Comprehensive Analysis of Plastic Pelletizing Technology: A In-depth Guide from Principles to Applications

Comprehensive Analysis of Plastic Pelletizing Technology: A In-depth Guide from Principles to Applications

What Exactly is Plastic Pelletizing?

Plastic pelletizing is a precision manufacturing process that converts various forms of plastic raw materials into standardized pellets. This seemingly simple physical processing actually involves complex materials science and engineering technology. As the basic form of the modern plastic industry, plastic pellets are as important as chips in the electronics industry.

From a microscopic perspective, the plastic pelletizing process is essentially a phase change process in which polymer materials undergo a "solid state - molten state - solid state" transformation. During this process, the molecular chains of the plastic undergo complex arrangement changes: in the initial state, the molecular chains are in a randomly coiled form; when heated to the molten state, the molecular chains gain sufficient kinetic energy and start to slide; in the cooling and solidification stage, the molecular chains rearrange according to the cooling conditions to form different crystalline structures. These changes in the microstructure directly affect the physical and chemical properties of the final pellets.

The geometric characteristics of plastic pellets are carefully designed and not arbitrarily determined. The typical pellet diameter is 2-5 mm, and the length is 3-5 mm. This size design is based on the following scientific considerations:

Heat conduction efficiency: ensuring that the center of the pellet can reach the melting temperature within a reasonable time.

Flow characteristics: optimizing the fluidity in the conveying pipeline to avoid bridging.

Metering accuracy: facilitating accurate volume or weight measurement.

Surface area to volume ratio: ensuring appropriate drying efficiency without easy caking.

From a material science perspective, plastic pellets can be divided into two major categories and six subcategories:

Classified by raw material source:

1.Virgin plastic pellets

Petroleum-based: produced by traditional petrochemical routes.

Bio-based: derived from renewable resources such as corn and sugarcane.

2.Recycled plastic pellets

Post-consumer recycled (PCR): from recycled end products.

Post-industrial recycled (PIR): from scrap materials during production.

Classified by polymer type:

General-purpose plastic pellets: PE, PP, PVC, PS, etc.

Engineering plastic pellets: ABS, PC, PA, POM, etc.

Special plastic pellets: high-end materials such as PEEK, PTFE, PI, etc.

Why Do Plastics Need to Be Converted into Pellet Form?

The adoption of pellet form for plastics is the optimal solution verified by decades of industrial practice. This form design is backed by profound engineering principles and economic considerations.

From a physics perspective:

Heat conduction uniformity: Spherical or cylindrical pellets exhibit excellent heat transfer characteristics during heating. Experimental data show that for a PP pellet with a diameter of 3mm in a 180°C hot air environment, the time for the center temperature to reach the melting point is approximately 42 seconds, with a temperature difference of no more than 3°C, while the temperature difference for a sheet material of the same mass can reach more than 15°C.

Volume stability: The bulk density of pellets is usually between 0.4-0.7g/cm³. This moderate density not only ensures storage efficiency but also ensures smooth flow in the hopper. In contrast, powder is prone to dusting, and block materials are prone to bridging.

Surface characteristics: The carefully designed surface roughness of pellets (usually in the range of Ra 1.6-3.2μm) can reduce the tendency to agglomerate without excessively increasing flow resistance.

From the perspective of processing technology:

Precise metering: The metering accuracy of the loss-in-weight feeding system of modern injection molding machines for pellets can reach ±0.3%, while the metering error of powder is usually more than ±1.5%.

Mixing uniformity: When it is necessary to add color masterbatches or other additives, the mixing uniformity between pellets can reach more than 98%, and the mixing time is 30% shorter than that of raw materials with irregular shapes.

Conveying efficiency: In pneumatic conveying systems, the conveying efficiency of pellet plastics can reach 5-8 tons per hour, and the energy consumption is about 25% lower than that of conveying sheet materials.

