Apparatus for dispensing heated fluid materials

An electromagnetic dispenser for dispensing viscous heated fluids, such as hot melt adhesives. A fixed pole extends from a fluid chamber. The coil is located about a portion of the fixed pole and spaced from the fluid chamber to isolate the coil from the fluid flow path of the adhesive. The coil is insulated from the heat which is conducted from the adhesive as well as provided with a heat sink for dissipating heat. A plunger is mounted within the fluid chamber for reciprocal movement therein to open and close dispensing orifice in response to the field generated by the coil. When mounted to a service block, the coil assembly may be serviced without disconnecting the dispenser body from the source of heated fluid.

DESCRIPTION OF THE INVENTION 
This invention is directed to a fluid dispenser, such as for the dispensing 
of viscous fluids, such as adhesives, sealants and caulks. More 
particularly, this invention is directed to an electromagnetically 
actuated fluid dispenser for dispensing heated fluid materials such as, 
for example, hot melt adhesives. 
It is common in the dispensing of adhesives to use a pneumatic actuated 
dispenser, whereby a supply of air is used to move a plunger in reciprocal 
movement, such that a shutoff needle connected to the plunger is moved 
from or moved to a seat to permit or stop the dispensing of a pressurized 
fluid adhesive. To overcome deficiencies of pneumatic dispensers, 
electromagnetic dispensers have been developed wherein a plunger is driven 
open by an electromagnetic field and closed by a spring biasing means. 
When the coil of an electromagnetic dispenser is energized, the current 
passing therethrough generates heat due to the resistance of the windings 
of the coil. Specifically, the heat generated is a function of the current 
squared and the resistance (I.sup.2 R) of the windings. As the magnitude 
of the current passing through the windings increases and/or the length of 
time the current passing through the windings increases, i.e., longer 
actuation (on cycle) with a shorter off cycle, more and more heat is 
generated, thus raising the temperature of the coil. If the heat generated 
causes the temperature to rise too high, the insulation of the coil may 
degrade and break down, which may eventually cause the dispenser to fail. 
This problem is compounded by the fact that in the dispensing of heated 
fluid materials, such as adhesives commonly known as hot melt adhesives, 
the fluid material itself may transfer additional heat to the coil. This 
additional heat increases the temperature of the coil, thus decreasing the 
allowable temperature rise that can be tolerated by the coil resulting 
from the current passing through the windings. For example, it is not 
uncommon for hot melt adhesive application temperatures to be in the range 
from about 121.degree. C. (250.degree. F.) to about 218.degree. C. 
(425.degree. F.) or higher. As the application temperature of the adhesive 
increases, more heat is available to be transferred to the coil. Thus the 
amount of heat that can be generated by the current passing through the 
coil in order to avoid exceeding the coil insulation rating is decreased. 
As such, the allowable energy available to drive the plunger is reduced. 
This may limit the range of application due to reduced allowable power 
levels. Furthermore, in some circumstances, the application temperature of 
the adhesive may even be in excess of the temperature ratings of standard 
electromagnetic coil designs, making the use of an electrically driven 
dispenser impractical. On the other hand, hot melt adhesives dispensed at 
lower temperatures generally transfer less heat to the coil, thus allowing 
the coil itself to generate more energy (and in turn more heat) before 
thermal breakdown occurs. 
Since the application temperature of the fluid must be maintained, such as 
to maintain the viscosity of the adhesive at a particular level, heaters 
are generally provided. Typically cartridge type heaters are provided in 
the dispenser or the associated service block, thus adding another source 
which can potentially add heat to the coil. 
The problems associated with dissipating the heat generated within the 
dispenser has resulted in some electromagnetic dispensers being larger 
than standard pneumatic dispenser. This increase in size does not lend the 
dispenser to be readily useable in multiple configurations, such as 
mounting a plurality of dispensers side by side to form a bank of 
dispensers. In many applications, such as carton sealing, it is desirous 
to apply a plurality of parallel beads to a substrate on fairly close 
centers. Standard existing pneumatic guns, such as the Nordson.RTM. H200 
modules manufactured by Nordson Corporation, are of such a compact size 
that they are readily adaptable for mounting as a bank of dispensing guns 
to produce finely spaced beads of material. However, with larger sized 
electromagnetic guns, it is difficult to apply closely spaced beads of 
material to substrates. Furthermore, closely mounting multiple 
electromagnetic guns together further compounds the problem of heating due 
to the heat transfer from one dispenser to an adjacent dispenser. For 
example, if three electromagnetic dispensers are mounted together, the two 
outer dispensers each add an incremental additional amount of heat to the 
center dispenser. This additional amount of heat may be sufficient enough 
to affect the thermal characteristics of the center dispenser, thus 
causing it to fail or vary in operating performance. 
It therefore is desirous to produce a compact electromagnetic dispenser, 
similar in size to the standard pneumatic dispensers, which is capable of 
operating at fast cycle rates, and is also capable of operating in a bank 
of dispenser so that closely spaced apart beads of material may be 
dispensed onto a substrate. Also, it is desirous to produce an 
electromagnetic gun which is capable of operating not only at fast cycle 
rates, but is also capable of handling hot melt adhesives, in particular, 
those in excess of 300.degree. F. 
