Fabricação de tiras metálicas de alumínio por fundição contínua reciclando latas de alumínio para bebidas
Data
2020-10-20
Autores
Ferreira, Lucas Veronez Goulart
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A reciclagem de latas de alumínio no Brasil tem sido uma atividade de grande importância econômica, social e ambiental visto que, atualmente, mais de 90% de todas as latas de alumínio produzidas são recuperadas por reciclagem (mais de 50% no caso de toda sucata de alumínio) e, principalmente, pelo fato da produção secundária de alumínio (reciclagem) consumir até 5% da energia total necessária para a produção primária. Neste trabalho, a produção de tiras metálicas a partir de material recuperado de latas de alumínio foi executada com o uso de um fundidor de tiras metálicas (Strip Caster) laboratorial que dispõe de dois cilindros de aço (diâmetro = 105 mm), refrigerados internamente por solução aquosa (1 parte de óleo e 9 partes de água). Foram executadas seis corridas com uma massa de material fundido de ≈ 1300 g, nas temperaturas de 650°C, 670°C, 710°C e 720°C. As velocidades superficiais dos cilindros foram de 0,16 e 0,2 m/s. A seleção de carga fundida das latas de alumínio foi baseada na quantidade de anéis rebitados (liga Al 5182) com o corpo (Al 3004) e tampa (Al 5182). Micrografias ópticas com e sem luz polarizada e com microscópio eletrônico de varredura (MEV) foram obtidas para avaliar a evolução microestrutural durante o processamento. A composição química para cada corrida e análise mecânica por testes de tração foram feitas após tratamento térmico de homogeneização seguida de laminação a frio (H18) e recozimento (O). As tiras metálicas produzidas apresentaram em torno de 2 mm de espessura, para um afastamento entre os cilindro de 1,5 mm. As micrografias mostraram que a estrutura das tiras metálicas apresenta duas regiões principais: 1.) uma superficial, majoritariamente formada por grãos com características colunares; e 2.) uma central, composta de grãos globulares e equiaxiais em formato de roseta. O crescimento de uma fase colunar direcional foi evidenciada a partir de um núcleo equiaxial que se formou ao longo do caminho que o material semissólido percorreu até atingir as paredes frias dos cilindros refrigerados. Esta fase cresceu em direção a fase líquida do material semissólido rica em átomos solutos. A partir daí, grãos com características eutéticas colunares se formaram próximos aos cilindros e grãos menores com segregação de átomos solutos na região central da tira. Os testes de tração nas condições H18 e O mostraram que o desempenho mecânico é fortemente influenciado pelo conteúdo de Mg, com o limite de resistência a tração de 264,0 MPa, para o caso em que havia a maior quantidade de Mg (1,26% em massa) e um mínimo de 210,1 MPa (0,13% de Mg em massa). Entretanto, uma fragilização na saída do laminador ocorreu, o que sugere, para uma aplicação industrial, a necessidade da utilização de refinadores de grão (e.g.: ligas a base de Ti e B) a fim de diminuir a fração de grãos colunares e assim evitar a formação de trincas intergranulares nessa região. Uma esteira de roletes funcionaria como um suporte ativo de sustentação e de tração das tiras metálicas na saída do laminador.
