Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
  • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

• This invention relates to a manufacturing method of R-Fe-B type sintered permanent magnets.
• the methylcellulose and/or the agar and water mixture as a binder which induces a sol-gel reaction at a specified temperature with a R-Fe-B type alloy pulverized powder is injection molded in the magnetic field; and after the obtained molded body is dehydrated and debindered, the molded body is sintered.
• this invention provides a manufacturing method of a R-Fe-B type sintered magnet which controls the amount of residual carbon and oxygen in the sintered body, improving the moldability of injection molding while preventing the degradation of magnetic characteristic, and which can provide a three-dimentionally complex shaped sintered magnet.
• R-Fe-B type sintered permanent magnets USP 4,770, 2233, JP-A-59-6008, JP-B-61-34242
• a R-Fe-B type bond magnet USP 4,902,361
• R-Fe-B type permanent magnet as well as R-Fe-B type bond magnet usually require compression molding in the magnetic field during a manufacturing process, only a simple shaped molded body is obtained.
• an injection molding method which has been widely used in many engineering fields, as a method to manufacture the above R-Fe-B type sintered magnet.
• a manufacturing method of a R-Fe-B type sintered permanent magnet JP-A-61-220315, JP-A-62-252919, JP-A-64-28303
• An alloy powder which is obtained by pulverizing a R-Fe-B type alloy ingot and a binder which contains thermoplastic resin such as polyethylene and polystyrene, etc. as kneaded and injection molded; after the debinder treatment, the molded body is sintered to obtain the magnet. Also, a manufacturing method of a R-Fe-B type sintered permanent magnet which employs an injection molding method (JP-A-64-28302) utilizing paraffin type wax as a binder is proposed.
• intermetallic compounds containing a rare earth element are likely to react with elements such as O, H, C, etc., and when binders such as thermoplastic resin and paraffin wax, etc. that are used in the above injection molding method are added to a R-Fe-B type alloy powder ad kneaded, the carbon and oxygen content usually increases due to the reaction with R.
• the debinder treatment, and sintering the considerable amount of carbon and oxygen remain in a sintered magnet. This results especially in degradation of magnetic characteristics, and remains an obstacle to application of a complex shaped product by injection molding to magnet parts.
• the above mentioned binder which is utilized in the usual the injection molding method is mixed with an alloy powder and heated to the melting point which is around 100°C ⁇ 200°C to melt the binder in the injection molding machine.
• the curie temperature (Tc) of R-Fe-B type permanent magnets is about 300°C ⁇ 350°C, it is difficult to orientate an alloy powder to.the magnetizing direction when it is heated close to the curie temperature. Also, there was a problem of requiring a large magnetizing current in orientation.
• a binder in the compression molding for Co type super alloy powder for injection molding a composition which comprises 1.5 ⁇ 3.5 wt% methylcellulose in the said alloy powder and a specified amount of additives, glycerin and boric acid, is proposed (USP 4,113,480).
• a binder for the injection molding for Y2O3-ZrO2 and alumina powder a mixture of 10 ⁇ 50 wt% agarose, agar in the said alloy powder, and to which deionized water and glycol are added is proposed (USP 4,734,237).
• binder of which the main ingredients are methylcellulose and agar
• a relatively large amount as described above is used.
• binder additives for example, plasticizer as glycerin, etc. as methylcellulose
• the considerable amount of carbon and oxygen remains even after injection molding and the debinder treatment and sintering. It resulted in degradation in magnetic characteristics of a R-Fe-B type permanent magnet, and remains an obstacle to application of a complex shaped part by the injection molding method to a magnetic parts.
• This invention concerns with a manufacturing method of a R-Fe-B type permanent magnet, wherein injection molding and sintering and employed; furthermore, it prevents the reaction between R elements and a binder and degradation of magnetic characteristics due to residual carbon and oxygen in the molded body. It does not require a large magnetizing current during the injection molding in the magnetic field, by improving the injection moldability to obtain a complex shaped, particularly, R-Fe-B type sintered anisotropic magnets for small products.
• the inventors have selected agar and/or methylcellulose as a binder which can keep the die temperature at less that 100°C during the injection molding, which can inhibit the reaction between R elements in a R-Fe-B type alloy powder and the binder, and decrease the amount of residual carbon and oxygen. Furthermore, as a result of studying its applicability to a R-Fe-B type alloy powder, the inventors found that as long as the R-Fe-B type alloy powder is of a specified average particle size, though it contains a large amount of water, even the methylcellulose concentration is less than 0.5 wt%, the sufficient fluidity and the molded body strength are obtained. Also, the similar effect was observed when less than 4.0 wt% of agar was utilized.
