Impregnation epoxy resins

Figure 36. Limiting oxygen index (LOI) of flammability resistance for carbon/carbon composites and related hybrid composites with epoxy resin impregnant, as functions of bulk density and resin content (64).

EpoceL [PallCoip.] Epoxy resin impregnated, cellulose paper filter medium. 

Keywords TRC, Textile Reinforced Concrete, epoxy resin, impregnated, ventilated fa9ade, sandwich fa ade... 

Williams N H (1967) Curing epoxy resin impregnated pipe at 2450 MHz, J Microw Power Electromagn Energ 2 123-127. 

CEM-3, a composite of dissimilar core materials, uses an epoxy resin impregnated, non-woven fiberglass core with epoxy resin impregnated, woven fiberglass cloth surface sheets. It is higher in cost than CEM-1, but is more suitable for plated through holes. CEM-3 has been used in early home computers, automobiles, and home entertainment products. 

The rotor coils are installed in the winding slots in the rotor body with conductor insulation of epoxy resin-impregnated glass fiber fabric between each conductor layer. The spaces at the side of the rotor coils function as ventilation chaimels. 

The elements thus formed are then inserted into a sheet steel container, vacuum dried and impregnated, with suitable non-PCB dielectric, which may be an oil dielectric or epoxy resin. The capacitor shell is then hermetically sealed, in oil dielectrics, to avoid any leakage of dielectric during operation. 

Until the 1970s the chemical used as the impregnating and dielectric medium for capacitor units was PCB (polychlorinated biphenyl) liquid. It was found to be toxic and unsafe for humans as well as contamination of the environment. For this reason, it is no longer used. The latest trend is to use a non-PCB, non-toxic, phenyl xylyl ethane (PXE-oil), which is a synthetic dielectric liquid of extremely low loss for insulation and impregnation of the capacitor elements or to use mixed polypropylene or allpolypropylene (PP) liquids as the dielectric. A non-oil dielectric, such as epoxy resin, is also used. 

Because carbon fibers of different diameters are available and because construction parameters can be varied, it is possible to engineer composites having desired characteristics. By varying the orientation, concentration, and type of fiber, materials can be developed for specific applications. The fibers can be layered at different angles to minimize directional differences in properties. Also, layers of fibers can be impregnated with epoxy resin to form sheets that can be shaped prior to polymerization of the resin. 

Essentially polymer-film capacitors comprise dielectric films (polymer or paper or both together) interleaved with aluminium electrodes, either as aluminium foil or, more commonly, in the form of a layer evaporated directly on the dielectric, and rolled together. They are sealed in an aluminium can or in epoxy resin. Because the dielectric films and evaporated electrodes have thicknesses of only a few microns and about 0.025 /mi respectively, volumetric efficiencies can be high. The dielectric films are polystyrene, polypropylene, polyester, polycarbonate or paper paper dielectrics are always impregnated with an insulating liquid. 

Because of their excellent processing characteristics, especially for impregnating wound coils or fabrics, epoxy resins have been widely used for cryogenic temperature applications. There are many different types of epoxy resins available. 

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

Figure 35. Mechanical properties of carbon/carbon epoxy-resin hybrid composites, compared with the properties of the composite skeletons before resin impregnation (61,62). The composite skeletons were prepared from Sigrafil HM 3 PAN-based fiber, rigidized with a phenolic resin, and densified by four cycles with coal-tar pitch plus sulfur the carbonization temperature was 1000°C. (a) Young s modulus.

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