US3739445A - Powder metal magnetic pole piece - Google Patents

Powder metal magnetic pole piece Download PDF

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Publication number
US3739445A
US3739445A US00102364A US3739445DA US3739445A US 3739445 A US3739445 A US 3739445A US 00102364 A US00102364 A US 00102364A US 3739445D A US3739445D A US 3739445DA US 3739445 A US3739445 A US 3739445A
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United States
Prior art keywords
alloy
percent
powder
pole piece
magnetic pole
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US00102364A
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English (en)
Inventor
J Gabriel
W Reilly
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Chromalloy Gas Turbine Corp
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Chromalloy American Corp
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Assigned to CHROMALLOY GAS TURBINE CORPORATION, A DE. CORP. reassignment CHROMALLOY GAS TURBINE CORPORATION, A DE. CORP. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: CHROMALLOY AMERICAN CORPORATION
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
    • 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
    • B22F3/12—Both compacting and sintering
    • B22F3/14—Both compacting and sintering simultaneously
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
    • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
    • C22C32/0026—Matrix based on Ni, Co, Cr or alloys thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S75/00—Specialized metallurgical processes, compositions for use therein, consolidated metal powder compositions, and loose metal particulate mixtures
    • Y10S75/95—Consolidated metal powder compositions of >95% theoretical density, e.g. wrought
    • Y10S75/951—Oxide containing, e.g. dispersion strengthened

