US3785881A - Method of manufacturing a body having anisotropic permanent magnetic properties by grinding with fatty liquid - Google Patents

Method of manufacturing a body having anisotropic permanent magnetic properties by grinding with fatty liquid Download PDF

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Publication number
US3785881A
US3785881A US00241201A US3785881DA US3785881A US 3785881 A US3785881 A US 3785881A US 00241201 A US00241201 A US 00241201A US 3785881D A US3785881D A US 3785881DA US 3785881 A US3785881 A US 3785881A
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United States
Prior art keywords
grinding
sintering
oxygen content
ageing
sintered
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Expired - Lifetime
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US00241201A
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English (en)
Inventor
P Naastepad
Liempd G Van
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US Philips Corp
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US Philips Corp
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Publication date
Priority claimed from NL7104566A external-priority patent/NL7104566A/xx
Priority claimed from NL7203267A external-priority patent/NL7203267A/xx
Application filed by US Philips Corp filed Critical US Philips Corp
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Publication of US3785881A publication Critical patent/US3785881A/en
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    • 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
    • H01F1/0555—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together
    • H01F1/0557—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together sintered
    • 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
    • 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
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling

Definitions

  • the final product may also comprise a constituent which consists of compounds which comprise a larger content of R than the compound M R itself, for example M R
  • M R A method of the type described is known from the Dutch published Pat. application No. 6907;499. In addition it may be concluded from the publication by F. Westendorp in Solid State Communications, volume 8, pp.
  • the sintering temperature must lie within a very particular temperature range to obtain high coercive forces, since it appears from said publication that the coercive force ,H of sintered material as a function of the sintering temperature strongly increases from a certain temperature for SMCo approximately 800C reaches a maximum (for SmCo at approximately 1,075C) and then decreases again rapidly. It is therefore obvious to sinter at such a temperature that a product having a maximum ,l-l is obtained.
  • a magnet manufactured in this manner generally has a great drawback: the coercive force and/or the shape of the demagnetization curve which is measured on the magnet, varies with time in that the coercive force of a part or of the whole of the permanent magnetic material from-which said magnet body is constructed, decreases in course of time.
  • This phenomenon which is expressed in that demagnetization curves measured at 2 different instants on a magnet body do not overlap each other, is termed the ageing of the magnet body.
  • a decrease of the coercive force and/or a change of the shape of the demagnetisation curve (the convexity) occurs upon ageing.
  • a variation of one of the said quantities, or of both quantities, is reflected in the quantity %M,H.. rM is to be understood to mean the value of the field which has to be applied to reduce the retentivity M, to half.
  • the value kM i will be used hereinafter.
  • the method according to the invention is characterized in that, in order to obtain a non-ageing sintered magnet body having an optimum combination of coercive force and shape of the demagnetization curve, the sintering is carried out at a temperature which is higher than the critical sintering temperature of the chosen composition, while both during sintering and during the manufacturing steps preceding the sintering, measures are taken to prevent the oxygen content of the final product to exceed a critical value to be determined with reference to a graph showing the relationship between the coercive force and the sintering temperature at various oxygen contents.
  • the quantity 'kMJ is not only a function of the sintering temperature but also of the oxygen content of the final product and that this relation is such that the higher the sintering temperature, the smaller is the amount of oxygen admissible to obtain an optimum combination of coercive force and convexity.
  • This has two consequences. On the one hand, at a fixed sintering temperature required to manufacture a non-ageing magnet, a higher 'rMJ" and in particular a higher coercive force can be reached than was initially assumed, provided the oxygen content is maintained sufficiently low.
  • sintering may be carried at a higher temperature than in the preceding case, while maintaining an acceptable value of combination of coercive force and convexity".
  • the temperature at which a powder of a given composition is to be sintered thus is not so critical as would be assumed, for example, on the basis of said article in Solid State Communications, if only a sufficiently low oxygen content is ensured.
  • the achievable density depends upon the oxygen content. The lower the oxygen content of the material to be sintered, the denser it can be sintered at one and the same temperature.
