Patent Publication Number: US-11021807-B2

Title: Electrolytic polishing method and device

Description:
TECHNICAL FIELD 
     The present invention relates to an electrolytic treatment, and in particular, to device and method in connection with the electrolyte circulation for the electrolytic polishing or the electrolytic plating. 
     BACKGROUND ART 
     A linear collider is being constructed as a facility for creating a state of Big Bang (International Linear Collider (ILC) Project). The linear collider, as shown in  FIG. 10 , uses a hollow pipe  100  made of niobium, that is provided with flanges  101   a  and  101   b  at both ends and has a diameter changing periodically in an axial direction. There are elements to obtain a predetermined effect in this experiment, and one is whether or not the inside of the niobium hollow pipe  100  is to be smooth. 
     The hollow pipe  100 , however, is subjected to excessive pressure and heat at forming, so that an inside surface becomes distorted unevenly. If such condition of the surface is left alone, the electric properties and the magnetic properties become uneven, with the result that it is not possible to impart a predetermined speed to the electrons and the positrons. Accordingly, methods for polishing the inside of the hollow pipe in a predetermined thickness have been developed as a countermeasure against such problem. 
     Generally, the chemical polishing and the electrolytic polishing are employed as the polishing method for not only the niobium hollow pipe but also the above-mentioned hollow pipe. In the present invention, the electrolytic polishing is described. 
     In case of electro-polishing the inside of the above-mentioned hollow pipe, in particular, the pipe having a non-straight and complicated inside shape, it becomes very important to treat bubbles generated from the electrolyte. In other words, when the bubbles are dwelling in the pipe, the inside of the pipe holding the bubbles becomes a rough condition and the surface does not become satisfied condition. 
     Japanese Unexamined Patent Application Publication No. 61-23799 discloses a device for electro-polishing the inside of the hollow pipe (a metallic hollow body) having a cell in a center of a longitudinal direction of the pipe (referred to as the “cell”, hereinafter). The device is configured to insert a liquid supply pipe to the center of the metallic hollow body while keeping the hollow pipe horizontally in the longitudinal direction, and supply the electrolyte from an end of the liquid supply pipe to the cell, wherein the electrolyte is supplied so as to immerse a lower half of the inside of the hollow body in the electrolyte by rotating the hollow body on a central axis of the hollow body. Here, the electrolyte is supplied from an end of the liquid supply pipe running through the center of the hollow body to the cell through a supply port disposed on a downside of the liquid supply pipe so as to face to the cell, and discharged from an other opening port of the hollow body. Under such configuration the state of the electrolyte flow to be supplied into the cell differs depending on a position, so that it occurs that the state of the polishing becomes uneven. 
     In order to improve the above-mentioned disadvantage and level the state of polishing, the invention disclosed in Japanese Unexamined Patent Application Publication No. 11-350200 is configured to supply the electrolyte in the perpendicular and upward direction from an upper side of the liquid supply pipe so as not to generate the flow of the electrolyte in the cell. 
     When the hollow pipe is placed horizontally in the longitudinal direction as above, however, it occurs that an upper half of the pipe is not immersed in the electrolyte. It is difficult to take no account of surface roughness caused by bubbles generated at the electrolysis. In Japanese Patent No. 5,807,938, the applicant of the present invention discloses a device for the electrolytic treatment (the electrolytic polishing and the electrolytic plating) while an axis of the hollow pipe is placed vertically so as to immense the whole of the inside of the hollow pipe in the electrolyte. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 61-23799, 
         Patent Literature 2: Japanese Unexamined Patent Application Publication No. 
       
    
     11-350200, and
     Patent Literature 3: Japanese Patent No. 5,807,938.   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     When using the device for performing the electrolytic polishing in the state that the axis of the hollow pipe is placed vertically, which is disclosed in the Japanese Patent No. 5,807,938, it is possible to polish the inside of the hollow pipe evenly to some extent, but it is insufficient when the precision level is required. 
