Dispensing – Processes of dispensing
Reexamination Certificate
2000-03-23
2001-07-10
Shaver, Kevin (Department: 3754)
Dispensing
Processes of dispensing
C222S504000
Reexamination Certificate
active
06257445
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus for dispensing viscous fluids and more specifically, to an electrically operated apparatus for dispensing viscous liquids, such as hot melt adhesives.
BACKGROUND OF THE INVENTION
Various viscous fluid dispensers have been developed for the precise placement of viscous fluid such as a hot melt adhesive. Generally, viscous fluid dispensers have a valve stem with a valve body on its distal end which is disposed on an upstream side of a valve seat and moved in an upstream direction to open the valve and in a downstream direction to close the valve. For purposes of this document, the term “upstream” refers to a direction or location that is toward or closer to the source or fluid inlet and away or further from the fluid outlet of the dispenser; and “downstream” refers to a direction or location that is toward or closer to a fluid outlet and away or further from a source or fluid inlet of the dispenser. Many viscous fluid dispensing applications require that the viscous fluid be applied to the substrate with sharply defined boundaries, that is, the leading and trailing edges of the applied pattern of fluid on the substrate fluid be sharply defined or delimited. Thus, it is necessary that the motion of the valve body be very fast, and the flow of viscous fluid be abruptly started and stopped. With the valve construction described above, when the valve opens, the valve body is moving in an upstream direction against the direction of flow of the fluid and has a tendency to delay and disrupt the flow of fluid out of the dispensing nozzle. Similarly, when the valve closes, the valve body is moving in the downstream direction with the direction of fluid flow and has a tendency to cause a small additional quantity of fluid to be dispensed.
To provide a sharper initiation and cut-off of fluid flow, a “snuff back” valve construction is known. With this construction, the valve body is disposed on a downstream side of a valve seat and moved in the downstream direction away from the valve seat to open the valve and in the upstream direction toward the valve seat to close the valve. Consequently, as the valve opens, the valve body is moving in the same downstream direction as the viscous fluid; and the viscous fluid begins to be dispensed simultaneously with the opening of the valve body. When the valve closes, the valve body is moving in the upstream direction and is effective to sharply cut-off the flow of viscous fluid. While such valves are operated by electric-pneumatic solenoids, due to the relatively short useful life of pneumatic solenoids and their inability to be precisely and repeatably controlled over the long term, it is desirable to provide an electrically operated viscous fluid dispenser of the above-described “snuff-back” design.
Such “snuff-back” electric fluid dispensers are known and are generally of the structure illustrated in FIG.
4
. An electrically operated viscous fluid dispenser or dispensing gun
20
comprises one or more dispensing modules or valves
22
mounted on a fluid distribution manifold plate
24
in a known manner. The dispensing valve
22
includes a dispenser body
26
and a fluid dispensing nozzle body
28
having a nozzle
30
through which droplets
32
of the viscous fluid are dispensed onto a substrate
34
. Relative motion between the substrate
34
and dispenser
20
is provided in a known manner.
A valve stem
36
is mounted within the dispenser body
26
and has a valve body
38
on its lower, distal end below or downstream of a valve seat
40
. The valve body
38
sealingly engages with a valve seat
40
to inhibit the flow of fluid from the dispenser
20
. A fluid inlet passageway
42
intersects the interior portion
44
of the dispenser body
26
and is connected to a fluid passage
46
in the manifold
24
which, in turn, is fluidly connected to a pressurized source of viscous fluid
48
, such as a hot melt adhesive. Arrows
49
indicate the flow path of the fluid entering through the fluid inlet passageway
46
and through the interior portion
44
.
An armature
50
is disposed within the interior portion
44
and is coaxially aligned with, and is often formed integrally with, a proximal end of the valve stem
36
. An electromagnetic coil
52
is disposed about the armature
50
. A return spring
54
biases the valve stem
36
and valve body
38
in an upstream, upward direction to a closed position at which the valve body
38
sealingly contacts the valve seat
40
, thereby interrupting the flow of viscous fluid through the nozzle
30
. The return spring
54
is normally a compression spring which is placed under compression within the bore
60
through engagement with an electromagnetic pole
56
. When supplied with electrical current, the coil
52
generates an electromagnetic field. The electromagnetic coil
52
must generate an electromagnetic field between the armature
50
and the pole
56
of sufficient strength so as to attract the armature
52
and the pole
56
together. Since the pole
56
cannot move, the armature
52
moves downward against the force of the spring
54
, thereby moving the valve body
38
downstream away from the valve seat
40
to its open position.
The design of the dispensing valve
22
of
FIG. 4
is known as a normally-closed design for the reason that when the coil
52
is de-energized, the spring
54
maintains the valve body
38
sealingly against the valve seat
40
, thereby holding the valve
22
in the closed position. Thus, the valve
22
is normally in, or defaults to, a closed state or position. Therefore, in the event of any electrical power failure to the coil
52
, the valve
22
is always mechanically biased to the illustrated closed position. Thus, the valve
22
always defaults to the closed position.
However, to provide that desired normally-closed capability, the armature
50
must be located within the interior
44
above the pole
56
; and further, the valve stem
36
must extend through a bore
58
within the pole
56
. Those structural features introduce several disadvantages in the operation of the valve. First, the bore
58
in the pole
56
reduces the mass of the pole
56
, thereby reducing the effectiveness and strength of the electromagnetic field produced by the coil
52
and pole
56
, thereby reducing their capability to move the armature
50
. Further, the viscous fluid presents a greater resistance to motion of the portion of the valve stem
36
located within the bore
58
than the portion of the valve stem
36
located outside the bore
58
. In addition, the valve stem
36
is substantially elongated to be able to pass through the length of the pole
56
, thereby increasing the mass that must be moved by the electromagnetic field. Therefore, the viscous fluid dispenser
20
of
FIG. 4
requires that the coil
52
and pole
56
provide a greater electromagnetic force in order to move the armature
50
, valve stem
36
and valve body
38
between the open and closed positions.
Second, the interior portion
44
extends over the entire length of the valve body
38
, and there are wetted surfaces throughout the entire length of the interior portion
44
of the valve body
38
. That large area of wetted surfaces increases the probability of the accumulation of char over the operating life of the dispenser
30
. Char is a fluid residue that accumulates on wetted surfaces and is most generally caused by a long term degradation of the viscous fluid. To minimize the potential accumulation of char, the design of the valve of
FIG. 2
has a further disadvantage of providing the viscous fluid inlet at the upper end of the dispenser body
26
, thereby requiring the viscous fluid to pass through the entire length of the dispenser body
26
prior to being dispensed by the nozzle
30
. That long and tortuous fluid flow path not only adds resistance to motion of the armature
50
and valve stem
36
in the viscous fluid, but in addition, the flow rate of the viscous fluid through the dispenser
20
may also be ad
Means Scott
Saidman Laurence B.
Cartagena M A
Nordson Corporation
Shaver Kevin
Wood Herron & Evans L.L.P.
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