Abstract:
A method is provided for separating particles having different triboelectric propensities. The method utilizes a voltage of less than five volts electrically charge a surface and to reduce the risk of fires and explosions that are associated with particle treatment facilities. The method charges a surface and the surface is used to attract particles. The method does not focus on charging particles. The method also utilizes apparatus in which the electric charge is frictionally produced by a member positioned on the inside of the apparatus.

Description:
This application is a continuation-in-part of application Ser. No. 09/021,431, filed Feb. 10, 1998, now U.S. Pat. No. 6,072,140, issued Jun. 6, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     This invention pertains to a particle separation method and apparatus. 
     More particularly, the invention relates to an apparatus and method for separating dielectric particles. 
     In a further respect, the invention relates to a particle separation apparatus and method which reduce the risk that a fire or explosion will occur during the separation of particulate. 
     In another respect, the invention relates to a particle separation apparatus and method which facilitates the separation of elongate fiber strands from a plurality of small substantially round particles. 
     2. Description of the Related Art including information disclosed under 37 C.F.R. 1.97 and 1.98. 
     A wide variety of particle separation apparatus is apparently known in the art. One such particle separation apparatus is illustrated in FIG.  1  and includes a cylindrical steel roller  10  which rotates in the direction of arrow E about axle  42 . A hopper  11  feeds a mixture of electrically non-conductive  12  and electrically conductive particles  13  onto the cylindrical outer surface or roller  10 . The size of the particles is greatly exaggerated for purposes of clarity. The positive side of the power supply is connected to the roller  10 . The roller  10  is grounded. An elongate wire  14  is spaced apart from and parallel to the cylindrical surface of roller  10 . The wire  14  serves as the negative electrode. A large voltage is directed through wire  14  to produce a corona around the wire. Negative ions move through the field produced by the wire to roller  10 . The conductive particles  13  conduct negative ions to roller  10 . Consequently, the conductive particles  13  fall off the surface or roller  10  or are thrown off roller  10  into bin  16 . In contrast to the conductive particles  13 , negative ions are believed to accumulate on the outer surface of each non-conductive particle  12  to cause each particle  12  to be attracted to the positively charged roller  10 . The negatively charged non-conductive particles are scrapped off by scraper  43  into bin  15 . Several disadvantages are associated with the apparatus of FIG.  1 . First, the high voltage required to form a corona around wire  14  increases the risk of explosion or fire during the separation of particulate. Seconded, while the apparatus of FIG. 1 is well suited for the separation of conductive and non-conductive particles, it ordinarily is not believed well suited for separation of two types of conductive particles (for instance copper and silver particles) or for separation of two types of non-conductive particles (for instance rubber and paper particles). 
     Accordingly, it would be highly desirable to provide an improved particle separation apparatus and method which would significantly minimize the risk of fire or explosion and which could be utilized to separate dielectric particulate. 
     Therefore, it is a principal object of the invention to provide an improved method and apparatus for separating particles. 
     A further object of the invention is to provide an improved method and apparatus for separating dielectric particles. 
     Another object of the invention is to provide an improved particle separation method and apparatus which minimizes the utilization of energy at levels which increase the risk of fire. 
     Still a further object of the invention is to provide an improved particle separation method and apparatus which can distinguish between particles of differing size and tribolelectric propensity. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     These and other, further and more specific objects an advantages of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the drawings, in which: 
     FIG. 1 is an elevation view illustrating a prior art particle separation apparatus; 
     FIG. 2 is a perspective view illustrating particle separation apparatus constructed in accordance with the principles of the invention; 
     FIG. 3 is an end view illustration a roller utilized in an alternate embodiment of the invention; 
     FIG. 4 is a side elevation view illustrating an alternate emobidment of the invention; and, 
     FIG. 5 is a perspective view illustrating an electrically chargeable panel utilized in the apparatus of FIG.  4 . 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, in accordance with my invention, I provide an improved method for separating particles. The method includes the steps of providing an article including a group of particles each having a selected weight and triboelectric propensity; electrically charging a surface to attract and hold particles in the particles in the group; contacting the surface with the particles in the group; and, neutralizing the electric charge on the surface such that the particles in the group can be removed from the surface. 
     In another embodiment of my invention, I provide an improved processing system including an article including a group of particles each having a selected weight and triboelectric propensity; apparatus for electrically charging the surface to attract and hold the particles in the group; apparatus for contacting the surface with the particles; and, apparatus for neutralizing the electric charge on the surface such that the particles can be removed from the surface. 
     In a further embodiment of my invention, I provide an improved processing system including a continuous belt; apparatus for moving the belt; at least one electrically chargeable surface connected to the belt; apparatus for electrically charging the surface to attract and hold particles each having a selected triboelectric propensity; and, means for neutralizing the electric charge on the surface. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, which describe the presently preferred embodiments for the purpose of illustrating the structure and use thereof and not by way of limitation of the scope of the invention, and in which like reference characters refer to corresponding elements throughout the several views, FIG. 2 illustrates a particle processing system which receives a stream of comingled particles falling under gravity as indicated by arrows A. The comingled particles include at least two separate groups of particles. The density, size, shape, electrical conductivity, modules of elasticity, color, weight, hardness, and other physical properties of each particle and/or group of particles can vary as desired; however, in the presently preferred embodiment of the invention, each group of particles consists of a dielectric. The first group of particles consists of generally spherical rubber particles having a maximum width in the range of about {fraction (1/32)} to ⅛ of an inch. The second group of particles consists of nylon and/or rayon fibers or lint having a length in the range of about {fraction (1/64)} to ¼ of an inch and width in the range of about {fraction (1/128)} to {fraction (1/32)} of an inch. These comingled particles can be produced by grinding automobile and truck tires and using magnets and other filtering apparatus to remove metal cord from the ground material. Each fiber particle in the second group of particles weighs less than each rubber particle in the first group of particles and weighs less than 50%, preferably less than 30%, of the weight of each rubber particle in the first group of particles. The rubber particles comprise 97% to 98.5% of the comingled particles. The nylon and/or rayon fibers comprise 1.5% to 3% by weight of the comingled particles. The comingled particles typically sell at a price of about $40.00 to $70.00 a ton. If, however, the fibers can be separated from the comingled particles the price per ton of the rubber increases very significantly. New butyl rubber sell for about $2,000.00 a ton. If most of the nylon and/or rayon fibers can be removed so that the particle mixture is only ¼% to ½% fibers and is 99.5 to 99.75% by weight rubber particles, then the price of the mixture typically increases from $40.00 to $70.00 per ton to $400.00 to $700.00 a ton. In addition, such a low fiber—particle mixture can be blended in with new rubber to make many products. 
     Nylon and rayon are each a dielectric. Table I provides the dielectric constant for each of a variety of common dielectrics. 
     
