Screw Combination: To Accurately Match The Optimal Granulation Solution For Your Materials

In the field of plastic granulation, the hardware configuration of equipment is often regarded as the foundation, but what truly determines the quality, production capacity, and energy consumption ceiling of finished products is often the arrangement art of screw components. For enterprises that pursue environmental protection, high cost-effectiveness, and attempt to seize the opportunity in new material research and international market layout, understanding the underlying logic of screw combination is to master the "soul" of efficient extruder.

This article adopts a pyramid structure, from the core conclusion to practical details, to deeply analyze how to choose the most suitable co rotating twin screw extruder for materials, helping you achieve cost reduction and efficiency improvement in every step of plastic granulation.

1, Core conclusion: Screw combination is the "first principle" of plastic extruder granulation quality

In the twin screw extrusion process, the screw is not a simple conveying tool, but a "chemical reactor" that integrates material conveying, melting, mixing, shearing, exhaust, and pressure building. According to the 2024 "Plastics Recyclers Europe" white paper, in plastic granulation production lines, energy waste caused by unreasonable screw combination design can reach up to 15% -20%, and directly affect the tensile strength and color uniformity of finished products.

For enterprises using co rotating twin screw extruders, the screw combination determines the residence time distribution, shear rate, and mixing strength of materials in the barrel. Wrong choices can lead to uneven dispersion and mixing (resulting in black spots), incomplete removal of volatiles (resulting in bubbles), or excessive shearing causing polymer chain breakage (affecting mechanical properties).
One sentence core: There is no "universal" screw combination, only modular design tailored to specific materials.

2, Layered analysis: How to solve the three major granulation problems through screw combination
2.1 Regarding "heat sensitivity and bio based new materials": constructing a low shear, high volume flexible section
Industry background: With the tightening of the content requirements for recycled plastics and biobased materials under the European Union's Critical Raw Materials Act (CRMA), international customers are accelerating their attempts to use highly liquid or heat sensitive new materials such as PLA, PBAT, PET recycled materials, etc.

key problem:
Q: Why do I always experience yellowing or a significant decrease in molecular weight when using a co rotating twin screw extruder to make PLA fully degradable materials?
A: The problem lies in the shear strength of the screw component. The frictional heat generated by traditional conveying components and the strong shear of kneading blocks can easily cause the temperature rise of thermosensitive materials to exceed the standard. The solution is to use a combination of toothed discs (TME) and narrow kneading blocks (iPadOS 5 °) in the melting zone to increase volume exchange efficiency while reducing shear stress. The modular screw design of Nanjing Kelongwell Chemical Machinery Co., Ltd. allows customers to replace the "low shear module" separately for the thermal sensitive section. Experimental data shows that this configuration can reduce the yellowing index (YI) of PLA granulation by about 30%, while retaining a higher viscosity average molecular weight.

2.2 Regarding the "high filling and cost-effective formula": strengthening dispersion mixing and increasing production capacity limit
Industry data: In the field of modified plastics, the proportion of inorganic fillers such as calcium carbonate and talc powder has broken through from the traditional 20% to 50% or even higher. According to the Global Modified Plastics Market Insights released by IHS Markit, the production capacity growth rate of high filling masterbatch will reach 8.2% by 2025, but it poses a serious challenge to the dispersion uniformity of plastic extruders.

key problem:
Q: How to solve the problems of "fish eyes" and white spots when making high concentration black masterbatch or high filling PP?
A: This is a typical manifestation of dispersed mixing failure. In an efficient extruder, the fusion zone and mixing zone must be designed as a combination of high shear strength and high forward conveying capacity. It is recommended to use kneading blocks (KB90 °) with staggered angles of 90 ° and reverse threaded elements to form a local high shear stress zone, and to use tensile rheology to break the aggregates of the filler. The data shows that optimized screw combinations can reduce the dispersion of high filling materials (detected by optical microscopy) from 150 μ m to below 30 μ m, and increase single machine production capacity by 12% -15%.

