Note: Descriptions are shown in the official language in which they were submitted.
1 336373
Apparatus For Spraving Hot Melt Adhesive
Field of the Invention
This invention relates to apparatus for
spraying hot melt adhesive, and, more particularly, to
an apparatus for spraying droplets of molten thermo-
plastic adhesive onto a substrate for subsequent
bonding with another substrate.
Backqround of the Invention
Hot melt thermoplastic adhesives have been
widely used in industry for adhering many types of
products, and are particularly useful in applications
where quick setting time is advantageous. One appli-
cation for hot melt adhesive which has met with
considerable commercial success is the fabrication of
cartons wherein the auick setting time of the hot melt
adhesive is useful in assembling the flaps of a carton
in high speed cartoning lines.
A number of dispensers have been employed to
deposit hot melt adhesive onto the flaps of cartons,
or on other substrates where quick setting time is
required. For example, one type of adhesive dispenser
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is a gun formed with an adhesive passageway connected
to a nozzle having a discharge orifice. The adhesive
is pumped through the gun and ejected from the dis-
charge orifice of the nozzle in the form of a rela-
tively thick bead of molten thermoplastic adhesivewhich is applied to the substrate. Another substrate
is then placed into contact with the first substrate
to "flatten" or spread out the adhesive bead over a
larger surface area so that an acceptable bond is
produced between the substrates.
One disadvantage of adhesive dispensers
which discharge an adhesive bead is that a relatively
large quantity of adhesive is required to obtain the
desired bond. Molten thermoplastic adhesive is highly
viscous and does not readily spread over the surface
of one substrate even when a second substrate to be
bonded thereto is pressed against the adhesive bead.
As a result, a relatively large quantity of adhesive
is required in forming the bead to ensure the surface
area of the bond between the substrates is sufficient
to adhere the substrates together.
Several attempts have been made in the prior
art to lessen the quantity of thermoplastic adhesive
required to bond two substrates together while obtain-
ing acceptable bond strength between the substrates.In one prior art apparatus, the hot melt adhesive is
transmitted under pressure to the discharge orifice of
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a nozzle. When the hot melt adhesive is ejected into
the ambient air, it atomizes and forms a spray or mist
of tiny droplets which are deposited onto the sub-
strate. These small droplets cover a larger surface
area than a single adhesive bead, and since bond
strength is dependent in part on the surface area
covered by the adhesive, a lesser quantity of adhesive
in droplet form can be emploved than is required with
an adhesive bead.
One problem with spraying molten thermoplas-
tic material in tiny droplets onto a substrate is that
in order 'or the adhesive to completely atomize before
it reaches the substrate, the nozzle must be posi-
tioned a relatively large distance from the substrate.
As a result, the small droplets are exposed to ambient
temperatures and tend to cool before they reach the
substrate. It has been found that with some types of
hot melt adhesives the droplets either harden before
they contact the substrate or fail to retain suffi-
cient specific heat after they reach the substrate topermit bonding to another substrate. Additionally,
nozzles of the type designed to spray thermoplastic
adhesive in atomized form can produce elongated
strings or fibers of adhesive instead of droplets when
the nozzle is first turned on and/or when the nozzle
is shut off. These strings of adhesive tend to clog
1 336373
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the nozzle and/or are deposited in that form onto the
substrate.
Another attempt to reduce the quantity of
adhesive utilized for cartoning applications and the
like is found in U.S. Patent No. 3,348,520 to Lock-
wood. The apparatus disclosed in the Lockwood patent
produces relatively large drops of molten thermoplas-
tic adhesive which are deposited onto one substrate
for bonding with another substrate. The individual
drops of adhesive are obtained by alternately opening
and closing valves located in the adhesive supply
lines upstream from nozzles connected to the supply
lines. One problem with apparatus of the type dis-
closed in the Lockwood patent is that the valves which
form the adhesive drops must open and close at ex-
tremely high rates to keep up with the speeds of
modern cartoning lines, and they tend to wear or fail
after relatively short periods of use.
Another approach in the prior art for
spraying hot melt adhesives is found in U.S. Patent
No. 4,7 1,252 to Colton. This patent discloses an
apparatus in which molten thermoplastic adhesive is
ejected through the discharge orifice of a nozzle and
a tube carrying pressurized air is positioned in the
center of the adhesive stream ejected from the nozzle.
As the pressurized air emerges from the tube, it
expands radially outwardly and breaks up the hot melt
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_5_ l 336373
adhesive in the stream to form droplets or blobs of
adhesive which are then deposited on the substrate.
Multiple air delivery tubes can be employed to control
the width of the spray pattern of droplets formed.
One problem with the apparatus disclosed in
the Colton Patent No. 4,721,252 is the potential for
cut-off drool when the apparatus is shut off, i.e.,
the formation of strings or fibers of adhesive in the
area of the nozzle and the air tubes when the flow of
adhesive is discontinued. Additionally, since the
pattern of the adhesive droplets deposited onto the
substrate is dependent on the number and location of
air delivery tubes, the entire nozzle must be removed
and replaced in order to change the spray pattern.
