Common indicators of graphite electrode

Resistivity, bulk density, mechanical strength, coefficient of thermal expansion, elastic modulus and so on are the main indexes to measure the quality of graphite electrode. The oxidation resistance and thermal shock resistance of graphite electrodes in use are related to the above indicators, and the accuracy of the machined products and the reliability of the connection are also important inspection items.

The quality of graphite electrodes depends on the performance of raw materials, process technology, management and production equipment, of which the performance of raw materials is the primary condition. Ordinary power graphite electrode, produced by ordinary grade petroleum coke, has low physical and mechanical properties, such as high resistivity, large linear expansion coefficient and poor thermal shock resistance, so the allowable current density is low.

● Resistivity

The resistance of a conductor to the passage of electric current. Numerically equal to the resistance of a conductor of length 1m and cross-sectional area 1m2 at a given temperature, reducing consumption in use. Usually measured by voltage drop method, the resistivity can measure the graphitization degree of graphite electrode, the lower the resistivity of graphite electrode, the higher the thermal conductivity, the better the oxidation resistance.

High-power graphite electrodes are produced from high-quality petroleum coke (or low-grade needle coke), and their physical and mechanical properties are higher than those of ordinary power graphite electrodes, allowing greater current density. Ultra-high power graphite electrodes must be produced using high grade needle coke. The joint quality of high power and ultra-high power graphite electrodes is particularly important. Not only the electrical resistivity and linear expansion coefficient of the joint blank are smaller than those of the electrode body, but also the joint blank should have higher tensile strength and thermal conductivity. In order to enhance the reliability of the electrode connection, the connector should be equipped with connecting bolts.

● Bulk density

Increasing bulk density is beneficial to reduce porosity, improve mechanical strength and improve oxidation resistance. However, if the packing density is too large, the thermal shock resistance will decrease. Other measures should therefore be taken to remedy this deficiency. Such as raising graphitization temperature to improve the thermal conductivity of electrodes and using needle coke as raw material to reduce the thermal expansion coefficient of finished products.

● Mechanical strength

The mechanical strength of graphite electrode is divided into three kinds: compressive strength, bending strength and tensile strength. The bending strength is mainly determined. The bending strength is a performance index related to fracture of graphite electrode in use. In the electric furnace, when the electrode is in contact with a non-conductive object, or due to collision collapse, strong vibration and other reasons, the graphite electrode is often in danger of being broken, and the graphite electrode with high bending strength is not easy to be broken.

● Modulus of elasticity

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 larger the modulus of elasticity, the greater the elastic deformation to produce the required stress, the larger the modulus of elasticity of brittle materials, and the smaller the modulus of elasticity of flexible materials.

● Thermal expansion coefficient

The thermal expansion coefficient of graphite is a very important parameter affecting the thermal performance of the electrode. The lower the value, the stronger the thermal stability of the domestic product, the higher the oxidation resistance, the less the performance breakage and the lower the consumption.more