Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
ANALYSIS OF THE OXIDATION LEVEL AND SURFACE CURVATURE ON EMISSIVITY USED IN INFRARED PYROMETRY
Submission Author:
Kamila Borba Silva Zanzi , SC
Co-Authors:
Kamila Borba Silva Zanzi, Tiago Vieira da Cunha, Anna Louise Voigt
Presenter: Kamila Borba Silva Zanzi
doi://10.26678/ABCM.COBEM2021.COB2021-1305
Abstract
In several manufacturing and quality control sectors present in the industry, non-contact temperature measuring instruments stand out as an important tool. Among these instruments, infrared pyrometers are widely used. Infrared pyrometers are temperature sensors that intercept and measure the thermal radiation emitted by an object with a fast response time. In this context, the emissivity of the object is an important parameter in determining its surface temperature, being influenced by the wavelength, temperature and surface conditions of the object. Therefore, like any other measuring device, temperature values measured with infrared pyrometers are also susceptible to errors. The increase in oxidation on the surface of metals, when submitted to heating cycles as is the case of welding processes, can significantly alter the emissivity of the material, in addition, the surfaces available for measuring the temperature do not always present the desired flatness, therefore, adjusting the emissivity of the material to be measured by the infrared pyrometer becomes a complex task. Therefore, the present work has the objective of assessing the effect of the surface curvature and the level of oxidation on the emissivity of the material. For this purpose, a methodology was used to analyze the emissivity of specimens, which consists on assessing the measured values of temperature with an infrared pyrometer and comparing them with the values obtained with a type K thermocouple, as well as the technique of partial blackening of the surface of specimens. Furthermore, tests were performed on oxidized carbon steel specimens in order to analyze the effects of oxidation on temperature acquisition. The specimens have the geometry of cylindrical bars, with a diameter varying from 2.5 to 8mm, in addition to a flat surface with thickness of 6.5mm. For different cross sections of the specimens, their surface was standardized by chemical pickling and the heating was accomplished by Joule effect, at temperature levels from 100 to 800°C. As a result, it was found that the increase in temperature and, consequently, the increase in surface oxidation, promotes an increase in the emissivity of the specimens. The emissivity stabilization trend was observed until it only represents the emissivity of the oxide layer. Furthermore, it was verified that the effect of the surface curvature has no significant effect on the emissivity values of the material.
Keywords
Infrared Pyrometer, oxidation, Surface Curvature
