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Structural Foam
The following sequence illustrates how the process works:
Prior to resin injection the mold is clamped with 1/4 ton per square inch minimum clamping pressure. The pre-blended material is held in the machine in an accumulator prior to injection.
The machine injects a precisely measured short shot of material. Structural Foam's thicker wall section along with the blowing agent boost allows rapid and low pressure filling.
After resin injection the cavity pressure is isolated and the blowing agent pressure continues to fill the mold cavity.
The blowing agent pressure continues to pack the mold even after the mold cavity is completely filled. This blowing agent pressure compensates for volumetric shrinkage as the plastic cools. The blowing agent becomes an internal "cushion"
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Steve Ham
Plastics 537 Hickory Street Highlands, NC 28741 USA |
Structural
Foam molding has been around since the sixties but remains unknown to many
product designers. It is a way to injection mold very large parts.
Traditional thermoplastic resins are used along with a blowing agent which
produces a molded article with a cellular core and solid skins. These
Polyethylene water tanks convey the concept of size capability:
