Soft magnetic component, and, method for producing soft magnetic component

Abstract

To improve rust resistance.SOLUTION: A soft magnetic component according to an embodiment of the present invention has a zinc layer formed on the surface of a sintered body made of iron powder. In other words, in the soft magnetic component according to an embodiment of the present invention, the surface of the sintered body is coated with a zinc layer. This allows for improved rust resistance. In addition, the method for producing the soft magnetic component according to an embodiment of the present invention includes a step of forming a zinc layer on the surface of a sintered body made of iron powder. In other words, in the method for producing the soft magnetic component according to an embodiment of the present invention, the surface of the sintered body is coated with a zinc layer. This allows for improved rust resistance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic part that can improve rust prevention properties, and a method for manufacturing a soft magnetic part. [Background technology]

[0002] BACKGROUND ART Conventionally, soft magnetic parts made by sintering iron powder have been known (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 60-145370 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional soft magnetic parts are prone to oxidation, and to improve their rust resistance, they must be immersed in rust-preventive oil or plated. If rust-preventive oil is used, they cannot be used in applications where oil is not permitted. On the other hand, if plating is performed, problems occur when the treatment solution penetrates into the pores, so a sealing process is required. As a result, a plating film is not formed in the sealing process, which may result in a decrease in rust resistance. An object of the present invention is to provide a soft magnetic part that can improve rust resistance, and a method for manufacturing a soft magnetic part. [Means for solving the problem]

[0005] In order to solve the above problems, a soft magnetic part according to a first invention is characterized in that a zinc layer is formed on the surface of a sintered body made of iron powder. In the soft magnetic part according to the first aspect of the present invention, the surface of the sintered body is coated with a zinc layer, which prevents iron from being exposed and improves rust resistance. Here, the soft magnetic parts include soft magnetic parts described below.

[0006] A method for manufacturing a soft magnetic component according to a second aspect of the present invention is characterized by including a step of forming a zinc layer on the surface of a sintered body made of iron powder. In the method for producing a soft magnetic part according to the second aspect of the present invention, the surface of the sintered body is coated with a zinc layer, which prevents iron from being exposed and improves rust resistance. Here, the process for forming the zinc layer corresponds to the zinc coating process or the degreasing-sintering-zinc coating process described later. [Effects of the Invention]

[0007] According to the soft magnetic part and the method for manufacturing the soft magnetic part of the present invention, it is possible to improve rust prevention properties. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a diagram showing the results of comparing the magnetic properties of the soft magnetic part according to the example and the soft magnetic parts according to comparative examples 1 and 2. [Figure 2] FIG. 10 is a diagram showing the results of a comparison of rust prevention properties between the soft magnetic part according to the example and the soft magnetic parts according to comparative examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] A soft magnetic part (hereinafter referred to as "soft magnetic part") according to an embodiment of the present invention will be described below. Soft magnetic parts can be applied to iron cores (plungers) used in electromagnetic actuators (electromagnetic valves, relays, solenoids, etc.) Soft magnetic parts are particularly suitable for use in environments where oil cannot be present, such as underwater or in coolant.

[0010] (Soft magnetic component configuration) First, the configuration of the soft magnetic part will be described. Soft magnetic parts are made by forming a zinc layer (zinc coating) on ​​the surface of a sintered body made of iron powder. In other words, soft magnetic parts are made by coating the surface of a sintered body made of sintered iron powder with zinc. The zinc layer is a layer in which zinc (Zn) is dispersed. In soft magnetic components, if the zinc content is less than 0.1 parts by mass per 100 parts by mass of iron, the rust prevention properties may be reduced. On the other hand, if the zinc content exceeds 2.0 parts by mass per 100 parts by mass of iron, the magnetic properties may be reduced. Therefore, it is preferable that the zinc content be 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of iron. Furthermore, if the density of the soft magnetic part is less than 6.5, the magnetic properties may be degraded. On the other hand, if the density of the soft magnetic part is more than 7.6, the mold may be damaged. Therefore, it is preferable that the density of the soft magnetic part is in the range of 6.5 to 7.6. In soft magnetic parts, the surface of the sintered body is coated with a zinc layer, which prevents the iron from being exposed and improves rust resistance.

[0011] (Manufacturing method for soft magnetic parts) Next, a method for manufacturing a soft magnetic part will be described.

