PROCESSING | MIXING TECHNOLOGY
Right: Farrel Pomini celebrated the 60th
of its FCM continuous mixing
technology earlier this year
anniversary
plastic fractions must be plasticised and mixed before pelletising, says Rolf Huesser, CEO of Promix Solutions. However, shifting some of that task to a device that incorporates static mixing and cooling technology can deliver benefits. Intended for installation between the outlet of the twin-screw extruder and the pelletiser, the Promix cooling mixer is designed to further mix and homogenise the raw materials and additives while providing precise temperature control and additional melt cooling. Its patented technology is said to combine a static mixer and high-perfor- mance static melt cooler. It features a lattice of hollow metal bars that intersect with each other and are designed to provide highly efficient mixing of the melt with cooling over its cross-section. Thermal oil can be circulated though the bars to
The Promix cooling mixer combines static mixer with advanced integrated thermal regulation to lift compound and pellet quality
provide control of melt temperature prior to pelletising. Promix says that an excessively high temperature of the material prior to pelletising will result in inconsistent granule size, reduced produc- tion capacity or could even shut down the process. The Promix unit is said to allow mixing to be carried out at high capacity without compromising quality. It provides effective yet gentle mixing, avoiding high shear intake and degradation of the compound. The cooling mixer technology is available for lab-scale applications processing a few kg/h up to industrial lines with throughputs of more than 10,000 kg/h. Promix technology is already being applied in injection moulding applications. In one example, an Asia-based manufacturer of inhaler housings was struggling with colour streaks in their injection moulded parts, leading to above-average reject rates and higher quality control and inspection costs. Increasing the back pressure, the usual solution for this type of defect, provided a slight improvement but resulted in longer cycle times and, consequently, lower productivity. “If you look closely, you will find machines in a
lot of injection moulding companies are not running optimally and (are producing) injection moulded parts that are causing problems. You can think of increased cycle times,
part warpage, colour streaks, high masterbatch consumption or weak points in flow seams,” says Promix Solutions’ Heusser. He says after installing a Promix mixing nozzle colour streaks were elimi- nated with cycle times being shortened by a further four seconds, which resulted in an overall produc- tivity increase that the customer put at 12.5%. The investment costs were paid back within two months.
Multiplicative mixing US single-screw systems maker Randcastle Extrusion Systems has developed a type of multiplicative mixer for compounding applications that Chief Executive Officer Keith Luker calls the Molecular Homogenizer. He says there are two types of multiplicative mixers: static and dynamic. The Molecular Homogenizer is a dynamic multipli- cative mixer, Luker says, claiming design and processing advantages over both static mixers and twin-screw extruders by providing dynamic multiplicative mixing. Static multiplicative devices emulate the Baker’s
Transformation, a mathematical concept that describes how a continuous process multiples the result. Luker says a simple way to explain the concept is to consider a piece of string that is repeatedly stretched, divided and reassembled. While the transformation itself (the process of folding and stretching) is simple, when it is applied many times the outcome becomes highly complex and difficult to predict. Typical multiplicative devices for polymers
emulate the Baker’s Transformation, with the most common multiplicative device being the twisted ribbon, which has a multiplier of two (meaning it doubles the layers with every twist), according to Randcastle. After eight twists, the twisted ribbon makes 256 layers. However, a disadvantage of static multiplicative
52 COMPOUNDING WORLD | November 2023
www.compoundingworld.com
IMAGE: FARREL POMINI
IMAGE: PROMIX SOLUTIONS
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