|
How Foam Expands
(blue text are active links)
Tempo is a sophisticated popcorn popper. We
control foam bead size and density with batch pre-expanders. We offer a variety
of puff bead granulations and raw feedstocks to meet customer needs. Flame
retardant and ESD grades of materials are available.
How Foam Expands
Expandable foams look like
table sugar, small granules of white or dark resin.
The resin is referred to as “beads” and it arrives in vapor sealed
containers.
The raw material has a
hydrocarbon blowing agent dissolved inside each bead. The natural blowing agent
inside your everyday popcorn is water, and it works in a similar way. When
heated, the blowing agent softens the bead, when boiling temperature is reached
the blowing agent begins to gasify, causing the softened bead to expand.
The beads are first
processed much like popcorn, in pre-expanding the
beads to a desired size.
By controlling the time and temperature of this "pre-expansion"
process, the bead size can be controlled to achieve various performance
characteristics of the final molded part.
After pre-expanding and
ageing the beads, they are blown into an aluminum mold which is heated with
steam, this bakes the beads so that they expand further until contained by the
mold wall, further heating causes the beads to fuse together until they lose
their individuality and become part of a solid mass of foam. If not provided
enough heat, the result is poorly fused beads with a "crumbly"
appearance, a condition often seen in the competing "wet molding"
process.
Once
the surface finish is optimized with the proper amount of heating, the mold
temperature is reduced to stop the internal vapor pressure of the blowing agent
inside the molded part. The mold is
finally opened after the part stops expanding.
The part is warm on removal from the mold and begins a shrinkage which is
built into the mold design so your molded part “shrinks to fit.”
(Picture above: Cellular structure of one expanded bead 100X)
|
