Electrical arc resistance

Electric arc resistance heated furnaces and electrical melting units are mainly used for refractory ceramic fibers, due to the high melting temperatures of the raw materials. In ovens with resistance heating the melt itself acts as the electrical resistance, since silicate melts generally become sufficiently conductive with increasing temperature to transport sufficient current, due to ionic conduction. 

Fillers and additives are specifically added to enhance the specific performance, reduce cost, change viscosity or improve processibility of resin systems (Owens Coming, 2003). Dry fillers usually make up the largest proportion (up to 50 wt%) of a resin formulation. Commonly used fillers in pul-trusion include calcium carbonate as a volume extender, alumina silicate or clay to build corrosion resistance and electrical insulation, and alumina trihydrate for better fiame or smoke retardation and electrical arc resistance. Additives are meant to tailor specific performance or properties. These typically include initiators to influence resin curing, mould release compounds such as metallic stearates or organic phosphate ester, antimony oxide for flame retardance, pigments for coloration and agents for surface smoothness and crack suppression. 

Electrical Arc resistance (trackinsr resistance IEC112) D495 V >600 >600 >600... 

To improve mechanical, physical, chemical, electrical, optical, thermal, or molding performance, additives may be combined with the resin matrix. Reaction catalysts include hexamethylene tetramine for phenolics. Mica, alumina, and silica provide electrical arcing resistance. Halogenated compounds are fire retardants while zinc stearate and wax-Uke materials improve part release from the mold cavity. The molding process is improved through solvent-Uke additives that reduce the charge s viscosity. Wetting... 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

Fig. 1. Main types of electric furnaces (a) resistance furnace, indirect heat (resistor furnace) (b) resistance furnace, direct heat (c) arc furnace (d) induction furnace. A, charge to be heated or melted B, refractory furnace lining C, electric power supply D, resistors E, electrodes F, electric arc G,...

Due to thek similarity to a-c furnaces, d-c furnaces can be substituted for neatly any a-c furnace including the open-arc, submerged-arc, and arc-resistance furnaces, provided that design criteria, particularly electrical parameters, are properly chosen. Currently, steel and ferrochrome is being made commercially in d-c furnaces and a siUcon metal pilot plant is being built. 

Electric heat provided by a resistance or by an electric arc can be substituted for the burning of a fuel. Electric furnaces can be designed in a variety of shapes and are more versatile than fuel-heated furnaces. The furnace atmosphere can be controlled independently of the chemistry of the combustion... 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

The ultrafine siUcon carbide produced in an electric arc is used as an insulation in cryogenic appHcations (152) (see Cryogenics). It generally increases the wear resistance of the paint film when added to paint formulations. 

Electrical and electronics are the largest end uses for PPS. Principal advantages of PPS are strength at high temperature, dimensional stabiUty, flame and arc resistance, and precision moldabiUty. Products are coimectors, cod bobbins, relays, and switches. The growth of electrical and electronic end uses is 10%. Apphances are the second largest ends uses for PPS resins as a replacement for phenoHc, but also for metal parts. 

High harmonic quantities (as for electric arc and resistance welders and electric arc and induction furnaces)... 

Arc Resistance ASTM D495. When an electric current is allowed to travel across the surface of an insulator the surface will become damaged over time and become more conductive. The arc resistance is a measure of the time (in seconds) required to make an insulating surface conductive under a high-voltage, low-current arc. 

Where plastics are to be used for electrical applications, then electrical properties as well as mechanical and other properties need to be considered. Whilst properties such as resistivity, power factor and dielectric constant are important, they may not be all-important. For example, although polyamides and many thermosetting plastics may show only moderate values for the above properties, they have frequently been used successfully in low-frequency applications. Perhaps more important for many purposes are the tracking and arcing resistance, which are frequently poor with aromatic polymers. 

Special quality steels - A vast range of special quality steels is made in electric arc furnaces by adding other metals to form steel alloys. The most commonly known of these is stainless steel, which has chromium and nickel added to form a corrosion-resistant steel. There are very many others however the very hard steels used to make machine tools, the steels specially formulated to make them suitable for engineering, steels developed to survive for decades the hostile environment of nuclear reactors, light but strong steels used in aerospace, extra tough steels for armor plating - to name but a few. 

Phenolic resins Good acid resistance, good electrical properties (except arc resistance), high heat resistance Compression molding, continuous lamination... 

Chromium, Cr, is a bright, lustrous, corrosion-resistant metal. Its name, which comes from the Greek word for color, was inspired by its colorful compounds. The metal is obtained from the mineral chromite, FeCr204, by reduction with carbon in an electric arc furnace ... 

The Subpart O standards apply to units that treat or destroy hazardous waste and which meet the definition of an incinerator. An incinerator is any enclosed device that uses controlled flame combustion and does not meet the criteria for classification as a boiler, sludge dryer, carbon regeneration unit, or industrial furnace. Typical incinerators1 2 3 include rotary kilns, liquid injectors, fixed hearth units, and fluidized bed incinerators (Table 23.1). The definition of an incinerator also includes units that meet the definition of an infrared incinerator or plasma arc incinerator. An infrared incinerator is any enclosed device that uses electric-powered resistance as a source of heat and which is not listed as an industrial furnace. A plasma arc incinerator is any enclosed device that uses a high-intensity electrical discharge as a source of heat and which is not listed as an industrial furnace. 

We can define the principal electrical properties of polymers in terms of four characteristics electrical resistance, capacitive properties, dielectric strength, and arc resistance. We can change the surface characteristics of a polymer by subjecting it to a corona discharge generated by a strong electrical field. Lastly, we must also consider the influence of other physical properties on the application of polymers in electrical applications. 

The arc resistance of a polymer is the length of time for which we can apply an electrical discharge to its surface before it breaks down and begins to conduct electricity. Breakdotvn typically takes the form of conductive carbonaceous tracks that are caused by oxidation due to locally high temperatures. Polymers -with lowpolarity typically fare better in this test than polar polymers. Arc resistance is reduced by dirt, moisture, and other surface contaminants. 

It responds well to a wide range of hydrocarbon fires and is blind to welding arcs except when very close to the detector. It can see through smoke and other contaminates that could blind a UV detector. It generally ignores lightning, electrical arcs and other forms of radiation. It is blind to solar radiation and resistant to most forms of artificial lighting. 

---