       
         
               
             
               
               
             
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Dielectric Constants for Common Materials 
               
             
          
           
               
                 Dielectric Constant 
                 Material 
               
               
                   
               
             
          
           
               
                 1.0 
                 Air 
               
               
                 25.0 
                 Ethyl alcohol 
               
               
                 2.5 
                 Transformer oil 
               
               
                 4.5 
                 Bakelite 
               
               
                 2.0 
                 Beeswax 
               
               
                 2.5 
                 Ebonite 
               
               
                 4.5-7.0 
                 Glass, various kinds 
               
               
                 6.0 
                 Mica 
               
               
                 4.1 
                 Micarta 
               
               
                 2.0 
                 Paper, dry 
               
               
                 2.3 
                 Paraffin 
               
               
                 4.0 
                 Plexiglas 
               
               
                 2.5 
                 Rubber, pure 
               
               
                 4.0 
                 Wood 
               
               
                 5.1 
                 Potassium Chloride 
               
               
                 2.7 
                 Asphalt 
               
               
                 4.0 
                 Iodine 
               
               
                 6.6 
                 Selenium 
               
               
                 6.32 
                 Corning 0010 
               
               
                 3.8 
                 Silica Glass 
               
               
                 2.1 
                 Teflon 
               
               
                 3.8 
                 Quartz, fixed 
               
               
                 3.0 
                 Paper, Royal grey 
               
               
                 2.6 
                 Polystyrene 
               
               
                 5 to 7.5 
                 Fiber 
               
               
                 5 to 7.5 
                 Formica 
               
               
                 5.1 to 5.9   
                 Porcelain 
               
               
                   
