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WO2004085129A1 - Procede et appareil de fabrication de pieces moulees conductrices par chauffage ohmique - Google Patents

Procede et appareil de fabrication de pieces moulees conductrices par chauffage ohmique Download PDF

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Publication number
WO2004085129A1
WO2004085129A1 PCT/CA2004/000435 CA2004000435W WO2004085129A1 WO 2004085129 A1 WO2004085129 A1 WO 2004085129A1 CA 2004000435 W CA2004000435 W CA 2004000435W WO 2004085129 A1 WO2004085129 A1 WO 2004085129A1
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WO
WIPO (PCT)
Prior art keywords
pellets
psi
polymer
pressure
electrodes
Prior art date
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.)
Ceased
Application number
PCT/CA2004/000435
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English (en)
Inventor
Yuqi Cai
Divya Chopra
John Fisher
Kalyan Ghosh
Larin Godfroy
James R. Guolla
Victor G. Matthews
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
DuPont Canada Inc
Original Assignee
DuPont Canada Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by DuPont Canada Inc filed Critical DuPont Canada Inc
Publication of WO2004085129A1 publication Critical patent/WO2004085129A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/0272—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould using lost heating elements, i.e. heating means incorporated and remaining in the formed article
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0213—Gas-impermeable carbon-containing materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0221—Organic resins; Organic polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0223—Composites
    • H01M8/0226—Composites in the form of mixtures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B29K2105/16—Fillers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/34—Electrical apparatus, e.g. sparking plugs or parts thereof
    • B29L2031/3468—Batteries, accumulators or fuel cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0258—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
    • H01M8/0263—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant having meandering or serpentine paths
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a method and apparatus for making conductive molded parts using resistive heating.
  • the method and apparatus described in this specification are used to mold fuel cell separator plates.
  • Polymer electrolyte membrane fuel cells comprise a membrane electrode assembly disposed between two current separator plates. Within the membrane electrode assembly lays a pair of fluid distribution layers, commonly referred to as gas diffusion layers and an ion exchange membrane. At least a portion of either the ion exchange membrane or gas diffusion layers is coated with noble metal catalysts. The ion exchange membrane is placed between the gas diffusion layers and is compressed to form the membrane electrode assembly.
  • the separator plates provide support to the MEA and act as a barrier, preventing mixing of fuel and oxidant within adjacent fuel cells. The separator plates also act as current collectors.
  • the separator plates may include flow field channels that assist with transport of liquids and gases within the fuel cell.
  • a typical separator plate also includes flow field channels on its surfaces to direct fuel reactants or oxygen, and reaction by-products such as water.
  • Graphite plates with machined flow fields have historically been used as separator plates for fuel cells. Due to their brittleness and high fabrication/machining cost, graphite plates are relatively expensive to make such that they cannot meet the requirements for large-scale commercialization of fuel cells.
  • US Patent No. 4,098,967 to Biddick et al. provides a bipolar plate fonned of thermoplastic resin filled with 40-80% by volume finely divided vitreous carbon.
  • Plastics employed in the compositions include polyvinylidene fluoride and polyphenylene oxide.
  • the plates are formed by compression molding dry blended compositions and possess specific resistance on the order of 0.002 ohm-cm.
  • US Patent No. 4,214,969 to Lawrence discloses a bipolar plate fabricated by pressure moulding a dry mixture of carbon or graphite particles and a fiuoropolymer resin.
  • the carbon or graphite particles are present in a weight ratio to the polymer of between 1.5:1 and 16:1.
  • the polymer concentration is in the range of 6-28% by weight and the volume resistivity of the plate is in the range of 1.2-3.5x10 "3 ohm-in.
  • US Patent No. 4,554,063-85 to Braun et al. discloses a process for fabricating cathode current collectors.
  • the current collector consists of graphite (synthetic) powder of high purity having particle sizes in the range from 10 micron to 200 micron and carbon fibers that are irregularly distributed therein and have lengths from 1 mm to 30 mm, the graphite powder/carbon fiber mass ratio being in the range from 10: 1 to 30:1.
  • the polymer resin used is polyvinylidene fluoride.