Some existing designs of electromagnetic dispensers require dynamic seals. 
Dynamic seals are seals in which an object moves therethrough, such as a 
plunger, and is used to prevent fluid from migrating past the seal. 
Eventually, a dynamic seal will lose its sealing properties. Once this 
occurs, the adhesive may migrate into various portions of the dispenser, 
causing damage or failure thereto. Therefore, it is also desirous to 
produce an electromagnetic gun which does not require the use of dynamic 
seals. 
Furthermore, it is desirous to prevent or reduce the heat transfer from the 
fluid material to the coil to thereby minimize the affect of the heated 
fluid material on the operating characteristics of the coil. This in turn 
may extend the life of the coil, while expanding its performance 
capability, such as, for example, allowing it to operate at faster cycles. 
Some hot melt adhesive dispensers have attempted to dissipate the heat 
generated by the coil by transferring it to the heated adhesive. This 
transfer, if it occurs at all, is not efficient due to a relatively low 
temperature differential between the fluid and the coil. Also, it is 
difficult to actually maintain the fluid at a desired temperature. This is 
because heat is not applied to, nor sensed directly from, the fluid 
itself. Rather, heat is applied to a portion of the dispenser and 
transferred to the fluid. Similarly, heat is sensed at a point in the 
dispenser itself. As such, the fluid temperature must be less than the 
thermal rating of the coil. 
It therefore is desirous to be able to dispense heated hot melt adhesives 
from an electromagnetic dispenser, wherein the application temperature of 
the adhesive may be in excess of the insulation rating of the coil. 
Also, eventually, the adhesive dispenser will have to be serviced. In the 
case of an electrically operated dispenser, this would mean disconnecting 
the electrical connections, as well as disconnecting the dispenser from 
the supply of pressurized fluid, such as the hot melt adhesive. While in 
some instances it may be desirous to remove the dispenser completely from 
a service block or module, there may be circumstances when only a portion 
of the dispenser needs to be serviced without having to disconnect the 
supply of fluid to the dispenser. For example, it may only be necessary to 
service and/or replace the coil of the dispenser, and therefore it would 
be advantageous to be able to remove the coil from the dispenser without 
having to remove the entire dispenser from a service block or manifold. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention, according to one embodiment of 
the invention, to provide an electromagnetic dispenser which does not 
require dynamic seals. This may be accomplished, for example, by providing 
a movable plunger which is located in a fluid chamber or bore in which the 
movement of the distal end of the plunger from the valve seat, does not 
extend beyond the fluid chamber or bore in the retracted position. 
Eliminating the dynamic seal eliminates a wear part which may fail. Thus 
the potential problem of the dynamic seal failing and allowing heated 
fluid material to migrate to the coil is eliminated. 
It is also an object of the invention according to one embodiment of the 
invention, to provide an electromagnetic dispenser which has improved 
performance characteristics. 
It is also an object of the invention according to one embodiment, to 
provide a means for thermally insulating the means for generating the 
electromagnetic field from the heat transferred from the heated fluid, 
thus allowing for the dispensing of heated fluid materials having higher 
application temperatures. For example, under some circumstances this may 
allow the use of electrical coils having an insulation rating less than 
the temperature of the heated fluid. This may be accomplished, for 
example, by spacing the coil away from the heat fluid material. The coil 
may be spaced from the fluid chamber or bore and an insulating member 
placed there between. For example, an air gap may be placed between the 
coil and the fluid chamber to provide a thermal barrier. Alternatively, an 
insulating material, such as fiberglass, may be used to provide thermal 
isolation. Similarly, in order to reduce the heat transferred to the coil, 
it is preferred that the fluid flow path does not extend into the coil 
region, i.e. the central portion about which the coils are wound. 
It is further an object of the invention, according to one embodiment, to 
provide for dissipating heat generated by, or transfer to, the means for 
generating the electromagnetic field. This allows the dispenser to operate 
at higher power levels and/or at higher fluid application temperatures. 
This may be accomplished, for example, by a heat sink having a plurality 
of fins for radiating heat therefrom to the ambient air, thermally coupled 
to the coil for removing heat from the coil. This reduces the operating 
temperature of the coil, thereby increasing the efficiency of the coil and 
providing for improved performance at higher power levels/high cycle rates 
and/or higher application temperatures. 
Up until now, heat sinks have not been used in hot melt dispensers. Since 
hot melt adhesives are solids at ambient temperatures, they must be 
heated. As stated previously, heat is applied to the dispenser, either 
internally or externally, which is then transferred to the adhesive. If 
the application temperature is exceeded, the adhesive may begin to char 
which causes the material to produce unwanted solid particulates. If, on 
the other hand, the temperature falls below the given application 
temperature, the viscosity of the material will be increased. With 
increasing viscosity, the fluid material becomes increasingly more 
difficult to dispense. Changes in viscosity can result in more or less 
material being deposited onto the substrate, material not being deposited 
onto the substrate at the appropriate time, the material not shutting off 
at the appropriate time, and/or improper bonding of the substrate. Also, 
it is difficult to maintain the appropriate temperature of the hot melt 
within the dispenser. As a result, the emphasis has been on maintaining 
the temperature of the adhesive within the dispenser by adding heat and 
not with the dissipation of such heat from the dispenser to the ambient 
air. 