[0012] (Example 1) First, a method for manufacturing a soft magnetic component according to a first example will be described. The method for manufacturing a soft magnetic component according to the first example includes a stirring step, a powder compacting step, a degreasing step, a sintering step, and a zinc coating step. First, a stirring process is performed. In the stirring process, a die lubricant is added to pure iron powder, and the mixture is stirred and mixed to produce a raw material powder. Water-atomized pure iron powder can be used as the pure iron powder. Examples of die lubricants that can be used include powders of metal soaps, such as zinc stearate and lithium stearate, powders of fatty acid amides, such as ethylene bisstearamide, and powders of wax-based lubricants, such as polyethylene. In this embodiment, 0.7 parts by mass of ethylene bisstearamide (EBS) is added as the die lubricant to 100 parts by mass of pure iron powder to produce the raw material powder. The raw material powder contains unavoidable impurities. Next, a powder compacting step is carried out. In the powder compacting step, the raw material powder is press-molded in a mold at a pressure of about 400 MPa to 1500 MPa to form a green compact. Next, a degreasing step is carried out. In the degreasing step, the green compact is heated under predetermined conditions in a predetermined atmosphere and at predetermined temperatures to sublimate and remove the die lubricant from the green compact. In this embodiment, degreasing is carried out in a degreasing furnace in an air atmosphere, an inert atmosphere, a reducing atmosphere, or a vacuum atmosphere, at a heating temperature in the range of 400°C to 800°C, and for a heating time in the range of 15 to 75 minutes. Here, the heating temperature in the degreasing step is lower than the heating temperature in the sintering step.

[0013] Next, a sintering process is carried out. In the sintering process, the green compact is heated under predetermined conditions in a predetermined atmosphere and at a predetermined temperature to form a sintered body. By sintering the green compact, adjacent metal particles are diffusion-bonded, and the metal particles are bonded to form a porous sintered body. In this embodiment, sintering is carried out in a sintering furnace under the following conditions: a reducing atmosphere (to reduce oxygen in the green compact), a heating temperature in the range of 900°C to 1200°C, and a heating time in the range of 5 to 25 minutes. Here, the reducing atmosphere can be a mixed gas of nitrogen gas and hydrogen gas, a mixed gas of argon gas and hydrogen gas, or hydrogen gas. In this embodiment, sintering is carried out in an atmosphere of a mixture of nitrogen gas (93%) and hydrogen gas (7%). Next, a zinc coating process is performed. In this zinc coating process, the sintered body is embedded in zinc oxide powder and heated under predetermined conditions in a predetermined atmosphere and at a predetermined temperature to form a zinc layer (zinc film) on the surface of the sintered body. In this embodiment, the sintered body is embedded in zinc oxide powder packed in an alumina boat and heated in a state covered with a porous or dense ceramic setter. In this embodiment, heating is performed in a sintering furnace in a reducing atmosphere (to reduce zinc oxide to zinc), at a heating temperature ranging from 775°C to 975°C, and for a heating time ranging from 5 minutes to 120 minutes. Here, the heating temperature in the zinc coating process is lower than that in the sintering process. In particular, if the heating temperature is lower than 775°C, sufficient zinc vapor may not be generated, resulting in an insufficient zinc layer on the surface of the sintered body. On the other hand, if the heating temperature exceeds 975°C, zinc may be sublimated, resulting in an insufficient zinc layer on the surface of the sintered body. Therefore, by setting the heating temperature within the range of 775°C to 975°C, it is possible to prevent the formation of an insufficient zinc layer on the surface of the sintered body. Here, the reducing atmosphere can be a mixed gas of nitrogen gas and hydrogen gas, a mixed gas of argon gas and hydrogen gas, or hydrogen gas. In this embodiment, heating is performed in an atmosphere of a mixture of nitrogen gas (93%) and hydrogen gas (7%). In this way, the soft magnetic part is manufactured.

[0014] In the first example of the manufacturing method for a soft magnetic component, the degreasing process, which removes die lubricant from the green compact, and the sintering process, which forms a sintered body, are separate processes. This allows the heating temperature in the degreasing process to be set lower than the heating temperature in the sintering process. This makes it possible to remove the die lubricant before sintering, preventing impurities from remaining in the sintered body. As a result, it is possible to prevent the magnetic properties of the soft magnetic component from deteriorating. In addition, in the manufacturing method for a soft magnetic component according to the first example, the sintering process for forming a sintered body and the zinc coating process for forming a zinc layer are separate processes. This allows the heating temperature in the zinc coating process to be set lower than the heating temperature in the sintering process. This makes it possible to prevent the formation of an insufficient zinc layer in the zinc coating process and to prevent distortion of the soft magnetic component.

