CARBON FIBER

 HISTORY

  • The aerospace industy was among the first to realize the benefits of composite materials.
  • The Voyager, which without refueling in 1986 , was constructed from graphite and aramid-reinforced plastics.

INTRODUCTION

  • Airplanes , rockets, and missiles all fly higher, faster, and farther with the help of composites.
  • The major reasons for the use of composite materials in spacecraft applications include weight savings as well as dimensional stability in wide range of temperature variation from -100 to +100.
  • Carbon-epoxy composite laminates can be designed to give zero coefficient of thermal expansion.
  • Although the terms 'carbon' and 'graphite' are used interchangeably.
  • The term carbon is used for any fiber carbonized to 90% or more.
  • Graphite fibers are more accurately defined as fiber that are carbonized around 99%.

APPLICATIONS

  • These fibers are used to reinforce polymers in the constuction of strong, rigid, lightweight and highly durable products such as car bodies, bicyles, golf club shafts, tennis rackets, fishing rods, firemen's suits, aircraft for space exploration etc.
In recent years, carbon fibers have become the leading reinforcement for high-performance composites. The less expensive carbon fibers produced from pitch have broadened the markets for these reinforcements.

MANUFACTURING

  • Carbon fibers are produced using PAN- based or pitch-based precursors. The precursor undergoes a series of operations.
  • Polyacrylonitrile and rayon fibers are most commonly used as starting materials.
  • In the first step, the precursors are oxidized by exposing them to extremely high temperatures.
  • Later, they go through carbonization and graphitization processes.
  • PAN-based carbon fibers are produced by the pyrolysis of polyacrylonitrile cyclizes at about 570 Fahrenheit and remains stable up to about 1290 Fahrenheit.
  • PAN-based fibers are most widely used for the fabrication of carbon fibers while pitch-based fibers (obtained from spinning purified petroleum or coal tar pitch) are stiffer and more brittle.
  • The temperature of formation is 1315 Celsius for fibers formed from PAN , while the graphite fibers are formed at 3450 Celsius.
  • The carbon fibers have also surface voids which are filled by surface treatment with a low-chain-length epoxy resin.

PROPERTIES

  • The diameter of carbon fiber is 5-8um , aramid fiber is 12.5um.
  • By elemental analysis, PAN-based carbon fibers contain 93-95% C , whereas graphite fibers contain up to 99% C.
  • Strength and modulus range depends on the grades.
  • Ranging from 1.7 to 3.5 GPa for strength & 230 to 830 GPa for modulus.

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