Summary of the Invention
It is therefore among the objectives of this
invention to provide an apparatus for spraying drop-
lets or blobs of molten thermoplastic adhesive which
controls the size of the adhesive droplets, which
controls the width of the spray pattern of the adhe-
sive droplets deposited onto a substrate, which
eliminates cut-off drool or stringing of adhesive and
which ensures that the adhesive droplets retain
sufficient heat when deposited on one substrate to
form a bond with a second substrate.
These objectives are accomplished in an
apparatus for spraying molten, hot melt thermoplastic
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adhesive wherein a stream of hot melt adhesive ejected
from the discharge orifice of a nozzle is impinged by
a stream of atomizing air which contacts the outside
of the adhesive stream to form droplets of adhesive
whose size is controlled by varying the velocity and
flow rate of the atomizing air so that such droplets
retain sufficient heat when they are deposited on a
substrate to subseauently bond to another substrate
placed in contact therewith. A stream of pattern-
shaping air, which is controlled separately from thestream of atomizing air, is directed against the
adhesive droplets before they reach the substrate to
variably control the size and shape of the pattern of
adhesive droplets on the substrate.
One aspect of this invention is predicated
upon the elimination of cut-off drool in the operation
of the apparatus, i.e., the elimination of elongated
fibers or strands of adhesive formed at the discharge
orifice of the nozzle when the flow of adhesive is
shut off. This is achieved in the instant invention
by valves which control the discharge of adhesive from
the nozzle of the spraying apparatus and the supply of
atomizing air and pattern-shaping air to the discharge
orifice of the nozzle.
The apparatus is fGrmed with an applicator
head having an adhesive passageway within which a
plunger is axially movable between an open position
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which permits passage of adhesive to the nozzle and
out its discharge orifice, and a closed position in
which the flow of adhesive is blocked. A plunger
control valve is mounted within a pilot air line
connected to the applicator head which controls the
movement of the plunger between the open and closed
position.
Atomizing air is supplied to the nozzle
through an atomizing air passageway which has an
atomizing air regulating valve connected therein.
Pattern-shaping air is supplied to the nozzle area
through a pattern-shaping air passageway having a pat-
tern-shaping air regulating valve connected therein
which is adjustable separately from the atomizing air
regulating valve. Both the atomizing air regulating
valve and pattern-shaping air regulating valve commu-
nicate with a common supply line carrying heated or
unheated air. This common supply line has a pilot-
operated air supply valve located upstream relative to
the regulating valves. Opening and closing of the
pilot-operated air supply valve is controlled by an
air control valve which communicates with a source of
pressurized, pilot air.
Movement of the plunger in the adhesive
supply passageway, and the flow of air through both
the atomizing air passageway and pattern-shaping air
passageway, are synchronized so that atomizing and
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pattern-shaping air is supplied to the area of the
discharge orifice of the nozzle both before the stream
of adhesive is ejected from the discharge orifice and
after the flow of adhesive is terminated. The air
control valve which operates the air supply valve is
an "unrestricted in-metered out" type of valve , i.e.,
it allows an unrestricted flow of pilot air to flow in
one direction therethrough so that the air supply
valve is pressurized and quickly opens to permit the
flow of a stream of atomizing air and a stream of pat-
tern-shaping air toward the discharge orifice of the
nozzle. On the other hand, the air control valve
meters the flow of air in the opposite direction
so that the air supply valve is slowly depressurized
and thus and slowly closes to stop the flow of atom-
izing and pattern-shaping air after the flow of
adhesive through the adhesive passageway has stopped.
This eliminates "cut-off drool" or the formation of
strings of adhesive at the discharge orifice of the
nozzle.
The plunger control valve which supplies
pilot air to axially move the plunger between the open
and closed posit on operates in the opposite manner
from the air control valve, i.e., such valve is a
"metered in-unrestricted out" type of valve. The
plunger control valve meters the supply of pilot air
therethrough to the plunger to delay movement of the
plunger from a closed to an open position so that the
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9 1 3 3 6 3 73
flow of adhesive through the discharge orifice of the
nozzle begins after the atomizing and pattern air flow
has been initiated. When the stream of adhesive needs
to be shut off, the plunger control valve is "unre-
stricted out", i.e., the pilot air flowing to the
plunger is allowed to bleed in the opposite direction
through the plunger control valve along an unrestrict-
ed path so that a spring can quickl~,7 return the
plunger to a closed position before the flow of air
from the atomizing and pattern-shaping air passageways
is discontinued.
