Injection Screw Barrel

Almet Makina Injection Screw Barrel

The screw and barrel used in plastic injection machines are the fundamental elements of the process of heating and melting the raw material and transferring it to the mold under pressure. The quality of production, efficiency, and machine life depend largely on the correct selection and use of these two parts. Therefore, the screw-barrel system is considered one of the most important parts of the injection line.

In this article, you can find simple and understandable information about the tasks, types, selection criteria, and maintenance tips of the screw barrel in the injection process.

1. What is the Duty of Screw and Barrel?

The screw and barrel manage the entire process from raw material granules to reaching the mold. Their duties can be summarized as follows:

• Material Transport: Granules are taken from the hopper and pushed forward.

• Melting and Mixing: The plastic is melted by temperature and friction, forming a homogeneous structure.

• Creating Pressure: The melted plastic is pushed towards the mold under pressure.

• Mold Filling: The material is transferred into the mold smoothly.

Incorrect choices in the screw-barrel system can lead to serious production problems such as low filling, non-homogeneous melting, surface defects, burn marks, or air bubbles.

2. What to Consider When Choosing a Screw Barrel?

The selection of the screw and barrel should be determined according to the plastic material to be used and the technical requirements of the product.

2.1 Material Strength

Different coatings and materials are preferred for different plastic types:

• Standard plastics such as PP, PE, PS, ABS: Standard nitration-coated screws are sufficient.

• Glass fiber reinforced plastics (PA GF, PBT GF): Bimetal screw and barrel are recommended.

• Materials requiring chemical resistance like PVC, POM, PET: Corrosion-resistant special coatings should be used.

2.2 Screw Diameter and L/D Ratio

• Screw diameter determines the material conveying capacity.

• L/D ratio (screw length / diameter) directly affects melting and mixing efficiency.

• While 20:1 and 25:1 ratios are sufficient in standard productions,

• values of 30:1 and above offer better performance in engineering plastics.

3. Screw Types and Applications

Different screw designs are preferred according to plastic types.

3.1 Standard General Purpose Screws

• They have a wide range of applications.

• They are used in common plastics such as PP, PE, PS, ABS.

• They are cost-effective.

Applications: Packaging, automotive parts, and general injection productions.

3.2 High-Performance Mixer Screws

• They ensure the homogeneous distribution of color additives and different granule types.

• They improve product quality.

Applications: Multi-color productions, medical and precision plastic parts.

3.3 Bimetal and Wear-Resistant Screws

• They offer high resistance against hard and abrasive raw materials.

• They are much more durable than standard screws.

Applications: Glass fiber reinforced plastics such as PA GF, PBT GF, and materials exposed to chemical effects.

4. The Importance of the Barrel and Proper Maintenance

Since the barrel is the main chamber where plastic granules are melted, surface quality and durability are extremely important.

• A worn-out barrel disrupts the flow of plastic, reducing production quality.

• This situation affects both machine performance and increases error rates.

For long-term use:

• Regular maintenance and cleaning should be done,

• If necessary, durability should be increased with special coatings,

• Bimetal coated barrels should be preferred for abrasive materials.

5. Advantages of Correct Screw-Barrel Selection

• More homogeneous plastic melting

• High surface quality and fewer production errors

• Energy efficiency and low operating costs

• More stable machine performance

• Long-lasting screw-barrel usage

A correctly selected screw barrel enhances the efficiency of the injection machine, improves production quality, and provides cost advantages to the operation.