  • the compression should be carried out at a pressure of 15 kB, preferably between 5 and kB.
  • the grinding to a fine powder should be carried out in the presence of a liquid which readily wets metal surfaces.
  • an organic liquid having a boiling point below 120C is used as a grinding liquid and which comprises a component having the property of preferentially wetting metal surfaces.
  • a preferred embodiment of the method according to the invention is characterized in that the liquid having the property of readily or preferentially, respectively, wetting metal surfaces is a fatty substance, such as a mineral, vegetable or animal oil.
  • Fatty substances are to be understood to mean herein fats, oils and waxes, that is to say: non-volatile, non-water-soluble, organic substances.
  • the application hereof during grinding turned out in general to result in sintered magnet bodies having a low oxygen content.
  • the methods according to the invention is characterized in particular in that M is Co and R is Sm, and the oxygen content is maintained below 0.5 percent and in particular below 0.45 percent.
  • the invention also relates to a sintered magnet body manufactured by means of any of the above methods.
  • FIG. 1 is a graph in which the magnetisation M is plotted against the externally applied demagnetizing field H for different magnet bodies
  • FIG. 2 is a graph showing the relationship between sintering temperature and coercive force
  • FIG. 3 is a graph showing the relative ageing as a function of the sintering temperature
  • FIG. 4 is a graph showing the relationship between %M,- r and the sintering temperature at various oxygen contents
  • FIG. 5 is a graph showing the relationship between pore volume and oxygen content of final products sintered at different temperatures
  • FIG. 6 is a graph showng the variation against time of the oxygen content of powders ground in different grinding liquids.
  • the invention is illustrated by means of investigations performed on Sm-Co magnets but the present invention is based on the fact that a critical sintering temperature and a critical oxygen content can be found in general for any M-R compound.
  • a number of Sm-Co powder samples for example, with an atomic ratio Sm Co equal to 4.4, obtained by pulverizing in a vibratory mill moldings under varying conditions influencing the oxygen contents to a size of from 2 to 20 u, were compressed after precompression at a pressure of 0.3 kB, under an isostatic pressure of 15 kB, the orientation taking place in a magnetic field of approximately 8,000 Oe.
  • the samples were then sintered for 30 minutes at several temperatures, varying from l,050 to l,150C. It is to be noted that sintering may be carried out under varying conditions. It may be carried out in a space which is maintained at a given vacuum (for example between 10" and 10 Torr) by means of a pump.
  • Another possibility is to sinter in an inert gas atmosphere, either by leading a constant gas flow over the sample, or by placing the sample in a closed space which is evacuated prior to sintering and then filled with an inert gas, for example, argon.
  • an inert gas for example, argon.
  • the temperature of 150C was necessary for the accelerated demonstration of any ageing phenomena.
  • FIG. 1 of the drawing shows such a curve.
  • the magnetization M is plotted on the vertical and the external magnetic field H on the horizontal.
  • the curve 1 is a demagnetisation curve characteristic of a permanent magnetisable body.
  • the magnetisation M is equal to zero.
  • the demagnetisation curve 2 is characteristic of a magnet body having a coercive force (,H lower than the (,I-I associated with curve 1.
  • a demagnetisation curve of the type 3 can be measured in a magnet body after ageing during a time t.
  • Such a curve shows a smaller convexity, while nevertheless the coercive force ,I-I remains the same. In such a case also it is called ageing of the magnet. Besides it is possible that both the coercive force and the convexity decrease upon ageing.
  • kM l s is plotted as a function of the sintering temperature at different oxygen contents.
  • values are recorded in the graph which are measured in magnets sintered at such temperatures that they may show ageing phenomena. In order to be able to compare the various values all measurements have been performed immediately after sintering before ageing has occurred in magnets sintered at too low temperatures.
  • a minimum oxygen level was reached by grinding in exclusively mineral oil, for example the oils available in trade as Tellus 33 and Tellus l5 (4). Since the oil remains on the powder particle and does not evaporate away, a good protection was obtained also after grinding.
  • the -excessive oil may be removed (washed away) in a later stage of the manufacturing process. When not all the oil is removed, the final product may contain Sm-carbide. However, this has no influence on the magnetic properties.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Power Engineering (AREA)
  • Hard Magnetic Materials (AREA)
  • Powder Metallurgy (AREA)
US00241201A 1971-04-06 1972-04-05 Method of manufacturing a body having anisotropic permanent magnetic properties by grinding with fatty liquid Expired - Lifetime US3785881A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL7104566A NL7104566A (en) 1971-04-06 1971-04-06 Anisotropic permanent magnets - by sintering body composed of cpd of cobalt and rare earth, yttrium or thorium
NL7203267A NL7203267A (en) 1972-03-11 1972-03-11 Permanent magnet prepn - using a powder mixture of low oxygen content and high sintering temp

