2. Main Classification Methods

2.1 Classified by Protective Atmosphere

1. All-hydrogen Forced Convection Bell-type Furnace

High-purity hydrogen is adopted as the protective medium with outstanding thermal conductivity and reducibility, delivering mirror-bright surface after steel annealing. Built-in high-power circulating fans drive forced gas circulation inside the furnace to realize uniform temperature field, which is the mainstream furnace type for cold rolling steel plants.

2. Nitrogen-hydrogen Mixed Atmosphere Bell-type Furnace

Mixed gas of nitrogen and hydrogen reduces operating costs, suitable for basic bright annealing of ordinary carbon steel and copper materials.

3. Vacuum Bell-type Furnace

The inner retort is evacuated and filled with a small amount of inert gas to avoid oxidation and decarburization, applicable to titanium alloys, cemented carbides and precision magnetic materials.

4. Ordinary Air Bell-type Furnace

No protective atmosphere, only used for stress relief and low-temperature tempering of common forgings, resulting in oxidized workpiece surfaces.

2.2 Classified by Heating Energy Source

• Electric heating bell-type furnace: Heated by resistance bands or radiant tubes with high temperature control precision and low emissions, widely used in small and medium-sized production lines.

• Gas-fired bell-type furnace: Heated by low-NOx burners with natural gas or coal gas, featuring large heat capacity for continuous production of heavy tonnage coils.

2.3 Classified by Furnace Shape

• Circular bell-type furnace: Specially designed for coils and wire rods with excellent sealing performance and even gas circulation.

• Rectangular bell-type furnace: Designed for large flanges, long shafts and plate forgings with regular loading space.

2.4 Station Configuration Mode (Industry Standard: One Heating Bell for Multiple Hearths)

Standard configuration: 1 heating bell + 2 furnace hearths + 2 inner retorts + 1 cooling bell

While one hearth is under heating and soaking, the other proceeds with cooling and unloading synchronously. The heating bell is reused alternately, greatly improving equipment utilization and lowering unit energy consumption.