Types of Injection Molding Machine Screws

The screw of the injection molding machine is a key component in the injection molding machine, responsible for melting the plastic particles and pushing them into the mold. According to different classification standards, the screw of the injection molding machine can be divided into many types.

1. Classification by plastic adaptability

General screw: also known as conventional screw, can process most thermoplastics with low and medium viscosity, including crystalline and non-crystalline civil plastics and engineering plastics. This is the basic form of screw, suitable for the processing of a variety of plastics.

Adaptability: The general screw has strong adaptability and can process a variety of plastics, including low and medium viscosity thermoplastics and crystalline and non-crystalline civil plastics and engineering plastics.

Design features: The length of its compression section is between the gradual type and the sudden type, about 4~5 pitches, and the processing requirements of different plastic products can be met by adjusting the process parameters.

Advantages: It avoids the need to frequently replace the screw and improves production efficiency. However, compared with the special screw, its plasticizing efficiency and energy consumption may be slightly inferior.

Special screw: used to process plastics that are difficult to process with ordinary screws, such as thermosetting plastics, polyvinyl chloride (PVC), high-viscosity polymethyl methacrylate (PMMA), etc. Special screws are different in design and material to meet the processing requirements of specific plastics.

2. Classification by screw structure and its geometric shape

Conventional screw: also known as three-stage screw, is the basic form of screw. It usually consists of a feeding section, a compression section and a homogenizing section, and is suitable for the processing of a variety of plastics.

New screw: various forms, including separation screw, diversion screw, corrugated screw, horizontal screw, non-metering section screw, two-stage exhaust screw, strong mixing screw, etc. These new screws have structural innovations to improve plasticization quality, reduce energy consumption or meet special processing needs.

3. Classification by other specific characteristics

Gradual screw: The groove depth gradually transitions from the feeding section to the homogenizing section, which is suitable for processing non-crystalline plastics with a wide softening temperature range and high viscosity, such as polyvinyl chloride (PVC).

Compression section characteristics: The compression section is relatively long, accounting for a large proportion of the total length of the screw (such as 50%), making the energy conversion process during plasticization relatively gentle.

Plasticizing effect: Due to the long compression section, the material stays in the screw for a long time, which is conducive to the preheating and plasticization of the material, especially suitable for plastics with poor thermal stability, such as PVC.

Applicable plastics: It is mostly used to process non-crystalline plastics with a wide softening temperature range and high viscosity.

Sudden change screw: The groove depth changes from deep to shallow within a short axial distance, mainly used for processing crystalline plastics with obvious viscosity and melting point, such as polyethylene (PE) and polypropylene (PP).

Compression section characteristics: The compression section is relatively short, accounting for a small proportion of the total length of the screw (such as about 5% to 15%), and the energy conversion process during plasticization is more intense.

Plasticizing effect: The shorter compression section makes the material stay in the screw for a shorter time, but the plasticizing efficiency is high and the shearing effect is strong, which is suitable for plastics that need to be plasticized quickly.

Applicable plastics: Mostly used for processing crystalline plastics with sudden melting points and low viscosity, such as polyolefins, PA, etc.

Mixing screw: It has strong mixing ability and is suitable for plastic processing that requires high mixing effect.

Exhaust screw: There are exhaust holes or exhaust grooves on the screw to remove the gas generated by the plastic during the melting process and improve the quality of the product.

Barrier type, pin type, DIS opening and diversion type, etc.: These screw types have specific structures and functions, such as barrier type screws are used to prevent plastic backflow, and pin type screws are used to enhance mixing effects.

4. Other classification methods

In addition to the above classification methods, injection molding machine screws can also be classified according to the number of screw heads (single head or variable head), screw material (such as high alloy steel, double alloy, etc.) and special uses (such as marble-specific screws).