     In case of polishing the hollow pipe having the cells of which diameters change periodically by using the device disclosed in Japanese Patent No. 5,807,938, the amount of polishing are measured at positions (m 1  to m 6 ,  FIG. 5 ) and the results are indicated in  FIG. 7 . A bulge from a small diameter part to another small diameter part is referred to the cell, hereinafter. 
     A series of 9 cells, each cell having 300 mm of the large diameter and 100 mm of the small diameter, is polished under 27 mA current for 3 minutes while supplying the electrolyte from a lower end and discharging the electrolyte from an upper end. The process is repeated in predetermined times. In this case, about 200 cc of gases (hydrogen gas) is generated per 1 minute in each cell, and the gases raise up together with the supplied electrolyte, so that the amount of gas increases in the upper position of the cell. 
     Under such condition, when measuring the amount of polishing at 6 points in the axis direction of each cell as shown in  FIG. 5  (m 1  to m 6 ), that is, at 54 points of the 9 cells, it is understood, as shown in  FIG. 7 , that the most polished part of each cell is a part above the large diameter part (corresponding to a shoulder part of each cell of the hollow pipe, in  FIG. 5 ), and there is a large difference of the amount of polishing depending on the positions of the inside of the cell. Looking through the plural cells, the above-mentioned part of the cell nearer to the upper end of the pipe (left,  FIG. 7 ) has a larger amount of polishing. When comparing the amount of polishing between the cell near to the lower end (right,  FIG. 7 ) and the cell near to the upper end, the difference of the amount of polishing is a little over 50 μm at the shoulder part and about 5 μm at the small diameter part. 
     As described above, in case of using the device in Japanese Patent No. 5,807,938, it is possible to ensure to level the amount of polishing of the inside of the cell or between the cells to some extent, however, it is insufficient when the further strictness is required. 
     The present invention is proposed in view of the above conventional problems, and has an object to provide with the electrolytic polishing device and electrolytic polishing method to control the amount of polishing depending on the position inside the cell, and reduce the difference of the amount of polishing between the cells. 
     Means of Solving the Problems 
     The present invention relates to the electrolytic polishing device for electrolytic polishing the hollow pipe. 
     Holding frames hold the hollow pipe vertically, and are pivotally supported on a rack so as to be vertically invertible about the vertical center of the hollow pipe. An electrode is inserted in the hollow pipe, and liquid buffers are disposed at upper and lower ends of the hollow pipe. 
     A valve mechanism switches a liquid circulation circuit so as to circulate an electrolyte in the hollow pipe from the lower liquid buffer to the upper liquid buffer, regardless of before and after the inversion of the invertible hollow pipe. Under such configuration, the electrolytic treatment is performed for a predetermined period while circulating the electrolyte in the hollow pipe before the inversion of the hollow pipe, and then the electrolytic treatment is performed for the predetermined period while circulating the electrolyte in the hollo tube after the inversion of the hollow pipe. 
     The switching of the valve mechanism may be carried out manually, or may use a switching control unit. In addition, the electrolytic treatment can be carried out by an electrolytic treatment control unit. 
     The steps of the electrolytic polishing using the above-mentioned device can be recognized as an invention of process. Specifically, in a state of circulating the electrolyte in the hollow pipe from the lower liquid buffer to the upper liquid buffer, the electrolytic polishing is performed for a predetermined period. Next, the electrolytic polishing and the circulation of the electrolyte are suspended. And then, the hollow pipe is inverted. In a state that the hollow pipe is inverted, the electrolytic polishing is performed for the predetermined period while circulating the electrolyte in the hollow pipe from the lower liquid buffer to the upper liquid buffer. 
     The above-mentioned steps are repeated as many times as necessary. 