Another aspect of this invention is pred-
icated upon controlling both the size of the droplets
formed from the adhesive stream, and the pattern of
droplets deposited on a substrate. This is achieved
by the air flow regulating valves in both the atomiz-
ing air passageway and the pattern-shaping air pas-
sageway which are controlled separately from one
another to vary the air flow therein. Heated or
unheated air is supplied through the air supply valve
to each of the regulating valves, and such regulating
valves are individually adjustable to direct a select-
ed portion of the air flow into the atomizing air
passageway and the pattern air passageway.
The air discharged from the atomizing air
passageway impacts the outside of the stream of
adhesive discharged from the nozzle so that the
1 3~6~3
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adhesive stream is broken up into blobs or droplets
having a diameter of preferably about 1/4-7/16 inches.
The width of the pattern of these droplets on a
substrate is primarily controlled by the pattern-
shaping air which contacts the droplets after they areformed but well before they reach the substrate.
The ratio of the flow rate and velocity of
the atomizing air to the pattern-shaping air is
adjustable by operation of the air regulating valves.
Generally, as the ratio of the velocity and flow rate
of the atomizing air to the pattern-shaping air is
adjusted so that the velocity and flow rate of the
atomizing air increases while that of the pattern-
shaping air decreases, a relatively narrow spray
pattern is produced on a substrate which contains
relatively small adhesive droplets. On the other
hand, if the ratio of the velocity and flow rate of
the atomizing air to the pattern-shaping air is
adjusted so that the velocity and flow rate of the
atomizing air decreases while that of the pattern-
shaping air increases, a relatively wide spray pattern
is produced on a substrate which contains relatively
large adhesive droplets.
Another aspect of this invention involves
the versatility of the applicator head herein in
accommodating different types of spraying applica-
tions. In one application, the applicator head is
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3363~3
adapted to mount to the gun body of a hand held spray
gun having an air control valve and a plunger control
valve each connected to a source of pressurized air
through a trigger operated supply valve. lhe applica-
tor head is mounted to the gun body and connected to
the air control valve and plunger control valve for
operation as described above.
Alternatively, a rod supported mounting
block is provided for connection to the applicator
head. The mounting block supports the air control
valve, the plunger control valve and carries a supply
line for adhesive, all of which are connected to the
applicator head as in the hand held spray gun applica-
tion. Pilot air to the air control valve and plunger
control valve is supplied through lines connected to a
controller, e.g., a programmable control device, which
is capable of automatically controlling the flow of
pilot air to the mounting block, and, in turn, the
applicator head.
In a still further embodiment, a manifold is
provided which is adapted to support a number of
individual applicator heads and control the flow of
pilot air and adhesive to each. In turn, the supply
of pilot air and adhesive to the manifold is con-
trolled by a programmable controller so that adhesive
is discharged from each of the applicator heads at the
1 ~3~7~
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desired intervals of time and with the desired pat-
tern.
Description of the Drawings
The structure, operation and advantages of
the presently preferred embodiment of this invention
will become further apparent upon consideration of the
following description, taken in conjunction with the
accompanying drawings, wherein:
Fig. 1 is an elevational view in partial
cross section of one embodiment of the adhesive spray
apparatus herein;
Fig. 2 is a cross sectional view taken
generally along line 2-2 of Fig. l;
Fig. 3 is a cross sectional view of the
applicator head herein taken generally along line 3-3
of Fig. l;
Fig. 4 is a schematic, unassembled view of
alternative structure for mounting the applicator head
of this invention to convert the system from a hand
held dispenser to an automatic dispenser; and
Fig. 5 is a diagrammatic view illustrating
the atomizing and shaping air impacting a stream of
dispersea hot melt adhesive.
Detailed Description of the Invention
Referring to Fig. 1, the adhesive spray
apparatus 10 is adapted for hand held operation and
comprises a spray gun 12 having a handle 14 connected
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to a gun body 16. A trigger 18 carried on a pivot 20
mounted to the gun handle 14 is connected by an
actuator 22 to a trigger rod 24 movable axially within
the gun body 16. The end of the trigger rod 24
opposite the trigger 18 is mounted to a connector
plate 26 which, in turn, contacts a valve plunger 28.
As shown in Figs. 1 and 2, a three-way
cartridge valve 30 is carried by the gun body 16 and
is operatively connected to the valve plunger 28. One
side of the cartridge valve 30 ls connected to a
source of actuating air (not shown) throuah a feed
line 32. Branch lines 34, 36 extend outwardly from
the cartridge valve 30 at outlet ports 38 and 40,
respectively, formed therein. In the presently
preferred embodiment, the cartridge valve 30 is a
commercially available item and orms no part of this
invention per se.
In order to open the cartridge valve 30 to
permit the flow of air from feed line 32 into each of
the branch lines 34, 36, the trigger 18 is first
pulled to the left as viewed in Fig. 1 carrying the
trigger rod 24 and connector plate 26 in the same
direction. Movement of the connector plate 26 rela-
tive to the valve plunger 28 opens an internal seat
(not shown) of the cartridge valve 30 allowing the
passage of air from the feed line 32 through cartridge
valve 30 and into each of the branch lines 34, 36.
