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Almet Machinery Injection Screw Barrel

The screw and barrel used in plastic injection machines are the key 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 largely depend on the correct selection and use of these two parts. That's why 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 duties, types, selection criteria, and maintenance tips of the screw barrel in the injection process.

1. What is the Role of the Screw and Barrel?

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

• Material Conveying: Granules are taken from the hopper and transported.

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

• Pressure Generation: 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 based on the plastic material to be used and the technical requirements of the product.

2.1 Material Strength

Different coating and materials are preferred for different types of plastics:

• Standard plastics like 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 such as 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 (length/diameter) directly affects melting and mixing efficiency.

• Ratios of 20:1 and 25:1 are sufficient for standard productions, while

• Values of 30:1 and above provide better performance in engineering plastics.

3. Screw Types and Applications

Different screw designs are preferred according to the types of plastics.

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 Mixing Screws

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

• They improve product quality.

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

3.3 Bimetal and Wear-Resistant Screws

• They offer high resistance to hard and abrasive materials.

• They have a much longer lifespan compared to 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

The barrel is crucial because it is the main section where plastic granules are melted, so surface quality and strength are extremely important.

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

• This not only affects machine performance but also increases the error rate.

For long-term use:

• Regular maintenance and cleaning should be done,

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

• For abrasive materials, bimetal-coated barrels should be preferred.

5. Advantages of the Correct Screw-Barrel Selection

• More homogeneous plastic melting

• High surface quality and less production errors

• Energy efficiency and low operating costs

• More stable machine performance

• Long-lasting screw-barrel usage

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