Economic benefit analysis:

The economic benefits brought by plastic pellets are reflected in all links of the industrial chain:

Link	Advantages of pellet form	Improvement in economic benefits
Transportation and storage	Increase loading density by 30%, reduce damage	Reduce logistics costs by 15-20%
Production and processing	Reduce preheating time and energy consumption	Save energy costs by 8-12%
Quality control	Reduce batch differences and improve yield rate	Reduce quality loss by 3-5%
Automated production	Compatible with standard equipment,reduce manual intervention	Improve production efficiency by 20-30%

It is particularly worth noting that the standardization of plastic pellets has made global trade possible. Plastic pellets produced in accordance with international standards such as ISO 1874 and ASTM D4000 can be processed in compliant factories anywhere in the world, which has greatly promoted the globalization of the plastic industry.

III. What Are the Key Steps in the Plastic Pelletizing Process?

Plastic pelletizing is a complex system engineering, and each process requires precise control. Below, we will conduct an in-depth analysis of the technical points and quality control nodes of each link.

Raw material pretreatment stage

Sorting and cleaning processes:

Modern sorting technology has developed from simple manual sorting to an intelligent system integrating multiple technologies:

Near-infrared (NIR) sorting: recognition accuracy up to 99%, processing capacity 3-5 tons per hour.
X-ray fluorescence (XRF): detects harmful substances such as heavy metals.
Electrostatic sorting: separates different materials with similar densities.

The cleaning system usually adopts a three-stage cleaning process:

1.Pre-cleaning: removes surface attachments, using 60-80°C hot water.

2.Main cleaning: adds cleaning agents, temperature 80-95°C.

3.Rinsing: rinses with clean water to ensure no residue.

Crushing technology:

Blade design: the gap between the moving blade and the fixed blade is 0.1-0.3mm to ensure a flat cut.
Screen selection: aperture 15-20mm to control the discharge size.
Rotation speed control: 500-800rpm to avoid overheating degradation.

Drying process:

Dehumidifying drying: the dew point temperature needs to reach below -40°C.
Hot air drying: air temperature 80-110°C, adjusted according to materials.
Vacuum drying: used for engineering plastics with strong hygroscopicity.

Key technologies for melt extrusion

Temperature zone control:

Taking typical PE pelletizing as an example, the five-zone temperature settings are:

1.Feeding zone: 160-180°C

2.Compression zone: 190-210°C

3.Melting zone: 210-220°C

4.Homogenization zone: 220-230°C

5.Head zone: 225-235°C

Screw configuration design:

Modern pelletizing machine screws adopt modular design, with common combinations:

Conveying section: deep groove design for rapid feeding.
Compression section: gradual compression with a compression ratio of 2.5:1-3:1.
Mixing section: equipped with pins or barrier elements to enhance mixing.
Venting section: negative pressure devolatilization with a vacuum degree of ≥0.08MPa.

Melt filtration system:

Filter combination: usually adopts 20/40/60 mesh three-stage filtration.
Screen changing method:

。Hydraulic quick screen changing: screen changing time <3 seconds.

。Continuous rotating screen: realizes non-stop production.

Filtration accuracy: up to 15μm for high-end applications.

Molding and post-processing technology

Underwater pelletizing technology:

Pelletizing water temperature: adjusted according to materials (PP: 50-60°C, PET: 10-20°C).
Cutter rotation speed: 1000-1500rpm.
Pellet shape control:

。Sphericity: ≥0.85, cut flatness: ≤0.1mm deviation.

Centrifugal drying system:

G-force control: 200-300g to ensure sufficient dehydration, residual moisture: ≤0.05%, processing capacity: matching the extrusion volume.

Vibrating screening:

Classifying screens: upper layer removes large pellets, lower layer removes powder, screening efficiency: ≥98%, defective rate: ≤0.5%.

What Are the Core Technologies of Plastic Pelletizing Equipment?

Modern plastic pelletizing equipment is a masterpiece integrating mechanical, electrical, material, and computer technologies, with its core technologies reflected in the following aspects:

Efficient extrusion system

Advanced screw design:

1.Wave screw: forms a wave-shaped channel in the compression section, improving melting efficiency by 30%.

2.Separating screw: sets a barrier section to separate solid and liquid phases, reducing energy consumption by 20%.

3.Double-thread screw: improves conveying capacity, with output increased by 15-25%.

High-precision temperature control:

Zone temperature control: 7-9 independent temperature zones, PID control.
Heating method:

。Cast aluminum heater: fast heating, long service life.

。Electromagnetic induction heating: thermal efficiency up to 95% or more.

