Whitepapers
Whitepaper Library
NuSil continues its commitment to silicone education with a new Whitepaper,
"Ultra Low Outgassing Silicone Materials," which was presented at the 10th
International SAMPE Conference in Tokyo, Japan. This Whitepaper discusses the
importance of using ASTM E 595-standard materials in aerospace applications, as
well as how formula and processing advancements have created
excellent-performing, low outgassing silicones.
For access to our entire Whitepaper Library, login to
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MyNuSil.
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Silicone Materials Series
Troubleshooting Silicone Materials Series:
Eliminating Bubbling Or Porosity
Bubbling (porosity) in silicone materials can adversely affect cured silicone
material properties, including tensile, tear, elongation and appearance. Design
and process engineers seeking to reduce or eliminate bubbles are encouraged to
characterize the phenomenon as primarily process- and/or material-related. Both
can contribute to bubbling, but changing one variable may eliminate the problem.
Process
The first stage of most silicone molding, dipping, wiping or potting
processes is the preparation of the material for cure. Two-part silicone systems
require mixing to cure. While automated processes can complete this stage
without introducing air into the system, they should be periodically inspected
to ensure this is the case.
Hand- or machine-mixing in an open air environment will introduce air to the
silicone, requiring the removal of the entrapped air by vacuum or centrifuge.
NuSil finds de-airing to be the most effective means of reducing air and other
gasses that can cause bubbling. The transfer of the silicone, mixed or not, to
the curing area, surface or mold needs to be designed to avoid air introduction.
Mold or cure area design is also critical to bubble elimination. Closed-mold
designs must avoid bubble creation or entrapment. Venting of the mold and other
techniques are effective at producing bubble-free molded part(s). NuSil can
provide a list of equipment manufacturers that provide help in these areas.
Processing conditions, from room temperature to injection port temperature,
are just a few examples of where temperatures should be closely monitored. In
molding processes, the injection pressure can play a significant role in bubble
reduction.
Material
During cure, silicone materials that undergo crosslinking contain reactive
species. Bubbling can arise from reactive components interacting with nearby
substrates or even cleaning materials. Therefore, evaluating substrate surfaces
in the design phase is an important step in eliminating incompatibility.
Cleaning procedures should remove virtually all traces of solvents and other
liquids that may volatilize in a heated curing process. The cure time and
temperature of silicone materials can be adjusted to minimize bubbling (e.g., if
a substrate outgases at high temperatures, a room-temperature or low-temperature
curing silicone can eliminate bubbling).
Processes, substrates and silicone materials differ for each situation;
therefore, any bubbling situation requires a specific solution. Contact your
local technical representative if you have specific questions. You may find your
representative’s contact information here.
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New Products & Developments
RTV Fluorosilicone Expands Line of Aircraft Adhesives
NuSil Technology has launched an extension to its line of adhesives/sealants.
FS3-3730 fluorosilicone adhesive/sealant is a one-part, fast-curing,
room-temperature vulcanizing (RTV) silicone that provides excellent elastomeric
properties.
"With the addition of FS3-3730, we are able to offer our customers another
high-quality option for aviation applications," said Brian Nash, vice president
of marketing and sales. "This translucent silicone bonds aggressively to most
surfaces and provides excellent performance when protecting or bonding hardware
components exposed to gasoline or aviation fuels."
For more information, visit http://www.nusil.com/ or contact Bill Riegler, Product
Director - Engineering Materials, at 805-684-8780 or New Products & Developments.
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