Electrode paste requirements for raw materials
The raw material for making electrode paste is composed of solid carbon material and binding material. The quality of the electrode paste is related to the material formula and process. Solid materials include anthracite, metallurgical coke, petroleum coke and pitch coke, and graphite electrode scraps. Anthracite is dense, high in carbon content, low in volatile matter and low in price. Adding anthracite can improve the electrical conductivity and thermal conductivity of the electrode. The binding materials are pitch and tar. Tar is added to adjust the softening point. The binder in the electrode paste decomposes and removes volatiles during the sintering process, and the residual carbon is transformed into a strong coke net, which has a coking effect, making the electrode a hard whole.
Anthracite requires less than 8% ash, less than 5% volatiles, and low sulfur content. It is necessary to use a shaft furnace or a rotary kiln to calcinate at a high temperature of 1473K for 18-24 hours under the condition of air isolation to remove volatile components, increase thermal stability and electrical conductivity, and greatly improve the mechanical strength.
Petroleum coke is made from petroleum residue oil through coking. The ash content of both cokes is required to be less than 1%. The volatile content of pitch coke is usually less than 1%, while the volatile content of petroleum coke is less than 7%. Both cokes need to be calcined before they can be used. Coal pitch is a residue with a boiling point greater than 633K obtained from the preliminary fractionation of tar refining oil. It is commonly known as asphalt. According to its softening point, it is divided into hard pitch, medium pitch and soft pitch.