HOW CANS ARE MADE
Cases can be aluminum, tin and glass with a capacity from 30 to 1000 cm3. Valve and spray head are situated on the upper part of the case. They are fitted with protective caps to protect from damage and clogging. As a rule there is a siphon tube inside the can through which liquid contents are supplied to the valve.
At the factory, each can is filled with a mixture of two liquid components, combined in a specific ratio: a mixture of active substances solution in alcohol, kerosene or other solvent and liquid inert volatile substance – propellant (usually fluorocarbon propane and butane mixture or carbon dioxide). Propellant vapor create tension of three atmospheres in the can at room temperature. By clicking on the spray head valve opens and the liquid mixture, pressurized by propellant vapor, is discharged through the siphon tube, the open valve and opening in the spray head into the atmosphere as a jet. The propellant that is contained in the mixture almost instantaneously evaporates, and a dense cloud of a plurality of tiny liquid droplets or solid particles of active product in the air – each the size of a few microns. Product consumption – about 1 ml per second.
Propellent-free packaging has almost the same structure, except that spraying of a liquid is not performed via propellant vapor jet, but pressurized air via a spray pump.
There are some types of cans from which active product comes out not as an aerosol cloud but as a foam or a paste.