- Email: [email protected]
Sealant with exfoliated graphite
about the gasket apertures which surround the combustion chambers, to augment the sealing pressure in those locations, it is feasible to apply the sinter overlays to other regions of the metal plate. Depending on the mode of application, the pressure-resistant overlays are combined with beads or elastomer overlays and synthetic resin overlays on the metal plate. In the case of multi-plate metal seals the pressureresistant overlays may be applied to one or more metal plates.
Polymer electrolyte fuel cell Title: Polymer electrolyte fuel cell Patent number: US 6210823 Date: 3 April 2001 Inventors: K. Hatoh et aL Assignee: Matsushita Electric Industrial Co
Ltd, Osaka-fu, Japan The invention relates to a polymer electrolyte fuel cell, in which a gaseous fuel, such as hydrogen, and an oxidant gas, such as air, are subjected to electrochemical reactions at gas diffusion electrodes, to simultaneously generate electricity and heat. A pair of catalytic reaction layers, mainly comprising a platinum metal catalyst on carbon powder, are attached to opposite faces of a polymer electrolyte membrane, which selectively transports hydrogen ions. A pair of gas-permeable, electrically conductive diffusion layers is arranged on the outer faces of the catalytic reaction layers, to constitute an electrode. A pair of conductive separator plates is arranged across the membraneelectrode assembly to mechanically fix the assembly and electrically connect the assembly in series. Part of the separator plate in contact with the electrode has a gas flow path to feed fuel gas to the electrode and to exhaust the gas from the reaction, with any excess gas. The unit cell includes a pair of electrodes, each with a catalytic layer, arranged across the membrane to yield a membrane-electrode assembly (MEA). The circumferential part of the membrane is interposed between a pair of sealing members, and a pair of separator plates are arranged across the MEA. A separator plate has a gas flow path for feeding gaseous fuel or oxidant gas to the electrode. The sealing member prevents the hydrogen and the air from leaking out of the fuel cell or from being mixed with each other. There is
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one separator plate with a gas flow path on one surface and a flow path for cooling water on its other surface for every two cells. An O-ring is interposed between the separator plates with the water coolant flow path, in order to prevent a leak. Another technique for preventing leaks of the gases and the cooling water arranges gaskets - of an appropriate resin or metal, and with the same thickness as the electrode - around the electrodes. In this structure, the clearance between the separator plate and the gasket is sealed with grease or adhesive. The clearance between the water coolant separator plates is also sealed with grease or adhesive. In such a structure, O-rings and gaskets are required to seal the heat transfer medium. These O-rings should be compressed to ensure sufficient electrical conductivity across the cooling plate. In such sealing methods a constant compressive force is required to maintain sufficient sealing. One structure inserts a coiled or disc spring between the tie rod and end plate. The compressive force ensures electrical contact between the respective constituents of the cells. In a structure that disposes the sealing members or O-rings around the electrodes in order to seal the gas, a relatively large plane pressure is required. This arrangement presses the sealing member or part between the pair of separator plates, to maintain sufficient sealing. It is thus required to maintain a relatively large compressive force. However, this makes the fastening mechanism including the end plates and the tie rods bulky and heavy, whereas the fuel cell is required to have less total weight. Long-term application of pressure to the seals and electrodes causes distortion of the constituents and so lowers the plane pressure required. A mechanism for absorbing the distortion is thus required in the fastening mechanism. One mechanism for this purpose installs a spring on the end of the tie rod. This also makes the whole fuel cell undesirably bulky. This fastening mechanism includes: •
An end plate at each end of the stack of cells.
•
An auxiliary plate outside the first end plate.
•
At least one means of restraint, which has a band-like shape and restrains a member on one end of an assembly, including the cell stack, the two end plates and the auxiliary plate, and a second member on the other end of the assembly to restrict separation or unfastening of the two members.
•
A screw fitted in a threaded hole in the auxiliary plate in such a way that the end of the screw comes into contact with the first end plate.
