Electrical and mechanical applications of molded graphite

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:

– Brushes for electric motors

– Current-collecting shoes for railroad conductor rails

– Heating elements for high-temperature furnaces

– Electrodes for lighting, electrical-discharge machining, and electric-arc furnaces.

– Fuel-cell components

– Anodes, cathodes, and buss bars of zinc-chloride, zinc-bromide, and other advanced batteries.

Mechanical applications: Fine-grain, high-density, and low-porosity molded graphite is extensively used for bearings and seals, particularly in high-temperature applications where conventional liquid lubricants degrade rapidly. It has excellent lubricating and frictional properties, it is chemical resistant, its high thermal conductivity helps dissipate the heat generated by rubbing action and, at high temperature, its compressive strength is superior to that of most other engineering materials.

However molded graphite can’t be used to seal materials that would attack it chemically, such as aqua regia, perchloric acid, and oleum. Sealing failure may also occur with abrasive materials such as chromic acid, chromic oxide, chrome plating compounds, potassium dichromate, sodium chromate, and sodium dichromate.

The following is a partial list of current commercial applications of bearing and seals:

– Seal rings for gas-turbine engines to protect compressor-shaft bearing and engine oil system for 600C gases, at rubbing speed of 150 m/s and 10,000 hours service.

– Seal rings in chemical pumps for corrosive-fluid transfer with a rubbing speed of 15m/s, operating up to 100C for 10,000 hours.

– Seal rings for water pumps of industrial and truck diesel engine, operating at 120C and 0.18 N/mm2 for 20,000 hours.

– Seals rings for automobile freon air compressor for air conditioning, operating up to 1.75 N/mm2 and 93C.

– Seal rings for home washing machine and dishwasher water pumps, operating at 0.28 N/mm2 and to 66C for 10 years.

– O-rings for cylinder heads of race-car engines.

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.

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


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