Abstract:
An electric motor is provided with a hollow rotating drive shaft extending along the central axis of the motor, a stationary liquid supply line and a rotating union which communicates with the liquid supply line and the hollow interior of the drive shaft for supplying liquid to the hollow interior of the drive shaft.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of pending U.S. patent application Ser. No. 12/446,812 filed on May 8, 2009 which is a national phase of PCT/CA2007/001885 and claims priority from U.S. provisional patent application Ser. No. 60/862,498 filed Oct. 23, 2006, all of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to centrifugal concentrators of the rotating bowl type for the separation of solids of higher density such as gold, iron or tin from a slurry containing solids of a lower density and liquid and more particularly to such centrifugal concentrators of the batch type. 
       BACKGROUND 
       [0003]    Various machines have been developed to separate particles of high density such as gold, iron or tin from tailings and other slurry streams using centrifugal concentration, using the centrifugal force created in a rotating bowl to separate the high density particles from the lower density slurry. The present applicant for example has invented batch centrifugal concentrators which are the subject of U.S. Pat. No. 4,824,431 and Canadian Patent no. 2149978, which are incorporated herein by reference. Such machines are designed to maximize the throughput of slurry, and are designed to withstand the heavy duty and wear arising from a relatively long-term operation at a mine. The rotating bowl is typically mounted on a shaft supported on large bearings, and is rotated by a motor beneath the machine which drives a drive belt connected to a sheave on the rotor shaft. 
         [0004]    Artisanal or small-scale mining is a mining activity which involves people working with simple tools and equipment, outside the legal and regulatory framework. Currently, it is estimated that there are many millions of people involved in artisanal mining around the world and that number is growing with the elevated price of gold. It takes place in the remote parts of the world&#39;s poorest countries. It usually involves the activities of single individuals or a small group of individuals who are impoverished and exploiting marginal deposits in harsh conditions. One common form of artisanal mining is placer gold mining or panning for gold. In order to separate the retrieved gold from the ore, the artisanal miner will often crush the ore and use mercury which combines with the gold to form an amalgam, and which can be separated from the other material as “cake”. The miners then heat the cake to burn off the mercury, leaving a residue of gold as well as causing health and environmental problems. There is therefore a need for a simple and inexpensive but environmentally safe method for artisanal miners to separate gold from particulate material. 
       SUMMARY OF INVENTION 
       [0005]    In order to provide a simple, inexpensive centrifugal concentrator for use in artisanal mining or other applications, the invention provides a centrifugal concentrator in which there is a common shaft for the drive motor and concentrator bowl. The cost of bearing assemblies is thereby minimized. The bowl is preferably driven and suspended from above to keep the motor out of the slurry area and maximize the simplicity of the design. A fluidizing fluid is preferably delivered through the common shaft. 
         [0006]    Thus according to the invention, an electric motor is provided with a hollow rotating drive shaft extending along the central axis of the motor, a stationary liquid supply line and a rotating union which communicates with the liquid supply line and the hollow interior of the drive shaft for supplying liquid to the hollow interior of the drive shaft. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    In drawings which illustrate a preferred embodiment of the invention: 
           [0008]      FIG. 1  is a perspective view of the centrifuge of the invention with water and power supplies and connections removed for ease of illustration; 
           [0009]      FIG. 2  is a partial vertical cross-section of the invention taken along lines  2 - 2  in  FIG. 1 ; 
           [0010]      FIG. 3  is a vertical cross-section of the invention taken along lines  3 - 3  in  FIG. 1 ; 
           [0011]      FIG. 4  is a detail cross-sectional view of the motor and rotor bowl as shown in  FIG. 3 ; 
           [0012]      FIG. 5  is a detail cross-sectional view of the rotor bowl as shown in  FIG. 3 ; 
           [0013]      FIG. 6  is a detail cross-sectional view of the motor as shown in  FIG. 3 ; 
           [0014]      FIG. 7  is a perspective view of the centrifuge of the invention showing the water supply connections; 
           [0015]      FIG. 8  is a perspective view of the centrifuge of the invention with a second embodiment of the tailings discharge arrangement; and 
           [0016]      FIG. 9  is a cross-sectional view of the embodiment of  FIG. 8  taken along lines  9 - 9  showing the flow of materials. 
