Controle automatizado de fornos para tratamento térmico em aços

Abstract

This work is aimed to propose a low cost automated control of steel heat treatment furnace implemented by a single computer system in order to control the temperature with precision and reduce the human interaction during the heat treatment process. It can be adapted on low cost commercial furnace used by small business. In this case, a platform open licensed with microprocessor is programmed with PID (Proportional-Integral-Derivative) controller that receive the temperature by a sensor and adjust the temperature. With reference in a defined specific heat treatment cycle, this activates the furnace resistors wherein a phase is connected with a load terminal of solid state relay (SSR), varying the power furnished to furnace, using the technical of Pulse Width Modulation (PWM) on the relay control terminal. The purpose of heat treatment is to cause desired changes in the properties of metal parts and the results depends on the control of temperature in function of time. Preliminary tests were performed comparing the results of D2 and D6 materials samples that were hardening and after tempering by the traditional method (visual and without control) and the PID system control proposed. Results by hardness and metallographic analysis showed a precision control and a better final hardness were obtained with a fine granular and homogeneous structure.