Large cylinders of synthetic graphite, joined end to end by threaded pins, that conduct the current into an electric arc furnace or ladle furnace and strike the arc that melts the charge. They are consumed as the furnace runs — around 1–2 kg per tonne of steel — so every EAF plant buys them continuously.
Also called
Graphite electrodes
UHP electrodes
HP electrodes
RP electrodes
Electrode nipples
Electrode pins
Needle coke
Carbon raiser
Graphite recarburiser
Graphite blocks
Carbon electrodes
AR
أقطاب الجرافيت ومنتجاته
ZH
石墨电极及石墨制品
DE
Graphitelektroden und Graphitprodukte
FR
Électrodes et produits en graphite
ES
Electrodos y productos de grafito
IT
Elettrodi e prodotti in grafite
TR
Grafit elektrotlar ve ürünleri
RU
Графитированные электроды и изделия из графита
Main formsElectrodes with pre-set or separate nipples (pins); graphite blocks and shapes; graphite carburiser
Typical sizesDiameter 75–800 mm (EAF mainly 400–750 mm); length about 1,500–2,700 mm
Main standardsIEC 60239 (dimensions and designation); producers' grade specifications
Key gradesUHP (ultra-high power), HP (high power), RP (regular power)
A graphite electrode is made from petroleum or coal-tar needle coke, bound with pitch, extruded into a cylinder, baked, impregnated with pitch and rebaked to close the pores, and finally graphitised — heated electrically to about 3,000 °C — which turns the carbon into graphite with high electrical and thermal conductivity and great resistance to thermal shock. The ends are machined with tapered sockets, and a threaded nipple (pin) of higher-grade graphite joins one electrode to the next, so a column can be added to from the top as it burns away at the tip.
Grades follow the power the furnace puts through them. UHP electrodes, made with premium needle coke, carry the very high current densities of modern AC and DC arc furnaces; HP grades serve medium-power furnaces and ladle furnaces; RP grades smaller and older furnaces and foundry use. Electrode consumption — from tip oxidation, sublimation in the arc and breakage — is one of an EAF's key cost figures and has fallen to around 1–2 kg per tonne of steel in efficient plants.
Graphite in other forms is also bought by steel plants: graphite and electrode scrap crushed into carburiser (recarburiser) to raise carbon in the bath, graphite blocks and plates for moulds and furnace parts, and carbon and graphite cathode blocks for aluminium smelting.
Because the GCC's steel is made in electric furnaces, the region is a large and steady electrode market: every melt shop and ladle furnace in Saudi Arabia, the UAE, Qatar, Oman, Kuwait and Bahrain uses them. Electrodes are imported, mainly from China, India, Japan, Europe and the USA, and a column's diameter and grade are fixed by the furnace's design.
Forms & sizes
Common EAF diameters
350, 400, 450, 500, 550, 600, 650, 700 and 750 mm (14–30 in); 800 mm for the largest furnaces
Ladle furnace diameters
Typically 250–450 mm
Lengths
1,800, 2,100, 2,400 and 2,700 mm for large diameters; shorter for small electrodes
Nipples (pins)
Tapered threaded connectors, 3 or 4 threads per inch, supplied loose or pre-set in one end
Carburiser
Graphitised petroleum coke and graphite scrap, 0.2–5 mm, fixed carbon about 98–99%
Standards & grades
Electrode grades are producers' own specifications; the international standard fixes dimensions so that electrodes from different producers fit one column.
Region
Standard
What it covers
International
IEC 60239
Graphite electrodes for electric arc furnaces — dimensions and designation of electrodes and nipples
Common grades
UHP
Premium needle coke; low resistivity, high strength, for high-power AC and DC furnaces
HP
Medium-power furnaces and ladle furnaces
RP
Regular power — small and older furnaces, foundries
Nipple grade
Higher strength and lower resistivity than the electrode body, matched to it
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