The kneading process is an important link that cannot be ignored in the homogeneous ultra-high power graphite electrode.
The main indicators of asphalt are softening point, coking value, and adhesion. The softening point of bonded asphalt used in U.S. carbon plants is about 110 ℃ (test method: air stereo). Germany vet production of bonded asphalt softening point at about 109 ℃, bonded asphalt coking value is generally about 55%. The ρ content of Japanese asphalt is around 20%, slightly lower than the U.S. asphalt. When using this kind of asphalt, the proportion of asphalt should be controlled. A high-power graphite electrode only needs to be impregnated once, so high-quality asphalt with high softening point and high coking value must be used as the binder to produce high-power graphite electrodes to achieve short-process production (less impregnation and less roasting).
During the kneading process of graphite electrode paste, the temperature affects the kneading effect and product quality. During the paste kneading process, pitch with a certain rheological property evenly penetrates the surface of the carbon-containing particles. Part of the pitch penetrates the internal voids (through holes and cavities) of the carbon-containing material, which can further improve the density and cohesiveness of the paste. Suppose the rheological properties of asphalt are adjusted to the best—the greater the permeability, the better the kneading effect. However, suppose the kneading temperature of the paste is too low. In that case, the rheological properties of the pitch will be poor, and it will be difficult to penetrate the voids of the carbonaceous material. At this time, the asphalt is difficult to mix and get out of the pot, and the plasticity of the paste is poor, which is not conducive to forming. If the kneading temperature is too high, the light components of the asphalt will become wet and cohesive, which are volatile and prone to condensation reactions. The asphalt adhering to the surface of the carbonaceous material is oxidized, the adhesion of the asphalt is reduced, the plasticity is poor, and the paste is formed. If the rheological properties of the asphalt are not good, the wetting and bonding effect of the asphalt cannot be guaranteed.
Therefore, the optimal kneading temperature of the asphalt mixture should be within the temperature range where the rheological properties of the asphalt are good and the asphalt composition remains unchanged. In this temperature range, the greater the wettability of the asphalt to solid carbon materials, the better the rheological properties of the asphalt. The more uniform the kneading of the asphalt paste, the better the plasticity. The final product reaches the ideal density, strength, and other physical and chemical indicators, which improves the yield and reduces the increased cost due to the increase in the number of dipping.