catalyst. For example, the foundry sand is sand containing chromium minerals (chromite sand). Alternatively, the foundry sand is silica sand such as Flattery 40H. Compared to silica sand, chromite sand has a higher refractory temperature and is therefore less susceptible to seizure. Furthermore, chromite sand has a lower thermal expansion coefficient than silica sand, making it less susceptible to cracking when the core 10 is formed, thereby improving the dimensional accuracy of the mold for the pump impeller 100. Furthermore, chromite sand has a higher specific gravity and a larger heat capacity than silica sand, which, when used to form the core 10, effectively cools the pump impeller 100 after casting. For these reasons, it is preferable to use chromite sand as the foundry sand. The ratio of the total weight of the resin and hardener to the weight of the foundry sand is, for example, adjusted to 1% or more. Additionally, the ratio of the total amount (weight) of resin and hardener to the weight of foundry sand is adjusted to, for example, 1% or more and 2.5% or less. For example, if the foundry sand is chromite sand, it is set to 1% or more and 2.0% or less. Furthermore, if the foundry sand is silica sand, the ratio of the total amount (weight) of resin and hardener to the weight of foundry sand may be higher than in the case of chromite sand. In this case, for example, the ratio of the total amount (weight) of resin and hardener to the weight of foundry sand (silica sand) may be adjusted to, for example, 1.2% or more and 2.5% or less.

[0034] The resin is a resin whose surface and interior are cured at approximately the same time. That is, the resin has the property of not causing unevenness in the progress of curing (or is less likely to cause unevenness). The surface refers to the part exposed to the outside, and the interior refers to the part other than the surface. The resin is a self-hardening resin that hardens at room temperature. In this embodiment, the self-hardening resin is a urethane resin. The urethane resin includes a phenol urethane resin, a polyol urethane resin, and an alkyd urethane resin.

[0035] The self-hardening resin is configured to harden by reacting with a curing agent. The reaction between the self-hardening resin and the curing agent is accelerated by a catalyst. The self-hardening resin is initially liquid and has a hardness of approximately 0, but begins to harden over time. In the semi-hardened state between when the resin begins to harden and when it is completely hardened, the resin is not completely solidified and is in a state where it can be elastically deformed. The greater the ratio of the total amount of self-hardening resin and curing agent contained in the sand material 13, the greater the strength of the self-hardening resin when it hardens.

[0036] An example of a combination of a self-hardening resin and a hardener is the phenolic resin solution, polymeric MDI solution, and catalyst used in PEP SET.

[0037] The ratio of the hardener to the total of the self-hardening resin and hardener is preferably smaller than the ratio of the self-hardening resin. The ratio of the hardener to the total of the self-hardening resin and hardener is preferably 20% or more and 40% or less. By reducing the ratio of the hardener, the viscosity of the self-hardening resin increases, and when the core vane mold 12 is removed in a semi-hardened state, the sand material 13 becomes elastic and its shape remains almost unchanged before and after removal of the core vane mold 12. In other words, the shape of the sand material 13 is maintained before and after removal of the core vane mold 12. In other words, even if the sand material 13 is removed while elastically deforming, the shape of the sand material 13 after removal of the core vane mold 12 will be approximately the same as the shape of the sand material 13 before removal of the core vane mold 12.

[0038] The proportion of the catalyst added to the sand 13 is smaller than the proportion of the self-hardening resin added to the sand 13. Preferably, the proportion of the catalyst added to the sand 13 is 1% or more of the self-hardening resin added to the sand 13. The proportion of the catalyst added to the sand 13 is preferably 1% or more and 10% or less of the self-hardening resin added to the sand 13, and more preferably 1% or more and 3% or less of the self-hardening resin added to the sand 13. A small proportion of the catalyst slows down the hardening rate of the self-hardening resin, allowing the semi-hardened state to be prolonged. Therefore, the hardening rate of the self-hardening resin may be adjusted by changing the proportion of the catalyst. Note that the higher the temperature of the sand 13, the faster the hardening rate of the self-hardening resin tends to be. Therefore, the hardening rate of the self-hardening resin may be adjusted by changing the temperature.

