How Fire Extinguishers Are Made?
The Manufacturing Process of Fire Extinguishers
Manufacture of the tank-type or cylinder fire extinguishers requires several manufacturing operations to form the pressure vessel, load the chemical agent, machine the valve, and add the hardware, hose, or nozzle.
1. Creating the pressure vessel
Pressure vessels are formed from puck-shaped (disc) blocks of special aluminum alloy. The puck is first impact extruded on a large press under great pressure. In impact extrusion, the aluminum block is put into a die and rammed at very high velocity with a metal tool. This tremendous energy liquifies the aluminum and causes it to flow into a cavity around the tool. The aluminum thus takes the form of an open-ended cylinder with considerably more volume than the original puck.
2. Necking and spinning
The necking process puts a dome on the open end of the cylinder by constricting the open end with another operation called spinning. Spinning gently rolls the metal together, increasing the wall thickness and reducing the diameter. After spinning, the threads are added.
The vessel is hydrostatically tested, cleaned, and coated with a powdered paint. The vessel is then baked in an oven where the paint is cured.
3. Adding the extinguishing agent
Next, the extinguishing agent is added. If the vessel is a “stored-pressure” type, the vessel is then pressurized accordingly. If a gas-cartridge is necessary to help expel the extinguishing agent, it is also inserted at this time.
After the extinguishing element is added, the vessel is sealed and the valve is added. The valve consists of a machined body made of metal bar stock on a lathe, or a plastic injected molded part on the economy versions. It must be leak free, and it must have provisions for threading into the cylinder.
4. Final assembly
The final manufacturing operation is the assembly of the actuating handle, safety pins, and the mounting bracket. These parts are usually cold formed—formed at low temperatures—steel or sheet metal forms, purchased by the manufacturer from an outside vendor. Identification decals are also placed on the cylinder to identify the proper fire class rating as well as the suitability for recharging. Many of the economy versions are for one time use only and cannot be refilled.