MACHINERY | TWIN SCREW EXTRUDERS


screw elements to facilitate increased channel volume or improved conveyance efficien- cy for handling such low bulk density flakes. Several options exist in the conveying screw elements such as two-flight ‘under-cut’ design or single-flight


Above: CPM’s new Global eXtruder Technology (GXT) line of twin-screw extruders offers a standardised platform that ensures uniformity


screw extruders is continuing to grow. Since its launch in February 2023, the company says it has increased its offerings, added manufacturing capabilities, stocked inventory, and reduced delivery times. In another market-supporting move, Bausano


has introduced a new initiative called the Reward Formula, which provides enhanced valuation for used MD series twin-screw extruders, incentivising their replacement with next-generation models (Compounding World January-February 2025). Before collection, a team of Bausano Experts will assess the condition of the extruder, offering up to 30% above market value for the machine. This creates a virtuous cycle, turning obsolete machinery into a valuable resource. “The goal is to offer our customers the opportunity to update their machin- ery and enhance the productivity of the plants according to a more eco-friendly business model,” said Giorgio Critelli, Area Manager of Bausano.


Modular designs To accommodate the growing diversity of materials and product demands, modular screw designs have become increasingly popular as they allow manufacturers to customise the screw configura- tion for specific tasks without having to invest in new equipment. Screw elements are now often designed to be easily interchangeable, which not only adds flexibility but helps to streamline the manufacturing process and reduce downtime. The debate between co-rotating and counter-rotating screws continues, with the former seeing recent advancements in screw geometry enabling them to handle more complex materials such as highly filled compounds. Also, recycled plastic feedstocks are often supplied in the form of flakes, and the co-rotating extruder can offer an appropriate barrel configuration to handle the intake. “The main feed barrel can be supplied in the


form of a 6D design versus the standard 4D design for increased open area to accommodate low bulk density flakes,” said CPM Process Engineer Daron Fraim. “There are various options for the conveying


18 COMPOUNDING WORLD | March 2025


elements with increased conveyance efficiency. The process section can also include additional side feed locations [where] additives such as thermal stabilisers or reactive components can be fed into the process section for polymer preserva- tion. When reprocessing plastics, there is always a loss in some properties. Specific additives can be supplied and incorporated to minimise degrada- tion and repair the polymer during processing.” Fraim continued: “The co-rotating twin screw


extruder is known for its mixing capability and the versatility of utilising industry standard or specialty mixing elements to reduce the overall shear stress on the material. For instance, there are offerings of a two-lobe kneading block with a modified tip clearance. Utilisation of these specialty elements can offer a gentler melting and mixing characteris- tic to preserve the polymer properties. The extruder is operated under starve fed conditions and can be conditioned to operate under low degree of fill with the incorporation of large pitch conveying elements for efficient devolatilisation. It can incorporate open barrel designs along the process section, which is particularly important in polycondensation polymers. Devolatilisation can be utilised early in the process section as the polymer is heated and melted to remove moisture. Single or multiple stage venting can also be incorporated to remove residual levels of unde- sired volatile content that may arise from side reactions or even VOC content that can cause odour or other undesired properties.” CPM’s new Global eXtruder Technology (GXT)


line of twin-screw extruders offers a standardised platform that ensures uniformity in design and technology regardless of a customer’s location. The platform consists of pre-designed or pre-engi- neered machines that can be built ahead of sale and delivered quickly, allowing customers to choose from various options. They are available with screw diameters ranging from 32 mm to 133 mm, torque densities of 13 Nm/cm³ and L/D ratios of between 40 and 48, with screw speed options of 600, 900 and 1,200 rpm at maximum power output. A modular design key allowing increased flexibility is seen as one of the most marketable


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IMAGE: CPM


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