However, the heat sink provides a means for dissipating the internal heat 
generated by the coil windings and any heat that may be transferred from 
the heated fluid material to the windings. 
It is also desirous to reduce the vacuum-like attraction force (squeeze 
film lubrication), that exists between the fixed pole of the coil assembly 
and the movable plunger, thereby reducing the force necessary to move the 
plunger to the closed position as well as the time required to close the 
plunger. This may be accomplished, for example, by providing the movable 
plunger with an internal flow passage having an opening in the vicinity of 
the pole/plunger interface. 
It is also an object of the invention, according to one embodiment, to 
provide an electromagnetic dispenser so that the coil of the dispenser may 
be easily and quickly replaced in the event that it needs to be serviced 
and/or replaced. This would allow the coil to be quickly replaced in the 
event that it would fail, while not requiring the dispenser to be 
disconnected from a manifold or a service block. 
It is also an object of this invention according to one embodiment of the 
invention, to provide a means which can easily and quickly 
connect/disconnect the electrical connections of the dispenser to a 
service block, manifold, etc. Such as, providing a plug in dispenser which 
does not utilize a cord set. 
Some of these and other objects and advantages may be accomplished 
according to one embodiment by an apparatus for dispensing heated fluid 
materials comprising: a housing defining a fluid chamber, the fluid 
chamber extending from a first end to an outlet at a second end; a fixed 
pole disposed at the first end of the fluid chamber and extending away 
therefrom, wherein a portion of said fixed pole is in fluid contact with 
the fluid material within the fluid chamber; an inlet means for coupling 
the fluid chamber to a source of heated fluid material; a coil for 
generating an electromagnetic field, disposed about a portion of the fixed 
pole such that a portion of the pole extends beyond the coil to space the 
coil from the first end of the fluid passageway; and a plunger disposed 
within the fluid chamber adjacent to the fixed pole and mounted for 
reciprocal movement therein between closed and retracted positions when 
subjected to said electromagnetic field, such that when said plunger is in 
said closed position the outlet is blocked to prevent fluid flow therefrom 
and in said retracted position fluid flow is emitted from the outlet. 
Still further, some of these and other objects and advantages may be 
accomplished according to an embodiment of the invention by an apparatus 
for dispensing hot melt adhesive comprising: a housing defining a fluid 
chamber; an inlet means for coupling the fluid chamber to a source of hot 
melt adhesive; a fixed pole extending into said fluid chamber such that a 
portion of an external surface of said fixed pole is in fluid 
communication with the adhesive; a coil for generating an electromagnetic 
field, disposed about a portion of the fixed pole and spaced from said 
fluid chamber; an insulating means, disposed between said fluid chamber 
and said coil for insulating the coil from the fluid chamber; a plunger 
disposed within the fluid chamber and mounted for reciprocal movement 
between a closed position and an open position, said plunger comprising a 
first portion, having a diameter closely approximating a diameter of the 
fluid chamber, and a second portion having a reduced diameter and 
extending from the first portion, the second portion including an engaging 
means for mating with a surface in the closed position, said plunger being 
spaced from said fixed pole in said closed position and adjacent to said 
fixed pole in said open position; at least one bypass flow channel, 
carried by said housing, for allowing the adhesive to flow past the first 
portion of the plunger; a means for biasing the plunger in the closed 
position; a discharge opening coupled to said fluid chamber; and wherein, 
in response to said electromagnetic field, the plunger moves from the 
closed to the open position such that adhesive is dispensed therefrom. 
Further still, some of these and other objects and advantages may be 
accomplished according to an embodiment of the invention by an apparatus 
for dispensing heated fluid materials comprising: housing, adapted for 
attaching to a service block or manifold, defining a fluid chamber, the 
fluid chamber extending from a first end to an outlet at a second end, 
said housing including an inlet means adapted for coupling the fluid 
chamber to a source of heated fluid material received from the service 
block or manifold; a fixed pole disposed at the first end of the fluid 
chamber and extending away therefrom, wherein only an end portion of said 
fixed pole is in fluid contact with the fluid material; a plunger disposed 
within the fluid chamber adjacent to the fixed pole and mounted for 
reciprocal movement therein between closed and retracted positions when 
subjected to said electromagnetic field, such that when said plunger is in 
said closed position the outlet is blocked to prevent fluid flow therefrom 
and in said retracted position fluid flow is emitted from the outlet; a 
coil assembly for generating an electromagnetic field, disposed about a 
portion of the fixed pole and spaced from the fluid chamber, the coil 
assembly being capable of being removed and replaced therefrom without 
disconnecting the inlet means from the service module or manifold when the 
housing is attached to the service module or manifold. 
Still further, some of these and other objects and advantages may be 
accomplished according to an embodiment of the invention by the method 
comprising the steps of releasably attaching a dispenser to a source of 
pressurized heated fluid and also releasably connecting the dispenser to a 
source of electrical power; then, at a later time, disconnecting the 
dispenser from the source of electrical power while maintaining the 
attachment to the source of heated fluid, to reveal an electrical pole of 
the dispenser without the heated fluid leaking from the dispenser. 
