Dental magnetic attachment magnet structure

Abstract

To provide a dental magnetic attachment magnet structure having attraction force and durability equal to or higher than those of conventional ones, manufactured at a low cost, and containing no Ni.SOLUTION: A dental magnetic attachment magnet structure includes: a cup yoke made of ferritic stainless steel containing substantially no Ni; a permanent magnet accommodated in a recess of the cup yoke; a shield disk consisting of a disk yoke made of ferritic stainless steel containing substantially no Ni and sealing an opening of the cup yoke, and a shield ring including a Cr layer or Au layer disposed on an outer periphery of the disk yoke; and a welded part where the cup yoke and an abutment part of the shield ring and the disk yoke are fixed by welding, and the entire magnet structure is configured to contain substantially no Ni.SELECTED DRAWING: Figure 1a

Description

[Technical Field]

[0001] The present invention relates to a dental magnetic attachment magnetic structure that uses the magnetic attraction force of a permanent magnet to hold dentures. [Background technology]

[0002] Fig. 6 is a schematic cross-sectional view showing a conventional magnetic attachment magnet structure. As shown in Fig. 6, a conventional dental magnetic attachment magnet structure 400 (hereinafter sometimes simply referred to as "magnet structure") has a structure in which a soft magnetic stainless steel disc yoke 414 and a non-magnetic stainless steel shield ring 415 are concentrically arranged in the opening of a soft magnetic stainless steel cup-shaped yoke 401, and the disc yoke 414 and the shield ring 415, and the shield ring 415 and the cup-shaped yoke 401 are welded all around to seal the permanent magnet 402. Furthermore, for example, Patent Document 1 (Japanese Patent Laid-Open Publication No. 5-95965) discloses the structure of a similar conventional magnetic attachment magnet structure.

[0003] Fig. 5 is a schematic cross-sectional view showing a denture having a magnetic attachment magnet structure attached to a keeper installed on a root plate embedded in an alveolar cavity. As shown in Fig. 5, this magnet structure 400 is embedded in a denture base 420, and is held to the root plate 422 by the magnetic attractive force with a soft magnetic keeper 423 installed on the root plate 422 embedded in an alveolar cavity 421. The magnet structure 400 must satisfy requirements such as being harmless to the human body, being chemically stable for a long period of time, and having a strong adsorptive force.

[0004] The dental magnetic attachment magnetic structure 400 is manufactured by inserting a permanent magnet 402 (e.g., a neodymium magnet) into the recess of a cup-shaped yoke 401, inserting a disk-shaped seal member 413 consisting of a disk yoke 414 and a shield ring 415 into the opening of the cup-shaped yoke 401, sealing the butt joints between the cup-shaped yoke 401 and the shield ring 415 and between the shield ring 415 and the disk yoke 414 by welding, and then smoothing the welds by polishing or grinding. When this magnetic structure 400 is attached to the keeper 423, the presence of the austenitic stainless steel shield ring 415 on the outer periphery of the disk-shaped seal member 413 blocks part of the magnetic path, allowing the magnetic flux of the permanent magnet 402 to flow efficiently through the magnetic circuit consisting of the keeper 423, cup-shaped yoke 401, and disk yoke 414, thereby generating a large adhesive force.

[0005] The disk-shaped seal member 413 is generally manufactured by inserting a ferritic stainless steel rod into an austenitic stainless steel pipe, drawing it to obtain a clad rod with an outer periphery made of austenitic stainless steel and a center made of ferritic stainless steel, and then cutting it into ring slices. The austenitic stainless steel used as the material for the shield ring 415 has traditionally been one in which the austenite phase was generated by dissolving nickel. However, because it contains nickel, magnetic attachment magnet structures cannot be used by patients who develop metal allergies due to nickel. For this reason, there is a demand for dental magnetic attachment magnet structures made of nickel-free stainless steel.

[0006] As an example of austenitic stainless steel that does not contain Ni, Patent Document 2 (JP 2012-92413 A) discloses a nitrogen-solubilized austenitic stainless steel in which nitrogen is dissolved in the stainless steel composition, and proposes a method for producing nitrogen-solubilized austenitic stainless steel by heating ferritic stainless steel at 1100 to 1250°C in a nitrogen atmosphere at approximately atmospheric pressure (nitrogen partial pressure: 80 to 86.7 kPa) to cause nitrogen to be absorbed from the stainless steel surface, thereby producing austenitic stainless steel.

