JPH04287302A - Permanent magnet and its manufacture - Google Patents

Abstract

PURPOSE:To suppress the concentration of surface magnetic flux densities to the end sections of a permanent magnet by forming a ferromagnetic coating film on the principal surface of the magnet body in such a way that the film at the end sections is made thicker than at the central part. CONSTITUTION:In order to rectify the uneven surface magnetic flux density of a magnet blank, the film thickness of a ferromagnetic coating film 2 formed on a permanent magnet body 1 at the end sections 3 on the principal surface of the body is, preferably, made 1.5 to 10 times as thick as that at the central part 4. When the film thickness of the film 2 at the end sections 3 is 1.5-10 times thicker than that at the central part 4, the rise of the permanent magnet at the end sections 3 can be suppressed to a height (y), since the surface magnetic flux density of the permanent magnet body 1 becomes smaller as the film thickness of the film 2 becomes thinner. When the film thickness of the film 2 is controlled in such way, the (x-y)/x becomes about 5-30% and the concentration of magnetic fluxes to the end sections can be suppressed by 5-30%. As a result, the area of the principal surface having a uniform magnetic flux density is also increased.

Description

Description: TECHNICAL FIELD The present invention relates to a permanent magnet in which surface magnetic flux density is suppressed from concentrating on the edges, and a method for manufacturing the same. [0002] Among permanent magnets with high performance, for example, R-Fe-B (R is one or more rare earth elements including Y)
In sintered magnets, in order to improve corrosion resistance and prevent rust, the surface of the permanent magnet body is subjected to pretreatment such as acid treatment, if necessary, and then coated with Ni, etc., by electroplating, etc. It has a membrane. [0003] However, since the surface magnetic flux of a permanent magnet body is more concentrated at the ends than at the center, if a Ni film with a uniform thickness is provided at the ends and the center, The surface magnetic flux is large at the ends of the main surface of the magnet and becomes small at the center, which causes a major performance defect when used in, for example, a voice coil motor. The main object of the present invention is to provide a permanent magnet in which surface treatment is applied to the permanent magnet to form a corrosion-resistant coating, and the material and thickness of the coating are controlled to suppress the concentration of surface magnetic flux density at the edges. and its manufacturing method. [Means for solving the problem] Such purpose is as follows (
1) to (9) are achieved by the present invention. (1) In a permanent magnet having a ferromagnetic film formed by electroplating on the surface of the permanent magnet body,
A permanent magnet characterized in that the ferromagnetic film is formed on the main surface of the permanent magnet body so that the ferromagnetic film is thicker at the ends than at the center. (2) The permanent magnet according to (1) above, wherein the film thickness at the end portion is 1.5 to 10 times the film thickness at the central portion. (3) The ferromagnetic film is made of Ni or N.
The permanent magnet according to (1) or (2) above, which is a plating film of i alloy. (4) The length of the main surface of the permanent magnet is 5 m.
The permanent magnet according to any one of (1) to (3) above, which has a diameter of m or more. (5) When forming a ferromagnetic film on a permanent magnet body by electroplating, the film formation rate at the ends of the main surface of the permanent magnet body is set higher than the film formation rate at the central part. A method for manufacturing a permanent magnet, comprising forming the ferromagnetic film on the surface so that the film thickness is greater at the edges than at the center. (6) The film is formed at a film forming rate at the end portions that is 1.5 to 10 times the film forming speed at the central portion, and the film thickness at the end portions is set to be 1.5 to 10 times the film forming rate at the central portion. The method for manufacturing a permanent magnet according to (5) above, wherein the permanent magnet is 1.5 to 10 times the thickness. (7) The current density of the electroplating is 0.2.
A/dm2 or more, the method for producing a permanent magnet according to (5) or (6) above. (8) The method for manufacturing a permanent magnet according to any one of (5) to (7) above, wherein the main surface has a length of 5 mm or more. (9) The ferromagnetic film is made of Ni or Ni
The method for producing a permanent magnet according to any one of (5) to (8) above, which is an alloy plating film. [0015] In the present invention, a ferromagnetic material is used as the material for the corrosion-resistant coating formed on the permanent magnet body, and it is utilized that the surface magnetic flux density decreases as the film thickness increases. In other words, the uniformity of electrodeposition during film formation is controlled, and the thickness of the ferromagnetic film is made thicker at the edges of the main surface and thinner at the center, thereby increasing the concentration of surface magnetic flux density at the edges of the permanent magnet. suppress. In order to regulate the uniformity of electrodeposition, the current density during electroplating is controlled so that the film formation rate at the edges is higher than that at the center. [Specific Configuration] The specific configuration of the present invention will be explained in detail below. In the present invention, electroplating is used as a method for depositing a ferromagnetic film on a permanent magnet. Other liquid phase plating, various vapor phase plating such as sputtering, ion plating, vacuum evaporation, dip coating, brush coating,
