What is the difference between Continuous Annealing and Batch Annealing
What is continuous annealing
Continuous annealing takes place in a continuous annealing line(CAL). A continuous annealing line (CAL) is divided into three parts, an entry section for strip cleaning, a furnace section and an exit section. The annealing process is running without interruption. Take example of a continuous annealing line for cold rolled stainless steel coil. The coil strip runs through tunnel furnace continuously and completes the annealing process. Below is a image of a continuous annealing line for processing cold rolled stainless steel coil.
Continuous annealing is a constant process without variation. Continuous annealing, by the virtue of the shorter annealing times, produces material with a finer grain size than BA. Therefore the mechanical properties differ for the same Temper number.
What is batch annealing
In batch annealing, tightly wound coils of cold rolled steel are stacked three or four high on bases with convector spacers between coils. A cover is lowered onto the stack and is sealed at the base. The atmosphere surrounding the coils is purged and replaced with slightly reducing atmosphere. A movable furnace is placed over the entire charge and the coils are heated to the “soaking” temperature, which depends on the steel grade to be made, as does the soak time. After the period at temperature, the furnace cover is removed and the charge is allowed to cool in a controlled manner. A typical batch cycle can range from 10 to 30 hours depending on the steel grade required.
Batch annealing takes place in bell type annealing furnace for stainless steel coils.
What is the difference of continuous annealing and batch annealing
The mechanical properties are better in Continuous Annealing with a higher consistency of physical properties which makes Continuous Annealing suitable in high speed automated lines. However the temper (hardness) is usually on the higher side of the ordered temper tolerance parameters as compared to Batch Annealed.
The lower softness of Batch Annealing gives it better drawing capability and is often preferred in slower lines and for components.
Batch Annealing properties can change from coil to coil as getting the exact same heat treatment in eacho is not possible across the entire ordered quantity.
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