EP0698435B1 - Procédé et installation de la métallurgie des poudres comprenant une lubrification électrostatique des parois de la matrice - Google Patents

Procédé et installation de la métallurgie des poudres comprenant une lubrification électrostatique des parois de la matrice Download PDF

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Publication number
EP0698435B1
EP0698435B1 EP19950113167 EP95113167A EP0698435B1 EP 0698435 B1 EP0698435 B1 EP 0698435B1 EP 19950113167 EP19950113167 EP 19950113167 EP 95113167 A EP95113167 A EP 95113167A EP 0698435 B1 EP0698435 B1 EP 0698435B1
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European Patent Office
Prior art keywords
die
lubricant
die cavity
metal powder
metal
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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
Application number
EP19950113167
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German (de)
English (en)
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EP0698435A1 (fr
Inventor
Ion I. c/o Quebec Metal Powders Ltd. Inculet
James D. c/o Quebec Metal Powders Ltd. Brown
J.S. Peter c/o Quebec Metal Powders Ltd. Castle
Peter c/o Quebec Metal Powders Ltd. Hansen
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Quebec Metal Powders Ltd
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Quebec Metal Powders Ltd
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Priority claimed from US08/479,464 external-priority patent/US5682591A/en
Application filed by Quebec Metal Powders Ltd filed Critical Quebec Metal Powders Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J3/00—Lubricating during forging or pressing
    • 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
    • B22F3/02—Compacting only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B30—PRESSES
    • B30B—PRESSES IN GENERAL
    • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
    • B30B15/0005—Details of, or accessories for, presses; Auxiliary measures in connection with pressing for briquetting presses
    • B30B15/0011—Details of, or accessories for, presses; Auxiliary measures in connection with pressing for briquetting presses lubricating means
    • 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
    • B22F3/02—Compacting only
    • B22F2003/026—Mold wall lubrication or article surface lubrication

