Based on differences in raw materials and the physicochemical properties of the finished product, graphite electrodes are classified into: regular‑power graphite electrodes (RP), high‑power graphite electrodes (HP), and ultra‑high‑power graphite electrodes (UHP).

The primary performance indicators for graphite electrodes include electrical resistivity, bulk density, mechanical strength, thermal expansion coefficient, and elastic modulus. The oxidation resistance and thermal shock resistance of graphite electrodes during service are closely related to these parameters, while the dimensional accuracy, machining quality, and joint reliability are also critical evaluation criteria.

● Resistivity

The resistance of a conductor to the flow of electric current. Numerically, it equals the resistance of a conductor 1 meter long with a cross-sectional area of 1 square meter at a specified temperature, thereby reducing energy losses during operation. It is typically measured using the voltage-drop method. The resistivity of a material serves as an indicator of the degree of graphitization in graphite electrodes: the lower the resistivity, the higher the thermal conductivity and the better the oxidation resistance.

● Bulk density

Increasing the bulk density helps reduce porosity, enhance mechanical strength, and improve oxidation resistance. However, if the tapped density becomes excessively high, thermal shock resistance will deteriorate. Therefore, additional measures should be implemented to address this drawback, such as raising the graphitization temperature to increase the electrode’s thermal conductivity and using needle coke as a raw material to lower the finished product’s coefficient of thermal expansion.

● Mechanical strength

The mechanical strength of graphite electrodes is classified into three types: compressive strength, flexural strength, and tensile strength. Flexural strength is the primary property measured, as it reflects the electrode’s resistance to fracture during service. In electric furnaces, graphite electrodes are prone to breakage when they come into contact with non-conductive materials or due to impacts, collapses, or severe vibrations; therefore, electrodes with high flexural strength are less likely to fracture.

● Elastic modulus

The elastic modulus is an important aspect of mechanical properties. It is a measure of a material’s ability to undergo elastic deformation, defined as the ratio of stress to strain within the elastic deformation range. A higher elastic modulus corresponds to greater elastic deformation for a given stress; brittle materials generally have higher elastic moduli, while ductile materials have lower ones.

● Coefficient of thermal expansion

The thermal expansion coefficient of graphite is a critically important parameter influencing the thermal performance of electrodes; the lower this value, the greater the thermal stability and oxidation resistance of domestically produced materials, resulting in reduced performance degradation and lower consumption during operation.

The quality of graphite electrodes depends on the properties of the raw materials, the manufacturing process, management practices, and production equipment, with the characteristics of the raw materials being the primary factor. For standard‑power graphite electrodes, which are produced using ordinary‑grade petroleum coke, the physical and mechanical properties are relatively poor—manifested in high resistivity, a large linear thermal expansion coefficient, and poor resistance to thermal shock—resulting in a lower permissible current density.

High‑power graphite electrodes are manufactured using high‑quality petroleum coke (or low‑grade needle coke), and their physical and mechanical properties surpass those of standard‑power graphite electrodes, permitting higher current densities. Ultra‑high‑power graphite electrodes must be produced with premium needle coke. For both high‑power and ultra‑high‑power graphite electrodes, joint quality is of paramount importance. Not only should the joint billet exhibit lower resistivity and a smaller linear thermal expansion coefficient than the electrode body, but it must also possess higher tensile strength and thermal conductivity. To enhance the reliability of electrode connections, connectors should be equipped with connecting bolts.