Publications (1)

Publication Number Publication Date
US3785881A true US3785881A (en) 1974-01-15

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ID=26644642

Family Applications (1)

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US00241201A Expired - Lifetime US3785881A (en) 1971-04-06 1972-04-05 Method of manufacturing a body having anisotropic permanent magnetic properties by grinding with fatty liquid

Country Status (8)

Country Link
US (1) US3785881A (OSRAM)
JP (1) JPS5120291B1 (OSRAM)
CA (1) CA977658A (OSRAM)
CH (1) CH591149A5 (OSRAM)
DE (1) DE2215301B2 (OSRAM)
FR (1) FR2135156B1 (OSRAM)
GB (1) GB1350318A (OSRAM)
IT (1) IT952517B (OSRAM)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3964939A (en) * 1974-12-26 1976-06-22 Bell Telephone Laboratories, Incorporated Bodies including passivated metal particles
US3970485A (en) * 1975-01-20 1976-07-20 Hitachi Magnetics Corporation Binder and lubricant removal from cobalt-rare earth alloys
US4881988A (en) * 1987-11-16 1989-11-21 Rjf International Corporation Novel flexible magnet for use in small dc motors
US5489343A (en) * 1993-01-29 1996-02-06 Hitachi Metals, Ltd. Method for producing R-Fe-B-based, sintered magnet
US20110241810A1 (en) * 2010-03-31 2011-10-06 Kabushiki Kaisha Toshiba Permanent magnet and method for manufacturing the same, and motor and power generator using the same

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL6907499A (OSRAM) * 1969-05-14 1970-11-17

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3964939A (en) * 1974-12-26 1976-06-22 Bell Telephone Laboratories, Incorporated Bodies including passivated metal particles
US3970485A (en) * 1975-01-20 1976-07-20 Hitachi Magnetics Corporation Binder and lubricant removal from cobalt-rare earth alloys
US4881988A (en) * 1987-11-16 1989-11-21 Rjf International Corporation Novel flexible magnet for use in small dc motors
US5489343A (en) * 1993-01-29 1996-02-06 Hitachi Metals, Ltd. Method for producing R-Fe-B-based, sintered magnet
US20110241810A1 (en) * 2010-03-31 2011-10-06 Kabushiki Kaisha Toshiba Permanent magnet and method for manufacturing the same, and motor and power generator using the same
US8568539B2 (en) * 2010-03-31 2013-10-29 Kabushiki Kaisha Toshiba Permanent magnet and method for manufacturing the same, and motor and power generator using the same
US10102950B2 (en) 2010-03-31 2018-10-16 Kabushiki Kaisha Toshiba Permanent magnet and method for manufacturing the same, and motor and power generator using the same

Also Published As

Publication number Publication date
FR2135156B1 (OSRAM) 1975-10-24
FR2135156A1 (OSRAM) 1972-12-15
DE2215301B2 (de) 1976-07-08
CH591149A5 (OSRAM) 1977-09-15
CA977658A (en) 1975-11-11
GB1350318A (en) 1974-04-18
DE2215301A1 (de) 1972-10-12
JPS5120291B1 (OSRAM) 1976-06-24
IT952517B (it) 1973-07-30

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