Thermal expansion and shrinkage of ramming paste

Thermal expansion and shrinkage of ramming paste

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Generally, when the cathode carbon block is lower than its roasting temperature, it shows a positive coefficient of thermal expansion as the temperature increases, while the ramming paste will shrink from curing temperature to the maximum roasting temper

 Generally, when the cathode carbon block is lower than its roasting temperature, it shows a positive coefficient of thermal expansion as the temperature increases, while the ramming paste will shrink from curing temperature to the maximum roasting temperature of the electrolytic cell, which is caused by the carbonization of the binder.

Because the coking of the binder is denser than the liquid binder, the particles are closer to the particles, and the volume contraction of the paste is shown on the macro level. It is because of the thermal shrinkage reaction that the ramming paste is prone to crack during the roasting start of the electrolytic cell, while the thermal expansion of the cathode carbon block may aggravate the cracking, but it is not the main cause.

The high shrinkage of the ramming paste increases the likelihood of crack formation and leads to premature penetration of electrolytes and liquid aluminum, greatly reducing tank life. During the operation of the tank, the ideal state is that the thermal shrinkage of the ramming paste always matches the thermal expansion of the cathode carbon block, and no cracks will occur due to the excessive thermal shrinkage of the paste, thus forming an intact cathode lining, but it is difficult to achieve in practice. This reminds us that when using ramming paste, care must be taken to use the corresponding charcoal block.

The shrinkage property of paste generally depends on the proportion of particle size of aggregate and the content of binder. The study shows that increasing the percentage content of small particles and decreasing the maximum size of coarse particles will increase the shrinkage of the paste. The main reason is that increasing the content of small particles in the ramming paste will increase the surface area of the paste, which is bound to increase the amount of binder, and increase the coking shrinkage of the binder during roasting.

If the shrinkage rate of the paste is reduced, the increase of coarse particles can offset part of the shrinkage of the binder coking and reduce the volume shrinkage of the paste. In addition, the increase of coarse particles can promote the strength of paste. Using reasonable particle size distribution and binder dosage to produce a paste with low shrinkage will reduce the possibility of premature infiltration and prolong the tank life.