How Does The Cutting Method Affect The Plastic Granulation Characteristics? —Full Analysis Of Pellet Cutting Technology For Twin-screw Extruder

In the field of plastic modification and recycling, a seemingly downstream process - granulation - actually has a decisive impact on the performance, cost, and even commercial success of the final product. Different cutting methods not only determine the morphology, uniformity, and surface smoothness of particles, but also directly affect the energy consumption, efficiency, and suitability for high-end applications of the production line. With the advancement of the global circular economy and the "dual carbon" goal, how to match the best cutting solution for efficient mixing equipment such as co rotating twin screw extruders has become a key issue that international customers who pursue high cost-effectiveness and environmentally friendly production must ponder deeply. This article will provide an in-depth analysis of the core principles and application boundaries of mainstream granulation technology, helping you make accurate decisions.

Key issue: Fast indexing
Q: As a customer who is new to plastic granulation, what aspects of granulation methods should I pay the most attention to?
Answer: The primary focus is on three points: material characteristics (such as whether it contains fiberglass, whether it is thermally sensitive), target production volume, and investment budget. For example, in laboratory or small-scale multi variety production, strip cutting may be the preferred option due to its flexibility and low initial cost; The advantages of large-scale, single material continuous production, high automation of underwater particle cutting, and excellent particle quality are obvious.

Q: I heard that underwater cutting has the best cutting effect. Is it suitable for all plastics?
Answer: It's not like that. Although the underwater granulator (UWP) can produce perfect spherical particles and has a high degree of automation, its system is complex and requires the largest investment. It is extremely sensitive to water temperature control and is more suitable for materials with higher melt strength, such as polyolefins. For certain high-temperature, viscous, or easily hydrolyzed materials in water, careful evaluation or selection of alternative solutions may be necessary.

Q: How to balance environmental requirements and costs when choosing the cutting method?
Answer: Environmental protection is not only reflected in the use of recycled materials. Efficient extruders combined with appropriate cutting methods can significantly reduce energy consumption and material loss per unit output. For example, air-cooled die surface heat cutting eliminates the cooling water drying process, directly saving energy; The advanced water ring granulation (WRP) system is closed, and the process water can be recycled and filtered for use, achieving water conservation and emission reduction.

1, Twin screw extruder: the core of efficient plasticization

The core of modern plastic granulation production lines is plastic extruders, among which co rotating twin screw extruders have become the mainstream choice in the fields of high-performance modification, masterbatch preparation, and recycling due to their excellent mixing, shearing, and self-cleaning capabilities.

This efficient extruder, with its precise "building block" screw design, can achieve uniform dispersion and distribution mixing of materials in a short period of time, ensuring the perfect fusion of additives, colorants, or recycled materials with the matrix resin. Its strong plasticizing ability provides stable and high-quality melt for the back-end cutting process, which is the first guarantee for obtaining excellent pellet quality.

2, Classification and characteristics of cutting methods

The granulation process is mainly divided into two categories: "cold cutting" and "hot cutting". Cold cutting refers to the process of cutting a molten material after it has cooled and solidified; Hot cutting refers to cutting immediately after the melt leaves the mold head. The following table summarizes the characteristics of three mainstream die surface hot cutting methods:
2.1 Water ring granulation (WRP)
·Principle: After the melt is extruded from the mold hole, it is cut by a rotating blade in the air, and the particles are immediately thrown into a tangential injection cooling water ring for cooling and transportation.
·Particle characteristics: Generate circular flat particles similar to pills.
·Advantages: Compact system, moderate degree of automation, low sensitivity to process fluctuations, investment and operating costs between pulling and underwater.
·Disadvantage: It is mainly suitable for high melt strength materials such as polyolefins, and has a certain production capacity limit (such as about 11000 pounds per hour).
·Typical applications: general plastic granulation, partial recycling material granulation.