[0015] (Example 2) Next, a method for manufacturing a soft magnetic component according to a second example will be described. The method for manufacturing a soft magnetic component according to the second example includes a stirring step, a powder compacting step, a degreasing and sintering step, and a zinc coating step. First, the stirring step is carried out. The details of the stirring step according to the second example are the same as those of the stirring step according to the first example. Next, a powder compacting step is carried out. The powder compacting step according to the second example is the same as the powder compacting step according to the first example. Next, a debinding and sintering process is carried out. In this process, the green compact is heated in a predetermined atmosphere and at a predetermined temperature to sublimate and remove the die lubricant from the green compact and form a sintered body. In this embodiment, debinding is carried out in the same furnace in a reducing atmosphere (to reduce oxygen in the green compact), at a heating temperature of 400°C to 800°C, and for a heating time of 15 to 75 minutes. Sintering is then carried out at a heating temperature of 900°C to 1200°C and for a heating time of 5 to 25 minutes. The reducing atmosphere can be a mixture of nitrogen gas and hydrogen gas, a mixture of argon gas and hydrogen gas, or hydrogen gas. In this embodiment, debinding and sintering are carried out in an atmosphere of nitrogen gas (93%) and hydrogen gas (7%). Next, a zinc coating process is carried out. The zinc coating process according to the second example is the same as the zinc coating process according to the first example. Here, the heating temperature in the zinc coating process is lower than the heating temperature in the degreasing and sintering process. In this way, the soft magnetic part is manufactured.

[0016] In the manufacturing method for a soft magnetic component according to the second example, degreasing to remove die lubricant from the green compact and forming a sintered body are carried out in a single step, which simplifies the manufacturing process. In addition, in the manufacturing method for soft magnetic components according to the second example, the degreasing and sintering process for forming the sintered body and the zinc coating process for forming the zinc layer are separate processes. This allows the heating temperature in the zinc coating process to be set lower than the heating temperature in the degreasing and sintering process. This makes it possible to prevent the formation of an insufficient zinc layer in the zinc coating process and to prevent distortion of the soft magnetic component.

[0017] (Example 3) Next, a method for manufacturing a soft magnetic component according to a third example will be described. The method for manufacturing a soft magnetic component according to the third example includes a stirring step, a powder compacting step, and a degreasing, sintering, and zinc coating step. First, the stirring step is carried out. The details of the stirring step according to the third example are the same as those of the stirring step according to the first example. Next, the powder compacting step is carried out. The powder compacting step according to the third example is the same as the powder compacting step according to the first example. Next, the degreasing, sintering, and zinc coating processes are carried out. In these processes, the green compact is embedded in zinc oxide powder and heated under predetermined conditions in a predetermined atmosphere and at a predetermined temperature. This sublimates and removes the die lubricant from the green compact, forming a sintered body and forming a zinc layer (zinc coating) on ​​the surface of the sintered body. In this embodiment, the green compact is embedded in zinc oxide powder packed in an alumina boat and heated with the boat covered with a porous alumina setter. In this embodiment, heating is carried out in a sintering furnace in a reducing atmosphere (to reduce oxygen in the green compact and reduce zinc oxide to zinc), at a heating temperature ranging from 775°C to 975°C, and for a heating time ranging from 5 minutes to 120 minutes. In other words, if the heating temperature is below 775°C, zinc vapor may not be generated, resulting in an insufficient zinc layer on the surface of the sintered body. On the other hand, if the heating temperature exceeds 975°C, zinc may be sublimated, resulting in an insufficient zinc layer on the surface of the sintered body. Therefore, by setting the heating temperature within the range of 775°C to 975°C, it is possible to prevent the formation of an insufficient zinc layer on the surface of the sintered body. Here, the reducing atmosphere can be a mixed gas of nitrogen gas and hydrogen gas, a mixed gas of argon gas and hydrogen gas, or hydrogen gas. In this embodiment, heating is performed in an atmosphere of a mixture of nitrogen gas (93%) and hydrogen gas (7%). In this way, the soft magnetic part is manufactured.

[0018] In the manufacturing method for a soft magnetic component according to the third example, degreasing to remove die lubricant from the green compact, forming a sintered body, and forming a zinc layer are carried out in a single step, which simplifies the manufacturing process.