• the carbon content in is the total binder is drastically reduced, and while the moldability during injection molding is improved, it turns into gel within a die below 100°C during injection molding, and it is possible to mold into a specified shape.
• the further dehydration treatment and the debinder treatment eliminate nearly all remaining oxygen and carbon in the molded body.
• the obtained sintered body has a drastically reduced amount of oxygen and carbon, and a three dimensionally complex shaped magnet with superior magnetic properties was obtained.
• the inventors coated the surface of the R-Fe-B type alloy powder with a resin prior to mixing with the above binder to inhibit the reaction between water and R elements in the alloy powder, to prevent oxidation of the alloy powder in various treatments after mixing them, and to decreases the amount of residual carbon in the obtained sintered body.
• the inventors found that the moldability during the injection molding is improved so that a three dimensionally complex shaped sintered magnet was obtained; and since almost all coated resin can be eliminated by the debinder treatment, the residual carbon in the sintered body did not increase.
• the inventors after investigating a method to maximally inhibit the reaction between R elements of magnetic powder particles and a binder to obtain stable magnetic properties, particularly, when utilizing a R-Fe-B type alloy powder consisting of a main ingredients alloy powder and a liquid phase alloy powder, a specified amount of transition metal pulverized powder is mixed with the said alloy powder, and after coating the surface of magnetic powder by the mechanofusion process in the inert atmosphere, the coating is made closely and uniform with the surface diffusion by heat treatment to completely isolate R elements of magnetic powder particles from the binder during intermediate processes: the binder kneading, injection molding, de-binder and sintering processes.
• the inventors found that the reaction between the R elements and the binder was prevented.
• the inventors found that by utilizing the vacuum heating method or heating in the hydrogen atmosphere and keeping it at a specified temperature, almost all carbon in methylcellulose and agar binders or in resin coatings are decarbonized; and the inventors also found that treatment time was drastically reduced in comparison to the usual binder consisting of paraffin wax and thermoplastics.
• the desirable average particle size is about 1 ⁇ 10 ⁇ m which comprises principal component of 8 at.% ⁇ 30 at.% R (provided R contains at least one of rare earth elements including Y), 42 at.% ⁇ 90 at.% Fe, 2 at.% ⁇ 28 at.% B; furthermore, it is most desirable to have the pulverized powder particle size of around 1 ⁇ 6 ⁇ m.
• Rare earth element R (provided R contains at least one of rare earth elements including Y) is desirable to contain least one of Nd, Pr, Ho, and Tb, or one of La, Sm, Ce, Er, Eu, Pm, Tm, Yb, and Y.
• R is less than 8 at.% the crystalline structure will be cubical structure with the identical structure as ⁇ -Fe, strong magnetic characteristics, especially the high coercive force can not be obtained.
• R exceeds 30 at.%, it results in many R-rich non magnetic phases which lower the residual magnetic flux density(Br), and the magnet with superior magnetic characteristics can not be obtained. Therefore, the desired concentration range for R is 8 at.% ⁇ 30 at.%.
• the desired composition range for B is 2 at.% ⁇ 28 at.%.
• the desirable composition range for Fe is 42 at.% ⁇ 90 at.%.
• the replacement of Fe by Co improves temperature characteristics without degrading the obtained magnet's magnetic characteristics, but exceeding 50% replacement of Co for Fe, is not desirable since it results in degradation of magnetic characteristics.
• Fe-B-R type permanent magnet Ti, Ni, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn, Zr, Bi, Hf, Cu, Si, S, C, Ca, Mg, P, H, Li, Na, K, Be, Sr, Br, Ag, Zn, N, F, Se, Te, and Pb.
• the addition of excess amount will decrease the residual magnetic flux density (Br), m and lower the maximum energy product; therefore, usually the total amount of less than 10 at.% is desirable. According to the additive elements, it is desirable to choose the total amount at less then 5 at.%, less than 3 at.%, etc.
• the desirable average particle size of a R-Fe-B type alloy powder is 1 ⁇ 10 ⁇ m.
