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High-tech precision dispensing equipment and a
new, two-component silicone material have
teamed up to create cutting-edge gasketing
techniques. High production rate applications
in a variety of industries, including
automotive, electronics, appliance,
airframe/aerospace and packaging, are driving
this new process.
Sealant Equipment & Engineering (SEE) of
Plymouth, Michigan identified a need created by
Dow Corning to develop an automated dispensing
system for their new Thixotropic 3-8186
silicone foam for Dispensed Foam Gasket (DFG)
applications. Eighteen months later, the
partnership has drastically improved the
development and use of foamed-in-place
gaskets.
DFG gasket material, coupled with the
Program-A-Bead 995 meter/mix/dispensing system,
will displace conventional, time-consuming,
manual gasketing methods. Die-cut taped foam
gaskets and preformed rubber gaskets cannot
compare in cost or quality to the new silicone
foam gaskets.
The silicone is transformed from its liquid
state to the desired cell structure foam
product by exactly proportioning and then
thoroughly mixing the two components. The
extruded silicone foam then expands and cures
in 10 minutes at 75°C – ready for
use or shipment.
The DFG silicone material must be dispensed at
a precisely controlled, mixed material flow
rate. A programmable robot or XYZ table will
control the dispense valve nozzle/tip speed
used to apply a predetermined bead of silicone
foam around the surface for a subject work
piece, and hence the foam gasket geometry being
dispensed is solely generated by the
programmable motion control equipment in a
non-synchronized manner.
Challenges and Solutions
Precisely metering and mixing the 1:1 parts by
weight material to create the proper foam cell
structure was one requirement in developing
this dispensing process. Another factor during
the design stages was that the mixed material
must be dispensed at a constant flow rate. The
silicone gasket must be dispensed quickly,
accurately and continuously to meet the most
demanding product applications.
These application requirements were SEE’s
primary challenges. They needed to design and
manufacture equipment that would, at aggressive
production rates, precisely meter, mix and
dispense the silicone to ensure the foaming
property and control the dispense rate to vary
the size of the foamed-in-place gasket without
interruption. The Program-A0Bead 995 emerged as
the system able to respond to the multiple
demands of the materials and the application
process.
At the heart of the system are the two positive
displacement, precision gear metering pumps
with integrated electronic controls. The
variable ratio, servo-driven, gear-metering
pumps can be controlled separately and jointly,
providing flexibility. The independent control
allows the silicone to be metered at ratios
other than the standard 1:1 (for use with other
materials).
While exact ratio proportion is essential,
thorough and efficient mixing is critical to
ensure the even cell structure of the silicone
foam. The equipment’s mixing is
accomplished with the See Foam, a compact,
motionless, multipath, static mixing system
that guarantees that the two material
components are thoroughly blended. The dispense
valve and multipath mixer eliminate the need
for a costly and high-maintenance dynamic-style
power mixer.
An integrated base purge feature eliminates the
need for solvent flushing and eliminates the
disposal of hazardous waste materials.
The No-Drip/Snuf-Bak design of the dispense
valve assures that the material will not drip
or leak from the outlet when it shuts
off.
The SeeFoam Dispense Valve is commonly fixtured
in a wrist of a multi-axes robot and then
positioned over the work piece. The robot
controller is programmed to send an output
signal to the Program-A-Bead dispense system to
control the on/off of the dispense valve
nozzle-tip. By using the positive displacement,
servo-driven, gear metering pumps, the dispense
process is surge- and pulse-free, which ensures
that the foam gasket is consistently sized
throughout the desired bead path.
System Advantages There are
numerous benefits from this marriage between
the DFG material and the Program-A-Bead 995.
First, the completely automated process ensures
exactly proportioned mixing while meeting
aggressive manufacturing schedules. In
addition, the system provided precision
dispensing that eliminates any quality
assurance concerns, and because the dispensing
process is programmably controlled, consistency
is the process drastically reduces waste, labor
and other related costs, these savings are
realized.
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