REFRACTORIES REVIEW: Advances, Installation & BOOM
AwardsThe 38th T.J. Planje-St. Louis Refractories Award was presented to George Taylor, who had a 38-year career with Chicago/Wellsville Fire Brick and its parent company, CFB Industries, Inc., which was sold to National Refractories in 2002. In his talk, "Life is Full of Ups & Downs," Taylor illustrated the change in the domestic refractories industry by citing the situation in Missouri. In 1964, Missouri had eight plants with a total capacity of 30 million bricks per year. By 2004, only two of the plants were operating, and 90% of the capacity had been closed.
The Al Allen Award, for the best published refractories paper in 2003-04, was given by the Refractory Ceramics Division to S. Ramachandran, K. Peaslee, Ph.D. and J. Smith, Ph.D. of the University of Missouri-Rolla for "Thermal Chemistry of Steel-Refractory Interactions in Continuous Casting Nozzles." The authors determined that gaseous species are the root cause of inclusions in molten steel, and the impurities in casting nozzles contribute to the buildup that restricts steel flow. A field trial will be run soon using a nozzle that was designed on the basis of this study.
Invited LectureC. Parr, Ph.D. of Lafarge Aluminates discussed "Low Cement Castables with Predictable Placement Properties: Dream or Reality." Parr noted that the hydration of calcium aluminate cement (CAC) is highly dependent upon temperature, and the reaction/hardening process involves three stages: dissolution, nucleation and precipitation. Upon placement, the concerns are working time, initial set and final set, which can be changed and controlled by additives, temperature, etc.
Castables with reliable placement properties are a reality today, if the many variables related to the raw materials, CAC, fillers and additives are controlled. The dream of developing a robust cementitious system that is less affected by the many interdependent variables, and that can be easily placed consistently, still remains. Further progress in achieving this dream will require more study of the complex interactions in the binder phase.
Dryout Theory and Experience (BOOM!!)H. Winkelbauer of ANH Refractories described the development of a computer program (DRYOUT) that models the drying of castables. Using physical data for the actual castable(s) involved, the program provides a specific dryout schedule, which allows for shorter dryouts compared with the conservative and generic dryout schedules of the past. In today's economic climate where "time is money," such a program will be valuable.
In "Blowups Happen," L. Krietz of Plibrico Co. reviewed case histories of castable installation explosions, also known as thermally induced structural failures (TISFs). Although castables commonly receive the initial blame for spalling/explosion incidents, in most cases investigation reveals other contributing factors and causes.
I. Cobane of Hotwork-USA discussed experiences with more than 20,000 castable dryouts since 1965. The company has observed that (a) castable spalling is more common in warm weather than cold weather, (b) spalls commonly occur at about 800ºF, and (c) explosive spalls frequently occur when heating resumes after a hold period at a specified temperature. Although much work has been done and published on castable dryout, problems still continue.
Materials and DevelopmentR. Racher of Almatis described a new dense synthetic refractory aggregate, called Bonite, which consists of >85% CA6. The nominal chemistry is 90% alumina, 8.5% CaO and 0.9% silica. The name Bonite is derived from the natural mineral Hibonite [Ca(Al,Ti,Fe)12O19]. The first trials of Bonite-based refractories are underway in the aluminum industry, where the product is expected to provide low wettability by molten aluminum. Other potential benefits exist in the cement, steel and petrochemical industries due to the product's high chemical resistance, high refractoriness and stability in reducing atmospheres.
C. Alt of Lafarge Aluminates discussed the development of improved flooring (castable) for the storage of 10-15 ton coils at an integrated steel plant. Such flooring must resist thermal shock and mechanical stress (point load and impact). This example illustrates how focused attention on a specific application can result in an improved product.
The St. Louis Symposium Proceedings can be obtained by contacting Patty Smith at the University of Missouri-Rolla, (573) 341-6256 or email@example.com.
Charles E. Semler, Ph.D., is an independent refractories consultant serving clients worldwide. He was a professor of ceramic engineering and director of the Refractories Research Center at The Ohio State University. He is a fellow of the ACerS, and also served as vice president-international and refractories division chairman. He is a distinguished life member of UNITECR and received the St. Louis Refractories Award in 1995. Semler can be contacted by phone (480) 895-9830 or fax (480) 895-9831.