• the average particle size of the alloy powder is less than 1 ⁇ m, due to the increased surface area of the alloy powder, as kneading ingredients the volumetric ratio of binder additives to the alloy powder must be increased to 1 : 1.2, which lowers the sintered density of the sintered product after the injection molding to 95% and not desirable.
• the average particle size exceeds 10 ⁇ m, the particle size is too large wherein the sintered product density saturates around 95%, and it is not desirable since the said density does not increase.
• the most desirable particle size range is 1 ⁇ 6 ⁇ m.
• the main phase alloy powder with the average particle size of 1 ⁇ 5 ⁇ m which comprises the principal component of 12 at.% ⁇ 25 at.% R (provided that R contains at least one of rare earth elements including Y), 4 at.% ⁇ 10 at.% B, 0.1 at.% ⁇ 10 at.% Co, and 68 at.% ⁇ 80 at.% Fe and at least 2 phases of the R2Fe14B phases and Rrich phase; and the liquid phase alloy powder with the average particle size of 8 ⁇ 40 ⁇ m which comprises the intermetallic alloy compound phase including R3Co between Co and R or Fe and R, partly R2(FeCo)14B, and 20 at.% ⁇ 45 at.% R (provided that R contains at least one rare earth element including Y), 3 at.% ⁇ 20 at.% Co, less than 12 at.% B, and the rest Fe are mixed at a specified ratio. After mixing these powders the resultant alloy powder with the average particle size of less
• the average particle size of two kinds of the raw materials is altered utilizing these alloy powder, by adding the excess amount of R ingredients discounting the oxides generation by rare earth elements, and by adding the excess liquid phase alloy powder, it is possible to generate sufficient amount of the liquid phase during the sintering process; thus, it can prevent the reaction between the R ingredients and the binder which degrades magnetic characteristics.
• the R content in order to obtain the main phase alloy powder, if the R content is less than 12 at.% it increases the ⁇ - Fe phase during the alloy melt which is not desirable; when the R content exceeds 25 at.%, the residual magnetic flux density (Br) decreases; therefore, the R content is desirable to be 12 at.% ⁇ 25 at.%.
• the B content is less than 4 at.%, the high coercive force (Hc) can not be obtained, and when it exceeds 10 at.% the residual magnetic flux density (Br) decreases; therefore, the B content is desirable to be 4 at.% ⁇ 10 at.%.
• the remainder comprises Fe and unavoidable impurities.
• the amount of Fe When the amount of Fe is less than 68 at.%, it becomes relatively rich in rare earth elements.
• the amount of Fe exceeds 80 at.% the remainder Fe portion excessively increases, and rare earth elements relatively decrease. It results in relative depletion of rare earth elements due to the oxidative reaction with a binder.
• Rare earth elements are necessary for the liquid phase sintering, so that the desirable Fe amount range is 68 at.% ⁇ 80 at.%.
• the liquid phase compound powder made of the intermetallic compound phase (a part of Co or the most of it can be replaced by Fe) between Co and R or Fe and R containing R3Co phase comprises the R3Co phase or a phase wherein a part of Co in the R3Co phase of R3Co phase is replaced by Fe.
• the central phase comprises either of RCo5, R2Co7, RCo3, RCo2, R2Co3, R2Fe17, RFe2, Nd2Co17, Dy6Fe2, DyFe, etc., and the above mentioned intermetallic compound phase, R2(Fe2Co)14B, and R 1.11 (FeCo)4B4, etc.
• the composition of the liquid phase compound powder changes the rate of amount of rare earth elements in the intermetallic compound.
• the R content is less than 20 at.%, when it is combined with the main phase alloy powder to manufacture a magnet, R is not supplemented sufficiently for the depletion of R due to partial oxidations of R in the main phase alloy powder, which results in insufficient generation of the liquid phase during the sintering. Also, when it exceeds 45 at.%, it has an undesirable effect of increasing the oxygen content.
• the Co concentration of more than 3 at.% is necessary, but when it exceeds 20 at.% the coercive force declines. Therefore, 3 ⁇ 20 at.% is appropriate for the Co , and rest can be replaced by Fe.
• the main phase alloy powder and /or the liquid phase alloy powder which comprises the intermetallic compound phase between Fe and Rcontaining R3Co and the R2(FeCo)14B phase, etc. it is possible to improve a permanent magnet with higher coercive force, higher corrosion resistance, and better temperature characteristics.
