Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F7/00—Magnets
  • H01F7/02—Permanent magnets [PM]
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/562—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of iron or nickel or cobalt
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated

Definitions

• This invention relates to R-Fe-B-base bonded magnets made in various shapes such as rings or discs, the corrosion resistance whereof is improved with a very clean metal film, and to high corrosion-resistant R-Fe-B-base bonded magnets exhibiting sharply improved corrosion resistance and adhesion properties, and a method of manufacturing the same, wherein, after filling pores therein with polishing powder, bonded magnet polishing chips, and inorganic powder by dry-process barrel polishing to seal the pores and smooth the surface, or, alternatively, without performing that sealing process, dry-process barrel polishing with a metal medium of pieces of Cu, Sn, Zn, Pb, Cd, In, Au, Ag, Fe, Ni, Co, Cr, Al and alloys thereof is used to press-fit fine ground pieces of those metals into the pores and resin surface on the surface of the bonded magnets, effecting a coating, or adequate electrical conductivity is imparted to the magnet surface by coating the magnet powder surfaces with fine metal pieces, making it possible to implement electrolytic plating directly, without
• bonded magnets which are made in various shapes such as rings and discs
• advances are being made toward higher performance, moving from conventional isotropic bonded magnets to anisotropic bonded magnets, and from ferrite-based bonded magnets to rare earth-base bonded magnets which exhibit higher magnetic strength, and also from Sm-Co magnetic materials to R-Fe-B bonded magnets which use R-Fe-B magnetic materials exhibiting, in sintered magnets, high magnetic properties, with a maximum energy product of 50 MGOe or higher.
• each magnet must be attached to an electrode.
• the electrodes leave marks that must be removed after the coating is made, thus requiring a touch-up operation.
• this method is problematic in that it requires a great number of process steps and is particularly unsuitable for small magnets.
• Plating solutions of specific compositions have been proposed as a method for implementing nickel plating with good film-forming efficiency on R-Fe-B bonded magnets (Japanese Patent Application Laid-Open No. H4-99192/1992), but here again there is still a danger that such solutions will penetrate into the bonded magnet, remain there, and cause rusting.
• the copper strike plating customarily performed prior to nickel plating is either strongly alkaline or strongly acidic, and hence is not suitable for processing R-Fe-B bonded magnets.
• NiP plating In order to impart wear resistance to electronic components, furthermore, and as an anticorrosion treatment for automobile steel panels and the like, practical NiP plating has been developed of a high-temperature acidic solution type, but this is unsuitable for application to R-Fe-B bonded magnets because it causes corrosion in the interior of the magnet.
• the inventors proposed a method wherein, using as a medium a mixture of a polishing agent and either a vegetable medium or a vegetable medium the surface whereof has been modified with an inorganic powder, barrel-polished is performed in a dry process, polishing agent powder and bonded magnet polishing chips are bonded with the fatty component of the vegetable medium to the pores in the bonded magnet, both sealing the pores and smoothing the surface thereof, and an electrically conductive layer is formed by non-electrolytic copper plating using an alkaline bath.
• One object of the present invention is to provide R-Fe-B bonded magnets that exhibit extremely high corrosion resistance, not rusting even in long-duration high-temperature high-humidity tests, and another object thereof is to provide a manufacturing method wherewith various corrosion-resistant coating films can be formed on the R-Fe-B bonded magnets uniformly and with extremely high bonding strength in order to realize high corrosion resistance.
• Another object of the present invention is to provide a manufacturing method, for highly corrosion-resistant R-Fe-B bonded magnets, comprising optimum industrial process steps for effecting corrosion-resistant coating films with high bonding strength and good dimensional precision on magnet surfaces that prevent plating solutions and cleaning fluids, etc., from penetrating into and remaining in porous R-Fe-B bonded magnets, as in conventional non-electrolytic plating methods.
• the inventors focusing on the importance of imparting extremely uniform electrically conductivity to base material surfaces in electroplating techniques for R-Fe-B-base bonded magnets exhibiting outstanding corrosion resistance and surface cleanness, conducted various investigations on methods for forming those electrically conductive films.
• the inventors furthermore made various investigations with a view to resolving the problems noted earlier in cases where smoothness is desired in bonded magnet surfaces, and, as a result learned that, by barrel-polishing a porous R-Fe-B bonded magnet in a dry process, using as a medium a mixture of a polishing agent formed by sintering an inorganic powder of Al 2 O 3 , SiC, or the like, and a vegetable medium such as fruit rind, corncobs, or the like, or, alternatively, a mixture of the polishing agent noted above and a vegetable medium the surface whereof has been modified with an inorganic powder noted above, it is possible to bond the polishing chips of the surface-oxidized layers of the magnetic powder configuring a bonded magnet, the modifying inorganic powder, and the polishing agent powder to the porous portions of that magnet, by the fatty component in the vegetable medium, thus sealing the pores therein, and simultaneously to smooth the surface thereof, and hence learned that an electrically conductive film can be formed directly to the
• the inventors further learned that other materials can be used for the metal medium in dry-process barrel polishing besides the copper pieces noted above, namely soft metal pieces of Sn, Zn, Pb, Cd, In, Au, and Ag having a Vickers hardness of 80 or below, and also Fe, Ni, Co, and Cr.