In various coating methods such as injection, hot-dip plating, and electrodeposition coating,
It is difficult to control the film thickness as in the present invention. Furthermore, unless the coating material is ferromagnetic, the surface magnetic flux cannot be made uniform. A ferromagnetic film formed by electroplating is useful because it has excellent mass productivity and not only improves corrosion resistance but also has a reinforcing effect on mechanical strength. FIGS. 3 and 2 show that the ends 3 and 2 of the main surface of the magnet body of the ferromagnetic film 2 formed on the magnet body 1 are formed when electroplating is performed at a locally uniform current density It shows the relationship between the film thickness distribution and the surface magnetic flux density in the central portion 4. As shown in FIG. 3, when the ferromagnetic film 2 is formed to have a uniform thickness on each part of the surface of the permanent magnet 1, when the surface magnetic flux density is measured with a magnetometer, the curve b in FIG. As shown in the figure, since there is a distribution in the magnetic flux density of the permanent magnet element, the surface magnetic flux density becomes large at the ends 3 of the main surface and becomes small at the central part 4. That is, at the ends, there is a swell of magnetic flux density having a height of x from the center. In the present invention, as shown in FIG. 1, in order to correct the non-uniform surface magnetic flux density of the magnet body, the main surface of the ferromagnetic coating 2 formed on the permanent magnet body 1 is The thickness of the end portion 3 is preferably 1.5 to 10 times the thickness of the center portion 4.
Double it. Since the surface magnetic flux density of the permanent magnet body 1 decreases as the thickness of the ferromagnetic coating 2 increases, the thickness ratio of the end portions 3 and the center portion 4 is set to the above value (1.5 to 10). As a result, the swelling due to the concentration of magnetic flux density at the end of the permanent magnet can be suppressed to the height y, as shown by the curve a in FIG. 2. In this case, (x-y)/x is 5 to 3
It becomes about 0%, and the concentration of magnetic flux density is suppressed by 5 to 30%. As a result, the area of the main surface having uniform magnetic flux density also increases. Ferromagnetic film 2 having such a film thickness distribution
can be obtained by changing the film formation speed between the end portion 3 and the center portion 4 during electroplating. Such a film thickness ratio of the ferromagnetic film 2 is such that the film formation rate of the central portion 4 is approximately 0.065 μm/min or more in the barrel plating method, particularly 0.08 μm/min or more in the rack plating method. 0.35μm/min or more, especially 0.4μm/min
This can be obtained by setting the film formation rate at the end portions 3 to be 1.5 to 10 times the film formation speed at the central portion 4. By setting the ratio of the film forming speed to such a value, the edges 3 and the center 4
The film thickness ratio can be set to the above value. [0023] In this way, the film formation rate is adjusted to
To change this, the electric field distribution at the end portions 3 and the center portion 4 may be controlled by the current density during electroplating. The current density is preferably 0.2 A/dm2 or more, particularly 0.5 A/dm2 or more. By setting the current density to such a value, an electric field distribution occurs between the end portion 3 and the center portion 4, and the end portion 3
The thickness of the ferromagnetic film 2 becomes thicker. However, if the current density is too large, hydrogen generation near the cathode will increase, hydrogen will be occluded, and the adhesion will decrease, so the current density is preferably 15 A/dm2 or less, especially 10 A/dm2. . [0024] The length of the main surface of the permanent magnet is 5 mm.
As mentioned above, it is usually preferable to set it as 10-100 mm. This is because by increasing the main surface length, electrolytic changes and film thickness changes at the ends can be increased. In such a case, a barrel plating method may be used, in which a plurality of permanent magnets are housed in a barrel, and the barrel is rotated and energized while the barrel and the magnets are in contact with each other. However, when using a rack plating method in which a magnet is held in a rack and energized, it is necessary to install a shielding plate, etc., to accurately control the current density and electrolytic distribution, and to form the film thickness distribution accurately. Can be done. As the material of the ferromagnetic film formed in this manner, metals, alloys, metal compounds, etc. can be used, but it is particularly preferable to use Ni and Ni alloys. By using Ni and Ni alloys as the ferromagnetic coating, the strength of the coating can be increased and an excellent antirust effect can be obtained. Examples of plating baths used for such Ni electroplating include Watt baths, sulfamic acid baths, borofluoride baths, and nickel bromide baths that do not contain a nickel chloride component. However, in this case, the dissolution of the anode is reduced, so it becomes necessary to replenish the bath with nickel ions. The nickel ions are preferably replenished as a nickel sulfate or nickel bromide solution. For example, among these, it is particularly preferable to use a sulfamic acid bath since the Ni coating exhibits higher peel strength, and examples include those having the following composition. Ni(NH2SO3)2 ・4H2O
150-600g/liter NiBr2
・6H2 O
0-30g/liter boric acid