• these additives too, as the additives mentioned above, the total amount of less than 10 at.% is desirable. The total amount of less than 5 at.% and less than 3 at.%, etc. can be selected according to the additive.
• the average particle size of the main phase alloy powder is less than 1 ⁇ m, the surface area of the alloy powder increases.
• the average particle size exceed 5 ⁇ m the sintered density saturates around 95 % due to a large particle size, and the improved density can not be obtained.
• the desirable average particle size rang is 1 ⁇ 5 ⁇ m.
• the reaction with the binder is about same as the alloy powder (the average particle size of 1 ⁇ 10 ⁇ m) with a uniform composition, no effects of additives to the main phase alloy powder is observed. Also, when the average particle size of the liquid phase compound powder exceeds 40 ⁇ m, the reaction with the binder is considerably inhibited; however, the sintering ability duing the sintering process, and the sintered density and the coercive force decrease. Therefore, the desirable average particle size of the liquid phase alloy powder is 8 ⁇ 40 ⁇ m.
• the main phase alloy powder and the liquid phase compound powder can be mixed with the 70 ⁇ 99 : 30 ⁇ 1 ratios; furthermore, 70 ⁇ 97 : 30 ⁇ 3 is desirable, and the alloy powder with the multiple compositions suitable for the magnetic characteristics can be obtained.
• the main phase alloy powder with the average particle size of 1 ⁇ 5 ⁇ m and the liquid phase alloy powder with the average particle size 8 ⁇ 40 ⁇ m in these ratios the total average particle size of the combined powder is less than about 20 ⁇ m, preferably less than about 10 ⁇ m, which is equal to the aforementioned uniformly composed alloy powder.
• the main phase alloy powder which combines two kinds of powder in the same way mentioned above, the main phase alloy powder and the liquid phase compound powder, the main phase alloy powder with the average particle size 1 ⁇ 5 ⁇ m wherein the R2Fe14B phase is the main phase which comprises 11 at.% ⁇ 13 at.% R (provided that R contains at least one rare earth element including Y), 4 at.% ⁇ 12 at.% B, the remainder Fe and unavoidable impurities, and the liquid phase alloy powder with the average particle size of 8 ⁇ 40 ⁇ m which comprises the intermetallic alloy powder phase between Co and R or Fe and R containing R3Co phase and partially R2(FeCo)14B phases, etc., 18 at.% ⁇ 45 at.% R (provided that R contains at least one rare earth element including Y), less than 12 at.% B, the remainder Co (a part of Co or most of it can be replaced by Fe) and unavoidable impurities.
• the alloy powder with a specified average particle size can be obtained.
• Whichever R-Fe-B type alloy powder is utilized by selecting from the optimal range of particle size for each system, in comparison to the usual transition metal powder for the injection molding, for example, Fe based alloy powder and Co based alloy powder, the average particle size is reduced one severalth to one tenth; and, in comparison to a binder additive utilized in the injection molding of the said transition metal powder, the amount of additives can be dramatically reduced.
• coating the above alloy powder by resin contributes to the control of the reaction between water and R elements after kneading of a binder, and control of the reaction between water and R elements during the gelation step at molding and the dehydration treatment after injection molding, and it is effective to stabilize and reduce the residual oxygen.
• methacryl resins polymethyl methacrylate (PMMA) and polymethylacrylate (PMA) etc.
• thermoplastics polypropylene, polystyrene, polyvinylacetate, polyvinylchloride, polyethylene, and polyacrylonytrile, etc.
• the desirable amount of additives 0.30 wt% of the alloy powder, which is equivalent to the resin coating film thickness of 50 ⁇ ⁇ 200 ⁇ is desirable.
• additives exceed 0.30 wt%, it is not desirable since the residual oxygen increases from the resin film.
• carbon contained in the coating resin can be eliminated by the debinder process in the hydrogen atmosphere as will be explained later, the residual carbon content does not increase in the molded body even the amount of coating resin increases.
• the desirable coating resin particle size is about 1000 ⁇ ⁇ 5000 ⁇ .
• the alloy powder thus obtained since it is relatively stable due to its oxygen content, it has the advantage of being able to recycle during the injection molding. Also, the coated alloy powder has the advantage of being able to injection mold without adding a lubricant.
• the raw material powder comprises the main phase alloy powder and the liquid phase alloy powder which comprises the intermetallic compound phase between Co and R or Fe and R containing R3Co, and a R2(FeCo)14B phase, etc.