       
    
    
     DESCRIPTION 
       [0017]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
         [0018]    With reference to  FIGS. 1 and 2 , the centrifuge of the invention is designated by reference numeral  10 . It has a rotor housing  12  comprising a hollow, rigid cylindrical drum, which is preferably formed from a standard 45-gallon drum. The top of the drum  12  is replaced with a motor support  14 , which supports motor  16 . Motor support  14  is provided with access openings  18  to provide access to the rotor  36  and motor support  14  provides a passageway for slurry feed pipe  24 . Drum  12  also has a cut-out forming a concentrate access door  20  and a tailings discharge port  22  ( FIG. 2 ). To stabilize the machine in operation, preferably the lower part of drum  12  is filled with concrete  26 , the surface of which forms a drain to connect to outlet port  22  through channel  28 . Secured to the underside of motor support  14  is annular rubber wear protector  30  which preferably is formed of a rubber automobile tire, having the same outer diameter as the inner diameter of drum  12 , and which may be formed by cutting an automobile tire in half diametrically. 
         [0019]    Motor  16  has a hollow drive shaft  32  ( FIG. 3-6 ) mounted on bearing assemblies  34 . Rotor  36  is mounted on the lower end of shaft  32 . Rotor  36  has a rotor bowl  38  of the same general type as disclosed in Canadian Patent no. 2149978. An impeller  37  is provided on the center of the floor of steel lower bowl section  41 . Impeller  37  has upstanding vanes to assist in the rotation of the slurry on the bottom of the rotor bowl  38  and to direct the slurry to the wall  39  of the rotor bowl. The wall  39  of rotor bowl  38  forms a smooth outwardly-inclined migration zone  40  lined with wear-resistant rubber, and a fluidized capture zone  42  above the migration zone, wherein the capture zone  42  has a number of fluidized annular cavities  44 . Cavities  44  are provided with a fluidizing fluid under pressure through apertures  46 . The capture zone is fluidized from a source of liquid under pressure located radially outwardly of the capture zone as follows. 
         [0020]    Fluidizing water under pressure is supplied to the cavities  44  from a stationary water supply line  50  which is connected to rotating union  52 . Rotating union  52  provides the water from stationary water supply line  50  to water line  54  which runs down the center of hollow shaft  32 . Hollow shaft  32  could itself also serve as the water supply line. Line  54  connects by a T-connection  56  to two rotating supply lines  58 . Rotating supply lines  58  provide the water to manifold  60  which communicates with apertures  46 . Supply line  50  is mounted to motor  16  by a bracket  17 , and has a control valve  19  ( FIG. 1 ) to regulate the flow and a pressure gauge  51  ( FIG. 7 ) to monitor the pressure. 
         [0021]    Motor  16  is, for example, a 2 horsepower 6 pole electric motor, suitable to be powered by a generator in a remote location, and which is modified to provide the hollow drive shaft described above. A frequency converter such as a Penta-Drive motor control can be provided with the power supply to control the speed of motor  16  in a range of about 900 to 1200 rpms. 
         [0022]    In operation, initially motor  16  is activated to rotate the rotor  36 . The slurry feed is introduced to the spinning rotor  36  through feed pipe  24 . Centrifugal forces cause the slurry to climb up the inner surface of the rotor bowl  38  before being expelled over the upper rim of the rotor, against rubber tire  30  and thence out of the drum  12  through discharge port  22 . Heavier target concentrate collects in fluidized cavities  44 . As the process advances, when the cavities  44  have been sufficiently filled with target concentrate, power to motor  16  is stopped, the rotation of bowl  36  slows, and water is sprayed through openings  18  using a wash hose, and from apertures  46 , to wash the concentrate out through channels  62  in the impeller  37  and lower floor of rotor bowl  38  and out through funnel  64 . Either a container can be inserted under funnel  64  through access port  20 , or a discharge pipe, not shown, can direct the concentrate outside the drum. 
