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FAQ & Granulator Terminology
Frequently Asked Questions
Rotor knives are mounted on the rotating drum of the granulator and do the primary cutting work. Stator knives (also called bed knives) are fixed, and the rotor knives pass against them to create a scissor-like cutting action. Both must be in good condition and set to the correct clearance for optimal particle size and throughput. Virtus Equipment and ZERMA America granulators use precision-ground rotor and stator knives available as direct replacement parts.
Knife clearance is the gap between the rotor knife edge and the stator knife edge at the point of closest approach. Too wide a clearance produces oversized particles and increases motor load. Too tight a clearance risks knife-to-knife contact and damage to the cutting chamber. Virtus Equipment replacement knives are ground to OEM tolerances so clearance is easy to set correctly after installation.
Yes. Virtus Equipment and ZERMA America are sister companies that sell the same line of industrial granulators — including low speed granulators, central granulators, heavy duty granulators, beside-the-press granulators, and pipe and profile granulators — under different brand names. Replacement granulator knives and wear parts are interchangeable across both brands for the same model series.
Replacement frequency depends on the material being processed, throughput rate, and whether knives are resharpened between replacements. Common indicators that replacement is needed include increasing particle size, rising motor amperage, unusual noise or vibration, and visible chipping or rounding of the cutting edge. Hard or abrasive materials like glass-filled resins and PVC will wear knives faster than softer materials.
A granulator uses a high-speed rotor with multiple precision knives to produce a uniform, controlled particle size — typically used for plastics recycling and regrind that goes back into production. A shredder uses slower, higher-torque cutting to reduce bulk volume without producing a consistent particle size. Granulators are the right choice when your downstream process requires consistent regrind. A combination shredder-granulator handles both size reduction and controlled regrind in one machine.
Yes. Virtus Equipment Direct supports LOG Injection Molding Machine customers in addition to Virtus Equipment and ZERMA America granulator customers. Contact our parts specialists at (239) 219-1500 or [email protected] for availability.
Industrial granulators can process a wide range of thermoplastics including polypropylene (PP), polyethylene (PE), ABS, polystyrene (PS), PVC, nylon, polycarbonate, and glass-filled engineering resins. The right machine type — low speed, central, heavy duty, or beside-the-press — depends on the material hardness, part geometry, and required throughput. Abrasive materials like glass-filled resins require harder knife grades and more frequent inspection.
A tangential feed granulator has a cutting chamber where the feed opening is positioned tangentially to the rotor rather than directly above it. This geometry allows the material to enter the cutting zone at a more favorable angle, improving cutting efficiency and reducing the tendency for material to bounce or bridge in the chamber. The ZERMA America and Virtus Equipment C-Series tangential granulators use this design and are well-suited for a wide range of plastic parts and film.
The easiest way is to contact our parts specialists directly at (239) 219-1500 or [email protected] with your machine model number and serial number. You can also browse the granulator knife catalog at virtus-equipment.com. Our team can cross-reference your model to the correct rotor knife, stator knife, and wedge knife part numbers and confirm availability before you order.
A sound enclosure (also called a noise enclosure or acoustic hood) is an optional panel system that surrounds the granulator cutting chamber and motor to reduce airborne noise levels in the production environment. Granulators — especially beside-the-press models — can generate significant noise during operation. Sound enclosures are commonly required in facilities with strict occupational noise regulations or where granulators are positioned near operators. ZERMA America and Virtus Equipment offer sound enclosure options on several granulator series.
Granulator knives are typically manufactured from tool steel grades selected for hardness, toughness, and wear resistance. Common grades include D2 (high-carbon, high-chromium tool steel) for general-purpose applications, and harder grades for abrasive materials like glass-filled resins. Virtus Equipment Direct replacement knives are manufactured to OEM specifications for Virtus Equipment and ZERMA America granulators, ensuring the correct steel grade and heat treatment for each model and application.
Granulator Terminology Glossary
Key terms used in the granulator and plastic size reduction industry — from machine types to knife geometry and regrind quality.
Low Speed Granulator
A granulator that runs at lower rotor RPM with higher torque compared to a standard granulator. Well-suited for thick-walled parts, hard engineering resins, and applications where dust and fines must be minimized. Low speed granulators are also quieter and produce less heat during cutting, which is important for heat-sensitive materials. The ZERMA America and Virtus Equipment LS-Series are examples of low speed granulator models.
