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Proceedings Paper

Infrared sensor for automated inspection of hot metal surface
Author(s): Joseph B. Setzer Jr.; Mohan Thangavelu
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Paper Abstract

A method of determining an infrared sensor for automated inspection of hot metal sheet is described. The sensor locates voids, inclusions, and surface defects characterized by a variation from background radiant flux. The sensor can be coupled with a commercially available processing system, developed for visible wavelength line scan cameras, to automatically track, classify and report product flaws in real time. Theory: For hot metals, emissivity is strongly dependent upon surface conditions. Any scratch on the material will radiatemore strongly than smooth regions due to multiple reflections between the sides of the indentation. Changes in emissivity are also observed where surface blemishes occur, with darker regions emitting more than lighter areas. In addition, any void or inclusion within the metal may result in conduction properties different from metal of homogeneous composition. If these flaws are near enough to the surface, they will alter the radiance in localized regions. Approach: To detect signal modulations of a few percent in areas as small as a scratch, a high resolution infrared scanner is required. In some hot metal sheet production facilities, the web width can range from three to seven feet while the line speed can exceed 1,000 ft/mm. In order to achieve 100% coverage under these conditions, the inspection system requires both a fast response sensor and rapid signal processing capability. Currently, there exists at least one commercially available image processing system capable of tracking and reporting surface anomalies in real time. Here we present a method for specifying a sensor based on properties of the target material, environmental considerations, and commercially available infrared detectors.

Paper Details

Date Published: 1 March 1990
PDF: 7 pages
Proc. SPIE 1313, Thermosense XII: An International Conference on Thermal Sensing and Imaging Diagnostic Applications, (1 March 1990); doi: 10.1117/12.21935
Show Author Affiliations
Joseph B. Setzer Jr., Kaiser Aluminum & Chemical Corp. (United States)
Mohan Thangavelu, Kaiser Aluminum & Chemical Corp. (United States)

Published in SPIE Proceedings Vol. 1313:
Thermosense XII: An International Conference on Thermal Sensing and Imaging Diagnostic Applications
Sharon A. Semanovich, Editor(s)

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