Door curtains on continuous heat treatment furnaces
A continuous furnace cannot close its doors, so the curtain does the sealing: it limits air ingress, heat loss and oxidation at the entry and exit.
Continuous furnaces move work through on a pusher, a roller hearth or a belt, and the doors stay open at both ends so parts can pass. Three consequences follow: outside air enters and convects against hot gas, oxygen reaches the work surface, and a conventional closed door cannot be used at all.
The door curtain, sometimes called a fire curtain, fills that opening. It is built from ceramic cloth, ceramic tape and glass cloth, combined or woven so that it drapes between the work and the opening while still letting the charge pass.
Selection depends on the process
Annealing, normalising, hardening, tempering and carbonitriding all put different demands on the curtain: atmosphere, temperature at the mouth, the profile of the charge and how often the curtain is disturbed. A curtain that suits a tempering line will not necessarily survive a hardening line with a heavy charge.
- Mouth temperature and atmosphere first, then cloth weight
- Reinforcement: glass filament, stainless wire or none
- Edge treatment and fixing, so the curtain hangs straight
Reference note. Figures and standard references are indicative and do not replace the project specification, the current edition of the standard, or product test reports for the specific supply.