Twin screw extruders are now a must-have for modern plastic processing. They mix better and are more flexible than single screw extruders. For manufacturers that want to get the most out of their production processes and get the best results for their unique applications, it is very important to know about the different types of twin screw extruders that are available.
How Do You Tell Different Types of Twin Screw Extruders Apart?
There are three basic ways to group twin screw extruders: the direction of the screw rotation, the way the screws interact with each other, and the shape of the screws. Each factor affects the performance of the extruder, so different types of twin screw extruders work better for different uses.
Sort by Screw Rotation Direction: Co-Rotating vs Counter-Rotating Twin Screw Extruders
- Co-rotating twin screw extruders have screws that rotate in the same direction at the same time, usually clockwise or counterclockwise. This configuration allows the material to flow through the machine in a steady and even manner, enabling excellent self-cleaning capabilities of the extruder machine. The material moves in a figure-eight pattern between the screws and gets mixed and homogenized thoroughly.
- Counter-rotating twin screw extruders have screws that rotate in opposite directions: one clockwise and the other counterclockwise. This opposing rotation creates intense contact zones between the screws, which helps materials become more pliable and allows for more pressure to build up.
Sort by Screw Interaction: Intermeshing vs Non-Intermeshing Twin Screw Extruders
- Intermeshing twin screw extruders feature screws that fit together very tightly, with the flights of one screw reaching into the grooves of the other. This tight fit makes for robust mechanical interaction, which lets shear and compression forces work well. Intermeshing designs can be further divided into two types: fully intermeshing (with no gap between the screw flight and the root) and partially intermeshing (with a tiny gap).
- Non-intermeshing twin screw extruders are twin screw extruders that have screws that work independently of each other without touching. The distance between the shafts is equal to the sum of the outer radii of both screws. This makes it possible for each screw to process its own channel. The non-intermeshing design reduces shear stresses and is great for working with materials that are fragile or sensitive to heat.
Sort by Screw Geometry: Parallel vs Conical Twin Screw Extruders
- Parallel twin screw extruders feature both the screw diameter and the distance between the two shafts staying the same along their whole length. This design provides sufficient processing length, which allows materials that require extensive mixing or devolatilization to remain in the system for the extended period they need.
- Conical twin screw extruders feature screws that get smaller from the feed portion to the discharge end. The axes are at an angle to each other, and the distance between the centers changes gradually over the length. This setup allows for a lot of material to flow into the feed zone and creates more pressure as the material flows toward the narrower discharge end.
The Eight Theoretical Types of Twin Screw Extruders
If you combine the three classification systems, you can come up with eight different types of twin screw extruders:
- Co-Rotating, Intermeshing, Parallel
- Co-Rotating, Intermeshing, Conical
- Co-Rotating, Non-Intermeshing, Parallel
- Co-Rotating, Non-Intermeshing, Conical
- Counter-Rotating, Intermeshing, Parallel
- Counter-Rotating, Intermeshing, Conical
- Counter-Rotating, Non-Intermeshing, Parallel
- Counter-Rotating, Non-Intermeshing, Conical
However, not all eight combinations are commonly manufactured or commercially viable, with industrial applications commonly using certain types of twin screw extruders for their needs.
What Are the Most Common Types of Twin Screw Extruders?
Co-Rotating Intermeshing Parallel Twin Screw Extruders
This is the most common setup for plastic extruder machines. These extruders are great for compounding jobs where product consistency is vital, including making masterbatch and engineering plastics. The modular design makes it easy to change barrel modules and screw elements to fit different processing needs.
Key Applications:
- Plastic compounding and masterbatch production (color, filler, engineering plastics, fluoroplastics, biodegradable plastics, thermoplastic elastomers, and cable material)
- Foam extrusion processing (PET, PP, PA, TPU foam sheets, boards, and beads)
- Thermoplastic composite manufacturing (long fiber reinforced thermoplastic pellets and unidirectional prepreg tapes)
- Sheet extrusion lines (PET, ABS single/multi-layer sheets)
- Reactive extrusion processes (TPU continuous polymerization)
Counter-rotating Intermeshing Conical Twin Screw Extruders
These extruders are great for processing PVC and are popular among plastic extrusion machine manufacturers. They build up pressure well and convey materials efficiently. The conical shape allows for more operating torque and load capacity than a parallel configuration.
Key Applications:
- Rigid PVC pipe and profile extrusion (UPVC pipes, window profiles, door frames)
- UPVC corrugated pipe production (drainage and sewer systems)
- Wood-plastic composite (WPC) processing (decking, fencing, outdoor furniture)
- High-filled compound processing (PVC + calcium carbonate, mineral-filled compounds)
- Thermally sensitive polymer processing (C-PVC, heat-sensitive formulations)
Counter-rotating Non-intermeshing Parallel Twin Screw Extruders
These extruders feature the highest free volume and lowest shear forces of any twin screw configuration. The independent screw operation provides superior distributive mixing and excellent devolatilization capabilities.
