Extrusion International 5-2020

30 Extrusion International 5/2020 COMPOUNDING To date, Buss has produced over 3,500 of these compound- ing systems in the formof customer- and application-specific solutions, exporting them to over 80 countries. Applications range from compounding high-performance engineering polymers with temperature- or shear-sensitive components, such as electrically conductive carbon blacks with filler con- tents as high as over 90%, to the production of formulations for the aluminum, chemicals and food processing industries. Buss’s current range of compounding extruders for the plas- tics and elastomer industry includes the COMPEO series, which is available in six sizes and is capable of processing up to 12,800 kg/h of thermoplastics. The key to success The highly effective and simultaneously gentlemixing action is the result of the particular way the Buss Kneader works. Firstly, its screw helix has two to four gaps per turn, which give rise to the characteristic flightswhichmeshwith station- ary kneadingpinsmounted in thebarrel. Secondly, the screw shaft simultaneously rotates and axially oscillates, perform- ing a complete forward and backward stroke from its start- ing position per revolution. The shear required for melting and dispersion arises in the shear gap between screw flights and kneading pins. Based on the working principle, the shear rate is independent of machine size and is directly proportional to the rotational speed of the screw shaft. This explains a further advantage of the Buss Kneader technology, the straightforward scal- ability from lab to production scale. Increasing variety of applications For many users who handle a wide range of products, the Buss Kneader is the system of choice thanks to its all-round capabilities. It has also become a technology leader in spe- cific niche areas. For instance, manufacturers of insulation formediumtoultra-high voltage cables by reactive extrusion appreciate its precise temperature control. In semi-conduc- tive compounds, the gentle dispersion of highly structured additives is key, while in other thermoplastics the decisive factor is compounding within tight processing windows. Applications in medical technology include the production of compounds for handling liquids and for sterile packaging for medicines, of compounds with antibacterial and antiviral properties and of adhesives, for example for dressings. The Buss Kneader’s moderate shear rates combined with very goodmixing characteristicsmean very small quantities of ad- ditives can be uniformly incorporated. In applications involving temperature- and/or shear-sensitive ingredients, for example in compounds based on PBT (poly- butylene terephthalate) or high-temperature-resistant poly- amide (PA), in thermosetswhichhave tobe compoundedbe- low crosslinking temperature, or in natural fiber-reinforced materials, the moderate shear rates mean compounding can be carried out within tight operational windows. Appli- cations range from electronic components via under-hood parts to weight-optimized aircraft or vehicle parts. BUSS AG Hohenrainstr. 10, CH-4133 Pratteln, Switzerland www.BUSScorp.com 75 years of Buss Kneader Technology 20 August 1945, the day graduate engineer Heinz List filed a patent for the principle of the continuous kneader, is regarded as this compounding technology’s birthday. Convinced by the concept, Buss AG inaugurated the first kneader test center in 1948 and delivered the first compounding systems for PVC and polystyrene in 1950, by which time List had become technical director. The company subsequently established this technology globally as the systemof choice for producing compounds both efficiently and particularly gently Innovation and Enhanced Performance in the Production of Multilayer Pipes A glimpse into the process chamber of the current generation of COMPEO kneaders showing the position of the barrel-mounted kneading pins, whichmesh with the flights of the modular screw shaft (© Buss)