• the inventors further discovered that by performing dry-process barrel polishing in a barrel apparatus, using aluminum pieces of undefined shape as the medium, fine pulverized aluminum pieces are press-fit into the porous portions and resin surface on the surface of the bonded magnet, forming a coating, or by performing a zinc substitution treatment on the surface of the aluminum coating layer formed on the surface of the R-Fe-B-base bonded magnet, with fine aluminum pieces similarly being coated to the surface of the magnetic powder, aluminum effluence during electroplating is prevented, making good electroplating possible, whereupon R-Fe-B-base bonded magnet plate-coated products can be obtained which exhibit outstanding corrosion resistance and little deterioration in magnetic properties.
• the present invention was perfected.
• Characteristic of a high corrosion-resistant R-Fe-B-base bonded magnet according to the present invention is that it has a metal coating layer on the surface of the magnet formed with metal pieces of Cu, Sn, Zn, Pb, Cd, In, Au, Ag, Fe, Ni, Co, Cr, and Al, or of alloys thereof, press-fitted in and coated on the porous portions and resin surface configuring the surface of the R-Fe-B-base bonded magnet, or with tine metal pieces coated on the surfaces of the magnetic powder configuring the surface, and an electrolytic plating layer formed with that metal coating layer intervening.
• a high corrosion-resistant R-Fe-B-base bonded magnet has the metal coating layer on the surface of the magnet formed with the metal pieces noted above press-fitted in and coated on the porous portions and resin surface configuring the surface of the R-Fe-B-base bonded magnet, or with fine metal pieces coated on the surfaces of the magnetic powder configuring the surface, after the porous portions forming the surface of the R-Fe-B-base bonded magnet have been sealed by the bonding thereto, with the fatty component in a vegetable medium, of polishing agent powder, bonded magnet polishing chips, and an inorganic powder, and an electrolytic plating layer formed with that metal coating layer intervening.
• a high corrosion-resistant R-Fe-B-base bonded magnet according to the present invention is that it has an aluminum coating layer formed, either with fine aluminum pieces press-fitted in and coated on the porous portions and resin surface configuring the surface thereof, or with fine aluminum pieces coated on the surfaces of the magnetic powder configuring the surface, has a zinc layer provided by a zinc substitution treatment on the surface of the magnet, and also has an electrolytic plating layer formed with that metal coating layer intervening.
• the R-Fe-B-base bonded magnets in view are both isotropic bonded magnets and anisotropic bonded magnets. They may be obtained, in the case of compression molding, for example, by, after adding and kneading in a thermosetting resin, coupling agents, and lubricants, etc., to the magnetic powder of the wanted composition and properties, performing compression molding, heating, and resin curing, and in cases of injection molding, extrusion molding, or rolling molding, by, after adding and kneading in a thermoplastic resin, coupling agents, and lubricants, etc., to the magnetic powder, performing injection molding, extrusion molding, or rolling molding.
• either isotropic or anisotropic powder can be used which has been obtained by any of a number of manufacturing methods including a fusion-pulverizing method wherein the desired R-Fe-B alloy is melted, cast, and then pulverized, a direct reduction diffusion method for obtaining powder directly by Ca reduction, a quick-cooling alloy method wherein the desired R-Fe-B alloy is melted, ribbon foil is obtained with a jetcaster, and that is pulverized and annealed, a gas atomizing method wherein the desired R-Fe-B alloy is melted, made into powder by gas atomizing, and heat-treated, a mechanical alloying method wherein the desired raw-material metal is made into powder, then made into fine powder by mechanical alloying and heat-treating, or a method (HDDR method) wherein the desired R-Fe-B alloy is heated in hydrogen to break it down and recrystallize it.
• a fusion-pulverizing method wherein the desired R-Fe-B alloy is melted, cast,
• the rare earth element R used in the R-Fe-B magnet powder accounts for 10 at.% to 30 at.% of the composition, but it is preferable that at least one element from the group Nd, Pr, Dy, Ho, and Tb be contained, or additionally that at least one element from the group La, Ce, Sm, Gd, Er, Eu, Tm, Yb, Lu, and Y be contained.
• one type of R will be sufficient, but in actual practice, because of the ease of obtaining mixtures of two types or more thereof (such as misch metal or didymium), etc., such can be used.
• R is a mandatory element in the types of magnet powders noted earlier. At less that 10 at.%, the crystalline structure becomes a cubic crystalline structure identical to that of ⁇ -iron, wherefore high magnetic properties, such as high coercive force in particular, are not obtained. When 30 at.% is exceeded, on the other hand, there will be many R-rich non-magnetic phases, the residual flux density (Br) will decline, and permanent magnets with outstanding properties will not be obtained. Thus the R content should be within the range of 10 at.% to 30 at.%.
• B is a mandatory element in the magnet powders noted earlier. At less than 2 at.%, a rhombohedral structure becomes the dominant phase, and high coercive force (iHc) is not obtained. When 28 at.% is exceeded, on the other hand, there will be many B-rich non-magnetic phases, and the residual flux density (Br) will decline, wherefore outstanding permanent magnets will not be obtained. Thus the B content should be within the range of 2 at.% to 28 at.%.
• Fe is a mandatory element in the magnet powders noted earlier. At less than 65 at.%, the residual flux density (Br) declines, whereas when 80 at.% is exceeded, high coercive force is not obtained. Hence the Fe content should be from 65 at.% to 80 at,%.
• the temperature characteristics can be improved without impairing the magnetic properties of the magnet.
