Abstract:
The present invention generally relates to a hot molten adhesive application machine. More specifically the present invention discloses a unique hot melt adhesive application machine having a novel construction whereby the reservoir of molten adhesive material is heated from within the molten adhesive. The adhesive pump, discharge hoses, and discharge applicators are heated by electrical resistance heating elements that may operate on 120 or 240 volt current. Further, a novel axial pump piston is disclosed whereby the pump cylinder bore may be machined to a lessor tolerance standard than previous pumps of this type.

Description:
RELATED APPLICATIONS 
     This application claims the priority of Provisional Patent Application Ser. No. 60/356,869 filed on Feb. 14, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a hot melt adhesive application machine. More specifically the present invention discloses a novel method and apparatus for supplying heat to the molten adhesive reservoir and providing heat to the molten adhesive discharge hoses and applicators. Further a unique and novel heated adhesive piston displacement pump mechanism is taught whereby the cost of manufacture of the pump has been reduced. 
     Heretofore, hot melt adhesive application machines basically comprised a heated reservoir from which the molten adhesive was removed by a piston displacement pump manufactured to exacting tolerances. In such a system the reservoir container is directly heated by any convenient means, whereby heat transfer is, by conduction, from the reservoir container into the reservoir of adhesive material. Therefore the reservoir must be maintained at a temperature above that of the molten adhesive to maintain heat flow into the molten adhesive since heat can only flow from a high temperature to a lower temperature. Since the reservoir container will typically comprise a relatively large surface area the reservoir shell represents a large heat conducting and/or radiating surface. Thus the outer surface of the reservoir shell must be heavily insulated to minimize heat loss from the reservoir to the surrounding environment. Nevertheless, heat will be lost to the surrounding environment. 
     Prior art hot melt adhesive application machines typically include electrical resistance heating elements within their supply hoses and applicators to prevent undesirable heat loss from the molten adhesive as it is conveyed from the pumping mechanism to the applicator. However, the typical prior art hot melt adhesive application machine discharge hose and applicators are manufactured to operate on, and are committed to operate on 120 or 240 volt electrical supply systems but not both. Therefore a manufacturer and/or supplier of such equipment must, necessarily, stock machines, discharge hoses and applicators, that operate on one or the other electrical systems. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention overcomes the above described disadvantages of prior art hot melt adhesive application machines. 
     The present invention teaches an electrically heated main displacement pump body that is partially submerged within the molten adhesive material thereby eliminating the necessity of heating the outside shell of the reservoir. By this technique heat from the submerged pump body first passes, by conduction, into the molten adhesive material and then to the reservoir outer shell. Thus, in heat transfer terms, the reservoir outer shell is the coolest part of the system thereby requiring less insulating material to prevent unnecessary heat loss to the surrounding environment. By the present invention the reservoir container may now be made of a material having a lower heat transfer conductivity than the metal containers of the prior art. For example, the molten adhesive reservoir might be made of a low conductivity resinous material or ceramic. 
     A further novel feature of the present invention is that the hot melt adhesive pump body, each hot melt supply hose and associated discharge applicator is separately heated by electric resistance heating circuits that may selectively operate on 120 volt or 240 volt AC current. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 presents a front elevational view of a hot melt adhesive applying machine embodying the present invention. 
     FIG. 2 presents a rear elevational view of the hot melt adhesive applying machine of FIG.  1 . 
     FIG. 3 presents a left side elevational view of the hot melt adhesive applying machine of FIG. 1 with discharge hose and applicator removed. 
     FIG. 4 presents a right side elevational view of the hot melt adhesive applying machine of FIG. 1 with discharge hose and applicator removed. 
     FIG. 5 presents a top plan view of the hot melt adhesive applying machine of FIG. 1 with discharge hose and applicator removed. 
     FIG. 6 presents a crossectional view taken along line  6 — 6  in FIG.  1 . 
     FIG. 6A is an enlarged crossection of the encircled area  6 A in FIG.  6 . 
     FIG. 6B is an enlarged crossection of the encircled area  6 B in FIG.  6 . 
     FIG. 7 presents a crossectional view taken along line  7 — 7  in FIG.  6 . 
     FIG. 8 presents an exploded, isometric, pictorial view of the air motor/pump assembly removed form the hot melt adhesive application machine. 
     FIG. 8A presents an isometric, pictorial view of the pump rod/piston assembly removed from the pump body. 
     FIG. 8B is a crossectional view taken along line  8 B— 8 B in FIG.  8 A. 