               
             
          
         
       
     
     The triboelectric propensity of a material is the propensity of a first material to become positively charged (give up electrons to a second material) when the first material is rubbed with the second material. A first material has a greater triboelectric propensity than a second material if the first material gives up electrons to the second material when rubbed by the second material. For example, in Table II, nylon has a greater triboelectric propsensity than hard rubber, wood, silk, etc. Glass has a greater triboelectric propsensity than nylon. 
     
       
         
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 Triboelectric Series 
               
               
                 Any material in this table becomes positively charged (i.e., it gives up 
               
               
                 electrons) when the material is rubbed with any material lower on the list. 
               
               
                 The farther apart the materials are on the list, the higher the charge will be. 
               
               
                 Surface conditions and variation in characteristics of some material may 
               
               
                 alter some positions slightly. 
               
               
                   
               
             
             
               
                 Positive polarity (+) 
               
               
                 Asbestos 
               
               
                 Rabbit&#39;s fur 
               
               
                 Glass 
               
               
                 Mica Nylon 
               
               
                 Wool 
               
               
                 Cat&#39;s fur 
               
               
                 Ca, Mg, Pb 
               
               
                 Silk 
               
               
                 Paper 
               
               
                 Cotton 
               
               
                 Wood 
               
               
                 Lucite 
               
               
                 Sealing wax 
               
               
                 Cork, Ebony 
               
               
                 Amber 
               
               
                 Polystyrene 
               
               
                 Polyethylene 
               
               
                 Rubber balloon 
               
               
                 Resins 
               
               
                 Cu, Ni, Co, Ag, Sn, As, Bi, Sb, Pd, C, Brass 
               
               
                 Para Rubber 
               
               
                 Sulphur 
               
               
                 Celluloid 
               
               
                 Hard rubber 
               
               
                 Vinylite 
               
               
                 Saran wrap 
               
               
                 Negative polarity (−) 
               
               
                   
               
             
          
         
       
     
