Abstract:
Systems and methods of dispensing a hot melt adhesive material that can be heated from a lower temperature flowable non-molten liquid state to a higher temperature molten liquid state, the systems and methods comprise: pumping with a pump the hot melt adhesive material in the lower temperature flowable non-molten liquid state into a supply conduit; passing the hot melt adhesive material through a heated thermal break in the supply conduit that allows free flowing movement of transitional non-molten and molten state material; heating the hot melt adhesive material in a heat exchanger connected to the heated thermal break to the higher temperature molten liquid state; and dispensing the hot melt adhesive material in the higher temperature molten liquid state from a dispenser in fluid communication with the heat exchanger.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to systems for dispensing liquid hot melt adhesive. More particularly, the present disclosure relates to a fluid line for connecting components within a hot melt dispensing system. For example, a fluid line may be used to connect a pump with a heat exchanger for a hot melt adhesive dispenser. 
         [0002]    Liquid 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. Liquid hot melt adhesive dispensing systems utilize glue, such as hybrid plastisols and the like, that are highly viscous liquids at room temperature, but that become activated by heat to become a lower viscosity molten liquid. The molten liquid is easier to pump and dispense once being heated. However, the molten liquid cannot be exposed to prolonged heating without charring. As such, it becomes important for liquid hot melt systems to activate the liquid hot melt adhesive as close as possible to the dispense point to reduce waste. 
         [0003]    A typical liquid hot melt adhesive dispensing system comprises a pump and a dispenser, between which is positioned a heater in close proximity to the dispenser. Such a system is described in U.S. Pat. No. 7,623,772 to Stumphauzer et al. Challenges arise, however, in removing molten liquid that solidified between the heater and the pump after the dispensing system is shut-down, such as for maintenance. Furthermore, molten liquid can migrate upstream, such as via thermal expansion, to an unheated portion of the system and begin to solidify into a plug. At some point, the plug can solidify to completely block flow of molten liquid. 
       SUMMARY 
       [0004]    A method of dispensing a hot melt adhesive material, the method comprising: pumping a hot melt adhesive material in a lower temperature flowable non-molten liquid state into a supply conduit; passing the hot melt adhesive material through a heated thermal break in the supply conduit that allows free flowing movement of transitional non-molten and molten state material; heating the hot melt adhesive material in a heat exchanger connected to the heated thermal break to a higher temperature molten liquid state; and dispensing the hot melt adhesive material in the higher temperature molten liquid state from a dispenser in fluid communication with the heat exchanger. 
         [0005]    A dispensing system for hot melt material, the dispensing system comprises a pump, a fluid line, a heat exchanger, a heated thermal break and a dispenser. The pump pumps hot melt adhesive material in a non-molten liquid state. The fluid line receives hot melt material from the pump. The heat exchanger heats the hot melt adhesive to a molten liquid state. The heated thermal break is disposed in the fluid line proximate the heat exchanger to allow free flowing movement of transitional non-molten liquid state and molten liquid state material before entering the heat exchanger. The dispenser receives molten liquid state hot melt material from the heat exchanger. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of a system for dispensing liquid hot melt adhesive including a pump, a fluid line having a heat break and a heated dispenser. 
           [0007]      FIG. 2  is a schematic of the fluid line connecting the pump and heated dispenser of  FIG. 1  illustrating a re-melting zone in the heat break. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The present invention provides a heated thermal break for a fluid line connecting a fluid pump and a heat exchanger coupled to a dispenser. The heat exchanger activates a material, such as a hot melt adhesive, by subjecting the material to a sufficient heat level. The heated thermal break prevents heated and activated material from the heat exchanger that migrates upstream due to thermal expansion from solidifying in the fluid line beyond the thermal reach of the heat exchanger. 
         [0009]      FIG. 1  is a schematic view of system  10 , which is a system for dispensing liquid hot melt adhesive. System  10  includes cold section  12 , hot section  14 , air source  16 , air control valve  17 , controller  18  and container  20 . In the embodiment shown in  FIG. 1 , hot section  14  includes heat exchanger  22 , thermal break  24 , and dispenser  26 , and cold section  12  includes pump  28 , air motor  30 , air valve  32  and cold line  34 . System  10 , for example, can be part of an industrial process for packaging and sealing cardboard packages and/or cases of packages. In alternative embodiments, system  10  can be modified as necessary for a particular industrial process application. 
         [0010]    Air source  16  is a source of compressed air that supplies compressed air to components of system  10  in both cold section  12  and hot section  14 . Air control valve  17  is connected to air source  16  via air hose  35 A, and selectively controls air flow from air source  16  through air hose  35 B to dispenser  26 . Air valve  32  is connected to air source  16  via air hose  35 C, and selectively controls air flow from air source  16  to motor  30 . Controller  18  is in communication with various components of system  10 , such as air control valve  17 , heat exchanger  22  and thermal break  24 , for controlling operation of system  10 . 
