machinery | Twin screw extruders
materials being processed. This is claimed to result in more uniform energy transfer into the compound material and the elimination of high, cyclical torsional shaft loads. The amount of energy transferred to the melt is also said to be reduced, lowering process temperatures, as is degradation of fillers and reinforce- ments caused by excessive shear. Steer also highlights its “next generation” Fractional
Steer claims its Melt Formation Element design eliminates shear peaks and high torsional shaft loadings
The latest Fractional Mixing Element design by Steer combines mixing and surface renewal during conveying
provide more control of energy usage during com- pounding, and to reduce stress-related wear to equipment. For example, with a Do/Di ratio of 1.71, the company says its Omega series of extruders now combines high free volume with a high specific torque of more than 17 Nm/cm2
. Steer says this provides the
lowest mean shear performance of any high-torque twin screw extruder. The company says that shear peaks have been
Right: This 65-mm
Coperion STS Mc11
series
machine uses a new gearbox designed to
handle higher torque levels
associated with Erdminger-type two-lobe kneading blocks for decades, pointing out that materials trapped between the upturning lobe on one shaft and down turning lobe on the adjacent shaft experience extreme compression and shear. During melting of polymers or initial dispersion of high loadings of fillers or reinforce- ments, solids become compressed prior to the melting of pellets or the wetting of fillers. This creates a momentary large torsional moment on the shaft where the kneading blocks are located. This cyclical loading and unloading of torque on the shafts can lead to accelerated shaft wear and premature failure. “It is also an inefficient use of energy since only a small portion of the material experiences the high pressures,” says a Steer Head of Global Compounding Rob Roden. Steer’s recently-released Melt Formation
Element is claimed to address these points, featuring fractional design lobes that eliminate shear peaks. The lobes of the elements are not positioned perpendicular to the axial flow of the material but are angled to provide gentle compression while forwarding the
32 COMPOUNDING WORLD | March 2016
www.compoundingworld.com
Mixing Element, which the company claims combines mixing and surface renewal during simple conveying. “As melt is moved down the screws it is exposed to efficient and effective elongational mixing. High surface renewal beneath the vent can improve the removal of volatiles. The elements can be used on most any conveying section and can be used in the discharge (metering) section to provide high pressure mixing and melt homogenisation,” according to Roden.
STS Mc11
Long fibre solutions Coperion is also expanding its offering in the area of long fibre technology for the European and Asian regions. In cooperation with ProTec Polymer Process- ing, which is located at Bensheim in Germany, it now offers complete installations for the production of long fibre reinforced thermoplastics (LFTs) using pultrusion technology. Glass, carbon, metal or natural fibres can be mixed into a polymer matrix using its technology. The LFT systems are based on Coperion’s ZSK Mc18 twin screw extruder models. The ZSK Mc18
series is typically used for polypropylene.
or
series is used in particular for products with a high torque demand (typically engineering plastics), while the STS Mc11
Coperion K-Tron equipment is used for feeding, while a Coperion Pelletizing Technology pelletizer equipped with special chopping rotor is used for producing the pellets (lengths normally range between 5mm and 12mm). Line speeds of up to 50 m/min are achievable, depending upon the polymer used. The ProTec impregnation die-head is designed so that it will not clog with filler material. “Roving unwinding with rotating coils, as well
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