     FIG. 8C presents an elevational view taken along line  8 C— 8 C in FIG.  8 B. 
     FIG. 9 presents a crossectional view taken along line  9 — 9  in FIG.  8 . 
     FIG. 10 presents an electrical diagram illustrating the 120 volt operation of the machine heating elements. 
     FIG. 10A illustrates the electrical circuit of each resistance heater system in FIG. 10 when configured for 120 Volt AC operation. 
     FIG. 11 presents an electrical diagram illustrating the 240 volt operation of the machine heating elements. 
     FIG. 11 a  illustrates the electrical circuit of each resistance heater system in FIG. 10 when configured for 240 Volt AC operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring generally to FIGS. 1 through 6, a hot melt adhesive application machine  10  is illustrated comprising a base frame or supporting stand  12  having a top cover  13  attached to base  12  by a multiplicity of nuts and bolts  19  as illustrated in the cutaway portion of top cover  13  in FIG.  1 . An open top, adhesive reservoir  14  having an outer reservoir shell  16  is suspended from top cover  13  as best seen in FIG.  6 . Thermal insulating material  25  is placed between reservoir  14  and shell  16  to reduce heat loss from the molten adhesive within reservoir  14 . Extending upward from top cover  13  is safety guard  18 . Positioned above safety guard  18  is a U shaped mounting bracket  22  having main control box  24  attached thereto. Mounting bracket  22  includes a handle  26  for lifting and/or carrying machine  10 . A hinged lid  28  is provided atop opening  125 , within the top cover  13 , for loading solid, hot melt adhesive into reservoir  14  as shown in FIG.  6 . 
     FIG. 8 presents an exploded isometric pictorial of the air motor/pump assembly within machine  10 . Air motor  30  is affixed to the top plate  52  of the pump body assembly  40  by four stanchions  54  as seen in FIGS. 6 and 8. Stanchions  54  are threaded into the body of air motor  30  and attached to top plate  52  by four flat headed, threaded fasteners  58 . Pump body  50  is affixed to the opposite side of plate  52  by four socket-headed screws  56  as illustrated in FIGS. 6 and 8. Prior to attaching plate  52  to pump body  50 , pump body  50  is first attached to top cover  13  by four socket-head screws  36  as illustrated in the cutaway portion in FIG.  4 . Although an air motor is disclosed herein, any suitable means of driving pump assembly  40 , such as an electric motor may also be used. 
     As best illustrated in FIGS. 6,  8 , and  9 , the top portion of the pump body&#39;s four comers are, machined away as best illustrated in FIG. 9 thereby creating four flat land areas  38  into which a threaded bore  42  is provided for attaching pump body  50  to top cover  13  with four socket-head screws  36  as illustrated in the cut-away portion of FIG.  4 . 
     An opening  60  is provided, within plate  52 , through which pump rod  65  passes and attaches to air motor driving rod  20  by coupling  126  as illustrated in FIG. 6. A pump piston assembly  70  is attached to the opposite end of pump rod  65  as illustrated in FIG.  8 A and is received within pump bore  66  as illustrated in FIG.  6 . Threaded into the bottom opening of pump bore  66  is pump check valve assembly  62 . A seal  64  is provided at the top of pump rod bore  68  sealingly engaging pump rod  65  as pump rod  65  reciprocates within pump rod bore  68 . A blind heater bore  67  is provided within pump body  50  receiving therein resistance-heating element  72 . Side opening  74 , within pump body  50  is provided for exit of the heating element feed wires  73  which are connected to pump body temperature control  96 . The temperature setting desired for the pump body is manually set as appropriate for the particular adhesive within reservoir  14 . For reference and control purposes a pump body thermometer  98  is provided to give a continuous read-out of the pump body temperature. Thermometer  98  is a simple typical stem type thermometer inserted into a stem receiving bore within the pump body (not shown). 
     Referring now to FIGS. 8,  8 A,  8 B, and  8 C, pump rod  65  is attached to air motor  30 , at its top end, by coupling  126  and to piston assembly  70  at its bottom end. The main body  95 , of piston assembly  70 , includes, at its top end, a side opening slot  122 . A second, more narrow “key way slot”  121  is cut into the top cover  120  of slot  122 . Key way slot  121  generally parallels slot  122 . The bottom end of pump rod  65  terminates with a circular knob  110  extended from said pump rod by a small diameter neck  112 . When piston assembly  70  is connected to pump rod  65  knob  110  slides into slot  122  with neck  112  being received within slot  121 . Thus piston assembly  70  has a small degree of freedom to move in a lateral direction but is not free to move axially with respect to pump rod  65 . This lateral freedom of movement by piston assembly  70  permits piston assembly  70  to self align within pump bore  66  as it translates axially therein. Coupling  126  connects air driving rod  20  to the opposite end of pump rod  65  in a similar manner as that used to connect piston assembly  70 . 
