Prepreg

Prepreg is the English abbreviation for preimpregnated fibers ( American: preimpregnated fibers ) to German: " pre-impregnated fibers ". Prepreg called a semi-finished, consisting of continuous fibers with an uncured thermosetting plastic matrix, the esp. in lightweight is employed. The continuous fibers can be present as pure unidirectional lamina as a tissue or scrim. Prepreg sheet form, wound onto rolls delivered.

Prepregs are machinable and therefore are mainly used in automated processes. They produce a uniform and high quality. Advantages are their low undulation and the high fiber volume fraction. By curing at high temperatures, short cycle times are possible. The processing requires a high Investitonsaufwand eg autoclaves, sticking robot, refrigerated warehousing.

Prepregs are not allowed with thermosetting fiber - matrix semi- finished products such as BMC ( Bulk Molding Compound) or SMC (Sheet Molding Compound ) to be confused, which is not continuous fiber fabric but shorter fiber snippets, usually <50 mm, included as fiber content. In the literal translation of the word prepreg it includes all thermoset fiber-matrix semi-finished products. In German-speaking prepreg is mainly used for a continuous fiber- reinforced thermoset semi-finished products.

Areas of application

  • In the aviation industry prepreg is processed in large quantities. While glass-fiber reinforced plastic is used primarily for small aircraft or the main rotor helicopter, the more expensive carbon fibers are increasingly in commercial aircraft and in the military technology of the new generation to the application. So, for example, the Airbus A380 is characterized by a high mass fraction of carbon fiber prepreg.
  • In the automotive industry, little prepreg is processed proportionately. Due to the high price of prepreg molding materials found there such as BMC or SMC application. An exception is the motorsport.
  • Space travel
  • Sports equipment
  • Sailing
  • Orthopedic technology both in orthotics and prosthetics in the
  • In electrical engineering as an "intermediate position " in multilayer printed circuit boards and as an insulating material for electrical machines and transformers
  • With wind turbines for rotor blade

Fiber types

As fiber types all common reinforcing fibers come into question. In practice, however, are mainly

  • Glass fibers
  • Basalt fibers
  • Carbon fibers
  • Aramid fibers

Processed into prepreg.

Matrix

One distinguishes the matrix systems after their curing temperature and the resin type. The curing temperature to a high degree influences the glass transition temperature and thus the use temperature. In military aircraft 180 ° C systems are primarily used.

Composition

The prepreg matrix consists of a mixture of resin and curing agent, in some cases even an accelerator. By freezing at -20 ° C is to prevent the resin reacts with the curing agent. The cold chain is interrupted, the reaction starts, and the prepreg is unusable. However, there are high temperature prepregs, which can be stored at room temperature for a certain time. These prepregs can be cured but only in an autoclave at elevated temperature.

By special ripening process and aggregates the desired stickiness ( tack ) is set. This makes it possible to stack the prepreg on convex shapes.

Resin types

It will be mainly used on epoxy resins. Vinyl ester-based prepregs are also available. Vinyl ester resins as having amine or cobalt accelerator must be preaccelerated their Vearbeitungszeit is shorter than prepregs based on epoxy resin at room temperature. As catalyst ( also called hardener ) are methyl ethyl ketone peroxides such as peroxide (MEKP ), acetylacetone peroxide ( AAP) or cyclohexanone (CHP ) are used. Vinyl ester resin is used at high impact stress.

Processing

Prepregs are cured under elevated temperature. They can be processed by the hot press technique or the Autoclave. In both techniques is increased by the pressure of the fiber volume fraction.

The autoclave technology the best qualities can be produced. The combination of pressure and vacuum components occur with very small air pockets.

Curing can be followed by an annealing process which is used to complete crosslinking.

  • Fiber-matrix semis
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