Fire doors are divided into normally closed fire doors and normally open fire doors according to the opening state. Normally closed fire doors are usually closed under the action of the door closer. Therefore, when a fire occurs, it can prevent the fire and smoke from spreading; the normally open fire door is usually in the open state under the action of the door closer. When a fire occurs, the automatic release switch is automatic, and the fire door closer is in the door closer and smooth Closed under the action of the positioner.