[0039] In Figure 9, the horizontal axis plots the time after mixing the self-hardening resin, curing agent, and catalyst, and the vertical axis plots hardness. In the example of Figure 9, the state in which the change in hardness remains approximately constant from 3 to 7 minutes is defined as the start of hardening. In the start of hardening state, the proportion of the liquid portion is greater than the proportion of the solid portion, resulting in low hardness. In the start of hardening state, the sand material 13 is configured to be filled into the core mold 1. In addition, the state in which the slope of the change in hardness remains constant from 7 to 9 minutes is defined as the semi-hardened state. The hardness of the semi-hardened state is greater than that of the self-hardening resin before hardening but less than that of the fully hardened self-hardening resin. In the semi-hardened state, the core vane mold 12 is removed from the sand material 13. In addition, the state in which the change in hardness remains constant after 9 minutes is defined as the fully hardened state. The time to reach the semi-hardened state, the hardness, and the time the semi-hardened state continues (the time until the fully hardened state) vary depending on the proportion of the self-hardening resin, curing agent, and catalyst.

[0040] As shown in Fig. 2, the main mold 20 includes an upper main mold 20a and a lower main mold 20b. The lower main mold 20b has a circular shape when viewed from the direction of the rotation axis, and is provided with a circular recess 20c inside which the core 10 is placed. The diameter of the recess 20c in the lower main mold 20b is configured to be approximately the same as or slightly larger than the outer diameter of the core 10. The upper main mold 20a is formed in a disk shape with the same outer diameter as the lower main mold 20b. The upper main mold 20a is provided with an opening 20d in the center through which molten metal can be poured.

[0041] In this embodiment, the main mold 20 is configured so that the upper main mold 20a forms the main plate portion 102 and the lower main mold 20b forms the side plate portion 103. As another example, the main mold 20 may be configured so that the upper main mold 20a forms the side plate portion 103 and the lower main mold 20b forms the main plate portion 102. Also, in this embodiment, the core 10 is arranged in the lower main mold 20b, and the upper main mold 20a is attached to the lower main mold 20b. As another example, the core 10 may be arranged in the upper main mold 20a, and the lower main mold 20b is attached to the upper main mold 20a.

[0042] A method for manufacturing the pump impeller 100 will be described with reference to Fig. 10. The method for manufacturing the pump impeller 100 includes a step of manufacturing the core 10 and a step of manufacturing the pump impeller 100.

[0043] First, we will explain in detail the process for manufacturing core 10. The process for manufacturing core 10 includes the steps of filling core mold 1 with sand material 13 containing resin, and removing core vane mold 12 from core main body mold 11 when the resin contained in sand material 13 is in a semi-hardened state.

[0044] Step S1 is a process of preparing a core mold 1. Specifically, as shown in Fig. 4, a core vane mold 12 is attached to a groove 111d of a core main body mold 11, and the core mold 1 is prepared.

[0045] In step S2, sand material 13 containing resin is filled into the core mold 1. Specifically, as shown in Fig. 5, sand material 13 is filled into the lower core body mold 11b of the prepared core mold 1, and then the upper core body mold 11a is attached to the lower core body mold 11b of the core mold 1. Step S2 is carried out within the time period for the hardening start state in Fig. 9. Then, the hole 111a is sealed and the mixture is hardened at room temperature.

[0046] In step S3, the core vane molds 12 are removed from the core main body mold 11 when the resin is in a semi-cured state, between when it starts to harden and when it is completely hardened. Specifically, as shown in FIG. 6, the core main body mold 11 is turned upside down and the lower core main body mold 11b is removed, thereby placing the sand material 13 and core vane molds 12 in the upper core main body mold 11a. As shown in FIG. 7, with the sand material 13 and core vane molds 12 placed in the upper core main body mold 11a, the core vane mold 12 is removed. That is, the core vane mold 12 is pulled out from the sand material 13. When removing the core vane mold 12, for example, it is removed by gripping the end 12a attached to the groove 111d. The step of removing the core vane mold 12 from the core main body mold 11 when the resin is in a semi-cured state is performed when a predetermined time has elapsed since the sand material 13 was filled. The predetermined time is obtained from the time it takes for the sand material 13 to reach the semi-hardened state and the duration of the semi-hardened state, as shown in Figure 9. The predetermined time varies depending on the compounding ratio and type of the resin, hardener, and catalyst mixed in the sand material 13. The filled sand material 13 may also be touched to check whether it is elastic.

[0047] In step S4, the resin is hardened. Specifically, as shown in FIG. 8, core 10 is produced by completely hardening the resin. Core 10 has pores 10a shaped like wing portions 101 formed therein by removing core vane mold 12. Core 10 also has protrusions 10b formed therein that correspond to recesses 111b in upper core main body mold 11a. Pores 10a are holes that penetrate in the direction of the rotation axis. Steps S1 to S4 are the processes for producing core 10.

