Method and apparatus for introducing differential stresses in endless

Abstract

The wide, thin, revolvable, flexible, metallic casting belts are made to incorporate differential patterns of residual internal longitudinal tensile and compressive stresses. The two marginal areas are residually longitudinally stretched more than the main middle area straddled by these margins. This main middle area is used as a moving mold and is expected to contact molten metal. Thus, the treated belts have two marginal areas in a state of mild longitudinal compression straddling the main middle area in a state of mild residual longitudinal tension. During casting, when hot metal comes into contact with the main middle area of such treated belt, the main middle area expands. Because of the built-in differential compensating stresses, the stresses throughout such belt during casting advantageously become balanced or equalized across the whole belt width. This equalized stress condition during casting assures that the critical moving belt mold area will be flatter than experienced with belts not having differential stress treatment. Thus, cast metal product typically will be improved in flatness, surface finish, section uniformity, soundness and metallurgy. Two methods are described for longitudinally stretching marginal areas relative to the middle area: (A) Use a work roller effectively of larger diameter toward its end than its middle for stretching both margins relative to the main middle area; (B) Use conventional cylindrical work rollers and heat (for expanding and slacking) the middle area during roller-stretching while leaving cold margins for residually stretching both margins relative to the main middle area.