A means of compression that generates a repulsive force to compress the cell stack when the screw is fitted in the threaded hole of the auxiliary plate. In one mode of this invention, the auxiliary plate includes an elastic metal plate which also functions as the compressive member. In another mode, the fastening mechanism also includes a second auxiliary plate outside the second end plate, and the compressive means is interposed between these two plates. A third mode includes a restraint with a band that surrounds the assembly, with its end fixed to the auxiliary plate. The restraint includes a pair of bands disposed on opposite sides of the assembly and fixed respectively to the ends of the auxiliary plate and the second end plate. In either of these configurations, the auxiliary plate linked with the restraint is divided into several parallel parts, and each divisional auxiliary plate has a threaded hole fitted with a screw. The compression between the second end plate and the second auxiliary plate is preferably a disc spring. The restraint is also preferably thermally insulating.
Sealant with exfoliated graphite Title: Sealing material Patent number: US 6177504 Date: 23 January 2001 Inventors: A.W. Addnson et aL Assignee: Federal-Mogul Technology Ltd, UK The invention relates to a sealing material comprising exfoliated graphite, thermosetting resin and a fibrous filler. Sealing materials comprising exfoliated graphite have been used as cylinder head gaskets and other types of seals in internal combustion engines, such as automobile engines for some time, since they have good heat resistance and stress relaxation properties. Graphite sheets have been found to have poor resistance to oil, and this has restricted their use, so ways of improving the oil resistance of graphite sheets have been studied. A prior graphite sheet had expanded graphite particles, heat-resistant fibres and an organic high-polymer binder as principal components, and was claimed to have improved oil and antifreeze resistance. Heat-resistant inorganic fibres such as rockwool, ceramic fibres, silicate fibres and surface-treated silicate fibres or heat-resistant organic fibres such as aromatic
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k~xiatien, 2025 M Sleet NW, Sure 800,Waddng~n. PC 2OO36;USA. ToE+I 202 367 1155 Fa~+l 202 3672155
En'mit:abma~dcsbax:om
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polyamide fibres and phenolic resin fibres can be used as the heat-resistant fibres. The length of the heat-resistant fibres was about 1-50 mm, with a thickness of 10-300 pm. In use, when a sealing material comprising exfoliated graphite is under pressure, extrusion of the material may occur, jeopardising the seal. This occurs considerably more easily when the graphite is oil-soaked than in an oil-free environment. Since such extrusion is an undesirable characteristic, it is desirable that extrusion of sealing material is avoided at pressures ordinarily experienced by them in oily environments. The pressure at which extrusion occurs (the extrusion collapse point) should be above such pressures. The present invention describes a sealing material characterised in that the material comprises 45-90 wt% exfoliated graphite, 5-20 wt% thermosetting resin, and 5-50 wt% fibrous filler which is heat-resistant to 250°C, where at least 90% of the fibres in the fibrous filler are <200 lim long, with an aspect ratio of <10:1. Sealing materials comprising fibrous fillers with such short fibre lengths and aspect ratios have considerably higher extrusion collapse points than elements of graphite foil comprising exfoliated graphite alone, graphite foil with phenolic resin, or graphite foil with phenolic resin and fibrous fillers with 1-50 mm-long fibre lengths. The sealing material may be in the
SealingTechnologyNo. 89
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form of a sheet or layer, for example a planar gasket such as an automotive head gasket. In other embodiments the sealing material is a moulded shape, such as a shaft sealing ring. The sealing material described in this patent may comprise 5-20 wt% thermosetting resin, and 5-30 wt% fibrous filler. It is convenient if the thermosetting resin is a phenolic resin. When a filler is used in which at least 90% of the fibres of the fibrous filler have a fibre length of less than 20 lam, a further increase in the extrusion collapse point is found, and so it is preferred to use fibres of this length. It is preferable to use a fibrous filler in which at least 90% of the fibres have a fibre length of less than 10 Fm. It is advantageous if the aspect ratio of the fibrous filler is less than 6:1. The exfoliated graphite is mixed with the fibrous filler (and, optionally, the powdered thermosetting resin) in the dry state, for example by gentle tumbling or in the airborne state. A layer of the mixture is then compacted, usually by passage between rollers, to form a coherent foil or sheet. Alternatively, the mixture may be compacted to other shapes, such as sealing rings. Such other shapes may also be made by remoulding the foil. When the resin is added as a free-flowing powder, it may subsequently be made to flow, prior to cross-linking, by heating the consolidated foil (optionally under pressure).