     Extending outward from either side of pump body  50  is at least one heated and insulated, molten adhesive supply hose  100  (see FIG. 2) connecting to a separately heated adhesive applicator  102 . A second heated and insulated supply hose  105  and heated applicator  107  may also be provided. Supply hoses  100  and  105  are threadedly connected to pump discharge outlets  106  and  108  as shown in FIGS. 6 and 8. Supply hoses  100  and  105 , and applicators  102  and  107  each have separate thermostatically controlled heating elements therein which will be discussed in further detail below. 
     Applicators  102  and  107  each include separate, manually adjustable, thermostatic controls  104  and  108  for controlling the temperature of the applicator. Supply hoses  100  and  105  each include separate thermostatic controls  110  and  112  having two preset positions, “HIGH” and “LOW.” However, if desired supply hoses  100  and  105  could be provided with manually controlled thermostatic controls as those provided on applicators  102  and  107 . 
     Referring now to FIGS. 6 and 7, attached to pump body  50  are heat transfer fins  80 A,  80 B  82 A and  82 B as best seen in FIG.  7 . As illustrated in FIG. 7, heat transfer fins  80 A and  80 B generally circumscribe the inner periphery of reservoir  14  maintaining a nominal distance or clearance  84  from the inside surface of reservoir  14 . Heat transfer fins  80  may be configured hexagonally as illustrated in FIG. 7, or may be curved so as to maintain a constant distance  84  from the inside surface of reservoir  14 . Heat transfer fins  80 A,  80 B,  82 A, and  82 B are attached to pump body  50  such that heat energy will be conveyed, by conduction, from pump body  50  into and throughout heat transfer fins  80 A,  80 B,  82 A, and  82 B. Thermal energy is then transferred, by conduction, from heat transfer fins  80 A,  80 B,  82 A, and  82 B into the adhesive within reservoir  14 . Preferably heat transfer fins  82 A and  82 B have a tapered top edge  86  including a “knife edge” profile for severing large pieces of solid adhesive that may be added to reservoir  14  during use of machine  10 . 
     Extending horizontally below heat transfer fins  80 A,  80 B,  82 A, and  82 B and generally parallel to the bottom surface of reservoir  14  is plate  88 . Octagonally shaped plate  88  is attached to the bottom of pump body  50  by any suitable manner, such as threaded screws. Heat transfer fins  80 A,  80 B, and bottom plate  88  generally form a heated supply hopper, having dividers  82 A and  82 B therein, into which solid adhesive shapes may be added for melting. A multiplicity of apertures  78  are provided to permit molten adhesive to pass therethrough and into the molten adhesive reservoir. A gap  85  is also preferred between the bottom of heat transfer fins  80 ,  82 , and bottom plate  88  for passage of molten adhesive into the molten adhesive reservoir. 
     FIG. 6B presents an enlarged crossectional view of pump inlet check valve assembly  62  as installed at the bottom of pump bore  66 . Check valve assembly  62  comprises an inlet fitting  76  extending upward into the inlet end of pump bore  66 . An inlet passage extends axially through fitting  76  comprising a first bore  78  diverging into a larger diameter second bore  79 . At the juncture of bore  78  and bore  79  a ball seat  90  is provided for receiving therein ball  92 . A diametrically extending roll pin  94  is provided to retain ball  92  within check valve assembly  62 . Thus a simple ball check valve is provided within the inlet end of pump bore  66  whereby fluid (molten adhesive) may flow into pump bore  66 , as piston assembly  70  moves upward, but is prevented from flowing out of pump bore  66  as piston assembly  70  moves downward. Inlet check valve assembly  62  may be threaded into pump bore  66 , installed as a force fitted insert, or any other convenient means. It is preferable to provide an inlet filter  45  (see FIG. 6B) to prevent the entry of any debris, that may have fallen into the adhesive reservoir, from entering check valve assembly  62 . 