• the above resin coating can be applied to the main phase phase alloy powder and/or the liquid phase alloy powder.
• the above resin coating can be applied after the main phase alloy powder is coated with the liquid phase alloy powder by the mechanofusion system; and the same effects as above are obtained in these cases.
• the R-Fe-B type alloy powder which comprises the above main phase alloy powder and the liquid phase alloy powder
• a specified amount of transition metal pulverized powder is mixed with the said alloy powder; and after the surface of magnetic powder particles is coated with the transition metal pulverized powder by the mechanofusion process in the inert atmosphere, coating is made fine and uniform by the surface diffusion through the heat treatment.
• the raw material powder in which the R content the magnetic powder particle and the binder are completely separated by the said coating can be utilized.
• transition metals for this coating transition metals excluding rare earth elements, among which Fe, Ni, and Cu are desirable.
• the Fe element is most desirable because it is most contained in the R-Fe-B type magnetic powder. If the content of the magnetic powder is adjusted in advance, no limit exists in the amount of the additive, and it is easy to form a relatively uniform coating around magnetic particles during the mechanofusion treatment due to its superior malleability. The Fe element is also relatively easy to obtain.
• transition metal powder reacts with the binder to form carbide and oxide compound, since they can be easily de-oxygenated and de-carbonized in vacuum at relatively temperature or by the momentary hydrogen stream, it is an ideal coating for the injection molded R-Fe-B type sintered magnet alloy powder.
• the average particle size of the transition metal powder of adhesion or coating is less than 0.02 ⁇ m, the transition metal powder itself becomes very reactive to form oxides and lacks metal's characteristic malleability.
• the average particle size exceeds 1 ⁇ m, the pulverized transition metal powder does not sufficiently adhere to magnetic powder particles by the mechanofusion during the coating treatment, and defects are likely to occur in the coating film.
• the desirable particle size is 0.02 ⁇ m ⁇ 1 ⁇ m.
• water is added to methylcellulose or agar which goes through the sol-gel transformation, or the combination of them, as the injection molding binder.
• methylcellulose When methylcellulose is used solely as a binder, if the amount is less than 0.05 wt% the molding strength is drastically reduced. Also, if the amount exceeds 0.50 wt%, the residual carbon and oxygen increase and magnetic characteristics degrade due to the lower coercive force. From these considerations, 0.05 wt% ⁇ 0.50 wt% is desirable. Furthermore, 0.1 wt% ⁇ 0.45 wt% is desirable, and 0.15 wt% ⁇ 0.4 wt% is most desirable.
• agar When agar is used solely as a binder, if the amount is less than 0.2 wt% the molding strength is drastically reduced. Also, if the amount exceeds 4.0 wt%, the residual carbon and oxygen increase and magnetic characteristics degrade due to the lower coercive force. From these considerations, 0.2 wt% ⁇ 4.0 wt% is desirable. Furthermore, 0.5 wt% ⁇ 3.5 wt% is desirable, and 0.5 wt% ⁇ 2.5 wt% is most desirable.
• methylcellulose and agar are used together as a binder, if the amount is less than 0.2 wt%, the molding strength is drastically reduced, and the mold releasing property between the molding die and the molded body degrades. Also, if the amount exceeds 4.0 wt%, the sintered density after sintering decreases, the residual carbon and oxygen increase, and magnetic characteristics degrade. From these considerations, 0.2 wt% ⁇ 4.0 wt% is desirable. Nevertheless, it is not desirable for the methylcellulose amount to exceed the amount when methylcellulose is solely used. Also, the total amount is desirable to be less than 3.5 wt% and less than 2.5 wt%.
• this invention is characterized in utilizing methylcellulose and/or agar together with water as a binder, and it is desirable to use deionized water which is deoxygenated to control its reaction with R.
• the water content is less than 8 wt%, the fluidity in molding degrades, and short shots are likely to occur.
• the water content exceeds 18 wt%, as the total binder content increases, the sintered density after sintering lowers, the residual oxygen increases, and magnetic characteristics degrade.
• the water content of 8 - 18 wt% is most desirable.
• the water content is selected within the range of 6 ⁇ 18 wt% giving consideration of methylcellulose and agar proportions.
• a small quantity of the agar binder can generate the viscoelasticity through it contains a large amount of water, so that the carbon content in the total binder is drastically reduced as the injection molding binder.