The recycling of aluminum beverage cans in Brazil has been an activity with great economical, social and environmental relevance as more than 90% of all cans are recovered by recycling (more than 50% of all aluminum scrap) and mainly because the secondary aluminum production (recycling) only demands 5% of the total energy necessary for the primary production. At the present work, the production of aluminum strips was done by a laboratorial Strip Caster that uses two steel cylinders (105 mm of diameter), internally cooled by a water solution (1 part of soluble oil and 9 parts of water). Six testes were performed by melting around 1300 g at pouring temperatures of 650 °C, 670 °C, 710 °C and 720 °C. Surface velocities were 0,16 and 0,2 m/s. The selection of the melted load was based upon the quantity of riveted rings (aluminum alloy 5182) with can body (Al 3004) and lid (Al 5182). Micrographies with and without polarized light and with scanning electron microscopy (SEM) were performed in order to evaluate the progression of the microstructure during the processing. The chemical composition at each run and mechanical analysis by tensile test were done after homogenization thermal treatment followed by cold rolling (H18 temper) and annealing. The produced strips showed 2 mm thickness as a function of the 1,5 mm cylinders gauge. Two main regions were observed at the internal structure of the strips by the micrographies: 1.) at the surface, largely made of columnar grains; and 2.) a central, mainly formed by globular and equiaxial rose-shaped grains. The columnar growth appears to have initiated from equiaxial nucleus which have grown on the way that the semi-solid material went by until reaching the cold walls of the cooled cylinders. This phase grew at the direction of the liquid phase rich in solute atoms. After that, eutectic grains with columnar characteristics were formed and grains with smaller contents of solute were observed in the central region of the strips. The tensile testes at H18 and O tempers showed that the mechanical performance is greatly influenced by Mg content, with tensile strength reaching a maximum of 264,0 MPa with the highest Mg content (1,26% weight) and a minimum of 210,1 MPa (0,13% Mg wt.). On the other hand, a hot fragility and the exit of the cooled rolls occurred which suggests that, for an industrial application, the use of grain refiners (e.g.: Ti and B alloys) might be necessary in order to reduce the fraction of columnar phase and therefore the formation of intergranular cracks. A row of rolls at the exit of the cooled cylinders could act as an active support and impose a traction force for the strips exiting the Strip Caster.
The recycling of aluminum beverage cans in Brazil has been an activity with great economical, social and environmental relevance as more than 90% of all cans are recovered by recycling (more than 50% of all aluminum scrap) and mainly because the secondary aluminum production (recycling) only demands 5% of the total energy necessary for the primary production. At the present work, the production of aluminum strips was done by a laboratorial Strip Caster that uses two steel cylinders (105 mm of diameter), internally cooled by a water solution (1 part of soluble oil and 9 parts of water). Six testes were performed by melting around 1300 g at pouring temperatures of 650 °C, 670 °C, 710 °C and 720 °C. Surface velocities were 0,16 and 0,2 m/s. The selection of the melted load was based upon the quantity of riveted rings (aluminum alloy 5182) with can body (Al 3004) and lid (Al 5182). Micrographies with and without polarized light and with scanning electron microscopy (SEM) were performed in order to evaluate the progression of the microstructure during the processing. The chemical composition at each run and mechanical analysis by tensile test were done after homogenization thermal treatment followed by cold rolling (H18 temper) and annealing. The produced strips showed 2 mm thickness as a function of the 1,5 mm cylinders gauge. Two main regions were observed at the internal structure of the strips by the micrographies: 1.) at the surface, largely made of columnar grains; and 2.) a central, mainly formed by globular and equiaxial rose-shaped grains. The columnar growth appears to have initiated from equiaxial nucleus which have grown on the way that the semi-solid material went by until reaching the cold walls of the cooled cylinders. This phase grew at the direction of the liquid phase rich in solute atoms. After that, eutectic grains with columnar characteristics were formed and grains with smaller contents of solute were observed in the central region of the strips. The tensile testes at H18 and O tempers showed that the mechanical performance is greatly influenced by Mg content, with tensile strength reaching a maximum of 264,0 MPa with the highest Mg content (1,26% weight) and a minimum of 210,1 MPa (0,13% Mg wt.). On the other hand, a hot fragility and the exit of the cooled rolls occurred which suggests that, for an industrial application, the use of grain refiners (e.g.: Ti and B alloys) might be necessary in order to reduce the fraction of columnar phase and therefore the formation of intergranular cracks. A row of rolls at the exit of the cooled cylinders could act as an active support and impose a traction force for the strips exiting the Strip Caster.
Descrição
Palavras-chave
Fundição de tiras, Reciclagem, Latas de alumínio, Solidificação rápida, Strip casting, Recycling, Aluminum cans, Fast solidification