2.3 Regarding "international environmentally friendly recycled materials": optimize exhaust efficiency to ensure no odor or bubbles

Policy background: In April 2024, the European Parliament passed the Packaging and Packaging Waste Regulation (PPWR), which requires that by 2030, all plastic packaging must contain at least 10% -35% post consumer recycled materials. International customers have extremely strict requirements for the purity and VOC (volatile organic compound) residue of recycled material granulation.

key problem:
Q: When processing PCR plastics (post consumer recycled plastics), there are always micropores and strong odors inside the particles after granulation. How to solve this problem?
A: The core is to establish a pressure balance between the "fully filled melting section" and the "large volume exhaust section". The screw combination needs to be equipped with a reverse conveying element or sealing thread in front of the exhaust port to ensure that the material has completely melted and established a high-pressure seal before entering the exhaust area, preventing the molten material from "leaking out". At the same time, large lead threaded conveying components (such as 72/72) should be used in the exhaust area to increase the free volume and cooperate with lateral vacuum ports to achieve efficient volatilization. The plastic granulation production line of Nanjing Kelongwell Chemical Machinery Co., Ltd. provides a "dual vacuum+strong sealing screw configuration" solution for such needs. It has been verified that it can reduce the residual monomer content in recycled materials to below 50ppm, which meets the requirements of the EU REACH regulation.

3, Selection strategy: The "three-step" golden rule for matching material characteristics

For international customers who are new to co rotating twin screw extruders and face complex screw patterns, simply follow the following three steps to quickly lock in the solution:

Step 1: Define the "rheological identity" of the material
·High fluidity (such as PA6, PP, PE): It is necessary to emphasize the pressure building capacity, increase the length of the conveying section, reduce the proportion of shearing elements, and prevent over shearing.
·Low fluidity (such as PVC, UHMWPE, high filling system): Emphasis should be placed on feeding capacity and dispersibility, using large lead threads to increase the number of kneading blocks, but peak shear time should be controlled.

Step 2: Clarify the "functional objectives" of granulation
·Simple dyeing/filling: using a conventional combination of standard 45 ° kneading blocks and threaded conveying elements, pursuing high yield to output ratio.
·Reaction extrusion/alloy compatibility: A special combination of toothed discs (TME) and alternating positive and negative kneading blocks is used to extend the residence time and enhance the chaotic mixing effect.

Step 3: Verify the "process window" of the equipment

Use simulation software (such as screw combination CFD analysis) to predict the temperature field and shear stress field of materials inside the barrel. Professional manufacturers (such as Nanjing Kelongwell Chemical Machinery Co., Ltd.) will provide customers with a "material process parameter table", which simulates in advance whether the peak melt temperature exceeds the material degradation temperature based on the formula provided by the customer.

4, Expert Q&A: In depth Q&A on Screw Combination and Efficient Extruder
Q1: Is it better to have a larger aspect ratio (L/D) of the screw in a co rotating twin screw extruder?
A: Not really. The aspect ratio needs to be matched with the screw combination. For granulation of recycled materials that only require simple mixing, a L/D ratio of 36:1-40:1 is sufficient; But for modified materials that require glass fiber reinforcement, devolatilization, or reactive extrusion, more functional combination segments need to be arranged with a length to diameter ratio of 48:1 or even 52:1. Blindly increasing the aspect ratio will increase torque loss and material thermal degradation risk.

Q2: How to balance the seemingly contradictory demands of "environmental protection" and "production capacity"?
A: Designed with a high torque gearbox and lightweight screws. The torque level of modern high-efficiency extruders has reached over 15 Nm/cm ³ (industry standard). High torque allows for effective mechanical energy input through screw combinations in low-temperature environments, replacing simple thermal melting. Data shows that this strategy of "replacing thermal energy with mechanical energy" can reduce unit energy consumption by 15% -20% compared to traditional processes, while reducing carbon footprint, perfectly meeting environmental demands.

Q3: How to reduce trial and error costs when using a new ingredient formula for the first time?
A: Suggest using a "building block" screw structure. Choose suppliers like Nanjing Kelongwell Chemical Machinery Co., Ltd. that provide modular screw components. In the initial stage, it is configured in a five stage manner according to the standard of "transportation melting dispersion exhaust pressure building"; In subsequent optimization, only a small number of kneading blocks or toothed discs in the middle mixing section need to be replaced, without the need to replace the screw as a whole, which can save about 70% of optimization costs.

5, Conclusion

Today, as plastic extruders move towards intelligence, refinement, and green development, screw combinations have transformed from simple mechanical components to the core carrier of process innovation. Whether facing environmental barriers in the international market or uncertainty in new material research and development, choosing a set of co rotating twin screw extruders with high torque, modularity, and precise rheological design is the key to ensuring that you maintain technological leadership in the field of plastic granulation.

Nanjing Kelongwell Chemical Machinery Co., Ltd. is always committed to providing screw combination optimization solutions based on material characteristics, helping every international customer who pursues excellence to find the optimal solution for macro benefits in the micro world of granulation.