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This term powder rolling is applied to the process, now established on an industrial scale, wherein a metal powder is fed continuously into a rolling mill which may be heated, and compacted between the rolls into strip. This strip is then passed through a sintering furnace and rerolled to finished size. In general the product does not have any advantage over strip produced by rolling cast billets, although in some cases superior homogeneity can be demonstrated as well as freedom from laminations that can arise from ingot defects. The main advantage is economic, and depends on the following features:
¡¤ The yield of finished strip from castings is low.
¡¤ The cost of fettling the ingot, of the extensive rolling, annealing and pickling, is considerable.
Powder rolling is economical, therefore especially in cases where the metal is produced cheaply as a powder directly during the extraction process, e.g. nickel, and in the case of a material that work-hardens rapidly and, therefore, requires many intermediate annealing and pickling operations during reduction of a rolling slab, e.g. stainless steel. The production of small quantities of special materials by powder rolling is increasing for applications such as cobalt- or nickel-base alloy strip for welding, nickel-iron strip for controlled expansion properties, special Cu-Ni-Sn alloys for electronics, porous nickel strip for alkaline batteries and fuel cell electrodes, composite bearings, etc. |
