JP7137531B2 - Pressure sensor with corrosion resistant magnet - Google Patents

Description

The present invention relates to a method of manufacturing a corrosion-resistant magnet and a pressure sensor with a corrosion-resistant magnet.

For example, as shown in Patent Document 1, a rice cooker includes a vacuum device, a positive pressure device, a pressure detection module (pressure sensor) provided in a lid, and a main body having a cooking chamber. , and a positive pressure device controlled based on a detection signal from a pressure detection module (pressure sensor) to control the pressure in the cooking chamber. In such pressure control, the vacuum device is operated in the suction stage of rice cooking, and the vacuum is drawn to a relatively high pressure below atmospheric pressure (101.33 kPa), and in the steaming stage, the vacuum is relatively low. A vacuum is drawn to pressure and the pressure in the cooking chamber is maintained at a 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 are generated in the rice cooker, which are one of the causes of the odor that interferes with the aroma of the rice. known to do.

In the pressure sensor described above, as a micropressure sensor for a rice cooker, a magnetic sensor consisting of a permanent magnet and a Hall element detects the displacement of a diaphragm that is displaced in accordance with the pressure of a fluid, thereby producing an output signal representing the pressure of the fluid. What is supplied is put to practical use. The surface of the base material of such permanent magnets is sometimes subjected to nickel plating.

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

In the above-mentioned rice cooker, when a pressure sensor including a magnetic sensor composed of the above-mentioned permanent magnet and Hall element is used, and the rice is repeatedly cooked, 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, and the detection accuracy (magnetic force detection capability) of the pressure sensor may be lowered. Therefore, it is desired to improve the corrosion resistance of the permanent magnet to the hydrogen sulfide component.

In view of the above problems, the present invention provides a method for manufacturing a corrosion-resistant magnet and a pressure sensor equipped with a corrosion-resistant magnet, which avoids corrosion of the magnet due to hydrogen sulfide components, It is an object of the present invention to provide a method for manufacturing a corrosion-resistant magnet that can improve the corrosion resistance of a magnet, and a pressure sensor provided with the corrosion-resistant magnet.

In order to achieve the above object, a pressure sensor provided with a corrosion-resistant magnet according to the present invention includes a lower housing having a pressure chamber communicating with a communication passage to which pressure to be detected is supplied, and a pressure receiving plate that is movable. A pressure plate displacement detecting portion for detecting displacement of the pressure plate corresponding to the pressure to be detected is provided in the base portion, and the base portion is joined around the pressure chamber of the lower housing. an elastically displaceable diaphragm partitioning the pressure chamber and the pressure receiving plate accommodating chamber, having a fitting portion fitted to the lower end portion of the pressure receiving plate that is displaced according to the pressure of the pressure chamber; an urging member disposed in the pressure plate housing chamber and urging the diaphragm in a direction to increase the internal volume of the pressure plate housing chamber, wherein the pressure plate displacement detection unit is a rare earth permanent magnet held by the pressure plate. Including a magnetic sensor that detects the magnetic flux density of the permanent magnet, the metal plating film formed on the surface of the base material and having corrosion resistance to hydrogen sulfide components, and the metal plating film covering the entire metal plating film and 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.

A method for manufacturing a magnet having corrosion resistance according to the present invention is a pressure sensor having a rare earth permanent magnet, and the entire surface of the base material of the permanent magnet supported by the movable portion is coated with metal plating having corrosion resistance against hydrogen sulfide components. A resin that forms a resin coating film that covers the entire metal plating film formed on the metal-plated permanent magnet and has a thickness greater than that of the metal plating film. and 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 manufacturing method of the corrosion-resistant magnet and the pressure sensor provided with the corrosion-resistant magnet according to the present invention, the permanent magnet is formed on the surface of the base material and is corrosion-resistant to hydrogen sulfide components. Since it has a metal plating film and a resin coating film that covers the entire metal plating film and has a thickness larger than the thickness of the metal plating film, corrosion of the magnet due to hydrogen sulfide components is avoided. Corrosion resistance can be improved.

