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Although it is still early afternoon as the 1991
sedan eases onto the freeway, the driver switches on his headlights. It is the
law in Canada. A sophisticated electronic module immediately senses the
presence of daylight, automatically reduces wattage to the headlights by 20
percent and switches off the unnecessary tail lights, prolonging the life of
the lamps. The electronic circuitry that controls the process is only one of a
wide variety of electronic and Electro-mechanical systems and components
manufactured by Lectron Products, a major supplier to the Big Three automakers.
This particular module, however, presented the Rochester Hills, Michigan,
manufacturer with a special set of problems.
Due to the part's under-bonnet location, the
automaker specified that not only must the part itself meet strict quality
standards, but it also must be able to withstand the rigors of an environment
where it would be subjected to water, salt, oil, gasoline and extreme
temperature fluctuations. A two-part reactive polyurethane, manufactured by
Biwax Corp., Des Plaines, Illinois, had already been tested and approved as the
specified potting material. Lectron turned to Thermal Innovations Corp.,
Manasquan, N.J., for a engineered design proposal on how best to employ the new
potting material.
Thermal Innovations responded by custom-designing an
automated turn-key potting system that combined in its own Seal-Cure
high-purity, special infrared pre-heat oven and infrared curing oven; an
automatic meter, mix and dispense system manufactured by Sealant Equipment and Engineering;
the Biwax
polyurethane potting material and a series of index conveyors to join them
together in a closed-loop system. The idea was to combine the state-of-the-art
technology in each area into a relatively simple cost-effective potting process
that could be operated by a few people and produce high quality modules.
Production
Steps
In the first step of the operation, modules are
loaded manually onto the conveyor for delivery to the pre-heat oven. Modules
are heated to approximately 70°C to remove any moisture retained by the PC
boards and to help ensure uniform flow of the potting material around the
board's intricate electronic components. This pre-heat oven is rated at 7.2kw
and is approximately 5.5 ft. long.
 After pre-heating, the modules are automatically
indexed and positioned underneath the automatic meter, mix and dispense
machine, a
See-Flo® 7.
After a sensor indicates
that a module is in place, the machine automatically dispenses a 100-cc shot of
the mixed potting material. The module then moves along the conveyor to the
curing oven, an infrared Seal-Cure oven which is the heart of the system. The
oven heats and accelerates the two-component (resin/catalyst) chemical reaction
at much lower ambient temperatures than conventional convection ovens. The
infrared oven transmits electromagnetic waves through the air which are
directed at the target module and absorbed. The special quartz infrared
emitters can be fine-tuned to accommodate the potting material's absorption
characteristics as well as the thickness of the material. This ability to
control energy output ensures that the material, rather than the heat sensitive
electronic components, warms and cures quickly. The Sure-Cure oven fully cures
the potted assembly in just 3 minutes with total energy efficiency. This
particular final cure oven is rated at 14.4 kW and is approximately 10 ft.
long. The module never reaches a temperature above 65°C. After the curing
process, modules are conveyed through a forced ambient air cooling section so
that an un-gloved operator can immediately unload the system.
 System
Components
The Lectron system uses a central command electrical
control panel for temperature zone control, conveyor indexing speed and
automatic dispensing. The system is easily monitored and was designed to plant
specifications. However, Thermal Innovations has the capability to design and
install sophisticated computer-controlled systems that can be integrated into
the most complicated computerized manufacturing, inventory and information
systems. The potting material, Biwax 82.643, has been custom formulated to meet
and exceed automotive requirements and for use in infrared curing operations.
The material is a two-part reactive polyurethane that exhibits many beneficial
characteristics, such as long pot life, low exotherm, low viscosity,
non-abrasiveness, 1:1 ratio, high-low temperature stability and environmental
resistance. It will cure at room temperature in the event of power failure. In
this application, the material needs to be fairly elastomeric when cured, so
that it protects delicate electronic components.
The
See-Flo® 7
meter, mix and dispense
machine was selected for its compatibility with the potting material and its
ability to be interfaced with an automated turn-key system. The part A and B
material components are supplied to the inlets of the metering cylinder
assemblies by gravity feeding from double-stacked 55-gallon drums. Precision
volumetric metering is accomplished by positive displacement, double-acting
balanced metering cylinders. When the signal to dispense is received from the
central command control panel, the air powered system reciprocates, forcing a
pre-determined volume (100-cc shot) of metered material through the non-moving
(static) mixer nozzle assembly. The disposable static motionless mixer produces
a high-quality and air-free blending of dual-component materials. The volume of
mixed material in the system is kept to minimum by blending immediately in the
nozzle prior to dispensing. When the dispense cycle is completed, the No-Flush
spool valve direction is reversed, creating a
Snuf-Bak™
action at the tip and ensuring
a positive No-Drip®
cut-off of the mixed
material.
Benefits
Currently the system is producing approximately 200
potted modules/hr. Rather than a normal cure time of 13-15 minutes, 3 minutes
in the Seal-Cure oven is sufficient. This greatly reduces oven bottlenecks and
work-in-process inventory. The oven is also much more energy efficient than its
convection counterpart, so savings are realized in that area as well. Benefits
in labour area are obvious; the system was designed specifically for a single
operator and comparatively simple operation. Low oven temperatures and reduced
need for solvent use in the dispensing equipment make the system safer and more
user-friendly. Installation is quick and easy, as all components are pre-wired
and pre-tested. A single exhaust system ties directly into existing plant
systems, and wiring is simplified. The system also is compact and offers good
use of floor space. "The entire potting operation is proving what cooperation
and communication among industry resources can accomplish in a relatively short
time," Biwax's Les Schober says. "Thermal Innovations, Sealant, Lectron and
Biwax all contributed, and each of us learned the benefits of the team effort
approach." Thermal Innovations' Nick Fusilli puts it another way. "We want
Manufacturers everywhere to become aware that the resources are available for
turn-key systems just like the Lectron project. We're working together to keep
one step ahead not only of our own competitors, but also of our own customers'
needs. New Material, new ways to dispense them, new curing processes -- all of
these things can come together in one integrated system if you are working with
suppliers who have established relationships among the various disciplines.
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