Extrusion Line

The complete set of equipment used in the extrusion process, from raw material handling to the final product.

Extruder

The machine that melts and pumps the plastic. It consists of a barrel, screw, and drive motor.

Hopper

The container that holds and feeds the plastic resin (usually in pellet form) into the extruder barrel.

Barrel

The heated, hardened steel cylinder that houses the extruder screw.

Die

The precision-machined tool mounted at the end of the extruder that shapes the molten plastic into the desired profile.

Screen Pack / Filter Pack

A stack of metal wire meshes placed between the screw and the die to filter out contaminants and create backpressure.

Breaker Plate

A thick, perforated metal plate that supports the screen pack.

Downstream Equipment

All equipment that handles the product after it exits the die. This includes cooling, sizing, pulling, and cutting units.

Upstream Equipment

Equipment that handles material before the extruder, such as dryers, blenders, and feeders.

Screw

The rotating shaft inside the barrel that conveys, melts, and pumps the plastic. Its design is critical to the process.

Flight

The helical ridge on the screw.

Root

The central shaft of the screw. The root diameter often changes along the screw's length.

Channel

The space between the flights.

Channel Depth

The distance from the root to the top of the flight. Changes in depth define the screw zones.

Feed Zone (Solid Conveying Zone)

The first section of the screw. Its deep flights convey solid pellets forward from the hopper.

Compression Zone (Transition Zone)

The middle section where the channel depth decreases. This compresses the material, which, combined with heat, melts the plastic.

Metering Zone (Melt Pumping Zone)

The final section with a shallow, constant channel depth. It generates pressure to pump the homogenized melt through the die at a consistent rate.

Length-to-Diameter Ratio (L/D Ratio)

The ratio of the screw's flighted length to its diameter (e.g., 24:1). A higher L/D ratio allows for better melting and mixing.

Compression Ratio

The ratio of the channel volume in the feed zone to the channel volume in the metering zone. It indicates the screw's melting capability.

Mixing Section

A specialized section on the screw (e.g., Maddock mixer, pineapple mixer) designed to homogenize the melt temperature and composition.

Vented Barrel (Two-Stage Screw)

A barrel with a vent port to remove moisture or volatiles. Requires a special two-stage screw with a decompression zone under the vent.

Die

The tool that shapes the extrudate.

Die Body / Die Holder

The main block of the die assembly.

Mandrel (Spider Mandrel, Torpedo)

A central pin used in dies for hollow profiles (like pipes) to form the inner surface.

Die Land

The final, parallel section of the die channel where the melt is stabilized before exiting. The length of the die land is critical for controlling surface finish and dimensions.

Adapter (Crosshead)

A section that connects the extruder barrel to the die, often used to change the flow direction (e.g., in wire coating).

Die Swell (Extrudate Swell)

The phenomenon where the extrudate expands as it exits the die due to the relaxation of polymer molecules. Die design must compensate for this.

Spider Legs

The arms that hold a mandrel in place inside a die. They leave witness lines (spider lines) on the extrudate where the plastic flows around them.

Coathanger Die / Manifold

The internal channel design in a flat sheet or film die that distributes the melt evenly across the width of the die.

Throughput (Output Rate)

The mass of material extruded per unit of time (e.g., kg/hour, lbs/hour).

Screw Speed (RPM)

The rotational speed of the extruder screw. A primary control for throughput.

Melt Temperature (T melt)

The actual temperature of the molten plastic as it exits the die.

Melt Pressure

The pressure of the molten plastic, typically measured just before the screen pack or die. High pressure can indicate a blockage.

Barrel Temperature Zones

The barrel is divided into multiple heating/cooling zones (e.g., rear, middle, front, adapter) to precisely control the melting profile.

Backpressure

The resistance to flow. Created by the screen pack, breaker plate, and die. Essential for proper melting and mixing.

Residence Time

The amount of time the plastic spends inside the extruder.

Parison

The tubular extrudate used in extrusion blow molding to make bottles.

Sizing (Calibration)

The process of setting the final dimensions of the still-molten extrudate. Often done with a vacuum sizer or sizing sleeve that uses vacuum and cooling water.

Cooling Tank / Water Bath

A long tank filled with water that cools the extruded product.

Haul-Off (Puller)

A device (often with caterpillar tracks) that grips the cooled product and pulls it at a constant speed, stabilizing the line.

Cutter (Saw, Guillotine Cutter)

Cuts the continuous extrudate to the desired length.

Winder / Coiler

A machine that winds flexible extrudates (like film, sheet, or tubing) onto rolls.

On-The-Fly Perforation / Punching

Downstream units that add holes or cutouts to the profile while it is moving.

Profile Extrusion

The extrusion of any continuous shape with a constant cross-section (e.g., window frames, deck railings).

Tube/Pipe Extrusion

Extrusion of hollow, cylindrical profiles.

Sheet Extrusion

Production of wide, flat sheets using a flat die and a set of cooling rolls (calendar stack).

Blown Film Extrusion

A process where a tube of plastic is extruded upward and inflated like a balloon, then collapsed to form a double layer of film.

Cast Film Extrusion

A process where the melt is extruded through a flat die directly onto a chilled roll to produce film.

Coextrusion

The process of extruding two or more different materials simultaneously through a single die to create a multi-layer product.

Extrusion Coating

The process of extruding a thin film of molten plastic onto a substrate like paper, foil, or fabric.

Surging

An unstable, cyclical variation in output, leading to inconsistent dimensions. Often caused by poor screw design or feeding problems.

Die Lines

Visible lines running in the machine direction on the extrudate, caused by a scratch in the die or contamination.

Melt Fracture

A surface defect where the extrudate appears rough or wavy, caused by excessive shear stress at the die entrance.

Degradation

The breakdown of the polymer due to excessive heat or shear, leading to discoloration, black specs, and loss of properties.

Shark Skin

A surface defect characterized by a matte, rough finish, often occurring at high output rates.