When You Should NOT Upgrade to Bimetallic

When replacing an extrusion screw barrel , many plastic processors face the same question:

Should we upgrade from a nitrided screw barrel to a bimetallic screw barrel?

Bimetallic Screw Barrel vs Nitrided Screw Barrel Comparison

A bimetallic screw barrel is often considered a premium solution because of its excellent wear resistance and longer service life. However, upgrading to bimetallic is not always the right decision.

For some extrusion applications, a high-quality nitrided screw barrel can already provide stable performance with a better cost-performance ratio.

The real question is not:
“Is bimetallic better?”

The better question is:
“Does your extrusion application actually require bimetallic protection?”
Choosing an unsuitable screw barrel material can increase your investment cost without improving production efficiency.

What Is the Difference Between Bimetallic and Nitrided Screw Barrel?

Before deciding whether to upgrade, it is important to understand the differences between these two screw barrel solutions.

• Nitrided Screw Barrel

  A nitrided screw barrel is usually manufactured from high-quality alloy steel such as 38CrMoAlA and treated through a nitriding process.

  During nitriding treatment, nitrogen elements penetrate into the steel surface, creating a hardened layer that improves:
  · Surface hardness
  · Wear resistance
  · Corrosion resistance
  · Fatigue strength
  · Service life

  Nitrided screw barrels are widely used in standard plastic extrusion applications where materials are relatively clean and non-abrasive.

  Typical applications include:

  Plastic Material	Suitability
  PE	Excellent
  PP	Excellent
  HDPE	Excellent
  Standard PVC	Good
  Virgin plastics	Excellent

  For many conventional extrusion lines, a properly designed nitrided screw barrel can already provide reliable production performance.

• Bimetallic Screw Barrel

  A bimetallic screw barrel is manufactured by adding a wear-resistant alloy layer onto the working surface of the barrel or screw flight.

  This special alloy layer provides superior protection against:
  · Abrasive fillers
  · Glass fiber materials
  · Mineral additives
  · Recycled plastics
  · Corrosive compounds

  Compared with nitrided treatment, bimetallic technology provides a thicker and more durable wear-resistant surface.

  Typical applications include:

  Plastic Material	Suitability
  Glass fiber reinforced plastics	Excellent
  Calcium carbonate filled PVC	Excellent
  Recycled plastics	Excellent
  Flame retardant compounds	Excellent
  Engineering plastics	Excellent

When You Should NOT Upgrade to a Bimetallic Screw Barrel

• 1. You Mainly Process Virgin Plastics

  If your production mainly uses clean virgin materials such as:
  · Virgin PP
  · Virgin PE
  · HDPE
  · Standard plastic compounds

  a nitrided screw barrel may already meet your production requirements.

  In these applications, wear is usually caused by normal friction rather than severe abrasion.

  Upgrading to a bimetallic screw barrel may increase your initial cost without creating significant benefits.

  For many standard extrusion applications, investing in correct screw design, compression ratio, and processing parameters can improve performance more effectively than simply upgrading materials.

• 2. Your Current Screw Barrel Service Life Is Acceptable

  Many customers think:
  “Bimetallic lasts longer, so it must always be better.”

  However, longer service life only creates value when your current screw barrel cannot meet your production needs.

  If your existing nitrided screw barrel:
  · Runs continuously without problems
  · Maintains stable output
  · Produces consistent product quality
  · Has an acceptable replacement cycle

  then upgrading may not provide a good return on investment.

  A better evaluation method is:
  Cost per production hour = Screw Barrel Cost ÷ Actual Service Life

  Sometimes a high-quality nitrided screw barrel provides a better overall economic solution.

• 3. Your Materials Do Not Contain Abrasive Additives

  The main reason customers choose bimetallic screw barrels is usually severe material wear.

  Bimetallic solutions are especially valuable when processing:
  · Glass fiber reinforced plastics
  · Mineral-filled materials
  · Calcium carbonate filled PVC
  · Recycled plastics with impurities
  · Abrasive masterbatch

  These materials contain hard particles that continuously damage the screw and barrel surface during extrusion.

  However, if your materials do not contain abrasive fillers, a nitrided screw barrel may already provide sufficient wear resistance.

  
  Extruder Screw Barrel Wear Problem

• 4. Your Production Volume Is Limited

  For companies with:
  · Low production hours
  · Small output requirements
  · Frequent material changes
  · Occasional extrusion production

  the longer lifespan of a bimetallic screw barrel may not justify the additional investment.

  A nitrided screw barrel can provide a better balance between:
  · Equipment cost
  · Production requirements
  · Maintenance budget

  The best choice is not always the most expensive option.

  The best choice is the one that matches your actual working conditions.

When Should You Upgrade to a Bimetallic Screw Barrel?

Although bimetallic screw barrels are not necessary for every application, they become valuable in demanding extrusion environments.

• 1. Your Screw Barrel Wears Too Quickly

  If you experience:
  · Frequent screw replacement
  · Reduced extrusion output
  · Increased maintenance frequency
  · Unexpected production downtime

  your current screw barrel material may not be suitable for your application.

  A bimetallic solution can significantly improve wear resistance and extend service life.

• 2. Your Production Uses Abrasive Materials

  Bimetallic screw barrels are recommended for applications involving:
  · Glass-filled engineering plastics
  · Highly filled PVC
  · Recycled plastic extrusion
  · Abrasive compounds

  These materials require stronger protection against mechanical wear.

• 3. Product Quality Becomes Unstable

  A worn screw barrel can lead to:
  · Poor plasticizing performance · Uneven material flow · Output fluctuation · Product quality problems

  Upgrading the screw barrel material can help maintain more stable extrusion performance.

How to Choose Between Bimetallic and Nitrided Screw Barrel?

Instead of choosing only based on price, consider these factors:

The correct screw barrel selection depends on:
· Plastic material
· Filler content
· Extrusion temperature
· Production hours
· Required service life
· Maintenance cost

Conclusion: Choose the Right Screw Barrel, Not the Most Expensive One

A bimetallic screw barrel provides excellent wear resistance and is an ideal solution for demanding extrusion applications.

However, it is not automatically the best choice for every plastic extrusion line.

For standard materials and normal production conditions, a high-quality nitrided screw barrel can provide excellent performance and better cost efficiency.

For abrasive materials, recycled plastics, or applications with frequent wear problems, upgrading to a bimetallic screw barrel can reduce downtime and improve long-term production reliability.

The right screw barrel specification can help you reduce maintenance costs, improve production stability, and achieve better overall performance.

Need Help Choosing the Right Screw Barrel?

Not sure whether you need a bimetallic screw barrel or nitrided screw barrel?

Send us your:
· Extruder model
· Screw diameter
· Plastic material
· Production application
· Current wear problems

Our technical team can recommend a suitable screw barrel solution based on your actual extrusion conditions.

Contact us today for professional screw barrel selection support.