Applying the Processing Chain for the Optimization of the Electrode Nipple Joint

The graphite electrode column used in electric arc steel shops (mini mills) is subject to consumption which can be divided into a continuous share (inevitable in principle) and an undesirable discontinuous share. The latter is caused by the breaking of electrode columns, which can arise as a result of exceeding the maximum graphite strength. Most failures of the electrode column occur in the highly stressed lower electrode-nipple joint. Longitudinal cracks and breaks at the bottom of the electrode socket and equatorial nipple breaks arc the most frequent failures in the electrode column. An unfavourable tuning of the coefficients of expansion of the nipple and electrode is mainly responsible for the failures. The fact of the different expansion capability of both is increased by the approaching parabolic temperature distribution in the electrode column cross-section. The development of the equatorial nipple break is favoured in the case of a big thermal load by decoupling the socket end faces which commences from the electrode surface. The reduction in the current-leading share of the electrode end faces causes an additional shift of the current into the nipple. Consequently this contributes to an overheating of the nipple.