[0007] However, austenitic stainless steel with dissolved nitrogen has the property of transforming into a mixed structure of ferrite and Cr nitride phases under high temperatures of approximately 700°C or higher and atmospheric pressure conditions. Therefore, heating cannot be performed during the welding of butt joints or extrusion of pipes when making pipes from plates of this material, or during stress relief annealing of the pipe material, and therefore it is not possible to manufacture pipe material for use in the shield rings. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 5-95965 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-92413 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a dental magnetic attachment magnet structure that has attractive force and durability equal to or greater than those of conventional ones, is low in manufacturing cost, and does not contain Ni.

[0010] In view of the above object, as a result of intensive research, the inventors have discovered that by producing a round bar material in which a shield ring portion made of a Cr layer or Au layer is formed on the outside of a core portion that becomes a disk yoke made of ferritic stainless steel that is substantially free of Ni, and slicing the round bar material, a substantially Ni-free shield disk consisting of a disk yoke that is substantially free of Ni and a shield ring portion made of a Cr layer or Au layer can be obtained, and that by combining a cup yoke made of ferritic stainless steel that is substantially free of Ni with a permanent magnet and the shield disk, and fixing the cup yoke, the shield ring layer, and the disk yoke by welding, a dental magnetic attachment magnet structure that is substantially free of Ni can be obtained, thereby completing the present invention.

[0011] In other words, the dental magnetic attachment magnet structure of the present invention is characterized by comprising a cup yoke made of ferritic stainless steel that is substantially free of Ni, a permanent magnet that is housed in the recess of the cup yoke, a shield disk consisting of a disk yoke made of ferritic stainless steel that is free of Ni and that seals the opening of the cup yoke, and a shield ring portion consisting of a Cr layer or Au layer arranged on its outer periphery, and a welded portion where the cup yoke, shield ring portion, and disk yoke butt together are fixed by welding, thereby making the entire magnet structure substantially free of Ni.

[0012] The Ni content of the cup yoke and the disk yoke is preferably 0.2% by mass or less. When the Ni content is 0.2% by mass or less, it can be considered that the Ni content is substantially zero.

[0013] The Cr content of the cup yoke and the disc yoke is preferably 17 to 32 mass %.

[0014] The Mo content of the cup yoke and the disk yoke is preferably 0.75 to 2.50 mass %.

[0015] The thickness of the shield ring portion made of a Cr layer or an Au layer is preferably 50 to 300 μm.

[0016] The shield ring portion is preferably formed by Cr plating or Au plating. The interface between the disk yoke and the shield ring portion, which is made of a Cr layer or an Au layer connected to the outer periphery of the disk yoke, is preferably joined by interdiffusion.

[0017] The thickness of the diffusion layer formed by mutual diffusion at the interface between the disk yoke and the shield ring portion is preferably 2 to 30 μm. [Effects of the Invention]

[0018] The dental magnetic attachment magnetic structure of the present invention has high attractive force and durability, and is substantially free of Ni, so it can be used by patients who develop metal allergies due to Ni. Furthermore, the dental magnetic attachment magnetic structure of the present invention allows the shield disk member to be produced more easily than with conventional methods, thereby reducing manufacturing costs. [Brief explanation of the drawings]

[0019] [Figure 1a] 1 is a schematic cross-sectional view showing an example of a magnetic attachment magnet structure of the present invention. [Figure 1b] 1 is a schematic plan view showing an example of a magnetic attachment magnet structure of the present invention. [Figure 2] 1 is a schematic cross-sectional view showing a shield disk of the present invention. [Figure 3a] FIG. 2 is a schematic diagram showing the diffusion state of Cr and Fe in a shield disk having a Cr-plated shield ring portion according to the present invention after heat treatment. [Figure 3b] 3 is a schematic diagram showing the diffusion state of Au, Fe, and Cr in a shield disk having an Au-plated shield ring portion according to the present invention after heat treatment. FIG. [Figure 4a] FIG. 10 is a schematic cross-sectional view showing a state in which laser welding is performed with the center of the shield ring portion as the center of the optical axis. [Figure 4b] 10 is a schematic cross-sectional view showing a state in which the butt joint between the shield disk and the cup yoke is laser-welded with the optical axis at its center. FIG. [Figure 4c] FIG. 10 is a schematic cross-sectional view showing the state in which the first line is laser welded at the butt joint between the shield disk and the cup yoke with the optical axis at the center, and the second line is laser welded at the interface between the shield ring portion and the disk yoke with the optical axis at the center. [Figure 5] 1 is a schematic cross-sectional view showing a denture having a magnetic attachment magnet structure attached to a keeper installed on a root plate embedded in a tooth alveolus. [Figure 6] FIG. 1 is a schematic cross-sectional view showing a conventional magnetic attachment magnet structure. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. However, the technical scope of the present invention is not limited to these preferred embodiments.

