Sensors from VEGA ensure reliable material supply in injection moulding machines

Continuous innovation in production techniques has made Haval a specialist in this field today. Every year around 5 billion single-use items and packagings leave the state-of-the-art production facility in Gemert, the Netherlands, and make their way to customers all over Europe. All products are developed in collaboration with reputable design agencies, focusing not only on design but also on the physical product requirements. As regulations are changing in the European Union, single-use items will be banned from 2021 onwards. However, Haval has long been placing emphasis on another mainstay, namely the production of food packaging used, for example, for the storage and sale of salads, vegetables, fruit, etc.

From the silo to the perfect shape

Whether disposable cutlery or packaging – the basis of all these products are high-quality plastic granulates of polystyrene and polypropylene. This raw plastic material is transported from the aluminium silos to the injection moulding machines, where it is melted and injected into the moulds under high pressure. The total volume of the nine storage silos is 900 m3. “To ensure reliable replenishment and smooth operation, we need accurate, trustworthy data on the quantities of plastic granulate in our stocks. If the raw material runs out, we would have to shut down one or more of our injection moulding machines,” explains Ron Kastermans, Production Manager at Haval BV. “We now rely on a combination of radar level measurement and VEGASCAN visualisation to keep that from happening.”

Multiple radar sensors of type VEGAPULS 68 and 69 are used in the silos. VEGAPULS 68 has been in use in two silos for more than seven years and still works perfectly. VEGAPULS 69 was installed in the other three silos. “The greatest challenge for level measurement was the low dielectric constant of the raw material – the plastic granulates have a Dk value of around 1.2”, explains Ron Kastermans further. “Another problem faced by the sensors was the dust generated by polystyrene. Yet it cannot be avoided, as polystyrene is one of the main materials we process.”

Before VEGAPULS 69 was introduced, the level was measured with a sensor based on the guided microwave measuring principle. This worked, to be sure, but as soon as interference signals had the same magnitude as the level echo, reliable measurement was not always possible. Unfortunately, this situation occurs with many plastic powders and granulates.  Their very low Dk values generate only weak reflections, as a large part of the radar signals is absorbed by the medium. Besides that, there are often interfering signals produced by plastic-specific fixtures and components installed inside the silos. Plastic powder is usually stored in high, very slender containers. Circumferential weld seams, even if they are only a few millimetres in size, often cause interfering reflections in such silos. In the worst case, there could be a weld seam every 50 cm, which would generate enough interference to completely drown out the useful signal. For Kastermans, ensuring the reliability of the measuring signal has top priority. “The most important thing for me in everyday operation is good measurement. It’s not even about having the very highest level of accuracy, but getting a continuous reliable result without malfunctions.”