The Relationship Between Screw and Barrel and Injection Molding

The screw and barrel are absolutely essential components in the injection molding process. Their relationship is inseparable, and they influence each other significantly.

1. Functions of the Screw and Barrel

Screw: The screw rotates within the barrel, responsible for conveying, melting, mixing, and metering the plastic material.
Barrel: The barrel encloses the screw, providing the space for the plastic to melt and mix. It also withstands the high pressures generated during the injection molding process.

2. The Screw and Barrel's Role in Injection Molding

Plasticization: The rotation of the screw and the heating of the barrel work together to plasticize the plastic. Inside the barrel, the plastic is heated and melted, then mixed by the screw to form a uniform molten plastic.
Injection: The screw moves forward within the barrel, injecting the molten plastic into the mold cavity. The screw's movement controls the injection speed and pressure.
Holding Pressure: After injection, the screw maintains a certain pressure to prevent the molten plastic from flowing back. This ensures the product's density and dimensional accuracy.
Cooling: The molten plastic within the mold cools and solidifies, forming the final product.
Ejection: The product is removed from the mold, completing one injection molding cycle.

3. The Screw and Barrel Structure and Injection Molding Parameters

Screw Structure: Screws are typically divided into three sections: the feed section, the compression section, and the metering section.
Feed Section: Receives and conveys the solid plastic material.
Compression Section: The crucial area where the material is compressed and plasticized.
Metering Section: Quantifies and homogenizes the plasticized material.
The screw's design directly affects the plasticization quality and injection volume. For example, changes in the screw channel depth and helix angle will affect plasticization performance and injection pressure.
Barrel Design: The barrel provides an enclosed environment for heating and plasticizing the material, supporting and guiding the screw. The barrel's length, diameter, smoothness of the inner wall, and dimensional accuracy all impact the flow and plasticization of the plastic within the barrel.
In the injection molding process, it's essential to select the appropriate screw and barrel structure and parameters based on the type of plastic, product requirements, and specifications of the injection molding machine. For example, when processing heat-sensitive plastics, a special screw design is needed to reduce thermal degradation. For high-viscosity plastics, greater plasticization capacity and injection pressure are required.

4. How Screw and Barrel Performance Affects Injection Molding

Plasticization Quality: The screw's design and barrel's temperature control directly influence the quality of plasticization. Good plasticization ensures the product has uniform color, good mechanical properties, and surface quality.
Injection Accuracy: The screw's metering accuracy and injection speed control affect the product's dimensional accuracy and weight consistency.
Production Efficiency: The screw's rotation speed and the barrel's heating efficiency impact the injection molding cycle time.

5. Selecting the Right Screw and Barrel

Choosing the right screw and barrel requires considering the following factors:

Type of Plastic: Different plastics have different melting temperatures and flow properties, requiring screws and barrels that match.
Product Size and Shape: The product's size and shape influence the screw's diameter and length.
Production Efficiency: High-volume production requires high-efficiency screws and barrels.
6. Screw and Barrel Maintenance

To ensure the long-term stable operation of the screw and barrel in the injection molding process, regular maintenance is necessary. This includes cleaning the screw and barrel, inspecting for wear, replacing worn parts, and adjusting process parameters. Through proper maintenance, you can extend the lifespan of the screw and barrel and improve the stability and reliability of the injection molding process.