     The comingled particles fall onto rotating cylinder or drum  17 . Drum  17  can be fabricated from any desired material but presently preferably is not a metal in order to minimize the likelihood that a spark may be generated which can cause a fire or explosion. Drum  17  is presently fabricated from a dielectric. Drum  17  is presently preferably PVC (polyvinyl chloride). Elongate generally rectangular metal plates  18  to  23  (presently aluminum) are conformed to and mounted on the inner surface of cylindrical drum in spaced apart parallel relationship. A motor or other means (not shown) are provided for rotating hollow drum  17  about centerline or axis X in the direction indicated by arrow D. Plates  18  to  23  are affixed to and rotate simultaneously with drum  17 . A generally rectangular strip  24  of nylon carpet is mounted in a fixed position in which strip  24  is generally parallel to axis X and is positioned such that each metal strip  18  to  23  rubs against strip  24  as the metal strip rotates past strip  24  in the direction indicated by arrow D. When a metal strip  18  to  23  rubs against carpet strip  24 , friction results which causes electrons to be transferred from stip  24  onto the strip  18  to  23 , producing an electrical potential in strip  18  to  23  which is greater than zero volts and less than about five volts. When a strip  18  to  23  becomes negatively charged, the outer cylindrical surface  17 A of drum  17  develops a negative charge. The negatively charged outer surface  17 A more strongly attracts and holds the lighter, more triboelectrically sensitive fiber particles than the heavier, less triboelectrically sensitive rubber particles. Less dense particles also tend to be more effectively attached and held by charged surface  17 A than more dense particles of the same size. Consequently, as drum  17  continues to rotate in the direction of arrow D, the heavier, denser, less triboelectrically sensitive rubber particles fall free form surface  17 A under the force of gravity (and/or are thrown free) and travel into storage bin  40 . In contrast, the lint particles continue to adhere to outer surface  17 A until the metal plate  18  to  23  which is immediately beneath such adhering particles contacts metal roller  25 . Roller  25  is, as indicated by arrow  26 , connected to ground. When a plate  18  to  23  contacts roller  25 , the negative charge in roller  25  is completely or substantial discharged, in which case the portion of outer surface  17 A immediately above plate  18  to  23  loses most or all of its negative charge, permitting the fibers to fall in the direction of arrow C into bin  41 . If desired, means (not shown) can also be provided to scrap off fiber particles in the manner shown in FIG.  1 . 
     After a plate is discharged by contacting roller  25 , the plate is again negatively charged when it rotates over carpet  24 . This charge—discharge cycle continues for as long as drum  17  continues to rotate and intermittently contact a plate with carpet  24  and roller  25 . Any means other than rug  24  can be utilized to generate a negative (or positive) charge on a plate  18  to  23  and/or the outer surface  17 A. 
     One important advantage of the invention is the lower voltage required to generate a charge on the outer surface  17 A. 
     Another advantage is the ability to position plates  18  to  23  inside drum  17  to reduce further the danger that a spark generated during the charging or discharge of a plate  18  to  23  could initiate an explosion or fire. As illustrated in FIG. 3, generally circular plates  29 ,  30  can be placed at either end of drum  17  to further enclose most of plates  18  to  23  and to enclose rug  24  and roller  25 . If desired, a metal roller  31  can be provided which rolls over the end of each plate  18  to  23  as it passes by roller  31 . Roller  31  is connected to ground to permit each plate  18  to  23  to discharge when it contacts roller  31 . Roller  31  continuously rotates in the location shown in FIG.  3  and does not move about axis X with roller  17 . 
     Still another advantage of the processing system of the invention is that it can be utilized to separate two groups of dielectric particles. 
     Yet another advantage of the processing system of the invention is that separation of two group of dielectric particles is often facilitated by allowing the particles to rub against one another prior to dispensing the particles in the direction of arrow A onto drum  17 . Such rubbing of particles can be promoted by directing the particles over a vibrating table which permits the particles to bump and rub against each other while moving the particles to the edge of the table so they fall in the direction of arrows A onto drum  17 . Since the fiber particles have a great triboelectric prospensity than the rubber particles, rubbing the fiber particles against the rubber particles tends to produce a positive surface charge on the fiber particles. Positively charging the fiber significantly improves the attraction between the negatively charged drum  17  and the fiber. 
     An alternate embodiment of the invention is illustrated in FIG.  4  and includes a continuous belt  44  mounted on driven rollers  36  and  37 . Rollers  36  and  37  move belt  44  in the directions indicated by arrows E and F. A plurality of panels  35  are mounted on belt  44 . Each panel  35  includes a rear elongate linear edge  46  which is pivotally attached to belt  44  in the manner described below. Each panel  35  also includes an outer surface  45  and can be electrically charged to attract particles having a selected triboelectric propensity. Panels  35  can be constructed in any desired manner as long as each panel  35  can be electrically charged to attract the desired particles. It is preferred that, as was the case of the embodiment of the invention illustrated in FIG. 2, the voltage utilized to create the electrical charge in each panel  35  and/or surface  45  be minimal. Charge induction means  38  is utilized to create an electric charge in each panel  35 . The charge induction means  38  can comprise any desired means and is usually, but not necessarily, adjacent or contacting either belt  44  and panel  35 . By way of example, the charge induction apparatus  24  utilized in FIG. 2 can be utilized to create a charge on panels  35 . 