• the amount of Co replacement exceeds 20% of the Fe, the magnetic properties conversely deteriorate, so that is undesirable.
• the Co replacement quantity is from 5 at.% to 15 at.% in the total quantity of Fe and Co, Br will increase as compared to when no replacement is made, wherefore that is desirable in order to obtain high magnetic flux.
• the presence of impurities that are unavoidable in industrial manufacture is permissible.
• the permanent magnet fabricability can be improved and lower costs realized by partially replacing B with at least one element from among the group C (4.0 wt.% or less), P (2.0 wt.% or less),S (2.0 wt.% or less), and Cu (2.0 wt.% or less), in a total quantity that is 2.0 wt.% or less.
• At least one element from the group Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Ga, Sn, Zr, Ni, Si, Zn, and Hf can also be added to the magnet powder to realize the benefit or improving the coercive force, improving the squareness of the magnetism reduction curve, improving fabricability, or reducing costs.
• the upper limit of the added quantity should be within such range as will satisfy the various conditions required to realize the desired values for the (BH)max and (Br) of the bond magnet.
• the binder used with injection molding may be a resin such as 6PA, 12PA, PPS, PBT, or EVA, that used with extrusion molding, calendar rolling, or rolling molding may be PVC, NBR, CPE, NR, or Hyperon, etc., and that used with compression molding may be an epoxy resin, DAP, or a phenol resin, etc.
• a known metal binder can be used.
• Other auxiliary agents may also be used, such as a lubricant to facilitate molding, a bonding agent for the resin and inorganic filler, or a silane-based or titanium-based coupling agent.
• the medium used when barrel-polishing in the sealing and smoothing treatment is either a mixture of a polishing agent such as ceramic material wherein inorganic powder of Al 2 O 3 , SiC, etc., is sintered, or metal balls, and a vegetable medium such as vegetable husks, sawdust, fruit rind, or corncobs, or a mixture of a polishing agent noted above and a vegetable medium noted above the surface whereof has been modified with an inorganic powder of Al 2 O 3 , SiC, etc., noted above.
• a polishing agent such as ceramic material wherein inorganic powder of Al 2 O 3 , SiC, etc.
• a known barrel can be used, and a common revolving barrel with a turning speed of 20 to 50 rpm, a centrifugal barrel with a turning speed of 70 to 200 rpm, or a vibrating barrel method wherein the vibration amplitude is 0.5 mm or greater but less than 50 mm can be used.
• the atmosphere in this barrel polishing may be atmospheric air.
• an inert gas atmosphere such as N 2 , Ar, or He gas, used singly or in a mixture, may be used.
• the barrel used is a revolving or vibrating barrel
• the treatment quantity will be too small to be practical, whereas when 90% is exceeded, stirring will be insufficient and adequate polishing cannot be effected.
• 20% to 90% of internal capacity is desirable.
• polishing agent used in the sealing and smoothing treatment in this invention there is no particular limitation on the polishing agent used in the sealing and smoothing treatment in this invention. Nevertheless, a mixture should be used containing a polishing agent with a particle size of 1 to 7 mm and preferably 3 to 5 mm or so, and a vegetable medium with a length of 0.5 to 3 mm and preferably 1 to 2 mm or so, or, alternatively, a mixture of the polishing agent noted above and a vegetable medium noted above wherein the surface has been modified with an inorganic powder.
• the magnet and medium mixture should be evenly stirred, performed under conditions wherein relative shifting motion is effected.
• the surface has been modified with an inorganic powder noted earlier
• a vegetable medium wherein a fatty component such as a wax has been coated by kneading onto the surface thereof, wherein the surface has then been evenly covered with an inorganic powder of Al 2 O 3 , SiC, ZrO, or MgO having a particle size of 0.01 to 3 ⁇ m, bonding that powder thereto.
• the powder of the polishing agent noted above that is a sealant the inorganic powder for modifying the surface of the vegetable medium, and the polishing chips from the bond magnet have a particle size of 0.01 to 3 ⁇ m.
• the ratio between the vegetable medium and polishing agent in the medium must be from 1/5 to 2, with a mixture having a ratio of 1 being preferred.
• the mixture ratio between the bond magnet and medium (bond magnet/medium) may be made 3 or lower.
• the polishing agent noted above functions to effectively grind away the surface oxidation layer of the magnet to smooth the surface thereof, and to beat and harden the sealing materials constituted by the polishing agent powder, the inorganic powder for modifying the vegetable medium surface, and the bond magnet polishing chips.
• the vegetable medium noted above functions to enhance the bonding strength of the sealing materials by effectively releasing the fatty component thereof.
• the present invention it is possible to lower the porosity of the bond magnet after the surface smoothing treatment to 3% or lower. It is possible not only to perform the smoothing-sealing treatment on the bond magnet surface, but also to remove the surface oxidation layer from the magnet and thus obtain active R-Fe-B magnetic powder surfaces.
• any known barrel apparatus whether revolving, vibrating, or centrifugal, etc.
• Metal pieces of undefined shape can be used, whether spherical, massive, or aricular (wire-form), etc.
• As to the sizes of the metal pieces below a size of 0.1 mm, too much time is required for adequate press-fitting and coating, so that is impractical, whereas at sizes exceeding 10 mm, the surface irregularities become great, making it impossible to cover the entire surface with the metal being used.
• metal pieces of sizes ranging from 0.1 to 10 mm are desirable, with 0.3 to 5 mm being preferable, and with a range of 0.5 to 3 mm being most preferable.