• lubricant out of glycerine, wax emulsion, stearic acid and water soluble acrylic resin.
• the binder is either methylcellulose or agar, and if the amount of lubricunt is less than 0.10 wt%, the density of molded body tends to be uneven. Particularly, when methylcellulose is utilized solely, and the amount exceeds 0.3 wt%, the molded body strength lowers so that 0.10 wt% ⁇ 1.0 wt% is desirable. When agar is utilized solely, and the amount exceeds 1.0 wt%, the molded body strength lowers so that 0.1 wt% ⁇ 1.0 wt% is desirable. When methylcellulose and agar are utilized together, the additive amount of the 0.1 wt% ⁇ 1.0 wt% range is selected, giving consideration to the methylcellulose and agar ratio.
• the die temperature of 70°C ⁇ 90°C is desirable. If the temperature is less than 70°C, when the molded body is removed deformation might take place due to the insufficient solidification. Also, when it exceeds 90°C the fluidity of the kneaded body deteriorates.
• the die temperature of 10°C ⁇ 30°C is desirable. If the temperature is less than 10°C, the fluidity of the kneaded body deteriorates. If it exceeds 30°C, the molded body might deform, when it is being removed due to the insufficient solidification.
• the injection temperature of 0 ⁇ 40°C is desirable. At the temperature less than 0°C the mixture freeze so that the fluidly lowers. Also, when it exceeds 40°C the fluidity becomes insufficient so that a short shot is likely to occur and not desirable. Also, when agar is utilized solely, the injection temperature of 75 ⁇ 95°C is desirable. If it is less than 75°C, the fluidity is not sufficient so that a short shot is likely to occur. Also, if it exceeds 95°C, bubbles due to water evaporation generate so that it causes void in the sintered body after sintering. Also, water evaporation lowers the fluidity of the kneaded body so that the said body clogs up the molding equipment and is not desirable.
• the injection molding pressure is less than 30 kg/cm2, a weld generates the uneven molded density, after sintering bend and waviness generate.
• methylcellulose when it exceeds 50 kg/cm2 flare generates and is not desirable, and 30 ⁇ 50 kg/cm2 is desirable.
• agar when agar is utilized solely and the pressure exceeds 70 kg/cm2, a flare generates and is not desirable, so that the pressure of 30 ⁇ 70 kg/cm2 is desirable.
• methylcellulose and agar when methylcellulose and agar are utilized together, considering the ratio of, methylcellulose and agar the die temperature, the injection temperature, and the injection molding pressure, etc., can be selected from the above range.
• the dehydration treatment is applied as a pre-processing step for the debinder treatment, but the dehydration method is not specified.
• the temperature varies according to the added amount of deionized water, but it is desirable to heat in the temperature range 20°C ⁇ at30 ⁇ 60°C/hr. If the rate is less than 30°C/hr, the finished product generates fractures and cracking due to rapid evaporation of water and is not desirable.
• the processing product when the processing product is small, it is desirable to raise the temperature at 40 ⁇ 60°C/hr at least in the 20 ⁇ 100°C range, and the dehydration process can be simplified. Also, by the time temperature reaches 100°C the most of water evaporates, so that the dehydration treatment is excess of the 100°C range is not necessary.
• this invention is concerned about the R-Fe-B type alloy powder which contains rare earth elements (R) as the principal component, it easily reacts with the atmospheric oxygen or oxygen in water.
• R rare earth elements
• the cooling rate is not specified; but if the cooling rate is too slow, the molded body might oxidize during the cooling process so that the faster cooling rate is desirable.
• the cooling temperature if less than -5°C ⁇ -100°C is desirable. If the temperature is higher than -5°C, it is not desirable since it takes a long time to dry. Also, the temperature is less than - 100°C, the electricity required for freezing drastically increases and is not desirable.
• vacuum during the vacuum is desirable to be higher than 1 x 10 ⁇ 3 Torr; and after the freeze vacuum drying, the processed product can slowly be brought back to room temperature.
• the temperature is raised at 100 ⁇ 200°C/hr in the hydrogen atmosphere and kept at 300 ⁇ 600°C for 1 ⁇ 2 hour.
• nearly all carbon in the methylcellulose and agar binder or coating resins is decarbonized; and, in comparison to the usual paraffin wax and thermoplastic binder, the treatment time is dramatically reduced.
