How to Control the Paste Kneading Temperature?

The kneading temperature is the main factor affecting the kneading effect. The kneading temperature can be divided into two temperature concepts of heating medium temperature and paste temperature. Under fixed heating conditions, the temperature of the heating medium can be regarded as stable. The temperature of the heating medium is mainly determined according to the softening temperature and viscosity change law of coal tar pitch. If medium temperature asphalt is used, when the steam pressure reaches 0.4~0.5MPa, the temperature of the heating medium can generally reach 140~150C, which is enough to ensure that the temperature of the paste reaches 135~145C. If modified blue is used, the temperature of the heat transfer oil should be 190~200C when it reaches the kneading pot, so that the temperature of the paste can reach 160~180C.

????The kneading temperature mainly affects the viscosity and surface tension of coal tar pitch. When the kneading temperature is low, the viscosity of coal tar pitch is high, the wetting effect is poor, and the kneading is uneven. The solid carbonaceous material and coal tar pitch cannot be mixed evenly. It cannot be melted evenly, resulting in uneven structure of the green body and uneven performance of the product. At the same time, the load on the kneading equipment is increased, which affects its service life. When the kneading temperature is high, the viscosity of coal tar pitch is small, the infiltration effect is good, the kneading is uniform, and the structure of the formed green body is uniform. Increasing the kneading temperature is beneficial for the coal tar pitch to fully penetrate into the carbonaceous material, but when the kneading temperature is too high, the properties of the coal tar pitch will change, the light components will decompose and volatilize, and some components will undergo polycondensation reaction and distribute in the solid carbonaceous material. The asphalt layer on the surface of the particles may be oxidized by air, making the plasticity of the paste worse, the carbon paste hardening or diverging, and hindering the uniform cooling of the paste, resulting in poor molding performance and lower molding yield.

????The most suitable kneading temperature of the paste should be determined according to the rheological properties of the coal tar pitch, that is, according to the viscosity-temperature curve of the coal tar pitch used, and the kneading temperature should be selected when the viscosity of the coal tar pitch is at a stable low viscosity stage. Generally speaking, the kneading temperature (or paste temperature) should generally be controlled within the range of 50~80C higher than the softening temperature of coal tar pitch. At this temperature, coal tar pitch has good fluidity and wetting ability. When medium temperature asphalt is used as binder for kneading, the kneading temperature of the lake material should be in the range of 130~155C. When using modified asphalt or high-temperature asphalt as the binder, the kneading temperature should be in the range of 160~200C. When the mixed binder composed of coal tar or total oil and coal tar pitch is used, the kneading temperature can be appropriately lowered.

????During the kneading process, the kneading temperature is not allowed to drop below the specified temperature, otherwise the wettability of the coal tar pitch binder to the solid carbonaceous material and the fluidity of the paste will be reduced, making kneading difficult. When the heating steam pressure is less than 0.4MPa, the kneading time should be extended, and when the heating steam pressure is lower than 0.35MPa, coal tar pitch should not be added. The kneading temperature also has a certain relationship with the climate, that is, kneading is more sensitive to the climate. In summer, the kneading temperature can be slightly lower; in winter, the kneading temperature should be increased appropriately. This is because the temperature in winter is low and the paste dissipates heat quickly after it is out of the pan. Therefore, the kneading temperature in winter should be slightly higher than that in other seasons.