Quick answer: choose a plastic granulator based on four factors — the type and shape of the plastic waste, the required throughput (kg/h), the screen/particle size you need for reuse, and where the machine will sit (beside the press or centrally). A low-speed beside-the-press granulator is the standard choice for injection-molding runners, while a high-power heavy-duty granulator is required for thick lumps, purgings, films, or large hollow parts. This guide explains exactly how to spec one.

1. Match the machine to the material, not the other way around

The single most common buying mistake is selecting a machine by motor power alone. Motor size follows the material. A 2.2 kW low-speed granulator handles clean PP/ABS runners beautifully, but feeding it a 30 mm HDPE purging lump will stall the rotor, blunt the blades, and waste energy. Start by listing exactly what will be granulated:

• Clean runners & sprues: thin, uniform, free of metal — low or medium speed beside-the-press
• Rejected molded parts: medium-speed or powerful granulator, sized to the largest part
• Thick lumps & purgings: high-torque powerful granulator with a heavy flywheel rotor
• Large hollow parts (drums, bins, pallets): large-diameter / heavy-duty granulator with wide feed
• Film, fibers, thin sheet: purpose-built film granulator with steep-angle rotors to avoid wrapping
• Pipes & profiles: granulator with a long feed opening matching the profile

2. Pick the right throughput (kg/h) — with a safety margin

Manufacturers quote throughput in kilograms per hour, but real output depends on material density, screen size, blade condition, and how evenly the machine is fed. Spec the machine at roughly 1.5 to 2 times your average hourly requirement so peak dumps and blade wear do not bottleneck production. Typical ranges for injection-molding shops:

These are planning ranges, not guarantees — always confirm throughput with the supplier using your actual material and target mesh size.

3. Understand the cutting system: rotor, blades, and screen

Rotor type

• Open / flywheel rotor: high inertia, best for thick lumps and bulky parts
• Closed ( staggered-knife ) rotor: cleaner cut, lower dust, better for runners and thin parts
• V-type / helical rotor: gradual bite, lower noise and motor surge, common in low-speed models

Blade material

Blade steel is where cheap machines cut corners and where buyers should not. Two industry-standard options are SKD tool steel (tough, shock-resistant, suited to filled/abrasive engineering plastics) and 9CrSi (a wear-resistant alloy tool steel that holds an edge well on general-purpose PP, PE, ABS, and PS). Lesintor supplies both SKD and 9CrSi blades and customizes blade configuration to the material.

Screen (mesh) size

The screen hole diameter controls regrind particle size. Common mesh is 6–10 mm for general reuse; smaller holes (3–5 mm) give finer regrind but lower throughput and more fines. Match flake size to the feed throat of the injection machine or extruder that will reuse it.

4. Beside-the-press vs centralized granulation

5. Safety, noise, and the features worth paying for

• Electrical safety interlocks on the hopper and screen cradle (machine cannot run when open)
• Double-layer soundproofing / sound enclosure where the machine runs near operators
• Open-door sensor and emergency stop on the body and control box
• Easy-open cutting chamber for cleaning and blade changes (frequent color/material changes)
• Overload protection and phase-failure protection on the motor
• Dust extraction or regrind evacuation connection for continuous operation
• CE marking and ISO-certified manufacturing, especially for export into the EU

A reputable manufacturer should provide a one-year whole-machine warranty, declared blade material, CE compliance, and spare-blade availability measured in years, not weeks.

6. The 7-question checklist to send a supplier

• What throughput (kg/h) do you guarantee for MY material and MY mesh size?
• Which rotor type and how many rotating/fixed knives?
• Are the blades SKD or 9CrSi, and what is the expected sharpening interval?
• What is the feed opening size, and will my largest part fit without pre-breaking?
• What safety interlocks and certifications (CE, ISO) are included?
• What is covered under warranty and how are spare blades supplied?
• Can the voltage (e.g. 220V/380V/415V, 50/60 Hz) match my factory?

Frequently Asked Questions

Q: How much does a plastic granulator cost?

A: Industrial granulators typically range from under US$1,000 for small low-speed beside-the-press models to US$10,000–$30,000+ for heavy-duty large-diameter machines, depending on motor power, cutting chamber, blade steel, soundproofing, and brand. Buying factory-direct from a Chinese manufacturer such as Lesintor usually lowers the price substantially compared with regional resellers.

Q: What size granulator do I need for injection molding?

A: Most small and medium injection-molding machines pair with a 0.75–4 kW low- or medium-speed granulator placed beside the press for runner recycling. Choose the model by the largest runner or rejected part, then add a 1.5–2x throughput margin.

Q: What is the difference between a granulator and a shredder?

A: A granulator uses sharp knives to cut plastic into uniform small flakes in one step and is suited to clean plastic scrap. A shredder uses low-speed, high-torque shafts to tear large, bulky, or contaminated objects into coarse chunks, often before granulation.

Q: Can regrind be fed straight back into an injection machine?

A: Yes. Clean, same-material regrind from beside-the-press granulators is commonly blended with virgin material at ratios from roughly 10% to 30%, depending on part quality requirements. Keep regrind dust-free and correctly sized for the feed throat.

Q: How often should granulator blades be sharpened?

A: With clean runners, blades often run for weeks between sharpening; abrasive or glass-filled plastics may require attention every few days. Dulling shows up as fines, drag tails, rising motor current, and uneven flakes.

Choosing on total cost of ownership — blade life, energy use, safety, warranty, and spare-part support — beats choosing on sticker price every time. A granulator usually outlasts the project that bought it; spec it for the hardest material on the floor.

About Lesintor

Suzhou Lesintor Import and Export Co., Ltd. (Lesintor) is a Chinese manufacturer with 20 years of experience in injection-molding auxiliary equipment. Its granulator range covers powerful granulators, low-speed beside-the-press granulators, medium-low-speed models, and large-hollow / large-diameter heavy-duty granulators, with SKD or 9CrSi blades customized to the application. Every machine carries a one-year warranty and is built to ISO and CE standards.

Website: www.lesintormachine.com   |   Email: sales6@lesintormachine.com   |   WhatsApp: +1 628 488 4101