1.  Field of the Invention
This invention relates to separating various recyclable materials from Municipal Solid Waste (MSW). 
2.  Description of the Related Art
Disc or roll screens are frequently used as part of a multi-stage material separating system.  Disc screens are used in the materials handling industry for screening large flows of materials to remove certain items of desired dimensions.  In particular, disc screens are used for classifying what is normally considered debris or residual materials.  This debris may consist of soil, aggregate, asphalt, concrete, wood, biomass, ferrous and nonferrous metal, plastic, ceramic, paper, cardboard, or other products or materials recognized as debris throughout consumer, commercial and industrial markets.  The function of the disc screen is to separate the materials fed into it by size.  The size classification may be adjusted to meet different applications. 
Disc screens generally have a screening bed having a series of rotating spaced parallel shafts, each of which has a longitudinal series of concentric screen discs separated by spacers which interdigitate with the screen discs of the adjacent shafts.  The relationship of the discs and spacers on one shaft to the discs and spacers on each adjacent shaft form an opening generally known in the industry as the InterFacial Opening or “IFO”.  The IFOs permit only material of acceptable size to pass downwardly through the rotating disc bed.  The acceptable sized material which drops through the IFO is commonly referred to in the industry as “accepts” or “unders”. 
The discs are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed.  Thus, materials which are larger than the IFO, referred to in the industry as “overs”, will be advanced on the bed to the outfeed end of the bed. 
It may be desirable to separate certain types of recyclable Municipal Solid Waste (MSW) from other types of recyclable or non-recyclable waste.  For example, recyclable MSW materials may include paper, old corrugated cardboard (OCC); and plastic, aluminum, steel, and glass containers.  These recyclable materials may need to be separated from other types of waste that may include wood, concrete, rocks, etc.  However, the recyclable MSW paper, cardboard, and containers may have sizes and/or shapes similar to other types of MSW waste.  Thus, existing disc screen systems that separate materials solely according to size may not effectively separate certain MSW recyclable materials.