     A similar ball check valve is installed within pump piston assembly  70 . Referring to FIGS. 6A and 8, piston assembly  70  comprises a main body  95  having an axial central bore  93  therein. Central bore  93  converges into a secondary, blind, axial bore  91 . Inserted into central bore  93  is a valve seat fitting  98  having an axial inlet bore  97  terminating with a ball valve seat  99  at its upper end. Positioned between valve seat  99  and secondary bore  91  is ball  81  and compression spring  83  biasing ball  81  toward valve seat  99 . At least one fluid passage  61  is provided extending from chamber  87 , within piston body  95 , into pump bore  66 . 
     In operation, as piston assembly  70  moves downward in pump bore  66 , check valve assembly  62  is closed whereby fluid (molten adhesive) forces ball  81 , within piston assembly  70 , to open thereby permitting fluid to flow through chamber  87  and passage way  61  of piston assembly  70  and into pump bore  66  above piston assembly  70  and around pump rod  65 . When piston assembly  70  reverses travel, at bottom dead center, and begins to move upward within pump bore  66 , ball valve  81  within piston assembly  70  closes and check valve assembly  62  opens admitting molten adhesive into pump chamber  66  below piston assembly  70 . The fluid atop piston assembly  70  is now forced upward, around pump rod  65 , exiting pump chamber  66  through fluid exit ports  106  and  108  into hose assemblies  105  and  100  respectively. After reaching top dead center the cycle repeats itself. 
     Pump rod  65  fits with minimal gap within pump rod bore  68  thereby minimizing by pass flow around pump rod  65 . Pressure relief channel  46  redirects any bypass flow back into reservoir  14  (see FIG. 6) thereby reducing hydraulic pressure on seal  64 . 
     In manufacture of pump body  50  pump rod bore  68  is drilled from the top of pump body  50  and pump bore  66  is opposingly drilled from the bottom of pump body  50  whereby both bores meet at mid body. Because of the self aligning attributes of piston assembly  70 , the accuracy of aligning the opposingly drilled bores is diminished from that which would be otherwise required for a non self aligning piston assembly. Also use of the above described self aligning piston assembly accommodates manufacturing the pump body in one rather than two or more, axially aligned sections each having the bore therein drilled before assembly of the two sections. Thus, by use of the above described self aligning piston assembly the need for accurately aligning the separate bores during manufacture is greatly diminished as the self aligning piston assembly, having lateral mobility, will accommodate concentricity errors. 
     Turning now to FIGS. 10 and 11, letters A, B, C, D, and E represent the resistance heaters within pump body  50 , supply hose  100 , applicator  102 , supply hose  105 , and discharge applicator  107  respectively. Each resistance heater circuit comprises two, in line, resistance heating elements R 1  and R 2  as illustrated in FIGS. 10 and 11. FIG. 10 illustrates the wiring arrangement for 120 volt operation and FIG. 11 illustrates the wiring arrangement for 240 volt operation. 
     When the user desires to operate the hot melt machine on 120 volts, as illustrated in FIG. 10, the user plugs connector  156  into line connector  150  and connector  160  into connector  152 , as illustrated. When connectors  156 ,  150 ,  160 , and  152  are connected in this way, each resistive heater, A, B, C, D, and E, is wired in a parallel circuit as illustrated in FIG.  10 A. 
     When the user desires to operate the hot melt machine on 240 volts, as illustrated in FIG. 11, the user plugs connector  152  into line connector  150 , and leaves connectors  156  and  160  free and unplugged as illustrated. When configured in this way each resistive heater, A, B, C, D, and E is wired in series as illustrated in FIG.  11 A. When wired to operate on 240 volts, as illustrated in FIG. 11, it is desired to plug connectors  156  and  160  into dead end connectors  154  and  168 , respectively, to prevent the possibility of human contact with the otherwise electrically hot connector pins. Connectors  150 ,  152 ,  154 ,  156 ,  160  and  168  are located within control box  24 . 
     As shown in FIGS. 10 and 11, hose  1  and applicator  1  are electrically connected to the machine using connector  123 . In a similar manner, hose  2  and applicator  2  are electrically connected to the machine using connector  124 . By virtue of the electrical topology disclosed in FIGS. 10 and 11, the hose and applicator peripherals, when attached, assume either a series electrical arrangement or a parallel electrical arrangement, as is appropriate for a given machine, with no modification of the peripherals themselves. 
     Although resistance heaters A, B, C, D, and E are shown in FIGS. 10 and 11 as each having two resistance heating elements, any number of heating elements may be employed. When employing more than two resistance heating elements the circuitry must be structured such that all resistive heating elements operate in parallel when operating on 240 volts and operate in series when operating on 120 volts. 
     While we have described above the principles of my invention in connection with specific embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation of the scope of my invention as set forth in the accompanying claims.