FIG. 4 is a diagram showing steps of a method for manufacturing a corrosion-resistant magnet according to the present invention; 1 is a cross-sectional view showing the structure of an example of a pressure sensor provided with a corrosion-resistant magnet according to the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an example of a magnet having corrosion resistance according to the present invention, along with a partial cross section;

FIG. 2 schematically shows the configuration of an example of a pressure sensor provided with a corrosion-resistant magnet according to the present invention.

The pressure sensor shown in FIG. 2 is arranged, for example, in a lid of a rice cooker (not shown). In FIG. 2, the pressure sensor includes an upper housing 12 arranged in the lid, a lower housing 10 having a communication pipe 10IN projecting toward the opening of a pot (not shown) in the main body of the rice cooker and communicating with the pot, A pressure plate 24 is movably arranged in the pressure plate accommodating chamber 12A of the upper housing 12, and the pressure plate 24 is connected to the pressure plate 24 and is connected to the pressure plate 24 according to the pressure in the pan as the pressure to be detected introduced through the communication pipe 10IN. and a coil spring as a biasing member that biases the pressure receiving plate 24 and the diaphragm 18 in the direction in which the volume of the pressure receiving plate housing chamber 12A increases, that is, in the direction in which the diaphragm 18 approaches the communicating pipe 10IN. 22, a permanent magnet 26 press-fitted into the magnet mounting hole of the pressure-receiving plate 24, and a signal processing circuit board 28 with a connector including a Hall element arranged in the upper housing 12 facing the permanent magnet 26. is composed of

The upper housing 12 is made of, for example, a heat-resistant resin material (ABS). The upper housing 12 is composed of a base portion which is welded to the joint surface of the lower housing 10 and a cylindrical portion which extends upward from the base portion and supports the signal processing circuit board 28 with connector.

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

Arc-shaped protrusions 12P are formed on the joint surface of the lower housing 10 in the base portion, for example, in the portion to be ultrasonically welded so as to be fitted into the grooves 10Ga and 10Gb of the lower housing 10, respectively. A groove 12G into which a flange portion 18B of a diaphragm 18 (to be described later) is inserted is formed around the pressure receiving plate accommodating chamber 12A adjacent to the protrusion 12P.

The diaphragm 18 is, for example, molded of 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 the base portion to form an outer edge of the flange. a portion 18B, a disc portion 18Fa that abuts against the end face of a hollow truncated cone portion 24CY at the bottom end of the pressure receiving plate 24, which will be described later, and a disc portion 18Fa that is integrally formed and fitted to the side surface of the truncated cone portion 24CY. an annular portion 18Fc that abuts on the projecting portion 24B adjacent to the truncated cone portion 24CY of the pressure receiving plate 24; 18M. The tapered surface portion 18Fb of the diaphragm 18 forming 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 disk portion 18Fa.

The pressure receiving plate 24 is made 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 signal processing circuit board 28 with connector. The permanent magnet 26 is formed in a thin plate shape from a rare earth magnet such as neodymium, samarium cobalt, or alnico. As shown exaggeratedly in FIG. 3, the permanent magnet 26 is, for example, 2 mm thick and 5 mm square. As will be described later, the permanent magnet 26 has a base material surface subjected to metal plating, for example, zinc plating or phosphate treatment, and the metal plating film or phosphate film is coated with a resin. As the resin film, for example, a resin coating film formed of an epoxy resin is used. A resin coating film formed of an epoxy resin is excellent in corrosion resistance against trace amounts of hydrogen sulfide components. As a result, as shown in FIG. 3, in the case of zinc plating, a zinc plating layer 26F having a 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. A resin film layer 26C made of epoxy resin and having a thickness of about 36 μm±4 μm is formed on the entire surface of the plating layer 26F. The main reasons for forming the resin film layer 26C with epoxy resin are, in addition to improvement in corrosion resistance to hydrogen sulfide, (1) high adhesion performance with the permanent magnet 26, and (2) high resistance to high temperature and high humidity. (Durability required to solve the inevitable problems in using rice cookers), (3) Thin coating of coating film is possible (Among many coating resins, epoxy resin is uniform This is because the focus was focused on the point that a thin film can be formed.

