Aerosol Spray Can

Spray cans produce an aerosol, the technical term for a very
fine spray. They do this by means of a pressurized propellant, which
is a liquid that boils at everyday temperatures. Inside the can, a
layer of gaseous pressure increased, and eventually it becomes so
high that boiling stops. when the nozzle is pressed, the gas pressure
forces the product up the tube in the can and out of the nozzle in a
spray or foam. The propellant may emerge as well but, now under
less pressure, it immediately evaporates.
First patented in the US in 1941, aerosol spray cans have been
used as convenient packages for an ever increasing range of
products including paints, insecticides, and shaving cream to name
a few. The can is filled with the product to be sprayed and the
propellant, a compressed gas such as butane or Freon. The gas is
partly liquefied by the pressure in the can, but there is a layer of free
gas above the liquid. As the can empties liquefied gas vaporizes to
fill the space.
The valve is normal held shut by the pressure in the can, and
by the coil spring directly below the valve stem. When the push
button is pressed, it forces the valve stem down in its housing,
uncovering a small a small hole which leads up through the stem to
the nozzle in the button. This allows the product to be forced up the
dip tube by the gas pressure in the can. The nozzle is shaped to give
a spray or a continuous stream.
To produce a fine mist, a propellant is used which mixes with
the product. The two leave the nozzle together and the propellant
evaporates a soon as it reaches the air, breaking the product in to
tiny droplets. The same technique used with a more viscous liquid
and a wider nozzle results in a foam. For a continuous stream of
liquid or more viscous material, a nonmixing propellant is used, and
the dip tube reaches into the product.
The widespread use of aerosol cans using Freon as the
propellant led scientists to believe by the late 1970s that the ozone
layer in the upper atmosphere, which filters out harmful Ultraviolet
radiation from the sun, could be destroyed by the large quantities of
fluorocarbons in the gas being release into the air. Federal controls
were introduced to ban the use of Freon, and other propellants are
now employed, notably butane which, however is dangerously
flammable.
Among young people in United States, conventional drug or
alcohol abuse has given away-for an increasing number of teen-
agers-to a practice called 'huffing', inhaling chemicals found in
aerosol sprays and other common household items such as cigarette
lighters, paint thinner, gasoline. Inhalant abuse is becoming
increasingly common among young middle-class teenagers. It is a
cheap, and sometimes deadly, thrill.









Yoon, Byung
Period 1

Aerosol Spray Cans
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