The annealing process in a bell-type annealing furnace can be divided into the following 12 steps:
- Loading the Furnace – Use an overhead crane to load an annealing batch onto an available furnace platform.
- Placing the Inner Bell – Use the crane to cover the loaded batch with an inner bell. Steps 1 and 2 together take approximately 25 minutes.
- Cold Sealing – Check that the inner bell is tightly sealed; 15 minutes.
- Pre-Purge – Introduce nitrogen gas to expel oxygen; 30 minutes.
- Placing the Heating Bell – Use the crane to place an idle heating bell over the inner bell; 8 minutes.
- Heating – Preheat the steel coils. Heating time depends on the specific process and varies for different batches.
- Removing the Heating Bell – After heating is completed, remove the heating bell with the crane; 8 minutes.
- Placing the Cooling Bell – Use the crane to place an idle cooling bell over the inner bell; 8 minutes.
- Cooling – Begin the initial cooling process. Cooling time depends on the process.
- Post-Purge – Blow nitrogen over the steel coils to clean them; 30 minutes.
- Removing the Cooling Bell – Remove the cooling bell with the crane; 8 minutes.
- Unloading the Furnace – First remove the inner bell, then remove all steel coils; 25 minutes.
In these 12 steps, except for the heating and cooling times which are determined by the process, the other operation times are basically fixed.