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  Method of manufacturing chromium plated article and chromium plating apparatusRelated Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Coating (process, Composition And Method Of Preparing Composition), Depositing Predominantly Single Metal Or Alloy Coating On Single Metal Or Alloy Using Specified Waveform Other Than Pure DcThe Patent Description & Claims data below is from USPTO Patent Application 20070068821. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates to a method of manufacturing a chromium plated article and a chromium plating apparatus, which can deposit a hard chromium layer on a work surface. [0002] In a hard chromium plating treatment for a general purpose, a hard chromium layer is deposited on a work surface. There are disadvantages in the method, in that cracks may appear in the chromium layer which reach a metal substrate, allowing substances which cause corrosion to come in contact with the metal substrate, thereby deteriorating the ability of the plated article to resist corrosion. Therefore, it has hitherto been general practice that selected parts of articles which are exposed to corrosive environments are subjected to a pre-treatment procedure of nickel plating or copper plating so as to form an undercoat having a film thickness of the same extent as the layer of hard chromium plating that is applied subsequently. However, this requires that the plating treatment be carried out twice by using different procedures for a pre-treatment step to create an undercoat and the subsequent step of applying a layer of chromium plating, with the result that there is an increase in manufacturing cost. [0003] On the other hand, it has already been ascertained that a chromium layer free from cracks can be formed by performing what is called pulse plating by use of a pulse current (refer to the Japanese Patent Application Disclosure No. 3-207884 (U.K. Patent Application Disclosure No. 2,236,763), for example). When this method is adopted, it becomes possible to obtain in one treatment step chromium plated parts with excellent corrosion resistance. This chromium treatment which is performed by using a pulse current has the problem that when parts are subjected to a thermal history, large cracks are apt to occur in a chromium layer. Therefore, there has been no other choice than to abandon the application of this chromium treatment to parts subjected to a thermal history. [0004] It might be thought that a tensile stress generated in a chromium layer due to thermal contraction is responsible for the phenomenon that cracks are apt to occur when parts are subjected to a thermal history. It follows, therefore, that the occurrence of cracks can be suppressed by causing a compressive residual stress capable of counterbalancing the above-described tensile stress to be present beforehand in the chromium layer or by suppressing the quantity of thermal contraction of the chromium layer itself. In this case, the thermal contraction of the chromium layer is affected by the quantity of lattice defects which are present in large amounts at the grain boundary of the chromium layer and, therefore, the total amount of the boundary is reduced by increasing the size of crystallites of the chromium layer (the total amount of the boundary is inversely proportional to the size of crystallites), whereby lattice defects are reduced and thermal contraction of the chromium layer can be suppressed. [0005] Paying attention to the above-described point, Yuichi KOBAYASHI, who is one of the present inventors, et al. have ascertained that the above-described occurrence of cracks caused by a thermal history can be prevented by causing a compressive residual stress of not less than 100 MPa to be present in the chromium layer and ensuring the size of crystallites of the chromium layer which is not less than 9 nm on average (however, the upper limit being 16 nm on average), and have already made this fact clear in the Japanese Patent Application Disclosure No. 2000-199095 (U.S. Pat. No. 6,329,071). And Yuichi KOBAYASHI et al. found out that as a method of depositing a chromium layer having such a large compressive residual stress and size of crystallites, it is effective to perform electroplating while adjusting the pulse waveform of a pulse current in a plating bath containing an organic sulfonic acid, and have also made this point clear in the Japanese Patent Application Disclosure No. 2000-199095. SUMMARY OF THE INVENTION [0006] Incidentally, methods of plating treatment include `continuous treatment` in which treatment is performed by causing a work to continuously flow within a treatment tank and `batch treatment` in which multiple works are put in a treatment tank and treated in a batch manner. If a continuous treatment is adopted in performing high-mix low-volume production, other works cannot be treated unless the treatment of one work which is to be treated with a prescribed size and under prescribed conditions is finished. Therefore, much waste is incurred in terms of efficiency and there is no other choice than to rely on batch treatment. [0007] When the chromium plating described in the Japanese Patent Application Disclosure No. 2000-199095 is actually performed in a batch manner, this method had the problem that there are considerable variations in the compressive residual stress and the size of crystallites in an obtained chromium layer even within one lot, with the result that it is difficult to stably obtain works (parts) which meet the above-described compressive residual stress of not less than 100 MPa and size of crystallites of not less than 9 nm on average. Furthermore, when the work length is large, this method had the problem that there are variations in the compressive residual stress and size of crystallites of an obtained chromium layer between a portion near a power supply section and a portion away from the power supply section even in the same work, with the result that it is difficult to stably obtain works (parts) which meet the above-described compressive residual stress of not less than 100 MPa and the size of crystallites of not less than 9 nm on average. [0008] The present invention has been made in view of the above-described problems. It is an object of the present invention to provide a method of manufacturing a chromium plated article and a chromium plating apparatus which enable chromium plated parts in which no crack occurs in a chromium layer as a matter of course, not only at temperatures near room temperature but also in a case where the parts are subjected to a thermal history, to be stably and uniformly