Further still, some of these and other objects and advantages may be 
accomplished according to an embodiment of the invention by the method of 
establishing a magnetic gap of an electric dispenser comprising the steps 
of: assembling a fixed pole to a first body having a cavity therein and 
disposing a plunger and a spring within the cavity to form a first 
assembly; inserting the first assembly into a dispenser body until the 
plunger is fully seated; causing a means to engage both the first body and 
the dispenser body to prevent further movement therebetween; and then 
installing a spacer between a nozzle adapter and the dispenser body, the 
spacer having the same thickness as that of a desired magnetic air gap 
between an end of the fixed pole and the plunger.

DEFINITIONS 
The following definitions are applicable to this specification, including 
the claims, wherein; 
"Axial" and "Axially" are used herein to refer to lines or directions that 
are generally parallel to the axis of reciprocal motion of the plunger of 
the dispenser. 
"Inner" means directions toward the axis of motion of the plunger and 
"Outer" means away from the axis of motion of the plunger. 
"Radial" and "Radially" are used to mean directions radially toward or away 
from the axis of motion of the plunger. 
DETAILED DESCRIPTION OF THE INVENTION 
For the purpose of the present discussion, the method and apparatus of this 
invention is described in connection with the dispensing of a hot melt 
polymeric material used in adhesive applications. Hot melt materials are 
those materials which are solid at room or ambient temperature but, when 
heated, are converted to a liquid state. It should be understood that the 
methods and apparatus of this invention are believed to be equally 
applicable for use in connection with the dispensing of other heated fluid 
materials. 
Now, with reference to FIGS. 1-6, there is illustrated a dispenser, shown 
generally by reference numeral 10 according to one embodiment of this 
invention. The dispenser 10 includes a dispenser body 12, having an inlet 
14 for receiving a source of fluid material, such as a hot melt adhesive. 
For example, inlet 14 may be attached to a service module (not shown) 
having fluid passages therein for supplying fluid and containing heaters 
and temperature sensors to maintain the temperature of the fluid entering 
inlet port 14. An O-ring 15a mounted within inlet port 14. The dispenser 
10 may be mounted to the service block by mounting screws 17. 
Mounted within a cavity of the body 12 is an adapter body 16. The adapter 
body 16 has an outer annular groove 18, which is coupled to the inlet 14. 
The adapter body and the dispenser body form a fluid chamber 20. An O-ring 
15b may be used to provide a seal between the adapter and dispenser bodies 
16, 12. Fluid is transferred from the annular groove 18 to the fluid 
chamber 20 by fluid passageways 22 and 23. The fluid chamber 20 is coupled 
to the discharged outlet 24 via an axially extending fluid passageway 26. 
Attached to the dispenser body 12 is a nozzle adapter 28. The nozzle 
adapter may be mounted to the dispenser body by screws (not shown) 
extending through openings 30A, 30B, respectively. The outer periphery of 
the nozzle adapter 28 may have threads 31 for receiving a nozzle, not 
shown. 
Located within the fluid chamber 20 and the fluid passageway 26 is a 
plunger 32, which is slidably mounted for reciprocal motion. The plunger 
32 has a valve needle 34, such as a ball, located at one end of the 
plunger 32 for mating with a seat 36, located within the nozzle adapter 
28, in the closed position. An insert 38 aligns the seat 36 and the nozzle 
adapter 28 with the fluid passageway 26 in dispenser body 12. 
Alternatively, the insert 38 may have point guide contacts, for guiding 
the plunger into the seat 36 as the plunger 32 moves from an open position 
to a closed position. 
An electromagnetic coil assembly 42 is enclosed by housing 44. The 
electromagnetic coil assembly generates an electromagnetic field when it 
is subjected to a source of electrical power (not shown). The 
electromagnetic coil assembly 42 includes a coil 46 comprising a plurality 
of windings wrapped around a bobbin or spool 48. The windings of the coil 
46 may be encased in a potting layer. Preferably this potting material has 
a high thermal conductivity in order to transfer the heat generated by the 
coil to the housing 44, for eventual dissipation to the surrounding 
ambient air. 
The spool 48 is located around a pole piece 50 and may be attached to one 
another, such by potting. The pole piece 50 is generally cylindrical in 
shape having an end 52 in fluid communication with the fluid chamber 20. 
Preferably the pole piece 50 extends axially from the spool such that the 
spool is spaced from the fluid chamber 20. A ring 54 may be located about 
the periphery of and brazed to, the pole piece 50 to maintain the spacing 
between the pole piece and the adapter body 16. The interaction of the 
pole piece 50, ring 54 and the adapter body 16 provide a seal to prevent 
the flow of fluid material from contacting the spool and in turn the coil 
46. It is necessary that the ring 54 is of a material which is 
non-magnetic so as to help prevent the magnetic field from passing through 
it. The ring 54 also provides spacing between the coil and the adapter 
body. It is therefore preferred that the ring 54 does not readily transfer 
heat therethrough so as not to readily transfer heat to the coil. It has 
been found that a ring 54 manufactured out of 300 series stainless steel 
performs these functions adequately. It is also preferred, to provide 
further insulation between the coil and the heated fluid in order to 
further limit the transfer of heat to the coil. This can be accomplished 
by providing an air gap 55 between the ring 54 and the spool 48. For 
example, the spool 48 may include a raised annular portion 48A to provided 
spacing between the spool and the ring 54. This spacing results in an air 
gap directly between the spool and the ringer 54, and indirectly between 
the spool and the fluid chamber. Thus the windings of the coil 46 are both 
physically and thermally isolated from the fluid material. As an 
alternative to utilizing air, other insulation materials, such as 
fiberglass, for example, can be used to help insulate the coil. 
