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  Method for manufacturing fuel cell metallic separatorUSPTO Application #: 20080108282Title: Method for manufacturing fuel cell metallic separator Abstract: A metallic separator according to a first embodiment is formed by obtaining a blank by rolling a metallic material having conductive inclusions, and removing a surface of the blank by 2% or more of the thickness of the blank. A metallic separator according to a second embodiment is formed by pressing a metallic plate so as to have a cross section including ridges and grooves alternatively, and removing parts of the ridged portions so as to make flattened surfaces. A metallic separator having conductive inclusions in its metal texture according to a third embodiment is formed by blasting a liquid containing two or more kinds of abrasives having different particle diameters to a blank after it has been rolled. A metallic separator having conductive inclusion in its metal texture according to a fourth embodiment is formed by blasting a passivation treatment liquid mixed with abrasives to the separator. (end of abstract) Agent: Arent Fox LLP - Washington, DC, US Inventors: Teruyuki Ohtani, Makoto Tsuji, Masao Utsunomiya, Koji Kotani USPTO Applicaton #: 20080108282 - Class: 451038000 (USPTO) Related Patent Categories: Abrading, Abrading Process, Utilizing Fluent Abradant, By Blasting The Patent Description & Claims data below is from USPTO Patent Application 20080108282. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This is a Divisional Application, which claims the benefit of pending U.S. patent application Ser. No. 10/309,320, filed Dec. 4, 2002. The disclosure of the prior application is hereby incorporated herein in its entirety by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a metallic separator which is installed in a proton-exchange membrane fuel cell and a method for manufacturing the same metallic separator. [0004] 2. Description of the Related Art [0005] In a proton-exchange membrane fuel cell, a laminated body in which separators are laminated on both sides of a flat plate-like membrane electrode assembly (MEA) is made to be one unit, and a plurality of units are stacked together to form a fuel cell stack. The membrane electrode assembly is of a three-layer construction in which an electrolytic membrane comprising an ion-exchanging resin is held between a pair of gas diffusion electrodes which constitute a positive pole (cathode) and a negative pole (anode). The gas diffusion electrode is such that a gas diffusion layer is formed on the outside of an electrode catalyst layer which contacts the electrolytic membrane. In addition, the separator is laminated in such a manner as to be brought into contact with the gas diffusion electrode of the membrane electrode assembly, whereby a gas flow path through which gas is allowed to flow and a coolant flow path are formed between the separator so laminated and the gas diffusion electrode. According to the fuel cell, for example, when hydrogen gas which is fuel is allowed to flow through a gas flow path which faces the gas diffusion electrode on the negative pole side, whereas oxide gas such as oxygen or air is allowed to flow trough a gas flow path which faces the gas diffusion electrode on the positive pole side, an electrochemical reaction occurs and current is generated. [0006] The separators need to have a function to supply electrons generated through a catalytic reaction of hydrogen gas on the negative pole side to an outside circuit, as well as a function to supply electrons from the outside circuit to the positive pole side. To this end, conductive materials, such as graphite and metallic materials, are used for the separators. In particular, the metallic materials are considered to be advantageous in that they have superior mechanical strength and that they can be formed into a thin plate which can eventually provide a separator light in weight and small in size. As the metallic separator, there is a separator which is manufactured by rolling stainless steel containing conductive inclusions which are deposited and/or dispersed therein into a thin plate, and forming by pressing the thin plate so as to have a cross section constituted by alternate ridges and grooves so that the grooves formed on front and back surfaces of the thin plate are used for the gas flow paths and coolant flow paths. The conductive inclusions are such as to contribute to the improvement in power generating performance by forming a conductive path. [0007] With the metallic separators so constructed, the ridges surfaces are brought into contact with gas diffusion electrodes of the membrane electrode assembly in a state in which the separators are assembled to the membrane electrode assembly. The ridged portions are formed into a trapezoid having sides which are slightly inclined so that the separator can easily be removed from the die after pressing. In addition, corners which are transitional portions from the surface of the ridged portion to the sides are inevitably formed into a round shape (R-shape) by bending. These constitute restrictions on the enlargement of actual contact areas to the membrane electrode assembly at the surfaces of the ridged portions. A reduction in contact area of the separator to the membrane electrode assembly leads to an increase in contact resistance and prevents the improvement of power generating performance. Therefore, the enlargement of the contact area is desired. In addition, some of separator, the surfaces of the ridged portions are each close to the round shape as a whole and hence their flattened surfaces become limited. As this occurs, it is difficult to ensure that a desired surface pressure is obtained at the surfaces the ridged portions which are in contact with the membrane electrode assembly, this also leading to an increase in contact resistance. [0008] Further, when stainless steel in which conductive inclusions are deposited and/or dispersed is rolled into a thin plate, there may be caused a case where an abnormal layer is produced on the surface of the thin plate in which conductive inclusions which are broken extremely finely by rolling are caused to aggregate. In case a fuel cell is constituted by separators in which the abnormal layers exist on the surfaces thereof and is then put in operation, the conductive inclusions existing in the abnormal layers drop, which leads to deterioration in power generating performance. [0009] Moreover, in the manufacture of separators as has been described above, since there exists a surface rolling-affected layer on a stainless steel plate, the steps are required of grinding to remove the surface rolling-affected layer so as to allow good conductive inclusions that have not been affected by rolling to be exposed on the surface of a base metal