Patent Application
20140263451
The present disclosure relates generally to systems for dispensing hot melt adhesive. More particularly, the present disclosure relates to a pump outlet assembly for pressure control.
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.
It is desirable in many hot melt applications that adhesive be dispensed at a substantially constant rate so as to provide a uniform layer of adhesive. Accordingly, conventional hot melt systems often use heated supply systems wherein the pump and dispenser are connected by a heated hose. The pump (typically a linear displacement piston pump with a single reciprocating piston) discharges melted adhesive from the tank with pressure that varies over the course of each pumping cycle. The hose carries melted adhesive from the pump to the dispenser, and acts as a fluid accumulator or pressure dampener to alleviate changes in pressure over the course of the pumping cycle of the pump.
According to one embodiment of the present invention, a pumping system comprises a pump, first and second channels, a valve, and an actuator. The pump pumps fluid according to a pumping cycle. The first channel has a first fluid flow orifice with a first diameter, while the second channel has a second fluid flow orifice with a second diameter greater than the first diameter. The valve is configured to direct fluid from the pump to the first channel in a first state, and to the second channel in a second state. The actuator is configured to switch the valve into the first state during a high pressure period of the pumping cycle, and into the second state during a low pressure period of the pumping cycle.
According to a second embodiment of the present invention, an adhesive system comprises a melt system, a pump, a dispenser, and an outlet assembly. The melt system melts adhesive, and the pump pumps the adhesive from the melt system according to a pumping cycle. The dispenser is configured to receive and dispense the adhesive from the pump. The outlet assembly is disposed between the pump and the dispenser to smooth melted adhesive pressure at the dispenser by routing the adhesive through a first diameter orifice during a first portion of the pumping cycle, and through a second diameter orifice during a second portion of the pumping cycle.
Components of cold section 12 can be operated at room temperature, without being heated. Container 20 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 glue such as ethylene vinyl acetate (EVA) or metallocene. Feed assembly 22 connects container 20 to hot section 14 for delivering the solid adhesive pellets from container 20 to hot section 14. Feed assembly 22 includes vacuum assembly 24 and feed hose 26. Vacuum assembly 24 is positioned in container 20. Compressed air from air source 16 and air control valve 17 is delivered to vacuum assembly 24 to create a vacuum, inducing flow of solid adhesive pellets into inlet 28 of vacuum assembly 24 and then through feed hose 26 to hot section 14. Feed hose 26 is a tube or other passage sized with a diameter substantially larger than that of the solid adhesive pellets to allow the solid adhesive pellets to flow freely through feed hose 26. Feed hose 26 connects vacuum assembly 24 to hot section 14.
Solid adhesive pellets are delivered from feed hose 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 36 to pump hot melt adhesive from melt system 30, through supply hose 38, to dispenser 34. Motor 36 can be an air motor driven by pulses of compressed air from air source 16 and air control valve 17. Pump 32 can, for instance, be a linear displacement pump such as a double-action piston pump driven by motor 36. In the illustrated embodiment, dispenser 34 includes manifold 40 and dispensing module 42. Hot melt adhesive from pump 32 is received in manifold 40 and dispensed via module 42. Dispenser 34 can selectively discharge hot melt adhesive whereby the hot melt adhesive is sprayed out outlet 44 of module 42 onto an object, such as a package, a case, or another object benefiting from hot melt adhesive dispensed by system 10. Module 42 can be one of multiple modules that are part of dispenser 34. 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 melt system 30, pump 32, supply hose 38, 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. In alternative embodiments, system 10 can be modified as necessary for a particular industrial process application. For example, in one embodiment (not shown), pump 32 can be separated from melt system 30 and instead attached to dispenser 34. Supply hose 38 can then connect melt system 30 to pump 32.