Central Granulator
A large-capacity granulator positioned centrally in a production facility to process scrap from multiple machines or production lines. Unlike beside-the-press granulators that serve a single machine, a central granulator handles higher throughput and a wider variety of feed stock. Central granulators typically use a conveyor or pneumatic system to collect scrap from multiple sources.
Heavy Duty Granulator
A granulator built with a reinforced cutting chamber, heavy-duty rotor, and hardened knife configuration designed for thick-walled parts, engineering resins, and high-throughput central granulating applications. Heavy duty granulators handle materials and feed sizes that would overload a standard granulator. The Virtus Equipment and ZERMA America H-Series is an example of a heavy duty granulator.
Beside-the-Press Granulator
A compact granulator positioned directly next to an injection molding machine, blow molder, or extruder to granulate runners, sprues, and trim scrap immediately at the point of generation. The regrind can be fed directly back into the machine hopper. Beside-the-press granulators are designed for low noise, low dust output, and easy integration into a tight production cell.
Pipe and Profile Granulator
A granulator designed specifically to process extruded pipe, tubing, and profile scrap — including PVC pipe, PE pipe, and complex extruded shapes. The cutting chamber geometry and knife configuration are optimized for long, continuous feed stock. Pipe and profile granulators are commonly used in PVC pipe manufacturing, window profile extrusion, and tubing production.
PVC Pulverizer
A plastic pulverizer (also called a disc mill) that reduces plastic to a fine powder rather than a granulated regrind. It uses two grinding discs to shear and grind material to a controlled powder particle size. PVC pulverizers are used in PVC dry-blend compounding, rotational molding, and powder coating applications where a granulated particle is too coarse.
Combination Shredder-Granulator
A two-stage machine that combines a primary shredder with a downstream granulator in a single integrated system. The shredder handles initial size reduction of bulky or thick-walled feed stock, and the granulator produces a controlled regrind particle from the pre-shredded material. Used when feed stock is too large or irregular to feed directly into a granulator.
Multi-Purpose Shredder
A heavy-duty size reduction machine designed to handle a wide variety of materials — including plastic, rubber, wood, paper, and mixed waste — in a single machine. Unlike a granulator, which is optimized for plastic regrind at a controlled particle size, a multi-purpose shredder prioritizes volume reduction and versatility. Used in recycling operations and applications where material type and feed form vary significantly.
Lump and Purge Granulator
A granulator designed to process injection molding purge material, large plastic lumps, and thick-walled scrap that would overload a standard granulator. Lump and purge granulators use a heavy-duty rotor, reinforced cutting chamber, and knife geometry optimized for hard, irregular feed stock. Commonly used at injection molding machines that process engineering resins and produce large purge slugs during color or material changes.
Wedge Knife
A knife geometry used on certain granulator rotor configurations where the knife is held in place by a wedge-style clamping system rather than a bolt-through design. Wedge knives allow faster knife changes and more consistent seating in the rotor pocket. They are common on ZERMA America and Virtus Equipment granulator models and are available as direct replacement parts from Virtus Equipment Direct.
Granulator Screen
The perforated screen that sits below the cutting chamber and controls the maximum particle size of the regrind output. Material is retained in the cutting chamber until it is small enough to pass through the screen holes. A smaller screen hole diameter produces finer regrind but reduces throughput. Screen size selection depends on your downstream process — injection molding typically uses 6–10mm screens.
Regrind
The granulated output from a plastic granulator — plastic scrap that has been size-reduced to a uniform particle suitable for reprocessing. High-quality regrind from a well-maintained granulator with sharp knives and correct clearance can be blended back into virgin material for injection molding, extrusion, or blow molding. Poor regrind caused by worn knives or incorrect clearance contains fines and oversized particles that degrade part quality.
Tangential Feed
A cutting chamber design where the feed opening is positioned tangentially to the rotor, allowing material to enter the cutting zone at a more favorable angle. This improves cutting efficiency and reduces bridging in the feed throat. Used on the Virtus Equipment and ZERMA America C-Series tangential granulators.
Sound Enclosure
An optional panel system that surrounds the granulator cutting chamber and motor to reduce airborne noise levels in the production environment. Commonly required in facilities with strict occupational noise regulations or where granulators are positioned near operators. Available as an option on several ZERMA America and Virtus Equipment granulator series.
Still Have Questions?
Our parts specialists in Fort Myers, FL are available to help you identify the right knives for your machine and answer technical questions about Virtus Equipment and ZERMA America granulators.
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