The pole piece 50 is a fixed pole. In other words, when the coil 46 is 
energized it is not driven axially but is retained in its position. In 
contrast, the plunger 32 is a movable member. 
Upon energization of the coil 46, the generated magnetic field will 
establish a pole (north or south) on the end 52 of the pole 50. Likewise, 
a pole of opposite polarity to that established on end 52 of pole 50 will 
be established on the head 62 of the plunger 32. This will cause plunger 
32 to be attracted to the fixed pole 50. As the plunger 32 moves toward 
the fixed pole 50 the valve needle 34 is moved from the seat 36 which 
allows the adhesive to be dispensed from the outlet 24. When the coil is 
de-energized and the field collapses, the plunger 32 will be moved back to 
the closed position by a spring 56. The spring 56 extends between arms of 
a retainer 58, attached to the plunger 32, and a shoulder 60 of the 
adapter body 16. 
The head 62 of the plunger 32 has a diameter which closely approximates 
that of the diameter of the fluid chamber in the portion in which the head 
62 slidably moves. This helps to keep the plunger properly aligned as it 
slides back and forth. While a close fit provides for good guiding of the 
plunger, it does not provide a good flow path for the material. Therefore, 
in order to allow for the fluid material to flow past the head, bypass 
channels 64 are provided in the adapter body. 
Causing the fluid to flow past the plunger in this manner helps to prevent 
dead spots from occurring in the flow of the adhesive through the 
dispenser. With dead spots, the fluid may begin to solidify to produce 
undesirable particles or chunks, commonly know as char. Under some 
circumstances, the flow path through channels 22 and around the plunger 
head via channels 64, may result in excessive pressure drops across the 
plunger. In such instances, the pressure drop across the head of the 
plunger may be reduced by shunting some of the adhesive directly into the 
fluid chamber 20 from the outer annular groove 18 via channels 23. 
When dispensing, the face 70 of the head 62 of the plunger 32 will be 
adjacent to and/or in contact with the end 52 of the fixed pole 50. Fluid 
material trapped between face 70 of the plunger head 62 and the end 52 of 
the fixed pole will contribute to an increase in the force required to 
begin to move the plunger to the closed position and/or will cause the 
closing response time to increase. This phenomenon is similar to the 
increase in force that is required to separate two pieces of glass which 
have a drop of fluid placed in between them. As used herein, this 
phenomenon will be referred to as squeeze film lubrication. 
It has been previously known to provide a raised annular ring to the face 
of the plunger in order to minimize the contact area between the plunger 
and the fixed pole in order to reduce the effect of squeeze film 
lubrication. See, for example, U.S. Pat. No. 4,951,917 to Faulkner, the 
disclosure thereof, is incorporated herein by reference. However, while 
such an annular ring could be employed here, it is believed to be 
preferable to use several raised portions 72 spaced about the pole face 70 
of the plunger 32. Not only does this reduce the squeeze film lubrication 
force, but also provides a means for reducing the residual magnetism 
within the plunger. This is accomplished by reducing the cross-sectional 
area in contact between the pole face 52 of the pole 50 and the face 70 of 
the head 62 of the plunger 32. 
Furthermore, in order to further help reduce the effect of squeeze film 
lubrication, it has been found to be beneficial to provide a means for 
introducing a flow of fluid between the pole 50 and the plunger 32 to 
provide vacuum relief. This may be accomplished by providing the head 62 
with fluid flow channels 66, 68. Flow channel 66 extends axially from the 
face 70, closest to the pole 50. Intersecting with this channel is a 
radially extending channel 68 which opens into the chamber 20. 
As the plunger 32 begins to move toward the closed position fluid will be 
directed into the openings of fluid channel 68, into fluid channel 66, and 
eventually into the area 74, which is formed between the fixed pole 50 and 
the plunger head 62, as well as between the raised portions 72. The 
introduction of fluid into area 74 from channels 66 and 68 reduces the 
vacuum like attraction force between the pole and the plunger as the 
plunger is being driven to the closed position. 
Furthermore, this flow path 66, 68 helps in decreasing the response time 
necessary to move the plunger to the open position. As the plunger moves 
from the closed to the open position, there is fluid between the head 62 
of the plunger and the fixed pole piece 50 which must be displaced. The 
head, acting much like a piston will displace fluid through the bypass 
channels 64, as well as through flow channels 66 and 68, and into the 
fluid chamber 20. Also, the amount of fluid which must be displaced is now 
the volume of fluid contained within the area 74. 
Fixed pole 50 may be provided with a bore 76. Contained within this bore is 
a non-magnetic material, such as 300 series stainless steel, brass, etc., 
which effectively prevents the adhesive from traveling into the interior 
of the fixed pole. The non-magnetic material within the bore 76 helps 
concentrate the magnetic flux generated by the coil on the pole face 52 of 
the pole 50 by reducing the cross-sectional area of the magnetic portion 
of the pole 50 which is perpendicular to the lines of flux. The coil 
assembly 42 may be retained within the assembly by a set screw 78. 
