Dimensionamento de sistema de controle de bombas hidráulicas em processo thermex para redução de fragilidade azul em barras metálicas

Abstract

Steel rebar is one of the most widespread materials in civil construction, where its mechanical properties are governed by international or exclusive technical standards in each country. At the end of the production of hot-rolled rebars, heat treatment takes place by means of cooling, such as Thermex. In this process, heterogeneity in the mechanical properties of the bar can occur, caused by non-uniform cooling throughout the metal part, including the fragility of 500 °F, which results in a decrease in toughness and ductility in the regions where the heat treatment was more intense, causing loss metal by non-compliant product. An automated system was developed to control the hydraulic pumps of the Thermex process, by means of a programmable logic controller, responsible for controlling the drive to regulate the pressure and water flow at the moment of entry of the bar, seeking to reduce the heat treatment intensity in its portion initial, as it is the part most affected by the blue fragility, where the regulated pressures and flows were dimensioned from results obtained through simulation, using the finite element method in computer software. Through the tensile test of the bars thermally treated by the dimensioned Thermex system, the values of yield limit, strength limit and elongation were obtained. When comparing these mechanical properties with the values obtained from the bar in normal condition and comparing with the reference values of the technical standard, a reduction of metallic loss per non-conforming product was perceived from 2.56% per rolled bar to 0.64%. The best state of properties was found in the test bar where the activation time was 3.4 seconds by the activation signal coming from photocell A3, at a pressure of 7 bar, over the first 12 meters of the bar. With the reduction of the blue fragility effect, we achieved a greater use of the bar, generating financial and environmental benefits, since the rework of the non-compliant portion was reduced, reducing energy and water consumption.