Even the smallest metal contamination in plastic granules can lead to significant problems in the processing of plastics or the production of compounds. Regardless of whether the granules will be used for the manufacture of injection parts, cables, films or profiles, the prevention of defects almost always requires considerable effort, and the elimination of marriage is even greater cost
There are many reasons for the appearance of metal inclusions in raw materials: for example, in the manufacturing process, metal screws are abraded in the extruder and small metal particles fall into the finished product (Fig. 1). Abrasion can occur in the pipes of the conveyor due to the high rigidity of the transported material. In addition, metallic contaminants can enter the granules due to damage to the melt filters or defective granulator. Neither with melt filters, nor with inductive metal separators or permanent magnets is it possible to provide complete protection against such contaminants. However, for some types of polymer products, the absence of metallic inclusions in the material is especially important. For example, high-voltage cables should be covered with a plastic insulator, 100% excluding the metal content in it. Otherwise, the cost of restoring and repairing a submarine cable after a short circuit can cost several billion dollars. It is also important to avoid metallic impurities when processing polymers by injection molding, where such contamination can cause damage or blockage of the hot runner systems. The mentioned points show that only absolutely pure raw materials can guarantee the highest possible quality of the final product. For this it is necessary to conduct continuous quality control in the production process. Therefore, manufacturers and processors of plastics carry out special checks as separate parties, and full product lines depending from the field of application of polymers. In addition to the control systems used in the manufacturing process and sorting should be carried out regularly sample verification. In turn, the company SIKORA developed a special autonomous control system
Figure 2. Sample control methods: when used optical cameras on the surface of the granules are detected contamination and discolored granules, using an X-ray chamber inside the granules, metal inclusions are detected which performs reliable pollution detection larger than 50 microns in plastic granules.
Standalone X-ray Based Systems
Thanks to X-ray technology, it is possible to look inside the granules using a non-destructive testing method (Fig. 2). In addition, the technology allows you to distinguish between different types of materials – granules and metal particles, because they differ in the degree of absorption or attenuation of x-rays. Consequently, even the smallest metal inclusions in raw materials can be detected using an x-ray system
monitoring and analysis developed by SIKORA.
Since the X-ray unit is hermetically sealed, the emission of radiation to the outside is excluded, thereby observing all established radiation protection standards, and the operator can use the unit without fear. The system is intuitively controlled. Operator puts material onto a sample pan that moves through control zone equipped with an x-ray camera. All the procedure takes 30 s. The projector emits contaminated
material color directly on the sample tray (fig. 3). At the same time, pollution is visualized and highlighted on the monitor, where information about the size and location of the inclusion appears (Fig. 4). This allows clearly identify the location of pollution and helps
it can be easily removed, for example for further testing in the laboratory. Thanks to x-ray image analysis 50 μm metallic contamination on the surface, as well as in opaque, colored and transparent Plastic granules are automatically detected, visualized and evaluated. Image of contaminated pellets can be increased on the monitor.
Analysis and data logging
Using specially developed software, the nature of the contaminants is visualized and assessed on the monitor, as well as their selection on the sample tray. In addition to creating a gallery of inclusion images, it will generate statistical data on their size, location and quantity. Previously recorded images of the material can be reused and analyzed any number of times. In addition to single checks, the system also allows serial tests. Therefore, any number of samples from the batch can be selected for analysis and scanned at the right time. Measured values are included in the overall rating. The data obtained gives users valuable information about the process and the quality of plastic granules.
In addition, a test certificate is attached to the system, containing all information about the quality of the verified raw materials, as well as a summary of test results. Through a network interface, the monitoring and analysis system can be connected to the company’s network, and the data obtained is exported for processing. In addition, the creation of a central and constantly updated data bank allows us to draw conclusions about the sources and causes. pollution. As a result, existing technological processes within the company or at suppliers may be
optimized to guarantee the highest possible product quality.