Definitions

  • This invention relates to ferrous powders and, in particular, to the compaction of such materials to form metal composite parts using powder metallurgy.
  • metal powders are pressed in a-die cavity to form a green compact which is then heat treated to form a metal composite part.
  • P/M powder metallurgy
  • a considerable amount of friction is generated between the metal powders and the surfaces defining the die cavity, causing both adhesive wear on the die surfaces and breakage of the green compact when it is released from the die cavity.
  • lubricants have been previously added to the metal powder mixture. These are generally referred to as internal lubricants since they are dispersed throughout the portion of metal powders to be compacted.
  • wet lubricants have not been used successfully since they promote clumping of the metal powder, thereby precluding the good flow characteristics normally desired of P/M materials. Dry lubricants have been used successfully since they are non-binding, and do not affect flow characteristics. Dry lubricants typically function by melting due to the pressure and temperature employed during compaction, thereby allowing the melted lubricant to flow. However, one consequence of the inclusion of any internal lubricant in the metal powder formulation is that the attainable final density and the strength of the metal composite part thus produced are less than theoretically possible when no lubricant is added.
  • Prior attempts to eliminate the inclusion of internal lubricant in the metal powder composition focused on spraying lubricants in liquid form on the die wall.
  • these lubricants included both liquid lubricants and dry lubricants that were dispersed in solvents.
  • drawbacks in the size and shape of the green compact arise due both to poor metering and distribution of liquid applied to the die wall.
  • use of dispersed dry lubricants poses numerous health, safety and environmental hazards due to the presence of volatile solvents. While the present inventors believed that it would have been useful to directly apply dry lubricants to the die wall surfaces, no apparatus or method for doing so was previously available.
  • FR-A 2 253 570 discloses an apparatus for lubricating of die molds wherein a selected lubricant is corona charged and thereafter applied to the inner walls of the mold on which the lubricant particles adhere. This apparatus still involves some of the disadvantages described above.
  • Another object of the present invention is to provide an apparatus capable of uniformly spraying a dry or wet lubricating material onto a die surface.
  • an apparatus for spraying a wet or dry lubricating material comprising: spraying means for spraying the lubricating material; charging means for applying an electrical charge to the lubricating material; and means for imparting a reversing potential to an electrode disposed on a powder metallurgy die.
  • the potential causes an electrical attraction to take place between the charged lubricating material and the powder metallurgy die.
  • the present invention provides a method for making a green compact comprising:
  • the present invention relates to a process for making a metal composite part comprising the steps above and further comprising:
  • the die cavity and the metal powder composition may be preheated to a high temperature of up to 371,1°C (700°F) prior to the compacting step.
  • the metal powder composition may be electrostatically charged, such as with triboelectric charging.
  • the present invention relates to a powder metallurgy apparatus comprising:
  • the lubricant is electrostatically applied to the wall surfaces of the die in either liquid or solid form. More specifically, the lubricant is electrostatically applied in the form of an aerosol of fine liquid droplets or solid particles.
  • the liquid droplets or solid particles have a size of 100 microns or less, more preferably 50 microns or less and most preferably 15 microns or less.
  • a thin lubricating coating can be applied quickly and uniformly on die wall surfaces which are at least partially conducting.
  • the electrostatically sprayed droplets or particles are drawn to and held on the wall surfaces by image forces which are induced by the approaching charged particle.
  • the same forces, combined with the space charge of the cloud of droplets or particles, allow the droplets or particles to wrap around corners so as to cover all parts of the wall surfaces.