• the metal pieces loaded into the dry-process barrel need not all be of the same shape or dimensions, but may be a mixture of different shapes and dimensions. It is also permissible to mix fine metal powder in with the metal pieces of undefined shape. These may, furthermore, be only the metal used, or an alloy, or a copper composite metal wherein copper is coated on cores of a different metal such as iron, nickel, or aluminum, etc.
• the ratio of loading in the dry-process barrel polishing namely the volumetric ratio between the magnet and the metal pieces (magnet/metal) be 3 or less.
• 3 is exceeded, too much time is required for metal press-fitting and coating, making that impractical, and granules of magnetic powder also comes loose from the surface of the bonded magnet.
• the quantity of bonded magnet and metal pieces loaded into the barrel polishing machine be from 20% to 90% of the internal capacity of the polishing machine. Below 20%, the process quantity is too small, making that impractical, while when 90% is exceeded, stirring is inadequate, whereupon thorough polishing cannot be accomplished.
• the press-fitted and coated fine metal pieces are powder or needle-shaped pieces.
• the size thereof exceeds a length of 5 ⁇ m, the bonding with the magnet surface is poor, leading to bonding flaws and peeling, etc., during electrolytic plating, wherefore this length should be 5 ⁇ m or less.
• a preferable range is 2 ⁇ m or less.
• the fine metal pieces are press-fitted into and coated on the soft resin surface and porous portions in the surface of the bonded magnet and coated onto the magnet powder surfaces in the surface of the bonded magnet.
• the quantity press-fitted in the resin surface and porous portions is greater closer to the surface, while the quantity contained in the interior of the resin layer gradually diminishes.
• the thickness of the press-fitted layer of metal on the resin surface and porous portions should be 0.1 ⁇ m or greater but no more than 2 ⁇ m. Below 0.1 ⁇ m, adequate electrically conductivity is not obtained, whereas when 2 ⁇ m is exceeded, even though there are no problems in terms of performance, more work time is required, making that impractical.
• the thickness of the metal coating layer on the surfaces of the magnetic powder on the bonded magnet surface should be 0.2 ⁇ m or less.
• the reaction between the magnetic powder surfaces and the fine metal pieces is a type of mechanochemical reaction, and bonding properties deteriorate when 0.2 ⁇ m is exceeded.
• the speed of revolution during dry-process barrel polishing in this invention should be 20 to 50 rpm for a revolving barrel, and 70 to 200 rpm for a centrifugal barrel, while the vibrating frequency should be 50 to 100 Hz in vibrating barrel polishing with a vibration amplitude of 0.3 to 10 mm.
• the atmosphere in the barrel polishing method may be atmospheric air.
• the atmosphere used in the barrel polishing method be an inert or inactive gas, or mixture of such gasses, such as N 2 , Ar, or He.
• the aluminum coating surface is subjected to zinc substitution in order to prevent aluminum effluence during the electroplating which follows thereafter.
• the zinc substitution method should be one that is performed with a solution containing zinc oxide, sodium hydroxide, ferric chloride, or Rossel salt, etc.
• the process conditions should be immersion in a bath temperature of 10 to 25°C and treatment time of 10 to 120 seconds.
• the processing order in the zinc substitution procedure should be washing ⁇ zinc substitution ⁇ washing. If there are contaminants or other adhering materials on the aluminum surface, washing should be performed by immersion degreasing in a solution of sodium carbonate and sodium triphosphate.
• the electroplating method should contain at least one type of metal selected from among Ni, Cu, Sn, Co, Zn, Cr, Ag, Au, Pb, and Pt, or have B, S, or P contained in an alloy thereof, with nickel plating being particularly desirable.
• the plating thickness should be 50 ⁇ m or less, and preferably from 10 to 30 ⁇ m. In this invention, plating is possible using a common watt bath in order that the press-fitting and coating of the fine metal pieces in the resin surface and porous portions described earlier function effectively, wherewith outstanding bonding characteristics and corrosion resistance are obtained.
• the order of process steps should be washing ⁇ nickel electroplating ⁇ washing ⁇ drying, and the pH of the nickel plating bath should be adjusted with basic nickel carbonate to a pH of 4.0 to 4.6, and the process temperature should be 50 to 60°C.
• nickel plating In nickel plating, a prescribed current should be drawn using the plating bath described above and electrolytic nickel plates for the anodes. Nickel electroplating is conducted to stabilize the deposition of the nickel of the nickel anode plates, and it is desirable to use Estland nickel chips containing sulfur in the electrodes.
• the process order in the plating method using a nickel plating bath should be washing ⁇ electroplating ⁇ washing ⁇ drying, with drying preferably performed at a temperature of 70°C or higher.
• plating bath tank can be used as the plating bath tank, depending on the shape of the bonded magnet, with a rack plating or barrel plating process being preferable for ring-shaped bonded magnets.
• the bonded magnets obtained were placed in a vibrating barrel and subjected to dry-process barrel polishing using short rod-shaped copper pieces having diameters of 1 mm and lengths of 1 mm to form an electrically conductive coating layer made of fine copper pieces.
• the thickness of the press-fitted and coated fine copper pieces on the resin surface was approximately 0.7 ⁇ m and the thickness of the coating on the magnetic powder surfaces was 0.1 ⁇ m.
