Graphite electrodes are mainly used in the electric arc furnace (EAF) steelmaking process to melt scrap steel. The electrode is made of graphite because it can withstand high temperatures. In an electric arc furnace, the tip of the electrode can reach 3,000 degrees Fahrenheit, which is half the surface temperature of the sun. The size of the electrode varies greatly, ranging from 75 mm in diameter to a maximum of 750 mm, and the longest can reach 2800 mm.
The main indicators of graphite electrode quality and performance are: bulk density db, electrical resistivity ρ, bending strength, elastic modulus E, thermal expansion coefficient α and ash content A%. According to these indicators of graphite electrodes and the differences between different national standards and manufacturing processes of raw materials, graphite electrodes are divided into ordinary power graphite electrodes (RP), high power graphite electrodes (HP), and ultra-high power graphite electrodes (UHP). The post-graphite electrode production plant can add high-density graphite electrodes (HD) and quasi-super-high graphite electrodes (SHP) according to the functional requirements of different users.
On the basis of national standards, each company has its own corporate standards, and customers will make their own order of quality standards. The relative volume density is the ratio of the quality management of the graphite electrode material sample to its volume. The unit is g/cm3. The larger the volume density, the denser the working electrode, which is positively related to the strength and the performance of the anti-oxidation system. Generally speaking, The greater the influence of the volume density of the same type of electrode, the lower its resistivity.
Resistivity is a parameter for measuring electrode conductivity. It refers to the resistance of the conductor to the current when the current passes through the conductor. The value is equal to the resistance of a conductor with a length of 1m and a cross-sectional area of 1m2 at a certain temperature, which reduces consumption during use.
The flexural strength is a parameter that characterizes the performance of the mechanical system of the graphite structure material. It is also called the flexural strength. It means that when the external force is perpendicular to the axis of the object, the object will bend to the instantaneous limit caused by the external force to resist the risk. Capacity, the unit is MPa. High-strength electrodes and joints are less likely to break when using the network.
The modulus of elasticity is an important aspect of mechanical properties. It is an index to measure the elastic deformation ability of a material and refers to the stress-strain ratio within the elastic deformation range. The greater the modulus of elasticity, and the greater the stress required for elastic deformation to generate, it simply, the greater the elastic modulus of brittle materials, the smaller the elastic modulus of flexible materials.
The thermal expansion coefficient of graphite as an electrode is a very important thermal performance parameter. The lower the value, the stronger the thermal stability of Chinese products. The higher the oxidation resistance, the performance can reflect the less fracture and consumption in use, the loss would be less.
Ash refers to other components in solid products other than carbon graphite. As the ash content in the electrode, graphite is directly affected by the ash content of the raw materials used. The ash content of petroleum coke needle coke is low. Therefore, the ash content of graphite passing through the electrode is generally not more than 0.5%, and the ash content within 1% has no effect on steelmaking. Obviously, but the impurity elements in the ash will reduce the performance of the anti-oxidation system of the working electrode, etc.
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