Liquids can be evenly distributed and conveniently dispensed using an aerosol can. Since it was first patented in 1927, the aerosol can has become an established component in various areas of life. One of its most popular applications was the invention of hairspray back in the 50’s. Whether hairspray, deodorant, paint, cleaner or even whipped cream – today the aerosol can is an inherent part of our daily lives and is used in various areas.
But how does an aerosol can work?
The can generally consists of a metal container made from aluminium or tin plate, and it is pressurised. Inside, there is a plastic uptake pipe that goes all the way down to the bottom. It is open at the bottom and connected to the valve or spray nozzle at the top.
Let’s take a look at our adhesive spray, for example. The can is full of liquid glue as well as a propellant. The propellant is responsible for the following: It must produce the necessary pressure to express the product out of the can evenly. When spraying, the liquid, or active ingredient, is sprayed out in many droplets. The propellant is a mixture of propane and butane.
When the can is filled, the gas is put under so much pressure that it turns to liquid and partially mixes with the active ingredient. Since propane butane in its gaseous state is lighter than the active ingredient, the non-mixed portion settles above the liquid.
This is called the expansion chamber. This is where sufficient pressure is created in order to transport the product outwards when the spray nozzle is actuated. The less liquid there is in the container, the more the gas expands. This ensures even pressure and that the can will be emptied completely.
High pressure
In most cans the pressure is between three and five bar, in other words, more than in a car tyre. There is a risk of the can bursting at temperatures higher than 50 degrees. The concave base of the aerosol can counteracts bursting of the can. However, it must be protected from direct sunlight and high temperatures. For this reason, cans that have an convex base should no longer be used.
In addition to the classic propellant propane butane, there are various gases, for instance nitrogen, that are also used. These are generally non-flammable, however they may have less constant pressure and a less even spray pattern. For this reason they are used wherever propane butane is undesirable as a propellant, for instance for non-flammable sprays or for products like hand protection foam, shaving foam or whipped cream.
The valve
The most important element of the can is the valve. There are various valve designs. There is a spring situated inside the plastic pipe on most frequently used valves. When you press the spray nozzle, it is pressed down and the valve opens. Thanks to the pressure inside the can, the propellant-active ingredient mixture can now escape through the uptake pipe, valve and spray nozzle.
To ensure that the valve doesn’t get clogged after use, depending on the valve it may be necessary to spray the can upside down so that some of the propellant escapes thereby cleaning the valve. But be careful: This shouldn’t be done too often or with too much force, otherwise too much of the propellant will be lost.
In addition, there is also the ball valve that you can spray from any position – even upside down. This valve is primarily used for liquid active ingredients, like cleaners for instance. The pigments in the paint or metal sprays can make the ball stick inside, which stops the valve from working.
Another alternative to this is the self-cleaning VPH valve with gas-phase opening where both the media and the propellant are emitted simultaneously. This causes virtually no sticking or residue. Another general rule is: The complexity of the valve is reflected in the price.
We use a spray nozzle for our metal sprays that is tilted 10 degrees upward. This means that the spray emits at an angle of ten degrees upwards so that the can doesn’t also get sprayed.
Preis wieder.
Wir verwenden für unsere Metallsprays zudem einen Sprühkopf, der 10 Grad aufwärts geneigt ist. Das heißt, das Spray tritt in einem Winkel von zehn Grad nach oben aus, damit die Dose nicht mit angesprüht wird.
Always shake well
A general rule: Always shake aerosol cans well before use in order to mix the propellant with the medium. In addition, small balls are added in metal sprays or in paints that mix up the metal or colour pigment deposits at the bottom of the can. The clicking sound is the ball hitting the walls of the can.
This enables easy and convenient dispensing of many products, like hairspray, deodorant, de-icer, fitting spray, ironing spray or the classic oven spray. The aerosol can definitely makes our daily lives a lot easier.
