Graphite Electrode forms an integral part of the EAF process used to manufacture steel. Its specifications have a major impact on the quality of metals produced, including its diameter and density. The mechanical strength of the electrode is also important, as it is subjected to significant bending deformation during its operation. The bending deformation of the electrode can lead to a loss in conductivity in the graphite structure. This leads to an increase in energy losses and decreased electrical capacity during the EAF/LF. To minimize the degradation, a clear understanding of deformation and stresses processes is needed.
Curvature is a function SOC. For higher SOCs, the slope of the curve increases. Despite this trend, the SOC-dependent curves are not linear and exhibit a large scattering of data points. This scattering can be attributed to the fact the SOC curves were obtained by fitting curves with quadratic equations, which are not a good approximate for nonlinear effects.
In addition, the curvature of the electrode is accompanied with a change in elastic modulus. As shown in Fig. 5, the elastic modulus of the anode increases with SOC and cycles, while that of the cathode decreases with SOC and cycles. This is most likely a result of the higher particle volume fraction and the larger stiffening effect of the anode, which leads to a greater number of particle-particle contacts and a greater compression strain.
It is clear that the modulus is decreasing with increasing normalized cycles and concentration. This shows that there is some damage caused by cycling. However, the modulus varies only within a narrow range. This means that there is a threshold of the modulus at which the extra-stress induced by the high concentration and cycle number is relieved due to damage.
In order to further understand the electro-chemo-mechanical coupled degradation mechanism, we conducted a series of stress relaxation experiments. We repeated load-unload cycles in tension and compression configurations with the faceplate separation of D = 30 mm kept constant for six hours. We measured the changes in curvature at different unloading levels.
Results from these experiments show that the anode elastic modulus changes significantly with the normalized concentration and cycles, while the cathode elastic modulus remains unchanged with the normalized concentration and cycles. This is a reflection of the difference between particle volume fractions in the anode's and cathode's, which may be a result from different binding material qualities. The anode's elastic modulus varies much more in compression than tension, while the cathode's elastic modulus varies much less in compression. This suggests that the elastic modulus of the anode is mainly controlled by its binder content. Moreover, anode modulus is less sensitive than cathode modulus to bending deformation.
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