Wear and distortion of the copper plates in the mold is a major concern in the operation of continuous casters.
The mold-wall temperature is one of the principal factors affecting mold distortion. Grooves machined in plates can significantly improve the efficiency of water cooling, thus, reducing the operating temperature of the mold and moderating the thermal gradients through-the-wall of the mold.
Consequently, lower thermal stresses result in improved performance of the mold and smaller distortion of the copper plates. Introduction of grooves, however, reduces the plate thickness available for wear and related refurbishing of the plates. Moreover, if the ligaments separating water from hot face in cooling channels become too thin, they may be subject to easy mechanical abuse. Some rational compromise is therefore needed in design. Such a compromise indeed should also include the alternative use of materials of appropriate plastic strength and other mechanical properties.
An inelastic thermal analysis of the mold plate in a continuous casting process was performed. The elastic-plastic response of the copper broadface plate was determined for the load history including start-up, steady operation and shut-down transient. Potential consequences of overflowing were also evaluated.
Two geometries of water cooling channels were analyzed. Although, within the first loading cycle permanent deformation occurs for both designs, the distortion of the plate with deeper and wider grooves is significantly reduced in comparison with the design of the existing plate. Thus, longer operation times including four-to-five times larger number of transient conditions during start-up and shut-down can be expected for the plate of new design. Tests performed on the used mold plates indicated that softening of copper occurred at local regions. This was attributed to the unsteady conditions when the temperatures exceeded the design values.
Analysis of overflowing indicated that the temperature of the upper ungrooved portion of the mold at such upset condition may rise up to 1100°F. Change of material properties and severe thermal loading cause further plastic distortion of the plate. Resulting lower plastic strength of the upper ungrooved part may also enhance the incremental accumulation of permanent distortion within the subsequent start-up and shut-down transient conditions.
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