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The cartridge valve 30 is placed in the closed posi-
tion by releasing trigger 18 so that a spring (not
shown) returns the trigger rod 24 and connector plate
26 to their original positions with respect to the
valve plunger 28. See Fig. 1.
The flow of air through the cartridge valve
30 into branch lines 34, 36 provides pilot air which
controls the flow of adhesive, and the flow of atomiz-
ing and pattern-shaping air, as discussed in detail
below. The structure for obtaining the air flow, and
for obtaining the adhesive flow, is described sepa-
rately below.
Atomizing Air and Pattern-Shapina Air
Referring initially to Figs. 1 and 2, the
gun body 16 is connected to a service body 41 which
mounts an applicator head 44. The service body 41
carries adhesive heaters and other electrical compo-
nents which form no part of this invention per se and
are not described herein. A support block 42 is
connected to the applicator head 44 having an air
supply valve 46 located at its base which receives
heated or unheated air from a supply line 48. The air
supply valve 46 comprises a plunger 50 which extends
between a pilot air chamber 52 and an air inlet
chamber 54 both formed in the support block 42. The
pilot air chamber 52 is formed with a port 55 connect-
ed to a pilot air supply line 57, which, in turn, is
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-15- 1 3 3 6 3 7 3
connected to the branch line 36 from cartridge valve
30. A seal 56 is interposed between the chambers 52,
54 and is formed with a bore within which the plunger
50 is axially slidable.
5The end of plunger 50 located within the
pilot air chamber 52 carries a head plate 58, and the
opposite end of piunger 50 located within the air
inlet chamber 54 mounts a plunger head 60. The
plunger head 60 is adapted to engage a seat 62 formed
10in the air inlet chamber 54 at the entrance to a
passageway 64 in the support block 42. The passageway
64 is connected at the abutting faces of support block
42 and applicator head 44 to an air supply passageway
66 formed in the applicator head 44. An O-ring 67 is
15positioned between the abutting faces of support block
42 and applicator head 44 to form a seal therebetween.
Flow of heated or unheated air into the air
supply passageway 66 of applicator head 44 is obtained
as follows. In response to movement of the trigger
2018, pilot air is supplied from the cartridge valve 30
into each of the branch lines 34 and 36. A pilot air
control valve 68 is connected between the branch line
36 and the pilot air supply line 57. The pilot air
control valve 68 a commercially available "unrestrict-
25ed in-metered out" type of actuating valve, i.e., the
flow of pressurized, pilot air is allowed to flow in
an unrestricted path in one direction through valve
1 336373
-16-
68, but the air flow in the opposite direction through
valve 68 is metered. When supplied with pressurized
air from branch line 36, the pilot air control valve
68 allows an unrestricted flow of pilot air there-
through which is transmitted through the pilot airsupply line 57 to the pilot air chamber 52 of valve
46. Pressurization of the pilot air chamber 52 moves
the head plate 58 of plunger 50 to the left as viewed
in Fig. 1, thereby unseating the plunger head 60 from
the seat 62 in air inlet chamber 54. As a result, air
supplied to the air inlet chamber 54 through supply
line 48 i5 allowed to enter the passageway 64 in
support block 42 and flow to the air supply passageway
66 in the applicator head 44.
When the trigger 18 is released, flow of air
through cartridge valve 30 to the branch lines 34, 36
is discontinued. In response, the pilot air control
valve 68 is operable to meter the flow of air there-
through which gradually bleeds back in the opposite
direction from the pilot air chamber 52 of valve 46
and through the pilot air supply line 57. As the air
pressure within pilot air chamber 52 gradually de-
creases, a spring 72 mounted within the air inlet
chamber 54 of air supply valve 46 forces the plunger
head 60 of plunger 50 into engagement with the seat 62
to close the flow of air from the air inlet chamber 54
into passageways 64, 66.
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Referring now to Fig. 3, the applicator head
44 comprises an upper cylinder 74 connected to a base
76 within which the air supply passageway 66 is
formed. The base 76 is formed with a stepped bore 78
having an upper end which mounts a sleeve 80, and a
smaller diameter, lower end forming an adhesive flow
passageway 82. The sleeve 80 is formed with an
annular slot 84 extending radially inwardly from the
outer surface thereof which communicates with the air
supply passageway 66 formed in the base 76. An
atomizing air branch line 88 is connected to the
annular slot 84, and a pattern-shaping air branch line
90 is also connected to the annular slot 84. These
branch lines 88, 90 receive air from the air passage-
way 66 via the annular slot 84 for transmission to a
nozzle 92 and air cap 94 mounted to the base 76 as
described below.