     The width of belt  44  can vary but presently is about equal to the width W of each panel  35 . Belt  44  can comprise a continuous rubber strip, can comprise a pair of spaced apart parallel continuous chains each connected to one end of each panel  35 , or can comprise any other structure for supporting and carrying panels  35  around rollers  36  and  37  in the manner illustrated in pan FIG.  4 . 
     Charge neutralization means  39  are utilized to neutralize or remove the electrical charge from a panel  35 . By way of example, the charge neutralization apparatus  25  utilized in the apparatus of FIG. 2 can be utilized as the charge neutralization means  39 . 
     Panels  35  presently comprise thin metal slats, but can comprise a thin layer of metal (forming surface  45 ) on a rubber member or take on any desired shape and dimension and construction. 
     In operation of the apparatus of FIG. 4, comingled particles fall in the direction of arrow G onto the outer surfaces  45  of overlaid panels  35 . In FIG. 4, overlaid panels  35  are shown spaced apart immediately beneath arrow G. This configuration is acceptable, but it is preferred that overlaid panels  35  contact each other as they pass beneath arrow G and over the charge inductions means  38 . Charge induction means  38  produces an electrical potential in each panel  35  overlaid on belt  44  which is greater than zero volts and less than about five volts. The negatively charged outer surface  45  more strongly attracts and holds the lighter, more triboelectrically sensitive fiber particles than the heavier, less triboelectrically sensitive rubber particles. Less dense particles also tend to be more effectively attached and held by charged surface  45  than more dense particles of the same size. Consequently, as belt  44  continues to move in the direction of arrow E and down around roller  36 , the heavier, denser, more triboelectrically sensitive rubber particles fall free from surfaces  45  under the force of gravity (and/or are thrown free) and travel downwardly in the direction of arrow H into storage bin  34 . In contrast, the lint particles continue to adhere to outer surface  45  until the charge neutralization means  39  removes the negative charge from belt  44 . When the negative charge in belt  44  is completely or substantially discharged, panels  35  each lose most or all of their negative charge, permitting the fiber particles to fall in the direction of arrow I into bin  33 . If desired, means (not shown) can also be provided to scrap off fiber particles. 
     After belt  44  is discharged by charge neutralization means  39 , contacting roller  25 , the belt (and each panel  35 ) is again negatively charged when it passes by charge induction means  38 . This charge—discharge cycle continues for as long as belt  44  is driven by roller  36  and/or  37  and moves in the directions indicated by arrows E and F. 
     When belt  44  moves down and around roller  36 , the force of gravity causes overlaid panels  35  to spread or fall apart from and lose contact with one another in the manner shown. This falling apart functions to electrically disconnect each panel from the panels passing over induction means  38 . 
     Each panel  35  is, as earlier noted, pivotally connected or hinged to belt  44  along the edge  46  of panel  35 . This pivotal connection, however, only permits each panel  35  to open or fall a selected distance (i.e., so each panel  35  is normal to belt  44 ) so that after belt  44  moves up, over, and around roller  37 , panels  35  will again fall and pivot under gravity into the overlaid configuration shown in FIG. 4 immediately beneath arrow G. However, the arrangement and mounting of panels  35  on belt  44  can vary as desired. Panels  35  need not overlie or contact each other when belt passes beneath arrow G and over induction means  38 . Panels  35  may be mounted on the underside or inside of belt  44 , much like strips  18  to  23  are mounted on the inside of cylinder  17 A in FIG.  2 . Panels  35  may not pivot and may each be attached to belt  44  in a permanent position spaced apart from other panels. Each panel can comprise a small metal dimple or area which is attached to the outer or inner surface of belt  44  and spaced apart from other dimples. And so on. 
     The apparatus of FIGS. 2 to  5  can, instead of being used to separate comingled particles, be utilized to remove particles from fabric or another article. For example, in FIG. 4, a strip of fabric  46  can be placed adacent to electrically charged panels  35  to pull lint or other particles from the strip of fabric  46  onto panels  35 . Or, fabric strip  46  can move past panels  45  in the direction of arrow E or in a direction opposite that of arrow E. While fabric strip  46  moves past panels  35 , particles can be pulled from strip  46  onto panels  35 . The article placed adjacent or in contact with panels  35  or with the apparatus of FIG. 2 can be held stationary or can be moved in any desired manner to facilitate removal from the article to panels  35  of desired particles or of other objects of any shape and dimension.