• the dehydrogen treatment process is necessary after the debinder treatment in the hydrogen atmosphere.
• the temperature at 50 ⁇ 200°C/hr and keeping it at 500 ⁇ 800°C for 1 ⁇ 2 hour in vacuum, nearly all absorbed hydrogen can be eliminated.
• the rate of heating in excess of 500°C can be selected at will, for example, 100 ⁇ 300°C/hr, etc. the usual heating method in sintering can be applied.
• this invention utilized the methylcellulose and / or agar and water as binder, the carbon content in the binder is initially lowered, so that even the heating rate is increased to, for example, 100 ⁇ 300°C/hr, the molded body does not generate fractures or crackings.
• the usual binder consisting of paraffin wax and thermoplastics, it has the advantage of shortening time required for the debinder treatment.
• the sintering condition of molded body after it is dehydrated and debindered, and the heat treatment condition after sintering can be selected according to the chosen alloy powder composition, they can be same as the usual manufacturing condition of the Fe-B-R type sintered permanent magnet.
• the sintering process at 1000 ⁇ 1180°C for 1 ⁇ 2 hour, and the aging process at 450 ⁇ 800°C for 1 ⁇ 8 hour, respectively, are desirable.
• the R-Fe-B alloy powder with specified average particle size is injection molded utilizing a specified amount of methylcellulose and/or agar binder, the drastic reduction of carbon and oxygen in the molded body after debinder is possible. Thus, it is possible to minimize the amount of carbon and oxygen in the finished sintered body product.
• the upper limits of carbon and oxygen contained in the sintered body can be less than 1300 ppm carbon, less than 10000 ppm oxygen; furthermore less than 1000 ppm carbon, less than 9000ppmoxygen; particularly, under the best conditions, the carbon content can be made less than 800 ppm and the oxygen content less than 8000 ppm.
• the sintered magnet with superior magnetic characteristics can be obtained.
• the maximum energy product of more than 4 MGOe, more than 10 MGOe, more than 15 MGOe can be obtained according to each condition; and more than 20 MGOe can be obitained under the best conditions.
• the injection molding kneaded mixture which comprises the R-Fe-B type alloy powder and the binder in which methylcellulose and/or agar and water are principal components
• the molded body which is molded the said mixture by injection molding machine
• the excess molded be produced during the molding called spoul and runner can be frozen and storage airtightly so that the reaction between the R content of the R-Fe-B type alloy powder and water can be controlled.
• the storage for a proved of time or a long duration will not increase the residual oxygen int he said mixture or the molded body.
• the amount of residual oxygen and residual carbon drastically reduced in the final sintered product, and the R-Fe-B type permanent magnet with the stable magnetic properties can be supplied.
• the final product of the R-Fe-B sintered permanent magnet can be supplied at low cost.
• This kneaded pellet was molded at the injection temperature and the die temperature shown in table 1 to obtain a 20 mm x 20 mm x 3 mm plate in the magnetic field (15 kOe).
• the obtained molded body was heated from room temperature to 100°C at 50°C/hr in vacuum, and was kept at this temperature for 1 hour. After completely dehydrating it, the temperature was raised to 500°C at 100°C/hr for the debinder treatment. It was further heated to and kept at 1100°C for one hour to sinter.
• the Ar gas was introduced to cool the sintered body to 800°C at 7°C/min.; then, it was cooled to 550°C at 100°C/hr, and was kept for 2 hours for aging.
• an acrylic binder is mixed with the alloy powder with the average particle size of 3 ⁇ m as a Example 1 to the 1 : 1 volumetric ratio. After kneading it at 160°C for 10 minutes and making it to a injection molding knead, it was injection molded into he die heated at 45°C in the magnetic field of 15 kOe, to produce a injection molded body, a 10 mm length x 10 mm width x 5 mm height plate by the usual method.
• Example 2 After the injection molded body was heated to 350°C at 6°C/hr to debinder in vacuum of 3 x 10 ⁇ 4Torr, it was sintered and heated under the same condition as in Example 1 to obtain a sintered anisotropic magnet.
• the measurement results of magnet characteristics, the residual oxygen content, and the residual carbon content were shown in Table 2.
