The production of graphite electrodes uses two basic raw materials: calcined petroleum needle coke and coal tar pitch. The manufacturing process is a continuous 24-hour operation that takes 6-8 weeks.
There are six distinct steps to make graphite electrodes:
UHP graphite electrodes are made in a wide range of sizes. Outside China the most widely used size is 24 inches, or 600 mm, in diameter. Showa Denko K.K. estimates this size represents about 40% of total demand ex-China. It is also the diameter most commonly produced by the company.
Graphite electrodes come in standard lengths up to 3,000 mm. Lengths longer than that are sometimes produced to meet specific customer requests. If asked by its customers, SDK can supply 3,600 mm long electrodes. Nearly all of its clients use standard-size electrodes, but some of them need a special length due to furnace or meltshop designs and clearances. The company claims to be the largest producer of supersize graphite electrodes in the world: 26-32 inches (650-800 mm) in diameter. The largest (32 inch) electrodes can carry average phase currents of over 130 kA for AC EAFs and over 160 kA for DC.
SDK sells graphite electrodes that are typically pre-set with a connecting pin, which allows one electrode to be joined together with another. In an EAF, three electrodes are typically joined together to form a column, with new electrodes added to the top of a column as electrodes are consumed upwards from the tip. In a DC furnace, one column is used, but in an AC furnace three columns are used simultaneously.
The rate at which graphite electrodes are consumed in an EAF depends on the steelmaking or other raw materials used, the grades of steel being produced, and the amount of supplemental (chemical) energy used. EAFs typically consume electrodes at a rate of around 2 kg per tonne of steel produced, with some specialty steel applications consuming at a slightly higher rate.