Key Applications:
- High-level devolatilization processes (removal of 30%+ volatiles and solvents)
- Petrochemical precursor processing (specialty chemical manufacturing)
- Pharmaceutical hot-melt extrusion (controlled drug delivery systems)
- Chemical reaction processes (continuous polymerization, reactive extrusion)
- Specialty polymer production (long residence time processing applications)
Which Twin Screw Extruder Is the Most Flexible in Use?
Comparing Modular Design Flexibility
- Co-rotating intermeshing parallel: Offers the most modular versatility because of its parallel barrel design. Manufacturers may quickly change out barrel segments, add feeding and vent ports, and change the screw pieces to work with different materials and formulations.
- Counter-rotating intermeshing conical: Not as flexible as parallel types. The conical taper needs custom-built modules, which makes plug-and-play setups impossible. However, some changes can still be made.
- Counter-rotating non-intermeshing parallel: Some flexibility. Parallel barrels allow for modular adjustments, but non-intermeshing screws are usually made for specific jobs, like devolatilization.
Which Twin Screw Extruder Is the Easiest to Clean?
Comparing Self-Wiping Capabilities
- Co-rotating intermeshing parallel: Great at cleaning itself. Close intermeshing screws constantly wipe each other’s flights, which almost gets rid of stagnant zones and makes it easy to switch between products quickly.
- Counter-rotating intermeshing conical: Has a good ability to clean itself, but lower speeds and a conical shape can leave small zones that need further cleaning.
- Counter-rotating non-intermeshing parallel: Not very good at cleansing itself. Because screws never touch each other, material can build up in some places, especially with sticky or high-viscosity formulations.
Which Twin Screw Extruder is the Best for Heat-Sensitive Materials?
Comparing Gentle Processing Capacities
- Co-rotating intermeshing parallel: Generate higher shear rates, but you can lower them by lowering the screw speed and optimizing the configurations specifically for the application. Not the first choice for substances that are very sensitive to heat.
- Counter-rotating intermeshing conical: Great for heat-sensitive materials. Lower screw speeds (typically 30-150 rpm) and opposing rotation minimize shear heating, making them ideal for PVC and temperature-sensitive plastics.
- Counter-rotating non-intermeshing parallel: Best for sensitive materials. Screws work on their own with very little mechanical shear, which almost completely removes the risk of heat damage.
Which Twin Screw Extruder Delivers the Highest Output?
Comparing Throughput and Pressure Build-Up
- Co-rotating intermeshing parallel: Delivers the highest throughput rates and can run at speeds of 400 to 900 rpm (some models can even go up to 1,800 rpm). Ideal for large-scale compounding and masterbatch production.
- Counter-rotating intermeshing conical: Not very fast, but can generate a lot of pressure. The conical taper naturally compresses material, which provides superior die pressure for pipe and profile applications.
- Counter-rotating non-intermeshing parallel: Lower throughput by design, optimized for devolatilization and gentle processing rather than high-volume production.
How Do You Choose the Right Twin Screw Extruder Type?
Choosing with Material Considerations
- Thermoplastic Processing: Co-rotating intermeshing parallel extruders are ideal for processing most thermoplastics because they mix well and have a high throughput.
- PVC Processing: Counter-rotating conical extruders are preferred for PVC applications since they can be gentler and build up pressure better.
- Heat-sensitive Materials: Non-intermeshing configurations minimize shear heating, which makes them perfect for materials that are sensitive to temperature.
Choosing with Production Requirements
- High Throughput: Co-rotating parallel extruders typically provide the highest production rates and are ideal for large-scale manufacturing operations.
- Precise Control: Counter-rotating extruders often provide you with better control over processing conditions, which makes them suitable for specialized uses that need very tight tolerances.
- Flexibility: Modular parallel extruders provide the greatest flexibility for processing various materials and formulations.
What Specifications Should You Consider in Twin Screw Extruder Selection?
When selecting types of twin screw extruders, some important technical details to think about are:
- Screw Diameter and L/D Ratio: They determine the amount of material that can be processed and the processing time taken, with larger screw diameters for greater throughput and longer L/D ratios for more residence time.
- Torque Density: This number (in Nm/cm³) tells you how well the extruder can handle high-viscosity materials, with higher ratings signifying better capacities.
- Screw Speed Range: Affects the rate of shear and the intensity of the mixing, with higher speeds leading to higher shear and better mixing but also risk of material degradation or overheating.
- Multi-Zone Barrel Design: This design accommodates independent heating and cooling systems and specific screw elements that let you set the temperature and processing conditions precisely across the barrel length.
- Feeding and Venting Capabilities: The number and position of feed ports, side feeders, and vacuum vents have a direct effect on how well you can add additives, get rid of volatile substances, or process multi-component compositions.
Partner with Chuangbo for Your Twin Screw Extruder Needs
Manufacturers who want to make their plastic processing operations as efficient as possible need to know about the many types of twin screw extruders. Each type has its own benefits for certain uses, so it’s important to choose the right one to get the best processing results.
Chuangbo is one of the top China plastic extruder machine manufacturers. We make co-rotating intermeshing parallel twin screw extruders that are great for mixing, flexibility, and productivity in a wide range of industrial settings.
Contact our expert team today to discuss your specific twin screw extruder needs and discover how our personalized configuration can enhance your production.
