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Steve Ham Plastics

Product Design and Process Technologist

 

Structural Foam

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:HDPE structural foam- thank you Wilmington MachineHDPE structural foam- thank you Wilmington Machine

 

 

 

 

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.Clamped mold prior to resin injectionClamped mold prior to resin 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.Short shot of resin injection beginsShort shot of resin injection begins

 

 

 

 

After resin injection is completed, 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".Blowing agent pressure does final packingBlowing agent pressure does final packing

Structural Foam molded as a low pressure short shot will exhibit "Swirl" or flow marks on the surface of the molded part. This natural occurrence results from the pressure drop on the leading edge of resin flow front during the mold filling phase of the process. 

 

 

East SideEast Side

The cantilever design by Jim Fox is all about maximizing the view of Whiteside Mountain from every room in the house.

Whiteside Mountain ViewWhiteside Mountain View

 

The center piece of the great room is a massive rock fireplace which carries the cantilever design elements.

FireplaceFireplace

 

The KiteHouse resembles a kite flying in the ridge top breeze.

KiteHouseKiteHouse

Life on top the ridge. At 4,500 feet, it's always cool and breezy.

South Facing DecksSouth Facing Decks