30 to 60 g/liter [0029] At this time, the water in the bath preferably does not contain chlorine, and the amount of chlorine in the bath is preferably 100 ppm or less. In this way, by removing the chlorine component from the plating bath, it is possible to mainly prevent blisters from occurring over time. [0030] The plating conditions may be such that the pH is 3 to 6, particularly preferably 4 to 5, and the temperature is about 20 to 70°C. If the pH is below this range, the magnet will dissolve, and if the pH exceeds this range, nickel hydroxide will precipitate and the plated film will become brittle. [0032] When a Ni alloy is used as the material of the ferromagnetic film, it may be an alloy containing one or more of Fe, Co, Zn, Mo, Cr, etc. and 60 wt% or more of Ni. . [0033] In the present invention, if necessary, the corrosion resistance of known double nickel plating and tri-nickel plating with different natural potentials as described in the plating technology guidebook (published by Tokyo Plating Materials Cooperative Association), page 115, can be improved. Multilayer plating for the purpose can also be preferably used. Alternatively, a copper plating layer may be used, and another ferromagnetic film, such as a Ni plating layer, may be superimposed thereon. When depositing the ferromagnetic film by electroplating, a rack plating method or a barrel plating method is appropriately applied depending on the size and shape of the magnet body. In general, large-sized magnets processed by rack plating require a large area of defect-free ferromagnetic material, so it is necessary to increase the thickness of the ferromagnetic coating. The desirable thickness of the ferromagnetic film is 20 to 30 μm at the center. On the other hand, the desirable thickness of a ferromagnetic coating formed only by electroplating on a magnet having a small surface area and weighing several tens of grams or less, which is processed in large quantities by barrel plating, is 10 to 20 μm at the center. [0037] If necessary, a ferromagnetic film formed by other methods such as an electroless plating layer or a resin layer formed by various coating methods may be formed on top of the ferromagnetic film formed by electroplating. In this case, it is possible to make the ferromagnetic film thinner by electroplating. When forming such a ferromagnetic film, various known pretreatments can be performed in advance. [0038] In the present invention, a typical example of a permanent magnet body on which a ferromagnetic film is formed is one containing R (wherein R is one or more rare earth elements including Y), Fe, and B. be. [0039] The content of R, Fe, and B is 5.5a
It is preferable that t%≦R≦30at% 42at%≦Fe≦90at% 2at%≦B≦28at%. In particular, when the permanent magnet body is manufactured by a sintering method, it is preferable that the permanent magnet body has the following composition. Rare earth element R
is at least one of Nd, Pr, Ho, and Tb.
species, or in addition, La, Sm, Ce, Gd, Er,
Those containing one or more of Eu, Pm, Tm, Yb, and Y are preferred. In addition, when using two or more types of elements as R, a mixture such as misch metal can also be used as a raw material. [0041] The content of R is preferably 8 to 30 at%. If it is less than 8 at%, the crystal structure becomes a cubic structure that is the same as that of α-iron, resulting in a high coercive force (iHc).
is not obtained and exceeds 30 at %, the R-rich nonmagnetic phase increases and the residual magnetic flux density (Br) decreases. [0042] The content of Fe is preferably 42 to 90 at%. When Fe is less than 42 at%, Br decreases, and when it exceeds 90 at%, iHc decreases. The content of B is preferably 2 to 28 at%. If B is less than 2 at%, a rhombohedral structure is formed, resulting in insufficient iHc, and if it exceeds 28 at%, B-rich nonmagnetic phase increases, resulting in a decrease in BR. Note that by replacing a portion of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics. In this case, if the Co substitution amount exceeds 50% of Fe, the magnetic properties will deteriorate, so the Co substitution amount is preferably 50% or less. In addition to R, Fe, and B, Ni, Si, Al, Cu, and Ca may be contained as unavoidable impurities in an amount of 3 at % or less of the total. Furthermore, by replacing a portion of B with one or more of C, P, S, and Cu, productivity can be improved and costs can be reduced. In this case, the amount of substitution is preferably 4 at% or less of the total amount. In addition, in order to improve coercive force, improve productivity, and reduce costs, Al, Ti
, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb
, Ge, Sn, Zr, Ni, Si, Hf, etc., may be added. In this case, the total amount added is 10 at%
The following is preferable. [0046] Such a permanent magnet body has a main phase having a substantially tetragonal crystal structure. The particle size of this main phase is preferably about 1 to 100 μm. [0048] It usually contains a non-magnetic phase of 1 to 50% by volume. [0049] Such a permanent magnet body is disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 185910/1983. [0050] The above permanent magnet body is preferably manufactured by a sintering method as described below. First, an alloy having a desired composition is cast to obtain an ingot. The obtained ingot was coarsely ground to a particle size of about 10 to 100 μm using a stamp mill or the like, and then
Pulverize to a particle size of approximately 0.5 to 5 μm using a ball mill or the like. The obtained powder is preferably compacted in a magnetic field. In this case, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 t/cm2. [0052] The obtained molded body was heated to 1000 to 1200°C.
Sinter for 0.5 to 5 hours and quench. Note that the sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. After this, preferably in an inert gas atmosphere,
Aging treatment is performed at ~900°C for 1 to 5 hours. [0053] In addition, any of various rare earth magnets can be applied to the present invention. [Examples] The present invention will be explained in more detail below with reference to specific examples. Example 1 14Nd-1Dy-7B- produced by powder metallurgy method
A sintered body with a composition of 78Fe (numbers are atomic ratios) was aged at 600°C for 2 hours in an Ar atmosphere to form a 56×4
The magnet was processed into a size of 0x8 (mm) and chamfered by barrel polishing to obtain a permanent magnet. Next, the samples of 10 permanent magnets were immersed in 10 liters of a treatment solution with a nitric acid concentration of 0.45N at 30° C. for 1 minute to dissolve the surface layer. After the above-treated sample was ultrasonically cleaned in ion-exchanged water, plating was performed by the rack method using a plating bath having the following composition. Plating current density is 0.1A/
dm2, the bath temperature was 50°C, and the bath pH was 4.5. Ni(NH2SO3)2 ・4H2O
600g/liter NiBr2 ・6
H2O1
0g/liter boric acid
40g/liter
The thickness of the plated film of this product was 35 μm at the ends of the main surface and 25 μm at the center, showing a substantially uniform thickness. The film thickness was measured using a Seiko electronic fluorescence X-ray film thickness meter. Further, when the surface magnetic flux density of this material was measured using a magnetometer, it was found to be 2700G at the ends and 1500G at the center, and x = 1200G. Separately, electroplating was carried out at a current density of 4 A/dm 2 using the same plating bath as above. The deposition rate of the plating film was 0.9 μm/min at the edge.
It is 0.45μm/min at the center, and the ratio is 2
:1. The thickness of the plating film of this product is 50 μm at the ends of the main surface and 25 μm at the center, and the ratio is 2:
It was 1. The surface magnetic flux density of the obtained sample was measured using a magnetometer, and it was 2500G at the edges and 1500G at the center.
So, y=1000G, (x-y)/x=17
%, the concentration of surface magnetic flux density at the end of the magnet body can be suppressed by 17%. From the above results, the film thickness ratio between the edges and the center is 1.
．． It can be seen that the permanent magnet of the present invention having a magnetic flux density of 5 to 10 can improve the concentration of surface magnetic flux density at the end. [0060] The permanent magnet of the present invention has a ferromagnetic coating whose thickness at the end of the main surface is 1.5 to 10 times that at the center, and the surface magnetic flux density at the end of the magnet body is concentration can be reduced by 5 to 30%.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a permanent magnet of the present invention.

