Four-shaft shredders are used for size reduction where the length and width of the shredded material needs to be controlled. Like two-shaft shredders, material is sheared between close-tolerance cutters located on counter rotating shafts. Material is primarily initially sheared by the two inside shafts and oversized material is recirculated by the outside two shafts until it has been reduced in size to the point where it can pass through the screen openings located in the screen positioned under the cutters.
The significant advantage of four-shaft shredders over two-shaft shredders is their ability to provide a consistent shred size as a result of the screen. The configuration of the four-shafts also promotes larger material passing through the cutters more quickly.