Shredding is the first size-reduction step in plastic recycling. A shredder, a slow, high-torque machine with rotating shafts and hooked blades, tears bales, film, woven sacks and bulky items into rough pieces a few centimetres across.
Shredding opens up compacted bales, frees trapped dirt and makes the material easy to convey, wash and feed into the next machine. It is followed by grinding in a granulator, which cuts the pieces into smaller, uniform flakes. Shredders are built to tolerate the stones, metal and other foreign objects that arrive with post-consumer waste, which would damage the faster-running knives of a granulator. Film and woven sacks, which wrap around ordinary cutters, are usually shredded first and then washed and densified by agglomeration.
