Patent ID: 8418947

Claim:
A shredding mechanism for shredding sheet material, the shredding mechanism comprising: first and second parallel shafts supported for rotation in opposite directions about respective parallel first and second axes; first and second rows of shredding units, wherein the first row of shredding units is mounted on the first shaft and the second row of shredding units is mounted on the second shaft for rotation with the first and second shafts, respectively, alternating shredding units of the first row of shredding units are interleaved between alternating shredding units of the second row of shredding units, the shredding units of the first and second rows overlap when viewed along the first and second parallel axes, each of the shredding units comprises a generally flat body having opposed first and second sides separated by the width of the flat body, and a periphery located between the first and second sides, a central opening passing through the flat body and through which one of the first and second shafts passes and engages the shredding unit, and at least one piercer slot in the flat body for engaging a piercer, wherein the at least one piercer slot extends into the flat body, along the width of the flat body, from the first side of the flat body, and the at least one piercer slot has an inner portion for engaging a piercer and an outer portion extending to and opening at the periphery of the flat body, first and second shredding discs fixedly attached, respectively, to the first and second sides of the flat body, wherein each of the first and second shredding discs includes an outer peripheral rim having a circumferential shearing edge extending outwardly beyond the periphery of the flat body for slitting the sheet material along a direction transverse to the first and second axes, and at least one piercer having a rear end disposed in the inner portion of the at least one piercer slot, and a front end projecting outwardly from the at least one piercer slot, beyond the periphery of the flat body and the shearing edges of the shredding discs attached to the flat body, for piercing and cutting the sheet material along a direction generally parallel to the first and second axes, wherein the front end has a width substantially equal to the width of the flat body plus widths of the first and second shredding discs, and at least one of the first and second shredding discs retains the at least one piercer in the at least one piercer slot, and at least one shearing edge of each of the shredding units in each of the first and second rows bears against a shearing edge of an adjacent shredding unit in the other of the first and second rows so that the shearing edges, bearing on each other, together slit the sheet material along the direction transverse to the first and second axes.