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July 1, 2004

2 Min Read
Structural foam takes on large parts

Using a two-stage injection system and nozzle location holes spread across the entire stationary platen on 6-inch centers, a new low-pressure molding machine can create very large parts with smaller force. Suitable for structural-foam, gas-assist, or other low-pressure processes, the Lumina LP from Wilmington Machinery can produce large, heavy, thick parts with 60-second cycles or more. In addition to bigger, single parts, the machine can also mold multiple parts in tools of disparate shapes and sizes in a single cycle.

The stationary platen's nozzle location grid allows for multiple nozzles going into the same or different parts. Resin is plasticated and then accumulated by way of a two-stage injection unit, which features an extruder and an injection shot accumulator.

The extruder can be sized according to desired throughput, and the accumulators can be adjusted to create maximum shot size without having to consider minimum shot size, percentage of shot left in the barrel, or maintaining a cushion, as is needed in conventional injection molding. The gas-over-hydraulic oil accumulator drives the injection unit, which is capable of rapid injection of very large shot sizes.

Wilmington representatives put the structural-foam press forward as a means competitive advantage by facilitating redesigned applications that have consolidated components into large, single parts—which, using standard injection molding, would require a machine of 1000 tons or more, increasing overall program price.

The process's low pressure also allows for the use of cheaper aluminum tooling, which is easier to move, quicker to machine, and conducts heat more effectively than steel. If a part exceeds the machine's clamp tonnage, it can be created using sequential molding, which can double the machine's molding capacity. Parts can be shot in sequence, with a brief dwell time for the resin. For aesthetic parts, wave molding can be used.

The high number of nozzles creates parts with reduced mold flows on the surface, and heavy parts can be molded with standard 25- and 50-lb shot accumulator systems. Inert nitrogen can be used for gas, and parts can be foam and gas-assist molded at the same time, allowing for less material use, and stronger, fully filled components.

The Lumina's modular melt manifold offers the flexibility and processing advantages of a hot runner system, and after the melt is transferred from the extruder to the accumulator, it can be shot simultaneously through all the nozzles, or be fired sequentially. Wilmington Machinery, Wilmington, NC; 910-452-5090; www.wilmingtonmachinery.com

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