[0021] FIG. 1a is a schematic cross-sectional view showing an example of a magnetic attachment magnetic structure of the present invention, and FIG. 1b is a schematic plan view showing an example of a magnetic attachment magnetic structure of the present invention.

[0022] (1) Overall structure As shown in Figures 1a and 1b, the magnetic attachment magnet structure comprises a cup yoke 1 made of ferritic stainless steel and substantially free of nickel (Ni), a permanent magnet 2 housed in the recess of the cup yoke 1, a shield disk 3 made of a disk yoke 31 made of ferritic stainless steel and substantially free of nickel (Ni), which seals the opening of the cup yoke 1, and a shield ring 32 made of a chromium (Cr) or gold (Au) layer. Finally, a welded joint 4 is formed by welding the disk yoke 31 and the shield ring 32 together. This configuration results in a magnetic attachment magnet structure that is substantially free of nickel (Ni), making it suitable for use by patients who suffer from Ni-related metal allergies. The Cr content of the cup yoke 1 and the disk yoke 31 is preferably 17-32% by mass, more preferably 24-32% by mass. The Ni content of the cup yoke is preferably 0.2% by mass, more preferably 0.1% by mass. The Mo (molybdenum) content of the cup yoke 1 and the disc yoke 31 is preferably 0.75 to 2.50 mass %.

[0023] In this magnetic attachment magnet structure 10, the cup yoke 1 and the disk yoke 31 made of ferritic stainless steel are magnetic bodies, and the shield ring portion 32 made of a Cr layer or an Au layer is non-magnetic, so that the side of the permanent magnet 2 facing the disk yoke 31 becomes one magnetic pole (the south pole in the figure), and the open end of the cup yoke 1 (the side facing the bottom surface of the recess in the cup yoke 1) becomes the other magnetic pole (the north pole in the figure), forming a magnetic circuit.

[0024] (2) Disc yoke Disk yoke 31 is preferably made of ferritic stainless steel (SUS447J1, SUSXM27, SUS444, etc.) that has excellent corrosion resistance and is substantially free of Ni. The Cr content of disk yoke 31 is preferably 17 to 32 mass%, more preferably 24 to 32 mass%. The Ni content of disk yoke 31 is preferably 0.2 mass% or less, more preferably 0.1 mass% or less.

[0025] (3) Shield disc 2 is a schematic cross-sectional view showing a shield disk of the present invention. Shield disk 3 comprises disk yoke 31 made of ferritic stainless steel that is substantially free of Ni, and shield ring portion 32 made of a Cr layer or Au layer arranged around the disk yoke. Conventionally, shield ring portion 32 is generally formed by covering a ferritic stainless steel rod (hereinafter referred to as disk yoke material) that will become the disk yoke with a tube made of austenitic stainless steel and then tightly attaching it to the disk yoke by drawing. However, in this embodiment, shield ring portion 32 is formed by Cr plating or Au plating. The thickness of shield ring portion 32 varies depending on the configuration of the magnetic circuit, but is preferably 50 to 300 μm, and more preferably 100 to 250 μm.

[0026] The shield ring portion 32 using Cr in the present invention cannot be formed by conventional drawing because Cr is a brittle material. In the present invention, the shield ring portion 32 using Cr is formed by electroplating Cr onto the surface of the disk yoke 31 material, followed by cutting. Conventional Cr plating has a thickness of up to about 10 μm, but after extensive research, we have developed a technology that allows Cr plating to a thickness of 300 μm.

[0027] Furthermore, we adopted Au plating because we found that forming the shield ring portion 32 using Au in the present invention is less costly than manufacturing the Au tube that covers the disk yoke material and then performing the drawing process to adhere it to the disk yoke material. However, Au plating is generally at most 5 to 10 μm thick, and there was no technology available for thick film plating of 50 to 300 μm. After extensive research, we developed a technology for thick film plating of 300 μm.

