Firing is a crucial process in ceramic production, conducted in thermal equipment—kilns. Ceramic kilns can be classified as follows: (1) By shape and operation mode, they are divided into intermittent kilns (such as downdraft kilns) and continuous kilns (such as tunnel kilns). (2) By heat source, there are flame kilns using fuels (coal, gas, heavy oil, etc.) and electric heating kilns. (3) By whether the flame contacts the product, they include open-flame kilns and muffle kilns (partitioned flame kilns). These ceramic firing kilns require different refractory materials due to their specific uses and working environments.
(一) Tunnel Kilns
Tunnel kilns are widely used modern kilns in the ceramic and refractory industries, favored for their high output, low fuel consumption, favorable working conditions, and ease of mechanization and automation.
- Classification of Tunnel Kilns
Tunnel kilns can be categorized based on multiple criteria:
- By heat source:
- Flame tunnel kilns, which use coal, gas, or oil as fuel.
- Electric tunnel kilns, which utilize electric heating elements for heating.
- By flame contact with the product:
- Open-flame tunnel kilns, where the flame directly enters the tunnel.
- Muffle tunnel kilns (partitioned flame kilns), which use a muffle plate to separate the flame from the products. Electric kilns can also adopt this muffle design.
- Semi-muffle tunnel kilns, where the muffle plate has openings to allow partial combustion products to interact with the products, or only the firing zone is muffled while the preheating zone remains open-flame.
- By internal transportation equipment:
- Kiln car tunnel kilns
- Push-plate tunnel kilns
- Roller-hearth tunnel kilns
- Conveyor-belt tunnel kilns
- Step-beam tunnel kilns
- Air-cushion tunnel kilns
- By the number of passages:
- Single-passage tunnel kilns
- Multi-passage tunnel kilns