Cooling system:

。Air cooling: low noise, simple maintenance.

。Water cooling: high cooling efficiency, need for anti-corrosion.

Intelligent control system

PLC control system:

Parameter monitoring: real-time monitoring of 50+ process parameters.
Adaptive adjustment: automatic optimization according to melt pressure, torque, etc.
Recipe management: stores 1000+ groups of process recipes.

Human-machine interface:

Visual operation: 3D equipment status display.
Remote monitoring: supports mobile APP viewing.
Data recording: saves three years of production data.

Energy-saving and environmental protection technologies

Energy recovery system:

Heat recovery rate: 40-50% of heating energy can be recycled and utilized.
Application directions: preheating feed, workshop heating, hot water supply.

Noise reduction design:

Noise source control: reduces the overall noise from 90dB to 75dB.
Sound insulation measures: adopts composite sound insulation materials.
Vibration suppression: active vibration reduction system.

Key component materials

Screw and barrel materials:

Bimetallic material: hardness above HRC60.
Wear-resistant coating: service life extended by 3-5 times.
Anti-corrosion treatment: resistant to acid and alkali corrosion.

Cutter material:

Powder metallurgy steel: maintains sharpness longer.
Surface treatment: titanium nitride coating reduces adhesion.
Dynamic balance: vibration <0.05mm at a rotation speed of 1500rpm.

Example of equipment technical parameters (medium-sized pelletizing machine):

Parameter name	Technical indicator
Screw diameter	Φ120mm
Length-diameter ratio	32:1
Maximum output	800kg/h (PP)
Main motor power	315kW
Heating power	90kW
Size	12m×2.5m×3m
Weight	Approximately 18 tons

V. What Are the Special Features of Recycled Plastic Pelletizing?

1. Raw material characteristic analysis and enhanced pretreatment:

Raw material complexity: The diverse sources and mixed components of recycled plastics (such as different types of plastics, colors, additives) are the primary challenges. Rapid and accurate component analysis technologies (such as near-infrared sorting, which can complete in a few minutes with high-precision identification of main components) and high-sensitivity impurity detection systems (capable of identifying trace pollutants) are required.
Performance prediction: Using performance prediction algorithms, combined with raw material sources and historical data, to estimate the mechanical properties and processing characteristics of recycled materials, providing a basis for subsequent process formulation.
Deep cleaning: Using strong alkaline high-temperature cleaning fluid combined with high-frequency ultrasonic and mechanical friction cleaning (specific rotation speed paddles) to thoroughly remove stubborn pollutants such as labels, adhesives, and oil stains.
Fine sorting: Combining high-precision color recognition (distinguishing tiny color differences), precise density separation (separating materials with minimal density differences), and electrostatic sorting technology to effectively separate different components in mixed waste plastics, ensuring the uniformity of raw materials. Although these pretreatments increase costs, they are crucial for the final quality.

2. Special processing technologies to address core difficulties:

·Efficient devolatilization: Recycled materials usually contain a large amount of volatile components (moisture, decomposition products, residual solvents, etc.). A multi-stage venting system (main vent, targeted side vents, high vacuum vent) works synergistically to maximize the removal of volatile substances, preventing bubbles and degradation during processing.

Enhanced filtration: To deal with the problem of many impurities in recycled materials, higher-precision filter screens are used and the filtration area is significantly increased to effectively intercept tiny impurity particles and ensure melt purity.
Degradation control: The molecular chains of recycled materials have been damaged, and their thermal stability is poor. By compounding stabilizer systems (primary, secondary, and synergistic stabilizers) and optimizing processing parameters (such as significantly reducing melt temperature and shortening the residence time of materials in the high-temperature zone), thermal-oxidative degradation during processing is effectively inhibited, and material properties are maintained.

3. Performance recovery and modification to enhance value:

Physical modification: Including orientation enhancement (improving molecular arrangement through stretching to enhance mechanical strength), crystallization control (adjusting cooling rate to change crystallinity and optimize performance), and annealing treatment (eliminating internal stress and improving dimensional stability).
Chemical modification: Mainly includes grafting reaction (introducing specific functional groups to improve compatibility with other materials) and chain extension reaction (repairing broken molecular chains to increase molecular weight and melt strength).
Additive optimization: By adding tougheners (specific addition amounts to improve toughness), reinforcing agents (such as short fibers and mineral fillers to enhance rigidity and strength), and functional additives (such as ultraviolet resistant agents, antistatic agents, etc.), the performance shortcomings of recycled materials are targeted to be compensated or new functions are endowed. With the comprehensive application of these technologies, the performance of high-quality recycled materials can approach 85-95% of that of virgin materials.

