Abstract:
The invention presents an apparatus and method for dross removal from coating lines. The invention utilizes magnets to collect dross either in suspension or which has accumulated at or near the bottom of a coating pot. The invention utilizes the magnetic properties of the dross to separate the dross from the non-magnetic coating metal. The use of magnets allows for removal of dross from the coating metal without simultaneously removing valuable coating metal from the coating pot.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a dross removal system for removing bottom dross from a coating line. Specifically, the invention relates to a dross removal system which utilizes magnetic elements to attract magnetic dross within a molten material in order to remove the dross from the material. 
     BACKGROUND OF THE INVENTION 
     In coating applications coating lines are used to generate a molten material which is maintained in a coating pot. The molten coating material is typically zinc. In these coating lines, specifically galvanizing lines, a material known as bottom dross is often created. The dross is generated from iron placed into the coating pots wherein iron combines with the zinc to create dross. The specific weight of the alloy is approximately 10% greater than the molten zinc and therefore settles to the bottom of the coating pot or accumulates as a suspension near the bottom of the coating pot. In order to produce quality galvanized material it is necessary to periodically remove the bottom dross. 
     Conventional methods of removing the dross include scooping out the dross manually or using mechanical devices. While the percentage of dross present in the coating pot relative to the amount of coating zinc is small, use of the known removal devices tends to remove large amounts of the molten zinc along with the dross. The removal of the zinc results in decreased efficiency and higher expenses because of loss of coating material. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for dross removal from a coating line comprising a coating pot for holding molten material having a bottom portion at or near which dross may accumulate, and a collection device for attracting and separating the dross from the molten material, wherein the collection device includes a magnetic field inducing element. 
     The present invention provides a dross removal system for coating lines comprising a coating pot for holding molten metal, for example zinc. Because bottom dross is continuously being generated in the molten material due to the coating process it is necessary to remove the bottom dross in order to produce a quality galvanized material. To this end, a first embodiment of the present invention utilizes a permanent or electromagnet to attract the dross and remove it from the molten material. Because the dross is magnetic and the molten material is not, the magnet provides an excellent device for separating the dross from the molten material without also removing the molten material. The magnet is placed into the coating pot and suspended therein. The magnet attracts the dross residing at or near the bottom of the pot. The magnet is periodically removed for cleaning. Using electromagnets allows turning the magnets on and off, allowing for easier cleaning. 
     In another embodiment a pump is coupled to the coating pot and continuously removes a combination of molten metal and dross particles from the coating pot and passes them onto a receiving area. The receiving area may be a settling container which includes a strong magnet or magnets in its bottom. As the molten metal and dross pass through the settling container the dross settles more quickly than the molten metal because it weighs approximately 10% more. Additionally, the dross particles are drawn to the magnets, creating even more separation between the dross particles and the molten metal. The remaining molten metal is returned to the coating pot or a premelter. The receiving area may also be a trough. In that case, a magnetic drum is positioned in close proximity to the molten metal in the trough. In one embodiment the magnetic drum is positioned such that at least a portion of the drum is submerged in the molten metal-dross combination which is pumped into the trough. In another embodiment, the magnetic drum is positioned above the trough but close enough to the molten metal to magnetically extract dross particles from the molten metal-dross combination. A conveyer belt is journaled about the drum. As the dross is attracted to the drum the conveyor belt carries the dross up and out of the trough and deposits the dross into a dross container positioned adjacent to the coating pot. 
     In another embodiment the dross is attracted to a magnetic element and conveyed up and out of the coating pot by a conveying system. The conveying system may be a multiphase solenoid coil wound about a tube that is placed into the coating pot. A sequential electrical dc current is applied to the coil windings beginning from the bottom and working upwards. A slow travelling wave is generated inside the tube. As the wave travels, it picks up magnetic dross particles and conveys them to the top of the tube. A constantly energized electromagnet is present at the top of the tube. As the dross material is conveyed upwards it is accumulated on the magnet. The magnet is periodically cleaned to remove the collected dross. The conveying system may also be a conveyor belt having a first end positioned at or near a bottom portion of the coating pot and a second end positioned above the molten metal. In that event, a magnetic plate is positioned abutting the conveyor belt on an interior side of the conveyor belt. The magnetic plate attracts the dross. As the dross is attracted to the magnetic plate the dross contacts the conveyor belt. The conveyor belt carries the attracted dross up and out of the coating pot and deposits the dross into a dross container positioned adjacent the coating pot. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a first embodiment of the present invention, greatly simplified. 