2.2 Underwater Particle Cutting (UWP)
·Principle: The cutting chamber is completely filled with water, and the melt is cut and cooled into shape in the water at the moment it leaves the mold hole.
·Particle characteristics: Thanks to the surface tension of water, ideal spherical particles can be formed with a smooth surface and uniform size.
·Advantages: The highest degree of automation, large output (designed throughput up to 70000 pounds per hour), good particle quality, less dust, and can handle almost all polymers. Sinopec adopts online modification followed by underwater cutting process in its flame retardant polypropylene production, ensuring the high quality and stability of the product.
·Disadvantages: The system is the most complex, with high investment and extremely high requirements for water temperature control accuracy.
·Typical applications: large petrochemical projects, high-end engineering plastics, food contact grade materials, high demand masterbatch.

2.3 Hot cutting of air-cooled mold surface
·Principle: After extrusion, the melt is directly cut by a cutting blade, and the particles are cooled and transported by high-speed airflow.
·Particle characteristics: The particle shape depends on the mold hole and cutting design.
·Advantages: No need for water treatment system, simple equipment, low energy consumption, especially suitable for scenarios with high environmental requirements or inconvenient water sources. For products like XL-PE cable material, air-cooled heat cutting is even a standard process in the industry.
·Disadvantages: Limited cooling efficiency, may not be suitable for high production or heat sensitive materials; Particles are prone to tailing.
·Typical applications: Cable materials, partially modified materials (such as high filling systems).

3, How to choose the cutting method based on the material ratio?
The material formula is the decisive factor in choosing the cutting method. The following guidelines are available for reference:
·Filling/reinforcement system: High filling (such as calcium carbonate) or fiberglass reinforcement materials will cause changes in melt strength and behavior. High filling LLDPE may shift from water ring cutting to air-cooled die surface hot cutting to save energy and reduce dust; However, long glass fiber reinforced materials usually need to be cold cut back into strips to avoid excessive damage to the fibers by the cutting blade.
·Toughening/elastic system: such as TPV (PP/EPDM), water ring hot cutting is often the preferred method, which can control costs while ensuring the appearance of particles.
·Reactive extrusion and special materials: Chemical cross-linked cable material (XL-PE) is preferred for air-cooled die surface hot cutting. For viscous materials such as TPU, although underwater cutting is often used, special pressure building design is required for the measuring section of the co rotating twin screw extruder.
·Recycled materials and biodegradable plastics: Recycled materials with complex compositions, such as water ring pellets, are widely recommended due to their good adaptability and moderate cost. For biodegradable materials such as PLA and PBAT, temperature control during the granulation process needs to be considered to prevent thermal degradation. Strip granulation or low-temperature underwater granulation are common options.

4, Environmental Protection and Cost Considerations: Future oriented Choices
For customers pursuing sustainable development, choosing a granulation method requires a full lifecycle perspective.
·Energy efficiency: Air cooling heat cutting directly eliminates the energy consumption of water cooling and drying; An efficient underwater pelletizing system, through optimized design, may have lower energy consumption per unit output than traditional strip production lines with extensive management.
·Material loss and quality: High quality cutting methods (such as UWP) produce the least amount of powder and defective particles, directly improving raw material utilization and reducing waste disposal costs.
·Return on Investment (ROI): Although the initial investment of the underwater pelletizer is large, its extremely high degree of automation can significantly reduce manual labor, and the ultra-high single line output can dilute fixed costs. For large-scale production, the long-term ROI may be better.
Conclusion

No cutting method is omnipotent. On the basis of the excellent mixing provided by the co rotating twin screw extruder, each technology has its own territory to guard, from the flexible and economical cutting of the strip, to the balanced and efficient cutting of the water ring, and to the top-level quality of underwater cutting. As a provider of equipment and technology, Nanjing Kelongwell Chemical Machinery Co., Ltd. is well versed in this field. We not only provide stable and reliable high-efficiency extruder hosts, but also plan and match the most suitable cutting solution for you based on your specific material formula, production capacity goals, and sustainable development vision.

In the world of plastic, every perfect particle begins with a thoughtful choice. Let us help you move towards excellence from the first step.