Page 60 - Plastics News October 2018

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Nordson to introduce the screen packs BKG® screen changers at

Fakuma 2018

ordson will introduce the screen packs at Fakuma as low-cost alternatives, increasing the productivity of the
N2018. The New screen packs for BKG® screen changers extrusion line and enhancing profitability.” Depending on
from Nordson Corporation effectively withstand the customer requirements, Nordson supplies the screen packs
pressures of extrusion, providing maximum filtration and with different layer combinations. One common structure,
optimum melt flow while ensuring a longer working life for example, has four layers, including two coarse square-
and greater reliability than low-end screen packs on the weave layers that serve as the outer components and a
finer internal square-weave layer. These provide support
and drainage functions and withstand high tensile forces.
The fourth layer is an optimized Dutch weave wire mesh
that serves as the fine filtration component. The small
geometric pore size of the Dutch weave layer ensures
high permeability. Filtration takes place crosswise with
respect to the direction of melt flow, enabling dirt
particles to be separated from the melt efficiently. “A key
factor for efficient filtration is permeability,” said Stefan
Woestmann, application engineer. “The Nordson screen
pack provides the optimum ratio of solid material and free
In photo of BKG® NorCon™ D-SWE screen changer, screen pack is volume, so that the polymer melt can use as many flow
visible just left of center as a round component with the Nordson paths as possible to make its way through the filtration
name on its face. medium. In processes with low-end screens, which are
not flow-optimized in this way, polymer melt builds up
market. The new multi-layer structure and exact fit to and causes a significant increase in pressure. This leads
cavity combine to prevent Screen failures and product to premature and costly screen changes and endangers
contamination, reducing downtime and yielding more the quality of the end product. If the polymer flow is not
saleable product .One key to the enhanced performance uniform, the end product cannot be either.”
of the new screen packs is a robust multi-layer structure
that prevents failures caused by the pressure differential—
up to 200 bar—encountered during filtration. One such
failure is “screen dimpling,” in which the mechanical
stress forces screen layers into the holes of the breaker
plate that supports the screen in the cavity. This distorts
the screen, breaking the peripheral seal and causing
contaminants to bypass the screen and become part of
the end product. Nordson precisely tailors the size of the
screen pack to the dimensions of the cavity, eliminating
the common problem of contaminant passing the screen
pack at the edges. In addition, all screen pack components
are ultrasonically pre-cleaned during manufacture to
eliminate contamination from the oil and grease used in
the weaving process. “The new Nordson screen pack design
maintains structural integrity while efficiently filtering out A common configuration for the new screen packs from Nordson
contaminants and ensuring optimal melt permeability,” has these four layers, as shown from left to right: coarse square
said Christian Schroeder, global product manager for melt weave; fine filtration; fine square weave; and coarse square weave.
delivery systems. “As a result, our screen pack yields more The outer coarse-weave layers provide support and drainage and
output between screen changes than screen packs offered withstand high tensile stresses.

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