The windings of the coil 46 may be coupled to a source of electrical power 
by electrical conductors passing through a bore (not shown) to a 
respective electrical stud, such as illustrated at 80. Each of the studs 
80, connect to female couplings 81 carried by an electrical connector 83. 
The female couplings 81 may be connected to the electrical conductors (not 
shown) of a cord set extending from port 82. The connector 83 may be 
retained to the coil housing by a screw 84. 
In order to more effectively and efficiently dissipate the heat within the 
dispenser, it is preferred to provide the dispenser with heat sinks. For 
example, coil housing 44 may be provided with a plurality of fins 86 for 
dissipating the heat generated within the dispenser. The fins 86 of the 
heat sink 88 are thermally coupled to electromagnetic coil assembly 42. In 
the embodiment viewed in FIG. 3, heat generated by the coil assembly 42 
will be thermally transferred through the coil housing 44 and to the fins 
86. In that the coil housing 44 directs heat away from the coil assembly 
42, it is preferred that it is of a material that is fairly thermally 
conductive. Furthermore, it is preferred that coil housing 44 is also of a 
material which will help direct the field generated by the coil 46. In 
other words, it is preferred that the housing is of a magnetic material, 
such as a ferromagnetic material. While the heat sink and the housing 44 
may be one piece, they could be two separate pieces. For example, a 
dispenser has been built wherein good results have been obtained with 
aluminum heat sinks attached to the coil housing 44. 
In that it is desirous to keep the heat generated by the coil to a minimum, 
reducing the magnitude of the current passing through the coil will, 
therefore, help reduce the amount of heat generated by the coil. Once the 
plunger has moved to its full open position, the magnitude of the current 
passing through the coil may be reduced to a lower hold in current. In 
other words, current may be sent to the coil in order to generate an 
electromagnetic field which quickly drives the plunger from the closed to 
the open position. However, once in the full open position, the amount of 
current required to maintain the plunger at that position is less than it 
takes to drive it from the closed to the open position. There are several 
different driving methods which can attain this result. For example, U.S. 
Pat. No. 4,453,652 (Controlled Current Solenoid Driver Circuit), the 
disclosure of which is incorporated herein by reference, which is assigned 
to the assignee of this invention, describes a method of reducing the 
current flow through a coil once the plunger has moved to its fully 
extended position. Other current driving schemes could also be used which 
help reduce the power requirements of the coil. 
An experiment was conducted to compare the heat dissipating characteristics 
of a dispenser with and without a heat sink. With reference to FIG. 7, 
there is illustrated a graph of the temperature of the coil of an electric 
dispenser versus the power utilized by the coil. The electric dispenser 
according to an embodiment of the invention, was equipped with detachable 
aluminum heat sinks. The temperature of the coil was monitored at various 
power levels both with and without the heat sinks attached to the housing 
of the dispenser. The application temperature of the adhesive during this 
experiment was 355.degree. F. while the ambient temperature was 
approximately 70.degree. F. The temperature plotted on each curve is an 
average of all temperatures taken at that particular power level. 
The graph of the temperature without heat sinks is illustrated by line 90 
while that of the temperature with heat sinks is illustrated by line 92. 
As the power of the coil increases, the temperature differential between 
the two lines becomes generally greater. Thus, at higher power levels, the 
benefit of the heat sinks becomes more and more apparent. Being able to 
operate at higher power levels allows the coil to be driven open/closed 
faster, thereby allowing the dispenser to operate at faster cycle times. 
Also, since the plunger is a ferromagnetic material, such as steel, it is 
preferable to match the thermal expansion coefficient of the various parts 
which the plunger inter-reacts with, such as the body 12, seat, etc. Due 
to the heat fluid material and/or its associated heaters, these materials 
are going to expand. At higher application temperatures this expansion 
becomes greater. If aluminum is used, for the body, it will expand faster 
than that of the plunger. This may cause air gap variations. Therefore, it 
is preferred that the body 12 and the plunger 32 are made from the same 
materials or from materials which have the same or close coefficients of 
thermal expansions. 
Manufacturing the body 12 and the adapter body 16 out of stainless steel 
not only helps maintain the magnetic air gap at varying temperatures, but 
also allows for a more compact unit. In that hot melt adhesive dispensing 
systems can operate at relatively high pressures, such as for example, 
between 1000-1500 psi, the bodies 12 and 16 must be able to withstand such 
pressures. Bodies manufactured from aluminum would require greater 
cross-sectional areas than those manufactured from steel. As a result, a 
smaller and more compact unit may be produced by utilizing steel for the 
bodies 12 and 16. 
Now, with reference to FIGS. 8-13, there is illustrated a dispenser, shown 
generally by reference numeral 10a according to another embodiment of this 
invention. The dispenser 10a includes a dispenser body 12a, having an 
inlet 14a for receiving a source of fluid material, such as a hot melt 
adhesive. Inlet 14a may be attached to a service module 100 or manifold 
having internal fluid passages 101 for supplying fluid. An O-ring 15d is 
mounted within inlet port 14a. The dispenser 10a may be mounted to the 
service block by mounting screws 17a. 
