Screw and Barrels for Co-rotating Parallel Twin screw extruder

Screw and Barrels for Co-rotating Parallel Twin screw extruder

High quenching and high tempering black alloy steel material especially for exporting.



Good quality and low price usually used in domestic.

Barrels assembling

Screw shaft with screw elements

Storage

Understanding Extruder Screws for Plastic Pelletizing

Q&A Guide for Recycling and Compounding Applications

Q1: What is an extruder screw in a plastic pelletizing machine?

An extruder screw is the core working component inside a heated barrel of a plastic pelletizing machine.

Its main functions are to convey, melt, mix, and homogenize plastic materials, and finally push the molten plastic toward the die for pelletizing.

In pellet production, the screw does not shape final products such as pipes, sheets, films, or profiles.

Instead, it prepares a stable, uniform melt that can be cut into plastic granules.

Q2: What types of extruder screws are used in plastic pelletizing?

Plastic pelletizing systems mainly use two types of extruder screws:

• Single-screw extruders

• Twin-screw extruders

Each type is selected based on material condition, mixing requirements, and pellet quality expectations.

Q3: How does a single-screw extruder screw work in pellet production?

A single-screw extruder is typically used for melting and pelletizing one main type of plastic, such as PP, PE, PS, or recycled materials.

The screw usually consists of four functional zones:

1.Feed zone – receives plastic flakes or granules

2.Compression zone – builds pressure and begins melting

3.Melting zone – completes plasticization

4.Metering zone – stabilizes melt flow before pelletizing

Most recycling pelletizing lines use single-screw extruders, especially when material composition is relatively stable.

Q4: What is a “full-flight” screw, and why is it common in recycling?

A full-flight screw has continuous screw flights without special mixing structures.

Advantages:

• Higher output

• Simple structure

• Stable operation

• Suitable for recycled plastics with consistent properties

This is why over 90% of standard recycling pelletizing lines use single-screw, full-flight screw designs.

Q5: What is a mixing section (darmage) in a single-screw extruder?

A mixing section (sometimes called darmage) is a specially designed part of the screw with notches or interruptions.

Purpose:

• Improve melt uniformity

• Enhance color or additive distribution

Trade-off:

• Better mixing

• Slightly lower output

It is typically used when recycled material quality fluctuates or when limited additives are introduced.

Q6: Why are twin-screw extruders preferred for compounding pelletizing?

Twin-screw extruders provide significantly stronger mixing and dispersion than single-screw machines.

They are commonly used for:

• Mixing different polymers

• Adding fillers, additives, or reinforcements

• Color masterbatch compounding

• High-performance or functional pellets

This process is known as plastic compounding.

Q7: What is the difference between co-rotating and counter-rotating twin screws?

• Co-rotating twin screws

Both screws rotate in the same direction

→ Excellent mixing, dispersion, and self-cleaning

→ Most common for plastic compounding pelletizing

• Counter-rotating twin screws

Screws rotate in opposite directions

→ Higher pressure, lower shear

→ Less common in standard plastic compounding

Q8: When should I choose a single-screw vs. twin-screw pelletizing extruder?

Application Requirement             Recommended Extruder

Single polymer recycling                 Single-screw

Stable material composition         Single-screw

Mixing different resins                      Twin-screw

Adding color masterbatch              Twin-screw

High dispersion additives               Twin-screw

Q9: Does screw design affect pellet quality?

Yes. Screw design directly influences:

• Melt homogeneity

• Pellet appearance

• Mechanical properties of granules

• Production stability

Factors such as screw length, diameter, compression ratio, and mixing elements all impact final pellet performance.

Q10: Are extruder screws used for making sheets, pipes, or films?

No.

In pelletizing systems, extruder screws are only used to produce plastic granules.

Shaping products like:

• Pipes

• Profiles

• Sheets

• Films

requires different extrusion systems and dies, which are not part of plastic pelletizing lines.

Q11: How should customers select the right screw and extruder?

The correct choice depends on:

• Raw material type (virgin or recycled)

• Mixing and dispersion requirements

• Output expectations

• Final pellet application

Clearly defining the pelletizing goal is the first and most important step toward selecting the right extruder and screw configuration.

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