The first reason why the thickness of the resin film layer 26C is set to a value in the range of 32 μm to 40 μm is that the permanent magnets 26 are press-fitted into the magnet mounting holes, so that the galvanized layer 26F and the resin film layer 26C are formed. This is to prevent the peeling off easily due to press-fitting. The second reason is that if the film thickness is relatively thick, exceeding 40 μm, the coating film will not be uniform, and in particular, it may accumulate at the ridgeline portions (corner portions of the magnet). A third reason is that if the film thickness is relatively thin, i.e., less than 32 μm, a film having a predetermined strength (peel strength and scratch strength) cannot be obtained.

Therefore, as will be described later, when rice is cooked, if a small amount of hydrogen sulfide is generated in the pan inside the rice cooker body, the small amount of hydrogen sulfide will be released to the pressure receiving plate via the pressure chamber 10A. The permanent magnet 26 having the zinc plating layer 26F and the resin film layer 26C has excellent corrosion resistance against hydrogen sulfide in the zinc plating layer 26F as compared with the nickel plating film even when it penetrates into the storage chamber 12A. Moreover, since the galvanized layer 26F is covered with the resin film layer 26C, which is an epoxy resin film that protects the galvanized layer 26F, corrosion of the magnet due to a small amount of hydrogen sulfide can be avoided. The pressure plate 24 made of a heat-resistant resin material (ABS) has excellent corrosion resistance against the trace amount of hydrogen sulfide component described above.

A spring receiving portion that engages with one end of the coil spring 22 is formed at the upper end portion of the pressure receiving plate 24 above the magnet mounting hole. The other end of the coil spring 22 is received in the annular groove of the adjusting screw member 14 . A protruding portion 24B is formed in the pressure receiving plate 24 at a position below the magnet mounting hole described above, and the annular portion 18Fc of the diaphragm 18 abuts thereon. ing. As a result, the pressure receiving plate 24 is supported by one end of the coil spring 22 and supported by the tapered surface portion 18Fb of the diaphragm 18, and is slidable on the inner peripheral surface forming the pressure receiving plate accommodating chamber 12A of the upper housing 12. be guided.

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

Therefore, when the tapered surface portion 18Fb of the diaphragm 18 is separated from the tapered truncated cone portion 24CY of the pressure receiving plate 24 based on the above-described negative pressure in the pot, the tapered surface portion 18Fb of the diaphragm 18 is separated from the tapered truncated cone portion 24CY of the pressure receiving plate 24. Since the reaction force of the diaphragm 18 itself acts against the force that pushes apart, the separation of the diaphragm 18 and the pressure receiving plate 24 is reliably 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 molded, for example, from a heat-resistant resin material (ABS). As shown in FIG. 2, the lower housing 10 is integrally formed with a plate-like portion 10B having a joint surface to which the base portion of the upper housing 12 is welded, and facing both ends of the plate-like portion 10B. and a connecting pipe 10IN coupled to the outer surface 10R facing the joint surface of the plate-like portion 10B. The communication pipe 10IN protrudes toward an opening of a pot (not shown) in the main body of the rice cooker and communicates with the inside of the pot. Each attachment portion 10F has an attachment hole 10a into which a fastening member for attaching the pressure sensor to the lid LB of the rice cooker is inserted.

Arc-shaped grooves 10Ga and 10Gb are formed adjacent to the portion of the joint surface where one end of each mounting portion 10F is coupled. A pressure chamber 10A communicating with a communication passage 16 in a communication pipe 10IN is formed in a central portion between the grooves 10Ga and 10Gb. The pressure chamber 10A is surrounded by a diaphragm 18 and a tapered surface portion 10IT one end of which is open to the joint surface. The tapered surface portion 10IT has, for example, a taper angle of approximately 30° or more and 45° or less. A stepped portion 10S having a predetermined depth Dp facing the disk portion 18Fa of the diaphragm 18 is formed at the end portion having the smallest diameter of the tapered surface portion 10IT. The inner diameter of the step portion 10S is set slightly larger than the diameter of the disk portion 18Fa of the diaphragm 18. As shown in FIG. As a result, a small chamber having the tapered surface portion 10IT is formed inside the lower housing 10. As shown in FIG. 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-like portion 10B of the lower housing 10 to the uppermost end surface of the upper housing 12 is lower than in the conventional case. As a result, the pressure sensor can be thinned (reduced in height).