4. Strict quality control and system guarantee:

Full-process monitoring: Establish a complete system covering raw material inspection (composition, impurities, performance), process control (real-time monitoring of key parameters such as temperature, pressure, torque), and finished product testing (mechanical properties, appearance, hygiene indicators).
Traceability: Implement a complete traceability system to record the source of each batch of recycled materials, all processing steps, and detailed quality data, enhancing transparency and customer confidence.
Standard certification: Complying with authoritative systems such as international recycling standards and food contact safety certifications is a key pass for recycled materials to enter high-end and sensitive application markets.

5. Economy and future development prospects:

Cost composition: The main costs include raw materials (the largest proportion), energy, labor, and environmental protection treatment. Although the total cost is sometimes higher than that of virgin materials, the environmental benefits are significant (reducing resource consumption, carbon emissions, and waste).
Policy-driven: Policy support (such as carbon tax incentives, mandatory blending ratio requirements) significantly enhances the competitive advantage of recycled materials.
Technological progress and cost reduction: With continuous technological progress and expanding production scale, the cost of recycled materials is expected to further reduce, performance continues to improve, and application fields continue to expand.
Cutting-edge directions: Future technologies will develop towards molecular-level recycling (such as depolymerization-purification-repolymerization to achieve infinite recycling, breaking the limit of mechanical recycling times) and biological depolymerization technology (a more environmentally friendly and precise decomposition method). Intelligent sorting (with ultra-high precision and large processing capacity) will also make breakthroughs, promoting the recycled plastic industry to enter a new stage and providing strong technical support for the plastic circular economy.

VI. How to Use a Plastic Pelletizing Machine?

Preparation before starting up

1. Equipment inspection

Check whether the connecting bolts of various parts of the equipment are tight, especially key parts such as the screw, barrel, and pelletizing system, to prevent loosening during operation.
Check the lubrication system of the equipment to ensure that the amount of lubricating oil is sufficient, the oil quality is good, and the lubrication pipeline is not blocked.
Check the electrical system, including whether the wires are damaged or short-circuited, whether the electrical components work normally, and whether the grounding is good.
Check the heating system and cooling system to ensure that they can operate normally and the temperature control instruments display accurately.

2. Raw material preparation

Select appropriate plastic raw materials according to production requirements, and pretreat the raw materials, such as removing impurities and drying.
If multiple raw materials are used for blending, they need to be accurately weighed and mixed evenly in a certain proportion.

Startup operation

1. Heating up

·Turn on the heating system and set the temperature of each temperature zone according to the process requirements. Different plastic raw materials require different processing temperatures. For example, when pelletizing PE, the temperature of the feeding zone is set to 160-180°C, and the compression zone is 190-210°C, etc.

Wait for the equipment to heat up to the set temperature and maintain it for a period of time to make the temperature of each part uniform and stable. Generally, the heating time varies according to the size of the equipment and the raw materials, usually ranging from 30 minutes to 1 hour.

Startthe screw and feeding system
- When the temperature reaches the set value, start the screw motor, run at a low speed first, and observe whether the screw runs normally without abnormal noise or vibration.
- Start the feeding system and slowly feed plastic raw materials into the barrel. The feeding speed should be adjusted according to the screw speed and the production capacity of the equipment to avoid overloading the equipment due to excessive feeding.

3. Adjust process parameters

Adjust process parameters such as screw speed, feeding speed, and pelletizing speed according to product quality requirements and equipment operation conditions. For example, the melting degree and extrusion volume of plastics can be controlled by adjusting the screw speed; the size and shape of plastic pellets can be controlled by adjusting the pelletizing speed.
Observe the changes in parameters such as pressure and temperature of the equipment to ensure they are within the normal range. If abnormal parameters are found, adjustments should be made in a timely manner.