[0048] Next, a process for manufacturing the pump impeller 100 is performed. In step S5, the manufactured core 10 is placed in the main mold 20. In this case, as shown in FIG. 2, the core 10 is placed in the lower main mold 20b so that the protrusion 10b abuts against the lower main mold 20b, and the upper main mold 20a is attached to the lower main mold 20b. With the core 10 placed, a gap is formed between the core 10 and the main mold 20 to form the main plate 102 and the side plate 103. Specifically, the main plate 102 is formed in the gap between the upper main mold 20a and the core 10, and the side plate 103 is formed in the gap between the lower main mold 20b and the core 10.

[0049] In step S6, molten metal is poured into main mold 20 in which core 10 is placed. The molten metal poured into main mold 20 solidifies in pores 10a of core 10, thereby forming blade portions 101. The molten metal flows between core 10 and main mold 20 and solidifies, thereby forming main plate portions 102 and side plate portions 103. In step S7, a process is carried out to remove main mold 20 and core 10. Specifically, after the molten metal has hardened, main mold 20 and core 10 are removed (broken) to form pump impeller 100. Steps S5 to S7 are the processes for manufacturing pump impeller 100.

[0050] [Example] As an example, a core 10 was manufactured using sand material 13, which was a mixture of phenolic resin (resin), polymeric MDI solution (hardener), catalyst, and chromite sand A301 (casting sand). The ratio of resin to sand material 13 was 0.7%, the hardener was 0.3%, and the catalyst was 0.007%. In other words, the ratio of resin to hardener in sand material 13 was 0.7:0.3 (7:3), and the hardener ratio to the total of hard resin and hardener was 30%. In addition, the mixing ratio of resin to catalyst in sand material 13 was 0.7:0.007 (1:0.01), and the catalyst added to sand material 13 was 1% of the self-hardening resin added to sand material 13. In the examples, the semi-cured self-hardening resin has a moderate viscosity, and even if the core vane mold 12 is formed from a resin that is difficult to deform, the sand material 13 will return to its original shape even if it is deformed when the core vane mold 12 is removed, so the shape of the pores 10a corresponding to the vane portions 101 will not be deformed, and a core 10 with sufficient strength could be manufactured. In addition, the resin remained in a semi-cured state for a sufficiently long time, making it easy to remove the core vane mold 12. The manufactured core 10 also had sufficient strength to be used as a casting mold.

[0051] From the results of the examples, the present inventors have found that when the ratio of hardener to the total of self-hardening resin and hardener is 30%, even if the core vane die 12 is made of a resin that is difficult to deform, the viscosity of the self-hardening resin in the semi-cured state increases because the ratio of hardener to the total of self-hardening resin and hardener is smaller than the ratio of self-hardening resin, preventing deformation of the shape of the pores 10a corresponding to the vane portions 101 and facilitating removal of the core vane die 12. The present inventors have also found that even when the ratio of hardener is smaller than the ratio of self-hardening resin, it is possible to manufacture a core 10 having sufficient strength. The present inventors have also found that the viscosity of the self-hardening resin in the semi-cured state increases as the ratio of hardener to the total of self-hardening resin and hardener is made smaller than the ratio of self-hardening resin. Furthermore, the inventors of the present application conducted extensive research into the range of the ratio of hardener to the total of self-hardening resin and hardener, and determined that a similar effect could be obtained within a range of approximately ±10% from 30% of the experimental results, and therefore derived a range of 20% to 40%.

[0052] The present inventors also discovered that when the proportion of catalyst added to sand 13 is 1% of the self-hardening resin added to sand 13, even if core vane mold 12 is made of a resin that is difficult to deform, the shape of pores 10a corresponding to vane portions 101 does not deform, and it is possible to manufacture core 10 with sufficient strength. The present inventors also discovered that when the proportion of catalyst is lower than the proportion of self-hardening resin, it takes time for the self-hardening resin to completely harden, so that the semi-hardened state can be extended, making it easier to remove core vane mold 12. The present inventors also conducted extensive research to determine the range of the proportion of catalyst added to sand 13 that allows for efficient production of core 10. As a result, they discovered that it is preferable to adjust the proportion of catalyst added to sand 13 to be between 1% and 10% of the self-hardening resin.

