Abstract:
An apparatus electrochemically removes fine metal particles from an oil in water emulsion. The apparatus has a container for accommodating the emulsion. A supply port supplies the emulsion to the container. A plurality of cathode plates and anode plates are located in the container to face each other. The water in the emulsion is electrolyzed when a predetermined direct voltage is applied between the plates. The fine metal particles float with hydrogen generated by the electrolysis. Al(OH) 3  attaches to H 2  bubbles. A discharge port is located in a lower part of the container for discharging the emulsion from which the fine metal particles, sludge, oil and greese have been removed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus and a method for removing fine metal particles and the like from a cutting oil used in cutting aluminum or the like, for example, for aircraft materials. More particularly, the present invention relates to an apparatus and a method for electrochemically removing fine metal particles from an emulsion to clean cutting oil. 
     Conventionally, when an aluminum alloy workpiece to be cut is machined into a desired shape using a cutting machine, cutting oil has been used for cooling the workpiece at the cutting location and for imparting fluidity to the metal chips. An emulsion of oil in water having a water:oil mixing ratio of 95:5 is mainly used. 
     To reuse the emulsion, fine metal particles, grease and lubricating oil are removed. According to the conventional removal operation, the used emulsion is subjected to centrifugation or filtration. 
     However, the fine metal particles have extremely small diameters, and further, the difference in the specific gravity between water and the fine metal particles, particularly of aluminum, contained in the cutting oil subjected to centrifugation is not large. Therefore, water and fine metal particles cannot be fully separated from each other by means of centrifugation. Meanwhile, when the emulsion is subjected to filtration, the fine metal particles that have very small diameters pass through the filter. Therefore, the fine metal particles contained in the emulsion cannot be removed completely. 
     Further, when a filter is used in the removal of fine metal particles, the fine metal particles clog the filter, and maintenance is needed. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide an apparatus and a method for removing electrochemically fine metal particles in an emulsion to clean and reuse the emulsion. 
     It is a second object of the present invention to provide an apparatus and a method for removing fine metal particles that reduce maintenance requirements and facilitates removal of fine metal particles. 
     To achieve the above objects, the present invention provides an apparatus for electrochemically removing fine metal particles in an oil and water emulsion. The apparatus includes a container for accommodating the oil in water emulsion. A supply port supplies the emulsion to the container. A plurality of cathode plates and anode plates are located in the container to face each other. The water in the emulsion is electrolyzed when a predetermined direct voltage is applied between each anode plate and each cathode plate. The fine metal particles along with sludge, greese and lubricating oil which is the main odor float with hydrogen generated by the electrolysis. A discharge port is located in the lower part of the container, and the oil in water emulsion is discharged without the metal particles. 
     The present invention also provides an electrochemical removing method for removing fine metal particles. The method includes supplying an oil in water emulsion to a container from a supply port on the container, supplying the emulsion between a plurality of anode plates and cathode plates located in the container to face each other, applying a predetermined direct voltage to the emulsion to electrolyze water in the emulsion and to remove the fine metal particles with hydrogen generated from the anode plate by the electrolysis, and discharging the emulsion, from which the fine metal particles have been removed, from the discharge port. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a perspective view showing a container of the apparatus for removing fine metal particles (remover) according to one embodiment of the present invention; 
     FIG. 2 is a perspective view of an internal part of the remover contained in the container shown in FIG. 1; 
     FIG. 3 is a cross-sectional view taken along the line  3 — 3  in FIG. 1; and 
     FIG. 4 is a cross-sectional view taken along the line  4 — 4  in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described below with reference to FIGS. 1 to  4 . 
     The oil in water emulsion referred to in this description is a mixture of water and an oil having a water:oil mixing ratio of 95:5. In the present embodiment, Sindol 3201 (trade name), manufactured by Houghton Japan Co., Ltd., is used as the emulsion. This emulsion has, as physical properties, a hydrogen ion concentration (pH) of 7.2 and a friction coefficient of 0.11. Further, the emulsion is used as a coolant for cutting or grinding aluminum or an aluminum alloy for aircraft materials. The used emulsion contains fine aluminum particles, sludge, lubricating oil for the cutting machine, grease, malodorous components and the like. 
