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Laser detects cracks in steel
Cracks in steel are normally detected late during casting and the defective steel must then be either scrapped or repaired. With new methods cracks can be detected earlier in the process, which saves both energy and materials.
Researchers at Swerim have studied and evaluated two new methods for detecting the cracks that can occur in steel during continuous casting. During casting, the steel solidifies while it glides through a line of water-cooled plates, and it is very difficult to detect surface cracks while the steel is still glowing.
Earlier inspection of steel with new methods
With the new method, the steel is inspected earlier during the casting process and any problems can be corrected before all that much steel has been cast. By inspecting the steel while it is still hot, in certain cases it can be sent directly to rolling before it has cooled. The steel mill subsequently saves considerable energy because the steel does not need to be heated anew before it is rolled.
Certain selected steel types have been studied during the project, both on a pilot and operational scale. The results show that steel makers can save more than 13 gigawatt hours each year in the short term by implementing the new methods. This corresponds to the annual electricity consumption of 520 private houses.
Laser detects cracks
The methods that Swerim has studied are laser triangulation and high-resolution photography with laser illumination. The first method describes the steel surface using distance measurements, and the other method is a visualisation method with the laser used as lighting to depict the surface.
Both methods can detect longitudinal cracks on hot and cold steel at a speed of 1–2 metres per minute, which corresponds to the speed of continuous casting.