Patent Publication Number: US-2013233702-A1

Title: Multi-Stationed Continuous Electro-Polishing System

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a multi-stationed continuous electro-polishing system and, more particularly, to a continuous electro-polishing system with multiple stations in each of which the gap between an electrode plate and a common metal strip is adjustable to adjust current density to reduce the roughness of the surface of the metal strip fast and evenly. 
     2. Related Prior Art 
     There are various methods for treating a surface of a large, thin metal sheet. To reduce the roughness of the surface, conventional methods are mainly direct contact processes such as grinding and contact polishing. However, the direct contact processes would entail two problems when they are used to treat a metal sheet that is less than 0.5 mm thick. At first, the metal sheet might be damaged. Secondly, the metal sheet might suffer residual stress. 
     Alternatively, the surface treatment of the metal sheet may be executed in an electrochemical or complicate manner. Electrochemistry is conducted at constant intensity since only one station is used and the gap between an electrode plate and the metal sheet is constant. The operation is therefore simple but it is difficult to effectively reduce the roughness of the surface of the metal sheet. 
     As described above, there is only an electrode plate connected to the negative electrode of a power supply while the metal sheet is electrically connected to the positive electrode of the power supply. With only one electrode plate, the electrochemistry is conducted at the constant intensity. To quickly process the large metal sheet in a long reaction tank, the operative parameters are confined in a small range, and it is difficult to effectively reduce the roughness of the surface of the large metal sheet. For continuous surface treatment of the metal sheet, there is a serious problem with the evenness. For example, in an electro-polishing process, the large, if thin metal sheet is fed at speed of 1 m/min, and each point of the surface of the metal sheet is treated for 3 min, an electro-polishing tank must be 3 meters long. The morphology of the surface of the metal sheet varies in such length. As the gap between the single electrode plate and the metal sheet is constant, the electrochemistry is conducted at the single constant intensity. The intensity cannot be adjusted corresponding to the changing morphology of the surface of the metal sheet. Hence, the operative parameters are confined in a narrow range, and the roughness of the surface of the metal sheet cannot be reduced effectively if there is a bubble on the surface of the metal sheet. 
     The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art. 
     SUMMARY OF INVENTION 
     It is the primary objective of the present invention to provide an efficient and effective continuous electro-polishing system for treating a surface of a large metal strip. 
     To achieve the foregoing objectives, the continuous electro-polishing system includes an electrolysis tank, a driving mechanism, electrode plates and a power supply. The electrolysis tank is filled with electrolyzing liquid. The driving mechanism is placed in the electrolysis tank for driving a metal strip into and out of the electrolysis tank. Each of the electrode plates is placed at an adjustable gap from the metal strip in the electrolysis tank. The power supply includes a positive electrode connected to the metal strip and a negative electrode connected to all of the electrode plates. 
     In an aspect, the electrolysis tank includes nozzles each placed between two adjacent ones of the electrode plates in the electrolysis tank for providing a jet to wash the metal strip of bubbles that occur in the electro-polishing. 
     In another aspect, the electrolyzing liquid is solution of acid selected from the group consisting of sulfuric acid, phosphoric acid, glycerol, nitric acid, hydrochloric acid, lactic acid, citric acid, chromic acid, phosphorous acid, and organic acid. 
     In another aspect, the driving mechanism includes two small rollers, two large rollers and two driving rollers. The small rollers are placed in the electrolysis tank near two ends. Each of the large rollers is placed in a respective one of the small rollers in the electrolysis tank. Each of the driving rollers is placed outside the electrolysis tank, near a respective one of the large rollers. 
     In another aspect, the metal strip is 0.5 mm to 0.005 mm thick and hence flexible. 
     In another aspect, the power supply operates in a continuous manner. 
     In another aspect, the power supply operates in an intermittent manner. Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described via detailed illustration of the preferred embodiment referring to the drawings wherein: 
         FIG. 1  is a cross-sectional view of a multi-stationed continuous electro-polishing system according to the preferred embodiment of the present invention; 
         FIG. 2  is an enlarged view of a portion of the multi-stationed continuous electro-polishing system marked with “a” shown in  FIG. 1 ; and 
         FIG. 3  is an enlarged view of another portion of the multi-stationed continuous electro-polishing system marked with “b” shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 through 3 , there is shown an efficient and effective continuous electro-polishing system according to the preferred embodiment of the present invention. The continuous electro-polishing system includes at least one electrolysis tank  1 , a driving mechanism  2 , a metal strip  3 , multiple electrode plates  4  and a power supply  5 . 
     The electrolysis tank  1  is filled with electrolyzing liquid  11 . The electrolyzing liquid  11  is solution of sulfuric acid, phosphoric acid, glycerol, nitric acid, hydrochloric acid, lactic acid, citric acid, chromic acid, phosphorous acid, or any proper organic acid. The electrolysis tank  1  includes multiple nozzles  12  placed therein. Each of the nozzles  12  is preferably placed between two adjacent ones of the electrode plates  4 . 
