Sensor-based sorting
Sensor-based sorting, also referred to as Ore sorting is an umbrella term for all applications where particles are singularly detected by a sensor technique and rejected by an amplified mechanical, hydraulic or pneumatic process. The technique is generally used in the particle size range between 0,5mm and 300mm. The throughput and also the operating costs of sensor-based sorters are lineary depending on the average particle size fed to the machine. Sensor-based sorters are used in the recycling and mineral processing industry as well as in the pharmaceutical and in the food industry. In mineral applications it is usually applied as a rougher stage stage for pre-concentration of coarse particle sizes (+20mm). Modern sensor-based sorters make use of all meterial characteristics which can be detected fast enough to enable a high material throughput. Used sonsors are optical sensors (visible spectrum, near infrared, X-ray, ultraviolet), electromagnetic sensors and LIBS (Laser-induced breakdown spectroscopy) sensors.
Functional principle of sensor-based sorting
The main subprocesses of sensor-based sorting are material conditioning, material presentation, detection, data processing and seperation. Material conditioning includes all operations which prepare the particles for beeing detected by the sensor. All optical sensors need clean material to be able to detect optical characteristics. Conditioning includes screening and cleaning of the feed material. The aim of the material presentation is the isolation of the particles by creating a single particle layer with the densest surface cover possible without particles touching each other and enough distance to each other allowing for a selective detection and rejection of each single particle. There are two types of sensor-based sorters: the chute type and the belt type. For both types the first step in acceleration is spreading out the particles by a vibrating feeder followed by either a fast belt or a chute. On the belt type the sensor usually detects the particels horizontally while they pass it on the belt. For the chute type the material detection is usually done vertically while the material passes the sensor in a free fall. The data processing is done in real time by a computer. The computer transfers the result of the data processing to an ultra fast ejection unit which, depending on the sorting decision, ejects a particle or lets it pass.
