Abstract:
Hot melt adhesive pellets are melted and pressure pumped in a controlled application pattern on the substrate at the application site. The high frequency power supply, induction heated melting susceptor, pressure pump, and pattern control electronics are all contained in a single unit within adhesive projection distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefits of provisional application Ser. No. 60/889771 filed Feb. 14, 2007, in the United States Patent &amp; Trademark Office. 
     
    
     FIELD OF THE INVENTION 
       [0002]    A method and apparatus for delivering melted material. The invention utilizes an induction-heated susceptor attached to a gerotor pump to melt and apply thermoplastic polymer materials. 
       BACKGROUND OF THE INVENTION 
       [0003]    Hot melt adhesive materials are currently applied by melting pellets or slats in a resistance heated reservoir, pumping the hot liquid with a resistance heated pump through a resistance heated hose, to heated valves and nozzles at the application point. Each of these individual zone temperatures are monitored and controlled. The startup of the system requires a delay for the material in the reservoir to melt. Flow resistance of viscous materials in the heated delivery hoses requires high fluid pressures. 
         [0004]    Maintaining a reservoir of hot material, pressure pumping for distant delivery, and maintaining heat in the delivery system elements are all wasted electrical energy. Thermoplastic materials retained at application temperature for long periods and overheating in the system forms char [crystallized particles] that need to be filtered before clogging application nozzles. Localized over temperature spots are a result of resistance element heating not being able to adequately expose the majority of the material to a heat conduction element that is not in excess of the target temperature. Extended melted material exposure to the atmosphere in the melt reservoir requires material additives to counter oxidation. 
         [0005]    Hot delivery elements, particularly delivery hoses, are a costly replacement item. Material changes are difficult and time consuming. The melt tank needs to be cleaned, and the pump delivery hoses purged. Higher melting temperature materials [400° to 450° F.] are particularly difficult to apply in the system. The invention addresses all of these problems in a small unit applied to localized melt and apply on demand. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention utilizes the efficient localized energy distribution of induction heating to combine the melting and pressure pumping of thermoplastic polymers. In this embodiment of the invention, hot melt adhesive materials are presented in a reservoir, melted by exposure to an induction heated susceptor whose energy input is coordinated with an adjoining positive displacement pump&#39;s delivery. The material is radial directed to the application substrate through an orifice or orifices in the pump face. These elements are combined with the pump motor in a housing that is mounted and directed at the application position. The high frequency power supply is attached to this frame along with the receiver of a pellet vacuum feeder. 24V DC power and four control lines communicate with the unit from a central DC power supply and remote control that can attend several application units in a coordinated pattern application system. All of the functions of a tank melter with heated hose delivery can be performed with this invention as a melt on demand system weighing only 4½ pounds and pattern placing 16 pounds pr hour of hot melt adhesive at 350° F. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a sectional view of the apparatus of the invention. 
           [0008]      FIG. 2  is a view including the attachment of the HF power supply and pellet receiver. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]      FIG. 1  is a partial cross section of the apparatus of the invention. Thermoplastic polymer pellets  1  migrate by gravity flow to the apex of hopper  2  where they contact thermal susceptor  3 . The susceptor is heated by the magnetic field  4  of inductor coil  5 . The interactions of these elements are described in detail in Lasko U.S. Pat. No. 5,584,419. 
         [0010]    Inductor coil  5  is cast in a ridged high temperature epoxy form  6  with its elongated surface exposed and spaced to transmit a uniform heat in susceptor  3 . This susceptor is formed in the shape of a cone from metal foam or perforated metal sheet with a defined open space to maximum surface area ratio. Pellets  1  in contact with the susceptor receive heat by conduction from the susceptor and migrate through the spaces in the susceptor as they liquefy and exit into annulus  7  between susceptor  3  and inductor coil  5 . Material transit depicted by arrow  8  requires only approximately two seconds of residency time in susceptor  5  to attain an application temperature. 
         [0011]    Liquid material flow depicted by arrow  9  is drawn into the gerotor pump suction cavity  10  that is formed by the lobed central rotor  11  and the matching exterior rotating element  12 . The high frequency power to inductor coil  5  is electronically matched to the variable displacement of the pump. This assures that the pump will have a continuous supply of liquid material and that the susceptor will melt material only on delivery demand. The gerotor pump elements  11  and  12  are encased in a ceramic housing  13 . The assembly of the moving gerotor elements and the static ceramic housing is positioned to intercept the magnetic field  4 . The mass of the susceptor  3  and gerotor elements  11  and  12  are designed to be proportionately conjoined in the magnetic field  4  to obtain the target operating temperature together from a cold start in a few seconds. Thermocouple signals from locations  14  at the susceptor and  15  at the gerotor are compared and the high frequency power to the inductor coil  5  is modulated to maintain the target temperature during operation. 
         [0012]    The pump drive shaft  16  is thermally isolated from the drive motor  17  by the non-conductive compliance element  18  in the spider alignment coupling components  19  and  19   a.  The axis aligned assembly of the inductor coil housing  6 , gerotor housing  13 , pump face housing and orifice plate  20 , and thermal insulator  21 , are compressed in the assembly by the connection of frame  23  and armature  22 . Spring washer  25  imparts a defined pressure to the assembly stack. Frame  23  is made of a polymer composite material that will not intercept and distort the magnetic field  4 . Frame  23  is open on two opposing sides for assembly and operation. Passages  26  in armature  22  allow air-cooling and assembly access for coupling  19 . 
         [0013]    The gerotor pump pressure cavity  27  delivers the liquid material to multiple peripheral projection orifices  28  through a short passage  29  in the gerotor pump face housing and orifice plate  20 . The delivery pattern of the exiting material  30  is controlled by the diameter of projection orifice  28  and the duration of the rotation of the gerotor pump. High temperature “O” rings and shaft seals are utilized throughout the assembly to confine the exit of hot material to only the projection orifices  28 . 
         [0014]      FIG. 2  illustrates a 1 KW 100 KHz power supply  31  attached to frame  23  by a set of seven power and control connection pins  32 . Air cooled high frequency power supply  31  is enclosed in a 5″×1.7×1.7 aluminum housing that is color coded for exchange to provide a specific material application temperature. A pellet vacuum feed system receiver  33  is shown in cross section attached to frame  23 . Pellets from a vacuum feeder enter at delivery hose connection  34  and as shown by arrow  35  settle to a controlled level  36  as required by the application rate. The pellet feed air as represented by arrow  37  is exhausted through cylindrical filter  38 . Power and control cable  39  provides DC current for high frequency power supply  31  and motor  17 . Control lines for signaling pump rotation motor  17  and a vacuum feed pellet level sensor are also included in this cable. The addition of these two items, high frequency power supply  31  and pellet receiver  33  complete an application system to continuously apply hot melt adhesives.