[0028] The shape of the shield disk 3 may be changed as needed by changing the shape of the bar material from which the disk yoke 31 is made to match the shape of the opening of the cup yoke.

[0029] (4) Heat treatment of shield disk components The shield disk 3 is obtained by cutting a bar material (hereinafter referred to as the shield disk material) into which a Cr or Au plating process has been applied to the surface, forming a shield disk 3. When cutting the shield disk material, the Cr or Au plating between the disk yoke 31 material and the shield ring portion 32 may peel off at the interface due to poor adhesion. To prevent this peeling during cutting, a diffusion layer is formed at the interface by heat treatment to enhance adhesion between the disk yoke material and the shield ring portion. Figure 3a is a schematic diagram showing the diffusion of Cr and Fe in a shield disk 3 having a Cr-plated shield ring portion 32 of the present invention after heat treatment. Figure 3b is a schematic diagram showing the diffusion of Au, Fe, and Cr in a shield disk 3 having an Au-plated shield ring portion 32 of the present invention after heat treatment. A Cr diffusion layer is formed in both the Cr plating and the Au plating. The interface between the disk yoke 31 and the shield ring portion 32, consisting of a Cr or Au layer connected to its outer periphery, is bonded by interdiffusion. The thickness of the diffusion layer formed by mutual diffusion at the interface between the disk yoke 31 and the shield ring part 32 is preferably 2 to 30 μm.

[0030] (5) Cup yoke The cup yoke 1 has a recess for accommodating the permanent magnet 2. The recess has dimensions that correspond to the size of the permanent magnet 2 to be accommodated, and the size of the portion into which the shield disk 3 is inserted is determined by the following formula (1): (Br×S)×0.8≦Sc×Bs≦(Br×S)×1.2 (1) [where Bs represents the saturation magnetization of the cup yoke 1, Br represents the residual magnetic flux density of the permanent magnet 2, S represents the cross-sectional area perpendicular to the magnetization direction of the permanent magnet 2, and Sc represents the effective area (area of ​​the magnetic portion) of the attraction surface of the cup yoke 1.] is preferably set to satisfy this.

[0031] The cup yoke 1 is preferably made of ferritic stainless steel (SUS447J1, SUSXM27, SUS444, etc.) that has excellent corrosion resistance and is substantially free of Ni. The Cr content of the cup yoke 1 is preferably 17 to 32 mass%, more preferably 24 to 32 mass%. The Ni content of the cup yoke 1 is preferably 0.2 mass% or less, more preferably 0.1 mass% or less.

[0032] (6) Welded parts The disc yoke 31, shield ring portion 32 and cup yoke 1 are fixed together by welding using laser light, and it is preferable that the target position of the center of the laser light is between the butt portion of the shield ring portion 32 and the cup yoke 1 and the interface between the shield ring portion 32 and the disc yoke 31.It is more preferable to select one of the following methods: single-line welding, in which the center of the laser light is the center of the shield ring portion 32, single-line welding centered on the butt portion of the shield ring portion 32 and the cup yoke 1, or double-line welding centered on the butt portion of the shield ring portion 32 and the cup yoke 1 and the interface between the shield ring portion 32 and the disc yoke 31.

[0033] The surface including the weld is preferably flattened to a predetermined depth to generate more suction force and to eliminate crack initiation points due to unevenness in the weld. After flattening, the weld depth at the butt joint between the shield ring portion 32 and the cup yoke 1 and at the interface between the shield ring portion 32 and the disk yoke 1 is preferably 30 μm or more, and more preferably 50 μm or more, to ensure sufficient weld strength.

[0034] (7) Permanent magnet It is preferable to use a neodymium magnet with a higher residual magnetic flux density Br than other permanent magnets as the permanent magnet 2. The Br of the neodymium magnet is preferably 1.3 T or more, and more preferably 1.35 T or more, because it is used together with the magnetic structure and must magnetically saturate the recessed end of the cup yoke that is in contact with the keeper that attracts to the magnetic structure and that houses the permanent magnet.