Outlet assembly 100 connects pump 32 to supply hose 38. Outlet assembly 100 is a variable orifice outlet assembly configured to reduce variation in fluid pressure at supply hose 38 and manifold 40 across the pumping cycle of pump 32. Outlet assembly 100 is described in detail below, with respect to
Pump 32 pumps hot melted adhesive from melt system 30 into inlet plenum 102 of outlet assembly 100 at inlet pressure PI. Inlet plenum 102 and outlet plenum 108 are chambers, passage, or reservoirs that accumulate liquid adhesive. Inlet pressure PI of liquid adhesive entering inlet plenum 102 varies as a function of the pumping cycle of pump 32 (see
Valve 110 is a switching valve that provides a path from inlet plenum 102 to either first passage 104 or second passage 106. In the depicted embodiment, valve 110 is a shuttle valve with sliding shuttle 112 having first and second openings 114 and 116. Inlet and outlet plena 102 and 108 are depicted as forked passages having separate branches leading respectively to and from inlet first passage 104 and second passage 106. First passage 104 includes first orifice 124, while second passage 106 includes second orifice 126. First and second orifices 124 and 126 are apertures narrower than first and second openings 114 and 116 and first and second passages 104 and 106. First and second orifices 124 and 126 have diameters selected to produce desired permanent pressure drops ΔP1 and ΔP2, respectively, between inlet plenum 102 and outlet plenum 108, as described in further detail below. First and second passages 104 and 106 have identical diameters, as do first and second openings 114 and 116, such that the diameters of first and second orifices 124 and 126 determine the difference between ΔP1 and ΔP2.
In the depicted embodiment, valve 110 has first and second valve states V1 and V2 corresponding to locations of sliding shuttle 112. Valve 110 is shown in first valve state V1, wherein sliding shuttle 112 aligns first opening 114 with first passage 104 and seals second passage 106, thereby providing a fluid path from inlet plenum 102 to outlet plenum 108 via first passage 104 and first orifice 124. In second valve state V2 (not shown), shuttle 112 aligns second opening 116 with second passage 106 and seals first passage 104, thereby providing a fluid path from inlet plenum 102 to outlet plenum 108 via second passage 106 and second orifice 126. In alternative embodiments, valve 110 may, for instance, be a ball valve or similar valve type with a single configurable or redirectable opening instead of separate first and second openings 114 and 116. When valve 110 is in first valve state V1, the permanent pressure drop between inlet and outlet plena 102 and 108 is ΔP1, as described above. When valve 110 is in second valve state V2, the permanent pressure drop between inlet and outlet plena 102 and 108 is ΔP2. Actuator 118 switches valve 110 between first and second valve states V1 and V2 over the course of the pumping cycle of pump 32. As described in further detail below, valve state V1 is used during each sustained stroke of pump 32, while valve state V2 is used during pump changeover.
Actuator 118 is a valve actuator such as a motor-driven or hydraulic actuator coupled to valve 110. Actuator 118 drives valve 110 in accordance with control line cl, a mechanical or electrical control line that matches states of valve 110 to the cycle of pump 32 as described in further detail below with respect to
In the depicted embodiment, first orifice 124 has a narrower diameter than second orifice 126. As is well known in the art, narrower apertures produce greater permanent pressure drops. Accordingly, ΔP1 across first orifice 124 is greater than permanent pressure drop ΔP2 across second orifice 126. By matching larger pressure drop ΔP1 with periods of high inlet pressure PI, and smaller pressure drop ΔP2 with periods of low inlet pressure PI, outlet assembly 100 reduces fluctuation in outlet pressure PO. To this end, actuator 118 switches valve 100 to valve state V1 during relatively high pressure sustained strokes of pump 32, and to valve state V2 during relatively low pressure changeover periods of pump 32. In this way, outlet assembly 100 produces a relatively uniform outlet pressure PO that varies substantially less over the course of each pumping cycle of pump 32 than inlet pressure PI.
In the depicted embodiment, first and second orifices 124 and 126 pass through first and second orifice plugs 120 and 122, respectively. First and second orifice plugs 120 and 122 are removable inserts that fit into outlet assembly 100 to provide orifices of desired diameters. First and second orifice plugs 120 and 122 may, for instance, be sealed threaded cylindrical components that screw into outlet assembly 100 to situate orifices 124 and 126 in first and second passages 104 and 106, respectively. First and/or second orifice plugs 120 can be swapped out for similar plugs with different diameter orifices so as to tune permanent pressure drops ΔP1 and ΔP2 to achieve reduced variation in outlet pressure PO across the pump cycle of pump 32. In alternative embodiments, first and second orifices 124 and 126 may be permanent structures formed within outlet assembly 100.
Although outlet assembly 100 has been described above as a variable outlet assembly having two separate orifices 124 and 126 with differing diameters, alternative embodiments may include more or fewer apertures. Some alternative embodiments, for instance, may dispense with valve 110 and replace orifices 124 and 126 with a single aperture with continuously variable diameter controllable to compensate for fluctuations in inlet pressure PI from pump 32. In other embodiments, valve 110 may switch between three or more orifice passages for greater granularity of pressure control as compared to the two-orifice embodiment described above.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