     As shown in FIGS. 1,  3  and  4 , a remover  10  includes a rectangular metallic container  11 . The container  11  has a pair of short sidewalls  12 , a pair of long sidewalls  13 , and a bottom plate  14 . The container  11  has an open top. A pair of small extensions  15  extend diagonally upward from the upper ends of the short sidewalls  12 , respectively. A pair of large extensions  16  extend diagonally upward from the upper ends of the long sidewalls  13 , respectively. Therefore, the opening of the container  11  is gradually increased by the small extensions  15  and the large extensions  16 . 
     A pair of sprockets  17  are rotatably supported by shafts  18  at opposite ends of the large extensions  16 , respectively. A chain  19  extends across each pair of sprockets  17 . A rectangular plate-like squeegee  20  is attached to and between the chains. The squeegee  20  is perpendicular to the chains, and the length of the squeegee  20  is substantially equal to the width of the short sidewall  12 . When the chains  19  move, the squeegee  20  moves in the left-light direction of FIG.  4 . 
     As shown in FIGS. 1 and 3, the first long sidewall  13  is provided with a rectangular supply container  21 . A plurality of supply ports  22  are defined in the first long sidewall  13 . The used emulsion is poured into the supply container  21  and enters the container  11  through the supply ports  22 . 
     A discharge port  23  is defined in the second long sidewall  13  to communicate with the inside of the container  11 . The discharge port  23  is connected to a vertical discharge conduit  24  which extends along the second long sidewall  13  and is open at its top. As shown in FIG. 3, the upper opening of the discharge conduit  24  and that of the supply container  21  are located at substantially the same vertical position. A rectangular receiving container  25  is attached to the middle of the discharge conduit  24  to cover a part of the discharge conduit  24 . The receiving container  25  is provided with a discharge pipe  26  communicating with the inside of the receiving container  25 . 
     The emulsion in the container  11  is discharged into the discharge conduit  24  through the discharge port  23 , and the emulsion overflows the discharge conduit  24  and flows into the receiving container  25 . 
     As shown in FIGS. 2 to  4 , in the container  11 , a pair of conductors  27  and  27   a , both made of a metal material, are located on the bottom plate  14  beside the long sidewalls  13 , respectively. The first conductor  27  is connected to a power supply (not shown), whereas the second conductor  27   a  is grounded. 
     On the first and second conductors  27  and  27   a , anode plates  29  and cathode plates  28 , both made of graphite, are arranged alternately at predetermined intervals. The end plate ends up with cathod plate  28 . The anode plates  29  each have a generally rectangular form, and the corner of each anode plate  29  that is adjacent to the second conductor  27   a  is cut away. Therefore, the lower end of each anode plate  29  is in contact with the first conductor  27 , and the cutaway portion of the anode plate  29  is spaced from the second conductor  27   a . Like the anode plates  29 , the cathode plates  28  each have a generally rectangular form, and the corner that is adjacent to the first conductor  27  is cut away. Therefore, the lower end of each cathode plate  28  is in contact with the second conductor  27   a , and the cutaway portion of the cathode plate  28  is spaced from the first conductor  27 . When a DC voltage is applied to the first conductor  27  from the power supply, the anode plates  29  and the cathode plates  28  are connected positively and negatively, respectively. The level of the DC voltage applied can be changed depending on the gap between the cathode plate  28  and the anode plate  29 . However, the voltage to be applied is preferably 10 V or higher, to ensure sufficient H 2  bubble generation, i.e., electrolysis of the emulsion to achieve efficient removal of aluminum, sludge, grease, malodorous components and the like. 
     Four synthetic resin bolts  31  penetrate all of the cathode plates  28  and the anode plates  29  at a central region of the plates  28 ,  29 . As shown in FIG. 4, a nut  32  made of a synthetic resin is engaged with the tip of each bolt  31 . Cylindrical spacers  33  made of a synthetic resin are fitted on the periphery of the bolts  31  between each adjacent cathode plate  28  and anode plate  29  pair. The spacers  33  keep constant gaps between each adjacent cathode plate  28  and anode plate  29  pair. 
