Steinert Group, based in Germany, has launched its UniSort BlackEye technology to overcome the difficulty that most optical sorting systems have with black plastic waste.
According to Steinert, recycling companies that produce mixed granules from black polyethylene and polypropylene of mixed quality could increase their selling price from about €200 per tonne up to €900. The technical difficulty is that black absorbs the visible and infrared wavelengths of electromagnetic radiation which confuses the sensors of traditional optical sorting machines.
The detection unit of sorting technology, which sits above the conveyor belt, has a camera system and imaging technology to analyse the light reflected from plastic flakes on the conveyor belt.
“The spectrum of this reflected light is missing certain frequencies that are characteristic of the different types of plastic. This means that each type of plastic has more or less its own ‘fingerprint',” said Steinert's managing director Hendrik Beel. “Using stored reference spectra, analysis software that was developed by the Steinert Group then recognizes whether an item is made of plastic, wood, glass, or paper, and whether it is a dark object.”
The analysis is reliable partly due to the fact that the camera does not scan the conveyor belt pixel by pixel. Instead, it simultaneously scans 320 pixels across the entire belt width, enabling small variations in the NIR spectrum to be detected.
The high speed of analysis means that within a fraction of a second, the system opens the appropriate high-speed valve for a blast of compressed air to eject the targeted material.
Beel said: “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 5,000 objects. This makes it ideal for efficient industrial applications for crushed plastic parts measuring between 10 and 30 millimetres.”
Steinert said that, on average, the UniSort BlackEye has a throughput rate of 1 tonne of plastic flakes per hour.