• the conditions under which the barrel polishing treatment was conducted were an atmosphere of argon gas, loading 50 bond magnets (having an apparent volume of 0.15 liters and weight of 100 g) and the copper pieces (having an apparent volume of 2 liters and weight of 10 kg) of the dimensions noted above into a vibrating barrel having a capacity of 3.5 liters, vibration frequency of 70 Hz, and vibration amplitude of 3 mm, constituting a total load volume that was 60% of the interior barrel capacity.
• the treatment was performed for 3 hours.
• the film thickness after plating was 20 ⁇ m on the inner diameter side and 22 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 1.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 2.
• the nickel electroplating conditions were a current density of 2 A/dm 2 , plating time 60 minutes, pH 4.2, and bath temperature 55°C, with a plating solution composition of 240 g/l nickel sulfate, 45 g/l nickel chloride, titrated nickel carbonate (for pH adjustment), and 30 g/l boric acid.
• the non-electrolytic copper plating conditions were a plating time of 20 minutes, pH of 11.5, and bath temperature of 20°C, with a plating solution composition of 29 g/l copper sulfate, 25 g/l sodium carbonate, 140 g/l tartrate, 40 g/l sodium hydroxide, and 150 ml 37% formaldehyde.
• the conditions for the electrically conductive film-coating process were a process time of 30 minutes using a treatment solution composition of 5 wt.% phenol resin, 5 wt.% nickel powder (particle size 0.7 ⁇ m or smaller), and 90 wt.% of MEK (methylethyl ketone).
• a phenol resin layer was pre-formed as a bonding layer using an immersion procedure, after which silver powder (particle she 0.7 ⁇ m or smaller) was made to adhere to the surface, after which a 7 ⁇ m electrically conductive coating layer was formed with a vibrating barrel. After the vibrating barrel treatment, nickel plating was performed under the same conditions as in Embodiment 1.
• the ring bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and 90% relative humidity. The results are indicated in Tables 1 to 3.
• the conditions for the vibrating barrel treatment were the use of a vibrating barrel having a capacity of 3.5 liters into which 50 bonded magnets were loaded, and performing the treatment for 3 hours using steel balls having an apparent volume of 2 liters and diameter of 2.5 mm for the medium.
• the bonded magnets were placed in the vibrating barrel and dry-process barrel polishing was performed with a vibration frequency of 70 Mz and vibration amplitude of 3 mm, in an atmosphere of argon gas, using short rod-shaped copper pieces having diameters of 1 mm and lengths of 1 mm to form an electrically conductive coating layer with fine copper pieces.
• the fine copper pieces were press-fitted into the resin surface and porous portions to a depth of approximately 0.7 ⁇ m and the thickness of the coating on the magnetic powder surfaces was 0.1 ⁇ m.
• the conditions for the barrel polishing process were that 50 bonded magnets (having an apparent volume of 0.15 liters and weight of 100 g) and copper pieces having the dimensions noted earlier (having an apparent volume of 2 liters and weight of 10 kg) were loaded into a vibrating barrel having a capacity of 3.5 liters, and the treatment was performed for 3 hours with an amplitude of 20 mm and the total loaded volume being 60% of the barrel capacity.
• the film thickness after plating was 21 ⁇ m on the inner diameter side and 23 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 800 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 3.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 4.
• the nickel electroplating conditions were a current density of 2 A/dm 2 , plating time 60 minutes, pH 4.2, and bath temperature 55°C, with a plating solution composition of 240 g/l nickel sulfate, 45 g/l nickel chloride, titrated nickel carbonate (for pH adjustment), and 30 g/l boric acid.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 2 were washed, subjected to a sealing and surface smoothing treatment as in Embodiment 2, again washed, and subjected to non-electrolytic copper plating.
• the plating thickness was 5 ⁇ m.
• nickel plating was performed under the same conditions as in Embodiment 2.
• the ring-shaped bonded magnets obtained were subjected to an environmental test (humidity resistance test) under the same conditions as in Embodiment 2.
• the results and film thickness dimensional precision (humidity resistance test) were conducted. The results are noted in Tables 3 and 4.
• the non-electrolytic copper plating conditions were a plating time of 20 minutes, pH of 11.5, and bath temperature of 20°C, with a plating solution composition of 29 g/l copper sulfate, 25 g/l sodium carbonate, 140 g/l tartrate, 40 g/l sodium hydroxide, and 150 ml 37% formaldehyde.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 2 were washed, then coated with a mixture of a phenol resin and nickel powder under the conditions noted below to form a 10 ⁇ m electrically conductive resin film.
• the magnets and 5 mm copper balls were then loaded to 60% barrel capacity in a vibrating barrel, and smoothing and polishing were performed by barrel polishing for 60 minutes with an amplitude of 20 mm.
• Nickel plating was then performed under the same conditions as in Embodiment 2.
• the ring-shaped bonded magnets obtained were subjected to an environmental test (humidity resistance test) under the same conditions as in Embodiment 2.
• the results and film thickness dimensional precision (humidity resistance test) were performed. The results are given in Tables 3 and 4.
• the electrically conductive coating process conditions were a process time of 30 minutes using a treatment solution composition of 5 wt.% phenol resin, 5 wt.% nickel powder (particle size 0.7 ⁇ m or smaller), and 90 wt.% MEK (methylethyl ketone).
• Ring-shaped bonded magnets measuring 25 mm (outer diameter) ⁇ 23 mm (inner diameter) ⁇ 3 mm (height) were manufactured by the same method as in Embodiment 1.
