Thermal stress fracture of refractory lining components: Part I. Thermoelastic analysis
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I.
INTRODUCTION
T H E R M A L stress fracture of refractory components of industrial linings of high-temperature furnaces and metallurgical process vessels is a thermal problem of widespread industrial importance. Refractory costs can account for a significant portion of the total operating costs of industrial processes. The two principal wear mechanisms of thermal stress fracture and corrosion-erosion differ in that the latter dominates during the refining or high-temperature stage of processing and is associated with relatively constant wear rates. Thermal stress fracture, on the other hand, is most likely to occur during heating up to and cooling down from operating temperature and can cause sudden catastrophic loss of brickwork of sufficient magnitude to halt production. Thermal stress fracture and corrosion-erosion are not completely unrelated. For example, refractory linings of metallurgical ladle processes encounter both severe chemical attack due to corrosive slags and frequent thermal cycling. One possible method of reducing the wear due to corrosion-erosion is the use of denser lining materials. However, since thermal shock resistance usually decreases with increasing density, such an approach is not viable without an accompanying improvement in thermal shock resistance of the lining component and/or better control of the thermal environment during the various stages of processing. These factors provide motivation for the study of the fracture behavior of brittle refractory lining materials subjected to thermal loading. The main origins of thermal stress in lining components are (i) boundary restraint, (ii) inhomogeneity, and (iii) nonlinear temperature distribution. Thermal stress due to boundary restraint can occur during the heating portion of the thermal cycle if insufficient expansion allowance is provided. Thermal stress due to inhomogeneity can develop as a result of differences in thermal and mechanical properties in different zones of the component, which can arise, for example, when the hot face has been altered due to peneE BRADLEY is Assistant Professor, Department of Metallurgical and Mineral Engineering, University of Wisconsin-Madison, Madison, WI 53706. A. C. D. CHAKLADER and A. MITCHELL are Professors, Department of Metallurgy, University of British Columbia, Vancouver, BC, Canada, V6T IW5. Manuscript submitted April 28, 1986. METALLURGICALTRANSACTIONS B
tration and/or chemical reaction of metal, slag, gases, etc. with the brick. Whether boundary restraint and inhomogeneity are primary sources of thermal stress is largely dependent on lining installation practice and type of process. This Work is solely concerned with the thermal stress fracture of traction-free refractories (no external loads or restraint) due to nonlinear temperature distribution. Regardless of application and lining construction, all industrial lining components undergo at least one thermal cycle during which the hot face is heated from ambient to operating temperature and cooled back again. During this cycle the de
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