JP2020198385A - Manufacturing method of magnet having corrosion resistance, and pressure sensor including magnet having corrosion resistance - Google Patents

Abstract

To avoid corrosion of a magnet due to a hydrogen sulfide component and improve the corrosion resistance of the magnet in a pressure sensor equipped with the magnet.SOLUTION: In a pressure sensor equipped with a magnet, for a rare earth permanent magnet 26, the surface of a base material is galvanized S1 or phosphate-treated, and the resin coating treatment S2 is applied to the entire surface of the metal plating film (galvanized layer 26F) or phosphate film to form a resin film layer 26C.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for manufacturing a magnet having corrosion resistance and a pressure sensor including the magnet having corrosion resistance.

In a rice cooker, for example, as shown in Patent Document 1, a vacuum device including a vacuum device, a positive pressure device, a pressure detection module (pressure sensor) provided inside the lid, and a main body having a cooking chamber, and a vacuum device. , And, it has been proposed that the positive pressure device controls the pressure in the cooking chamber by controlling the operation based on the detection signal from the pressure detection module (pressure sensor). In such pressure control, the vacuum device is operated in the suction stage in rice cooking, and is evacuated to a relatively high pressure of vacuum degree below atmospheric pressure (101.33 kPa), and in the steaming stage, the vacuum degree is relatively low. It is evacuated to pressure and the pressure in the cooking chamber is maintained at negative pressure.

In a rice cooker, for example, as shown in Patent Documents 2 and 3, when rice is cooked, trace amounts of hydrogen sulfide and ammonia components that cause one of the odors that hinder the aroma are generated in the rice cooker. It is known to do.

In the above-mentioned pressure sensor, as a micro pressure sensor for a rice cooker, an output signal indicating the pressure of the fluid is generated by detecting the displacement of the diaphragm that is displaced according to the pressure of the fluid by a magnetic sensor composed of a permanent magnet and a Hall element. What is supplied is put to practical use. The surface of the base metal of such permanent magnets may be nickel-plated.

JP-A-2019-10495 Tokukousho 46-24062 Japanese Unexamined Patent Publication No. 9-56343

In the above-mentioned rice cooker, when a pressure sensor including the above-mentioned permanent magnet and a magnetic sensor composed of a Hall element is used and rice cooking is repeated, the nickel-plated permanent magnet is corroded by the above-mentioned hydrogen sulfide component. There is a risk of As a result, the magnetic force of the permanent magnet is attenuated, so that the detection accuracy (magnetic force detection ability) of the pressure sensor may decrease. Therefore, it is required to improve the corrosion resistance of the permanent magnet to the hydrogen sulfide component.

In consideration of the above problems, the present invention is a method for manufacturing a magnet having corrosion resistance and a pressure sensor including a magnet having corrosion resistance, which avoids corrosion of the magnet due to a hydrogen sulfide component and is a magnet. It is an object of the present invention to provide a method for manufacturing a magnet having corrosion resistance, which can improve the corrosion resistance of the magnet, and a pressure sensor including the magnet having corrosion resistance.

In order to achieve the above object, the pressure sensor provided with the corrosion-resistant magnet according to the present invention has a lower housing having a pressure chamber communicating with a communication passage to which a pressure to be detected is supplied, and a pressure receiving plate can be moved. The pressure receiving plate accommodating chamber arranged in the base portion is provided in the base portion and the pressure receiving plate displacement detecting portion for detecting the displacement of the pressure receiving plate according to the detected pressure is provided, and the base portion is joined around the pressure chamber of the lower housing. An elastically displaceable diaphragm that has a fitting portion that is fitted to the lower end of the pressure receiving plate that is displaced according to the pressure of the pressure chamber and separates the pressure chamber and the pressure receiving plate accommodating chamber. A pressure member provided in the pressure receiving plate accommodating chamber and urging the diaphragm in a direction of increasing the internal volume of the pressure receiving plate accommodating chamber, and the pressure receiving plate displacement detection unit is a permanent magnet of rare earth held in the pressure receiving plate. Including a magnetic sensor that detects the magnetic flux density of the metal plating film, the permanent magnet covers the entire metal plating film, which is formed on the surface of the base metal and is corrosion resistant to the hydrogen sulfide component, and the metal plating film. It is characterized by having a resin coating film having a film thickness larger than the film thickness.

The metal plating film may be a zinc plating film, and the resin coating film may be an epoxy resin film.