  • the coating is uniform because the charge retained on previously deposited particles tends to deflect incoming particles or droplets to uncovered sites.
  • Suitable apparatus for electrostatically applying lubricating materials in conformity with the present invention include, for example the following components: a nozzle for spraying a solid or liquid lubricant; a substrate which constitutes a P/M die disposed beneath the nozzle and a polarity reversing DC high-tension power source.
  • lubricant is sprayed from the nozzle and is provided with a triboelectric charge.
  • the die is connected to ground, electrical attraction acts between the lubricating material and the die, and the lubricant reaches the P/M die to be deposited thereon.
  • a reversible DC voltage of from 100 V-50 kV is applied to an electrode which is electrically isolated from the die to enhance the attraction of the unipolarly charged lubricant to the die.
  • the lubricants that can be electrostatically sprayed in accordance with the present invention ideally have a low electrical conductivity and sufficient resistivity so that the charges are retained in the deposited droplets or particles for a sufficient period of time to ensure adherence to the die wall surfaces.
  • the lubricants can be in either dry or liquid forms.
  • Suitable dry lubricants include metal stearates, such as zinc stearate, lithium stearate, and calcium stearate, ethylene bistearamide, polyolefin-based fatty acids, polyethylene-based fatty acids, soaps, molybdenum disulfide, graphite, manganese sulfide, calcium oxide, boron nitride, polytetrafluoroethylene and natural and synthetic waxes.
  • metal stearates such as zinc stearate, lithium stearate, and calcium stearate
  • ethylene bistearamide polyolefin-based fatty acids, polyethylene-based fatty acids, soaps, molybdenum disulfide, graphite, manganese sulfide, calcium oxide, boron nitride, polytetrafluoroethylene and natural and synthetic waxes.
  • ethylene bistearamide such as that sold commercially by L
  • Suitable liquid lubricants include liquid-dispersed solid lubricants discussed above; oil-based lubricants such as petroleum oils, silicone oils, and hydrocarbon oils; solvent-based lubricants such as polyglycols and polyphenyl ethers; and water-based lubricants such as soaps and aqueous wax emulsions.
  • All solid and liquid lubricants may be used as single component lubricants, or may be used in admixtures of two or more lubricants. Additionally, solid and wet lubricants of various types may be used in any combination as may be desired.
  • lubricant in solid particle or liquid droplet form is ejected from nozzle which is preferably provided by a Tribogun®.
  • the solid lubricant particles may be sprayed dry or, if desired, dispersed in any suitable solvent or solvent system.
  • the solid lubricant particles or liquid lubricant droplets may be ejected in air, or in another dispersant such as isopropyl alcohol, n-hexane, butane, Freon® fluorinated hydrocarbon (trademark of E. I. Du Pont de Nemours & Co.) and the like. If a dispersant other than air is used as a medium for dispersing solid lubricant particles or liquid lubricant droplets, the dispersant is allowed to subsequently evaporate.
  • the lubricant particles or droplets are electrostatically sprayed to a thickness such that the ejection pressure required to eject the green compact is minimized.
  • the thickness can be varied to achieve desirable ejection forces to the extent that it does not affect P/M properties.
  • the type of metal powder composition used in the present invention may be any conventional metal powder composition, including but not limited to iron, steel, or steel alloyed powders.
  • Typical iron powders are the Atomet® iron powders manufactured by Quebec Metal Powders Limited (QMP) of Tracy, Quebec, Canada, the assignee of the present invention.
  • Typical steel or steel alloyed powders include Atomet® 1001, 1001 HP, 4201, 4401, and 4601 manufactured by QMP.
  • the metal powder generally has a maximum particle size of less than about 300 microns, preferably less than about 212 microns.
  • the metal powder may also be bound with a suitable binder such as those disclosed in U.S. Patent Nos. 3,846,126; 3,988,524; 4,062,678; 4,834,800; and 5,069,714, the disclosures of which are hereby incorporated by reference. Those skilled in the art readily will be able to identify alternative or equivalent metal powders.
  • the lubricant is electrostatically charged by triboelectric charging.
  • the lubricant may be so charged by passing the composition on a puff of air through a coiled Teflon tube.