[0035] Furthermore, the coercive force Hcj of the neodymium magnet is preferably 1100 kA / m or more, and more preferably 1280 kA / m or more, to prevent a decrease in magnetic force in the temperature range in which the dental magnetic attachment is used. [Example]

[0036] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0037] Example 1 A 2.4 mm diameter, 200 mm long round bar made of ferritic stainless steel (equivalent to SUSXM27 steel) with a composition of 26% by mass Cr, 1% by mass Mo, and the remainder Fe (including 0.08% by mass Ni as an impurity) was chromium-plated using a high-efficiency bath for a length of 150 mm from the end to form a 200 μm thick chromium plating film. It was then heat-treated at 900°C for 10 minutes under a reduced pressure of 0.2 Pa. EPMA analysis of a cross section perpendicular to the axis of the removed round bar revealed a 20 μm thick chromium diffusion layer at the interface between the chromium-plated layer and the ferritic stainless steel. The round bar was ground to a diameter of 2.7 mm and then cut to an axial thickness of 0.25 mm to form a shield disk.

[0038] Using ferritic stainless steel with the same composition as the disk yoke, we created a cup yoke with a diameter of 3.5 mm, a height of 1.35 mm, and a recess with a diameter of 2.7 mm and a depth of 0.75 mm to accommodate a neodymium magnet, and a neodymium magnet with a diameter of 2.65 mm and a thickness of 0.5 mm. The neodymium magnet was inserted into the recess of the cup yoke, and a shield disk was inserted to cover it.

[0039] 4a is a schematic cross-sectional view showing the state of laser welding with the center of the shield ring as the center of the optical axis. As shown in Fig. 4a, the center of the optical axis of the laser beam 5a was aligned with the center of the shield ring, and full-circumference welding was performed with a 450 μm-wide bead to seal the neodymium magnet.

[0040] After welding, the welded surface was polished by 0.05 mm to a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 5.0 to 5.1 N (measured on five pieces).

[0041] Example 2 A 2.4 mm diameter, 200 mm long round bar made of ferritic stainless steel (equivalent to SUSXM27) with a composition of 26% by mass Cr, 1% by mass Mo, and the remainder Fe (including 0.08% by mass Ni as an impurity) was gold-plated from the end to a length of 150 mm using a high-efficiency bath to form a 200 μm thick gold plating. The bar was then heat-treated at 900°C for 10 minutes under a reduced pressure of 0.2 Pa. EPMA analysis of a cross section perpendicular to the axis of the removed round bar revealed a 10 μm thick Cr diffusion layer at the interface between the gold-plated layer and the ferritic stainless steel. The round bar was then ground to a diameter of 2.7 mm and cut to an axial thickness of 0.25 mm to form a shield disk.

[0042] Using ferritic stainless steel with the same composition as the disk yoke, we created a cup yoke with a diameter of 3.5 mm, a height of 1.35 mm, and a recess with a diameter of 2.7 mm and a depth of 0.75 mm to accommodate a neodymium magnet, and a neodymium magnet with a diameter of 2.65 mm and a thickness of 0.5 mm. The neodymium magnet was inserted into the recess of the cup yoke, and a shield disk was inserted to cover it.

[0043] As shown in FIG. 4a, the optical axis of the laser beam 5a was aligned with the center of the shield ring portion, and a 450 μm wide bead was welded all around to seal the neodymium magnet.

[0044] After welding, the welded surface was polished by 0.05 mm to a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 4.9 to 5.1 N (measured on five pieces).

[0045] Example 3 A Cr-plated shield disk was produced in the same manner as in Example 1, and a neodymium magnet was inserted into the recess of the cup yoke, with the shield disk inserted to cover it. Figure 4b is a schematic cross-sectional view showing the state in which laser welding was performed with the butt joint between the shield disk and the cup yoke at the center of the optical axis. As shown in Figure 4b, the center of the optical axis of laser beam 5a was aligned with butt joint 4a between the shield ring portion and the cup yoke, and full-circumference welding was performed with a 230 μm-wide bead to seal in the neodymium magnet.

[0046] After welding, the welded surface was polished by 0.05 mm to give a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 5.1 to 5.2 N (measured on five pieces).

[0047] Example 4 An Au-plated shield disk was produced in the same manner as in Example 2, and a neodymium magnet was inserted into the recess of the cup yoke, with the shield disk then inserted to cover it. As shown in Figure 4b, the optical axis of laser light 5a was aligned with the butt joint 4a between the shield ring and cup yoke, and a 230 μm-wide bead was used for full-circumference welding to seal in the neodymium magnet.

