Steinert Group, sorting systems manufacturer for the recycling industry based in Widdersdorfer, Germany has launched its latest optical sorting system, the UniSort BlackEye, aimed at increasing the purity of black polymer fractions.
The system, which will be on show at IFAT 2016 in Munich at the end of the month, is said to produce purer granules “so valuable that the investment in the device quickly pays off”.
According to Steinert, recycling companies that produce mixed granules from purchased black polyethylene and polypropylene (PE/PP) currently pay a market price of about €200 per tonne, depending on the material’s polyolefin (PO) content. If they could concentrate the mixture into valuable fractions such as PE and PP they would be able to obtain a price of up to €900 for the granules.
However, the company said that the problem is that the sensors of traditional optical sorting machines have to date been unable to distinguish the different types of black plastics from one another, because the soot used to blacken the plastic absorbs the visible and infrared wavelengths of electromagnetic radiation.
“The UniSort BlackEye closes this gap and makes a pure separation of comminuted black components possible,” explained Hendrik Beel, managing director at the Steinert Group. “The investment pays off quickly because it enables operators to produce pure and thus more valuable granules.”
At the heart the sorting system is a detection unit, which is located above the conveyor belt and equipped with Hyper Spectral Imaging (HSI) technology. The manufacturer said that the system works by using a light to illuminate the plastic flakes on the conveyor belt, while a camera system analyses the reflected light.
“The spectrum of this reflected light is missing certain frequencies that are characteristic of the different types of plastic,” said This means that each type of plastic has more or less its own ‘fingerprint’,” says Beel. “Using stored reference spectra, analysis software that was developed by the Steinert Group then recognises whether an item is made of plastic, wood, glass, or paper, and whether it is a dark object.”
One of the reasons why this analysis was said to be especially reliable is due to the fact that the camera doesn’t scan the conveyor belt pixel by pixel. Instead, it simultaneously scans 320 pixels across the entire belt width, enabling even tiny variations in the NIR spectrum to be detected.
1 TPH of Plastic Flakes
To separate polyolefins such as polyethylene (PE) and polypropylene (PP) from one another? Or to sort other types of plastic such as polyvinyl chloride (PVC), polystyrene (PS) and polymers out of a mixture of materials, the company said that its software transmits the corresponding position data to the compressed air system installed at the end of the conveyor belt.
Within a fraction of a second, the system is claimed to be able to open the appropriate high-speed valve so that a perfectly aimed blast of compressed air causes the targeted material to be ejected.
“The UniSort BlackEye operates quickly enough to scan belts moving at up to four metres per second. During this time, it can scan about 35 million detection points or up to 5000 objects,” said Beel. “This makes it ideal for efficient industrial applications for crushed plastic parts measuring between 10 and 30 millimetres.”
On average, the UniSort BlackEye was said to have a throughput rate of one tonne of plastic flakes per hour.
Another feature is a stabilising system called Active Object Control (AOC) to ensure the plastic flakes stay on the conveyor belt at such high speeds so that detection precision remains high.
“We are ensuring that the plastic parts hardly move after they are detected and that the position data remain unchanged for the ejection system,” explained Beel. “It enables much higher belt speeds and thus higher throughput rates than with standard systems. This makes sorting even more efficient.”
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