The method for producing a corrosion-resistant magnet according to the present invention is a metal plating that is resistant to corrosion against hydrogen sulfide components on the entire surface of the base material of a permanent magnet supported by a moving part in a pressure sensor including a rare earth permanent magnet. A resin that covers the entire metal plating film formed on the permanent magnet that has been subjected to the metal plating treatment and the process of performing the treatment, and forms a resin coating film having a film thickness larger than the thickness of the metal plating film. It includes a step of performing a coating process.

The metal plating film may be a zinc plating film, and the resin coating film may be an epoxy resin film.

According to the method for manufacturing a corrosion-resistant magnet according to the present invention and the pressure sensor provided with the corrosion-resistant magnet, the permanent magnet is formed on the surface of the base material and has corrosion resistance to the hydrogen sulfide component. Since it has a metal plating film and a resin coating film that covers the entire metal plating film and has a film thickness larger than that of the metal plating film, it avoids corrosion of the magnet by the hydrogen sulfide component and prevents the magnet from corroding. Corrosion resistance can be improved.

It is a figure which shows the process of the manufacturing method of the magnet which has corrosion resistance which concerns on this invention. It is sectional drawing which shows the structure of an example of the pressure sensor provided with the magnet which has the corrosion resistance which concerns on this invention. It is a perspective view which shows an example of the magnet which has corrosion resistance which concerns on this invention together with a partial cross section.

FIG. 2 schematically shows the configuration of an example of a pressure sensor including a magnet having corrosion resistance according to the present invention.

The pressure sensor shown in FIG. 2 is arranged inside the lid of a rice cooker (not shown), for example. In FIG. 2, the pressure sensor includes an upper housing 12 arranged inside the lid, a lower housing 10 having a communication pipe 10IN that protrudes toward the opening of a pot (not shown) in the rice cooker body and communicates with the pot. The pressure receiving plate 24 that is movably arranged in the pressure receiving plate accommodating chamber 12A of the upper housing 12 and the pressure receiving plate 24 that is coupled to the pressure receiving plate 24 and introduced through the communication pipe 10IN according to the pressure in the pot as the detected pressure. Coil spring as an urging member for urging the diaphragm 18 and the pressure receiving plate 24 and the diaphragm 18 in the direction in which the volume of the pressure receiving plate accommodating chamber 12A increases, that is, in the direction in which the diaphragm 18 approaches the communication pipe 10IN. The main elements are the 22, the permanent magnet 26 that is press-fitted into the magnet mounting hole of the pressure receiving plate 24, and the signal processing circuit board 28 with a connector that includes a Hall element that faces the permanent magnet 26 and is arranged in the upper housing 12. It is configured to include.

The upper housing 12 is formed of, for example, a heat-resistant resin material (ABS). The upper housing 12 is composed of a base portion welded to the joint surface of the lower housing 10 and a tubular portion that is connected to the base portion and extends upward to support the signal processing circuit board 28 with a connector.

A pressure receiving plate accommodating chamber 12A partitioned by a diaphragm 18 is formed inside the lower portion of the tubular portion. A female screw portion 12FMS into which the male screw portion 14MS of the adjusting screw member 14 for adjusting the urging force of the coil spring 22 is screwed is formed in the inner peripheral portion of the upper portion of the tubular portion. A signal processing circuit board 28 with a connector is arranged at the right end of the tubular portion. The signal processing circuit board 28 with a connector as the pressure receiving plate displacement detecting unit includes a magnetic sensor (Hall element) that detects the magnetic flux density of the permanent magnet 26 supported by the pressure receiving plate 24. The pressure receiving plate accommodating chamber 12A communicates with the inside of the lid of the rice cooker through an air vent hole (not shown).

An arcuate protrusion 12P that is fitted into the grooves 10Ga and 10Gb of the lower housing 10 is formed on the joint surface of the lower housing 10 at the base portion, for example, at the portion that is ultrasonically welded. Further, a groove 12G into which the flange portion 18B of the diaphragm 18 described later is inserted adjacent to the protrusion 12P is formed around the pressure receiving plate accommodating chamber 12A.

The diaphragm 18 is formed of, for example, a silicone rubber having a predetermined thickness (for example, a thickness of 0.3 mm or more and 0.5 mm or less), and is inserted into a groove 12G formed in a truncated cone to form an outer edge. The portion 18B, the disc portion 18F abutting on the end surface of the hollow truncated cone portion 24CY at the lowermost end of the pressure receiving plate 24, which will be described later, and the disc portion 18F formed integrally with the disc portion 18F and fitted to the side surface of the truncated cone portion 24CY. A movable portion that can be elastically displaced by connecting the tapered surface portion 18Fb, the annular portion 18Fc that is in contact with the overhanging portion 24B adjacent to the truncated cone portion 24CY of the pressure receiving plate 24, and the annular portion 18Fc and the above-mentioned flange portion 18B. It consists of 18M. The tapered surface portion 18Fb of the diaphragm 18 forming a part of the recess has a taper angle, for example, 5 ° corresponding to the taper angle α of the hollow truncated cone portion 24CY of the pressure receiving plate 24 to be fitted. That is, the fitting portion of the diaphragm 18 is formed by the tapered surface portion 18Fb of the diaphragm 18 and the disc portion 18Fa.

