Extruder parts Screw Segment barrel and liner for Plastic resin mixing, compounding and granulation with halogen-free flame retardant

For HFFR compounding, the extruder's screw elements, barrel, and liners must be constructed from highly wear-resistant materials (like bi-metallic alloys or Tungsten Carbide coatings) to withstand the extreme abrasion from mineral flame retardants. Their design also focuses on efficient mixing and gentle heat control to achieve a uniform compound while maintaining polymer integrity.

1. Screw Elements

• Function: They are the core components mounted on the screw shafts inside the barrel. Their primary role is to convey, melt, mix, and pump the plastic material.

• Key Features for HFFR:

  • Material: Typically made from wear-resistant alloys (e.g., bi-metallic). HFFR compounds often contain abrasive mineral fillers like magnesium hydroxide (MDH) or aluminum hydroxide (ATH), which cause severe wear.

  • Surface Treatment: Often coated with hard, wear-resistant coatings like Tungsten Carbide (WC) or applied with specific hardening techniques (e.g., nitriding) to significantly extend service life.

  • Design: Special mixing elements (e.g., kneading blocks, mixing pins) are crucial to ensure homogeneous dispersion of the flame retardant fillers within the polymer matrix without degrading the base resin.

2. Barrel

• Function: The barrel houses the rotating screws and forms the enclosed chamber where plasticization and mixing occur under high temperature and pressure.

• Key Features for HFFR:

  • Liner/Bushing: The inner surface of the barrel is typically lined with a removable liner or bushing. This is the part that directly contacts the material and bears the brunt of the wear.

  • Material: Like the screws, these liners are made from extremely wear-resistant materials. A common construction is a bi-metallic barrel, where the outer shell is strong steel, and the inner liner is a centrifugally cast wear-resistant alloy (e.g., Xaloy, Reiloy).

  • Cooling: Often equipped with efficient cooling channels to manage the heat generated by the high shear stresses and filler friction, preventing material degradation.

3. Liners / Bushings

• Function: These are the replaceable inner sleeves of the barrel. They protect the main barrel body from wear and can be replaced, which is more economical than replacing the entire barrel.

• Key Features for HFFR:

  • They are specifically designed to be the primary wear component.

  • Made from the hardest available materials to resist the abrasive nature of HFFR fills. Common choices include advanced bi-metallic alloys or liners with Tungsten Carbide coatings.

  • Their replaceability is a key maintenance feature for extruders processing highly abrasive materials.