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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.
 Nearly two years ago, Sealant Equipment &
Engineering (SEE), identified a need created by
Dow
Corning to develop an automated dispensing system for their new
Thixotropic 3-8186 silicone foam for Dispensing 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
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 exacting proportioning and then
thoroughly mixing the two components. The extruded silicone foam then expands
and cures in 10 min 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 productions 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-A-Bead 995 emerged as the system
able to respond to the multiple demands of the material and 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
SeeFoam, a compact, motionless, multi-path,
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 is shut
off.
The
SeeFoam Dispense
Valve is commonly fixtured in a wrist of a multi-axis 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 program
controlled, consistency is ensured. Furthermore, since the process drastically
reduces waste, labour and other related costs, these savings are realised.
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