Field of the Invention
[0001] The present invention generally relates to liquid dispensing technology and, more
specifically, to adhesive dispensers using heated or unheated manifolds and valve
modules to selectively dispense liquid adhesive.
Background of the Invention
[0002] Existing hot melt adhesive dispensers operate at relatively high temperatures, such
as above about 250°F (121°C). Present dispenser configurations have high temperature
surfaces exposed to personnel. Considerable measures are taken to guard or insulate
the dispensing equipment from nearby personnel. However, this also reduces the ease
with which the equipment may be serviced by such personnel.
[0003] Many hot melt dispensers include a heated manifold for supplying hot liquid adhesive
to one or more valve modules. Very often, these manifolds are heated by cartridge
heaters or other heating elements contained within the manifold. The manifold may
therefore contain high tolerance bores for receiving the heaters. Air gaps can exist
between the heaters and the manifold resulting in localized hot spots or overheating.
Over time, these hot spots will cause heater failure. In some cases, it may also be
difficult to obtain highly uniform heating of a manifold through the use of internal
heaters. For example, small manifolds or irregularly-shaped manifolds may not easily
permit the use of cartridge heaters or cast-in-place heaters.
[0004] Present methods of supplying liquid hot melt adhesive can also result in adhesive
stagnation and air pocketing. This contributes to char formation and related overheating
problems which then adversely affect dispenser performance. Also, the typical circular
cross sectional flow area of liquid supply passages is an inefficient heat transfer
configuration. Many manifolds are also constructed of cast metal thus leading to lower
strength threads and difficulty in accommodating a liquid filter.
[0005] Another problem arising when dispensing viscous liquids, such as hot melt or room
temperature adhesive, relates to the formation of tailing, stringing or drooling of
adhesive upon liquid cut-off. The inertial effects of fluid flow may prolong adhesive
cut-off, therefore resulting in these undesirable effects. In a traditional valve
arrangement, liquid adhesive flows parallel to a valve stem into the valve seat area.
When the end of the valve stem is lifted from the seat, the flow path is relatively
straight. As the valve stem approaches the seat, the liquid inertia combines with
the decreasing flow area between the valve stem and the seat edge thereby resulting
in increased liquid flow velocities. These increased velocities can lead to stringing,
tailing or drooling of adhesive after cut-off. When dispensing hot melt adhesives,
the same cut-off problems can arise if the adhesive is not maintained at the proper
set point temperature in the nozzle.
[0006] It would therefore be desirable to provide dispensing apparatus for dispensing liquid
hot melt or room temperature adhesive and overcoming problems in the art such as those
mentioned above.
Summary of the Invention
[0007] In one aspect of the invention, a valve is provided for dispensing viscous liquids,
such as hot melt adhesives or room temperature adhesives. The valve includes a valve
seat having an orifice and a sealing surface located around the orifice. A valve stem
is movable between open and closed positions with respect to the valve seat and includes
one end with a recess and a sealing edge located around the recess. The sealing edge
is engaged with the sealing surface of the valve seat in the closed position and is
spaced from the sealing surface in the open position. The recess is designed to provide
a more tortuous flow path for the liquid to reduce the localized liquid flow velocities
and thereby reduce undesirable cut-off effects, such as stringing, tailing or drooling
of adhesive.
[0008] Another aspect of the invention relates to a unique, temperature controlled valve
module. More specifically, the valve module dispenses heated liquids at a predetermined
set point temperature, such as in the case of the application temperature of a hot
melt adhesive. The valve module includes a module body having a liquid cavity communicating
with a dispensing orifice, a valve seat disposed generally between the liquid cavity
and the dispensing orifice and a valve stem mounted for movement within the cavity
between engaged and disengaged positions relative to the valve seat for selectively
dispensing liquid from the dispensing orifice. In accordance with this aspect of the
invention, a heating element is thermally coupled with the module body and a temperature
sensor is also thermally coupled with the module body for detecting the temperature
of the liquid. This coupling may be a direct incorporation within the module body
or, for example, may be separate pieces in thermal contact. Advantageously, this configuration
more accurately controls the liquid temperature at the desired set point temperature
within the dispensing orifice or nozzle. This results in better cut-off and less stringing
of viscous liquids, such as hot melt adhesive.