The base 76 is formed with a threaded bore
96 which receives an atomizing air regulating valve 98
therein. The regulating valve 98 has a chamber 100
connected to a discharge orifice 102. A plunger 104
is carried by the regulating valve 98 which includes a
rod 106 extending axially therethrough. The outer end
of the rod 106 is connected to a cap 108 exteriorly of
the valve 98. The inner end of rod 106 has a tapered
edge llO which is adapted to mate with a seat 112
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formed in the regulating valve 98 at the intersection
of chamber 100 and discharge orifice 102.
An annular slot 114 is formed in the outer
surface of regulating valve 98 which is connected to
S the atomizing air branch line 88 carrying air from
supply line 57. Radial passageways 116 connect the
annular slot 114 to the chamber 100 of the regulating
valve 98 upstream relative to the discharge orifice
102. The flow of air rom branch line 57 through the
flow path defined by passageways 64, 66, branch line
88, slot 114, passageways 116 and chamber 100 is
controlled as it passes through discharge orifice 102
by rotating the cap 108 and thus moving the rod 106
axially within the regulating valve 98. Axial move-
ment of the rod 106 varies the space between the
tapered edge 110 of rod 106 and the seat 112 at the
entrance to the discharge orifice 102 which, in turn,
controls the flow rate of air passing therebetween.
Atomizing air is ejected from the discharge
orifice 102 of regulating valve 98 into a connector
passageway 118 formed in the base 76 of applicator
head 44. This connector passageway 118 terminates in
an annular chamber 120 formed at the upper end of a
threaded bore 122 in base 76 within which the nozzle
92 is mounted. The nozzle 92 is formed with a plural-
ity of radial passageways 124 having upper ends which
communicate with the annular chamber 120. The
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opposite, lower end of the radial passageways 124
terminate at the tip 126 of the nozzle 92 within an
annular atomizing air discharge passageway 128 formed
between the outer surface of the nozzle tip 126 and a
facing surface 130 of the air cap 94. As discussed
below, atomizing air discharged from the atomizing air
discharge passageway 128 impacts a stream of adhesive
ejected from the nozzle 92 to break up such adhesive
into droplets for deposition onto a substrate.
Referring again to Fig. 3, pattern-shaping
air is transmitted to the nozzle 92 in a manner
similar to the atomizing air described above. The
pattern-shaping air branch line 90 connected at one
end to the air passageway 66 via annular slot 84
communicates at its other end with a pattern-shaping
air regulating valve 132. The structure and operation
of pattern-shaping air regulating valve 132 is identi-
cal to that of atomizing air regulating valve 98 and
is not repeated herein. The same reference numerals
are used on regulating valve 132 to designate the same
structure as in regulating valve 98, with the addition
of a "prime" to the reference numbers for the pat-
tern-shaping air regulating valve 132.
The discharge orifice 102' of pattern-
shaping air regulating valve 132 communicates with a
connector passageway 134 formed in the base 76 of
applicator head 44. The connector passageway 134
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1 336373
-20-
terminates at an annular chamber 136 formed in the
base 76 which, in turn, is connected to a plurality of
radial passageways 138 formed in the nozzle 92. The
radial passageways 138 are connected to an annular
chamber 140 formed around the periphery of nozzle 92.
The chamber 140 communicates with one end of a pair of
pattern air-shaping passageways 144 formed in air cap
94. The opposite end of the pattern air-shaping
passageways 144 terminate at at least one orifice 146
formed in each air horn 148 OL air cap 94. As de-
scribed in more detail below, pattern-shaping air is
ejected from the discharge orifice 146 OL each pattern
air-shaping passageway 144 and impacts the droplets of
hot melt adhesive formed by the atomizing air ejected
from the atomizing air discharge passageway 128. This
pattern-shaping air controls the width of the pattern
of adhesive deposited onto a substrate, i.e., the
height and width of the pattern of droplets on the
substrate.
As best shown in Figs. 1 and 3, both regu-
lating valves 98, 132 are connected to the common air
supply passageway 66 and thus the total flow of air in
the system is divided among the atomizing air and pat-
tern-shaping air branch lines 88, 90. An important
aspect of this invention, is that the regulating
valves 98, 132 are separately adjustable so that the
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flow rate of the air streams therethrough can be
varied independently of one another.
Hot r-~elt Adhesive Supply
Referring now to Fig. 3, the structure for
delivering hot melt adhesive to the nozzle 92 is
illustrated. The upper cylinder 74 is formed with the
stepped bore 156 having a lower end connected by an
adhesive connector passageway 150 to a supply line 152
from a source of adhesive (not shown). See also Fig.
1. This lower end of stepped bore 156 mounts the
upper portion of sleeve 80 thus forming a flow path
for molten hot melt adhesive from passageway 150 in
upper cylinder 74 into the adhesive flow passageway 82
in base 76 of applicator head 44. The upper end of
stepped bore 156 mounts a packing cartridge 158 formed
with a recess 162. A compression spring 163 is
received within the recess 162, and mounts to the
upper end 164 of a plunger 165 which is carried by the
packing cartridge 158 and is axially movable there-
along. A header plate 166 is mounted at the top of
plunger 165 by a nut 168 forming an air chamber 171
between the packing cartridge 158 and header plate
166. The outer edge of header plate 166 seals against
an inner wall 169 of a cap 170 forming the top of
applicator head 44. Pilot air is supplied by a feed
line 153 connected to a passageway 154 formed in the
upper cylinder 74 beneath the header plate 166 of
plunger 165 and into air chamber 171. See also Figs.
