Mastering Plastic Recycling Granulating: Techniques and Innovations You Need to Know

Plastic granulation is a size-reduction process that remakes post-industrial plastic materials into uniform granules suitable for reprocessing. Utilizing high-torque rotary cutting systems, granulators apply controlled mechanical shear and impact forces (along with heat) to fracture and reduce plastic materials into consistent, flowable feedstock for downstream recycling or compounding applications. 

A quality recycling granulator is a key component in the plastic recycling process. This article will cover core granulating techniques, equipment options, and how blade quality affects output efficiency and product quality.

How Plastic Granulating Fits Into the Recycling Cycle

Plastic granulation is a critical intermediate step within the broader plastic recycling lifecycle. Following collection, sorting, and cleaning stages, granulation turns crushed and decontaminated plastic waste into homogeneous granules that serve as raw material for remanufacturing.

In closed-loop recycling systems, granulation is critical in transforming recovered plastic waste into material that can be repeatedly reprocessed into similar end-use products. It supports a circular economy model by ensuring that end-of-life plastic components are not downcycled or landfilled but reconstituted into material compatible with manufacturing requirements.

Key Stages of the Plastic Granulating Process

Understanding each stage of the plastic granulating process helps recyclers optimize quality and throughput. Every single step plays a role in turning scrap plastic into valuable feedstock. 

Cleaning and Shredding

This step ensures incoming waste is free of contaminants that could degrade equipment or final pellet quality. Heavily soiled plastics, like those used in industrial waste, undergo coarse washing to remove abrasive materials, followed by centrifugation and shredding. Additional rinsing, alkaline soaking, and frictional agitation may help eliminate embedded debris and oil residues. Final drying removes residual moisture to prevent extrusion instability.

Clean, dry feedstock is vital for consistent melt flow and granule uniformity, but there are potential challenges:

• Incomplete cleaning increases the risk of equipment wear, poor adhesion in molding, or discoloration in pellets.
• Improper drying can lead to hydrolytic degradation in moisture-sensitive polymers.

Extrusion and Melting

During this stage, clean, shredded plastic is converted into a molten state for reshaping. The material is conveyed into the extruder, where it's subjected to controlled heat and shear. The molten plastic is pushed through a die to form continuous strands.

Stable melt flow results in uniform strand formation, which is crucial for consistent pellet size and shape. Overheating may lead to polymer degradation, off-gassing, or color shifts. Uneven melt can create strand breakage or voids during cooling. A plastic recycling machine with a consistent melt is essential. 

Cooling and Cutting

This is when extruded strands are converted into granules. Strands cool (typically in water baths) to solidify them before being chopped by sharp blades into uniform pieces of plastic. 

Rapid and uniform cooling preserves polymer integrity, preventing warping or stress cracking. Precision cutting blades ensure consistent pellet dimensions for reliable feeding in downstream processes. Beware of dull or misaligned blades, which can cause irregular pellet sizes, among other issues.

Types of Plastic Granulators and When to Use Them

There are several types of granulator machines, each with their unique benefits.

• Beside-the-Press Granulators: Their compact footprint and mobility make them ideal for decentralized operations designed for closed-loop recycling. These granulators have limited capacity and may be unsuitable for heavy or abrasive materials.
• Central Granulators: Engineered for high-volume operations and typically installed in a fixed location within a facility. They handle large parts and consolidate scrap from multiple production lines. Their construction supports continuous processing but requires additional infrastructure for material transport.
• Heavy Duty Granulators: Built for extreme workloads and industrial-scale recycling. Their reinforced construction enables continuous processing of thick-walled parts, rigid plastics, rubber, and cables. Though these granulator plastic recycling machines require more capital and energy, their durability and throughput suit them to dense material streams.
• Low-Speed (Screenless) Granulators: These granulators operate at reduced RPMs to minimize dust, noise, and fines while delivering consistently sized granules, typically without screens. They're ideal for soft plastics and rubber, though they are not appropriate for hard or bulky materials.

Common Granulation Challenges and How to Solve Them

Even the most advanced granulating systems face challenges that hurt performance and increase operational costs. Identifying these issues early and knowing how to fix them can help extend equipment life and reduce downtime. 

Blade Dulling or Breakage

Rapid dulling and uneven cutting lead to equipment vibration and costly downtime. In the wrong circumstances, blade breakage can even be dangerous to workers and equipment. The solution is premium-grade, high-chrome alloy tool steel that extends blade life under high-load conditions, such as cutting-filled or abrasive plastics. 

Granule Size Inconsistency

Granule size inconsistency, meaning a mix of fines, longs, and irregular fragments, can disrupt processes where uniform melt flow is critical. This issue typically comes from dull blades, which tend to tear or crush plastic rather than cleanly cut it. Sharp blades are crucial for achieving uniform granule size.

Why Blade Quality Impacts Granulating Performance

The sheer volume of plastic that a granulator processes for plastic recycling is enormous. Millions of tons of plastic need to be processed every year in the United States alone. To accomplish this, machines need premium-quality blades. The quality of the blade significantly influences cut quality, equipment life, and product consistency over time.

Here's what to look for:

• Blade Geometry: Optimized geometries (including rake angle, cutting edge profile, and clearance) reduce energy consumption and prevent plastic from smearing or melting instead of slicing cleanly.
• Blade Hardness: Blade hardness affects wear resistance and durability. Look for premium-grade, high-chrome alloy tool steel.
• Blade Sharpness: Dull blades crush or tear material, causing irregular shapes, fines, and dust, which can compromise downstream processes.

Benefits of Custom Blade Solutions for Recyclers

Custom blades are tailored to specific machines, materials, and production goals. Custom solutions deliver cleaner cuts, reduce changeouts, and minimize costly downtime.

Hyde Industrial Blade Solutions brings over 150 years of expertise in metallurgy and custom industrial blade design. All of Hyde's granulator blades are 100% custom-made at its Southbridge, MA headquarters, where heat treating, laser cutting, and precision quality control are handled in-house.

Hyde customers benefit from 24-hour quote turnaround, 3- to 4-week lead times, and rapid delivery from a complete on-hand inventory. From Hyde's industrial knives for recycling to granulators and pelletzers for plastics processing, we're committed to quality in plastic recycling granulating.

Signs It's Time to Upgrade Your Granulating Setup

A recycling operation may need to re-evaluate its granulation system if one of the following factors is present:

• Inconsistent granule quality
• Frequent blade replacements
• Decreased productivity
• Increased energy costs
• Unexpected noise

Get More from Every Pound of Plastic Waste

Ready for blades that last longer and perform better? At Hyde, we've spent over 150 years perfecting industrial blades and plastic granulator blades. They're crafted in the USA and built to outlast the competition. Give us a ring at 508-765-4759, or get a quote today.