[0009] The valve or valve module may be used in an apparatus for dispensing liquid hot melt
adhesive, including a manifold, a dispensing module connected with the manifold, a
heater thermally coupled with the manifold and a thermally insulating cover structure
surrounding the module and the manifold for preventing exposure of personnel to the
hot manifold and module surfaces. The cover structure is preferably formed of a plastic
material having a low thermal conductivity and preferably includes a plurality of
outwardly projecting fins for further dissipating heat. Ideally, the outer edges of
the fins are maintained at a temperature below a burn threshold temperature. Also
preferably, air spaces or gaps are formed between the cover structure and the module
and between the cover structure and the manifold for decreasing heat transfer to the
cover structure.
[0010] Also preferably, a thin film heater is bonded directly to the manifold. The thin
film heater supplies heat directly through outer surfaces of the manifold. In this
way, the manifold may be small and/or irregularly-shaped and still be heated in a
uniform and efficient manner. Power consumption is also reduced, especially when combined
with the thermally insulating cover structure. Preferably, the heater incorporates
a sensor for temperature control purposes and may also incorporate a thermal fuse
or thermostat for protection against overheating.
[0011] An alternative manifold assembly comprises a manifold body including an inlet bore
having an interior wall and a liquid supply passage communicating with the inlet bore.
A heater is thermally coupled with the manifold body. A supply connector extends within
the inlet bore and is configured therewith to provide better heat transfer and manufacturing
advantages, such as thread elimination and alternative connection orientations. The
supply connector includes an interior flow passage, an exterior annular recess disposed
adjacent the interior wall of the inlet bore, and at least one port communicating
between the interior flow passage and the exterior annular recess. The annular recess
communicates with the liquid supply passage of the manifold. The inlet bore preferably
extends completely through the manifold and is preferably a smooth bore. A pair of
seals extend around the connector each respectively engaging the interior wall on
opposite sides of the liquid supply passage. In one alternative, the connector further
comprises a filter retained in the interior flow passage for filtering the liquid
hot melt adhesive flowing into the exterior annular recess.
[0012] These and other advantages, objects and features of the invention will become more
readily apparent to those of ordinary skill in the art upon review of the following
detailed description of the preferred embodiment taken in conjunction with the accompanying
drawings.
Detailed Description of Drawings
[0013]
Fig. 1 is an exploded perspective view of a hot melt adhesive dispensing apparatus
constructed in accordance with a preferred embodiment of the invention;
Fig. 2 is an assembled perspective view of the hot melt dispensing apparatus shown
in Fig. 1;
Fig. 2A is an enlarged cross sectional view of a thin film heater of the invention;
Fig. 3 is a cross sectional view of the apparatus taken along line 3-3 of Fig. 2;
Fig. 4 is a cross sectional view taken along line 4-4 of Fig. 3;
Fig. 5 is a cross sectional view of a manifold assembly, similar to that shown in
Fig. 1, but showing an alternative liquid inlet connector;
Fig. 6A is a fragmented, partial cross sectional view of a valve assembly in accordance
with the invention shown in a closed position;
Fig. 6B is a fragmented, partial cross sectional view similar to Fig. 6A, but showing
the valve assembly in an open position; and
Fig. 7 is a fragmented cross sectional view which schematically illustrates a valve
module constructed in accordance with another alternative of the invention.
