Fast and reproducible sample inspection of plastic pellets
SORTCO GmbH & Co KG is a specialist for optical and mechanical sorting of shape and color deviations in plastic pellets. Further focal points are dust removal and metal separation of plastic raw materials. In March 2021, the company opened a new, state-of-the-art sorting service center in Niederzissen/Rhineland-Palatinate, Germany, where both optically demanding technical plastics and standard plastics are cleaned. The PURITY CONCEPT V, an optical inspection and analysis system from SIKORA, is used for final sample inspection after the sorting process.
The highest purity of engineering plastics is a decisive feature for the quality of the end products, especially for use in the automotive, aerospace as well as medical and information technology industries. The requirements for the purity of the materials are correspondingly high. Since 2015, SORTCO has been active as a contract sorter and professionally prepares plastic pellets according to customer requirements. “The goal of all sorting orders is a high-purity product,” says Mr. Hilger Groß, Head of Sales & QM at SORTCO, adding, “We aim to supply our customers with material which is so clean that it is at least equivalent to virgin material. Therefore, our sorting includes a 100 % inspection of all individual pellets.”
The sorting is carried out by means of different inspection methods. For the optical inline inspection and automatic sorting, two PURITY SCANNER ADVANCED from SIKORA are used at SORTCO. Following the sorting, the random sample inspection of the pellets for final quality control is performed with SIKORA’s laboratory testing system PURITY CONCEPT V (pic 1). “With the system, we inspect a pellet quantity defined with the customer and agree on the inspection frequency. For 1,000 kg of pellets, for example, between 1 and 3 samples of approximately 100 g each are inspected.” The test material is distributed on the sample tray, automatically guided through the inspection area and inspected by a camera within a few seconds. A projector marks contaminated material in color directly on the sample tray. At the same time, the contaminated material is displayed and marked on the monitor, indicating the size of the contamination. Individual contaminated pellets can be selected and magnified. On the sample tray, these are simultaneously visualized optically by crosshairs (pic 2).
There are several inspection methods for the random inspection of plastic pellets on the market. However, according to SORTCO, the inspection and analysis system from SIKORA has proven to be the leader in this field due to its functionality, reliability and speed. “Only with SIKORA, the test material lies on a sample tray without any movement. Thus, the analysis image shows an unsurpassed image quality. With alternative systems, the specimen is in motion, whereby blurring of the image makes an unambiguous evaluation more difficult,” explains Groß and continues, “With the PURITY CONCEPT V, we can make reliable statements about the product quality very quickly, very easily and, above all, reproducibly. A clear competitive advantage is the projector. All detected contamination is precisely marked via a light spot or colored crosshairs and can be easily removed from the sample tray. These can be further examined and analyzed to draw a conclusion about the cause of the defect.” Clear assignment of contamination and follow-up checks are possible at any time and do not have to be carried out manually by the operator. Groß also cites the clearly structured test report as a quality inspection certificate for the customer that complies with the requirements of ISO 9001:2015, as well as the testing speed of only about 15 seconds per sample inspection as clear advantages of the system. “Including all handling, we have a representative test result within 2 minutes. That is unbeatable on the market.”
There is hardly any type of contamination that the system cannot not detect. The PURITY CONCEPT V is far superior then the human eye. Humans initially recognize only large contrasts; smaller and lighter defects are overlooked. The system immediately identifies all color deviations from a size of 50 µm. These are often burns of the polymer in varying intensity, the so-called black specks, specks, burns or also brown or yellow specks. The size and number of all colored defects and contamination in the pellets are recorded. An unlimited number of individual tests or alternatively serial tests can be performed. Up to 100 individual tests can be combined into one overall result. The test results are documented and automatically made available to the customer together with the sorting results and the quantity balance after completion of the order. Usually, test samples are stored for 12 months. However, the test data is also available at SORTCO beyond this period so that customers can refer to it, for example, in the event of a complaint from the end user.
Innovative and reliable inspection systems for purity testing are essential for sorting at SORTCO. Inspection and sorting systems will continue to gain importance in the industry in the future. According to Groß, this is due to the increasing visual demands placed on products, but also to the high costs associated with machine downtime and repairs to hot runner systems and injection molds. At the same time, sorting reduces injection molding waste, which, in addition to the economic benefits, also helps protecting the environment. “With the opening of our sorting service center in Niederzissen, we will install more inspection and sorting machines,” Gross reveals. The creation of new sorting capacities is only one aspect of this. In the future, the main focus will be to reliably detect defects from a minimum edge length of 50 µm and to separate them in the best possible way. “With SIKORA, we have found a partner whose systems meet these requirements not only for the random sample inspection, but also for the sorting.”
