Electrical Electronic

The electrical and electronic industry continues to be not only one of the major areas for plastic applications, but a necessity in many applications worldwide with their many diversified electrical performance capabilities. They principally provide dielectric or insulation capabilities. The field can be a steady direct current (DC) field or an alternating current (AC) field and the frequency range may vary such as from 0 to 1010 Hz.

The usual plastics are good insulators, however there are plastics that conduct electricity using certain plastics but more so by the addition of fillers such as carbon black and metallic flake. The type and degree of interaction depends on the polarity of the basic plastic material and the ability of an electrical field to produce ions that will cause current flows. In most applications for plastics, the intrinsic properties of the plastics are related to the performance under specific test conditions.

The properties of interest are the dielectric strength, the dielectric constant at a range of frequencies, the dielectric loss factor at a range of frequencies, the volume resistivity, the surface resistivity, and the arc resistance. The last three are particularly sensitive to moisture content in many materials. These properties are determined by the use of standardized tests such as those described by ASTM or UL. The properties of the plastics are temperature and/or moisture dependent as are many of their other properties. Temperature and/or moisture dependence must be recognized to avoid problems in electrical products made of plastics.

Electric currents can vary from fractions of a volt such as in communications signals to millions of volts in power systems. The currents carried by the conductor range from microamperes to millions of amperes. With this wide range of electrical conditions the types of plastic that can be used are different; no one plastic meets the different operating conditions. The selection of the materials and the configuration of the dielectric to perform under die different voltage, current, and frequency stresses are the primary design problem in electrical applications for plastics.

The dielectric materials interact with the electrical fields and alter the characteristics of the electric field. In some cases this is desirable and in others it is deleterious to the operation of the system and must be minimized. Both the selection of the plastic and the configuration of the dielectric can meet required performances.

An important area for the use of plastics in electrical applications is at the terminations of the conductors. The connectors that are used to de the wires into the equipment using the power, or used to connect the wires to the power source, are rigid members with spaced contacts. These are designed to connect with a mating unit and to the extension wires. The other type of wire termination is terminal boards where there are means to secure the ends of the wire leading to the equipment and the internal wiring in the equipment. These termination units require adequate dielectric strength to resist the electric field between the conductors, good surface resistivity to prevent leakage of current across the surface of the material of the connector, good arc resistance to prevent permanent damage to the surface of the unit in case of an accidental arc over, and good mechanical properties to permit accurate alignment of the connector elements so that the connectors can be mated properly.

Electrical devices often require arc resistance, as a high current, high-temperature will ruin many plastics. Some special arc resisting plastics are available. The most serious cases may require cold mold, glass-bonded mica, or mineral-filled fluorocarbon products. Lesser arcing problems may be solved by the use of polysulfone, polyester glass, DAP-glass, alkyd, melamine, urea, or phenolics. With low-current arcs, general-purpose phenolic and glass-filled nylon or polycarbonate, acetal, and urea may be used very satisfactorily. A coating of fluorocarbon film will improve arc resistance in some cases. All circuit breaker problems must be scrutinized with respect to product performance under short-circuit conditions and mechanical shock.

Electromagnetic interference (EMI) or radio frequency interference (RFI) as well as static charge is the interference related to accumulated electrostatic charge in a nonconductor. As electronic products become smaller and more powerful, there is a growing need for higher shielding levels to assure their performance and guard against failure. Conductive plastics provide EMI/RFI shielding by absorbing electromagnetic energy (EME) and converting it into electrical or thermal energy.

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