obtained by batch treatment. Those skilled in the art can easily understand the other objects of the present invention with reference to the specification and drawings. [0009] The first aspect of the present invention is a method of manufacturing a chromium plated article which includes: immersing a plurality of works in a chromium plating bath; and depositing a chromium layer having a desired compressive residual stress on a surface of each of the works by using a pulse current, wherein a waveform of the pulse current supplied to each of the works is made uniform irrespective of the works by adjusting inductance of a wiring from a pulse power source to each of the works. [0010] The second aspect of the present invention is a method of manufacturing a chromium plated article which includes: immersing a plurality of works in a chromium plating bath; and depositing a chromium layer having a desired compressive residual stress on a surface of each of the works by using a pulse current; wherein the works are disposed in an apparatus which comprises a plurality of anodes and a plurality of cathodes disposed in such a manner as to correspond to each of the plurality of works, an anode holding body which is connected sequentially to the plurality of anodes and is connected to a positive pole of a pulse power source, and a cathode holding body which is connected sequentially to the plurality of cathodes and is connected to a negative pole of the pulse power source; and wherein chromium plating is performed, with the pulse power source connected to a middle part of one of the anode holding body and the cathode holding body, and the pulse power source connected to both ends of the other. [0011] The third aspect is that in the method of manufacturing a chromium plated article in the second aspect, at least one inductance of the anode holding body and the cathode holding body becomes large with increasing distance from a connection to the pulse power source. [0012] The fourth aspect is that in the method of manufacturing a chromium plated article in the third aspect, inductances between the plurality of electrodes are set at a ratio of 1:2:3: . . . sequentially, in a direction of spacing from the connection to the pulse power source. [0013] The fifth aspect is that in the method of manufacturing a chromium plated article in the second aspect, each of the plurality of anodes is cylindrical, and each of the works connected to the plurality of cathodes is inserted into each of the plurality of anodes. [0014] The sixth aspect is that in the method of manufacturing a chromium plated article in the second aspect, each of the works is arranged in one row at a prescribed spacing, and the anodes are disposed in a plurality of pairs in a face-to-face relation, with each of the works interposed therebetween. [0015] The seventh aspect is that in the method of manufacturing a chromium plated article in the sixth aspect, the anode holding body includes a first anode holding part on one side and a second anode holding part on the other side, and the plurality of anodes includes a first anode group on one side and a second anode group on the other side, the first anode holding part on one side and the second anode holding part on the other side are respectively provided in positions below or above the first anode group on one side and the second anode group on the other side, and the plurality of cathodes are provided in positions below or above the works. [0016] The eighth aspect is that in the method of manufacturing a chromium plated article in the sixth aspect, the inductance between the plurality of cathodes of the cathode holding body is twice as large as the inductance between the plurality of anodes of the anode holding body. [0017] The ninth aspect of the present invention is a chromium plating apparatus which immerses a plurality of works in a chromium plating bath and deposits a chromium layer having a desired compressive residual stress on a surface of each of the works by using a pulse current, wherein inductance of a wiring from a pulse power source to each of the works is set so that a waveform of the pulse current supplied to each of the works is made uniform irrespective of the works. [0018] The tenth aspect of the present invention is a chromium plating apparatus which immerses a plurality of works in a chromium plating bath and deposits a chromium layer having a desired compressive residual stress on a surface of each of the works by using a pulse current. This chromium plating apparatus comprises: a plurality of anodes and a plurality of cathodes disposed in such a manner as to correspond to each of the plurality of works; an anode holding body which is connected sequentially to the plurality of anodes and is connected to a positive pole of the pulse power source; and a cathode holding body which is connected sequentially to the plurality of cathodes and is connected to a negative pole of the pulse power source, wherein the pulse power source is connected to a middle part of one of the anode holding body and the cathode holding body, and the pulse power source is connected to both ends of the other. [0019] The eleventh aspect of the present invention is that in the chromium plating apparatus in the tenth aspect, at least one inductance of the anode holding body and the cathode holding body becomes large with increasing distance from a connection to the pulse power source. [0020] The twelfth aspect of the present invention is that in the chromium plating apparatus in the eleventh aspect, inductances between the plurality of electrodes are set at a ratio of 1:2:3: . . . sequentially in a direction of spacing from the connection to the pulse power source. [0021] The thirteenth aspect of the present invention is that in the chromium plating apparatus in the tenth aspect, each of the plurality of anodes is cylindrical, and each of the works connected to the plurality of cathodes is inserted into each of the plurality of anodes. [0022] The fourteenth aspect of the present invention is that in the chromium plating apparatus in the tenth aspect, each of the plurality of works is arranged in one row at a prescribed spacing, and the anodes are disposed in a plurality of pairs in a face-to-face relation, with each of the works interposed therebetween. Continue reading... Full patent description for Method of manufacturing chromium plated article and chromium plating apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of manufacturing chromium plated article and chromium plating apparatus 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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