TPT September 2019

AR T I C L E

Sikora AG

Combination of light table and automatic sample testing for offline inspection and analysis of the smallest contamination By Sikora AG, Germany

Conventional technologies for offline inspection and analysis of plastic material On the markets established technologies for sample testing inspection and analysis of plastic material are subsequently described. A distinction is made between manual light tables and automated optical inspection systems. Manual light tables are commonly used in the industry for a visual sample testing and incoming goods inspection of plastic material. The material to be inspected is illuminated on a table and manually inspected for contamination by an operator. This time-consuming method depends on the respective auditor. The respective form on the day, experience and amount of time the operator is investing in the inspection of the material are just a few factors that influence the quality of the test result, hence, only a limited repeatability is given. Reflective and highly transparent pellets further complicate the manual visual inspection. Further limits are detectable sizes of contamination for the human eye as well as their classification into size classes [2] . Alternative optical inspection devices available on the market feed the test material through a hopper and a channel into the inspection area. Thereby, pictures of the material are taken successively. Distinct allocations of contamination to the graphic material as well as a follow-up inspection are not possible. Optical sample testing with automatic light table system and evaluation The combination of visual light table and automatic sample testing is an innovative technology. The operator places the test material on a sample tray. The automatic light table transports the tray with the material through the inspection area, which is equipped with a CMOS line scan colour camera.

Increasing quality requirements in the plastics industry Plastics, as they are used in the medical sector, or in aerospace and automotive industries, require the highest quality standards as well as reliable control and processing of raw materials. Contamination may occur during the different process steps for the production of plastic products. During pellet extrusion, for example, cracking in the form of black specks can occur in the material due to temperature peaks. If they enter the further production process, the absolute purity of the final product is no longer guaranteed – sometimes with severe consequences. In the production of medical tubes, contaminants in the raw material can lead to a full loss of production. Before production may start again, the whole production line has to be cleaned. In the area of injection moulding, purity is a crucial criterion. Thus, spray nozzles can block due to contaminants, which may cause high subsistent costs. Quality standards in the plastics processing industry present great challenges for plastic manufacturers as well as the processing industry. Inspection and analysis of raw material before it enters the production process is thus industrial standard. In order to ensure the highest quality of the material and of the final product, plastic manufacturers use online inspection and sorting systems. They inspect the material, detect contaminants, coloured anomalies and inhomogeneities in the ongoing production process and automatically sort out contaminated material [1] . Furthermore, systems for sample testing or incoming goods inspection and analysis of plastic material are used. This offline inspection and analysis provides material manufacturers and processors with key information on contamination, the causes of contaminants as well as on their own production processes and is, therefore, essential in future-oriented production lines.

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SEPTEMBER 2019