     FIG. 2 is a cross-sectional view of a second embodiment of the present invention. 
     FIG. 3 is a perspective view of a third embodiment of the present invention. 
     FIG. 4 is a cross-sectional view of a fourth embodiment of the present invention. 
     FIG. 5 is a perspective view of a fifth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     Referring now to the drawings, wherein like numerals indicate like elements, there is shown in FIG. 1 a first embodiment of the present invention. The invention includes a coating pot  10  maintaining a non-magnetic molten material  12 , for example zinc. Located at or near the bottom of the coating pot  10  is accumulated dross  14 . The dross  14  accumulates over time due to interaction between the molten material  12  and workpieces (not shown) placed into and taken out of the molten material during the application. A magnet  16  is suspended in the coating pot  10  such that a first end of the magnet is positioned at or near the bottom of the coating pot  10 . Magnet  16  may be either a permanent magnet or an electromagnet. An electromagnet may be turned on and off, thereby making cleaning easier. As the magnet  16  is suspended in the molten material  12 , it attracts the finely dispersed magnetic dross  14 . The magnet  16  will collect only the dross  14  and will not attract the non-magnetic molten material  12 . The magnet  16  remains in the coating material  12  continuously except when it is periodically removed for cleaning. 
     FIG. 2 illustrates a second embodiment of the present invention. This embodiment includes a coating pot  10  holding molten material  12 . Suspended at or near the bottom of the coating pot is accumulated dross  14 . This embodiment includes a tube  18  positioned at or near the bottom of the coating pot  10 . The tube  18  includes inlets  19  providing an opening to the interior of the tube  18 . The tube  18  is connected to a pump  20 . The pump  20  draws material from the coating pot  10 , including molten material  12  and dross  14  into the tube  18 . The pump  20  conveys the removed material to a settling area  22  via a passage tube or launder  24 . The settling area  22  provides one or more subsettling areas and in a preferred embodiment two subsettling areas  26  and  28 . Each subsettling area  26  and  28  maintains a plurality of magnets  30  just below the bottom of the subsettling areas  26 ,  28 . As the material removed from the coating pot  10  via pump  20  is conveyed to the settling area  22 , the magnets  30  will attract the dross  14  to the bottom of the subsettling areas  26 ,  28  without attracting the molten material  12 . This provides improved separation between the dross  14  and the molten material  12 . The molten material which remains after separation is passed back to the coating pot  10  or into a molten bath (not shown). 
     A third embodiment of the present invention is illustrated in FIG.  3 . This embodiment includes a coating pot  10  holding the molten material  12  wherein the dross has developed and accumulated in a suspension at or near the bottom of the coating pot  10 . This embodiment further includes an inlet tube  40  having inlets  42 . The inlets  42  allow a combination of the molten metal and the suspended dross  14  to enter the tube. The tube  40  is connected to a pump  44 , which draws the molten metal-dross combination into the suction tube  40 . The pump  44  is driven by a pump motor  46 . Also connected to the pump  44  is an outlet tube  48 . The molten metal-dross combination drawn into the tube  40  is forced into the tube  48  by the pump  44 . The tube  48  carries the molten metal-dross combination up and out of the coating pot  10  and into a receiving trough  50 . Associated with the receiving trough  50  is an electromagnetic drum  52  positioned in close and operative proximity to the trough  50 . In one embodiment, a lower portion of the magnetic drum  52  resides within the trough  50  such that the lower portion of the magnetic drum  52  is submerged in the molten metal-dross combination once the pump  44  begins operation and forces the molten metal-dross combination into the trough  50 . In another embodiment, the lower portion of the magnetic drum  52  is positioned above the molten metal-dross combination and the dross particles are extracted from the molten metal-dross combination by magnetic force supplied by the magnetic drum  52 . An endless belt conveyor  54  operates with the magnetic drum  52  and an additional roller  56 . The conveyor belt  54  may be made of stainless steel. A container  58  receives the dross which has been removed from the molten metal-dross combination by the system. The system further includes a return pipe  60  for returning the molten metal to the coating pot  10  once the dross  14  has been removed. 