Detailed Description of Preferred Embodiments
[0014] Referring to Figs. 1 and 2, a hot melt adhesive dispensing apparatus 10 of the invention
includes a dispensing module 12 and a liquid supply manifold 14. Dispensing module
12 is positioned within a mounting bore 14a of manifold 14 by a set screw 15. An air
actuation cap 16 covers the upper end of dispensing module 12 and includes heat dissipating
fins 16a. A solenoid valve 18 is connected to air actuation cap 16 by an adapter 20
having a flange 22. A seal 24 is disposed between air actuation cap 16 and adapter
flange 22. As will be described in greater detail below, adapter 20 directs pressurized
air into module 12 through air actuation cap 16 to actuate a valve within module 12
between open and closed positions. Respective mufflers 26, 28 are connected within
threaded exhaust ports 30, 32 of adapter 20. A central supply port 34 receives an
air supply connector 36. Port 34 connects with supply port 38 of solenoid valve 18.
Respective exhaust ports 30, 32 of adapter 20 connect with exhaust ports 40, 42 of
solenoid valve 18. A suitable seal (not shown) is disposed between solenoid valve
18 and adapter 20. Solenoid valve 18 further includes air outlets 44, 46 for actuation
purposes. An electrical connector 48 is provided for connecting solenoid valve 18
to suitable electrical control devices for actuation control purposes.
[0015] A thin film heater 50 is preferably adhered to the outer surface of manifold 14.
For example, an inner silicone layer of thin film heater 50 may be vulcanized to the
outer surface of manifold 14. Heater 50 may be formed in various manners, such as
by sandwiching an etched foil electrical trace between suitable thin material layers,
such as silicone, Kapton® or PTFE. Alternatively, a wire element may be used as the
electrical trace between such thin film materials. The preferred thin film heater
50, as shown in the enlarged cross sectional view of Fig. 2A, is comprised of a thin
etched-foil heating element 50a sandwiched between two layers 50b, 50c of high temperature
silicone rubber. The etched-foil heating element or trace 50a may be formed to generate
heat uniformly or non-uniformly. In the latter regard, more heat may be generated
in areas of the manifold 14 that require such additional heat, for example, to provide
a more uniform temperature profile throughout the manifold 14. Heater 50 may optionally
be bonded to the outside surface of the manifold 14 with a high temperature adhesive.
Heater 50 is maintained in intimate contact with the manifold, which is an advantage
over commonly used insert-style cartridge heaters. Additionally, the area through
which heat is transferred is greater than that of a cartridge heater. This lowers
the watt density requirements of the heater, i.e., it lowers the required watts per
unit of heat transfer area.
[0016] Heater 50 includes wire leads 52 connected with a suitable power source for supplying
electrical current to the resistive electrical trace and wire leads 54 for connecting
a temperature sensor 56 with a conventional temperature control. Sensor 56 may be
used in a conventional feedback control system for controlling the amount of heat
delivered to manifold 14 through heater 50. A fuse or thermostat 58 may be connected
in series with the power leads 52 of heater 50 for electrically disconnecting heater
50 in the event of an excessive temperature condition. A cord set 60 connects with
leads 52, 54, and an electrical grounding lead (not shown). Heater 50 further includes
a hole 62 for receiving fastener 15 during assembly against manifold 14. An inlet
connector 64 is affixed to manifold 14 by engaging threaded portions 14b, 64a. A recessed
area 66 is formed in manifold 14 for heat transfer reduction, as will be discussed
below.
[0017] In addition to air actuation cap 16, additional covering structure is provided in
the form of cover halves 70, 72 which house manifold 14. Cover halves 70, 72 likewise
include heat dissipating fins 70a, 72a. Cap 16 and cover halves 70, 72 are preferably
formed from a high temperature plastic such as polyphenylene sulfide (PPS). Preferably,
the material has a low thermal conductivity. Fins 16a, 70a and 72a further act to
dissipate heat and reduce the temperature of the outer touchable surfaces. Preferably,
the outer touchable surfaces are reduced to a temperature at or below 167°F (75°C),
although the internal components may be at application temperatures at 250°F (121°C)
or higher. Respective seals 74, 76 are disposed between cover halves 70, 72 and manifold
