Avaliação do efeito da injeção de gás sobre a flotação de inclusões em um distribuidor de lingotamento contínuo

• Ano de defesa: 2016
• Autor(a) principal: Alexandre de Freitas Gomes de Mendonca
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Materiais e de Minas; Engenharia Metalúrgica; Engenharia metalúrgica
• Link de acesso: http://hdl.handle.net/1843/BUBD-AEAGK2

The technological development of steel grades with high internal and superficial quality requires special manufacturing processes with accurate control. This development is aimed at supplying steel products with high mechanical performance and cleanliness level to competitive markets. The steelmaking industry uses several techniques to control and reduce the effects of non-metallic inclusions in steel. The main control items are the oxygen content of the steel in the converter, practice of steel deoxidation, floatation of inclusions during secondary refining and the use of flow modifiers in the tundish. There are different kinds of flow modifiers, such as weirs, dams and impact pad (turbulence reducing) that can lead to appropriate conditions for inclusion removal.The removal of inclusions in the continuous casting tundish has been intensively investigated through physical and mathematical modeling. Recently, gas injection in the tundish has been considered as an alternative to improve inclusion removal. Several works have analyzed the effects of the gas injection and its interaction with the inclusions. However, there are opportunities for more investigations regarding theeffect of gas flow rate, location of the gas injection system and bubble distribution on the inclusion removal efficiency. In the present work, a physical model of an industrial tundish with nominal capacity of40 metric tonnes, built in a 1:3 scale, was used to analyze gas injection and its effect on the fluid flow pattern and inclusion removal. The overall inclusion removal efficiency was evaluated in the system output for different positions and rates of gas injection flow from the plugs, for two specific tundish internal settings, using online inclusions counting method. Also, experiments were carried out to determine residence timedistribution curves, RDT, for specific flow conditions. The parameters determined the removal efficiency were compared to the RTD curves to decide which system configuration is more efficient for the cleanliness of the steel. The study demonstrates that there is improvement in the efficiency of inclusion removal for tundish with flow modifiers compared to tundish without flow modifiers. Configurations of tundish with gas injection have a better inclusion removal efficiency, in both configurations, without and with flow modifiers. In general, analysis of residence time distribution curves demonstrated that the ratio between the plug volume and dead volume decreased as the injected gas flow rate andremoval efficiency increased. Thus, only the analysis of the characteristic volumes of the tundish is not sufficient to conclude which internal tundish configuration is the best one aiming at maximum efficiency of inclusions removal. The best inclusion removal efficiency was obtained in a tundish with weir and dam, with plug positioned at 56cm of distance from the ladle shroud and operating with gas flow rate between 2 to 3Nl/min. This configuration presented a removal efficiency of 75%, and has an acceptable disturbance level in the metal/slag interface due to the gasrelease.