1 and 2.
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The lower end 172 of plunger 165 extends
downwardly from the upper cylinder 74 through the
adhesive flow passageway 82 in base 76 to the nozzle
tip 126 of nozzle 92. An adhesive discharge passage-
way 178 (shown closed) is formed in the nozzle 92having an upper end connected to the adhesive flow
passageway 82 in base 76 and a discharge orifice 180
at the nozzle tip 126. The nozzle tip 126 is tapered
at the discharge orifice 180 to mate with the tapered
tip 184 formed in the lower end 172 of plunger 165 to
control the flow of adhesive therethrough.
The flow of adhesive through the spray
apparatus 10 is obtained by axial movement of the
plunger 165 relative to the discharge orifice 180 in
the nozzle 92, and movement of the plunger 165 is
controlled as follows. Air entering the branch line
34 through operation of valve 30, as described above,
flows to a plunger control valve 186 connected to
branch line 34. In turn, the plunger control valve
186 controls the flow of pilot air into the feed line
153 and through the passageway 154 formed in the upper
cylinder 74 beneath the header plate 166 of plunger
165.
The plunger control valve 186 is a standard,
commercially available "metered in-unrestricted out"
type of actuating valve. In other words, the flow of
pilot air from branch line 34 is metered in one
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1 336373
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direction through the plunger control valve 186 into
feed line 153 and through the passageway 154 and then
beneath the plunger header plate 166. In response to
the pressurization of passageway 154, the header plate
5166 is forced upwardly from the top of the upper
cylinder 74 toward the cap 170 thereabove. In turn,
the tapered tip 184 of plunger 165 is lifted upwardly
from the tapered seat in nozzle tip 126 so that
adhesive flowing through the adhesive discharge
10passagewav 178 in nozzle 92 is ejected from the
discharge orifice 180 of nozzle tip 126. In moving
upwardly as viewed in Fig. 3, the plunger 165 places
the compression spring 163 in compression against the
lower guide 160.
15To return the plunger 165 to a closed
position relative to the nozzle 92, the plunger
control valve 186 is operable to permit the unre-
stricted flow of air in the opposite direction there-
through, i.e., the air contained beneath the header
20plate 166, in air chamber 171, within passageway 154
and within feed line 153 is allowed to bleed back
through plunger control valve 186 without restriction
and then vents to atmosphere through the three-way
cartridge valve 30. When the above-described pilot
25air path to the plunger header plate 166 is depres-
surized, the compression spring 163 forces the plunger
172 downwardly as viewed in Fig. 3 so that its tapered
` -24- l 3 3 6 3 7 3
tip 184 seats within the discharge orifice 180 of the
nozzle tip 126.
System Operation
An important aspect of this invention is
that the plunger control valve 186 and pilot air
control valve 68 connected to branch lines 34 and 36,
respectively, operate so that atomizing air and
pattern-shaping air are supplied to the area of the
nozzle tip 126 both before the adhesive flow through
the nozzle 92 is initiated, and after the adhesive
flow therethrough is terminated. As mentioned above,
the pilot air control valve 68 is an "unrestricted
in-metered out" type of valve whereas the plunger
control valve 186 is a "metered in-unrestricted out"
type of valve. As a result, pilot air is quickly
supplied by the pilot air control valve 68 to the air
supply valve 46 which, in turn, allows atomizing air
and pattern-shaping air to flow to the area of the
noz~.le tip 126 as described above. At the same time,
the plunger control valve 186 is "metered in" so that
pressurization of the air chamber 171 in upper cylin-
der 74 is slightly delayed. The axial, upward move-
ment of the plunger 165, and subsequent discharge of
adhesive from nozzle 92, therefor occurs after atomiz-
ing air and pattern-shaping air are present at the
nozzle tip 126. On the other hand, the "unrestricted
out" plunger control valve 186 ensures that the flow
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of adhesive from nozzle 92 is terminated before the
pilot air within the pilot air chamber 52 of air
supply valve 46 is bled off by the "metered out" pilot
air control valve 68, thus allowing air supply valve
46 to close and stop the air flow to the atomizing and
pattern-shaping air lines.