• the bonded magnets obtained were placed in a vibrating barrel and subjected to dry-process barrel polishing, using short rod-shaped tin pieces having diameters of 2 mm and lengths of 1 mm, to form an electrically conductive coating layer of fine tin pieces.
• the press-fitting depth of the fine pieces in the resin surface was approximately 0.9 ⁇ m and the coating thickness on the magnetic powder surfaces was 0.4 ⁇ m.
• the barrel polishing treatment conditions were the same as m Embodiment 1.
• the film thickness after plating was 22 ⁇ m on the inner diameter side and 23 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 5.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 6.
• the copper electroplating conditions were a current density of 2.5 A/dm 2 , plating time 5 hours, pH 10, and bath temperature 40°C, with a plating solution composition of 20 g/l copper and 10 g/l free cyanogen.
• the nickel electroplating conditions were the same as in Embodiment 1.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 3 were placed in a vibrating barrel and a dry-process barrel treatment was conducted, using rod-shaped zinc pieces having diameters of 1 mm and lengths of 2 mm, to form an electrically conductive coating layer of fine zinc pieces.
• the press-fitting depth of the fine zinc pieces in the resin surface was approximately 0.8 ⁇ m and the coating thickness on the magnet powder surfaces was 0.2 ⁇ m.
• the barrel polishing treatment conditions were the same as in Embodiment 1.
• Embodiment 3 copper and nickel plating were conducted under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 5.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 6.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 3 were placed in a vibrating barrel and a dry-process barrel treatment was conducted, using rod-shaped lead pieces having diameters of 1 mm and lengths of 1 mm, to form an electrically conductive coating layer of fine lead pieces.
• the press-fitting depth of the fine lead pieces in the resin surface was approximately 0.9 ⁇ m and the coating thickness on the magnet powder surfaces was 0.6 ⁇ m.
• the barrel polishing treatment conditions were the same as in Embodiment 1.
• Embodiment 3 copper and nickel plating were conducted under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 5.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 6.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 3 were washed and subjected to non-electrolytic copper plating.
• the plating thickness was 5 ⁇ m.
• copper and nickel plating were conducted under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 5.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 6.
• the non-electrolytic copper plating conditions were the same as in Comparison 1.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 3 were washed, and then a 10 ⁇ m electrically conductive coating film was formed with a mixture of a phenol resin and nickel powder. After this treatment copper and nickel plating were performed under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 5.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 6.
• the non-electrolytic copper plating conditions were the same as in Comparison 2.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 3 were washed, a phenol resin layer was preformed as a bonding layer by an immersion method, silver powder (particle size 0.7 ⁇ m or smaller) was made to adhere to the surface thereof, and a 7 ⁇ m electrically conductive coating layer was formed in a vibrating barrel. After the vibrating barrel treatment, copper and nickel plating were conducted under the same conditions as in Embodiment 3. The ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%. The properties of the magnets after the humidity resistance test are noted in Table 5.
• an environment test humidity resistance test
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 6.
• the non-electrolytic copper plating conditions were the same as in Comparison 3.
• Surface condition at humidity resistance test time Film thickness dimensional precision ( ⁇ m) Manufacturing method Embodiment 3 No change (no rusting) 22 ⁇ 1 Sn film layer + Cu, Ni plating Embodiment 4 No change (no rusting) 22 ⁇ 1 Zn coating layer + Cu, Ni plating Embodiment 5 No change (no rusting) 22 ⁇ 1 Pb coating layer + Cu, Ni plating Comparison 6 Spot rusting after 130 hours 26 ⁇ 2 Non-electrolytic Cu plating + Cu, Ni plating Comparison 7 Minute rusting after 250 hours 32 ⁇ 9 Electrically conductive resin layer + Cu, Ni plating Comparison 8 Minute rusting after 330 hours 28 ⁇ 10 Electrically conductive film layer + Cu, Ni plating
• Ring-shaped bonded magnets measuring 34 mm (outer diameter) ⁇ 31 mm (inner diameter) ⁇ 8 mm (height) were manufactured by the same method as in Embodiment 1.
• the obtained magnets were subjected to a sealing and smoothing treatment with Al 2 O 3 spherical barrel stones having an average diameter of 3 mm, using a vibrating barrel, under the same conditions and using the same method as in Embodiment 2.
• the bonded magnets were next placed in a vibrating barrel and subjected to dry-process barrel polishing, using short rod-shaped pieces of tin, zinc, and lead having diameters of 1 mm and lengths of 1 mm to form an electrically conductive coating layer of fine metal pieces.
• the press-fitting depths of the fine metal pieces in the resin surface and porous portions, and the coating thickness on the magnetic powder surfaces, are indicated in Table 7.
• the barrel polishing treatment conditions were the same as in Embodiment 2.
• the film thickness after plating was 21 ⁇ m on the inner diameter side and 22 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 1000 hours at 80°C and relative humidity of 90%. The results thereof and the film thickness dimensional precision are noted in Tables 8 and 9.
• the copper and nickel electroplating conditions were the same as in Embodiment 2.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 6 were washed, subjected to a sealing and surface smoothing treatment as in Embodiment 6, again washed, and subjected to non-electrolytic copper plating.
• the plating thickness was 5 ⁇ m. After non-electrolytic copper plating, copper plating and nickel plating were performed under the same conditions as in Embodiment 6.