  • the resin is dissolved in, for example, dimethylformamide.
  • Graphite powder and carbon fibers are then added and the resulting lubricating grease-like mass is brought to the desired thickness by spreading on a glass plate and is dried for about 1 hour at about 50°C.
  • the plates were also formed by casting, spreading, or extrusion.
  • US Patent No. 5,582,622 to Lafollette discloses bipolar plates comprising a composite of long carbon fibers, a filler of carbon particles and a fiuoroelastomer.
  • PCT publication WO 00/44005 discloses a shaped article having particular use as a conductive plate in a fuel cell having a volume resistivity of less than 10 "2 ohm-cm and being made from a composition comprising about 5 to about 50% by weight of nickel-coated graphite fibers of a length less than 2 cm, and about 0.1 to about 20% by weight of the graphite, of a non-liquid-crystalline thermoplastic binder resin.
  • moulding compositions for providing current collector plates which include conductive fillers in various forms, including powder and fiber.
  • High purity graphite powder is preferred having a carbon content of greater than 98%.
  • the graphite powder preferably has an average particle size of approximately 23 to 26 microns and a BET-measured surface area of approximately 7- 10 m 2 /g.
  • the description indicates that fibers having a surface area of less than 10m 2 /g coupled with a fiber length in excess of 250 microns are typical. Carbon fibers are specifically mentioned in the description.
  • the preferred composition contains 45-95 weight percent graphite powder, 5-50 weight percent polymer resin and 0-20 weight percent metallic fiber, carbon fiber and/or carbon nanofiber.
  • US Patent No. 6,248,467 to Wilson et al. claims a bipolar plate moulded from a thermal setting vinyl ester resin matrix having a conductive powder embedded therein.
  • the powder may be graphite having particle sizes predominantly in the range of 80-325 mesh.
  • Reinforcement fibers selected from graphite/carbon, glass, cotton and polymer fibers are also described.
  • the process for making conductive separator plates includes blending a composition of a polymer and conductive filler, and then heating the blend in a clamped mold under pressure to a temperature above the polymer's glass transition temperature.
  • the molten blend is then cooled down while still under pressure to a second temperature below the glass transition temperature. Subsequently the pressure is released and the molded plate is ejected at this second temperature. It has been found that this second temperature at which the molded article is ejected has an effect the final conductivity of the part. It has also been found that this critical ejection temperature may be material dependent.
  • Thermal cycling refers to the independent steps of heating the blend and then cooling it in a mold in order to manufacture the final separator plate. Heating of the mold can be done by electrically heating the mold parts or by circulating hot oil within the mold parts, whereas cooling is done by circulating a coolant such as water within the mold parts. This type of thermal cycling is time consuming and energy inefficient, and it involves expensive tooling, which can easily fail after several thermal cycles. It is desirable, therefore, to eliminate thermal cycling from the molding process in order to make the process more cost effective and eliminate other wear and tear problems associated with it.
  • the present invention provides a method and apparatus for making conductive molded parts using resistive heating.
  • a method of manufacturing a conductive molded article, in particular a conductive separator plate, from a mixture of polymer and conductive fillers is provided.
  • an apparatus for making conductive molded parts using resistive heating.
  • the preferred embodiment of the present invention can provide many advantages. For example, it eliminates the problems associated with thermal cycling as it involves only a single stage of heating targeted on the compound. It also reduces the cycle time for manufacturing the part as the heat transfer is targeted on the material. The mold/tooling does not need to be heated up or cooled down, thus avoiding unnecessary expansion contraction problems associated with the heating/cooling of the tooling.
  • Figure 1 is schematic drawing of a typical fuel cell
  • Figure 2 is a perspective view of a conductive collective plate
  • Figure 3 is a schematic drawing illustrating the preferred embodiment of the method of the present invention.
  • Figure 4 is a schematic diagram illustrating another embodiment of the method of the present invention.
  • Figure 5 is a cross section view of a preferred apparatus of the present invention used for making conductive molded parts using resistive heating.
  • Figure 6 is a cross section view of another embodiment of the apparatus of the present invention used for making conductive molded parts using resistive heating.
