National Plastics Exposition in Chicago (June 22-26) will
be a great place to scout new green materials' technologies. Look for the latest engineering ideas ranging
from bioplastics to new materials and processes that reduce component weight.
promising idea for design engineers is microcellular foam, which will be demonstrated
at the Engel booth (24000) in McCormick
use of supercritical gases such as nitrogen during injection molding produces a 10-percent-or-more reduction in part weight and significant energy savings. And because
cycle times are reduced, presses are 20 to 33 percent more productive. The technology, originally developed
at MIT, is targeted at precision and engineered plastic components with maximum
wall thicknesses of less than 3 mm.
parameters such as flatness and warpage are also improved because pack and
hold phases in the injection cycle are eliminated.
at Southco, a major fastening technology
company, are among the super users of the MuCell foam process. "We typically seek to achieve a five-percent
weight reduction, but our customers aren't overly concerned with that," says
Southco's Principal Engineer Glenn Anderson. "They're primarily after
improved quality. We do experience cycle-time savings to some degree based on
the part being produced, but that's more of a side benefit at this point in
says Southco has achieved as much as a 40-percent reduction in part weight.
achieved improved torque strength and better dimensional control on a
glass-filled nylon push-to-close part, in addition to improved manufacturing
efficiency. Warping and sink marks caused by thick cross sections were
eliminated with the MuCell process. Anderson
says another major benefit is aesthetics.
leveraged the technology improvements to win business in the automotive
looking for a competitive edge for potential programs," says Bill Sokurenko,
business development manager at Southco. "The automotive industry is high on
innovation, but they're also very conservative. MuCell helped us win business on
large automotive programs because of the benefits we gained." Southco has made
more than six million parts a year for automotive customers with the MuCell
still looking at highly engineered, functional
touch points in vehicles that are
A-surface components (where MuCell could be applied), whether they're on the
instrument panel or in an around the general cockpit area," says Sokurenko.
The big new
push for the microcellular foam will be in large-part automotive applications.
At the NPE,
Engel will be showing parts made on a 1,000-ton press using the "core-back"
process, in which the back of the mold is partially extracted after an initial
mold filling. The foam continues to expand, creating a multilayer structure.
announced the core-back process reduced component weight up to 30 percent
and will be used on parts for 2011 model-year cars. Initial target applications
for the process include instrument panel retainers and door panel liners.
combine core-back and the MuCell process, you can essentially saturate the polymer
with super-critical fluid, or gas in its super-critical state, while keeping the
mold closed under pressure," says David Bernstein, president of Trexel, which
was granted an exclusive license to market the MuCell process. The mold can
then be precisely opened to get maximum expansion. "You get a much thicker
part, but one that is much less dense, in fact as much as 75 percent less
dense," says Bernstein.
The bubbles in the outer
layer are microscopic to ensure necessary strength and rigidity, while the size
of the bubbles in the core layer can be adjusted to reduce its density as
desired. Because the core back process controls the foam's structure, it can be
used to enhance the heat insulation and acoustic characteristics of plastic
parts, according to Mazda.
Braig, president of Engel's North American operations, says the process is
suited for any flat parts. "Design engineers can now re-think the mechanics on
some existing applications in plastic because dramatic weight reductions are
realistic," Braig says. Trials can be conducted at Engel's factory in York, PA, one of two
remaining factories in the United
States that make injection-molding machines.
of the MuCell process is not easy. Southco's Glenn Anderson says, "A person
implementing the MuCell technology really has a steep learning curve to
understand how to make the process work and how to ensure reliable output.
Also, if you're making a plastic bucket, for example, you may not really care
that much about the mechanical properties. You're interested in how does it
look and how much money can I save. With engineered fasteners, we need to make
sure we have the design margins where we need them so that we don't have any
issues downstream. Each tool brought its
own characteristics in terms of how you would mold solid or in MuCell."
Braig says, "To succeed with core-back, you need precision machine technology."
Position and clamp force need to be precisely controlled.
300 machines globally are now making parts with the MuCell process. Other
commercial parts include electrical components, electronics, business equipment
and printer components, as well as packaging containers.
is totally different from gas-assist injection molding, in which gas goes into
a mold cavity following resin injection and is used to push the melt stream to
the cavity wall. In the MuCell process, supercritical fluid is injected in the
barrel, and is part of the melt stream.
process works without chemical blowing agents, hydrocarbon-based physical
blowing agents, nucleating agents or reactive components. As a result, the
Trexel process can handle a wider range of melt indexes than conventional
In one of
the newer developments, MuCell can now be applied to long-fiber reinforced
thermoplastics (LFRT) from Ticona.
warp-free, light-weight parts molded of Celstran LFRT are now a viable option
for OEM designers and injection molders developing large parts and structural
profiles," says Steven Bassetti, marketing manager for Ticona. "The Ticona team, working in conjunction with
Trexel, developed extensive data for the Celstran LFRT grades using
polypropylene and nylon 6 and that will help customers predict the performance
of parts made with the MuCell process using the new screw."
produces LFRT grades through use of pultrusion technology that fully impregnates
the long fibers to deliver optimal reinforcement to the plastic matrix. Unlike conventional short-fiber reinforced
materials, the longer fibers present in molded parts mechanically interact with
each other to form an internal glass fiber "skeleton" that limits anisotropic
shrinkage and greatly reduces warpage.
screw design uses a lower compression ratio, 2.0:1 as compared to 2.5:1, and
incorporates significant changes to the center restriction element and the
wiping and mixing sections to reduce shear.
Testing on these screws has been done using the MuCell process with up
to 0.6-percent nitrogen in a Celstran LFRT grade that uses 40-percent glass-fiber-filled polypropylene without observing process variations.
green highlights at the National Plastics Exposition will be new plastics made from renewable
resources. Some of the key players include:
DuPont (West Hall, booth 113011) is
expected to exhibit its latest plastics made from agriculturally sourced polylactic
acid. Sorona EP, Hytrel
RS and Zytel RS include renewably sourced biobased ingredients and can deliver
additional benefits, such as improved stain resistance, appearance and better
durability when compared to their petroleum-based counterparts. For example, Sorona EP polymers contain
between 20-percent and 37-percent renewably sourced material (by weight)
derived from corn. Initial grades with 15-percent and 30-percent
glass reinforcement were made available last year for development programs.
Metabolix (West Hall, booth 119020) will
show products made from its Mirel polymers, which are harvested from vats of
genetically modified microbes that feed on glucose from plants, such as corn. Metabolix
and Archer Daniels Midland Co. are
commercializing Mirel through a joint venture called Telles. The first
commercial-scale Mirel production plant is being constructed adjacent to ADM's
wet corn mill in Clinton, IA. Commercial product is expected to be
available from the plant this year.
Hall, booth 13a) has hooked up with Brazilian sugar cane producer CrystalSev to
a 700 million lbs/yr polyethylene plant in Brazil â the biggest such plant ever
contemplated. The molecular structure of the sugar-derived polymer will be
identical to the structure of plastics made from naphtha or natural gas liquids.
Dow is the biggest producer of PE in the world. The plant is expected to start
production in 2011 and will have a capacity of 350,000 metric tons annually.