         [0011]    Components of cold section  12  can be operated at room temperature, without being heated. Container  20  is a vessel containing a quantity of liquid non-molten hot melt adhesive for use by system  10 . Suitable adhesives can include, for example, a hybrid plastisol described in U.S. Pat. No. 7,772,313 to Stumphauzer et al. Container  20  is coupled to inlet  36  of pump  28 . Motor  30  drives pump  28  to provide pressurized hot melt adhesive to outlet  38 . In one embodiment, motor  30  comprises a reciprocating air motor that drives a piston within pump  28 . 
         [0012]    Outlet  38  is coupled to cold line  34 , which connects to thermal break  24  at coupling  40 . Cold line  34  and thermal break  24  together form fluid line, or conduit,  41  that joins outlet  38  of pump  28  to inlet  42  of heat exchanger  22 . Thermal break  24  is connected to controller  18  via coupling  43 A, which is shown schematically for connecting to coupling  43 B. Flowable, non-molten liquid hot melt adhesive enters heat exchanger  22  and is heated to a temperature that transforms, or activates, the adhesive into a molten liquid, which reduces the viscosity of the hot melt adhesive. Heat exchanger  22  is connected via mixer  52  to dispenser  26 , which includes manifold  44  and module  46 . Heat exchanger  22  and module  46  are connected to controller  18  through wiring extending through conduit  48 . 
         [0013]    Molten liquid hot melt adhesive from pump  28  is received in manifold  44  and dispensed via dispensing module  46 . Mixer  52  ensures that the constituent components of the hot melt adhesive material are evenly dispersed within the fluid. Dispenser  26  can selectively discharge hot melt adhesive whereby the hot melt adhesive is sprayed out of outlet  50  of module  46  onto an object, such as a package, a case, or another object benefiting from hot melt adhesive dispensed by system  10 . Module  46  may include an electrically or pneumatically activated valve that receives power from conduit  48  or air hose  35 B. Module  46  can be one of multiple modules that are part of dispenser  26 . In an alternative embodiment, dispenser  34  can have a different configuration, such as a handheld gun-type dispenser. Some or all of the components in hot section  14 , including manifold  44  and module  46 , can be heated to keep the hot melt adhesive in a liquid state throughout hot section  14  during the dispensing process. 
         [0014]    Materials dispensed by system  10  are highly viscous, flowable liquids at room temperatures, but are low viscosity, molten liquids when activated at elevated temperatures, often as high as 300° Fahrenheit (˜149° Celsius). Heat exchanger  22  imparts enough thermal energy to the material to activate the material into a molten liquid that is more easily dispensed at dispenser  26 . In one embodiment, heat exchanger  22  may comprise a device as is described in the aforementioned U.S. Pat. No. 7,623,772 to Stumphauzer et al. Once the material is activated, it will solidify into a solid after retreating from the activation temperature. As such, the molten liquid hot melt adhesive must be heated at all times or it will solidify and block-up system  10 . Heat exchanger  22  is positioned in close proximity to dispenser  26  to minimize the need for heating of the molten liquid hot melt adhesive. 
         [0015]    Due to thermal expansion that occurs in the material, it is possible for activated liquid hot melt adhesive to migrate upstream from heat exchanger  22  toward pump  28 . Because pump  28  is located in cold section  12  of system  10 , the molten liquid hot melt adhesive will eventually solidify after transitioning through a molten and non-molten mixed state. The solidified material will form a plug that, at first, reduces pressure to dispenser  26  and decreases shot size of dispenser  26 , thereby decreasing consistency of system  10 . Eventually, the plug will grow to block flow to dispenser  26  altogether. Heated thermal break  24  provides a heated buffer between pump  28  and heat exchanger  22  to maintain heating of any activated, molten liquid hot melt adhesive that migrates upstream of heat exchanger  22 . 
         [0016]      FIG. 2  is a schematic of fluid line  41  of system  10  of  FIG. 1  showing heated thermal break  24  positioned between pump  28  and heat exchanger  22 . Heat exchanger  22  is connected to manifold  44  and module  46  of module  26  via mixer  52 . Pump  28 , heat exchanger  22  and dispenser  26  are configured to operate the same as in  FIG. 1 . Thermal break  24  includes conduit  54  and heating device  56 , which results in conduit  54  having un-heated section  58  and heated section  60 . 
