Abstract:
A hot melt system includes a melt system, a feed system, a dispensing system, and a pump. The melt system melts the pellets to produce a liquid, and the pump delivers the liquid to the dispensing system. The feed system is coordinated with the operation of the pump to control the amount of pellets delivered to the melt system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/556,574, filed on Nov. 7, 2011, and entitled “AUTO GATE VALVE,” the disclosure of which is incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to systems for dispensing hot melt adhesive. More particularly, the present disclosure relates to a feed system for admitting hot melt pellets to the melt system. 
         [0003]    Hot melt dispensing systems are typically used in manufacturing assembly lines to automatically disperse an adhesive used in the construction of packaging materials such as boxes, cartons and the like. Hot melt dispensing systems conventionally comprise a material tank, heating elements, a pump and a dispenser. Solid polymer pellets are melted in the tank using a heating element before being supplied to the dispenser by the pump. Because the melted pellets will re-solidify into solid form if permitted to cool, the melted pellets must be maintained at temperature from the tank to the dispenser. This typically requires placement of heating elements in the tank, the pump and the dispenser, as well as heating any tubing or hoses that connect those components. Furthermore, conventional hot melt dispensing systems typically utilize tanks having large volumes so that extended periods of dispensing can occur after the pellets contained therein are melted. However, the large volume of pellets within the tank requires a lengthy period of time to completely melt, which increases start-up times for the system. For example, a typical tank includes a plurality of heating elements lining the walls of a rectangular, gravity-fed tank such that melted pellets along the walls prevents the heating elements from efficiently melting pellets in the center of the container. The extended time required to melt the pellets in these tanks increases the likelihood of “charring” or darkening of the adhesive due to prolonged heat exposure. 
       SUMMARY 
       [0004]    According to the present invention, a feed system of a hot melt system is coordinated with operation of a pump so that hot melt solids are delivered to the hot melt system as a function of a rate at which hot melt liquid is being pumped. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a block diagram of a hot melt adhesive system. 
           [0006]      FIG. 2  is a perspective view of a dispenser, pump, and melt system of the hot melt adhesive system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0007]      FIG. 1  shows system  10 , which dispenses hot melt adhesive. System  10  includes cold section  12 , hot section  14 , air source  16 , air control valve  18 , controller  20 , air hoses  22 A and  22 B, and motor  24 . In the embodiment shown in  FIG. 1 , cold section  12  includes container  26  and valve system  28 . Hot section  14  includes melt system  30 , pump  32 , and dispenser  34 . Air source  16  is a source of compressed air supplied to air motor  24 , which drives pump  32 . Air control valve  18  is connected to air source  16  via air hose  22 A, and selectively controls air flow from air source  16  through air hose  22 B to motor  24  of pump  32 . Controller  20  is connected in communication with various components of system  10 , such as air control valve  18 , melt system  30 , pump  32 , and/or dispenser  34 , for controlling operation of system  10 . System  10  also includes valve  36 . Valve  36  may be a gate valve or other valve capable of selectively admitting hot melt pellets to melt system  30  from container  26 . 
         [0008]    Components of cold section  12  can be operated at room temperature, without being heated. Container  26  can be a hopper for containing a quantity of solid adhesive pellets for use by system  10 . Suitable adhesives can include, for example, a thermoplastic polymer adhesive such as ethylene vinyl acetate (EVA) or metallocene. Valve system  28  connects container  26  to hot section  14  for delivering the solid adhesive pellets from container  26  to hot section  14 . 
         [0009]    Solid adhesive pellets are delivered from container  26  to melt system  30 . Melt system  30  can include a container (not shown) and resistive heating elements (not shown) for melting the solid adhesive pellets to form a hot melt adhesive in liquid form. Melt system  30  can be sized to have a relatively small adhesive volume, for example about 0.5 liters, and configured to melt solid adhesive pellets in a relatively short period of time. Pump  32  is driven by motor  24  to pump hot melt adhesive from melt system  30  to dispenser  34 . Motor  24  can be an air motor driven by pulses of compressed air from air source  16  and air control valve  18 . Pump  32  can be a linear displacement pump driven by motor  24 . In various embodiments, dispenser  34  may include a manifold and dispensing modules. Dispenser  34  can selectively discharge hot melt adhesive onto an object, such as a package, a case, or another object benefiting from hot melt adhesive dispensed by system  10 . In some embodiments, dispenser  34  can be a handheld gun-type dispenser, for example. Some or all of the components in hot section  14 , including melt system  30 , pump  32 , and dispenser  34 , can be heated to keep the hot melt adhesive in a liquid state throughout hot section  14  during the dispensing process. System  10  can be part of an industrial process, for example, for packaging and sealing cardboard packages and/or cases of packages. 
