Extruder Screws and Barrels

We measure screws in our Warehouse. If you need exact measurements, let us know!

Screws and barrels are the backbone of plastics processing, enabling efficient and consistent extrusion. Understanding their types and features is essential for optimizing performance in various applications. Below, we outline the key features, and the main types of screws used in extrusion to help you make informed decisions for your processing needs.

Screws play a pivotal role in melting, mixing, and transporting plastic within the barrel. A standard screw will have Three Zone Design.

·  Feed Zone: Maintains a constant depth to feed plastic particles into the extrusion system.

·  Compression Zone: Gradually reduces depth to build pressure and eliminate air pockets.

·  Metering Zone: A consistent, shallow depth optimizes the melt and readies it for extrusion.

Key Terminology

Length-to-Diameter Ratio (L/D): Refers to the ratio of the screw's length to its outer diameter. It's calculated by dividing the screw's flighted length by its nominal diameter.  Commonly around 24:1, though other variations like 30:1 exist, depending on application requirements.

Compression Ratio: Refers to the ratio between the channel depth in the feed zone of the screw and the channel depth in the metering zone. Typical ranges are from 2 to 4, ensuring efficient material processing and pressure building.

Flight Width: Flights are the helical, raised ridge on a screw that moves the plastic material along within the screw's barrel. Approximately 10% of the barrel diameter, striking a balance between durability and melt flow.

Common enhancements will include nitriding and alloy caps to resist wear and corrosion.

Some screws will have Maddock Sections to incorporate flutes for enhanced mixing and thermal uniformity. Certain screws are bored with central passages for water or oil cooling to optimize specific material processing.

There are several types of screws as well, standard screws are designed for general-purpose extrusion across a range of materials. These types of screws have a simplistic structure with the typical three-zone configuration.

Barrier Screws are Ideal for materials requiring highly efficient melting and mixing. Suitable for thermoplastics and applications where precise temperature control is crucial. These types of screws feature parallel channels for melt and solid pellets. This ensures unmelted pellets are gradually converted to melt, boosting energy efficiency.

Vented Screws are used in two-stage extrusion systems, particularly effective where removal of moisture, air, or volatile compounds is necessary. These screws Incorporate a vent zone to release gases after the material reaches a complete melt stage. This is typically found in long screws (e.g., 70% vent length) to accommodate complex processing needs.

Double-Flighted Screws are useful for high-temperature needs, such as extrusion coating. They Provide two parallel paths in specific sections to improve melt uniformity and heat transfer.

Pro Tip: When choosing the correct screw and barrel for your extrusion system assess material properties and processing needs. Analyze application-specific requirements (e.g., venting or intensive mixing). Maintenance is equally critical. Regular inspections of the screw flights, barrel clearance, and wear-resistant coatings can prolong equipment lifespan and ensure consistent performance. 

There are several types of barrels that are generally classified based on their manufacturing process. They are typically made from high-quality, heat-treated steel alloys. They house the rotating screw inside for the plastic extrusion process.

Whether it’s standard screws for versatile applications or advanced designs like barrier and vented screws, selecting the right extrusion components is key. While rarer, we do on occasion carry barrels as well. For more guidance or inquiries about your specific needs, contact us today to find the perfect solution for your plastics processing operations. We measure and inspect all our screws here in-house at Arlington Plastics Machinery. We keep several screws in stock at any given time so give us a call today if you have any questions or are looking for a screw to get your operations back up and running!