14. An identification plate 78 may be affixed to cover half 70.
[0018] Turning now to Figs. 3 and 4, a fastener 82 connects mounting plate 80 through cover
half 70 to manifold 14. An additional recessed area 84, like recessed area 66, is
formed in manifold 14 for reducing heat transfer to cover half 72. Areas 66 and 84
form thermally insulating gaps between cover halves 70, 72 and manifold 14. A supply
passage 90 is formed in manifold 14 and communicates with an annular recess 92 contained
within mounting bore 14a. Supply passage 90 enters annular recess 92 at a tangential
entry point 94 to assist with liquid circulation. At least one supply port, and preferably
multiple supply ports 96, are formed in a module body 98. These ports 96 communicate
with an interior cavity 100 within module body 98. Cavity 100 contains a cartridge
102 as more fully disclosed and claimed in U.S. Patent Application No. 08/963,374,
assigned to the assignee of the present application
[0019] A nozzle mounting portion 104 includes a dispensing orifice 106 which is opened and
closed by a valve stem 108. Nozzle mounting portion 104 will typically be externally
threaded to carry an internally threaded nozzle (not shown). Valve stem 108 is supported
for longitudinal movement with respect to a valve seat 107 by a guide 103 of cartridge
102. Valve stem 108 carries a piston assembly 110 proximate an opposite end. A button
112 bears against this end of valve stem 108 under the bias of a spring 114 contained
within a cap 116. Cap 116 is crimped within module body 98 and sealed by an O-ring
118. On an opposite side of piston assembly 110, a retainer 120 is threaded within
module body 98 and holds cartridge 102 in place. An air seal 122 engages valve stem
108 and a liquid seal 124 engages valve stem 108. Respective O-rings 126, 128 seal
the exterior of cartridge 102 against the interior of cavity 100 and O-rings 130,
132 seal the exterior of module body 98 against mounting bore 14a on opposite sides
of liquid supply recess 92.
[0020] A pair of fasteners 140, 142 affix air actuation cap 16 to module body 98. Specifically,
module body 98 is affixed and aligned within air actuation cap 16 such that ports
144, 146 align with ports 148, 150 of cap 16. O-rings 152, 154 seal the respective
junctions between ports 144, 148 and ports 146, 150. Outlet passages 156, 158 respectively
communicate with ports 148, 150 and receive pressurized air from passages 160 and
162 in adapter 20. Passages 160, 162 respectively receive pressurized air from passages
44 and 46 in solenoid valve 18. When pressurized air is directed through port 144
into an upper piston chamber 164, piston assembly 110 will move downward to move valve
stem 108 against seat 107 to the closed position shown in Figs. 3 and 4. Conversely,
when pressurized air is directed through port 146 into a lower piston chamber 166,
piston assembly 110 will be moved upward against the bias of spring 114 thereby moving
valve stem 108 to an open position to dispense liquid from dispensing orifice 106.
As will be apparent from Figs. 3 and 4, air gaps are created respectively between
air actuation cap 16 and module body 98 and between respective cover halves 70, 72
and heated manifold 14. These air gaps act as thermal insulators to assist in preventing
heat transfer from the hot module body 98 and manifold 14 into respective cover structures,
i.e., cap 16 and cover halves 70, 72.
[0021] Referring to Fig. 5, an alternative manifold assembly 200 is shown and, particularly,
an alternative supply connection is shown in place of connector 64. Manifold assembly
200 includes a manifold body 202 having a supply passage 204. In all respects except
those discussed in connection with Fig. 5, manifold body 202 may take the form of
manifold 14. A bore 206 receives a supply connector 208. A pair of O-rings 210, 212
seal smooth bore 206 on opposite sides of supply passage 204. Supply passage 204 leads
to a dispensing module, such as module 12 discussed in the first embodiment. An annular
recess 214 is formed on the outer surface of connector 208 and communicates with passage
204. Connector 208 further includes an internal bore 216 adapted for connection to
a pressurized supply of, for example, liquid hot melt adhesive. Connector 208 is affixed
within smooth bore 206 by a flange portion 218 and a nut 220 which is tightened to
draw flange portion 218 and nut 220 against manifold body 202 through the interaction
of respective internal and external threads 222, 224. Nut 220 may be affixed to or
integrally formed with a filter 226 which extends within bore 216. Alternatively,
the filter 226 may be eliminated and nut 220 may be modified accordingly into another
fastening structure. One end 226a of filter 226 sealingly engages bore 216 to ensure
that liquid flows into filter 226. Liquid flows through filter 226 and into a plurality
of radial ports 228 leading to annular recess 214.