         [0010]    Valve system  28  is a mechanism for replenishing melt system  30 . In alternative embodiments, valve system  28  may be replaced by any type of valve or other device which is capable of selectively admitting defined quantities of adhesive pellets from container  26 . By mechanically coupling valve system  28  to pump  32  and valve  36 , valve system  28  may drive valve  36  to admit a quantity of pellets from container  26  sufficient to replenish melt system  30  on each cycle of pump  32 . Where pump  32  draws the same quantity of liquefied adhesive on each cycle, the quantity of pellets admitted by valve system  28  may be equal to the quantity of liquefied adhesive drawn by pump  32 . 
         [0011]    As pump  32  is driven by motor  24 , liquefied adhesive is transferred from melt system  30  through pump  32  to dispenser  34 . In order to minimize char of the liquefied adhesive, the quantity of liquefied adhesive in melt system  30  should be minimized. However, there must be sufficient liquefied adhesive available in melt system  30  for each cycle of pump  32  to draw. Thus, valve system  28  admits to melt system  30  an amount of pellets from container  26  sufficient to replenish the melted adhesive drawn by pump  32 . This may be accomplished by mechanically coupling valve  36  to valve system  28 , which is in turn mechanically coupled to pump  32 . 
         [0012]      FIG. 2  is a perspective view of an embodiment of the invention, showing portions of cold section  12  and hot section  14 . The embodiment shown in  FIG. 2  shows many of the same components as laid out in  FIG. 1 , including container  26 , valve system  28 , melt system  30 , and pump  32 . As shown in  FIG. 2 , container  26  is a dry goods hopper. Container  26  may be used to hold unmelted hot melt pellets. Melt system  30  is shown as a tank of melted adhesive. In other embodiments, melt system  30  may be a small container with resistive heating elements as described above. Motor  24  may be, for example, an air motor or an electric motor, or any other motor capable of driving pump  32  in a reciprocating fashion. Dispenser  34  ( FIG. 1 ) connects to outlet port  38 . In alternative embodiments, the dispenser may be made up of additional parts which direct liquefied adhesive towards desired targets. 
         [0013]    As pump shaft  42  moves to the right (with respect to  FIG. 2 ), pump linkage  40  is moved at shaft-linkage connection  44 . Pump linkage  40  pivots counterclockwise about pivot  46 , pushing valve linkage  48  to the left (with respect to  FIG. 2 ) via sliding connector  50 , causing valve  36  to close off container  26  from melt system  30 . Conversely, when pump shaft  42  moves to the left, pump linkage  40  pivots clockwise about pivot  46 , pulling valve linkage  48  to the right via sliding connector  50 , and causing valve  36  to open. Thus, because container  26  is above melt system  30 , gravity causes pellets to fall into melt system  30 . 
         [0014]    In the embodiment shown in  FIG. 2 , melt system  30  is connected to container  26  by way of valve system  28 . Valve system  28  and melt system  30  are both connected to pump  32 . The inlet for pump  32  connects to the outlet of melt system  30  at interface  52 . Valve system  28  is connected to pump  32  by way of pump linkage  40 . Pump  32  is also connected to motor  24 .  FIG. 2  shows one example of pump linkage  40 . As shown in  FIG. 2 , pump linkage  40  is a direct mechanical linkage including a pivot. Pump linkage  40  mechanically connects pump  32  to valve system  28 . 
         [0015]    In the embodiment shown in  FIG. 2 , valve system  28  opens when pump  32  moves in one direction, and closes when pump  32  moves in the other direction, due to pump linkage  40 . In the embodiment shown in  FIG. 2 , this coupling of valve system  28  and pump  32  results in additional hot melt pellets being added to melt system  30  each time pump  32  transfers liquefied adhesive to dispenser  34 . In other embodiments, pump linkage  40  may cause valve system  28  to add hot melt pellets at other times in response to movement of pump  32 . For example, valve system  28  could be opened by pump linkage  40  at the other end of the movement of pump  32  by eliminating the pivot point shown pump linkage  40  of the embodiment shown in  FIG. 2 . Many other embodiments of pump linkage  40  are possible, so long as the periodic movement of pump  32  results in a corresponding or related periodic opening and closing of valve system  28 . Pump linkage  40  coordinates the movement of pump  32  to the feed rate of unmelted pellets through valve system  28 . 
         [0016]    The pairing of valve system  28  with pump  32  by pump linkage  40  allows system  10  to admit the proper amount of unmelted hot melt pellets without complex systems for measuring them. By adjusting the size of valve  36  and how long valve system  28  remains open for each stroke of pump  32 , a quantity of hot melt pellets is added to melt system  30  via valve system  28  that is roughly equal to the quantity of hot melt adhesive that is removed from melt system  30  via pump  32 . Accordingly, no measurement system is required to determine when and how many hot melt pellets must be added to melt system  30  during use. 
         [0017]    While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.