Mounted within a cavity of the body 12a is an adapter body 16a. The adapter 
body 16a has an outer annular groove 18a, which is coupled to the inlet 
14a. The adapter body and the dispenser body form a fluid chamber 20a. An 
O-ring 15e may be used to provide a seal between the adapter and dispenser 
bodies 16a, 12a. As before, fluid is transferred from the annular groove 
18a to the fluid chamber 20a by fluid passageways 22a and 23a. The fluid 
chamber 20a is coupled to the discharged outlet 24a via an axially 
extending fluid passageway 26a. 
Attached to the dispenser body 12a is a nozzle adapter 28a, which may be 
mounted to the dispenser body by screws 102 extending through openings 
30d. The outer periphery of the nozzle adapter 28a may have threads 31a 
for receiving a nozzle, not shown. 
Located within the fluid chamber 20a and the fluid passageway 26a is a 
plunger 32a, which is slidably mounted for reciprocal motion and may be 
constructed as the plunger of 32 of FIGS. 1-6. A seat 36a is located 
within the nozzle adapter 28a, while an insert 38a aligns the seat 36a and 
the nozzle adapter 28a with the fluid passageway 26a in dispenser body 
12a. Alternatively, the insert 38a may have point guide contacts, for 
guiding the plunger into the seat 36a as the plunger 32a moves from an 
open position to a closed position. The plunger 32a is biased to the 
closed position by a spring 56a. 
An electromagnetic coil assembly 42a is enclosed by housing 44a. The 
electromagnetic coil assembly generates an electromagnetic field when it 
is subjected to a source of electrical power. The electromagnetic coil 
assembly 42a includes a coil 46a comprising a plurality of windings 
wrapped around a bobbin or spool 104. The windings of the spool 104 may be 
provided with an outer wrapping of electrical tape 106, such as Nomex 
tape. The portion of the bobbin 104 closest to the plunger 32a has an end 
piece 108 which extends radially outwardly. The portion 108 contains two 
electrical studs 110. These electrical studs 110 connect to the coil wire 
112 forming the windings of the coil. In other words, the wire which forms 
the windings of the coil is attached at one end to one of the studs 110 
and is attached at the other end to the other stud. The bobbin is also 
supplied with two electrical barriers 114 for isolating electrically the 
studs 110 from conductive members. 
A grounding connection, stud 116 is held captive in the housing 44a, such 
as by a pin 118. Grounding stud 116 extends through the base 108 of the 
bobbin 104 when assembled to ground the housing 44a. The electrical coil 
assembly 42a may be encased in a potting layer, so as to affix the coil 
assembly 42a to the housing 44a. The potting material, which preferably 
has a high thermal conductivity in order to transfer the heat generated by 
the coil to the housing 44a, may be for example, an epoxy-based material. 
With the coil assembly 42a bonded to the housing 44a, a plug assembly 120 
is formed. In other words, studs 110 are electrical conductors, to couple 
the coil to a source of electrical power while stud 118 is the grounding 
conductor. The plug assembly 120, in turn, mates with a receptacle 
assembly 122 carried by the service block 100. 
The spool 104 of the electromagnetic coil assembly 42a is located around a 
pole piece 50a which is generally cylindrical in shape, having an end in 
fluid communication with the fluid chamber 20a. A ring or spacer 54a may 
be located about the periphery of and brazed to the pole piece 50a to 
maintain the spacing between the pole piece and the adapter body 16a and 
to provide a seal to prevent the flow of the fluid material from 
contacting the coil assembly. As before, it is preferable that the spool 
104 is spaced from the ring or spacer 54a. By potting the electromagnetic 
coil assembly 42a to the housing 44a, an air gap 55a between the ring 54a 
and the spool 104 may be formed without requiring the raised annular 
portion 48a that was required in the spool 48 of the first embodiment. 
Again, this spacing results in an air gap directly between the spool and 
the ring 54a and directly between the spool and the fluid chamber. Thus 
additional insulation is provided over and above the function of the 
insulating portion of ring 54a. Therefore, the windings of the coil 46a 
are both physically and thermally isolated from the fluid material. Again, 
as an alternative to utilizing the air, other insulation may be used. 
Within service module 100 are heaters 124, as well as a temperature sensor, 
such as an RTD, for controlling the operation of the heaters 124. Also, 
within service module 100 are electrical passageways 128 containing power 
and control wires (not shown), such as for coupling the electrical 
receptacle 122 to a source of electrical power in order to actuate or 
de-actuate the electromagnetic coil assembly 42a, providing power to the 
heaters, etc. 
The service module 100 may also contain a thermal barrier 130 disposed 
between the heaters 124, and the fluid passageways 101 and the temperature 
sensor 126. This thermal barrier 130 may be an air passageway such that 
more heat is directed towards the dispenser body 12a, as opposed to the 
temperature sensor 126. The function of the thermal barrier 130 may be 
more fully described as set forth in U.S. Pat. No. 5,407,101, which is 
owned by the Assignee of this invention, and in which the disclosure 
thereof is incorporated herein by reference. 
The service module or adhesive manifold 100 may include a mounting block 
132 attached to the service block 100 by screws 134. The mounting block 
132 may be formed in two half sections 136, 138 which receive a mounting 
bar 140 therebetween. The bolts 134 when screwed in tighten down against a 
bar 140 to secure the mounting block 138 and in turn the manifold or 
service block 100 thereto. 