     Effects of the Invention 
     According to the above-mentioned configuration, the electrolytic treatment is performed while inverting the hollow pipe at predetermined time interval as well as circulating the electrolyte from a bottom of the hollow pipe and pushing out upwardly the bubbles generated by the electrolytic treatment together with the circulating electrolyte, so that it is possible to control the unevenness of the amount of polishing depending on the inside position of the cell constituting the hollow pipe and the position between the cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a device of the present invention; 
         FIG. 2  is a schematic view of the present invention; 
         FIG. 3  is a detailed view of a liquid supply circuit; 
         FIG. 4  is a perspective view showing an electrode used by the present invention; 
         FIG. 5  is a view showing measurement positions; 
         FIG. 6  shows a status of the electrolytic polishing made by the present invention; 
         FIG. 7  shows a state of the electrolytic polishing made by a comparative example; 
         FIG. 8  shows a state of the electrolytic polishing made by an other comparative example; 
         FIGS. 9( a ) and 9( b )  are photos showing statuses before or after the electrolytic polishing treatment by the present invention; and 
         FIG. 10  is a view showing the hollow pipe. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     &lt;Structure&gt; 
       FIG. 1  is a perspective view showing an outline of the present invention, and  FIG. 2  is a schematic view showing a liquid supply/discharge circuit and a control unit for electrolyte of the device shown in  FIG. 1 . 
     A rack  50  has right and left props  51   a  and  51   b  standing a predetermined height and spacing out a predetermined interval. Right and left holding frames  60  are supported at each center of the vertical direction (an axis direction of the hollow pipe) by the right and left props  51   a  and  51   b  of the rack  50  via a horizontal rotating axis  61 . 
     Flanges  111   a  and  111   b  are mounted in large diameter parts of the cells positioned at upper and lower ends of the hollow pipe  100 . The flanges  111   a  and  111   b  are pinched by clips  201   a  and  201   b  attached to the holding frames  60 , and thereby the flanges  111   a  and  111   b  are fixed on the holding frames  60 . Accordingly the hollow pipe  100  is set to the holding frames  60 . Besides, the positions of fixing the hollow pipe  100  on the holding frames  60  are not limited to the upper and lower flanges  111   a  and  111   b , if necessary, the hollow pipe  100  may be fixed on the holding frames  60  at any part to be reinforced by means of the same flanges and clips. 
     The above described flanges  111   a  and  111   b  are divided into two parts in the diameter direction. The two divided flanges are connected each other with screws and so on at the diameter part of the cell of the hollow pipe  100 , so that each flange  111   a  and  111   b  can be fixed on the hollow pipe  100 . 
     At the upper and lower ends of the hollow pipe  100 , liquid buffers  300   a  and  300   b  are disposed using flanges  101   a  and  101   b , and the liquid buffers  300   a  and  300   b  are respectively connected with circulation pipes  301  (a liquid supply pipe  301   a  and a liquid discharge pipe  301   b  that are described hereinafter). The two circulation pipes  301  are connected with a liquid tank  15  through a valve mechanism  302  and a pump  303 . Besides, the valve mechanism  302  shown in  FIG. 2  includes all valves illustrated in  FIG. 3  described after, but the valve mechanism  302  in this embodiment means three-way valves  302   a  and  302   b  mainly. 
     The circulation pipe  301  consists of the liquid supply pipe  301   a  and the liquid discharge pipe  301   b , since the hollow pipe  100  is inverted upside down at a predetermined intervals as described later, a pipe on a side to be connected with the liquid buffer  300   a  at the lower end of the hollow pipe  100  becomes the liquid supply pipe  301   a  and the other pipe on the other side to be connected with the liquid buffer  300   b  at the upper end of the hollow pipe  100  becomes the liquid discharge pipe  301   b.    
     Considering the necessity of rotating an electrode  20  during the electrolytic treatment and the inverting of the hollow pipe  100  as described hereinafter, coupling members  70  (for example, gear units) connected with a motor for rotating the electrode  20  are arranged on both ends of an electrode axis  21  of the electrode  20 . 
       FIG. 3  is a view more precisely showing the circuit for supplying the electrolyte to the hollow pipe  100  shown in  FIG. 2 . 