[0022] There are various advantages to the configuration shown in Fig. 5. For example, the
configuration eliminates the need to form threads in the manifold. A supply hose may
be attached to either side of the manifold by inserting connector 208 from an opposite
direction. The configuration prevents adhesive stagnation and air accumulation points
within the manifold. The configuration is also relatively simple to machine. Finally,
the connector and manifold design improves heat transfer by utilizing a thin-walled
annular flow space. For example, if the annular space formed by annular recess 214
is compared to a typical cylindrical flow passage of equal flow area and "D" represents
the diameter of the typical cylindrical cross section, while "D
o" represents the outer diameter of the annular space and "D
i" represents the inner diameter of the annular space, then the following equation
applies:

or

If we assume D=0.250" (0.635cm) (typical) and D
o = 0.625" (1.588cm), then: D
i = 0.573" (1.455cm) and the thickness of the annular space is

It follows that the surface per unit flow length available for transfer of heat in
each case is:


Therefore, the ratio of the annular cross section to the circular cross

That is, the annular configuration produces approximately four to five times more
surface area for heat transfer.
[0023] Figs. 6A and 6B illustrate a valve 250 in accordance with the invention. This valve
250 may be used in place of valve seat 107 and valve stem 108 as illustrated in the
first embodiment. Valve 250 comprises a valve stem 252 and a ball 254 utilized as
a valve seat. Ball 254 is rigidly affixed, as with a suitable adhesive, within mounting
structure 256 which may be part of a nozzle or valve body. A typical nozzle member
258 may be used and includes a dispensing orifice 260. Ball 254 includes a discharge
passage 262 aligned with valve stem 252 and dispensing orifice 260. The end of valve
stem 252 includes a recess 264, which may be an annular recess as shown or another
recess preferably of irregular shape for forcing changes in flow direction. When valve
stem 252 is in the closed position shown in Fig. 6A, a sealing line of contact 266
is made between the outer edge of recess 264 and the outer surface of ball 254 immediately
outside of discharge passage 262. When valve stem 252 is lifted from ball 254, but
moving toward ball 254 (Fig. 6B), liquid will flow into annular recess 264 and create
turbulence before exiting through discharge passage 262 and dispensing orifice 260.
This turbulence, coupled with the tortuous flow path and localized high pressure zone,
will reduce the discharge flow velocity upon valve closure.-Reduced liquid discharge
velocities will likewise reduce stringing, tailing or drooling of viscous liquids,
such as room temperature or hot melt adhesive, upon cut-off. In the full open position,
moderate fluid path directional changes and little turbulence will exist to ensure
full flow at dispensing orifice 260. Another advantage to valve 250 is that sealing
line 266 is much larger in diameter than dispensing orifice 260. With such a relationship,
the amount of stem lift required to reach a full flow condition is less than a traditional
ball and seat valve.
[0024] Fig. 7 illustrates an alternative, temperature controlled valve module 280. Valve
module 280 includes a module body 282 having a liquid cavity 284. A valve stem 286
is mounted for reciprocating movement within cavity 284 and with respect to a valve
seat 288 associated with a nozzle 290. In a typical manner, when valve stem 286 is
lifted from valve seat 288, such as in the air-actuated manner discussed above, liquid
will travel through cavity 284 and then through a dispensing orifice 292 within nozzle
290. A supply passage 294 supplies liquid, such as hot melt adhesive, to cavity 284.
In accordance with the invention, a heater 296, which may be a cast-in-place heating
element, is preferably embedded within the mass of module body 282. As one example,
module body 282 may be formed of a heat conductive metal such as aluminum. A temperature
sensor 298 is also coupled to module body 282, such as by being embedded in body 282.
