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3) Semi-coke formation stage of the binder: 450 ~ 550 ℃. The binder in the product itself decomposes and polymerizes. At this stage, the polycondensation reaction occurs continuously at the same time as the decomposition reaction. With the intensification of the reaction, the viscosity of the melt gradually rises, and the rising resistance of light volatiles increases, so that the amount of volatiles gradually decreases, while the heavy condensates continue to increase.
In addition, as the polycondensation reaction continues to intensify, the heavy components in the binder continue to polymerize into bitumen coke and combine with the aggregates in the product to form a preliminary semi-coke, called "bridge coke" because of the formation of carbon aggregates into a solid body. At this stage, if the heating rate is too fast, the polycondensation reaction will be too violent, resulting in void defects in the internal structure of the product, making it difficult to obtain coke with uniform structure (bridge coke). Our company provides an arc furnace electrode.
4) High-temperature sintering stage (half coke becomes full coke stage): 550 ~ 850 ℃. As the temperature further increases, the semi-coke continues to coking, and the structure changes further. The internal dehydrogenation reaction generates hydrogen and methane, forming a grid carbon structure with a larger molecular weight. The formation of this structure makes the coke more stable and stable, forming a coke that is homogeneous with the skeleton particles.
5) Cooling stage: 850 ℃ to ambient temperature (25 ℃). After the roasting temperature is raised and the temperature is kept constant for a certain period of time, the product is gradually cooled to 400 ℃ according to the specified cooling rate, and then naturally cooled from 400 ℃ to the ambient temperature (25 ℃).
Due to the decrease in temperature, shrinkage will occur in the product. For this reason, the cooling rate must be controlled to avoid the occurrence of cracks. The reason for the cracks is mainly due to the shrinkage rate of the product shell is greater than the center shrinkage rate, resulting in the external stress generated by the product outward and beyond the mechanical strength of the product shell.
The above information is provided by the graphite electrode supplier.