The pressure receiving plate 24 is formed of, for example, a heat-resistant resin material (ABS), and has a magnet mounting hole into which a permanent magnet 26 is press-fitted at a position facing the above-mentioned signal processing circuit board with a connector 28. The permanent magnet 26 is formed in a thin plate shape by a rare earth magnet, for example, a magnet of neodymium, samarium-cobalt, or alnico. As shown in exaggerated and enlarged in FIG. 3, the permanent magnet 26 is formed, for example, with a thickness of 2 mm and a square shape of 5 mm. As will be described later, the permanent magnet 26 is subjected to a metal plating treatment, for example, a zinc plating treatment or a phosphate treatment on the surface of the base material, and then a resin coating is performed on the metal plating film or the phosphate film. The resin film is, for example, a resin coating film formed of an epoxy resin. The resin coating film formed of the epoxy resin has excellent corrosion resistance against a trace amount of hydrogen sulfide component. As a result, as shown in FIG. 3, in the case of the zinc plating treatment, a galvanized layer 26F having a film thickness in the range of about 5 μm or more and about 30 μm or less is formed on the entire surface of the base material of the permanent magnet 26, and zinc is formed. A resin film layer 26C made of epoxy resin having a thickness of about 36 μm ± 4 μm is formed on the entire surface of the plating layer 26F. The main reasons why the resin film layer 26C is formed from the epoxy resin are (1) high adhesion performance to the permanent magnet 26 and (2) high resistance to high temperature and humidity, in addition to improving corrosion resistance to hydrogen sulfide. (Resistance required to solve unavoidable problems when used in rice cookers), (3) Thin film coating of coating film is possible (Epoxy resin is uniform among many coating resins. This is because we focused on the point that a thin film can be formed).

The reason why the thickness of the resin film layer 26C is set to a value in the range of 32 μm or more and 40 μm or less is that the permanent magnet 26 is press-fitted into the magnet mounting hole, so that the galvanized layer 26F and the resin film layer 26C This is to prevent the magnet from being easily peeled off by press fitting. The second reason is that when the film thickness is relatively thick over 40 μm, the coating film is not uniform and may be accumulated on the ridge line portion (corner portion of the magnet). Furthermore, the third reason is that when the film thickness is relatively thin, which is less than 32 μm, a film having a predetermined strength (peeling strength / scratch strength) cannot be obtained.

Therefore, as will be described later, when rice is cooked, if a trace amount of hydrogen sulfide component is generated in the pot inside the rice cooker body, the trace amount of hydrogen sulfide component should be generated through the pressure chamber 10A through the pressure receiving plate. The permanent magnet 26 having the galvanized layer 26F and the resin film layer 26C has excellent corrosion resistance to hydrogen sulfide as compared with the galvanized film, even when the galvanized layer 26F has penetrated into the accommodation chamber 12A. Moreover, since the galvanized layer 26F is coated with the resin film layer 26C, which is an epoxy resin film that protects the galvanized layer 26F, corrosion of the magnet by a trace amount of hydrogen sulfide component can be avoided. The pressure receiving plate 24 formed of a heat-resistant resin material (ABS) is excellent in corrosion resistance to the above-mentioned trace amount of hydrogen sulfide component.

A spring receiving portion that is engaged with one end of the coil spring 22 is formed at the upper end portion of the pressure receiving plate 24 than the above-mentioned magnet mounting hole. The other end of the coil spring 22 is received by the annular groove of the adjusting screw member 14. At a position below the above-mentioned magnet mounting hole in the pressure receiving plate 24, an overhanging portion 24B to which the annular portion 18Fc of the diaphragm 18 is in contact is formed, and a hollow truncated cone portion 24CY is formed at the lowermost end. ing. As a result, the pressure receiving plate 24 is supported by one end of the coil spring 22 and slidable on the inner peripheral surface forming the pressure receiving plate accommodating chamber 12A of the upper housing 12 while being supported by the tapered surface portion 18Fb of the diaphragm 18. You will be guided.