  • the charge-to-mass ratio of the triboelectrically charged lubricant should be above 0.2 ⁇ C/g, generally above 0.6 ⁇ C/g, with a charge-to-mass ratio of greater than about 1.2 ⁇ C/g being preferred. Of course, the polarity of the charge-to-mass ratio may vary depending upon the materials selected.
  • the total charge of the charged lubricant may be measured with an electrometer. (The charge-to-mass ratio may be measured by collecting the charged lubricant in a double Faraday pail. The mass of the composition charged is readily determined by carefully removing all powder collected in the Faraday pail and weighing on a standard balance with a sensitivity of 1 mg.)
  • the metal powder composition is compacted in a die 4 of any desired shape.
  • the die may be adapted to include warm pressing and any configuration to achieve near net shape compaction and to facilitate ejection from the die cavity.
  • Compaction can be conducted with any process, including warm pressing and cold pressing.
  • warm pressing is conducted at a pressure of about 4.63 ⁇ 10 8 Pa to 9.27 ⁇ 10 8 Pa [30 to 60 tsi (tons per square inch)] and at a temperature of about 50 to 300°C
  • cold pressing is conducted at a pressure of about 2.32 ⁇ 10 8 Pa to 9.27 ⁇ 10 8 Pa [15 to 60 tsi] and at a temperature of about 15 to 50°C.
  • the green compact After the green compact is ejected from the die cavity, it is sintered to form the metal composite part. Any conventional sintering process can be employed to form the metal composite part according to the present invention. Preferably, sintering is conducted at a temperature of 1,000 to 1,300°C and for a period of 10 to 60 minutes. Since the green compact may preferably omit all internal lubricant, the sintering may include induction heating. In this event, presintering may be omitted.
  • this invention is also suitable for use in any P/M process, for example, including the organic binding processes such as those disclosed in U.S. Patent No. 5,069,714, the double-press double-sinter processes such as those disclosed in commonly assigned co-pending U.S. Patent Application Serial No. 08/067,282, filed May 26, 1993, and the processes for manufacturing a soft composite iron material such as those disclosed in commonly assigned co-pending U.S. Patent Application Serial No. 08/060,965 filed May 14, 1993.
  • the metal composite part made according to the present invention is capable of achieving, if desired, a final density of greater than 7.30 g/cm 3 and/or a sintered strength of greater than 2,000 MPa.
  • Particularly high green densities may be achieved in accordance with the present invention when the pressed compositions contain from small amounts of internal lubricant, on the order of 0.1 - 0.4 wt. %, preferably 0.2 - 0.3 wt. % (in contrast to the 0.75 wt. % commonly used conventionally, in the absence of die wall lubrication).
  • a rectangular (TRS) die having wall surfaces will be electrostatically sprayed with a solid Acrawax® lubricant by blowing Acrawax® particles by means of compressed air into a tribogun. The charged particles will then be sprayed onto the die wall surfaces.
  • the die will then be heated to a temperature of 80°C and a metal powder composition of Atomet® 4401 + 1.0% Cu + 2.2% Ni + 0.7% C will be injected.
  • the metal powder composition will then be compacted in the die at pressures of 4.63 ⁇ 10 8 Pa, 6.18 ⁇ 10 8 Pa, 7.72 ⁇ 10 8 Pa and 9.27 ⁇ 10 8 Pa [30, 40, 50, and 60 tsi] while the die temperature is maintained at 250°C.
  • the predicted compressibility curve is illustrated in Figure 1.
  • Example 1 The process as described in Example 1 was conducted except that 0.5% zinc stearate solid lubricant was ⁇ blended in the metal powder composition and the die was not electrostatically sprayed with any lubricant.
  • the compressibility curve is illustrated in Figure 1 and the green and sintered properties of the compacts at 50 tsi are shown in Table 1.
  • both the green strength of the green compact and the sintered strength of the metal composite part formed by compacting the metal powder composition in the die electrostatically sprayed with graphite will be substantially higher than those formed by compacting the metal composition blended with 0.5% zinc stearate in the die not electrostatically sprayed with any lubricant.
  • the final density will be higher for the metal composite part formed by compacting in the die electrostatically sprayed with graphite.
  • a rectangular die having wall surfaces will be electrostatically sprayed with Acrawax lubricant by blowing Acrawax particles by means of compressed air into a tribogun in which the graphite particles are charged by direct current.
