Dow Corning ® brand silicone gels are easily applied by a variety of methods.
A general overview of these processes is given below. For more specifics,
please refer to the Tutorial on Processing Gels and Encapsulants.
Some gels are supplied in bladder paks that avoid direct air contact with the
liquid gel components. This allows the use of air pressure over the pak in a
pressure pot for dispensing. Air pressure applied directly on the liquid gel
surface, without the Bladder pak, is not recommended since the gel can become
supersaturated with air. Then as the gel is dispensed bubbling can occur.
The Bladder paks not only solve this, but also have the benefits maintaining
cleanliness and avoiding contamination in the gel.
In general the gels are supplied as two-part products that are mixed in a 1:1
ratio (Part A & Part B). There are one-part gels available which eliminate the
need for mixing. Gels can be dispensed manually or using one of the many
different types of meter mix equipment available. Typically the two components
are of matched viscosity and are readily mixed with static or dynamic
mixers. Automated meter-mix is normally used for high volume processes. In low
volume, manual weighing and simple hand mixing may be appropriate.
For assistance in designing a process tailored to the needs of your
application, contact Dow Corning’s technical experts in the Application Center.
The two components are added in the proper ratio to a clean container and then
hand stirred gently but thoroughly. For some products, the two parts are
different colors to help judge adequate mixing. If air entrapment is a
problem, it may be necessary to de-air the material after mixing to ensure
that the cured material is bubble free. The mixed material is then poured into
the unit to be encapsulated. The filled unit can also be vacuum de-aired
before curing to remove any last air. Take care during any de-airing process
since foaming and significant expansion of the mixed material can occur.
Automated meter-mix equipment is typically used for higher volume production
processes. These systems consist of a separate feed reservoir and pump for
each component. The systems are set to achieve the desired 1:1 ratio of the
two components. The materials are then fed through a dispense head attached to
a static mixer which is used to achieve a uniform mix. The dispense head is
used to control the amount of material that is dispensed into the part. Static
mixer tubes may need to replaced or cleaned when the process is shut down for
long periods to avoid having the gel cure in the mix tube. If air entrapment
in the cured material is a problem, it may be necessary to de-air the material
in the feed reservoirs or in extreme cases, deair the material in the parts.
Manual Mixing and Dispense
Manual dispense units have separate chambers for each component which connect
to a common static mixer tube. Applying pressure to the plungers on the
chambers pushes the material through the static mixer. This can be done
manually by squeezing a hand trigger or can be gas powered. Static mixers are
typically disposable one-time use units and may need to replaced or cleaned
when not being used for long periods to avoid having the gel cure in the mix
tube. These units can be supplied pre-filled and ready to use or can be loaded
with mixed and de-aired material immediately before use.