Abstract:
An electromagnetic pump has a supply section and a magnetic force pumping section wherein flow of a electrically conductive material through the supply section is opposite to the flow of the material in the magnetic force pumping section in some examples. Multiple coils surround the supply and magnetic force pumping sections. Current flowing through the multiple coils creates magnetic fields that magnetically couple with a magnetic material disposed between the supply and magnetic force pumping sections so that the fields penetrate the electrically conductive material in the magnetic force pumping section substantially perpendicular to the desired flow direction which maximizes the magnitudes of magnetic forces applied to the electrically conductive material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/464,317 filed Apr. 21, 2003, hereby incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to electromagnetic pumps that move an electrically conductive fluid by interaction with magnetic fields.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electromagnetic pumps can be used to pump electrically conductive fluids, such as an electrically conductive molten metal composition. An advantage of an electromagnetic pump is that the fluid can be magnetically induced to move through a tube or conduit without the use of mechanical pump components inside of the conduit.  
           [0004]    Known electromagnetic pumps are either submersed in, or integrally attached to, the source of the electrically conductive fluid, such as a metal melting and/or melt holding furnace. These pump installations are difficult to service and maintain. Therefore there is the need for an efficient and easily maintainable electromagnetic pump that is not integrally attached to the source of the electrically conductive fluid.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In one aspect, the invention is apparatus for and method of pumping an electrically conductive material in a pump having a supply section or volume, and a magnetic force pumping section or volume. In one example of the invention the directional flow of the material through the supply section is opposite to the directional flow of the material through the magnetic force pumping section. Multiple coils surround the supply and magnetic force pumping sections. Current flowing through the multiple coils creates magnetic fields that magnetically couple with a magnetic material disposed between the supply and magnetic force pumping sections so that the fields penetrate the electrically conductive material in the magnetic force pumping section substantially perpendicular to the desired flow direction. This field orientation maximizes the magnitudes of the magnetic forces applied to the electrically conductive material in the magnetic force pumping section.  
           [0006]    These and other aspects of the invention are set forth in the specification. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The figures, in conjunction with the specification and claims, illustrate one or more non-limiting modes of practicing the invention. The invention is not limited to the illustrated layout and content of the drawings.  
         [0008]    [0008]FIG. 1 is a side perspective view of one example of an electromagnetic pump of the present invention.  
         [0009]    [0009]FIG. 2 is a side elevational view of one example of an electromagnetic pump of the present invention.  
         [0010]    [0010]FIG. 3( a ) is a side sectional view through line A-A in FIG. 2 of one example of an electromagnetic pump of the present invention.  
         [0011]    [0011]FIG. 3( b ) is a top sectional view through line B-B in FIG. 2 of one example of an electromagnetic pump of the present invention.  
         [0012]    [0012]FIG. 3( c ) is a partial sectional view of the interface region for inner, mid and outer tubes, and magnetic material, used in one example of an electromagnetic pump of the present invention.  
         [0013]    [0013]FIG. 4( a ) is a simplified schematic diagram of a power supply and power distribution to induction coils used with an electromagnetic pump of the present invention.  
         [0014]    [0014]FIG. 4( b ) is a vector diagram illustrating one example of phase distribution of the output of a power supply to the induction coils used with an electromagnetic pump of the present invention.  
         [0015]    [0015]FIG. 5 is a side sectional view of another example of an electromagnetic pump of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring now to the drawings, wherein like numerals indicate like elements, there is shown in the figures one example of electromagnetic pump  10  of the present invention for pumping an electrically conductive material, such as an electrically conductive molten metal. In FIG. 1, twelve induction coils ( 12   a  through  121 ) as further described below, are surrounded by a plurality of vertical magnetic shunts  14  held in place by shunt supports  16 , which are attached to base  18  at one end, and to yoke  20  at the opposing end. The base and yoke may optionally be formed from a magnetic material to provide bottom and top magnetic field containment. Other shunt and outer support arrangements as known in the art may be used in lieu of the shunt and support arrangements shown in FIG. 1. Pump inlet  24  and pump outlet  22  in this non-limiting example of the invention, are cylindrically formed from a suitable heat-resistant material.  
         [0017]    Referring now to FIG. 3( a ), which is a side sectional of electromagnetic pump  10  shown in FIG. 2, optional thermal insulator  26  separates the induction coils from the interior of the pump and provides a means for molten metal (melt) heat retention for melt in the pump. In this non-limiting example of the invention, the thermal insulator is substantially shaped as an open cylinder bounded by base  18  and yoke  20 . Outer tube  28  in this non-limiting example of the invention, is a substantially cylindrically-shaped tube that has a closed rounded bottom and an opened top with a protruding lip around the opening. The outer tube&#39;s lip sits on top of yoke  20 .  