TexasAiZM ~ 3254TA~J. CollegeSta~o~ TX 77S43-~,~1, USA. Tel:+1 979~8457417 Fax:+I 979 845 1835
Further heating, normally to a higher temperature, then cross-links the resin. Alternatively, the powdered resin can be made to distribute itself more effectively through the foil by soaking in solvent and then drying. A preferred method of introducing resin is to compress the exfoliated graphite to a relatively low density (e.g. 0.5 kg/m3), so that some porosity is maintained. Liquid resin (solution or suspension in water) is then allowed to soak in. After drying, the low-density foil is compressed further to give the required final density. The graphite sheet preferably has a final density of 0.7-1.5 kg/m 3. Final densities below this range are too weak and compressible, while higher densities tend to be too hard and incompressible, resulting in a poor seal. A particularly preferred fibrous filler is wollastonite, the fibre length of which falls within the ranges of the present invention. In addition to increasing the stress at which extrusion begins, shorter fibres and lower aspect ratios make it easier to mix the fibrous filler with the exfoliated graphite. This gives a more homogeneous product, which may contribute to improved performance. A particular application of this sealing element is in a multi-layer steel gasket, as a thin coating on the gasket to fill fissures. Such a sealing element will typically be 50-100 lam thick, and preferably approximately 75 pm thick.
@
Polymer electrolyte fuel cell Title: Polymer electrolyte fuel cell Patent number: US 6210823 Date: 3 April 2001 Inventors: K. Hatoh et aL Assignee: Matsushita Electric Industrial Co
Ltd, Osaka-fu, Japan The invention relates to a polymer electrolyte fuel cell, in which a gaseous fuel, such as hydrogen, and an oxidant gas, such as air, are subjected to electrochemical reactions at gas diffusion electrodes, to simultaneously generate electricity and heat. A pair of catalytic reaction layers, mainly comprising a platinum metal catalyst on carbon powder, are attached to opposite faces of a polymer electrolyte membrane, which selectively transports hydrogen ions. A pair of gas-permeable, electrically conductive diffusion layers is arranged on the outer faces of the catalytic reaction layers, to constitute an electrode. A pair of conductive separator plates is arranged across the membraneelectrode assembly to mechanically fix the assembly and electrically connect the assembly in series. Part of the separator plate in contact with the electrode has a gas flow path to feed fuel gas to the electrode and to exhaust the gas from the reaction, with any excess gas. The unit cell includes a pair of electrodes, each with a catalytic layer, arranged across the membrane to yield a membrane-electrode assembly (MEA). The circumferential part of the membrane is interposed between a pair of sealing members, and a pair of separator plates are arranged across the MEA. A separator plate has a gas flow path for feeding gaseous fuel or oxidant gas to the electrode. The sealing member prevents the hydrogen and the air from leaking out of the fuel cell or from being mixed with each other. There is
(~
one separator plate with a gas flow path on one surface and a flow path for cooling water on its other surface for every two cells. An O-ring is interposed between the separator plates with the water coolant flow path, in order to prevent a leak. Another technique for preventing leaks of the gases and the cooling water arranges gaskets - of an appropriate resin or metal, and with the same thickness as the electrode - around the electrodes. In this structure, the clearance between the separator plate and the gasket is sealed with grease or adhesive. The clearance between the water coolant separator plates is also sealed with grease or adhesive. In such a structure, O-rings and gaskets are required to seal the heat transfer medium. These O-rings should be compressed to ensure sufficient electrical conductivity across the cooling plate. In such sealing methods a constant compressive force is required to maintain sufficient sealing. One structure inserts a coiled or disc spring between the tie rod and end plate. The compressive force ensures electrical contact between the respective constituents of the cells. In a structure that disposes the sealing members or O-rings around the electrodes in order to seal the gas, a relatively large plane pressure is required. This arrangement presses the sealing member or part between the pair of separator plates, to maintain sufficient sealing. It is thus required to maintain a relatively large compressive force. However, this makes the fastening mechanism including the end plates and the tie rods bulky and heavy, whereas the fuel cell is required to have less total weight. Long-term application of pressure to the seals and electrodes causes distortion of the constituents and so lowers the plane pressure required. A mechanism for absorbing the distortion is thus required in the fastening mechanism. One mechanism for this purpose installs a spring on the end of the tie rod. This also makes the whole fuel cell undesirably bulky. This fastening mechanism includes: •
An end plate at each end of the stack of cells.
