Extrusion International 3-2020

49 Extrusion International 3/2020 sorting system that combines X-ray with optical technolo- gies and, therefore, automatically detects and separates color deviations and metal inclusions down to a size of 50 μm. By using the system, repairs and follow-up costs can be avoided and costs for machines and personnel as well as down times and scrap can be significantly reduced. Quality assurance at plastic manufacturers, compounders and processors Smallest process variations in compounding plants can already cause changes in the technical and optical char- acteristics of the pellets and the future product. Thermal and mechanic overloads of the polymer, contamination caused by the production environment or a work over- load of the staff can result unnoticed in contaminated pellets in the form of black specks, yellowing, burns, met- al, dust etc. During pellets sampling, which is a common method for the industry, contamination often remain undetected because the sample amount in relation to the delivered quantity and to the actual amount of contamination is too low. Furthermore, contamination can occur pooled in one or several bundles and also homogeneously spread over many bundles. Therefore, the taken samples are mostly used for simple offline incoming goods inspection. In the past, plastics with optical defects or contamina- tion were often sold with discounts to compounders or processors. The goods were modified or processed into other compounds with lower dosage. Alternatively, they were processed into products with non or only small opti- cal demands. Charges with metallic contamination were demetallized by means of inductive metal separators and reapplied for a new purpose. While first optical sorting systems were primarily designed and used in Europe in case of an emergency scenario at the manufacturers, a service sector in the area sorting has been developed since the 2000s. The pellets to be sorted are transported to the service provider in their target packaging, where they are optically sorted, newly packed in original bun- dles and picked up again from the manufacturer a few days later. This procedure is inconceivable for manufacturers of high quality and extremely pure raw material such as polyeth- ylene for cable applications. The quality demands in the area of e+e (electric + electronic), in medical or aerospace are that high that any risk of foreign contamination must be eliminated in order to avoid image and consequential damages in the millions. In addition, for mass produc- tion of plastics with very high quality demands and for compounders of technical raw material, a 100 % online inspection with automatic sorting is required. Online inspection and sorting of plastic pellets The online inspection and sorting system developed by SIKORA AG does not only use optical technologies, but also combines those optionally with an X-ray camera. Therefore, even the smallest, in raw material included metal particles can be detected by the system. Further- more, black specks and color deviations are detected by the optical cameras. Faulty pellets are separated immedi- ately after detection via compressed air. The integrated software provides the operator with a statistical evaluation with information about the size, area and number of the detected contaminants during production. In addition, impurities are saved in an image gallery. The image information often gives a conclusion about the reason for contamination and support the op- erator in the optimization of the production processes. The recorded data is permanently retrievable and can be separately evaluated at any time. The relevant size for the detection of pellet defects re- quired by manufacturers and compounders has been ap- prox. 100 μm since the 1990s. Due to further technical de- velopments, resolutions from 35 µm or even lower have been possible for some years now. A high resolution, however, is not a guarantee for the elimination of black specks, color deviations and metal inclusions. A safe sub- sequent sorting process firstly requires a high detection probability. SIKORA AG offers this as a unique feature by using up to four optical cameras and an X-ray unit. De- pending on the expected contamination and application, The online inspection and sorting system detects metallic contamination inside the pellet as well as black specks and burns on the pellet’s surface