  • the charged particles will then be sprayed onto the die wall surfaces and a metal powder composition of Atomet® 1001 will be injected into the lubricated die.
  • the metal powder composition will then be cold pressed in the die at pressures of 4.63 ⁇ 10 8 Pa, 6.18 ⁇ 10 8 Pa and 7.72 ⁇ 10 8 Pa [30 tsi, 40 tsi, and 50 tsi].
  • the predicted compressibility curve is illustrated in Figure 1.
  • Example 2 The process as described in Example 2 was conducted except that 0.4% zinc stearate solid lubricant was added to the metal powder composition and the die was not electrostatically sprayed with any lubricant.
  • the resultant compressibility curve is illustrated in Figure 1.
  • green compacts formed by warm pressing metal powder compositions in a die electrostatically sprayed with a Acrawax lubricant will have a green density ranging from about 7.0 to about 7.5 g/cm 3 , which is higher than the green density range of about 6.9 to 7.4 g/cm 3 achieved by green compact formed by warm pressing the metal powder compositions blended with 0.5% zinc stearate in a die that was not electrostatically sprayed with any lubricant.
  • green compacts formed by cold pressing metal powder compositions in a die electrostatically sprayed with Acrawax lubricant will have a lower green density at 4.63 ⁇ 10 8 Pa and 6.18 ⁇ 10 8 Pa [30 and 40 tsi] than green compacts formed from cold pressing metal powder compositions blended with 0.4% zinc stearate in a die that was not electrostatically sprayed with any lubricant.
  • the green density of both will be substantially the same.
  • Metal powder compositions of Atomet® 1001 will be separately blended with 0.0, 0.2, and 0.4% Acrawax® C ethylene bistearamide wax, and will be cold pressed at various pressures in a die whose wall surfaces will have been previously electrostatically sprayed with zinc stearate.
  • the predicted compressibility and green strength curves are shown in Figure 2 and Figure 3, respectively.
  • Figures 2 and 3 demonstrate the predicted effects of including a solid lubricant in the metal powder composition prior to compaction.
  • Figure 2 shows that including a solid lubricant in the metal powder composition will have minimal effect on the green density of the green compact at move than 6.18 ⁇ 10 8 Pa [tsi greater than 40].
  • Figure 3 shows that the green strength of the green compact that will be formed by compacting the metal powder composition with no Acrawax® C will be substantially higher than the green strength of the metal powder compositions blended with 0.2 and 0.4% Acrawax C.
  • the lubricants were applied to a test die constructed of two aluminum cylinders and an acrylic base such that the base held the two cylinders in place with a constant distance of 1.3 cm between them.
  • the cylinders projected 3.5 cm above the acrylic base, leaving an annular cavity 1.3 cm and 3.5 cm in cross-section.
  • the outside diameter of the cavity was 12 cm.
  • the charged lubricants emerged from the Teflon® tube approximately 10 cm above the test die but were not deposited uniformly or with adequate quantity on the walls of the die cavity.
  • the charge-to-mass ratio for each lubricant was calculated by dividing the total charge by the mass of powder collected in the Faraday pail. In the case of the graphite and boron nitride powders the results were erratic with some changes in polarity. Both the Acrawax® and lithium stearate powders charged positively.
  • Table 2 shows the measured charge-to-mass ratio for five samples of each of Acrawax® or lithium stearate, and the average charge-to-mass ratio of the respective five samples.
  • Sample Acrawax®, ⁇ C/g lithium stearate, ⁇ C/g 1 (+)2.32 (+)1.50 2 (+)1.89 (+)0.69 3 (+)2.52 (+)1.05 4 (+)2.25 (+)2.40 5 (+)2.42 (+)1.40 Average (+)2.28 (+)1.41
  • a ring electrode was placed around the outside of the die. A potential was applied to the electrode and a puff of triboelectrically charged lubricant was deposited in the die as described above.
  • Deposition in the die of the charged lubricant occurred very quickly and provided a thick, uniform layer of charged lubricant on one surface of the die.
  • charged lubricant was deposited only on the outside surface of the inside ring of the die; with a reversal in polarity, charged lubricant was deposited only on the inside surface of the outside ring of the die.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Powder Metallurgy (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Claims (13)

