Continuous casting nozzle clogs create serious productivity and quality losses in the steel industry. The buildup between the tundish and the mold, due to a variety of inclusions, can decrease productivity by causing either decreasing the casting time or requiring the nozzle be replaced, which also increases cost. These inclusions could also come loose and enter the steel mix, resulting in possible mechanical failures and quality failure due to inclusions. This is particularly true of aluminum-killed low-carbon low-silicon steel in a continuous billet caster that use aluminum as a deoxidation agent.
There are four general types of nozzle clogs: deoxidation products, solidified steel, complex oxides, and reaction products. Buildup of deoxidation products can be the same particle size as is found in the mold, ranging from 1-20 microns, and consists of whichever particles were used as the deoxidizer, such as alumina. Solidified steel occurs when the cast nozzle preheat is inadequate, allowing the steel to freeze within the nozzle. Complex oxides or nonmetallic materials such as calcium aluminates or calcium sulfates, assimilate deoxidation particles and thereby increase the volume of the clog. Reaction products consists of deoxidation particles that react with either air or oxygen and show increased clogging as soluble aluminum concentration is increased.
With the exception of solidifying steel, these causes of clogs can be reduced by monitoring the steel for inclusions as they go from the tundish into the mold flux. By using the ASPEX PSEM eXpress, the desktop scanning electron Microscope with Metal Quality Analyzer (MQA) software platform, manufacturers are able to analyze steel sample for inclusions before they go to the nozzle, allowing for less likelihood of clogging and increasing the cleanliness of the steel product.
The MQA is capable of routine monitoring to improve maintenance issues such as:
• Tundish clogging and erosion minimization
• Nozzle clogging due to calcium aluminates or magnesium spinels
• Varying calcium additions to optimize castability
• Hardware changes, such as tundish linings and their overall effects
By allowing manufacturers to know the size, shape, and elemental composition of the inclusions in the steel line directly on the shop floor, the MQA provides the necessary information to reduce or eliminate the inclusions upstream.
The Aspex PSEM with MQA alerts manufacturers to potential casting nozzle clogs, preventing costly downtime and saving energy consumption, ensuring that they are producing a clean, quality product efficiently.
Reference:
Aspex, http://www.aspexcorp.com/industries/metals.html
SpringerLink, http://www.springerlink.com/content/74063541u0415gt7/
Rackers, K., and B.G. Thomas. 78th Steelmaking Conference Proceedings, Nashville, TN, April 2, 1995, Iron and Steel Society, Warrendale, PA, Vol. 78, 1995, pp. 723-734. http://ccc.illinois.edu/PDF%20Files/Publications/95_ISS%5B1%5D.Conf.paper_post.pdf