•
An auxiliary plate outside the first end plate.
•
At least one means of restraint, which has a band-like shape and restrains a member on one end of an assembly, including the cell stack, the two end plates and the auxiliary plate, and a second member on the other end of the assembly to restrict separation or unfastening of the two members.
•
A screw fitted in a threaded hole in the auxiliary plate in such a way that the end of the screw comes into contact with the first end plate.
A means of compression that generates a repulsive force to compress the cell stack when the screw is fitted in the threaded hole of the auxiliary plate. In one mode of this invention, the auxiliary plate includes an elastic metal plate which also functions as the compressive member. In another mode, the fastening mechanism also includes a second auxiliary plate outside the second end plate, and the compressive means is interposed between these two plates. A third mode includes a restraint with a band that surrounds the assembly, with its end fixed to the auxiliary plate. The restraint includes a pair of bands disposed on opposite sides of the assembly and fixed respectively to the ends of the auxiliary plate and the second end plate. In either of these configurations, the auxiliary plate linked with the restraint is divided into several parallel parts, and each divisional auxiliary plate has a threaded hole fitted with a screw. The compression between the second end plate and the second auxiliary plate is preferably a disc spring. The restraint is also preferably thermally insulating.
Sealant with exfoliated graphite Title: Sealing material Patent number: US 6177504 Date: 23 January 2001 Inventors: A.W. Addnson et aL Assignee: Federal-Mogul Technology Ltd, UK The invention relates to a sealing material comprising exfoliated graphite, thermosetting resin and a fibrous filler. Sealing materials comprising exfoliated graphite have been used as cylinder head gaskets and other types of seals in internal combustion engines, such as automobile engines for some time, since they have good heat resistance and stress relaxation properties. Graphite sheets have been found to have poor resistance to oil, and this has restricted their use, so ways of improving the oil resistance of graphite sheets have been studied. A prior graphite sheet had expanded graphite particles, heat-resistant fibres and an organic high-polymer binder as principal components, and was claimed to have improved oil and antifreeze resistance. Heat-resistant inorganic fibres such as rockwool, ceramic fibres, silicate fibres and surface-treated silicate fibres or heat-resistant organic fibres such as aromatic
SealingTechnologyNo.89
CALENDAR
-Evem
-
Fax:+54 '1 373 '~Lr~l
P ~
r~m
E m a a : ~ ~ r.,ood~Z,m~H~r,~ eo~4~ W~ 13-15 , ~ e 2B01~
-,
L
~
'IL,I : ~
~ IA~ zoa~gz~
-27-30 N ~ 200i ~ l~,k~ Z0elShow Tok~.t~m Oz~m:t:Soomr~ of h~m ' r , ~ ment~ M~m-k~
3-1-,~ ~ 10S.eSZZ,.~.
Tel:.~.813 3434 L,~I FI~.~Iil~ 3434 60~R5 '
Fax:+4~ 69 7$64 N I
http'J/Www.j~p/~:hem
h~p-J~w~a~mas~.de
9..i0 May ZOO1
,
Tet:+ 4 4 1 2 ~ : 7 ~ ,.