• the ring-shaped bonded magnets obtained were subjected to an environmental test (humidity resistance test) under the same conditions as in Embodiment 6.
• the magnet properties before and after the humidity resistance test are noted in Table 8.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 9.
• the non-electrolytic copper plating conditions were the same as in Comparison 4.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 6 were washed, a mixture of phenol resin and nickel powder was coated on to form a 10 ⁇ m electrically conductive resin coating film, and the magnets were loaded together with 5 mm steel balls into a vibrating barrel, to 60% of barrel capacity, and smoothing and polishing were performed by barrel polishing for 60 minutes at an amplitude of 20 mm.
• Ring-shaped bonded magnets measuring 21 mm (outer diameter) ⁇ 18 mm (inner diameter) ⁇ 4 mm (height) were manufactured by the same method as in Embodiment 1.
• the bonded magnets obtained were placed in a vibrating barrel and dry-process barrel polishing was performed, using short rod-shaped Fe, Ni, Co, and Cr pieces having diameters of 0.7 mm and lengths of 0.5 mm to form an electrically conductive coating layer of fine pieces of those metals.
• the press-fitting depths of the fine metal pieces in the resin surface and the coating thickness on the magnetic powder surfaces are noted in Table 10.
• the barrel polishing treatment conditions were the same as in Embodiment 1.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 7 were washed and subjected to non-electrolytic copper plating.
• the plating thickness was 6 ⁇ m.
• copper and nickel plating were conducted under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 12.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 13.
• the non-electrolytic copper plating conditions were the same as in Comparison 1.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 7 were washed, and then a 10 ⁇ m electrically conductive coating film was formed with a mixture of a phenol resin and nickel powder. After this treatment copper and nickel plating were performed under the same conditions as in Embodiment 7.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 12.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 13.
• the non-electrolytic copper plating conditions were the same as in Comparison 2.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 7 were washed, a phenol resin layer was preformed as a bonding layer by an immersion method, silver powder (particle size 0.7 ⁇ m or smaller) was made to adhere to the surface thereof, and a 7 ⁇ m electrically conductive coating layer was formed in a vibrating barrel. After the vibrating barrel treatment, copper and nickel plating were conducted under the same conditions as in Embodiment 7. The ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%. The properties of the magnets after the humidity resistance test are noted in Table 12.
• an environment test humidity resistance test
• Ring-shaped bonded magnets measuring 29 mm (outer diameter) ⁇ 25 mm (inner diameter) ⁇ 5 mm (height) were manufactured by the same method as in Embodiment 1.
• the obtained magnets were subjected to a sealing and smoothing treatment with Al 2 O 3 spherical barrel stones having an average diameter of 3 mm, using a vibrating barrel, under the same conditions and using the same method as in Embodiment 2.
• the bonded magnets were next placed in a vibrating barrel and subjected to dry-process barrel polishing, using short rod-shaped pieces of Fe, Ni, Co, and Cr, having diameters of 0.5 mm and lengths of 0.4 mm to form an electrically conductive coating layer of fine metal pieces.
• the press-fitting depths of the fine metal pieces in the resin surface and porous portions, and the coating thickness on the magnetic powder surfaces, are indicated in Table 14.
• the barrel polishing treatment conditions were the same as in Embodiment 2.
• the film thickness after plating was 20 ⁇ m on the inner diameter side and 22 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 1000 hours at 80°C and relative humidity of 90%. The results thereof and the film thickness dimensional precision are noted in Tables 16 and 17.
• the copper and nickel electroplating conditions were the same as in Embodiment 2.
• the zinc substitution treatment conditions were a process time of 40 seconds, bath temperature of 22°C, and solution composition of 300 g/l sodium hydroxide, 40 g/l zinc oxide, 1 g/l ferric chloride, and 30 g/l Rossel salts.
• the film thickness was 0.01 ⁇ m.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 8 were washed, subjected to a sealing and surface smoothing treatment as in Embodiment 6, again washed, and subjected to non-electrolytic copper plating.
• the plating thickness was 5 ⁇ m. After non-electrolytic copper plating, copper plating and nickel plating were performed under the same conditions as in Embodiment 8.
• the ring-shaped bonded magnets obtained were subjected to an environmental test (humidity resistance test) under the same conditions as in Embodiment 8. The results thereof and film thickness dimensional precision are noted in Tables 16 and 17. The non-electrolytic copper plating conditions were the same as in Comparison 4.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 6 were washed, a mixture of phenol resin and nickel powder was coated on to form a 10 ⁇ m electrically conductive resin coating film, and the magnets were loaded together with 5 mm steel balls into a vibrating barrel, to 60% of barrel capacity, and smoothed and polished by barrel polishing for 60 minutes at an amplitude of 20 mm.
• Ring-shaped bonded magnets measuring 20 mm (outer diameter) ⁇ 17 mm (inner diameter) ⁇ 6 mm (height) were manufactured by the same method as in Embodiment 1.
• the bonded magnets obtained were placed in a vibrating barrel and subjected to dry-process barrel polishing, using short rod-shaped aluminum pieces having diameters of 0.8 mm and lengths of 1 mm, to form an electrically conductive coating layer of fine aluminum pieces.
• the press-fitting depth of the fine pieces in the resin surface was approximately 0.9 ⁇ m and the coating thickness on the magnetic powder surfaces was 0.5 ⁇ m.
