Machine Identification Process

The material to be sorted is fed onto an acceleration conveyor to spread the material to a single layer.

  • A vibratory feeder is typically used to feed the high speed belt; this is done for the following advantages:
    • Material reaches stability on the acceleration conveyor faster due to the smaller drop (transition) between the vibratory equipment and the conveyor.
    • The vibratory feeder helps spread the material to the full width of the acceleration conveyor, which helps in producing a single layer material for the optical sorter.

The material is accelerated and scanned on a single layer at approximately 12 inches from the head pulley

Side view of Optical Sorter

Side View of Optical Sorter

The material identification is done through an NIR camera.

  • The material is identified according to know NIR spectral image
    • For example, plastics such as PVC have distinctive spectral images in NIR which permits the machine to identify the desired material.

Typical PVC NIR Spectral Image

Typical PVC NIR Spectral Image

Machine Ejection Process

The detection across the width of the conveyor is sub-divided into sections or zones. Each zone will activate the ejection process.

  • The possible ejection zones depend on the material presented:
    • Larger or smaller zones will be used to the material size to eject
    • Custom detection zones are possible for flake size material;

There are 2 possible ejection valve configurations:

  • Standard valves - used for most of the plastics to be sorted
  • Heavy duty valves - mainly used for heavier pieces such as wood in C&D

Once the material has been indentified there are 2 possible scenarios for ejection:

  • Ejection up
    • The upward ejection process works in the way that the selected material is redirected in an upward manner in the ejection chute.

Upward Ejection diagram

Upward Ejection diagram

  • Ejection down
    • The downward ejection process works in the way that the selected material is redirected in to stop the normal trajectory of the material in the ejection chute.

Downward Ejection

Downward Ejection

There are advantages and disadvantages to both set-ups:

  • The downward ejection process is more likely to have other materials in the ejected fraction. The reasons are:
    • Rolling material on the belt may not accelerate or reach the appropriate speed. This will lead to material not making it over the diverted plate regardless of the ejection.
    • Another disadvantage would be the distance from the ejector to the ejected material. In the downward ejection process there is a greater chance of "catching" surrounding material since the air jet will be wider at a greater distance.
  • The downward ejection process also has advantages
    • The rejected material is easier to "catch" in the downward position
    • The risk of "flipping" a container is less likely than on the upward ejections.
  • The upward ejection process is more precise because:
    • The ejector is closer to the object
    • If material does not accelerate properly it will fall into the non ejected fraction, thus not contaminating the ejected fraction.
  • The upward may miss a piece
    • In the upward ejection process some cases may occur where the desired material will occasionally "flip" in the air but not totally make it over the diverter chute.
  • The customer's needs, plant layout and application typically dictate the most adequate ejection process for the application.