  • the present invention provides a method of manufacturing conductive molded parts, preferably current separator plates for use in fuel cells, using the conductive nature of the compounded material and its ability to heat up under pressure on the passage of an electric current through the material.
  • Resistive heating refers to the heating of the conductive material when an electrical current is passed through the material. The heating occurs because of the increased resistance resulting from poor contact between pellets of the conductive material. Resistive heating is common to many applications but one of the main embodiments of the present invention is the application of resistive heating for molding conductive separator plates for fuel cell applications.
  • a typical polymer electrolyte membrane fuel cell comprises a membrane electrode assembly disposed between two conductive separator plates 5.
  • the membrane electrode assembly includes an ion exchange membrane 10 and two gas diffusion layers 15.
  • conductive separator plates 5 generally comprise at least one flow field channel 20, which allows gas or liquid to flow to and from the fuel cell.
  • the conductive separator plates 5 typically carry either fuel or oxidant on any side of the conductive separator plate 5 depending upon the design of the fuel cell or fuel cell stack.
  • the conductive separator plates 5 are generally manufactured from a blend of a polymer and conductive fillers.
  • the polymer can be any thermoplastic polymer such as a liquid crystalline polymer, polyphenylene sulphide, styrene maleic anhydride, polyvinylidene fluoride, polyolefins or any other polymer having characteristics similar to a thermoplastic polymer.
  • the polymer is an aromatic polyester resin such as that available from E.I. du Pont de Nemours and Company under the trademark ZENITE®.
  • the conductive fillers include graphite particles, graphite fibers, carbon blacks, metal particles, metal fibres, metal-coated fibres, conductive ceramic fillers, carbon nanotubes and mixtures thereof.
  • the conductive fillers may be in any suitable shape such as flakes, spheres, fibres and irregular shapes.
  • Preferred conductive fillers are graphite fibers and graphite powders.
  • the graphite fiber is preferably a pitch-based graphite fiber having a fiber length distribution range from 15 to 500 ⁇ m, a fiber diameter of 8 to 15 ⁇ m, bulk density of 0.3 to 0.5 g/cm 3 and a real density of 2.0 to 2.2 g/cm 3 .
  • the graphite powder is preferably a synthetic graphite powder with a particle size distribution range of 20 to 1500 ⁇ m, a surface area of 2 to 3 m 2 /g, bulk density of 0.5 to 0.7 g/cm 3 and real density of 2.0 to 2.2 g/cm 3 . Further details regarding the composition of the conductive separator plates may be found in U.S. Patent No. 6,379,795 Bl, which is incorporated herein by reference.
  • the method of the present invention involving molding of conductive separator plates using resistive heating is also applicable to blends where the polymer is a thermoset like a vinyl ester, phenol formaldehyde, melamine formaldehyde, etc.
  • the current separator plate is molded from a composition as described in co-pending of PCT patent application no. PCT/CA03/00202 filed February 13, 2003, the complete specification of which is hereby incorporated by reference.
  • the composition includes from about 1 to about 50% by weight of a plastic, from about 0 to about 70% by weight of a graphite fibre filler having fibres with a length of from about 15 to about 500 microns, and from 0 to about 99% by weight of a graphite powder filler having a particle size of from about 20 to about 1500 microns.
  • the plastic is selected from thermoplastic and thermosetting plastics and elastomers, and most preferably the plastic is a thermoplastically processable polymer.
  • the composition comprises:
  • pitch-based graphite fiber fiber length distribution range: 15 to 500 micrometre; fiber diameter: 8 to 10 micrometre; bulk density: 0.3 to 0.5 g/cm 3 ; and real density: 2.0-2.2 g/cm );
  • resistive heating is used to melt a blend of a polymer and conductive fillers, and the molten blend is molded into a conductive part, preferably a separator plate.
  • the general process for resistance heating is set out in U.S. Patent No. 4,673,450 to Burke, which is hereby incorporated by reference. However, its application to the molding of conductive parts has not yet been explored.
