Graphite electrodes are composed of a mixture of finely divided, calcined petroleum coke mixed with about 30% coal tar pitch as a binder, plus proprietary additives unique to each manufacturer. This mixture is extruded at approximately 220°F, the softening temperature of pitch, to form a cylindrical rod known as a "green electrode". The green electrode is now given a controlled bake in a reducing atmosphere at temperatures as high 1800°F and again impregnated with pitch to increase its strength and density and lower the electrical resistivity. The electrodes are now ready to be graphitized, i.e. converting the amorphous carbon into crystalline graphite. This is accomplished by passing an electric current through them and heating them to as much as 5000°F. The graphitizing consumes as much as 3000-5000kWH/ton of electrode. The final product is strong, dense, and has a low electrical resistivity. Lastly the electrode is machined to its final shape. Into each end of the electrode is a recess in which threads are machined. These are used to accept a threaded nipple manufactured in the same way so that the electrode column can be lengthened as it is consumed.
Electrodes are commonly available in sizes from 15 - 30 inches in diameter varying lengths to 10 feet. They come in three grades: regular and premium and the newer DC grade. Historically, electrode consumption has been as high as 12-14 pounds per tons of steel, but through continuous improvement in electrode manufacturing and steelmaking operations, this has been reduced to the neighborhood 3.5 to 4.5 pounds per ton. Most electrode consumption is through oxidation and tip sublimation, with some small pieces lost around the connecting joint. A considerable portion is also lost to mechanical breakage caused by scrap scrap cave-ins in the furnace or crushing the electrode into the charge.
Refractory like Magnesia carbon bricks for electric arc furnace, ladle furnace, high quality fused magnesia and high purity flake graphite as raw material,organic is added as binding,and a certain quantity antioxidant agent is also added.
|MgO (% )≥||80||78||76|
|Apparent Porosity( %) ≤||5||5||5|
|Cold Crushing Strength (Mpa) ≥||40||40||40|
|Thermal modulus rupture(MPa) (1400ºC×0.5h)≥||12||12||12|