and, furthermore, allowing the exposed conductive inclusions to protrude so as to reduce the contact resistance. However, there has existed a problem that a naturally oxidized film is formed on the surface of the base metal between the step of grinding and removing the surface rolling-affected layer and the step of allowing the conductive inclusions to protrude. Once a naturally oxidized film is formed on the surface of the base metal, even if the step of allowing the conductive inclusions to protrude is implemented thereafter, the effect on the improvement in conductivity by the step of allowing the conductive inclusion to protrude cannot be obtained sufficiently due to the existence of the naturally oxidized film. Owing to this, in order to obtain sufficient conductivity, a complicated step must be implemented further, leading to another problem that the production costs are increased. [0010] Further, after the process of grinding to remove the surface rolling-affected layers so that the conductive inclusions are allowed to protrude in the vicinity of the surfaces of the stainless steel plate to thereby reduce the contact resistance, a process is conducted of applying to newly produced surfaces of the stainless steel plate a treatment for providing corrosion resistance thereto. In related art, the passivation treatment has been used for providing the corrosion resistance to the newly produced surfaces. However, there has been existing a problem that a naturally oxidized film is formed on the newly produced surface during the passivation treatment. The naturally oxidized film is inferior to a film in a passive state in corrosion resistance, and therefore, a further provision of corrosion resistance has been required. However, even if the passivation treatment is implemented after a naturally oxidized film has been formed, the naturally oxidized film interrupts the passivation of the newly produced surface, and therefore, the corrosion resistance improvement effect by the passivation treatment cannot be attained sufficiently. Due to this, in order to obtain a sufficient corrosion resistance, a further complicated step has to be implemented, this leading to another problem that the production costs are increased. SUMMARY OF THE INVENTION [0011] A first object of the present invention is to provide a fuel cell metallic separator formed by pressing so as to have a cross section constituted by alternate ridges and grooves wherein contact areas of surfaces of ridged portions to a membrane electrode are enlarged to secure a desired surface pressure, whereby the contact resistance is reduced to thereby improve the power generating performance and a method for manufacturing the same separator. [0012] A second object of the present invention is to provide a fuel cell metallic separator manufactured by rolling a metallic material having conductive inclusions, wherein the fuel cell metallic separator is not affected by abnormal layers of conductive inclusions produced on the surfaces thereof by rolling, whereby its power generating performance is attempted to be improved, as a result, and a method for manufacturing the same separator. [0013] A third object of the present invention is to provide a method for manufacturing a fuel cell metallic separator in which grinding a surface rolling-affected layer on a base metal and allowing conductive inclusions to protrude can be implemented in a single step. [0014] A fourth object of the present invention is to provide a method for manufacturing a fuel cell metallic separator in which a passivation treatment can be applied to newly produced surfaces obtained by grinding on a base metal at the same time as the grinding to remove surface rolling-affected layers. [0015] In order to accomplish the first object above, the following means are adopted. According to a first aspect of the present invention, there is provided a fuel cell metallic separator comprising: [0016] a metallic plate having alternatively ridges and grooves in a cross section which are formed by pressing, each of the ridge portions having a flattened surface which is brought into contact with a membrane electrode assembly, the flattened surface being formed by removing a part of the ridged portion after pressing. [0017] In the fuel cell metallic separator, it is preferable that a removed amount of the surface of the ridged portion is 3 .mu.m or larger. [0018] Further, according to a second aspect of the present invention, there is also provided a method for manufacturing a fuel cell metallic separator comprising: [0019] forming a metallic plate having alternatively ridges and grooves in a cross section, by pressing, and; removing a part of each of the ridged portions so that each of the ridge portions has a flattened surface. In this method, it is preferable that a removed amount of the surface of the ridged portion is equal to or larger than 3 .mu.m. As a method for removing the surface of the ridged portion, there are an electrochemical method such as electrolytic etching, a chemical method such as etching and a physical method such as cutting or sandblasting. [0020] Further, the inventor came to know that the thickness of the abnormal layer produced on the surfaces of the separator by rolling is something like in the order of 2% of the total thickness, and therefore the present invention was eventually completed based on this knowledge. Namely, in order to accomplish the second object above, according to a third aspect of the present invention, there is provided a fuel cell metallic separator formed by rolling a metallic material having conductive inclusions and removing a surface of the metallic material after rolling by an amount corresponding to 2% or more of a thickness of the metallic material after rolling so that the conductive inclusions are allowed to protrude from the surface of the metallic material after rolling. [0021] According to the fuel cell metallic separator of the third aspect of the present invention, since the surfaces of the separator are removed by 2% or more of the thickness of the metallic material after the material has been rolled, abnormal layers produced on the surfaces of the metallic material by rolling are removed. Therefore, the surfaces of the metallic material are made good and the conductive inclusions are allowed to protrude therefrom. Due to this, when the metallic separators so manufactured are incorporated in a fuel cell, the contact resistance relative to a membrane electrode assembly is reduced to thereby improve its power generating performance. Continue reading... Full patent description for Method for manufacturing fuel cell metallic separator Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for manufacturing fuel cell metallic separator patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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