         [0023]    The combination of the channels  62  through impeller  37  and rotor bowl  38  to funnel  64  enables rapid concentrate recovery. This method of discharging concentrate around a rotor baffle in the bottom of the rotor is disclosed in U.S. Pat. No. 4,824,431 and Canadian Patent no. 2149978. It results in short off line time for rinsing concentrate, which is useful for tin and tantalum applications as well as gold. Having the drive/support for the rotor bowl above the rotor bowl allows a simple, stationary funnel unobstructed below the bowl with a hose attached to it to recover concentrate. The hose is ducted outside the drum. Recovering concentrate is the then done by washing it out around the baffle and into the funnel/hose assembly when the rotor is stopped or at least turning very slowly. This makes for rapid concentrate recovery after each concentrating cycle, which is important for applications where the gold is locked in another mineral, and also for tin and tantalum. 
         [0024]      FIG. 8  shows a second embodiment of the tailings discharge in which a pipe  80  is connected at  82  to the outlet of bowl  38  to wash the tailings directly to an outlet  84  in the bottom of drum  12 , as further illustrated in  FIG. 9 . In the embodiment shown in  FIGS. 8 and 9 , rather than providing concrete to stabilize drum  12 , the sand and tailings  88  are allowed to build up in the bottom of the drum, below outlet  86 , which serves to stabilize the centrifuge during operation. 
         [0025]    While fluidizing water has been disclosed as the fluid being delivered through hollow shaft  32 , other gases or fluids such as compressed air or hydraulic fluid may be delivered in the same way to the rotor. In this way the present applicant&#39;s variable lip centrifuge as disclosed in co-pending international patent application no. PCT/CA2006/000596, filed Apr. 13, 2006, which is incorporated herein by reference, could also be configured with the drive motor above and supporting the rotor. 
         [0026]    While use of a fluidized capture zone has been disclosed above, the invention is also useful without a fluidizing section. In that case shaft  32  is solid, while maintaining the advantage that the shaft serves both as the motor drive shaft and to suspend the rotor. In this variant the machine can also be configured with the drive motor above and supporting the rotor. Since supply of fresh water for fluidizing is often difficult in the artisanal mining context, it may be preferable to construct the device in this way for some applications, though the capture of concentrate is less efficient than with the fluidized capture zone and more frequent stoppage of the device will be required. 
         [0027]    By utilizing the shaft of the motor both to drive and suspend the rotor, the number of bearing assemblies and other moving parts required for the machine is reduced and the cost is thereby reduced. Allowing the miner to assemble the machine using local 45-gallon drums and tires further reduces expenses. The 45 gallon drum can also be used as a convenient shipping container for the machine. The bowl is preferably driven and suspended from above to keep the motor out of the slurry area and maximize the simplicity of the design. However the drive motor could also be mounted below the rotor while still using the common hollow shaft both to drive and support the rotor and deliver the fluidizing fluid. 
         [0028]    The discovery that the hollow drive shaft of a motor can be used both to drive a rotating element and deliver a fluid has been found to have other useful applications, such as a lawn or garden sprinkler, wherein a series of liquid outlets is provided at the end of the hollow drive shaft. Where the liquid is air, the same arrangement can be used to inject air into the rotating agitator blade of a flotation machine. The same arrangement can be used to pass hydraulic fluid through one or more passages to power a tool attached to the rotating drive shaft. 
         [0029]    As will be apparent to those skilled in the art, various modifications and adaptations of the structure above described may be made without departing from the spirit of the invention. While the preferred embodiment has been described in the context of the separation of higher density particles from a slurry, it will be apparent to those skilled in the art that the invention has similar application in the separation of any two flowable substances of differing density, whether solid particles from solid particles, liquid from liquid or solid particles from liquid.