Processing: Foam Processing
is used in a wide variety of foam products on the market today - everything from
carpet padding to aircraft arm rests to drinking cups.
The most familiar
type of foam is termed expanded polystyrene (EPS). EPS beads contain a blowing
agent which, when heated, causes the beads to expand from 2 to 50 times their
original size. The amount of expansion is controlled by time and temperature.
Processors heat the beads mostly using continuous steam. They are agitated in
a large steam chamber. As they expand, they flow out the top - much like popcorn
out of a popper - from 3 to 12 hours before final processing.
For small, finished parts, the beads are fed into closed molds for shape
molding, where steam is injected to expand them to fill the mold cavity. The mold
is then cooled and the completed product is removed.
For larger applications processors use block molding, where a large mold
cavity is filled with beads, closed, and subjected to an influx of steam which
causes the block to fuse and set. After curing, the block is cut, usually by hot
wires, into sheet, slab, or custom shapes.
Flexible foam sheet is produced by extrusion. A variety of resins may
be used, but polystyrene (PS) is by far the most popular.