What is Injection screw?

The injection screw is a critical component in plastic injection molding machines. It is a helically shaped metal shaft that rotates inside a heated barrel, and its primary function is to plastify the thermoplastic material—melting and homogenizing it—and then inject it under pressure into the mold to form the final part.

Its screw-like design enables it to simultaneously perform several key tasks: conveying plastic pellets from the hopper to the compression zone, melting the material through friction and conduction, mixing additives or colorants, and finally accumulating and pushing the molten material into the mold during the injection phase.

The injection screw consists of three main sections:

1. Feed zone: where solid pellets are introduced and begin to be transported.

2. Compression zone: where the material is melted under pressure and homogenized.

3. Metering (or pumping) zone: where the molten plastic is accumulated before injection.

The screw’s design varies depending on the type of material being processed, the final product, and the specific requirements of the application. There are general-purpose screws and specialized ones—for example, for materials with high glass fiber content, technical polymers, bioplastics, or shear-sensitive additives.

The injection screw is rotated by a hydraulic or electric motor and also moves axially during the injection phase to push the molten material into the mold through the nozzle. This forward motion, known as “screw advance,” is critical for controlling injection pressure, speed, and the volume of material delivered into the mold cavity.

Proper maintenance of the injection screw is vital to ensure product quality and process efficiency. Wear on the flights, corrosion from aggressive materials, or cross-contamination between materials can lead to part defects, color variation, burnt residues, or unstable cycle times.

At Plásticos Lezo, we take great care with every aspect of the plastification system, including the condition and configuration of the injection screw, as part of our commitment to quality and precision. We constantly monitor screw performance on each machine and perform routine cleaning, inspections, and preventive replacements to ensure optimal melt homogeneity, stable cycles, and minimal scrap.

We also tailor the screw type to suit the project when needed—whether working with recycled plastics, high-viscosity materials, reinforced compounds, or parts with complex geometry. This technical flexibility allows us to take on high-demand projects and ensure consistent, repeatable results in both short and long production runs.

In summary, the injection screw is the heart of the plastification system in an injection molding machine. Its proper design, maintenance, and adjustment are fundamental to producing high-quality parts, optimizing energy use, and protecting the longevity of both the mold and the machine. At Plásticos Lezo, we understand its importance as a key element in achieving excellence in injection molding.