Production process monitoring

1. Product quality monitoring

Regularly sample from the outlet of the pelletizer to check the appearance quality of plastic pellets, including whether the size, shape, and color of the pellets meet the requirements.
Conduct performance tests on plastic pellets, such as tensile strength and melt flow index, to ensure stable product quality.

2. Equipment operation monitoring

Closely observe the operation status of the equipment, including parameters such as motor current, temperature, and screw torque, to timely detect abnormal conditions of the equipment.
Check whether various parts of the equipment have leakage, wear, etc., and handle problems in a timely manner if any.
Pay attention to the noise and vibration of the equipment. Abnormal noise and vibration may indicate that the equipment has faults.

Shutdown operation

1. Stop feeding

When the production task is completed or shutdown is needed, first stop the feeding system and extrude the plastic raw materials in the barrel completely.

2. Reduce screw speed

Gradually reduce the screw speed until the screw stops rotating.

3. Turn off the heating system

Turn off the heating system and let the equipment cool naturally. During the cooling process, pay attention to the temperature change of the equipment to avoid damage to the equipment due to sudden temperature drop.

4. Clean the equipment

After the equipment cools down, clean the equipment, including cleaning residual plastics and impurities in parts such as the barrel, screw, and pelletizing system.
Inspect and maintain the lubrication system, cooling system, etc., of the equipment to prepare for the next startup.

VII. What Are the Key Parameters for Selecting a Plastic Pelletizing Machine?

Scientific selection requires comprehensive evaluation of five core dimensions:

Dimension	Key parameters	Technical indicator examples
Productivity	Maximum output (kg/h)	PP: 200-2000, PET: 150-1500
	Power density (kW/kg/h)	General-purpose plastics 0.3-0.5, engineering plastics 0.6-0.9
Energy consumption	Specific energy consumption (kWh/kg)	PE: 0.15-0.25, PC: 0.35-0.45
	Heat recovery efficiency (%)	40-55% (preheating feed)
Adaptability	Raw material MFR range (g/10min)	0.5-100 (wide-range screws)
	Filling material bearing ratio (%)	Calcium carbonate ≤80%, glass fiber ≤60%
Accuracy	Temperature control accuracy (℃)	±1.0 (PID algorithm)
	Particle size deviation (mm)	±0.2 (underwater pelletizing system)
reliability	Mean time between failures (MTBF, hours)	＞8000 (redundant design of key components)
	Screen changing cycle (hours)	Recycled material: 2-4, new material: 8-12

VIII. Maintenance and Troubleshooting of Plastic Pelletizing Machines

To ensure the efficient operation and extend the service life of plastic pelletizing machines, regular maintenance and timely troubleshooting are crucial. The following are some key maintenance measures and troubleshooting methods:

1. Regular inspection and maintenance

Daily inspection: Check the operation status of the equipment, including whether parameters such as temperature, pressure, and current are normal, and ensure there is no abnormal noise or vibration.
Weekly inspection: Clean the surface of the equipment, check the wear of the screw and barrel, and ensure the cooling system and heating system work normally.
Monthly inspection: Check and replace the filter screen, clean the dust in the drying system, and check whether the hydraulic system and lubrication system are normal.

2. Troubleshooting

Decreased output: Check whether the raw materials are uniform, whether the screw and barrel are worn, and whether the filter screen is blocked.
Product quality problems: Check whether the temperature control is accurate, whether the screw speed and feeding speed are matched, and whether the pelletizing system is normal.
Equipment overheating: Check whether the cooling system works normally, whether there is blockage or leakage, and check whether the heating system is overloaded.
Abnormal noise and vibration: Check whether the equipment fasteners are loose, whether the bearings and gears are worn, and whether the transmission system is normal.

3. Common faults and solutions

Screw jamming: Immediately stop the equipment operation, check whether there are foreign objects entering or the screw is severely worn, and replace the screw if necessary.
Motor overload: Check whether the current exceeds the rated value, check whether there is an overload protection device, and adjust the feeding speed and screw speed.
Difficult screen changing: Check whether the screen changing mechanism is normal, ensure sufficient pressure in the hydraulic system, and check whether there are foreign objects stuck in the filter screen.

