Estudio geométrico y metalúrgico del ensanchamiento y laminación

Abstract

Tesis para optar al título de Magister en Ciencia y Tecnología de Materiales

Un programa de laminacion comprendido en mas de 100 experimentos, fue planificado con la finalidad de investigar el efecto de los factores geometricos y metalurgicos sobre el ensanchamiento. Las laminaciones se realizaron en frio y en caliente para el aluminio y cobre, y en caliente para el acero SAE 1010; todas sin lubricacion. Las variables de estudio fueron: reduccion de altura, relacion ancho/espesor, diametro de cilindros, temperatura, tamaño de grano y fibrado mecanico. El rango de temperatura empleado para cada material fue el normalmente usado en la industria. El diferente comportamiento del aluminio respecto al cobre y al acero en el ensanchamiento durante el laminado en caliente, exigio la determinacion del coeficiente de friccion en estos materiales. La realizacion de 46 ensayos de comprension de anillos, mostro la variacion del coeficiente de friccion con la temperatura para estos materiales y evidencio su efecto en el ensanchamiento. Los resultados de ensanchamiento producidos en el laminado en caliente del acero fueron comparados con los proporcionados por 21 formulas empiricas seleccionadas y elaboradas para estas condiciones; indicando un mayor acercamiento la formula propuesta por Roux. Esta formula junto con la propuesta por Shinokura y Takai, fueron evaluadas en un calibrado real de uso industrial, corroborando la buena prediccion del ensanchamiento proporcionadas por tales formulas. La ampliacion de estos 21 modelos a la laminacion en caliente del cobre y aluminio establece, que haciendo uso de un factor de correcion de 0.77 para el aluminio y 1.6 para el cobre asi como de los coeficientes de friccion encontrados, la formula propuesta por Tselikov predice los valores de ensanchamiento encontrados en la experimentacion. Un analisis de la resistencia a la influencia en caliente del acero, en la direccion longitudinal y transversal de laminado, mediante 25 ensayos de torsion, determina que la resistencia en ambas direcciones es la misma y que la influencia de la orientacion de las inclusiones solo tienen efecto en la ductilidad.|A rolling program, which involved more than 100 experiments, was planned with the purpose of finding out the effects of geometrical and metallurgical factors on spread. Rollings were carried out both in cold and hot conditions for aluminum and copper, and in hot condition only for steel - SAE 1010. All operations were performed without lubrication. Variables under study were height reduction, width/thickness relationship, roll diameter, temperature, grain size and mechanical fibering. The temperature range applied for each material was that normally used in industry. The different behavior of aluminum when compared with copper and steel during hot rolling, needed the determination of friction coefficients for those materials. 46 ring compression tests carried out showed the variation of friction coefficient with temperature for those materials, and demonstrated its effect on spread. Results obtained with hot rolled steel were compared with 21 empirical formulas selected and adapted for these conditions. They indicated that Roux expression is the one that gives the best approximation. This formula, together with the one proposed forward by Shinokura and Takai, were evaluated when applied to an industrial roll pass design, confirming their accuracy. The extension of those 21 models to copper and aluminum hot rolling, showed up that using a 0.77 correction factor for aluminum and 1.6 for copper, besides friction coefficient being assessed, Tselikov formula foretell real spread values. An analysis of hot yield strength in steel, both in longitudinal and transverse rolling directions, carried out through 25 torsion tests, shows that strength in both directions is the same, and that the influence of inclusions -specially their orientation- only affects ductility.

A rolling program, which involved more than 100 experiments, was planned with the purpose of finding out the effects of geometrical and metallurgical factors on spread. Rollings were carried out both in cold and hot conditions for aluminum and copper, and in hot condition only for steel - SAE 1010. All operations were performed without lubrication. Variables under study were height reduction, width/thickness relationship, roll diameter, temperature, grain size and mechanical fibering. The temperature range applied for each material was that normally used in industry. The different behavior of aluminum when compared with copper and steel during hot rolling, needed the determination of friction coefficients for those materials. 46 ring compression tests carried out showed the variation of friction coefficient with temperature for those materials, and demonstrated its effect on spread. Results obtained with hot rolled steel were compared with 21 empirical formulas selected and adapted for these conditions. They indicated that Roux expression is the one that gives the best approximation. This formula, together with the one proposed forward by Shinokura and Takai, were evaluated when applied to an industrial roll pass design, confirming their accuracy. The extension of those 21 models to copper and aluminum hot rolling, showed up that using a 0.77 correction factor for aluminum and 1.6 for copper, besides friction coefficient being assessed, Tselikov formula foretell real spread values. An analysis of hot yield strength in steel, both in longitudinal and transverse rolling directions, carried out through 25 torsion tests, shows that strength in both directions is the same, and that the influence of inclusions -specially their orientation- only affects ductility.