  • the present invention is a method of molding a conductive article comprising the steps of:
  • the compounded pellets 30 are conductive and offer insignificant resistance to the passage of the electric current through them. However, the contact resistance between the compounded pellets 30 offer high resistance to electrical current, leading to localized heat build up at the surface of the compounded pellets 30. This heat build up melts the polymer component in the compounded pellets 30, and the molten polymer then fuses together under applied pressure 40.
  • Pressure 40 may be applied after the electric current is passed through the compounded pellets 30 and the polymer is melted.
  • an initial pressure of between about 5 psi and about 100,000 psi, preferably between about 500 and about 50,000 psi, more preferably between about 1000 psi and about 20,000 psi is applied until the maximum current is reached and thereafter further pressure is applied to facilitate fusion of the molten pellets.
  • between about 100 and about 25,000 psi of pressure is applied to the compounded pellets, preferably between about 1000 psi and about 20,000 psi, and more preferably between about 3000 psi and about 15,000 psi.
  • the electric current is applied to the compounded pellets 30 until the polymer component of the pellets is fully melted and fused into a uniform mass or molded part.
  • the resistance of the mass or part decreases and the electric current can then be removed.
  • the decrease in resistance is measured by observing the change in voltage since current is kept constant. Initially, the voltage reduces significantly and eventually levels off at a lower value with time.
  • the fused composition is then allowed to cool under pressure and form into the conductive molded part, such as the separator plate.
  • flow field channels 20 may be molded onto the separator plates before the electric current is removed and the cooling occurs. This can be done by stamping the flow fields onto the fused composition.
  • the electrodes 34 and 36 can also have flow field designs imprinted on one or both of their surfaces, which would result in molded plates with flow fields on one or both sides.
  • the process of the present invention may also be used to mold preforms, which are molded blank plates that are then treated to further processing steps to manufacture the finished conductive article.
  • a preform has a density between the density of the cold compounded pellets and that of the final molded part. This preform can be used in a subsequent stamping operation to obtain the final molded separator plate with flow fields, and with high density and conductivity.
  • FIG 4 illustrates a second embodiment of the present invention.
  • the pellets 30 are fed into a cavity 50 as shown.
  • the core plate 52 and the base plate 54 are clamped in the press.
  • An electrical potential 56 is applied across electrodes 58 and 60.
  • the conductive pellets 30 are heated.
  • the pellets 30 are heated until their polymer component fully melts and are fused into a uniform mass or molded part. When fusion is complete, the resistance of the mass or part decreases and the electric current can then be removed.
  • Figure 5 illustrates in cross section a preferred apparatus for making conductive molded parts using resistive heating.
  • the top plate 70, insert 72, side walls 74 and bottom plate 76 are all made of a conductive material such as brass.
  • the top insulation 78, bottom insulation 80 and insulator tubing 82 are all made of an insulating material.
  • the conductive pellets 30 are placed in the cavity 84 defined by the insert 72 and the bottom plate 76.
  • An electrical potential is applied between the insert 72 and the bottom plate 76 so that an electrical current is caused to pass through the pellets 30.
  • the Pressure (indicated by arrow 86) is applied to top plate 70, for example by a mold clamp.
  • the compounded pellets 30 offer resistance to the passage of electrons, thereby causing the pellets 30 to heat up. The heat and pressure thus help in molding the conductive compounded pellets 30 into the final desired shape.
  • the electrical potential 85 and pressure 86 are removed and the molded part is removed.
  • the final molded part is preferably in the shape of a disc of 2.65 cm diameter. It will be noted that in the apparatus of Figure 5, the direction of the pressure 86 is parallel to the direction of flow of electrical current between the insert 72 and the bottom plate 76. [0063] A second embodiment of the apparatus of the present invention is illustrated in Figure 6.
  • the core plate 90, side walls 92 and base plate 94 are made of an insulator material. Only the two electrodes 96 and 98 are made up of electrically conductive material like brass.
  • a cavity 100 is defined by the core plate 90, side walls 92, base plate 94 and electrodes 96 and 98.
  • the compounded pellets 30 are fed into the cavity 100 as shown.
  • the core plate 90 and base plate 94 are clamped under pressure 102.