Preferably, sensor 298 is located an equal or approximately equal distance "d1" from
the liquid in passage 294 as the distance "d1" between heater element 296 and passage
294 and generally the distance between heater element 296 and the liquid passing into
nozzle 290. Distances "d2" are also approximately equal as shown. These spatial relationships
help ensure that the temperature sensed by sensor 298 is the same temperature as the
temperature of the liquid entering nozzle 290. Heater element 296 is preferably located
centrally within the mass of module body 282 to help ensure uniform heating, at least
in the vicinity of nozzle 290. Module 280 may be used with or without an insulated
dispenser apparatus, such as apparatus 10 described above. Temperature sensor 298
is preferably connected with a conventional temperature control system which regulates
heater 296 to maintain a desired set point temperature based on feedback from temperature
sensor 298. Valve module 280 maintains the temperature of nozzle 290 at the desired
set point temperature and this results in better cut-off or, in other words, less
stringing, tailing and drooling of the liquid upon valve closure. Preferably the mass
of module body 282 disposed on one side of heating element 296 is at least approximately
equal to the mass on the opposite side of heating element 296 to promote uniform heat
transfer.
[0025] Whilst the present invention has been illustrated by a description of various preferred
embodiments and while these embodiments have been described in some detail, additional
advantages and modifications will readily appear to those skilled in the art. The
various features of the invention may be used alone or in numerous combinations depending
on the needs and preferences of the user.
1. A valve (250) for dispensing viscous liquids, the valve comprising a valve seat (254)
having an orifice (260) and a sealing surface located around the orifice, and a valve
stem (252) movable between open and closed positions with respect to the valve seat
(254) and having an end with a recess (264) and a sealing edge located around the
recess (264), the sealing edge being engaged with the sealing surface in the closed
position and being spaced from the sealing surface in the open position.
2. A valve module (280) for dispensing heated liquids at a predetermined set point temperature,
the valve module comprising a module body (282) having a liquid cavity (284) communicating
with a dispensing orifice (292), a valve seat (254, 288) disposed generally between
the liquid cavity (284) and the dispensing orifice (292), a valve stem (252, 286)
mounted for movement within the cavity between engaged and disengaged positions relative
to the valve seat (288) for selectively dispensing liquid from the dispensing orifice,
a heating element (296) coupled to the module body (282), and a temperature sensor
(298) coupled to the module body for detecting the temperature of the liquid.
3. The valve module of Claim 2, wherein the heating element (296) is embedded within
the module body (282).
4. The valve module of Claim 3, wherein the temperature sensor (298) is embedded within
the module body (282).
5. The valve module of any one of Claims 2 to 4, wherein the module body (282) further
includes a liquid supply passage (294) in fluid communication with the liquid cavity
(284), the heating element (296) and the temperature sensor (298) being located at
approximately equal distances from the liquid supply passage (294).
6. The valve module of any one of Claims 2 to 5, wherein the valve seat (254) has an
orifice (260) and a sealing surface located around the orifice, and the valve stem
(252) has an end with a recess (264) and a sealing edge located around the recess,
the sealing edge being engaged with the sealing surface in the closed position and
being spaced from the sealing surface in the open position.
7. The valve of Claim 1 or valve module of Claim 6, wherein the valve seat further comprises
a substantially spherical element (254).
8. The valve of either Claim 1 or Claim 7 or valve module of Claim 6 or Claim 7, wherein
the recess (264) is formed with an irregular shape for forcing changes in flow direction
of the liquid when the valve stem is in the open position.
9. The valve or valve module of Claim 8, wherein said irregular shape is an annular groove
surrounding a central projection for forcing said changes in flow direction.