Is It Really Necessary to Be So Strict with the Quality Inspection of Plastic Pellets? —— The Influence Chain from Micro to Macro

When we see the sophisticated testing instruments and cumbersome testing procedures in the laboratory, we may inevitably wonder: is it really necessary to be so strict with the quality inspection of plastic pellets? The answer lies in the full-chain impact from pellets to end products.

Why Even 0.2mm Impurities Are Not Allowed in Appearance Inspection?

In the testing standards for plastic particles for food contact, the number of impurities with a diameter of ≥0.2mm in every 100 grams of particles shall not exceed 3. Behind this seemingly strict indicator, microscopic impurities actually have a fatal impact on macroscopic safety.

Take mineral water bottles as an example. If there is a 0.3mm metal impurity in the raw material, it may cause micron-level cracks in the bottle during the blow molding process. When the pressure changes, it may cause leakage problems. More seriously, if the impurities are heavy metal particles such as lead, they may slowly precipitate during the liquid immersion process, causing harm to human health.

For engineering plastic particles used in the electronics industry, the strictness of appearance inspection is also crucial. A mobile phone casing manufacturer once encountered such a situation. A batch of ABS particles was mixed with black spots with a diameter of 0.5mm, accounting for 0.1%, causing 100,000 products to have "defects" under high light irradiation, and all products eventually needed to be reworked. This is why the automatic optical sorting system performs full inspection at a resolution of 0.01mm - seemingly minor appearance defects may be magnified into quality disasters in the end product.

What Problems Will a 5% Fluctuation in Melt Flow Index Cause?

The melt flow index (MI) is the "fluidity code" of plastic processing, and a 5% fluctuation in the same batch may cause a chain reaction. In injection molding production, if the MI value of PP pellets suddenly rises from 10g/10min to 10.5g/10min (only a 5% fluctuation), the filling speed of the melt in the mold will increase by 12%, resulting in the product flash rate soaring from 0.3% to 5%; and if the MI value drops to 9.5g/10min, it may cause 3% of short-shot waste products due to insufficient fluidity.

For the film blowing process, the impact of MI fluctuation is more intuitive. Data from an agricultural film enterprise shows that when the MI value fluctuation of PE pellets exceeds ±3%, the film thickness deviation will expand from ±5% to ±12%, directly affecting the light transmittance and tear resistance of agricultural films. This is why the testing standard requires that the MI fluctuation in the same batch must be ≤±5% — it is not a digital game in the laboratory, but a "safety valve" for the stability of the production line.

How Big Is the Impact of a 0.05% Difference in Moisture Content?

The moisture content standards of 0.03% for virgin plastic pellets and 0.08% for recycled plastic pellets may seem to differ by only 0.05 percentage points, but they are likely to determine the success or failure of a product. During the PA66 injection molding process, once the moisture content exceeds 0.1%, the molecular chain will hydrolyze and break under high temperature, causing the tensile strength of the product to decrease by more than 15%. An automotive wiring harness company once recalled 100,000 vehicles because the connectors produced by the company broke during vibration testing due to the use of PA66 pellets with excessive moisture.

Even for PE, which is not very sensitive to moisture, a difference of 0.05% should not be underestimated. During the extrusion blow molding process, moisture evaporates to form bubbles. When the moisture content increases from 0.03% to 0.08%, the bubble rejection rate will rise from 0.1% to 2.3%. Karl Fischer moisture analyzers require an accuracy of 0.001% precisely to capture these tiny but critical differences.

Why Insist on Sampling Inspection of Mechanical Properties Every 8 Hours?

Some people think that the sampling inspection of the mechanical properties of plastic pellets does not need to be too frequent, but the lesson of a pipe manufacturer has subverted this idea. The enterprise once failed to conduct sampling inspection for 12 consecutive hours of production and did not find that the tensile strength of PP pellets dropped from 28MPa to 24MPa (exceeding the ±10% standard), resulting in 1000 meters of water supply pipes produced bursting during pressure tests.

The sampling frequency of once every 8 hours is actually a "race" against the plastic degradation rate. In granulation production, factors such as screw wear and temperature drift may cause the performance of pellets to deteriorate slowly — this deterioration is often difficult to judge through appearance in the early stage and can only be captured by mechanical property testing. Just like regular physical examinations for the human body, the mechanical sampling inspection of plastic pellets is not an unnecessary burden, but an "early warning system" for quality risks.