[0053] Furthermore, the inventors of the present application changed the proportion of catalyst added, taking into account the effect of ambient temperature on the catalyst. They found that in summer, when ambient temperatures are above 30°C, the high ambient temperature raises the temperature of the sand 13 above room temperature (20°C), accelerating the catalytic reaction. Therefore, even if the proportion of catalyst added to the sand 13 is 1% of the self-hardening resin, it is possible to semi-harden the resin to a degree that allows for easy removal of the core vane mold 12, and the work time required to manufacture a pump impeller remains unchanged or is slightly shortened. Furthermore, in winter, when ambient temperatures are below 10°C, the low ambient temperature lowers the temperature of the sand 13 below room temperature, and the catalytic reaction remains unchanged or is slightly slower. At this temperature, they found that adding a proportion of catalyst to the sand 13 of 3% of the self-hardening resin allows for the resin to semi-harden to a degree that allows for easy removal of the core vane mold 12, and the work time required to manufacture a pump impeller remains unchanged or is slightly shortened. From these results, the inventors of the present application have found that it is more preferable to adjust the catalyst added to the sand material 13 within the range of 1% to 3% of the self-hardening resin, taking into consideration the temperature of the sand material 13.

[0054] (Effects of the embodiment) In this embodiment, the following effects can be obtained.

[0055] In this embodiment, as described above, the process for manufacturing core 10 includes the steps of filling core mold 1, which includes one-piece core main body mold 11 that forms the external shape of core 10 and core vane molds 12 that are attached within core main body mold 11 and have a twisted shape that corresponds to vane portions 101, with sand material 13 that contains resin, and removing core vane molds 12 from core main body mold 11 in a semi-cured state, which is between the start of curing and complete curing. Thus, by including the step of removing core vane molds 12 from core main body mold 11 in a semi-cured state, core vane molds 12 can be removed before the resin completely cures, allowing for the use of core vane molds 12 that are less likely to deform when filled with sand material 13. This makes it possible to prevent a decrease in precision in the portion of core 10 that corresponds to vane portions 101 of the formed core 10. Furthermore, by including a step of filling core mold 1, which includes one-piece core body mold 11 that forms the external shape of core 10, and core vane mold 12 that is attached within core body mold 11 and has a twisted shape that corresponds to vane portions 101, with sand material 13 that contains resin, there is no misalignment between the members that make up the portions that correspond to the shape of vane portions 101, unlike when a separable core mold is used. This makes it possible to prevent a decrease in the accuracy of the portions of core 10 that correspond to the shape of vane portions 101. As a result, the portions of core 10 that correspond to the shape of vane portions 101 can be formed with high accuracy.

[0056] Furthermore, in this embodiment, the core vane mold 12 in a semi-cured state has a greater hardness than the resin in the semi-cured state. As a result, the core vane mold 12 has a greater hardness than the resin in the semi-cured state, which makes it possible to suppress deformation of the core vane mold 12 when filling with sand 13, and therefore makes it possible to form the portion of the core 10 corresponding to the shape of the vane portion 101 with even greater precision.

[0057] Furthermore, in this embodiment, the sand material 13 contains a resin whose surface and interior are hardened at approximately the same time. As a result, in a semi-hardened state, the surface and interior have approximately the same hardness, and therefore, unlike when the interior hardness is lower than the surface hardness, the sand material 13 can be prevented from deforming inward when pressed from the surface side. As a result, even if the sand material 13 is pressed from the surface side when removing the core vane mold 12, deformation of the sand material 13 can be effectively prevented, and therefore deformation of the sand material 13 before and after removing the core vane mold 12 can be effectively prevented.

[0058] In this embodiment, the sand material 13 includes either a self-hardening resin that hardens at room temperature or a gas-hardening resin that hardens when exposed to gas. By using a self-hardening resin, the sand material 13 hardens simply by being left at room temperature, eliminating the need for special hardening procedures. Furthermore, by using a gas-hardening resin, the sand material 13 can be adjusted to a semi-hardened state by adjusting the amount of gas injected.

[0059] In this embodiment, the sand material 13 further contains a self-hardening resin and a hardener, and the ratio of the hardener to the total of the self-hardening resin and the hardener is smaller than the ratio of the self-hardening resin. The inventors of the present application have found through examples (experimental examples) that the small ratio of the hardener increases the viscosity of the self-hardening resin in a semi-hardened state, making it easier to remove the core vane mold 12.

[0060] In this embodiment, the ratio of the curing agent to the total of the self-hardening resin and the curing agent is 20% or more and 40% or less. With a curing agent ratio of 40% or less, the viscosity of the self-hardening resin in a semi-hardened state increases, making it easy to remove the core vane mold 12. Furthermore, with a curing agent ratio of 20% or more, the self-hardening resin can be sufficiently hardened.

