Die with innovative gauge adjuster lets sheet extrusion maintain strict standards, boosts output


Breakthrough extrusion die technology from Nordson Corporation has enabled King Plastic Corporation to achieve a substantial increase in productivity while continuing to manufacture stress-free, high-flatness sheet held to strict gauge tolerances.
Well known as a sheet-industry innovator with special capabilities for heavy-gauge products, King Plastic recently installed a Nordson EDI™ sheet die equipped with the new SmartGap™ mechanism, which makes possible changes in thickness with unprecedented speed and extends the range of thicknesses that can be produced without shutting down the production line. King Plastic uses the die to manufacture monolayer sheet for its King StarBoard® family of marine products and coextruded sheet for its King ColorCore® sheet for signs and other multi-color applications. Thus far the company has operated the SmartGap die for thicknesses of up to an inch (25.4 mm) but intends to expand its usage to 1 ½ in. (38.1 mm) sheet, according to Jeff King, owner and president.

 “With the SmartGap die we are adding well over a day’s worth of production every month by eliminating much of the downtime required for job changes and gauge adjustments,” said Mr. King. “Because our sheet goes through multiple distribution channels and is fabricated under a wide range of conditions, an essential factor in our success has been to maintain exceedingly high standards for quality and consistency. The new die from Nordson enables us to hold these standards with minimal need for operator intervention.”  Nordson’s patent-pending SmartGap lip and land positioner uses a single-point adjustment mechanism that changes the lip gap while simultaneously modifying the length of the lip land to provide the most appropriate conditions for the newly adjusted thickness as the sheet exits the die. (The lip land is the final gap in the die that forms the lip exit.) By mechanically linking the adjustment of these two key process variables for the first time, the SmartGap system ensures a proper set-up of the die and takes substantial time and guesswork out of the process for achieving desired sheet properties. 
“With a conventional die, making a significant thickness change requires shutting down the line and changing the lip components, a process that can take up to eight hours from shutdown to startup,” said Dale Givens, director of operations. “The SmartGap system eliminates almost all of this downtime.”

The single-point adjustment mechanism also speeds up the process of fine-tuning thickness, Mr. Givens noted. “The operator can do adjustments on the fly when increasing the die gap, keeping the line running without having to rethread. Guided by a die gap readout gauge, basically it’s a matter of one person using a wrench to turn a bolt. What used to take up to an hour now takes three or four minutes.”  Mr. Givens also cited improvements in coextruding the King ColorCore sheet. This has an ABA structure whose thin cap layer can be engraved away to expose a core layer of a different color, making possible, for example, a multi-color sign. “Layer uniformity has improved across the board due to the fine-tuning of the flow channels and the changes in land length.” Another time-saving benefit of the SmartGap system involves cleaning the die. “Because the lips slide so extensively, all of the flow surfaces can be fully exposed,” said Mr. Givens. “By closing the lips to the minimum gap, it is possible to avoid having to take the lips apart when the die is split for cleaning.” 

“At Nordson we believe the SmartGap system to be the first real breakthrough in sheet die technology since the start of this century,” said Sam G. Iuliano, Nordson EDI chief technologist. “It eliminates the uncertainties and compromises that have often accompanied significant changes in thickness.” With a SmartGap die, the operator sets the thickness-change process in motion by using an adjustment mechanism at the end of the die to make a new setting for the lip gap. Simultaneous change in the length of the lip land automatically takes place on an as-needed basis, depending on the target sheet thickness. Thus, for thin sheet, the lip land is short, which helps to control back-pressure at smaller die gaps, reduces deflection, and lessens the need for draw-down. For mid-range sheet, the lip land changes from short to medium length, providing sufficient pressure for effective adjustments to the flexible lip of the die while helping to reduce swelling of the extrudate. For thick sheet, the lip land is extended to full length, increasing back pressure at large lip gaps and promoting fully developed flow. Prior to the development of the SmartGap system, sheet dies with a medium-sized lip land often had to serve for the full range of gauge variation. This has caused processors to struggle with product quality, especially at the thinner and thicker extremes of their product range.

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