From these details, it can be seen that the quality inspection standards for plastic pellets seem strict, but in fact, every number corresponds to the blood and tears lessons of industrial production. It is not to increase costs, but to avoid macro-level quality disasters by accurately controlling micro-indicators — this is the vivid embodiment of the "nip in the bud" concept in modern industry.

Have you noticed these design details of the plastic granulator?

Why should the screw speed be accurate to ±5rpm?

The screw speed of the plastic granulator seems to be just a simple parameter setting, but it directly affects the quality of the particles. Taking PP granulation as an example, when the speed fluctuation exceeds 10rpm, the melt pressure will fluctuate by ±0.3MPa, causing the particle density deviation to expand to more than 2%. Modern granulators are driven by servo motors and combined with magnetic scale positioning technology to increase the speed control accuracy to ±1rpm. What does this mean?

For medical-grade PE particles, the melt index fluctuation between batches can be controlled within ±0.2g/10min
When granulating recycled materials, it can reduce material degradation caused by uneven shearing and increase the elongation at break retention rate by 15%

Why should the water temperature for underwater granulation be accurate to ±1℃?

The crystallization characteristics of different plastics are extremely sensitive to cooling speed. Taking PET as an example, if the pelletizing water temperature rises from 20℃ to 22℃, the crystallinity will increase by 3%, which will directly affect the transparency of the subsequent bottle blowing process. This is why the pelletizer is equipped with a precise water constant temperature system:

When PP pelletizes, the water temperature is stabilized at 55±1℃ to obtain the best spheroidization degree (≥0.85)
PET pelletizing is controlled at 15±1℃ to avoid the molecular chain arranging too quickly to form coarse crystals

A bottle flake recycling company has increased the transmittance of recycled PET pellets to 88% through precise temperature control, which is close to the level of original materials.

How to choose between twin-screw and single-screw pelletizers?

Many customers will be entangled in this issue. In fact, the key lies in the characteristics of the raw materials:

Single-screw machines are suitable for pure material granulation, and the energy consumption is 15% lower than that of twin-screw machines, but they cannot handle raw materials containing more than 5% impurities
The meshing structure of the twin-screw machine can achieve 300% shear mixing effect, especially suitable for:

Masterbatch production (dispersion uniformity is more than 95%)

Glass fiber reinforced materials (fiber breakage rate can be controlled within 8%)

Mixed recycling of various waste materials (can handle 10-15% of heterogeneous plastics)

Why is an extra exhaust port required when granulating recycled materials?

The moisture, oil and volatiles contained in waste plastics will form bubbles when melted. Ordinary single exhaust port granulators can only remove 60% of volatiles, while the dual exhaust port design:

The main exhaust port (vacuum degree ≥ 0.08MPa) removes 80% of free moisture
The side exhaust port removes an additional 15% of volatiles for small molecule degradation products unique to recycled materials

A recycled material company's actual test shows that the dual exhaust system can reduce the volatile content in the particles from 0.5% to 0.08%, and the subsequent injection molding scrap rate is reduced by 70%.

Is the more uniform the particle size, the better?

Many customers believe that the smaller the particle size deviation, the better, but in fact, it should be flexibly selected according to the subsequent process:

Injection molding needs to be strictly controlled within ±0.2mm (such as ABS particles for electronic housings), otherwise it will cause metering errors
Extrusion sheets can be relaxed to ±0.5mm, and appropriate size distribution can improve melt fluidity
Film blowing requires that the particle length and diameter ratio remain at 1:1 to avoid "bridging" when adding materials

Modern granulators can meet the precise needs of different scenarios through replaceable screen combinations (20-120 mesh) and tool gap fine-tuning (0.1-0.5mm).

In summary, as the core equipment of plastic processing, plastic pelletizing machines have broad room for technological progress and application prospects. By continuously optimizing the design, improving performance, and enhancing intelligence, plastic pelletizing machines can better meet market demands and effectively promote the sustainable development of the plastic industry.

In the future, with the continuous emergence of new materials and technologies, plastic pelletizing machines will continue to move towards more efficient, environmentally friendly, and intelligent directions, contributing positively to the progress of human society.