[0048] After welding, the welded surface was polished by 0.05 mm to give a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 5.0 to 5.2 N (measured on five pieces).

[0049] Example 5 A Cr-plated shield disk was manufactured in the same manner as in Example 1, and a neodymium magnet was inserted into the recess of the cup yoke, with the shield disk inserted to cover it. Figure 4c is a schematic cross-sectional view showing the first laser welding performed at the butt joint between the shield disk and the cup yoke, with the optical axis at the center, and the second laser welding performed at the interface between the shield ring part and the disk yoke, with the optical axis at the center. As shown in Figure 4c, the optical axis of laser beam 5a was aligned with the butt joint 4a between the shield ring part and the cup yoke and the interface 4b between the shield ring part and the disk yoke, and two locations were fully welded with a 230 μm-wide bead to seal in the neodymium magnet.

[0050] After welding, the welded surface was polished by 0.05 mm to a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 4.8 to 4.9 N (measured on five pieces).

[0051] Example 6 An Au-plated shield disk was produced in the same way as in Example 2, and a neodymium magnet was inserted into the recess of the cup yoke, with the shield disk then inserted to cover it. As shown in Figure 4c, the optical axis of laser light 5a was aligned with the butt joint 4a between the shield ring part and the cup yoke and the interface 4b between the shield ring part and the disk yoke, and the two places were welded all around with a 230 μm-wide bead to seal in the neodymium magnet.

[0052] After welding, the welded surface was polished by 0.05 mm to a smooth finish, and a magnetic structure with a diameter of 3.5 mm and a height of 1.3 mm was produced. The attractive force of this magnetic structure was 4.8 to 5.0 N (measured on five pieces).

[0053] Comparative Example A tube of austenitic stainless steel having a composition of 18% by mass Cr, 12% by mass Ni, 2.5% by mass Mo, and the balance Fe was placed over a round bar of ferritic stainless steel (equivalent to SUSXM27) having a composition of 26% by mass Cr, 1% by mass Mo, and the balance Fe (including 0.08% by mass Ni as an impurity) with a diameter of 2.4 mm, and the bar was subjected to drawing, followed by cutting perpendicular to the axial direction to a thickness of 0.25 mm to produce a shield disk. This was used to replace the shield disk used in Example 1, and a magnetic structure having a diameter of 3.5 mm and a thickness of 1.3 mm was produced in the same manner as in Example 1. The magnetic attraction force of this magnetic structure was 4.9 to 5.0 N (measured on five pieces).

[0054] The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention also includes design changes that do not deviate from the gist of the invention, including various modifications and alterations that would occur to a person with ordinary knowledge in the field of the present invention. [Explanation of symbols]

[0055] 1: Cup yoke, 2: Permanent magnet, 3: Shield disk, 4: Welded part, 4a: Butt joint, 5a: Laser light, 31: Disk yoke, 32: Shield ring part

Claims

1. A dental magnetic attachment magnet structure comprising: a cup yoke made of ferritic stainless steel containing substantially no Ni; a permanent magnet housed in a recess of the cup yoke; a shield disk consisting of a disk yoke made of ferritic stainless steel containing substantially no Ni that seals the opening of the cup yoke and a shield ring portion consisting of a Cr layer or Au layer arranged on its outer periphery; and a welded portion where the cup yoke, the shield ring portion, and the disk yoke are butted together by welding.

2. 2. The dental magnetic attachment magnetic structure according to claim 1, wherein the boundary between said shield ring portion and said disk yoke is joined by mutual diffusion.

3. 2. The dental magnetic attachment magnetic structure according to claim 1, wherein said shield ring portion is formed by Cr plating or Au plating.

4. 4. The dental magnetic attachment magnetic structure according to claim 3, wherein the thickness of said shield ring portion is 50 to 300 μm.

5. 2. The dental magnetic attachment magnetic structure according to claim 1, wherein the Ni content of said cup yoke and said disk yoke is 0.2 mass % or less.

6. 2. The dental magnetic attachment magnetic structure according to claim 1, wherein the Cr content of the cup yoke and the shield disk is 17 to 32 mass %.

7. 2. The dental magnetic attachment magnetic structure according to claim 1, wherein the Mo content of the cup yoke and the shield disk is 0.75 to 2.50 mass %.

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