  1. Procédé pour fabriquer un compact vert comportant les étapes consistant à :
    fournir une matrice ayant une cavité définie par des surfaces de paroi,
    choisir une composition de poudre métallique adaptée pour la métallurgie des poudres,
    choisir un lubrifiant de paroi de matrice adapté pour la métallurgie des poudres,
    charger triboélectriquement le lubrifiant avec un rapport charge sur masse situé au-dessus de 0,2 µC/g,
    attirer électrostatiquement ledit lubrifiant chargé sur une surface de paroi de ladite matrice,
    charger de manière réversible la polarité de la matrice,
    remplir la cavité de matrice avec la composition de poudre métallique, et
    compacter ladite composition de poudre métallique située dans ladite matrice pour former un compact vert.
  2. Procédé selon la revendication 1, dans lequel le lubrifiant est pulvérisé électrostatiquement sous forme sèche.
  3. Procédé selon la revendication 2, dans lequel le lubrifiant est pulvérisé électrostatiquement sous forme de particules solides.
  4. Procédé selon la revendication 1 ou 3, dans lequel ledit compactage est effectué à une température d'environ 50°C à 300°C.
  5. Procédé selon la revendication 4, dans lequel le lubrifiant est choisi parmi des stéarates métalliques, le bistéaramide d'éthylène, des acides gras à base de polyoléfine, des acides gras à base de polyéthylène, des savons, le disulfure de molybdène, le graphite, le sulfure de manganèse, l'oxyde de calcium, le nitrure de bore, le polytétrafluoroéthylène ou des cires naturelles ou synthétiques.
  6. Procédé selon la revendication 1, dans lequel le lubrifiant est choisi parmi des lubrifiants solides dispersés dans du liquide, des lubrifiants à base d'huile, des lubrifiants à base de solvant, et des lubrifiants à base d'eau.
  7. Procédé selon la revendication 4, dans lequel la composition de poudre métallique est choisie parmi le fer, l'acier, ou des poudres d'acier allié.
  8. Procédé selon la revendication 7, dans lequel la composition de poudre métallique n'est pas mélangée avec un lubrifiant quelconque.
  9. Procédé selon l'une quelconque des revendications 1 à 3, comportant de plus les étapes consistant à :
    enlever ledit compact vert de la matrice, et
    fritter ledit compact vert pour former une partie métallique composite.
  10. Procédé selon la revendication 9, dans lequel la partie métallique composite a une densité supérieure à 7,30 g/cm3.
  11. Procédé selon la revendication 9, dans lequel la partie métallique composite a une résistance frittée supérieure à 2000 MPa.
  12. Dispositif de métallurgie des poudres comportant :
    des moyens pour recevoir une matrice ayant une cavité de matrice,
    des moyens de chargement triboélectrique pour charger un matériau lubrifiant de paroi de matrice,
    des moyens de pulvérisation pour pulvériser le matériau lubrifiant chargé triboélectriquement dans ladite cavité de matrice,
    des moyens pour produire un champ électrique d'inversion dans ladite cavité de matrice, et
    des moyens pour chauffer ladite cavité de matrice.
  13. Dispositif de métallurgie des poudres comportant :
    des moyens pour recevoir une matrice ayant une cavité de matrice,
    des moyens de chargement triboélectrique pour charger un matériau lubrifiant de paroi de cavité,
    des moyens de pulvérisation pour pulvériser le matériau lubrifiant chargé triboélectriquement dans ladite cavité de matrice,
    des moyens pour produire un champ électrique d'inversion dans ladite cavité de matrice, et
    des moyens pour chauffer un mélange de poudres et des moyens d'introduction pour intoduire le mélange de poudres chauffé dans ladite cavité de matrice.
EP19950113167 1994-08-24 1995-08-22 Procédé et installation de la métallurgie des poudres comprenant une lubrification électrostatique des parois de la matrice Expired - Lifetime EP0698435B1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US479464 1983-03-28
US29497994A 1994-08-24 1994-08-24
US08/479,464 US5682591A (en) 1994-08-24 1995-06-07 Powder metallurgy apparatus and process using electrostatic die wall lubrication
US294979 2001-06-04

Publications (2)

Publication Number Publication Date
EP0698435A1 EP0698435A1 (fr) 1996-02-28
EP0698435B1 true EP0698435B1 (fr) 2000-04-19

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EP (1) EP0698435B1 (fr)
JP (1) JP3383731B2 (fr)
CA (1) CA2156872C (fr)
DE (1) DE69516343T2 (fr)
ES (1) ES2147583T3 (fr)

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GB0517952D0 (en) 2005-09-02 2005-10-12 Avx Ltd Method of forming anode bodies for solid state capacitors
JP5673364B2 (ja) * 2011-06-02 2015-02-18 トヨタ自動車株式会社 離型剤の塗布方法と塗布装置
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Also Published As

Publication number Publication date
JPH08100203A (ja) 1996-04-16
JP3383731B2 (ja) 2003-03-04
EP0698435A1 (fr) 1996-02-28
ES2147583T3 (es) 2000-09-16
DE69516343D1 (de) 2000-05-25
DE69516343T2 (de) 2000-10-19
CA2156872C (fr) 2005-08-23
CA2156872A1 (fr) 1996-02-25

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