The taper angle α of the hollow truncated cone portion 24CY is set to, for example, an angle in the range of 3 ° or more and 5 ° or less. As a result, the diameter of the tapered truncated cone portion 24CY increases as it approaches the communication pipe 10IN of the lower housing 10.

Therefore, when the tapered surface portion 18Fb of the diaphragm 18 acts in the direction of separating and pulling the tapered truncated cone portion 24CY of the pressure receiving plate 24 based on the negative pressure in the pan, the tapered surface portion 18Fb of the diaphragm 18 acts. Since the reaction force of the diaphragm 18 itself acts against the force of pushing the diaphragm 18, the situation where the diaphragm 18 and the pressure receiving plate 24 are separated is surely avoided. That is, the fitting portion separation avoiding means is formed by the hollow truncated cone portion 24CY, the tapered surface portion 18Fb of the diaphragm 18, and the disk portion 18Fa.

The lower housing 10 is formed of, for example, a heat-resistant resin material (ABS). As shown in FIG. 2, the lower housing 10 is integrally formed with the plate-shaped portion 10B on which the joint surface to which the base portion of the upper housing 12 is welded is formed, facing both ends of the plate-shaped portion 10B. The mounting portion 10F to be attached and the communication pipe 10IN coupled to the outer surface 10R facing the joint surface of the plate-shaped portion 10B are included. The communication pipe 10IN is assumed to protrude toward the opening of the pot (not shown) in the rice cooker body and communicate with the inside of the pot. Each mounting portion 10F has a mounting hole 10a into which a fastening member for mounting the pressure sensor is inserted into the lid LB of the rice cooker.

Arc-shaped grooves 10Ga and 10Gb are formed adjacent to each other on the joint surface where one ends of the mounting portions 10F are joined. A pressure chamber 10A communicating with the communication passage 16 in the communication pipe 10IN is formed in the central portion between the grooves 10Ga and 10Gb. The pressure chamber 10A is surrounded by a diaphragm 18 and a tapered surface portion 10IT whose one end opens with respect to the joint surface. The tapered surface portion 10IT has, for example, a taper angle of about 30 ° or more and 45 ° or less. At the end of the tapered surface portion 10IT having the minimum diameter, a stepped portion 10S having a predetermined depth Dp facing the disk portion 18F of the diaphragm 18 is formed. The inner diameter of the step portion 10S is set to be slightly larger than the diameter of the disc portion 18F of the diaphragm 18. As a result, a small chamber having the tapered surface portion 10IT is formed inside the lower housing 10. Since the internal volume of the small chamber in the lower housing 10 is relatively small, the height from the lower end surface of the plate-shaped portion 10B of the lower housing 10 to the uppermost end surface of the upper housing 12 is lower than that of the conventional one. As a result, the pressure sensor can be made thinner (lowered).

A rib 16D that evenly divides the communication passage 16 into two is integrally formed inside the communication pipe 10IN. One end surface of the rib 16D as a stopper portion is on a plane common to the surface of the above-mentioned step portion 10S, and is flush with the surface of the so-called step portion 10S. The other end surface of the rib 16D extends until it coincides with the lower end surface of the communication pipe 10IN. By providing the rib 16D in this way, it becomes difficult to insert a rod-shaped cooking utensil or the like through the opening at the lower end of the communication pipe 10IN, so that undesired damage to the diaphragm 18 and the pressure receiving plate 24 is avoided.

In such a configuration, when the pressure in the pot inside the rice cooker body rises and the pressure in the pressure chamber 10A becomes a positive pressure equal to or higher than the atmospheric pressure through the communication passage 16 of the communication pipe 10IN, the pressure receiving plate 24 and the diaphragm When the 18 is raised, the position of the permanent magnet 26 of the signal processing circuit board 28 with a connector relative to the Hall element changes, so that an output signal representing the positive pressure is transmitted from the signal processing circuit board 28 with a connector. Become. On the other hand, when the pressure in the pot inside the rice cooker body drops and the pressure in the pressure chamber 10A becomes negative pressure below atmospheric pressure through the communication passage 16 of the communication pipe 10IN, the pressure receiving plate 24 and the diaphragm 18 drop. As a result, the position of the permanent magnet 26 of the signal processing circuit board 28 with a connector relative to the Hall element changes, so that an output signal representing negative pressure is transmitted from the signal processing circuit board 28 with a connector.

