How does continuous annealing differ from batch annealing of steel strip?

The primary differences between batch and continuous annealing of steel strip lie in the processing method, duration, and resulting material properties.1

Batch Annealing

In this process, multiple coils are stacked on a base and enclosed within a sealed shell containing an inert atmosphere. A gas-fired bell furnace is lowered over the stack to heat the steel. This method is characterized by:
* Duration: The total processing time, including cooling, typically ranges from 50 to 120 hours.1
* Temperature: The steel is held at lower temperatures, generally around 680°C (1,260°F).1
* Outcome: It produces very soft steel, which is a key advantage for certain applications.1

Continuous Annealing

In this dynamic process, the strip is pulled through a tall furnace, moving continuously between rolls. Key features include:
* Duration: Processing is significantly faster, often taking only about one hour per coil.1
* Temperature: The strip is heated to higher temperatures (e.g., 780°C or 1,440°F) and held for only a few seconds before rapid cooling.1
* Outcome: While the resulting steel is not as soft as batch-annealed material, the process offers superior uniformity in mechanical and surface properties.1