         [0017]    As discussed earlier, pump  28  provides flowable, room temperature, un-activated liquid hot melt adhesive to fluid line  41  and heat exchanger  22 . Heat exchanger  22  imparts thermal energy to the liquid hot melt adhesive to raise the temperature of the liquid hot melt adhesive to an activation temperature. The activation temperature melts and fuses the constituent components of the liquid hot melt adhesive into a molten liquid hot melt adhesive. Mixer  52  ensures that the constituent components are fully melted and blended into homogeneous glue. Manifold  44  receives the molten liquid and provides it to one or more of modules  46 , which dispense the molten liquid at outlets  50 . 
         [0018]    Ideally, as system  10  operates, all activated molten liquid hot melt adhesive progresses through system  10  and leaves at outlet  50 . Thus, all molten liquid hot melt adhesive that solidifies when the temperature decreases past the activation temperature, such as when system  10  is shut-down, would be contained in heated components of system  10 , such as heat exchanger  22 , mixer  52  and dispenser  26 , in hot section  12  ( FIG. 1 ). Upon start-up of system  10 , the solidified hot melt adhesive can be melted by the heated components. However, due to thermal expansion of the molten liquid hot melt adhesive, activated liquid hot melt adhesive can travel from heat exchanger  22  toward pump  28  within fluid line  41 . Without the use of heated thermal break  24 , this activated liquid hot melt adhesive will eventually solidify in cold section  14  ( FIG. 1 ) potentially causing problems at shut-down and during dispensing operations, as previously discussed. 
         [0019]    Heated thermal break  24  is connected into fluid line  41  to provide a heating zone of sufficient temperature and length that facilitates controlled re-melting of any solidified or semi-solidified material. Heating device  56  extends along a portion of conduit  54  to provide heating that forms a temperature gradient (as illustrated in  FIG. 2 ) between heat exchanger  22  and unheated section  58 . Activated molten liquid hot melt adhesive from heat exchanger  22  will migrate upstream into conduit  54  of thermal break  24 , all the way through heated section  60  and into unheated section  58 . The molten liquid hot melt adhesive will cool the further away it gets from heated section  60  and heating device  56 , turning into a non-molten and molten transitional state material. 
         [0020]    The transitional state material will form into a plug having a diameter smaller than that of conduit  54  in unheated section  58 . The pressure of pump  28  pushes the plug back towards heat exchanger  22  through heated section  60 . Heated thermal break  24 , specifically heated section  60 , allows the plug to move freely within fluid line  41  before entering heat exchanger  22 . Unheated section  58  provides a runway that allows the plug to more freely enter heated section  60 . Thus, the lengths of unheated section  58  and heated section  60 , the diameters of unheated section  58  and heated section  60 , the materials of unheated section  58  and heated section  60 , and the amount and location of heat from heating device  56  can all be selected to control the formation and remelting of plugs within fluid line  41  to thereby mitigate the risk of a plug interfering with free flow of material through system  10 . 
         [0021]    In one embodiment, heated section  60  and unheated section  58  have the same inside diameter as each other, thereby allowing the plug to be easily pushed through thermal break  24 . In one particular embodiment, heated section  60  and unheated section  58  are made from the same piece of tubing or pipe, thereby being free of couplings and joints where plugs can get hung-up and block flow through fluid line  41 . Conduit  54  may be made of flexible or rigid components. Additionally, in various embodiments, heated section  60  and unheated section  58  may be coated with a lining that has a low coefficient of friction that also facilitates pushing of the plug through thermal break  24 . In one embodiment, the coefficient of friction for conduit  54  is lower than the coefficient of friction for heat exchanger  22 . In one particular embodiment, conduit  54  comprises a stainless steel tube coated with a polytetrafluoroethylene (PTFE) lining 
         [0022]    In one embodiment, heating device  56  comprises a resistive heat tape wound around conduit  54 . However, any suitable heating device may be used. Heating device  56  can be configured to apply constant heating along its entire length, or can apply different amounts of heating in different zones along its length. This can be done by placing a single heating device along the length of heated section  60 , or by placing multiple heating devices with the same or different wattages at different locations along heated section  60 , respectively. Alternatively, a single heating device may be fabricated to produce zones with different amounts of heating, such as by using resistive heat tape with varying diameters or thicknesses. In various embodiments, one or more heating devices  56  are used to produce higher amounts of thermal energy near heat exchanger  22  than near unheated section  58 . Heating device  56  need not provide sufficient heating to activate the hot melt adhesive liquid, but does provide sufficient heating to allow solidified hot melt adhesive material to return to a flowable liquid state. Thereafter, heat exchanger  22  provides thermal energy and mixing required to activate any liquid hot melt adhesive that may have been insufficiently or partially activated or mixed. 
         [0023]    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.