MACHINERY | TWIN-SCREW EXTRUDERS
Right: New covers on the latest ZSE iMaxx extruder from Leistritz are the most obvious of many design improvements
Improving control and insight into the compounding process is critical in achieving optimal production efficiency, a point demonstrated in a recent technical paper by Leistritz President and General Manager Charlie Martin and Assistant Lab Manager Brian Haight. “Almost every product benefits by strategically managing how shear and energy is imparted to the materials being processed,” they claim. Martin and Height refer to experimental data
generated comparing Do/Di 1.5 and Do/Di 1.66 model extruders with interchangeable process sections mated to the same gearbox. Initial tests were carried out with a neat powder PE resin with a 40:1 L/D process section and 40hp motor. Further experiments were performed to compare the resulting melt temperature for different melting zone screw configurations with a 2 MFI PP pelletised resin. The screw design in the melting zone directly impacts the melt temperature, and is significant, say Martin and Haight. “Temperature setpoints in this zone will also contribute to the melt temperature. Perhaps counter-intuitively, higher setpoints generally result in a lower melt temperature. Often overlooked, pressure generation at the discharge of the TSE also adds to
the melt temperature. The more restrictive the front end, the higher the pressure and corresponding melt temperature.” Large-scale applications and growing consumer
interest are resulting in a greater call for biodegradable products in several compounding processes, according to Comac, which says it has developed customised processing solutions for various types of biomaterials. “The combination of our twin-screw extruder, designed for gentle mixing, with specific degassing and liquid injection systems allows us to get optimal results in terms of quality and production capacity,” the company claims. Comac has developed systems that accommodate the specific processing needs of PLA and starch-based polymers. “To allow gentle mixing we have studied an optimised screw profile
KM inline system colours the future
KraussMaffei used its K2019 display in Dusseldorf, Germany, last year to demonstrate auto- mated and fully closed loop controlled production of col- oured compounds. Running on a 42D ZE 28 Bluepower laboratory extruder, the exhibit was upcy- cling PP scrap and combined liquid colour, inline spectral photometry, and full recording of process data.
KM considers its Liquid Color
Compounding technology as highly suitable for masterbatch manufactur- ers, in particular, who need to respond flexibly to customer demands. Because the liquid colours are metered directly in to the extrud- er, there is no need for the conven- tional intermediate step of manufac- turing a monoconcentrate, which makes the process especially eco- nomical and suitable even for very
22 COMPOUNDING WORLD | March 2020 Above: KraussMaffei’s Liquid Color
Compounding technology was running throughout the K2019 show
small volumes and special colours. The company says that even convert- ing from dark to light is possible without any problem due to the self-cleaning effect of the twin-screw extruder. During the demonstration, the line was automatically switched between nine different colours for a
PP masterbatch charged with talc. The spectral-photometric inline monitoring system used high- resolution glass fibre sensors to measure the light reflected by the melt during the process, comparing this with a defined target value to detect even the slightest difference in brightness or colour in real time. This was then automatically corrected in real time with no need for sampling and no loss of material. The ZE 28 BluePower also collected
and recorded production data synchronously throughout the demonstration, including pressures, temperatures, rotational speeds, volume flows of all upstream and downstream components. Metering units and pelletiser were also integrated together with the extruder in the overall system control. �
www.kraussmaffei.com
www.compoundingworld.com
IMAGE: LEISTRITZ
IMAGE: KRAUSSMAFFEI
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