         [0018]    First closing means  30  seats over yoke  20  and the protruding lip of the outer tube. Second closing means  32  seats over first closing means  30 . Outlet  22  is disposed between the first and second closing means. Mid tube  34  in this non-limiting example of the invention is a substantially cylindrically-shaped tube that is opened at both ends with the upper end having a protruding lip around the opening. The mid tube&#39;s lip is seated in a recess in second closing means  32 . The first and second closing means are arranged to form an outlet annular volume  42  that connects the interior passage of outlet  22  to riser annular volume  44  that is disposed between the outer wall of mid tube  34  and the inner wall of outer tube  28 . Third closing means  36  seats over second closing means  32 . Inner tube  40  in this non-limiting example of the invention is a substantially cylindrically-spaced tube that has an open bottom and a closed top. As best seen in FIG. 3( c ) the perimeter of the inner tube&#39;s open bottom forms a fluid tight seal with the perimeter of the mid tube&#39;s open bottom. Magnetic material  46  is disposed in a volume between the outer wall of inner tube  40  and the inner wall of mid tube  34  as further described below. Fourth closing means  38  seats over third closing means  36  and the closed top of inner tube  40 . Inlet  24  is disposed between the third and fourth closing means and its interior passage is connected to the interior passage of inner tube  40 . FIG. 3( b ) is a sectional view that illustrates the spatial relationship of components in a horizontal plane.  
         [0019]    The above non-limiting examples of the invention provide a convenient means for assembly or disassembly of pump  10 . Removal of fourth closing means  38  allows inlet  24  and inner tube  40  to be raised out of the pump. Further removal of third closing means  36  allows magnetic material  46  and mid tube  34  to be raised out of the pump. Further removal of second closing means  32  allows removal of outlet  22 . Further removal of first closing means  30  allows removal of outer tube  28 .  
         [0020]    The above examples of the invention provide a convenient means for changing the angular orientation between inlet  24  with outlet  22 . In a particular installation, supply and outlet conduit (not shown in the drawings) that are to be connected to inlet  24  and outlet  22  respectively, may not be oriented to accept the 180 degrees angular orientation (looking down on the top of the pump) between the inlet and outlet for pump  10  as shown in FIG. 1. First closing means  30  and second closing means  32  may be rotated and secured into a position different from that shown in FIG. 1 to change the angular orientation of inlet  24  to outlet  22 , which outlet is contained by the first and second closing means. Third closing means  36  and fourth closing means  38  may be rotated and secured into a position different from that shown in FIG. 1 to change the angular orientation of outlet  22  to inlet  24 , which inlet is contained by the third and fourth closing means.  
         [0021]    Molten metal flows through pump  10  in the direction indicated by the arrows in FIG. 3( a ). The melt enters the pump through inlet  24  and flows down the interior cylindrical passage of inner tube  40 . This section of the pump is referred to as the supply section. The melt then moves by magnetic forces, as further described below, up riser annular volume  44  (the magnetic force pumping section), into outlet annular volume  42 , and finally out of the pump through outlet  22 . In other examples of the invention, outlet  22  may connect directly to riser annular volume  44  rather than being intermediately connected to it by outlet annular volume  42  formed between the inner wall of mid tube  34  and the inner annular walls of the first and second annular closing means. The outer tube, mid tube and inner tube are formed from a suitable heat resistant material such as a ceramic composition. One non-limiting type of ceramic composition that may used to cast the outer, mid and inner tubes, as well as inlet  24  and outlet  22  is a silicon-aluminum-oxynitride composition known as sialon.  
         [0022]    As disclosed above an applied magnetic force causes the electrically conductive melt to flow through pump  10 . There is shown in FIG. 4( a ) one diagrammatic example of supplying power to the induction coils to cause the molten metal to flow through pump  10  by magnetic force. Power supply  48  is a three-phase output power supply with variable output frequency and output voltage. One suitable type of supply is a solid state supply with a pulse width modulated output. FIG. 4( b ) is a vector diagram illustrating a six-cycle connection scheme from the power supply to the coils that is used to produced magnetic forces that act on the molten metal in riser annular volume  44  to force the melt up the riser annual volume and through outlet  22 , and thus pulling molten metal through pump  10  from a suitable source of molten metal that can be connected to inlet  24 . As illustrated in the diagram and vector diagram, the six-cycle scheme is created by sequentially connecting each of the three phases with alternating positive and negative phase orientation. That is phase +AB is followed by phase −BC, which is followed by phase +CA, which is followed by phase −AB, which is followed by phase +BC, which is followed by phase −CA. The six-cycle connection scheme for induction coils  12   a  through  12   f  repeats for induction coils  12   g  through  12   l . The choice of a six-cycle connection scheme is not limiting, but a six-cycle scheme (with 30 electrical degrees phase angle between voltages in adjacent coils) provides a more uniform flow rate than, for example, a three-cycle scheme (with 60 electrical degrees phase angle between voltages in adjacent coils). Since the magnitude of the output voltage of power supply  48  is directly proportional to the magnitude of the magnetic force applied to the molten metal, varying the output voltage of the power supply will vary the magnetic lifting force and flow rate of a molten metal through the pump.  