     Two ports of the 3-way valve  302   a  for supplying the liquid are connected each other so as to couple the liquid supply pipe  301   a  and the liquid discharge pipe  301   b , and the other port of the 3-way valve  302   a  is connected with a liquid tank  15  through a pump  303 . In the same manner, two port of the 3-way valve  302   b  for discharging the liquid are connected, in parallel to the 3-way valve  302   a  for supplying the liquid, so as to couple the liquid supply pipe  301   a  and the liquid discharge pipe  301   b , and the other port of the 3-way vale  302   b  takes back the liquid to the liquid tank  15 . 
     In addition to the liquid tank  15 , a pure water tank  16  storing the pure water for cleaning is disposed separately, and a cleaning pipe  401  is connected with two ports of 3-way valve  402   a  for supplying the water so as to couple liquid buffers  300   a  and  300   b . In parallel to the 3-way valve  402   a  for the supplying the water, two ports of 3-way valve  402   b  for discharging the water are connected so as to couple the two liquid buffers. The other port of the 3-way valve  402   a  for supplying the water is connected to the pure water tank  16  through a pump  403 , and the other port of the 3-way valve  402   b  for discharging the water takes back the water to the pure water tank  16 . 
     The deteriorated electrolyte and the post-cleaning pure water are stored in a drainage tank  17 . The liquid buffer  300   a  is connected to the liquid supply pipe  301   a  and the cleaning pipe  401  through 2-way valve  304   a , and the liquid buffer  300   b  is connected to the liquid discharge pipe  301   b  and the cleaning pipe  401  through 2-way valve  304   b . The 2-way valve  304   a  and the 2-way valve  304   b  are switched between the electrolytic treatment and the cleaning treatment. 
     &lt;Electrolytic Treatment&gt; 
     Under the above-mentioned configuration, the hollow pipe  100  is fixed on the holding frames  60  by means of the clips  201   a ,  201   b  and the flanges  111   a ,  111   b , and then the electrode  20  is inserted in the hollow pipe from the top of the hollow pipe  100 . The structure of the electrode  20  is not limited in particular, but this embodiment uses the electrode disclosed in Japanese Patent No. 5,807,938, since it needs to electro-polish a weld zone of the cell (the large diameter part, in particular). Next, the upper and lower liquid buffer  300   a  and  300   b  are liquid-tightly attached on both ends of the hollow pipe  100 , and the coupling members  70  set on the electrode axis  21  of the electrode  20  is coupled with the motor  71  that is a driving unit for rotating the electrode  20 . 
     After the preparation as described above is finished, each valve  302   a ,  302   b  constituting the valve mechanism  302  is set so as to circulate the electrolyte from the lower liquid buffer of the hollow pipe  100  to the upper liquid buffer, and then the electrolyte is supplied from the bottom of the hollow pipe  100  by the pump  303 . In the state of circulating the electrolyte in the hollow pipe  100 , the electrolytic treatment is started. While continuing to circulate a predetermined amount of the electrolyte per unit time, the electrolytic treatment is performed with a predetermined current for a predetermined period. The electrolytic treatment is carried out by applying a negative to the electrode  20  and a positive to the hollow pipe  100  while rotating the electrode  20  by the motor  71 . Next, after temporally stopping supplying the liquid and the electrolytic treatment, the hollow pipe  100  is inversed together with the holding frames  100 . 
     After that, the valve mechanism  302  (the 3-way valve  302   a  and  302   b ) is switched so as to circulate the electrolyte from the lower liquid buffer  300   a  to the upper liquid buffer  300   b , and then the electrolytic treatment is performed under the same conditions (time, current) as above. Besides, the valves constituting the valve mechanism  302  indicate all valves illustrated in  FIG. 3 , such as the liquid supply valve  302   a , the liquid discharge valve  302   b , the water supply valve  402   a , the water discharge valve  402   b , and so on. In this embodiment, however, the valves to be switched for circulating the electrolyte are the liquid supply valve  302   a  and the liquid discharge valve  302   b . That is to say, after inverting the hollow pipe  100 , the liquid discharge valve  302   b  changes to the liquid supply valve  302   a  while the liquid supply valve  302   a  changes to the liquid discharge valve  302   b . In order to achieve the object of the present invention, “circulating the electrolyte upward from the below”, it needs to switch the liquid supply valve  302   a  and the liquid discharge valve  302   b.    
