Plastics Recycling
Granulator and Shredder Rotor / Stator Knives
Engineered to cut through contamination, glass fibre and reinforced polymers. D2 and M2 HSS options, with optional TiN or CrN PVD coating to extend service interval by 2–4× on the same line.
Working principle
How the rotor-stator shear cut works
Open-rotor and closed-rotor geometries cut by impact shear, not by slicing. The geometry choice, hook angle and clearance angle are dictated by substrate, throughput and contamination class.
A granulator rotor carries a ring of knives rotating past a stationary bed knife. Material enters the cutting gap and is sheared by impact, not by the kind of clean slicing a slitter performs. Open-rotor (cut-and-throw) geometries push the cut product out of the cutting chamber with the same rotation; closed-rotor (scissor-cut) geometries rely on a downstream screen to size the output.
The two failure modes we see most often — micro-chipping on glass-fibre and progressive welding on sticky polymer — both trace back to the same root cause: edge preparation and clearance angle were specified for the wrong substrate family.
Open rotor (cut-and-throw)
3 or 5 blades. Lower friction, higher throughput. Best for film, fibre, low-density feedstock.
Closed rotor (scissor-cut)
3 or 5 blades + matched bed. Cleaner cut, tighter granulate. Best for rigid plastic and engineering polymer.
V-cut / claw profile
For shredders. Aggressive bite on bulky post-consumer parts and purgings.
Engineering scope
Six specification levers for plastics recycling
Recycling lines are abrasive, impact-loaded and inconsistent. Each variable below is selected against substrate, throughput and contamination class — not against the cheapest steel on the shelf.
Substrate range
PET, HDPE, LDPE, PP, PA66 and other engineering polymers, including glass-fibre reinforced grades up to 50 % GF, mineral-filled compounds, and post-consumer feedstock with contamination (paper labels, metal specks, abrasive fines).
Rotor / stator configurations
Standard 3- and 5-blade rotor sets with matching bed knives. Open-rotor (cut-and-throw) and closed-rotor (scissor-cut) geometries. V-cut and claw profiles for shredders. Knife seat and slot dimensions to OEM specification.
Material grades
D2 (1.2379 / SKD11) for general-purpose cutting, M2 high-speed steel (1.3343) for impact-loaded rotors. Hardness HRC 58–62 D2, HRC 60–64 M2. Vacuum heat-treatment with double-temper for dimensional stability.
PVD coating options
TiN, TiCN and CrN coatings per ISO 14574 extend service interval 2–4× on glass-fibre and mineral-filled feedstock. CrN preferred for high-temperature reclaim lines. Coating thickness 2–4 µm, applied after final grind.
Hook and clearance angles
Hook angle 8°–15° for general-purpose, 18°–22° for high-throughput reclaim. Clearance angle 2°–4° rotor, 3°–5° bed knife. Aggressive angles on contaminated feedstock; conservative angles on glass-fibre to limit chipping.
Tolerances and regrind
Standard ± 0.01 mm thickness, ± 0.02 mm length, parallelism 0.02 mm across the cutting edge. Up to 4 regrinds permitted on standard D2 knives before the cutting edge falls below OEM geometry. Regrind service available in-house.
Specifying granulator or shredder knives?
Send the OEM model, rotor diameter, current knife grade and the typical feedstock mix. We will return a written quote with material, hardness, coating option and expected service interval within one business day.