         [0023]    The magnetic forces generated in riser annular volume  44  are substantially vertical in the upwards direction since the magnetic field generated around each of the coils substantially forms a magnetic circuit with magnetic material  46  and the field path through the molten metal in the riser annular volume is substantially horizontally-oriented. If a hot molten metal is pumped by electromagnetic pump  10 , magnetic material  46  must have a Curie temperature (point at which the magnetic material loses its magnetic properties) greater than the temperature of the molten metal flowing through the pump. For these applications a high Curie temperature magnetic material must be used. For example, molten aluminum typically may flow through the pump at a temperature of ranging from 680° C. to 800° C. For this application the magnetic material must have a Curie temperature of at least 850° C. which is the maximum temperature of the aluminum melt plus design margin. One suitable type of high Curie temperature magnetic material  46  for this application is a class of iron-cobalt alloys known as permendur.  
         [0024]    It is preferable, but not required, that each induction coil be formed as a thin-wire, multiple-turn (typically 500 or more turns) coil commonly referred to as a bobbin magnetic coil since it is formed by winding thin wire around a bobbin that is removed after winding. Since the magnitude of magnetic force created by a magnetic field is directly proportional to both current flow through the coil and the number of turns in the coil, using a coil with a large number of turns keeps the required output current from power supply  48  at a low level for a given magnitude of magnetic force.  
         [0025]    If the source of molten metal to the pump is located below the horizontal level of inlet  24 , pump  10  will need to be initially primed by filing the interior passage of inner tube  40  with melt. One method of accomplishing this is by attaching a vacuum pump to outlet  22  and drawing a vacuum on the melt flow passages within pump  10  to suction melt from a supply of molten metal connected to inlet  24 . In other examples of the invention, the top of inner tube  40  may be open and penetrate through fourth closing means  38  in, for example, a funnel-shaped opening into which molten metal can be poured to prime the pump by filling the inner tube.  
         [0026]    When pump  10  is not in use, stationary molten metal in the pump may cool and “freeze” within the pump&#39;s internal flow passages. To prevent this from happening, a cyclical emptying and filling of riser annular volume  46  with molten metal may be electromagnetically accomplished. Reversing the direction of all phase vectors in FIG. 4( b ) will create a magnetic force on molten metal in riser annular volume  46  that will force it down and push molten metal back though inlet  24  to the source of molten metal connected to the inlet. Subsequently reversing all phase vectors back to the directions shown in FIG. 4( b ) will create a magnetic force that will cause molten metal to rise up in the riser annular volume. This jogging motion of molten metal will prevent freezing of molten metal in the pump when it is not in use. In other examples of the invention, if a three phase power supply is used, cyclically reversing two of the phases with, for example, solid state switches, can also be used to accomplish the electromagnetic jogging motion of melt in the pump. In other examples of the invention, a heating medium, such as a circulating hot gas or liquid, or an electric heating element, may be provided in the volume between thermal insulator  26  and the outer wall of outer tube  28 .  
         [0027]    [0027]FIG. 5 illustrates another example of an electromagnetic pump of the present example. In this example, inlet  24   a  is at the bottom of the pump and molten metal is electromagnetically pumped directly up riser annular volume  46  as generally described in previous examples of the invention. In this particular example since molten metal does not flow through the inner tube, the inner tube may be a totally enclosed tube or other inner structural element that serves as a means for containing magnetic material  46  between the inner structural element and mid tube  34 .  
         [0028]    Other types of power supply and distribution arrangements are contemplated within the scope of the invention. For example, multiple single phase power supplies may be used; each coil may be powered by an individual power supply; or separate power supplies may power individual groups of coils. Further although in the above examples of the invention the inner, mid and outer tubes have their longitudinal axes vertically oriented, the longitudinal axes of the tubes may be otherwise oriented without deviating from the scope of the invention.  
         [0029]    The examples of the invention include reference to specific electrical components. One skilled in the art may practice the invention by substituting components that are not necessarily of the same type but will create the desired conditions or accomplish the desired results of the invention. For example, single components may be substituted for multiple components or vice versa.  
         [0030]    The foregoing examples do not limit the scope of the disclosed invention. The scope of the disclosed invention is further set forth in the appended claims.