     The driving mechanism  2  includes at least two small rollers  21  placed in the electrolysis tank  1 , at least two large rollers  22  placed above the electrolysis tank  1 , and at least two driving rollers  23  placed above the electrolysis tank  1 . Each of the small rollers  21  is placed near a respective one of two ends of the electrolysis tank  1 . Each of the large rollers  22  is placed near a respective one of the small rollers  21 . Each of the driving rollers  23  is placed near a respective one of the large rollers  22 . 
     The metal strip  3  is moved into and the out of the electrolysis tank  1  by the driving mechanism  2 . The metal strip  3  includes a surface  31  in need of polishing. The metal strip  3  is about 0.5 to 0.005 mm thick and hence flexible. 
     The electrode plates  4  are placed in the electrolysis tank  1 . There is an electrolysis gap  41  between each of the electrode plates  4  and the surface  31  of the metal strip  3 . The electrolysis gaps  41  are different from one another. 
     The power supply  5  of course includes a positive electrode  51  and a negative electrode  52 . The positive electrode  51  is electrically connected to the metal strip  3 . The negative electrode  52  is electrically connected to all of the electrode plates  4 . The power supply  5  may supply electricity in a continuous or intermittent manner. 
     In operation, by the smaller rollers  21 , the large rollers  22  and the driving rollers  23  of the driving mechanism  2 , the metal strip  3  is moved into and out of the electrolysis tank  1 . The elevation of the metal strip  3  in the electrolysis tank  1  is determined by the small rollers  21 . The power supply  5  is turned on to produce a current that flows through the positive electrode  51 , the metal strip  3 , the electrolysis liquid  11 , each of the electrode plates  4  and the negative electrode  52 , thus executing the electrolysis. Accordingly, the metal strip  3  is electro-polished by the electrolyzing liquid  11  contained in the electrolysis tank  1 . 
     By adjusting the elevation of an electrode plate  4  relative to the metal strip  3  in the electrolysis tank  1 , adjusted is the electrolysis gap  41  between the electrode plate  4  and the metal strip  3 , i.e., between the negative electrode  52  and the positive electrode  51 . The larger an electrolysis gap  41  is, the higher the resistance is therein. In compliance with the Faraday&#39;s law, the higher the resistance is, the lower the current density is. Preferably, the first electrolysis gap  41  is set to be smaller than the second electrolysis gap  41  that is set to be smaller than the third electrolysis gap  41 . Hence, the current density in the first electrolysis gap  41  is higher than the current density in the second electrolysis gap  41  that is higher than the current density in the third electrolysis gap  41 . The electro-polishing of the metal strip  3  gets less intense as the metal strip  3  is moved through the first, second and third electrolysis gaps  41 , and this is desired as the roughness of the metal strip  3  gets lower. Hence, there is a large process window, and the quality of the electro-polishing of the surface  31  of the metal strip  3  is good. 
     As mentioned above, each of the nozzles  12  is placed between two adjacent ones of the electrode plates  4  in the electrolysis tank  1 . Each of the nozzles  12  sends a jet of electrolyzing liquid. The jets are useful for washing the metal strip  3  of bubbles that occur and attach to the metal strip  3  because of the electro-polishing, thus removing defects such as recesses or bosses from the metal strip  3 . That is, the jets reduce bubble-incurred shielding and enhance the electro-polishing. 
     Referring to  FIGS. 2 and 3 , there is shown the morphology of the surface  31  of the metal strip  3  in an enlarged scale. Referring to  FIG. 2 , before the electro-polishing, the roughness of the surface  31  of the metal strip  3  is high, i.e., the surface  31  of the metal strip  3  includes many sharp peaks  311 . In the electro-polishing, the charge is more intense at the peaks  311  than in the other regions of the surface  31  of the metal strip  3 . That is, the electro-polishing at the peaks  311  is more intense than in the other regions of the surface  31  of the metal strip  3 . Accordingly, layers of metal at the peaks  311  are thicker than layers of metal in the other regions of the surface  31  of the metal strip  3 . 
     Hence, referring to  FIG. 3 , the peaks  311  disappear after the electro-polishing. 
     As described above, in the multi-stationed continuous electro-polishing system, the electrolysis gap  41  between each of the electrode plates  4  and the surface  31  of the metal strip  3  is adjustable independent of the other electrolysis gaps  41 . The current density gets higher as the metal strip  3  is moved through the electrolysis gaps  41 . Hence, the electro-polishing gets less intense as the roughness of the surface  31  of the metal strip  3  gets lower. Thus, the electro-polishing can be executed on a large metal strip effectively and efficiently, and the quality of the surface  31  of the metal strip  3  is even and good. The electro-polished metal strip  3  can be used in a thin-film solar cell, flat panel display or a reflector. 
     The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.