  • An electrical potential 104 is applied between electrodes 96 and 98. At the onset of an electric current passing through pellets 30, the conductive pellets 30 begin to heat up.
  • the electrical potential can be removed and core plate 90 is undamped to remove pressure 102.
  • the molded part may then be ejected.
  • the final molded part is preferably a 3"x3" square.
  • the pellets 30 are relatively heated more quickly than in the case of the apparatus of Figure 5 because the distance that the electrons must travel across the pellets 30 is longer.
  • the direction of the pressure 102 is perpendicular to the direction of flow of current between electrodes 96 and 98.
  • the methods of the present invention may be used to mold conductive articles like bipolar plates, pump parts, conductive bins, conductive protective caps etc..
  • the conductive pellets 30 are sandwiched between the electrodes at a certain pressure and electric current is passed from one electrode to the other through the pellets 30. This melts the plastic and the pressure compacts and fuses the molten material into a mass or molded part. The part is ejected after it cools, preferably down under pressure.
  • a conductive compounded mixture of ground liquid crystalline polymer, graphite fiber and graphite powder as described for Example 1 was melted and pressed into a disk using an Enerpac® press and a molding apparatus.
  • the molding apparatus consisted of a core and a cavity as shown in Figure 5 forming two electrodes insulated by an insulator tube.
  • the electrodes were connected to a portable Miller® arc welder that supplied an electrical current with a maximum voltage of 23 volts and a current of 80 amperes.
  • the size of the compounded pellets ranged from 4- 12mm.
  • Sample A was prepared using an electrical current of 5.3 volts and 50 amperes and an applied pressure of 300 psi for 60 seconds. Pressure was applied to the compounded material directly after the electrical current was applied.
  • Sample B was prepared under an electrical current of 6.5 volts and 50 amperes and an applied pressure of 300 psi for 60 seconds. The electrical current was applied to the compounded material for 15 seconds before the pressure was applied to the sample. [0073] An initial pressure of 100 psi was applied to Sample C until the electrical current reached 6.5 volts and 50 amperes. The initial pressure was applied for 60 seconds and then increased to 1550 psi for another 60 seconds.
  • a conductive compounded mixture of ground liquid crystalline polymer, graphite fiber and graphite powder as in Example 1 was melted and pressed into a disk with 2.65 cm diameter using a Wabash® press and the molding apparatus described in Example 2.
  • the molding apparatus was placed between the Wabash® press and the cavity of the mold was filled with the compounded material.
  • the clamps of the Wabash® press were closed over the sample at a first low pressure (Pi) to compress the compounded material lightly while offering high resistance to the passage of electrical current.
  • Electric current was passed through the material for a time (t ⁇ ) and the pressure was increased to a second pressure (P 2 ) for a second length of time (t 2 ). The electric current was then stopped and the material was allowed to cool.
  • Table 2 Properties of Sample Compositions
  • the apparatus illustrated in Figures 4 and 6 was used in order to try to further improve the properties of the final molded plate.
  • the objective was to mold a 3"x 3" blank plate having a thickness of 2 - 2.5 mm.
  • the electrical current was made to pass through the longest possible distance across the compounded pellets in order to maximize resistance.
  • the direction of the applied pressure was perpendicular to the direction of the flow of current.
  • This molding apparatus was placed between the clamps of the Wabash® press and the cavity of the mold was then filled with the compounded pellets.
  • the clamps of the Wabash® press were closed at pressure, P.
  • the electrical current was passed through the compounded material for time, t.
  • the voltage, V and current, A were measured during time, t.
  • the resistance, R was then calculated by dividing Voltage, V by current, A. At the end of time, t the mold was cooled under pressure, P for cooling time tl seconds. The density, contact resistivity and flexural properties of the molded plates were then measured.
  • the compounded material consisted of 80%> graphite powder (Thermocarb® from Conoco) and 20% Zenite® 800, which was melt blended using a Buss® kneader.
  • the compounded material was resistive molded into 3"x3" plates using the apparatus described above.
  • the process parameters and final plate properties are summarized in Table 3 below.
  • Table 3a Process parameters for resistive molded 3"x3" plates molded with
  • Table 3b Properties of resistive molded 3"x3" plates molded with 80% Thermocarb® and 20% Zenite® 800 compound.