Definitions

  • ABSTRACT A powder metallurgy produced wear resistant magnetic pole piece for use as a pickup head with magnetic playback tapes is provided made of a magnetically soft ferrous alloy containing effective amounts of silicon and aluminum. A powder of the alloy is oxidized to provide a thin oxide on the particles thereof. The powder is then hot pressed in vacuum at an elevated temperature into a dense sintered body. The presence of oxide in the grain boundaries confers wear resistant properties to the alloy. An oxygen content of about 3,400 to 4,400 ppm is preferred.
  • Magnetic playback television tapes employ magnetic pole pieces as pickup heads for playing back pictures recorded thereon.
  • four pole pieces are employed in an assembly, each pole piece being soldered every 90 within a panel guide wheel near the periphery thereof.
  • the guide wheel rotates about a central axis and wears against a magnetic playback tape of gamma iron oxide.
  • the pickup face of each pole piece, which is disposed at the periphery of the wheel, is the only part that contacts the tape in service.
  • the gap between the tape and wheel becomes too great for proper magnetic performance (permeability, coercivity, etc.) such that the picture is generally degraded, thus requiring frequent replacement with new pole pieces at, for example, IOO-hour intervals.
  • the pole pieces are made of a soft magnetic material comprising an iron-base alloy containing approximately 9.4 percent by weight of silicon and 5.7 percent by weight of aluminum. conventionally, the alloy is cast into a desired shape and the individual pole pieces machined from the casting, since the alloy is too brittle to withstand conventional working operations, such as rolling, forging, forming and the like.
  • the casting usually has a coarse grained microstructure of less than ASTM 4 accompanied by limited wear characteristics. It would be desirable to provide a soft magnetic alloy of the foregoing type characterized by improved wear resistance and capable of being employed for prolonged periods of time in frictional contact with magnetic playback tape containing gamma iron oxide.
  • Another object is to provide as an article of manufacture a sintered soft magnetic alloy characterized by improved wear resistance as a magnetic pole piece when employed in rubbing contact with a moving magnetic tape of gamma iron oxide.
  • FIGS. 1 and 2 illustrate magnetic pole pieces pro cuted in accordance with the invention
  • FIG. 3 depicts, schematically, one embodiment of a die assembly which is employed in producing hot pressed products in accordance with the invention.
  • FIG. 4 is a reproduction of a photomicrograph taken at 500 times magnification showing a typical microstructure oxide surrounding the grains of the magnetic alloy.
  • One embodiment of the invention resides in a powder metallurgy method of producing a magnetically soft ferrous alloy containing an effective amount of silicon and aluminum ranging from about 2 to 12 percent silicon and from about 2 to 10 percent aluminum for use in the manufacture of magnetic pole pieces characterized by improved resistance to wear when in rubbing contact with a moving magnetic playback tape of gamma iron oxide.
  • a classified powder of the alloy is first thermally oxidized in air at an elevated temperature to provide a thin oxide film at the surface of the particles and the oxidized powder is then hot consolidated to a substantially fully dense body having a fine grained metallographic structure with the oxide film encapsulating the grain boundaries thereof.
  • the oxide film improves wear resistance without substantially adversely affecting the magnetic properties.
  • the invention also provides as an article of manufacture a consolidated sintered magnetic alloy containing effective amounts of silicon, aluminum, oxygen, and the balance essentially iron suitable for use in magnetic pole pieces for use with magnetic playback tapes.
  • the magnetic alloy is advantageously produced as a vacuum hot pressed billet from thermally oxidized alloy powder of particle size ranging from about 10 to 20 microns. This results in a fine grained fully dense pressing in which the wear performance is substantially superior to the cast alloy product.
  • the benefit provided by the product is attributed (l) to grain refinement which offers more grain boundary area than the cast structure; and (2) to the presence of a localized oxide film in the grain boundary.
  • the powder metallurgy alloy is particularly suitable for magnetic pole pieces of the type shown in FIGS. 1 and 2, FIG. 1 showing a typical panel guide wheel 10 having four magnetic pole pieces (11, l2, l3 and 14) located at intervals around the periphery of the wheel.
  • the actual wear surface of each of the pole pieces i.e., surfaces 11A, 12A, 13A and 14A, extend slightly beyond the periphery of the wheel as shown.
  • An enlarged view of a pole piece 15 is depicte d with the wear surface 15A indicated as shown.
  • the alloy composition consisting essentially of approximately 9.4 percent silicon (e.g. 9.4% i 0.4%), approximately 5.7 percent aluminum (e.g. 5.7% i 0.3%), and the balance essentially iron, is preferably in the vacuum cast form.
  • the vacuum cast ingots are ground clean, remelted and then atomized using an inert gas (preferably argon) preferably jet controlled using proper processing parameters (i.e., pressure, purity, flow, etc.) to achieve maximum yield of spherical powder in preferably the 10 to 20 micron range.
  • the material is classified to extract the 10 to 20 micron spherical powder, and the plus 20 micron oversize powder is processed by conventional ballmilling in a stainless steel mill containing a charge of la-inch stainless steel balls.
  • a typical milling procedure consists of a 750 gram charge of the alloy powder dispersed in 1,500 cc of denatured alcohol to act as a refrigerant and to reduce contamination.
  • the milled powder is vacuum dried in a metal desiccator at 25 to 30 inches Hg with the oven temperature not exceeding F.
  • the milled product is then classified to remove the 10 to 20 micron powder. Milling times and rotation speeds are controlled to assure that flake" powder shapes are not developed, otherwise, such powder contributes to an anistropic metallurgical structure and a non-uniform performance in the field.
  • the milled powder has an irregular shape and is preferably blended with the unmilled atomized spherical powder. Tests have indicated an optimum blend ratio to be 5 parts of milled powder to 1 part of atomized powder. The blend ratio may vary from about 4 to l to as high as about 7 to l. A typical charge of powder is homogeneously mixed for 1 hour prior to pressing. Where intermediate handling and storage times exceed 48 hours, the powder is stored in evacuated containers under a vacuum level of 10" Torr or better.
  • a 600-gram charge of atomized (spherical shape) and milled (irregular shape) powder is blended and the blended powder is first pre-oxidized at 600 F for 1 hour in air.
  • One method is to uniformly spread the powder of 10 to micron size between two fine mesh stainless steel screens confined within the side walls of a stainless steel tray with side ports to allow the powder to be pre-oxidized similar to a fluid bed system in a recirculating air environment.
  • the powder is visually inspected at ten times magnification under stereo binoculars for oxide color uniformity and to assure absence of agglomeration.
  • An oxygen content of about 3,400 to 4,400 ppm by weight has been found very advantageous, although the oxygen content may vary from about 2,000 to 8,000 ppm.
  • An oxide layer around particles of 10 to 20 microns average size may range in thickness up to about 2 microns.
  • the powder (e.g., 600 to 800 grams) may be directly hot pressed to the desired shape, or the powder charge may be first cold pressed to a cylindrical shape under 300 psi pressure and thereafter hot pressed to form the desired product.
  • the hot pressing is carried out under vacuum (e.g., 5X10 Torr) at a pressure (18,000 psi) sufficient to provide a substantially fully dense sintered body.
  • the hot pressing is preferably carried out at a temperature of about 1,050 C, the temperature being reached in 3 hours, held for 1 hour at temperature and then cooled to black heat in 2 hours.
  • the die and punch assembly is shown schematically in FIG.
  • a graphite foil disc 19A (0.005 inch thick) is placed on the inner end face of punch 19 within cavity 17 as shown; the cavity is lined with graphite foil to provide a sleeve thereof; and the powder material 22 then charged therein from the opposite end.
  • Another graphite foil disc 18A is placed on top of the powder and punch 18 then inserted into the cavity in compression relationship to the powder charge. Pressure is applied to both punches in the direction of arrows 20 and 21 using a 30-ton capacity press.
  • the graphite foil (discs and sleeve) help to eliminate contamination during the hot pressing cycle and also avoids fusion of the powder to the die and punches.
  • a minimum pressure of lbs. (dial reading) is applied from room temperature to l,050 C, at which time the 18,000 psi load is applied and held for 1 hour. Thereafter, the power is shut off and the pressure released. As the pressed part reaches black heat, an Argon back fill is employed to obtain rapid cooling under inert conditions.
  • the density obtained is substantially equal to full density (for example, at least 99.9 percent of theoretical).
  • the cylindrical product is cleaned by grinding or machining and the opposite faces are finished parallel for subsequent cutting into magnetic pole pieces.
  • the final hardness on the Rockwell C" scale is generally at least about 50 R
  • the preferred primary grain size of the final product lies within the ASTM 8 to l 1 range as measured in accordance with ASTM E112 at 100 times magnification.
  • voids and inclusions not exceed a singular defect size greater than 10 microns.
  • the distribution of defects should be such that the average distance between defects is at least 10 times greater than the maximum defect diameter.
  • a fully dense, hot consolidated product produced in accordance with the invention comprises approximately by weight 9.4 percent silicon, approximately 5.7 percent aluminum and the balance essentially iron.
  • the alloy contains oxygen within the preferred range of 3,400 to 4,400 ppm, which provides a metallographic structure having the desired grain boundary oxide film exhibiting optimum wear resistance for magnetic pole pieces produced from the product.
  • FIG. 4 illustrates such a microstructure.
  • actual field testing was employed. Wear rates versus time data have disclosed that the powder metallurgy product exhibits at least a three to one improvement in pole piece life as compared to the same alloy in the conventionally cast form but without oxygen.
  • a powder metallurgy method is provided of producing a hot consolidated magnetically soft ferrous alloy suitable for use in the manufacture of magnetic pole pieces.
  • the ferrous alloy powder contains an effective amount of silicon and aluminum ranging from about 2 to 12 percent sili-con, from about 2 to 10 percent aluminum, about 2,000 to 8,000 ppm oxygen, and the balance essentially iron.
  • the oxygen is added to the powder by pre-oxidation to provide a thin oxide film thereon and then hot consolidated at an elevated temperature sufficient to provide a substantially fully dense sintered body.
  • milled and/or unmilled atomized powder produced from vacuum cast alloy having a particle size range of about 325 mesh 5 microns and, more advantageously, from about 10 to 20 microns, the preferred alloy composition ranging by weight from about 9 to 9.8 percent silicon, about 5.4 to 6 percent aluminum, about 3,300 to 4,400 ppm oxygen, and the balance essentially iron.
  • a particular composition is one containing approximately 9.4 percent silicon, approximately 5.7 percent aluminum, and the balance essentially iron.
  • the sintered body is generally characterized metallographically by a grain size within the ASTM 8 to 11 range.
  • the temperature may range from about 1,000 to l,l00 C with the preferred temperature being about l,050 C.
  • the pressure to achieve substantially full density may range from about 12,000 to 20,000 psi (e.g. 18,000 psi).
  • the preferred temperature of 1,050 C is reached in about 3 hours, the compressed powder being held at temperature for 1 hour and thereafter cooled to black heat in 2 hours.
  • a longer time of pressing is employed, while at the higher temperature range, a lower time interval is used.
  • the temperature may range from about 450 to 650 F and, more preferably, from about 500 to 600 F.
  • a hot consolidated sintered powder metallurgy shape of said magnetically soft ferrous alloy consisting essentially of about 2 to 12 percent silicon, about 2 to percent aluminum, and the balance essentially iron,
  • said sintered alloy being characterized by a thin encapsulating film of thermally produced oxide sur rounding the grains thereof which confer improved wear resistance to said alloy,
  • the amount of oxygen ranging from about 2,000 to 8,000 ppm.
  • the sintered powder metallurgy alloy of claim 1 wherein the average grain size ranges from about 10 to 20 microns, wherein the composition consists essentially of about 9 to 9.8 percent silicon, about 5.4 to 6 percent aluminum and the balance essentially iron, wherein the oxygen content of said alloy rangest from about 3,300 to 4,400 ppm, and wherein the average grain size of said sintered alloy is within the range of about ASTM 8 to 11.
  • a magnetic pole piece formed from a magnetically soft ferrous alloy characterized by improved wear resistance when employed in rubbing contact with a moving magnetic playback tape of gamma iron oxide,
  • pole piece being formed of a sintered alloy composition consisting essentially of about 9 to 9.8 percent silicon, about 5.4 to 6 percent aluminum, and the balance essentially iron,
  • the grain size of said sintered alloy being within the range of about ASTM 8 to 1 l and being characterized by a thin encapsulated film of thermally produced oxide surrounding the grains thereof which confer improved wear resistance to said alloy, the amount of oxygen ranging from about 3,300 to 4,400 ppm.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Powder Metallurgy (AREA)
US00102364A 1970-12-29 1970-12-29 Powder metal magnetic pole piece Expired - Lifetime US3739445A (en)

