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Composite Helmets
Composite helmet shells are made up of a mixture of thermoset resins and glass fiber.
The thermoset resin is the “glue” which is needed to hold glass fibers together in a
composite helmet shell. Thermoset resins are a family of plastics that do not melt but
chemically degrade at high temperatures. Thermoset resins are created by mixing two base
materials just like epoxy glues. (Epoxy glues are thermoset resins). One of the ingredients
is a catalyst that, when combined with the other agents and heat during molding, will
solidify the mixture, locking itself and the glass fibers into a rigid state. In compression
molding applications, very little catalyst is used so that the liquid resin remains stable at
room temperature; the heat and pressure of the molding operation initiates the chemical
reaction to solidify the resin.
Bullard Feature
What Goes Into a Bullard Fire Helmet
Thermoset resins by themselves have relatively little strength; the strength of a thermoset
composite material comes primarily from the fibers of glass or other materials that are
bonded together by the resin.
The challenge in designing an effective composite material is getting the right mix of a
good thermoset resin and high content of glass. The glass fiber is heavier than the resin,
so getting the right mix also creates the best potential for a lighter helmet shell. Most fire
helmets today have a glass content of approximately 50%.
High Performance Thermoplastics
Until relatively recently, it was possible to obtain either great heat resistance or great
impact resistance, but not both in the same material. Thanks to new thermoplastic
advancements, thermoplastics can now exhibit a high quality surface finish, impact
resistance and heat resistance. While today’s advanced thermoplastics can perform at
temperatures exceeding 500˚ F (260˚ C), thermoplastics can be sensitive to some chemical
solvents.
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