     The above-mentioned electrolytic treatment can be carried out manually by inverting the hollow pipe  100 , switching the valve mechanism  302 , and controlling the required current and voltage, but these steps can be carried out automatically using a control unit  400 . In this case, the control unit  400  inverts the hollow pipe and switches the supplying of the liquid, that is, it is sure to supply the electrolyte upward from the lower liquid buffer  300   a  and control the electrolytic treatment (time, current, and etc.). 
     While supplying the electrolyte from the lower end of the hollow pipe  100  at a flow rate of 5 L/min, the electrolytic treatment is carried out for 3 minutes under 200 to 270 mA/cm 2  and around 16 to 17 V. The electrolyte treatment is called as one processing. In addition, the processing is carried out one more time after inverting the hollow pipe  100 . The processing is repeated 31 times, which is called as a unit treatment. After the plural unit treatments are carried out for the inside of the hollow pipe  100 , the amount of polishing at each measurement point in  FIG. 5  (m 1  to m 6 , and in all cells) is illustrated in  FIG. 6  by the average of the plural unit treatments. 
     The amount of polishing at the small diameter part is stable at about 20 μm, and the amount of polishing at the large diameter part is around 30 to 35 μm. Beside, in  FIG. 6 , the serial numbers are assigned from a top measurement point to a bottom measurement point in order (the same applies to  FIGS. 7 and 8  described hereinafter). 
       FIG. 7  shows a result of a comparative example. In the comparative example, the electrolytic treatment is suspended after the electrolytic treatment for a predetermined period (3 minutes) while supplying the electrolyte from the lower end of the hollow pipe  100 , and then restarted after pushing out the bubbles dwelling around the shoulders of the cells while keeping supplying the electrolyte, of which treatment is repeated the same number of times as above. It is understood that the amount of polishing around the shoulder of the large diameter part becomes 80 to 90 μm, which differs 50 μm from the amount of polishing around the small diameter part. 
       FIG. 8  shows a result of the other comparative example. In the other comparative example, the electrolytic treatment and the supply of the liquid are suspended temporarily after the electrolytic treatment for the predetermined period (3 minutes same as above) while supplying the electrolyte from the lower end, and then the electrolytic treatment is carried out while supplying the electrolyte from the upper side of the hollow pipe  100 . After the electrolytic treatment for the predetermined period (3 minutes), both the electrolytic treatment and the supply of the electrolyte is stopped, of which treatment is repeated the same number of times as above. The results of the treatments are show in FIG.  8 . The amount of polishing of the small diameter part is 20 to 25 μm, which does not differ greatly from a case of inverting the hollow pipe  100 , but the amount of polishing of the large diameter part becomes 45 μm, and the difference between the amount of polishing of the large diameter part (the positions of the shoulders of the cells) and the amount of polishing of the small diameter parts becomes large. 
       FIG. 9  shows photos by a microscope showing a weld zone (the large diameter part) on the inside of the hollow pipe before and after the treatment in the present invention.  FIG. 6  shows the effect of the present invention according to the amount of polishing of each part.  FIG. 9  shows that the inside of the hollow pipe  100  is finished as mirror-finished surface, and the state of the surface becomes smooth as expected. 
     Specifically, the bulge part (cell) of the hollow pipe  100  is formed as follows; cup-shaped bodies cutting into halves at the largest diameter part of the cell are coupled mutually, and the coupled parts are welded. Since the light to be irradiated is diffused before the treatment of the present invention ( FIG. 9( a ) ), only an unclear picture can be obtained on the whole. After the treatment ( FIG. 9( b ) ), however, it is understood that the surface are finished as mirror-finished surface, the debris at the weld zone is removed completely. 
     Accordingly, the above described results indicate that the electrolytic treatment while inverting the hollow pipe by means of the device according to the present invention is effective. 
     In the above embodiment, it is defined that the time for the electrolytic treatment before the inverse is the same as the time for the electrolytic treatment after the inverse, but it may be allowed to change the time of the electrolytic treatment depending on the conditions. For instance, there are cases that the upper side of the bulge is different in shape from the lower side of the bulge, or the upper side of the bulge is different in material from the lower side of the bulge. 