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US (1) US3739445A (de)
CH (1) CH560956A5 (de)
DE (1) DE2165098C3 (de)
FR (1) FR2120843A5 (de)
GB (1) GB1325248A (de)
IT (1) IT941057B (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019239A (en) * 1973-09-26 1977-04-26 Hoganas Aktiebolag Method of producing magnetite article
US4029501A (en) * 1976-01-26 1977-06-14 Rca Corporation Method of preparing improved magnetic head material
US4069043A (en) * 1976-01-19 1978-01-17 Carpenter Technology Corporation Wear-resistant shaped magnetic article and process for making the same
US4409633A (en) * 1978-03-13 1983-10-11 Akai Electric Company Limited Mn-Zn Single crystalline ferrite head and a method of making the same
US4532737A (en) * 1982-12-16 1985-08-06 Rca Corporation Method for lapping diamond
US5183631A (en) * 1989-06-09 1993-02-02 Matsushita Electric Industrial Co., Ltd. Composite material and a method for producing the same
US5350628A (en) * 1989-06-09 1994-09-27 Matsushita Electric Industrial Company, Inc. Magnetic sintered composite material
US20130160492A1 (en) * 2011-12-23 2013-06-27 Guillermo R Villalobos Polished, hot pressed, net shape ceramics
WO2018037356A1 (en) 2016-08-23 2018-03-01 Medicem Ophthalmic (Cy) Limited Ophthalmic lenses with aspheric optical surfaces and method for their manufacture
US10629370B2 (en) * 2015-07-10 2020-04-21 Toyota Jidosha Kabushiki Kaisha Production method of compact

