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Pre-preg is a term for "pre-impregnated" composite fibers where a matrix material, such as epoxy, is already present. The fibers often take the form of a weave and the matrix is used to bond them together and to other components during manufacture. The matrix is only partially cured to allow easy handling; this is called B-Stage material and requires cold storage to prevent complete curing. B-Stage pre-preg is always stored in cooled areas since heat accelerates complete polymerization. Hence, composite structures built of pre-pregs will mostly require an oven or autoclave to cure.
There are several advantages and disadvantages of the B-Stage pre-preg process in comparison to the hot injection process. Pre-preg allows one to impregnate the fibers on a flat workable surface, or rather in an industrial process, and then later form the impregnated fibers to a shape which could prove to be problematic for the hot injection process. Prepreg also allows one to impregnate a bulk amount of fiber and then store it in a cooled area for an extended period of time to cure later. Unfortunately the process can also be time consuming in comparison to the hot injection process and the added value for pre-preg preparation is at the stage of the material supplier.
Recent advances in Out-of-Autoclave (OOA) processes hold promise for improving performance and lowering costs for composite structures. Using vacuum-bag-only (VBO) for atmospheric pressures, the new OOA processes promise to deliver the less than 1 percent void content required for aerospace primary structures. Led by material scientists at Air Force Research Lab, the technique would save the costs of constructing and installing large structure autoclaves ($100M saved at NASA) and making small production runs of 100 aircraft economically viable.
- "Out-of-autoclave prepregs: Hype or revolution?". Composites World. Retrieved 2011-01-03.
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