In an example of the method for manufacturing a magnet having corrosion resistance according to the present invention, as shown in FIG. 1, for example, the base material (plating material) of the magnet made of neodymium described above (with a thickness of 2 mm). A 5 mm square material) is prepared, and the plating treatment S1 is performed on the entire surface of the base material. In the plating treatment S1, for example, the surface of the base material (plating material) is first degreased, and then the adhering degreasing liquid is washed with water and then pickled. As a result, the iron base material of the base material is exposed. Next, the adhered pickling solution is washed with water, then subjected to a flux film treatment to promote the alloy reaction between iron and zinc, and then dried. The base metal treated as described above is immersed in a zinc bath according to predetermined plating conditions. As a result, the galvanized layer is formed on the entire surface of the base metal with a film thickness in the range of about 5 μm or more and about 30 μm or less. The zinc plating layer may be, for example, a plating layer containing zinc as a main component, and may be Zn plating, Zn—Al alloy plating, Zn—Mg alloy plating, or the like.

Finally, the base metal on which the galvanized layer is formed is cooled with warm water in order to suppress the growth of the alloy layer of iron and zinc. As a result, the plating process S1 is completed. Subsequently, the resin coating treatment S2 is performed on the base material on which the zinc plating layer is formed. The resin coating treatment S2 is carried out by, for example, a fluid dipping method in which a powder (epoxy resin) is melted by the heat of a heat-treated work (base material on which a zinc plating layer is formed) to obtain a coating film. It is said. The flow dipping method is carried out until the film thickness of the resin film layer 26C is in the range of 32 μm or more and 40 μm or less. Subsequently, the magnetizing treatment S3 is performed on the base material on which the resin coating film of the epoxy resin is formed. Then, the inspection S4 of the magnetic characteristics of the magnetized magnet is performed. As a result, a permanent magnet 26 recognized as a non-defective product after inspection can be obtained.

In the above example, an example of the pressure sensor according to the present invention was applied to a rice cooker, but the present invention is not limited to such an example, and an example of the pressure sensor according to the present invention is applied to other cooking utensils. Of course, it may be. Further, the above-mentioned lower housing 10 has a mounting portion 10F formed integrally facing both ends of the plate-shaped portion 10B, but the present invention is not limited to such an example, and for example, each mounting portion has its own mounting portion. The plate-shaped portion 10B may be arranged so that the central axes intersect at a predetermined angle.

10 Lower housing 10A Pressure chamber 10IN Communication pipe 12 Upper housing 16 Communication passage 18 Diaphragm 24 Pressure receiving plate 26 Permanent magnet 26F Zinc plating layer 26C Resin film layer

Claims (6)

A lower housing having a pressure chamber communicating with a communication passage to which the pressure to be detected is supplied,
A pressure receiving plate housing chamber in which the pressure receiving plate is movably arranged is provided in the base portion, and a pressure receiving plate displacement detecting portion for detecting the displacement of the pressure receiving plate according to the detected pressure is provided, and the base portion is the lower. With the upper housing joined around the pressure chamber of the housing,
An elastically displaceable diaphragm that has a fitting portion that is fitted to the lower end of the pressure receiving plate that is displaced according to the pressure of the pressure chamber and that separates the pressure chamber from the pressure receiving plate accommodating chamber.
It is provided with an urging member which is arranged in the pressure receiving plate accommodating chamber and urges the diaphragm in a direction of increasing the internal volume of the pressure receiving plate accommodating chamber.
The pressure receiving plate displacement detecting unit includes a magnetic sensor that detects the magnetic flux density of a rare earth permanent magnet held on the pressure receiving plate, and the permanent magnet is formed on the surface of the base metal and is resistant to corrosion against hydrogen sulfide components. A magnet having corrosion resistance, which comprises a certain metal plating film and a resin coating film that covers the entire metal plating film and has a film thickness larger than the film thickness of the metal plating film. A pressure sensor equipped with. The pressure sensor according to claim 1, wherein the metal plating film is a zinc plating film. The pressure sensor according to claim 1, wherein the resin coating film is an epoxy resin film. A process of performing a metal plating treatment on the entire surface of the base material of the permanent magnet supported by a moving part of a pressure sensor equipped with a rare earth permanent magnet to have corrosion resistance against hydrogen sulfide components.
A resin coating treatment is performed to cover the entire metal plating film formed on the permanent magnet subjected to the metal plating treatment and to form a resin coating film having a film thickness larger than the film thickness of the metal plating film. A process and a method of manufacturing a metal having corrosion resistance, including. The method for manufacturing a magnet having corrosion resistance according to claim 4, wherein the metal plating film is a zinc plating film. The method for manufacturing a magnet having corrosion resistance according to claim 4, wherein the resin coating film is an epoxy resin film.

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