• the barrel polishing treatment conditions were the same as in Embodiment 1.
• the film thickness after plating was 19 ⁇ m on the inner diameter side and 21 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 18.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 19.
• the nickel electroplating conditions were the same as in Embodiment 1.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 9 were washed and subjected to non-electrolytic copper plating.
• the plating thickness was 6 ⁇ m.
• copper and nickel plating were conducted under the same conditions as in Embodiment 3.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 18.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 19.
• the non-electrolytic copper plating conditions were the same as in Comparison 1.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 9 were washed, a phenol resin layer was preformed as a bonding layer by an immersion method, silver powder (particle size 0.7 ⁇ m or smaller) was made to adhere to the surface thereof, and a 7 ⁇ m electrically conductive coating layer was formed in a vibrating barrel. After the vibrating barrel treatment, nickel plating was conducted under the same conditions as in Embodiment 9.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 18.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 19.
• the non-electrolytic copper plating conditions were the same as in Comparison 3.
• Surface condition at humidity resistance test time Film thickness dimensional precision ( ⁇ m) Manufacturing method Embodiment 9 No change (no rusting) 20 ⁇ 2 Al coating layer (zinc substitution) + Ni plating Comparison 16 Spot rusting after 120 hours 27 ⁇ 2 Non-electrolytic Cu plating + Ni plating Comparison 17 Slight rusting after 270 hours 28 ⁇ 10 Electrically conductive resin layer + Ni plating Comparison 18 Slight rusting after 300 hours 26 ⁇ 10 Electrically conductive coating layer + Ni plating
• Ring-shaped bonded magnets measuring 36 mm (outer diameter) ⁇ 33 mm (inner diameter) ⁇ 3 mm (height) were manufactured by the same method as in Embodiment 1.
• the bonded magnets obtained were placed in a vibrating barrel and subjected to dry-process barrel polishing, using short rod-shaped aluminum pieces having diameters of 0.5 mm and lengths of 0.7 mm, to form an electrically conductive coating layer of fine aluminum pieces.
• the press-fitting depth of the fine pieces in the resin surface was approximately 1.1 ⁇ m and the coating thickness on the magnetic powder surfaces was 0.6 ⁇ m.
• the barrel polishing treatment conditions were the same as in Embodiment 1.
• the film thickness after plating was 17 ⁇ m on the inner diameter side and 19 ⁇ m on the outer diameter side.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 500 hours at 80°C and relative humidity of 90%. The properties of the magnets after the humidity resistance test are noted in Table 20. The surface condition results and film thickness dimensional precision at the time of the humidity resistance test are noted in Table 21.
• the copper and nickel electroplating conditions were the same as in Embodiment 2.
• the zinc substitution treatment conditions were a process time of 40 seconds, bath temperature of 22°C, and solution composition of 300 g/l sodium hydroxide, 40 g/l zinc oxide, 1 g/l ferric chloride, and 30 g/l Rossel salts.
• the film thickness was 0.01 ⁇ m.
• Ring-shaped bonded magnets obtained by the same method as in Embodiment 10 were washed, subjected to a sealing and surface smoothing treatment as in Embodiment 10, again washed, and subjected to non-electrolytic copper plating.
• the plating thickness was 6 ⁇ m.
• copper plating and nickel plating were performed under the same conditions as in Embodiment 10.
• the ring-shaped bonded magnets obtained were subjected to an environment test (humidity resistance test) for 1000 hours at 80°C and relative humidity of 90%.
• the properties of the magnets after the humidity resistance test are noted in Table 20.
• the surface condition results and film thickness dimensional precision at the time of the humidity resistance test are given in Table 21.
• the non-electrolytic copper plating conditions were the same as in Comparison 4.
• Ring-shaped bonded magnets obtained by the same method as that in Embodiment 10 were washed, and then a 12 ⁇ m electrically conductive coating film was formed with a mixture of a phenol resin and nickel powder, under the conditions noted below. These magnets were loaded together with 2 mm steel balls in a vibrating barrel to 70% of barrel capacity and smoothing and polishing were performed by barrel polishing for 90 minutes.
• porous R-Fe-B-base bonded magnets are subjected to barrel polishing in a dry process, using as a polishing medium either a mixture of a polishing agent and a vegetable medium, or a polishing agent and a vegetable medium modified with inorganic powder.
• a polishing medium either a mixture of a polishing agent and a vegetable medium, or a polishing agent and a vegetable medium modified with inorganic powder.
• the R-Fe-B-base bonded magnets are barrel polished in a barrel apparatus, in a dry process, using aluminum of undefined shape such as spherical, massive, or aricular (wire-form), and of required dimensions, press-fitting pulverized fine aluminum pieces into the resin surface and porous portions of the bonded magnet surface and coating the same therewith, or coating the magnetic powder surfaces with fine aluminum pieces, thereby forming an aluminum coating film on the surface of the R-Fe-B-base bonded magnets, then subjecting the surface of that aluminum coating layer to a zinc substitution treatment, thus making it possible to form an electrolytic plating layer that is tight and which has no pin holes, and to obtain R-Fe-B-base bonded magnets exhibiting extremely outstanding corrosion resistance.
• aluminum of undefined shape such as spherical, massive, or aricular (wire-form)
• press-fitting pulverized fine aluminum pieces into the resin surface and porous portions of the bonded magnet surface and coating the same therewith, or coating the magnetic powder surfaces

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