Applications of molded graphite

In the last twenty yeeu or so, several major applications of molded graphite have developed into an important, complex, and diverse industrial market. Because of this diversity, the classification of these applications is a critical factor if a proper perspective of the industry is to be obtained. 

Electrodes for the Production of Electric-Arc Steel. As shown in Table 5.11, the production of electrodes for steel eind aluminum processing is the largest application of molded graphite, in terms of both tonnage and dollars. As mentioned in Sec. 1.1, electrodes are one of the original applications and have been manufactured with essentially the same process for almost a century. 

Other Molded Graphite Applications in Semiconductor Processing. The following is a partial list of current applications of molded graphite in semiconductor processing... 

Electrical applications of molded graphite are well established and the material has been a standard for many years due to its chemical inertness, good electrical conductivity and ability to withstand the heat of electrical arcing with minimum damage. The following is a list of current applications ... 

Other mechanical applications of molded graphite include glass-lehr roll bearings, roller bearings for jet-engine exhaust nozzles, metering seats for gasoline pumps, vane pumps for air compressors, rupture disks, and many others. 

The basic process was invented by E. G. Acheson, who produced the first molded graphite in 1896. The original eipplications of molded graphite were electrodes for electric-arc furnaces and movie projectors. Many improvements have been made since then and the applications have increased considerably in scope. Molded graphite is found in almost every comer of the industrial world and forms the base of the traditional graphite industry. 

The thermal expansion of molded graphite is an important property since many applications involve high temperature, and expansion values must be known accurately. 

The technology of molded graphite is versatile, improvements in the manufacturing techniques are continuously made and the scope of applications is gradually expanding. This expansion is the direct result of asizeable research effort carried out by many workers in universities, government laboratories, and industry. 

Electrodes for Aluminum Production. Aluminum is processed electrolytically and the production of the necessary electrodes is the second-largest application of molded greiphite (see Table 5.11 above) The anodes are similar to those used in electric-arc steel production and are also manufactured from petroleum-coke filler and coal-tar pitch. The aluminum collects at the cathodes which are large blocks lining the electrolytic cell. These cathodes were originally made of baked carbon based on anthracite coal but, in recent years, have been upgraded and are now made of molded graphite from petroleum coke. 

A specialized group of applications is found in aerospace systems which include rocket nozzles and reentry nose cones (shown in Fig. 5.16) where the performance of molded graphite has been excellent, due to its high-temperature strength and resistance to erosion and thermal-shock (see Ch. 9). 

For hundreds of years sticky surfaces have been dusted with powder (e.g., talc) to keep them separated. Talc is broadly used in cable and profile extrusion to obtain a smooth surface. Similarly, in injection molding, the application of aluminum trihydroxide gives a better surface finish. Talc, CaCOs, and diatomite provide anti-blocking properties. Graphite and other fillers decrease the coefficient of friction of materials. PTFE, graphite and M0S2 allow the production of self-lubricating parts. Here, PTFE, a polymer in powder form, acts as a filler in other polymers. Matte surfaced paint is obtained by the addition of silica fillers. 

Molded graphite, being black, has high emissivity, which is an important advantage in high-temperature applications. Table 5.10 lists the total emissivity of several carbon and graphite materials and selected metals for comparison.I i... 

Melting, Smelting, and Casting of Metals. Molded graphite has numerous e iplications in the processing of ferrous and non-ferrous metals and alloys such as copper, copper-nickel, brass, bronze, zinc, aluminum alloys, nickel and its alloys, precious metals, and grey and ductile irons.l°ll °l The wide variety of these applications is shown in the following partial list ... 

In some of these applications, it is necessary to coat the surface of the molded graphite with a more inert coating such as pyrolytic graphite, boron nitride (BN) or silicon carbide (SiC), to prevent contamination and reaction with the graphite at high temperature. The coating is usually done by CVD as reviewed in Ch. 7. 

Molded graphite is one of the best material for nuclear-fission applications since it combines high neutron-moderating efficiency and a low neutron-absorption cross section, good mechanical strength and chemical resistance, ease of machinability, and relatively low cost. ... 

Many potential applications of carbon fibers in batteries have been reported but their inherent high cost compared to conventional electrode materials such as graphite powder, porous carbon, and molded carbon have precluded their use in commercial applications so far (see Ch. 10, Sec. 3.0). PI... 

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