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This tutorial will give some basic considerations for connector design. Dow
Corning can help consult on the specifics of your connector for use with
connector sealant pads. Some solutions services include but are not limited
to application development, process development, automation and production
startup.
To find out more or request these services from Dow Corning please visit our Solutions Web Section.
We can also send you our more complete technical paper covering connector
design guidelines. Please contact us requesting this paper.
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Contact Shape
Gel seals are less sensitive to aggressive contact features than rubber
monoblock seals. Because gels easily re-heal, they are not affected as much
by features that cut through the gel, unlike monoblock grommets that do not
reheal if cut. However, seal performance is affected by excess removal of
gels, which can occur with contacts with scoop-like features and sharp edges.
For these reasons, rounded contacts typically provide excellent sealing for
many insertions and extractions of the connector. Box-shaped contacts
generally are not a problem but some can have sharp edges (a minimum of 0.5 mm
radius is recommended). Lanced contacts provide the most difficulties in
maintaining sealing effectiveness due to the abrasive contact designs which
could cause tears in the gel material during insertion/ extraction.
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Contact Count
Functionally, the performance of gel seals is not affected by contact count.
Gel seals perform equally well for low contact count connectors as well as
for high contact count connectors. In addition, performance is not affected
by the connector loading factor. The performance is the same regardless of the
number of contacts that are installed into the connector cavity.
Connector size and contact count can affect the economics of gel seals. Small
and irregular pad shapes can be less economical to produce.
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Contact Size
The importance of the contact size is that it determines the size of the
contact cavity that the gel must span. Larger cavities are more difficult due
to the soft nature of the gel. Contacts larger than 2.8 mm can present
problems for connector sealant pads. Smaller contact sizes, such as 0.6 mm,
are excellent for sealing with gel. Connector sealant pads can be an enabling
technology for these types of connectors.
Contact Pitch
Gel grommets do not restrict the thickness of the connector body between pins
and therefore allow contacts to be placed at minimum center to center spacing
(pitch). Thin wall sections of less than 0.5 mm provide adequate support for
the gel grommet to create a seal. In addition an extremely thin layer of gel
is sufficient to create a seal. Therefore, even large wires can be placed on
minimum spacing while still allowing sufficient gel between adjacent wires to
create a seal.
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Relation of Contact to Cavity Size
The fit of the contact into the contact cavity is important for gel seal
designs. The area of the contact cavity opening versus the cross-sectional
area of the contact must be considered. When the frontal area of the contact
is less than or equal to 55 % of the cavity area, then low contact insertion
forces will result. As the percentage increases, the insertion force will
increase. In particular, as the area percentage increases above 85%, it
becomes possible to shear off pieces of gel during contact insertion which can
degrade long term sealing performance. The clearance between contact and
contact cavity wall should be > 0.15 mm all around.
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Special Case of Mixed Contact Sizes
When a mixture of contact sizes must be accommodated by a single gel grommet
seal, then the largest contact size and pitch will determine the gel
configuration. This situation is most common in electronic interfaces where a
few power contacts are required, but where most of the interface is low level
signals. The best solution is to segment the connector to isolate the larger
contacts and therefore allow different sealing solutions to optimize the
system.
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