Extrusion International 2-2024

48 Extrusion International 2/2024 PROCESSING Paying attention to detail High quality components are important. To prevent scratches, dots or dents on the sheet surface and attain the demanded quality at high output, the surface of each roller – from the roll stack to the winder – has to be with pre- mium surface finish. The web guiding at all roll- ers, and especially the wrapping angles and the diameter of the guiding rollers, must be aligned for processing extra-thick sheet. Last but not least, the optimum fine settings all over the process and the right tension settings on the sheet web are essential for suc- cessful production. Keep dust away Crystal clear, extra-thick APET sheet should be produced in a relatively dust-free environment, as APET has a propensity for static charges. Oth- erwise, dust will be “sucked” to the sheet during production and can create scratches. “Dust might seem to be a tiny issue, but all of the measures mentioned above are null and void if the produc- tion environment is not relatively free of it,” Ru- pert Becker concludes. SML offers a number of different technologies for the production of APET. For extra-thick ther- moforming sheet for crystal-clear applications, SML recommends single screw extrusion systems in com- bination with upstream dehumidifying dryers, where the raw material is pre-treated. SML Maschinengesellschaft mbH Gewerbepark Ost 32, 4846 Redlham, Austria www.sml.at Optimization Process Parameters for PVC Compounding using a COMPEO Kneader The excellent mixing capabilities of BUSS Co-Kneaders can be attributed to the unique operating principle which features simultaneous rotation and axial oscillation of the mixing and kneading screw shaft. The oscillating screw shaft ensures intensive material exchange in an axial direction by multiple splitting, folding, and reorientation of the product. This principle is very suitable for many demanding applications, while the flexibility of the compounder offers a series of aspects that can be optimized for PVC compounds. F ollowing is a description of optimized machine pa- rameters of the COMPEO kneader that contribute to high productivity and optimum quality of the PVC com- pounds. • Optimized intake zone with back venting and ex- panded volume intake. Two features were improved: intake length and expanded volume intake section (EVI) • Flexible process section which can be configured us - ing 3-flight or 4-flight technology or a combination of both to optimize the transition/mixing zones • Flexible discharge concept with conical twin screw or single screw in cascade configuration One area of optimizing the intake zone is the inlet length. If the inlet length is too short, the material in- take becomes the bottleneck for the whole process (not sufficient back venting, and fluidization of pow - der). If the inlet is too long, it will waste process length. Therefore, the target is to find the optimum length of the inlet opening through different trials with typical PVC grades. The findings are shown in diagram 1, where the throughput remains unchanged above 2 L/D and is reduced below 2 L/D. So, the ideal inlet length for the COMPEO machine is 2 L/D. A further aspect of optimizing the inlet zone refers to the optimization of the EVI (expanded volume intake). This EVI can be influenced by the single screw design of the BUSS Kneader as it allows flexible variation of the outer screw diameter and its length. The target is to find optimum EVI parameters. The first is the ratio between the inner and outer di - ameter. Thereby the inner diameter remains the same. This influences the free volume by the intake to get the dryblend in. The second variable reviewed is the length of the EVI.