FIG. 2 is a graph showing the surface magnetic flux density distribution of the permanent magnet in FIG. 1;

FIG. 3 is a sectional view showing a conventional permanent magnet.

[Explanation of symbols]

1 Permanent magnet 2 Ferromagnetic coating 3 Main surface end 4 Central part of main surface

Claims (9)

[Claims] 1. A permanent magnet having a ferromagnetic coating formed by electroplating on the surface of the permanent magnet, wherein the ferromagnetic coating is disposed on the main surface of the permanent magnet body more toward the ends than the center. A permanent magnet characterized by having a thick layer. 2. The film thickness at the end portion is 1 of the film thickness at the center portion.
．． The permanent magnet according to claim 1, which is 5 to 10 times larger. 3. The ferromagnetic film is made of Ni or Ni
The permanent magnet according to claim 1 or 2, which is a plating film of an alloy. [Claim 4] The length of the main surface of the permanent magnet body is 5 mm.
The permanent magnet according to any one of claims 1 to 3, which is the above. 5. When forming a ferromagnetic film on a permanent magnet body by electroplating, the film formation rate at the ends of the main surface of the permanent magnet body is set higher than the film formation rate at the center part, and A method of manufacturing a permanent magnet, characterized in that the ferromagnetic film is formed so that the thickness of the ferromagnetic film is greater at the ends than at the center. 6. A film is formed so that the film forming rate at the end portion is 1.5 to 10 times the film forming speed at the central portion, and the film thickness at the end portion is set to be the same as the film thickness at the central portion. 6. The method for manufacturing a permanent magnet according to claim 5, wherein the permanent magnet is 1.5 to 10 times as large as 1.5 to 10 times. 7. The current density of the electroplating is 0.2A.
The method for manufacturing a permanent magnet according to claim 5 or 6, wherein the permanent magnet is at least /dm2. 8. The method for manufacturing a permanent magnet according to claim 5, wherein the main surface has a length of 5 mm or more. 9. The method for manufacturing a permanent magnet according to claim 5, wherein the ferromagnetic film is a Ni or Ni alloy plating film.