  • the compounded material consisted of 70% graphite powder (Thermocarb® from Conoco) and 30% Zenite® 800, which was also melt blended using a Buss® kneader. The compounded material was resistive molded into 3"x3" plates. The process parameters and final plate properties are summarized in Table 4 below.
  • Table 4a Process parameters for resistive molded 3"x3" plates molded with 70% Thermocarb® and 30 % Zenite® 800 compound.
  • Table 4b Properties of resistive molded 3"x3" plates molded with 70% Thermocarb® and 30% Zenite® 800 compound.
  • the preferred method of the present invention also permitted conductive parts to be molded in about 60 seconds. This promises that significantly lower cycle times may be obtained compared to the existing compression molding technology.

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  • Manufacturing & Machinery (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

L'invention concerne un procédé et un appareil servant à mouler une plaque de séparation conductrice destinée à être utilisée dans une pile à combustible, à partir de pastilles (30) comprenant un composant polymérique et des matières de charge conductrices. Le procédé de l'invention met en oeuvre un chauffage ohmique destiné à faire fondre le composant polymérique. Le procédé consiste à: placer les pastilles dans un moule (31) et entre deux électrodes (34, 36); appliquer sur les électrodes un potentiel électrique pour fair passer un courant électrique au travers des pastilles afin de créer sur ces dernières une chaleur localisée pouvant faire fondre leur composant polymérique; appliquer une pression (40) sur les pastilles; laisser fondre le polymère; cesser d'appliquer le potentiel électrique sur les électrodes; et laisser le polymère en fusion refroidir sous pression pour former la plaque de séparation conductrice.
PCT/CA2004/000435 2003-03-25 2004-03-24 Procede et appareil de fabrication de pieces moulees conductrices par chauffage ohmique Ceased WO2004085129A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US45740603P 2003-03-25 2003-03-25
US60/457,406 2003-03-25

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010031586A1 (fr) * 2008-09-22 2010-03-25 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Procédé pour déformer des objets ainsi qu'objets déformables
WO2017095532A3 (fr) * 2015-10-12 2017-10-19 Rapid Heat Sinks, LLC Câble en fibres de carbone cristallines et son procédé de fabrication
DE102024109704A1 (de) * 2024-04-08 2025-10-09 PE-Innovation.UG (haftungsbeschränkt) Vorrichtung und Verfahren zur Herstellung von Bipolar-Platten für einen Brennstoffzellenstack

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US4252513A (en) * 1978-08-29 1981-02-24 Mcphersons Limited Process for curing thermosetting resins and elastomers
EP0586707A1 (fr) * 1992-02-27 1994-03-16 Sumitomo Chemical Company, Limited Materiau electro-durcissable, ses applications et son procede de mise en uvre
WO2000002268A2 (fr) * 1998-07-01 2000-01-13 Ballard Power Systems Inc. Ensemble d'electrodes membranes assurant l'interconnexion des voies d'ecoulement de gaz reactifs dans les piles a combustible ondulees
WO2000044005A1 (fr) * 1999-01-19 2000-07-27 E.I. Du Pont De Nemours And Company Compositions de cristaux liquides polymeres, thermoplastiques, aromatiques, conductrices et moulables par injection
US20030044483A1 (en) * 2001-09-05 2003-03-06 Cabak James E. Compression molding with protective sleeves for preforms

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010031586A1 (fr) * 2008-09-22 2010-03-25 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Procédé pour déformer des objets ainsi qu'objets déformables
WO2017095532A3 (fr) * 2015-10-12 2017-10-19 Rapid Heat Sinks, LLC Câble en fibres de carbone cristallines et son procédé de fabrication
US10471628B2 (en) 2015-10-12 2019-11-12 Rapid Heat Sinks, LLC Crystalline carbon fiber rope and method of making same
DE102024109704A1 (de) * 2024-04-08 2025-10-09 PE-Innovation.UG (haftungsbeschränkt) Vorrichtung und Verfahren zur Herstellung von Bipolar-Platten für einen Brennstoffzellenstack

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