     &lt;Electrode&gt; 
     The structure of the electrode is explained hereinafter briefly according to  FIG. 4 , since it was disclosed in Japanese Patent No. 5,807,938. 
     A wing electrode  22  is formed by arranging at least one or plural wings  22   a ,  22   b  . . . ( 4  wings shown in Figure) in a circumferential direction of the electrode axis  21  at equal intervals, and an outer edge of the wing has a shape corresponding to an inner shape of the bulge of the hollow pipe  100  to be polished. 
     Each wing  22   a ,  22   b  . . . constituting the wing electrode  22  has the flexibility. When the wings are wound around the electrode axis  21 , the diameter of the wing electrode  22  becomes a minimum. The wing electrode  22  in such state can be housed in a housing tube  29  concentric with the electrode axis  21 . The housing tube  29  is provided with a slit group  23  (slits  23   a ,  23   b  . . . ), and each slit  23   a ,  23   b  . . . is positioned so as to correspond to a tip of each wing  22   a ,  22   b  housed in the housing tube  29 . The wings  22   a ,  22   b  . . . are inserted in each slit  23   a ,  23   b  . . . of the slit group  23  so as to slightly project each tip of the wings toward an outside of the housing tube  29 . Under such configuration, when rotating the electrode axis  21  and the housing tube  29  relatively, the tip of each wing  22   a ,  22   b  . . . can be inserted and extracted in a radial direction. It can be configured that each diameter of the tips of wings  22   a ,  22   b  . . . is adjustable (a diameter adjusting unit: the electrode axis  21 +the wing electrode  22 +the housing tube  29 +the slit group  23 ). 
     The wing electrode  22  changes to two modes, such as a housing state and a working state as mentioned hereinafter. Specifically, in the housing state, the tip of each wing  22   a ,  22   b  . . . is slightly projected from each slit  23   a ,  23   b  . . . of the housing tube  29 , and in the working state as shown in  FIG. 4 , each outer edge of the wing  22   a ,  22   b  . . . is pushed out near to an internal peripheral surface of the hollow pipe  100  by relatively rotating the electrode axis  21  and the housing tube  29  (a distance between the outer edge of each wing  22   a ,  22   b  . . . and the internal peripheral surface of the hollow pipe  100  is approximately 1 cm, for example). 
     Since at least the outer peripheral end of each wing is made of metal and electrically connected to the electrode axis  21 , when an electric field is applied between the electrode  20  and the hollow pipe  100  in the working state, the inside of the hollow pipe  100  is electro-polished. 
     It is needless to say that the same number of the wing electrodes  22  as the cells of the hollow pipe  100  is arranged on the electrode axis  21 . 
     INDUSTRIAL APPLICABILITY 
     As described above, the electrolytic polishing in the present invention is configured to perform the electrolytic polishing of the inside of the hollow pipe by inverting the hollow pipe repeatedly at the same time of pushing out the generated bubbles by circulating the electrolyte from the lower end of the hollow pipe, so that the inside can be polished evenly, and it is very effective to apply the invention to the product requiring precise polishing like the hollow pipe for the linear collider, in particular. 
     DESCRIPTION OF THE REFERENCE NUMERAL 
     
         
         
           
               20  Electrode 
               21  Electrode axis 
               22  Wing electrode 
               22   a ,  22   b  Wing 
               23  Slit group 
               23   a ,  23   b  Slit 
               29  Housing tube 
               50  Rack 
               51   a ,  51   b  Prop 
               60  Holding frame 
               61  Rotational axis 
               70  Coupling member 
               100  Hollow pipe 
               111   a ,  111   b  Flange 
               201   a ,  202   b  Clip 
               300   a ,  300   b  Liquid buffer 
               301  Supply/discharge pipe ( 301   a : Liquid supply pipe,  301   b : Liquid discharge pipe) 
               302  Valve mechanism 
               303  Pump