• Example 2 Utilizing two kinds of the non-coated alloy powders and resin coated alloy powders obtained above, in the same manner as in Example 1, the binder, water, additives which kind and quantity is shown to Table 3 were added and kneaded at room temperature; and the obtained kneaded pellets were injection molded at the injection molding temperature and the die temperature shown in Table 3 to obtain a 20 mm x 20 mm x 3 mm plate in the magnetic field (15 kOe). Moreover, glycerine was used as an additive.
• the heat dry method wherein the molded body is heated from room temperature to 100°C at 50°C/hr in vacuum and kept at this temperature for 1 hour to completely to dehydrate it
• the freeze vacuum dry method wherein the said molded body was rapidly chilled to -50°C and kept at the said temperature for 24 hours to completely dehydrate it.
• Residual oxygen content ppm
• Residual carbon content ppm
• Br(kG) iHc(kOe) BH
• max MGOe 6 7700 620 9.2 14.5 20.3 7 7300 600 9.4 14.0 21.2 8 7000 850 9.5 13.4 21.7 9 7650 820 9.4 12.6 21.3 10 8700 820 8.9 9.6 17.4 11 8000 800 9.2 11.3 19.3 12 7100 840 9.2 11.0 20.3
• the analytical data of this mixed powder is as follows: 13.9 at% Nd, 0.45 at% Pr, 0.26 at% Dy, 3.6 at% Co, 6.4 at% B, and the remainder Fe.
• Example 2 Utilizing the mixed alloy powder, as in Example 1 the same kind and quantity of binders, water, additives as in Table 5 were added and kneaded at room temperature. The obtained kneaded pellets were injection molded at the injection temperature and the die temperature shown in Table 5 to obtain a 20 mm x 20 mm x 3 mm plate in the magnetic field (15 kOe). Moreover, glycerine was utilized as the additive.
• a dehydration treatment of the molded body As a dehydration treatment of the molded body, one of the following methods were utilized: the heat dry method wherein the molded body is heated from room temperature to 100°C at 50°C/hr in vaccum and kept at this temperature for 1 hour to completely to dehydrate it; and the freeze vacuum dry method wherein the said molded body was rapidly chilled to -50°C and kept at the said temperature for 24 hours to completely dehydrate it. Next, it was subjected to the debinder treatment by the vacuum heating method in Example 1; then, it was sintered under the same conditions as in Example 1, and the aging treatment was applied.
• the mixed powder wherein 7.0 wt% of the pulverized iron powder with the average particle size of 0.02 ⁇ m was added was placed in the mechanofusion system (Hosokawa Micron Ltd., Am-20FV); and after it was filled with Ar gas, while controlling the temperature by water to keep the arm head less than 50°C during operation, the rolling speed was kept at 700 rpm for 3 hours to obtain Fe powder coated alloy powder.
• the said alloy powder was injection molded, dehydrated, debindered utilizing the above processes, and sintered.
• the mechanofusion treated powder was heat treated at 550°C for 2 hours; in the vacuum environment of 2 x 10 ⁇ 5 Torr and when the obtained powder was studied under the electron microscope, the particle surface of the main phase alloy powder and the liquid phase alloy powder were adhered by dense and smooth Fe particles.
• Table 5 shows whether the Fe film present or not, the kind of binders, the amount of additives, and the dehydration method employed in each magnet.
• Residual oxygen content ppm
• Residual carbon content ppm
• Br(kG) iHc(kOe) BH
• max MGOe
• the analytical data of this mixed powder is as follows; 11.4 at% Nd, 2.82 at% Pr, 0.11 at% Dy, 4.2 at% Co, 6.4 at% B, and the remainder Fe.
• This kneaded pellets were injection molded at the injection temperature of 25°C and the die temperature kept at 80°C to obtain a 20 mm x 20 mm x 8 mm plate in the magnetic field (15 kOe).
• This molded body is dehydrated and debindered employing the same dehydration treatment of vacuum heating and the debinder treatment as in Example 1, or the dehydration treatment of vacuum heating or the dehydration treatment of freeze vacuum drying, and the debinder treatment of heating in the hydrogen atmosphere and the dehydrogenation treatment as in Example 2; furthermore, the dehydration treatment of vacuum drying at room temperature, and the debinder treatment of heating in the hydrogen atmosphere and the dehydrogenation treatment then, it was sintered and aged int he same conditions in Example 1.
• Table 7 shows the dehydration treatment and the debinder treatment utilized for each magnet.

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• 1993
  • 1993-06-24 EP EP19930304944 patent/EP0576282B1/de not_active Expired - Lifetime
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