A rib 16D is integrally formed inside the communicating pipe 10IN to equally divide the communicating passage 16 into two. One end surface of the rib 16D as a stopper portion is on the same plane as the surface of the above-described stepped portion 10S, and is flush with the so-called surface of the stepped portion 10S. The other end face of the rib 16D extends until it matches the lower end face of the communicating pipe 10IN. By providing the rib 16D in this way, it becomes difficult to insert a rod-shaped cooking utensil or the like from the opening at the lower end of the communicating pipe 10IN, so that the diaphragm 18 and the pressure receiving plate 24 are prevented from being undesirably damaged.

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

In one example of the method for manufacturing a corrosion-resistant magnet according to the present invention, as shown in FIG. A 5 mm square material) is prepared, and plating processing S1 is performed on the entire surface of the base material. In the plating process S1, for example, first, the surface of the base material (plating material) is degreased, and then the degreasing liquid adhered is washed with water and pickled. This exposes the iron base of the base material. Next, after the adhered pickling liquid is washed with water, a flux film treatment is applied to promote the alloy reaction between iron and zinc, and then dried. The base material treated as described above is immersed in a zinc bath according to predetermined plating conditions. As a result, a galvanized layer is formed on the entire surface of the base material with a film thickness in the range of approximately 5 μm to approximately 30 μm. 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 with the galvanized layer formed thereon is cooled with warm water to suppress the growth of the alloy layer of iron and zinc. This completes the plating process S1. Subsequently, a resin coating treatment S2 is performed on the base material on which the galvanized layer is formed. The resin coating treatment S2 is performed by, for example, a fluidized bed dipping method or the like in which the powder (epoxy resin) is melted by the heat of the heat-treated workpiece (base material on which the galvanized layer is formed) to obtain a coating film. will be The fluidized immersion method is performed until the film thickness of the resin film layer 26C reaches a range of 32 μm or more and 40 μm or less. Subsequently, a magnetization process S3 is performed on the base material on which the resin coating film of the epoxy resin is formed. Then, an inspection S4 of the magnetic properties of the magnetized magnet is performed. As a result, a permanent magnet 26 that is recognized as a non-defective product after inspection is obtained.

In the above example, an example of the pressure sensor according to the present invention is 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 can be applied to other cooking utensils. It is of course possible to In addition, although the lower housing 10 described above has mounting portions 10F integrally formed facing both ends of the plate-like portion 10B, the present invention is not limited to such an example. It may be arranged in the plate-like portion 10B 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 coating layer

Claims (3)

a lower housing having a pressure chamber communicating with a communication passage to which pressure to be detected is supplied;
A pressure plate displacement detection section is provided for detecting a displacement of the pressure plate corresponding to the pressure to be detected, the pressure plate accommodating chamber having a pressure plate accommodating chamber in which the pressure plate is movably disposed, and the base portion being connected to the lower portion. an upper housing joined around the pressure chamber of the housing;
an elastically displaceable diaphragm that partitions the pressure chamber from the pressure receiving plate housing chamber, the diaphragm having a fitting portion that is fitted to the lower end portion of the pressure receiving plate that is displaced according to the pressure of the pressure chamber;
a biasing member arranged in the pressure receiving plate housing chamber and biasing the diaphragm in a direction to increase the inner volume of the pressure receiving plate housing chamber;
The pressure plate displacement detection unit includes a magnetic sensor for detecting the magnetic flux density of a rare earth permanent magnet held by the pressure plate. A corrosion-resistant magnet comprising a metal plating film and a resin coating film covering the entire metal plating film and having a thickness greater than that of the metal plating film. a pressure sensor. 2. The pressure sensor according to claim 1, wherein said metallic plating film is a zinc plating film. 2. The pressure sensor according to claim 1, wherein said resin coating film is an epoxy resin film .

Images