Fax:+44 1234 750074 E m m l I : ~ ~
k~xiatien, 2025 M Sleet NW, Sure 800,Waddng~n. PC 2OO36;USA. ToE+I 202 367 1155 Fa~+l 202 3672155
En'mit:abma~dcsbax:om
Geo~ Ted-~~ ~
USA
Asso~atto~ZOZSM
Tel: +1 202 367 1155 Fax:+1 202 367 2155
hu~,ww.~
polyamide fibres and phenolic resin fibres can be used as the heat-resistant fibres. The length of the heat-resistant fibres was about 1-50 mm, with a thickness of 10-300 pm. In use, when a sealing material comprising exfoliated graphite is under pressure, extrusion of the material may occur, jeopardising the seal. This occurs considerably more easily when the graphite is oil-soaked than in an oil-free environment. Since such extrusion is an undesirable characteristic, it is desirable that extrusion of sealing material is avoided at pressures ordinarily experienced by them in oily environments. The pressure at which extrusion occurs (the extrusion collapse point) should be above such pressures. The present invention describes a sealing material characterised in that the material comprises 45-90 wt% exfoliated graphite, 5-20 wt% thermosetting resin, and 5-50 wt% fibrous filler which is heat-resistant to 250°C, where at least 90% of the fibres in the fibrous filler are <200 lim long, with an aspect ratio of <10:1. Sealing materials comprising fibrous fillers with such short fibre lengths and aspect ratios have considerably higher extrusion collapse points than elements of graphite foil comprising exfoliated graphite alone, graphite foil with phenolic resin, or graphite foil with phenolic resin and fibrous fillers with 1-50 mm-long fibre lengths. The sealing material may be in the
SealingTechnologyNo. 89
1316 F~c-~I420.TZZ29m ~ : e ~ ~ h~J~em.~
•lll: +~4 l ~
25-28 February200Z lg~h h m r - , , , ~ Pump umr¢ s y W m ~ Houston,TX, USA
Cmtad: TurbomaddneryL a b ~ .~Tel:+85Z ZB652633
•
feE,+31 20 549 i212 Email:d.heems~rai.nl
.. "..... Faxz'+~2 Z8~61770
form of a sheet or layer, for example a planar gasket such as an automotive head gasket. In other embodiments the sealing material is a moulded shape, such as a shaft sealing ring. The sealing material described in this patent may comprise 5-20 wt% thermosetting resin, and 5-30 wt% fibrous filler. It is convenient if the thermosetting resin is a phenolic resin. When a filler is used in which at least 90% of the fibres of the fibrous filler have a fibre length of less than 20 lam, a further increase in the extrusion collapse point is found, and so it is preferred to use fibres of this length. It is preferable to use a fibrous filler in which at least 90% of the fibres have a fibre length of less than 10 Fm. It is advantageous if the aspect ratio of the fibrous filler is less than 6:1. The exfoliated graphite is mixed with the fibrous filler (and, optionally, the powdered thermosetting resin) in the dry state, for example by gentle tumbling or in the airborne state. A layer of the mixture is then compacted, usually by passage between rollers, to form a coherent foil or sheet. Alternatively, the mixture may be compacted to other shapes, such as sealing rings. Such other shapes may also be made by remoulding the foil. When the resin is added as a free-flowing powder, it may subsequently be made to flow, prior to cross-linking, by heating the consolidated foil (optionally under pressure).
TexasAiZM ~ 3254TA~J. CollegeSta~o~ TX 77S43-~,~1, USA. Tel:+1 979~8457417 Fax:+I 979 845 1835
Further heating, normally to a higher temperature, then cross-links the resin. Alternatively, the powdered resin can be made to distribute itself more effectively through the foil by soaking in solvent and then drying. A preferred method of introducing resin is to compress the exfoliated graphite to a relatively low density (e.g. 0.5 kg/m3), so that some porosity is maintained. Liquid resin (solution or suspension in water) is then allowed to soak in. After drying, the low-density foil is compressed further to give the required final density. The graphite sheet preferably has a final density of 0.7-1.5 kg/m 3. Final densities below this range are too weak and compressible, while higher densities tend to be too hard and incompressible, resulting in a poor seal. A particularly preferred fibrous filler is wollastonite, the fibre length of which falls within the ranges of the present invention. In addition to increasing the stress at which extrusion begins, shorter fibres and lower aspect ratios make it easier to mix the fibrous filler with the exfoliated graphite. This gives a more homogeneous product, which may contribute to improved performance. A particular application of this sealing element is in a multi-layer steel gasket, as a thin coating on the gasket to fill fissures. Such a sealing element will typically be 50-100 lam thick, and preferably approximately 75 pm thick.
@