     In operation the molten metal-dross combination is removed from the coating pot  10  by the pump  44 . The molten metal-dross combination is received by the trough  50 . When the magnetic drum  52  is energized it attracts the dross  14  from the molten metal-dross combination. As the drum rotates, as illustrated in FIG. 3, the conveyor belt  54  moves about the magnetic drum  52  and the additional roller  56 . As the magnetic drum  52  rotates, the dross  14  is drawn to the conveyor belt  54  and held there by the magnetic field of the drum  52 . As the conveyor belt  54  moves around the magnetic drum  52  it carries the dross  14  away from the magnetic drum  52  into the container  58 . The purified molten metal is returned to the coating pot via return tube  60 . 
     The fourth embodiment of the present invention is illustrated in FIG.  4 . This embodiment includes a coating pot  10  holding the molten material  12  wherein dross  14  has developed and settled to the bottom of the coating pot  10 . This embodiment further includes a tube  32  inserted into the coating pot  10  and molten material  12  such that a first end  32   a  of the tube is placed at or near the bottom of the coating pot  10  in close proximity to accumulated dross  14 . A second end  32   b  of the tube is positioned just above the highest level of the molten material  12  providing a passage way from the bottom of the coating pot  10  to just above the molten material  12 . Wound about the tube  32  is a multi-phase solenoid coil  34  extending from the first end  32   a  of the tube to the second end  32   b  of the tube. The coil  34  provides multiple sections as shown, for example, in FIG. 4 wherein the coil  34  includes groups A, B, and C. This embodiment is shown having six sections separated into three groups of two elements; however, it is not intended to limit the invention to three groups specifically. Each group A, B, and C is coupled to a switch  36 . The switch  36  is positionable between contact points a, b, and c. Each contact point corresponds to one of the groups A, B, and C, respectively. When the switch  36  engages a particular one of the contact points a, b, or c the corresponding group A, B, or C is coupled to a power source  38 . By successively switching between the three contact points the three magnetic groups A, B, and C are successively powered. This results in generating a slow travelling wave inside the tube  32 . This wave will attract the magnetic dross  14  and urge it towards the top of the coating pot  10 . As the dross  14  reaches the upper end of the tube  32   b  it will be accumulated on a constantly energized electromagnet  40  maintained at the top of tube  32 . The magnet  40  will periodically be removed and cleaned in order to remove any collected dross  14 . 
     A fifth embodiment of the present invention is illustrated in FIG.  5 . This embodiment includes a coating pot  10  holding the molten material  12  wherein dross has developed in a suspension at or near the bottom of the coating pot  10 . This embodiment further includes a pair of rollers  62   a ,  62   b . The rollers  62   a ,  62   b  support a conveyor belt  64  and at least one roller is driven by a motor  66 . The system also includes a magnetized plate  68  disposed between the rollers  62   a ,  62   b  and on an interior side of the conveyor belt  64 . In operation, the motor  66  drives the rollers  62   a ,  62   b , which in turn drive the conveyor belt  64 . Because the plate  68  is magnetized, dross  14  suspended in the coating pot  10  is attracted to the plate  68 . The magnetic field generated by the magnetic plate  68  holds the dross  14  against the conveyor belt  64  as the conveyor belt  64  moves up and out of the coating pot  10 . As the conveyor belt  64  travels across the magnetic plate  68  the dross  14  is moved towards the top of the coating pot  10 . Once the dross  14  reaches the top of the conveyor belt  64  about the upper pin  62   b  the dross  14  is then fed to a receiving container  70  which receives the dross  14  removed from the coating pot  10 . 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.