     The container  11  contains a substantially U-shaped partition  34  made of a synthetic resin. The partition  34  has a pair of upright portions located substantially along the center of the outermost anode plate  29  and that of the outermost cathode plate  28 . A connecting portion which connects the pair of upright portions of the partition  34  is located between the plates  28 ,  29  and the bottom plate  14  of the container. 
     Next, the method of using the remover  10  for removing fine metal particles in an emulsion is described. 
     When an aluminum workpiece is cut, the emulsion a coolant is delivered into the supply container  21  and is supplied to the container  11  through the supply ports  22 . As shown in FIG. 4, since each supply port  22  is positioned between a cathode plate  28  and an anode plate  29 , the emulsion flows through the supply ports  22  into the spaces between the plates. Further, in FIG. 4, a part of the partition  34  is located between the rightmost cathode plate  28  and the associated short sidewall  12 , and no supply port  22  opens into the spaces defined between that cathode plate  28  and short sidewall  12 . Therefore, the emulsion does not flow into the space between that cathode plate  28  and that short sidewall  12 . Likewise, the emulsion does not flow into the space defined between the leftmost catode plate  28  and the associated short sidewall  12 . 
     When a DC voltage of 10 V (a current of 50 A) is applied to the first conductor  27  from a power supply, the anode plates  29  and the cathode plates  28  are connected positively and negatively, respectively. The large aluminum chips settle due to gravity to the bottom section of supporting plates  14 . 
     The emulsion flows into the spaces defined between the plates  28 ,  29 . The water in the emulsion undergoes electrolysis. As a result, hydrogen bubbles (H 2 ) are generated from the cathode plates  28 , while hydroxide ions (OH − ) are generated by the anode plates  29 . Fine aluminum particles, which remain unsettled, are dispersed in the solution, dissolved, and converted into aluminum ions (A 1   3+ ) 
     Next, as shown in FIG. 4, hydrogen bubbles (H 2 ) generated at the cathode plates  28  ascend through the emulsion as fine bubbles, which causes an upward flow in the solution, and hydroxide ions (OH − ) generated from anode paltes  29  react with Al 3+  to form Al(OH) 3 . Al(OH) 3  is attached to ascending H 2  bubbles, since Al(OH) 3  has the characteristics of stickness. Thus, the solution is stirred to facilitate bonding of the OH −  ions with the aluminum ions. As a result, particles of aluminum hydroxide Al(OH) 3  are formed. The ascending hydrogen bubbles adhere to the aluminum particles sludge, grease and malodorous contained in the emulsion and then float upward to the liquid surface. 
     Unnecessary aluminum, sludge, grease, malodorous components and the like are separated from the used emulsion by floating or settling to form a clean emulsion in the central portion of the solution. Further, since aluminum hydroxide is formed, almost no hydroxide ions remain in the emulsion. In addition, almost all hydrogen ions are converted to hydrogen molecules, so the emulsion is kept neutral. 
     The used oil in water emulsion is continuously supplied to the container  11  through the supply ports  22 . Thus, the clean emulsion is discharged to the discharge conduit  24  through the discharge port  23 . Further, the clean emulsion flows into the discharge conduit  24  until the fluid level reaches the level in the container  11  and then overflows the discharge conduit  24  into the receiving container  25 . The clean emulsion is recovered in a recovery container, not shown, through the discharge pipe  26 . Thus, clean oil in water emulsion, which maintains as the original coolant oil characteristics, is recovered. 
     The sprockets  17  are rotated, and the chains  19  move the squeegee  20  to sweep over the liquid surface. Thus, as shown in FIG. 3, the squeegee  20  scrapes matter from the liquid surface, including fine aluminum particles, sludge, grease and the like. Finally, after completion of the above operation, the aluminum chips deposited on the bottom plate  14  of the container  11  are removed. In the present embodiment, floating aluminum chips having particle size less than 1 μm or smaller can be removed effectively. 
