A process, consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, such as steel. This process also simultaneously produces desired changes in microstructure, as in other properties, such as improvement of mechanical or electrical properties, increase in stability in dimensions, facilitation of cold work, etc. Two types of process annealing may be used in tinplate manufacture, batch (box) annealing (BA) or continuous annealing (CA).
Batch (Box) Annealed (BA): The process by which a large, stationary stack of steel coils (4 coils high) is subjected to a long heat-treating cycle. This process enables the cold-rolled sheet to fully recrystallize into the softest possible product conforming to customer specifications. It produces steel having mechanical properties which range from deep drawing quality to hard stiff material suitable to resist pressure or vacuum on can ends.
Continuous Annealed (CA): A process by which the steel is rapidly heated, soaked and cooled at a confirmed rate by passing the coil at a relatively high speed through a furnace consisting of numerous sections. Because of the shorter anneal cycle, CA produces material having a finer grain size than BA.