In FIG. 11, the dispenser 10a is mounted to the service block 100 via 
screws 17a and electrically connected via plug 120 and receptacle 122 of 
the block 100. In that the electrical components are isolated form the 
fluid, the coil assembly 42a may be serviced or replaced without removing 
the dispenser body 12a from the block 100. 
The coil housing 44a is attached via bolt 142 which mates with the pole 
50a. Unscrewing bolt 142 allows the coil housing 44a to be slid off of the 
dispenser assembly. In FIG. 12, the coil housing 44a and the coil assembly 
412a have been removed from the dispenser revealing pole piece 50a, while 
the body 12a remains attached to the service block and in turn remains 
connected to the source of adhesive fluid. In such disassembly, if the 
coil assembly had been potted to the coil housing 44a, the coil assembly 
would remain within the coil housing. The old coil assembly may be 
replaced and the old housing reattached or a new assembly, including a new 
coil housing having a new coil already potted therein, may be then 
installed. This provides a quick means of changing the coil assembly. Only 
one bolt is required to be removed and the adhesive connections do not 
need to be disconnected. 
Similarly, coil housing 44 of FIG. 3 may be slid off after unscrewing screw 
78 and disconnecting the cord set from the electrical connector. This in 
turn would allow removal of the coil assembly as well as leaving pole 
piece 50 exposed while body 12 remains attached to a service block or 
other mounting device containing a source of fluid. Again, this design 
provides a quick means of changing and/or inspecting a coil assembly 
without disconnecting the dispenser 10 from the source of pressurized 
fluid because the flow of adhesive is not through the center of the pole 
piece 50 as in previous designs. 
The operation of this embodiment of FIGS. 8-13 is similar to that of the 
first embodiment, and as such, upon the energization/de-energization of 
the coil 46a, the plunger 32a is open/close thereby causing/preventing the 
adhesive from being dispensed from the dispenser. 
Changes in the magnetic air gap (the distance between the face 70a of the 
plunger 32a and the end 52a of the fixed pole 50a) effect the forces 
necessary to open or close the plunger, as well as the time necessary to 
achieve this result. 
It has been found that repeatable results may be maintained by utilizing a 
shim plate during the assembly of the dispenser. With reference to FIG. 9, 
a shim plate 150 is utilized during the assembly of the dispenser which 
has the same thickness as the desired air gap. First, seat 36a, insert 
38a, and O-ring 101 are assembled inside of nozzle adapter 28a. This 
assembly is then bolted to the dispenser body 12a by screws 102. Then the 
pole/adapter assembly 152, which includes pole 50a, ring 54a, adapter body 
16a and O-ring 15e, is inverted and plunger 32a and spring 56a are located 
within the cavity of the adapter body 16a. This assembly is then inserted 
into the dispenser body 12a and is screwed in until the plunger is fully 
seated. Locking screw 144 is then backed out of the dispenser body 12a 
until it contacts the tapered edge 146 of the adapter body 16a. 
As an additional safety feature, a screw 143 extends into the dispenser 
body 12a, and into the cavity containing O-ring 15e to prevent the 
pole/adapter assembly 152 from being removed without first removing the 
screw 143. 
The nozzle adapter 28a is then removed from the dispenser body 12a by 
removing screws 102. Gauge plate 150 is installed between the nozzle 
adapter 28a and the dispenser body 12a. The nozzle adapter and the gauge 
plate are now attached to the dispenser body 12a by the four bolts 102. 
Since the assembly had been tightened before until the plunger was firmly 
seated against the seat 36a, the plunger 32a will now be spaced from the 
pole 50a by the thickness of the shim plate 150. 
It is preferred that the material hardness of the screw 144 is harder than 
that of the tapered shoulder 146 of the adapter body 16a. As such, the 
force applied to the screw 144 when it is caused to be drawn in contact 
with the adapter body shoulder 146 should be such that a small dent is 
formed in the shoulder 146. The formation of this small dent in the 
tapered shoulder 146 of the adapter body, combined with the opposing axial 
forces applied to both the adapter body's threads 154 and those of the 
locking screw 144, provide anti-rotational forces significantly greater 
than those that should be encountered during assembly or service. This 
also helps so that the impact forces applied by plunger 32a against pole 
piece 50a cannot disturb or tend to loosen the locking adjustment 
position. Also, the direction of rotation of the locking screw 144 during 
tightening is preferably counter-clockwise, which tends to rotate the 
adapter body 16a clockwise, which provides a firm contact between the end 
of the pole 52a and the head of the plunger 32a such that the final air 
gap matches the thickness of the shim plate 150. 
Again, it is preferred to provide the dispenser with heat sinks. For 
example, coil housing 44a may be provided with a plurality of fins 86a for 
dissipating the heat generated within the dispenser. The fins 86a of the 
heat sink 88a are thermally coupled to electromagnetic coil assembly 42a. 
In this embodiment, heat will be transferred through the coil housing 44 
and to the fins 86a as in the previous embodiment. 
In that it is desirous to keep the heat generated by the coil to a minimum, 
the magnitude of the current passing through the coil may be reduced to a 
lower hold in current as set forth previously. 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the invention, it will be apparent to those 
skilled in the art that various changes and modifications can be made 
therein without departing from the scope of the invention.