     The present embodiment has the effects described below. 
     When the emulsion flows into the space defined between the plates  28 ,  29 , hydrogen (H 2 ) are generated at the cathode plates  28  and ascend in the form of bubbles, which causes an upward flow in the emulsion. Then, aluminum hydroxide attached to H 2  bubbles floats to the liquid surface. Further, during floating process, sludge, grease and the like adhere to H 2  bubbles which are aluminum hydroxide and are carried to the liquid surface. As a result, fine aluminum particles, sludge, grease, malodorous components and the like are separated to produce clean oil in water emulsion. 
     Fine aluminum particles and the like in the emulsion are removed according to the method, which uses electrolysis. Therefore, this method requires no maintenance such as cleaning of clogged filters, which is required when a filter is used. Thus, the operation is more efficient. 
     Hydroxide ions generated at the anode plates  29  are bonded to aluminum ions to form aluminum hydroxide. In addition, hydrogen ions are converted to hydrogen. Therefore, the emulsion is kept neutral. This prevents corrosion of workpieces, which can occur when the emulsion is reused. 
     Since the anode plates  29  and the cathode plates  28  are arranged alternately, the emulsion flowing into the spaces between the plates  29 ,  28  is reliably electrolyzed. This ensures formation of hydrogen and aluminum hydroxide to produce a clean emulsion. 
     The anode plates  29  and the cathode plates  28  are arranged alternately at fixed intervals through the spacers  33  respectively. Therefore, a fixed amount of emulsion flows into each space between the plates  28 ,  29 , which results in a homogeneous reaction. 
     The clean emulsion is delivered to the discharge conduit  24  through the discharge port  23  until the level reaches the fluid level in the container  11 . The emulsion then overflows the discharge conduit  24  and is received by the receiving container  25 . Therefore, the remover  10  requires no apparatus for pumping the clean emulsion, which reduces costs. In addition, by continuously supplying used emulsion through the supply ports  22 , clean emulsion can be continuously recovered from the discharge conduit  24 . 
     The container  11  has the squeegee  20 , which is designed to move along the liquid surface in the direction of movement of the chains  19 . Therefore, aluminum, sludge, grease and the like floating on the liquid surface are scraped off. 
     The cathode plates  28  and the anode plates  29  each have a flat plate shape. Therefore, the plates  28 ,  29  provide large contact areas for the emulsion, which improves the efficiency of removing aluminum, sludge, grease, malodorous components and the like, as compared with bar-shaped plates  28 ,  29 . 
     An electrolytic treatment and chemical reactions were carried out in removing impurities from an emulsion to compare them in terms of throughput. In the comparison test, an 88 cm 3  cell was used for this treatment. 
     In the electrolytic treatment, the remover of this embodiment was used. In this treatment, fine aluminum particles and sludge contained in a used emulsion were removed completely, and grease was almost removed. 
     The present embodiment can be modified and practiced as follows. 
     The remover  10  may be used, for example, for an emulsion used in cutting and grinding of a metallic material other than aluminum, for example, an aluminum alloy, iron or nickel. 
     The discharge conduit  24  may be omitted. In such a case, the clean emulsion is directly recovered through the discharge port  23 . 
     The anode plates  29  and the cathode plates  28  may be modified to have cylindrical shapes or the like. 
     The anode plates  29  and the cathode plates  28  may be formed from lead oxide, carbon felt, carbon wool or the like. Meanwhile, in the case where the oil in water emulsion has a low aluminum concentration, the anode plates  29  and the cathode plates  28  may be formed from a metal such as titanium, stainless steel or the like. 
     The sprockets  17 , the chains  19  and the squeegee  20  may be omitted. Aluminum, sludge and grease floating on the liquid surface may be collected and recovered, for example, by blowing air from one small extension  15  toward the other small extension  15 . 
     The partition  34  may be omitted. The objective is to minimize the unreacted zone. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.