The operation of valves 68, 186 in this
manner substantially eliminates cut-off drool, i.e.,
the formation of strands or thin fibers of adhesive in
the area of the nozzle tip 126. No excess adhesive is
allowed to remain in the area of the discharge orifice
180 of the nozzle tip 126 after the flow of adhesive
is discontinued because the atomizing air and pat-
tern-shaping air continues for some period of time
after the flow of adhesive is shut down. Similarly,
no start-up drool or formation of strand-like fibers
of adhesive is obtained when the flow of adhesive is
initiated because the atomizing air and pattern-shap-
ing air is directed to the nozzle tip 126 prior to the
time the adhesive flow begins.
As shown in Fig. 5, an adhesive stream 188
is ejected from the discharge orifice 180 cf nozzle
tip 126 and encounters the atomizing air ejected from
the atomizing air discharge passageway 128. The
atomizing air expands radially outwardly from the
discharse passageway 128 and impacts the exterior
surface of the adhesive stream 188 with sufficient
flow rate and velocity so that the adhesive stream 188
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is broken up into globules or droplets 190 for deposi-
tion onto a substrate 192. These droplets 190 are
then impacted by pattern-shaping air ejected from the
discharge orifices 146 in the air horns 148 to control
the width of the pattern of adhesive droplets 190
deposited onto the substrate 192.
An important aspect of this invention is the
versatility of the operation of applicator head 44 in
accommodating a number of different types of hot melt
adhesives to obtain the cesired size and pattern of
adhesive droplets 190. Thermoplastic adhesives have a
relatively long "open time", i.e., the time in which
they remair. sufficiently molten to bond one substrate
to another, but the open time of different types of
thermoplastic adhesive varies from one to another.
Moreover, some thermoplastic adhesives are pressure
sensitive and thus have an extended open time wherein
the adhesive can provide an effective bond even after
it cools.
The applicator head 44 of this invention is
operable to spray various types of hot melt adhesives
in droplet form such that the individual droplets 190
are large enough to retain their specific heat once
deposited onto a substrate 192 for a sufficient time
period to permit a second substrate to be adhered to
the first substrate 192. This is achieved in the
instant invention by the provision of separate control
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valves 98 and 132 for the atomizing air and pattern-
shaping air, respectively.
For example, the flow rate of the atomizing
air and its velocity are primarily responsible for the
size of the adhesive droplet produced for a given
nozzle design. An increase in flow rate and velocity
of the atomizing air tends to decrease the size of the
adhesive droplets 190 because the adhesive stream 188
is impacted more violently by the higher velocity
atomizing air which breaks it up into smaller droplets
190. On the other hand, a decrease in the flow rate
and velocity or the atomizing air tends to produce
droplets 190 of larger size because of the reduced
turbulence or violence of the impact between the
slower moving atomizing air and adhesive stream 188.
In this manner, the size of the droplets 190
can be adjusted for different types of hot melt
adhesives to match or correspond to the open time
thereof so that the droplets 190 are large enough to
retain their specific heat once deposited onto the
substrate 192 for a sufficient time to create an
effective bond with another substrate. Generally, hot
melt adhesives with limited open time should be
sprayed in relatively large droplets 190 and the size
of the droplets 190 can be decreased as the open time
of the adhesive increases or when using pressure
sensitive adhesives.
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The velocity and flow rate of the pattern-
shaping air is adjustable primarily by adjustment of
pattern-shaping air regulating valve 132 to control
the width of the pattern of droplets 190 deposited
onto the substrate 192. For example, as the velocity
and flow rate of the pattern-shaping air increases,
the pattern of droplets 190 tends to widen. On the
other hand, as the flow rate and velocity of the
pattern-shaping air decreases, the resulting pattern
of droplets 190 narrows on the substrate 192.
It is contemplated that in most instances,
the ratio of the flow rate and velocity of atomizing
air to pattern-shaping air would be adjusted instead
of adjusting only one of the atomizing air stream or
the pattern-shaping air stream while maintaining the
other constant. For example, adjustment of the ratio
of atomizing air to pattern-shaping air so that the
velocity and flow rate of the atomizing air increases
while the velocity and flow rate of the pattern-
shaping air decreases, results in the formation of arelatively narrow spray pattern on substrate 192
consisting of relatively small droplets 190. Adjust-
ment of the ratio of atomizing air to pattern-shaping
air so that the velocity and flow rate of the atomiz-
ing air decreases while the velocity and flow rate ofthe pattern-shaping air increases results in the
formation of a relatively wide spray pattern on
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substrate 192 consisting of relatively large droplets
190 .
Given the wide varietv of thermoplastic
adhesives which are commerciallv available, and the
differing requirements of the types of applications
for which such adhesives are utilized, it is contem-
plated that the ratio of the flow rate and velocity of
atomizing air to pattern-shaping air for a particular
application would be determined by experimenting with
the settings of the atomizing air regulating valve 98
and pattern-shaping air regulating valve 132. Addi-
tionally, the particular configuration of the nozzle
92 employed in the applicator head 44 affects the
velocity of the atomizing air and the pattern-shaping
air depending upon the dimensions of the annular
atomizing air passageway 124 and the two pattern-
shaping air orifices 146 in the air horns 148 of the
air cap 94.
