Instead of using molded parts where each shape and size is built with a specific mold, an advanced method of "pultrusion" was developed and applied for the US Navy LPD amphibious assault vessels and the Military Sealift Command T-AKE replenishment ships. The pultrusion process is based on a continuous production of woven or non-woven fibers, impregnated with resin and pulled through heated die. As depicted below, this method produces 20- to 30-foot long parts of a consistent cross-section. To make these louvers, only three different cross sections were needed: frames, vane blades and spacer bars.
The selection of FRP composite base materials is focused on the type of resin and the type of glass fiber used for structural reinforcement. For military shipboard applications, the primary driver for material selection is the structural requirement to withstand shock and vibration impacts as qualified per US Navy requirements MIL-S-901D and MIL-STD-167-1, respectively.
Resins are available with different chemical compositions such as vinyl ester and the finished parts will be painted to provide a uniform final product that matches the ship’s color. Special paint treatments to create an icephobic surface are used to prevent ice buildup on ships that are deployed in cold weather conditions. Finally, the addition of alumina trihydrate to the base resin enables the components to meet ASTM-E-162 flame spread, ASTM-E-662 smoke generation and ASTM-E-1534 time to ignition and heat release requirements specified by the US Navy.
These shapes are cut to length, have their ends shaped using butted or tongue-and-groove connections, and finally fixed together with epoxy adhesive.