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5638671B2 (de) * 1972-11-16 1981-09-08
JPS5210819A (en) * 1975-06-12 1977-01-27 Kiyoshi Inoue Malleable high permeability alloy for high frequency
JPS5271311A (en) * 1975-12-11 1977-06-14 Nippon Musical Instruments Mfg Method of producing ironnsiliconnaluminium alloy
JPS5852554B2 (ja) * 1976-10-07 1983-11-24 潔 井上 高周波用可鍛性高透磁率合金
US4561892A (en) * 1984-06-05 1985-12-31 Cabot Corporation Silicon-rich alloy coatings
DE69014210T2 (de) * 1989-01-10 1995-06-22 Matsushita Electric Ind Co Ltd Magnetkopf und Herstellungsverfahren.
CN107866570A (zh) * 2017-12-15 2018-04-03 东北大学 一种用于粉末冶金温压成形的设备

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3661570A (en) * 1970-04-03 1972-05-09 Rca Corp Magnetic head material method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3661570A (en) * 1970-04-03 1972-05-09 Rca Corp Magnetic head material method

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019239A (en) * 1973-09-26 1977-04-26 Hoganas Aktiebolag Method of producing magnetite article
US4069043A (en) * 1976-01-19 1978-01-17 Carpenter Technology Corporation Wear-resistant shaped magnetic article and process for making the same
US4029501A (en) * 1976-01-26 1977-06-14 Rca Corporation Method of preparing improved magnetic head material
US4409633A (en) * 1978-03-13 1983-10-11 Akai Electric Company Limited Mn-Zn Single crystalline ferrite head and a method of making the same
US4532737A (en) * 1982-12-16 1985-08-06 Rca Corporation Method for lapping diamond
US5183631A (en) * 1989-06-09 1993-02-02 Matsushita Electric Industrial Co., Ltd. Composite material and a method for producing the same
US5350628A (en) * 1989-06-09 1994-09-27 Matsushita Electric Industrial Company, Inc. Magnetic sintered composite material
US5352522A (en) * 1989-06-09 1994-10-04 Matsushita Electric Industrial Co., Ltd. Composite material comprising metallic alloy grains coated with a dielectric substance
US20130160492A1 (en) * 2011-12-23 2013-06-27 Guillermo R Villalobos Polished, hot pressed, net shape ceramics
US10629370B2 (en) * 2015-07-10 2020-04-21 Toyota Jidosha Kabushiki Kaisha Production method of compact
WO2018037356A1 (en) 2016-08-23 2018-03-01 Medicem Ophthalmic (Cy) Limited Ophthalmic lenses with aspheric optical surfaces and method for their manufacture

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Publication number Publication date
DE2165098B2 (de) 1975-04-10
CH560956A5 (de) 1975-04-15
IT941057B (it) 1973-03-01
FR2120843A5 (de) 1972-08-18
DE2165098A1 (de) 1972-07-06
DE2165098C3 (de) 1975-11-20
GB1325248A (en) 1973-08-01

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