The following examples provide representa-
tive of parameters for the atomizing air and pattern-
shaping air flow rates, in a nozzle 92 and air cap 94
of the type shown in the Figs., which have been proven
experimentally to provide acceptable results for a
given application.
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Example 1
Type of Adhesive: Eastman Ai48 adhesive
Adhesive Temperature: 375F
Adhesive Flow Rate: 300 g/min
Nozzle Spacing: 12" from substrate
Atomizing Air Flow Rate: 2.76 scfm
Pattern-Shaping Air Flow Rate: 3.22 scfm
Using the type of adhesive and adhesive flow
rate given above, the stream of adhesive discharged
from the spray nozzle was impacted in this Example 1
by a stream of atomizing air having a flow rate of
2.76 scfm. This produced adhesive blobs or droplets
190 having a transverse dimension of about 1/4" to
7/16". The pattern of droplets 190 obtained by the
stream of pattern-shaping air at a flow rate of 3.22
scfm was approximately 14" in width. For the type of
adhesive utilized, the size of the droplets 190 was
considered sufficient to insure that they would have
sufficient open time for the desired application.
Example 2
Type of Adhecive: Eastman A148 adhesive
Adhesive Temperature: 375F
Adhesive Flow Rate: 300 g/min
Nozzle Spacing: 1," from substrate
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Atomizing Air Flow Rate: 3.47 scfm
Pattern-Shaping Air Flow Rate: 3.21 scfm
In this example, the same adhesive and
adhesive flow rate was employed as in Example 1. The
difference in this example is that the flow rate of
the atomi~ing air was increased relative to the flow
rate of the pattern-shaping air. This produced
adhesive droplets 190 which were slightly smaller in
transverse dimension, and also the pattern width
decreased so that the droplets 190 were more tightly
grouped together, than in Example 1.
Alternative System Confiqurations
Referring now to Fig. 4, a schematic illus-
tration is provided of the adaptability of applicator
head 44 to different dispensing systems. The applica-
tor head 44 is useful for hand-held types of opera-
tions as shown in Figs. 1-3 and at the top of Fig. 4,
and for more automated applications as shown in
intermediate and lower segments of Fig. 4 wherein the
applicator head 44 mounts to different support means
which supply pilot air, adhesive and heated air to the
applicator head 44.
More specifically, the uppermost portion of
Fig. 4 illustrates the applicator head 44 in combina-
tion with the spray gun 12 shown in Fig. 1 and
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discussed in detail above. This combination would be
utilized in hand held applications for applicator head
44 such as certain types of assembly operations.
Referring to the center portion of Fig. 4,
the spray gun 12 is eliminated and replaced by a
mounting block 200 supported by a rod 202. The
mounting block 200 carries the service block 41 which,
in turn, mounts the applicator head 44 in a position
to support the support block 42. The service block 41
is formed with a port 204 to receive pilot air for the
plunger 165 of applicator head 44 and a port 209 for
hot melt adhesive. A port 206 is formed in support
block 42 to receive air for the atomizing and pat-
tern-shaping passageways of applicator head 44, and a
port 208 is also formed in support block 42 to receive
pilot air for operating an air supply valve (not
shown) such as the air supply valve 46. The embodi-
ment in the center of Fig. 4 operates in an essen-
tially identical manner to that disclosed in Figs. 1-3
and 5 except that the supply of pilot air and hot melt
adhesive thereto is preferably controlled by a pro-
grammable controller (not shown) instead of a hand
operated trigger 18 as in spray gun 12.
Referring to the bottom portion of Fig. 4, a
manifold 210 is illustrated which is supported on a
mounting rod 212. The manifold 210 is adapted to
mount several applicator heads 44 on either of its
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sides, each of which are operated by a programmable
controller (not shown). In the manifold there shown,
ports are provided to mount two applicator heads on
one side and one applicator head on the opposite side.
To this end, the manifold 210 is formed with ports 214
adapted to connect to the port 154 of applicator head
44 to supply pilot air for moving the plunger within
applicator head 44. Hot melt adhesive is transmitted
into the passage 150 of applicator head 44 from ports
216. Additionally, the manifold 210 is formed with
ports 218 which connect to the port 66 in applicator
head 44 to supply air for the atomizing air and
pattern-shaping air passageways thereof. The manifold
210 has suitable passageways (not shown) which connect
control air supply line 215 with ports 214, hot melt
adhesive supply line 219 with ports 216 and shaping
and atomizing air supply line 219 with ports 218.
While the invention has been described with
reference to a preferred embodiment, it should be
understood by those skilled in the art that various
changes may be made and equivalents may be substituted
for elements thereof without departing from the scope
of the invention. Therefore, it is intended that the
invention not be limited to the particular embodiment
disclosed as the best mode contemplated for carrying
out the invention, but that the invention will include
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all embodiments falling within the scope of the
appended claims.
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