[0019] (Example) Next, an embodiment of the present invention will be described. Fig. 1 is a diagram showing the results of comparing the magnetic properties of the soft magnetic part according to the example and the soft magnetic parts according to comparative examples 1 and 2. Fig. 2 is a diagram showing the results of comparing the rust prevention properties of the soft magnetic part according to the example and the soft magnetic parts according to comparative examples 1 and 2. As an example of the present invention, a soft magnetic part was manufactured using the soft magnetic part manufacturing method according to the second example described above. In the powder compacting process, a cylindrical green compact with an outer diameter of 16 mm, an inner diameter of 8 mm, and a total length of 5 mm was formed at a powder compacting pressure of 800 MPa. In the debinding and sintering process, a debinding treatment was performed in a reducing atmosphere (a mixture of 93% nitrogen gas and 7% hydrogen gas) at a heating temperature of 400°C for 15 minutes, followed by a sintering treatment at a heating temperature of 1100°C for 15 minutes. In the zinc coating process, the sintered body was embedded in zinc oxide powder packed in an alumina boat and zinc-coated with the boat covered with a porous alumina setter. In this case, the zinc coating process was performed in a reducing atmosphere (a mixture of 93% nitrogen gas and 7% hydrogen gas) at a heating temperature of 875°C for 15 minutes. The average particle size of the zinc oxide powder was set to 0.6 μm. Furthermore, as Comparative Example 1, a soft magnetic part was manufactured by omitting the zinc coating process in the manufacturing method for a soft magnetic part according to the above-described Example 2. The manufacturing conditions for each process (stirring process, powder compacting process, and degreasing / sintering process) were the same as those for the soft magnetic part according to the Example. In Comparative Example 2, a soft magnetic component was manufactured using the manufacturing method of the soft magnetic component according to the second example described above, but using a different raw material powder from that used for the soft magnetic component according to the example, and omitting the zinc coating process. In Comparative Example 2, in the stirring process, raw material powder was produced by adding 0.8 parts by mass of ethylene bisstearamide (EBS) as a die lubricant to 100 parts by mass of copper-coated iron powder, in which the iron powder surface was coated with 20 parts by mass of copper. The raw material powder was compacted into a cylindrical compact with an outer diameter of 16 mm, an inner diameter of 8 mm, and a total length of 5 mm at a compaction pressure of 800 MPa. The compact was then degreased in a reducing atmosphere (a mixture of 25% nitrogen gas and 75% hydrogen gas) at 400°C for 15 minutes, and subsequently sintered at 770°C for 15 minutes.

[0020] First, for the soft magnetic parts according to the examples, the change in weight of the sintered body before and after zinc coating treatment was measured (n=2 average). As a result, the weight of the soft magnetic part according to the example increased by 0.18% due to the zinc coating treatment. Furthermore, the maximum magnetic flux density and magnetic permeability were measured for each of the soft magnetic parts according to the example and comparative examples 1 and 2 when a magnetizing force of 4000 A / m was applied. As a result, as shown in Fig. 1, the soft magnetic component according to the example had a maximum magnetic flux density of 1.52 T and a magnetic permeability of 3746 μm. On the other hand, the soft magnetic component according to the comparative example 1 had a maximum magnetic flux density of 1.52 T and a magnetic permeability of 3788 μm. On the other hand, the soft magnetic component according to the comparative example 2 had a maximum magnetic flux density of 0.25 T and a magnetic permeability of 62 μm. This confirmed that the soft magnetic parts according to the examples had higher magnetic properties than the soft magnetic parts according to comparative example 2. In particular, it was confirmed that the soft magnetic parts according to the examples had magnetic properties equivalent to those of the soft magnetic parts according to comparative example 1.

[0021] Furthermore, the soft magnetic parts according to the example and comparative examples 1 and 2 were immersed in distilled water and the occurrence of rust over time was visually observed. As a result, as shown in Figure 2, for the soft magnetic parts according to the example, after about two hours, a thin brown color spread in the distilled water, confirming that only a small amount of rust had occurred. On the other hand, for the soft magnetic part according to comparative example 1, the occurrence of rust spots was confirmed after about one hour. On the other hand, for the soft magnetic part according to comparative example 2, the occurrence of rust spots was confirmed after about two hours. This confirmed that the soft magnetic parts according to the example had higher rust prevention properties than the soft magnetic parts according to the first and second comparative examples.

[0022] (Action of the present invention) In the soft magnetic component according to the embodiment of the present invention, a zinc layer is formed on the surface of a sintered body made of iron powder. That is, in the soft magnetic component according to the embodiment of the present invention, the surface of the sintered body is coated with a zinc layer. This prevents the iron from being exposed, and improves rust resistance. Furthermore, the method for manufacturing a soft magnetic component according to the embodiment of the present invention includes a step of forming a zinc layer on the surface of a sintered body made of iron powder. That is, in the method for manufacturing a soft magnetic component according to the embodiment of the present invention, the surface of the sintered body is coated with a zinc layer. This prevents exposure of iron and improves rust resistance.

Claims

1. A soft magnetic part characterized in that a zinc layer is formed on the surface of a sintered body made of iron powder.

2. A method for manufacturing a soft magnetic part, comprising the step of forming a zinc layer on the surface of a sintered body made of iron powder.

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