[0061] Furthermore, in this embodiment, the sand material 13 further contains a catalyst, and the proportion of catalyst added to the sand material 13 is smaller than the proportion of self-hardening resin added to the sand material 13. As a result, the inventors of the present application have found through examples (experimental examples) that, since the proportion of catalyst is small, it takes time for the self-hardening resin to completely harden, and therefore the semi-hardened state can be extended, making it easier to remove the core vane mold 12.

[0062] Furthermore, in this embodiment, the ratio of the catalyst added to the sand material 13 is 1% or more and 10% or less of the self-hardening resin added to the sand material 13. With a catalyst ratio of 10% or less, it takes time for the self-hardening resin to completely harden, so the semi-hardened state is extended, and the core vane mold 12 can be easily removed. Furthermore, the present inventors have found through examples (experimental examples) that when the catalyst ratio is 1% or more of the self-hardening resin, it is possible to prevent the time until complete hardening from becoming excessively long, and also to easily remove the core vane mold 12.

[0063] In this embodiment, the self-hardening resin is one of furan resin, urethane resin, and alkaline phenol resin, which allows core 10 to be easily and accurately manufactured using sand 13 containing furan resin, urethane resin, or alkaline phenol resin.

[0064] (Variation) The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than the above description of the embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0065] For example, in the above embodiment, the pump impeller of the present invention is configured to cause a fluid to flow through the pump, but the present invention is not limited to this. In the present invention, the pump impeller may be configured to break up foreign matter that has flowed into the pump.

[0066] In the above embodiment, the pump impeller is a closed impeller having a main plate and a side plate, but the present invention is not limited to this. In the present invention, the pump impeller may be a semi-open impeller having a main plate but no side plate.

[0067] In the above embodiment, the resin is a self-hardening resin, but the present invention is not limited to this. In the present invention, the resin may be a gas-hardening resin that is hardened by a gas.

[0068] In the above embodiment, the self-hardening resin is a urethane resin, but the present invention is not limited to this. In the present invention, the self-hardening resin may be either a furan resin or an alkaline phenol resin. [Explanation of symbols]

[0069] 1 Core mold 10 Core 11 Core body type 12 Core vane mold 13 Sand material 20 Main Type 100 Pump Impeller 101 Wing 102 Main plate part

Claims

1. a step of manufacturing a core, which is a mold for forming blade portions having twisted shapes with different inclination angles as viewed from the rotation axis direction of the pump impeller; and a step of manufacturing the pump impeller by placing the core in a main mold that is a casting mold for forming at least a main plate portion that is arranged on one side of the blade portion in the rotation axis direction, The step of manufacturing the core includes: a step of filling a core mold with sand material containing resin, the core mold including an integrated core body mold that forms the external shape of the core, and a core vane mold that is attached within the core body mold and has a twisted shape that corresponds to the vane portion; and removing the core vane mold from the core body mold when the resin is in a semi-hardened state between when it starts to harden and when it is completely hardened.

2. The method for manufacturing a pump impeller according to claim 1 , wherein the core vane mold in the semi-cured state has a hardness greater than that of the resin in the semi-cured state.

3. The method for manufacturing a pump impeller according to claim 1 , wherein the sand material contains the resin, the surface and the interior of which harden substantially simultaneously.

4. The method for manufacturing a pump impeller according to claim 3 , wherein the sand material includes either a self-hardening resin that hardens at room temperature or a gas-hardening resin that hardens by gas.

5. The sand material further includes the self-hardening resin and a hardener, The method for manufacturing a pump impeller according to claim 4 , wherein a ratio of the curing agent to a total of the self-hardening resin and the curing agent is smaller than a ratio of the self-hardening resin.

6. The method for manufacturing a pump impeller according to claim 5, wherein a ratio of the curing agent to the total of the self-hardening resin and the curing agent is 20% or more and 40% or less.

7. The method for manufacturing a pump impeller according to claim 4 , wherein the sand further contains a catalyst, and the proportion of the catalyst added to the sand is smaller than the proportion of the self-hardening resin added to the sand.

8. The method for manufacturing a pump impeller according to claim 7, wherein the ratio of the catalyst added to the sand material is 1% to 10% of the self-hardening resin added to the sand material.

9. 6. The method for manufacturing a pump impeller according to claim 5, wherein the self-hardening resin is any one of a furan resin, a urethane resin, and an alkaline phenol resin.

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