how are those fashionable plastic "containers" we see
sold in stores like the container store and target made? The items, from
chinese take-out boxes which are marketed as gift giving items, and
pseudo-briefcases, are made out of one piece of plastic folded in>various
ways. I wondered if they were cut out from sheets?
Most "one piece" plastic items are manufactured by a process called:
The parts/procedure consist of a 3-D hollow template or mold the shape of
the article being produced. The mold is usually made of steel. The plastic
is formulated in advance to have the desired properties such as color,
viscosity at elevated temperature [You'll see why in a moment.],
flexibility, and so on. The list of properties can be long. The plastic is
heated to a temperature above its glass transition temperature. That is the
temperature where it becomes molten -- the viscosity of honey or even
higher, depending on the equipment. The molten plastic is then squirted
[injected] into the mold by a piston or by high pressure air. The mold has
been heated to a temperature somewhat lower than the glass transition
temperature. The molten plastic fills all the nooks and crannies of mold,
but cools below the glass transition temperature, and hardens,so it no
longer flows. The mold is snapped open, and the plastic piece pops out and
goes on down the assembly line, cooling more as it goes along.
These are big, fast machines that can produce hundreds or thousands of
articles per minute, depending upon the size and complexity of the article.
If you look at the bottom of a soda bottle, or some inconspicuous place on
some other plastic article, and see a little "nib", it was probably formed
by injection molding.
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Update: June 2012