Types and characteristics of screw barrels for extruders

The screw and barrel of an extruder are the core components of a plastic extruder, and their design and materials have a significant impact on the quality and output of extruded products. Below are several common types and characteristics of extruder screw barrels.

1. Gradient screw barrel
The gradient screw barrel starts from the feeding section, and the depth of the screw groove gradually decreases until it reaches the head of the screw. This type of screw is mainly used for soft and hard polyvinyl chloride, polyolefin, etc.

2. Measurement type screw barrel
The metering screw barrel has a measuring section of 4-60 equally spaced and deep, and the pressure and material flow rate at the screw head are relatively stable. Therefore, the extruded products have good quality and are widely used in polyvinyl chloride, polyolefin, and engineering plastics. The feeding section of this type of screw is equidistant and of equal depth, while the depth of the screw groove in the compression section gradually decreases.

3. Mutant screw barrel
The mutated compression segment is very short, only 1-2D. The feeding section and measuring section are both equally spaced and of equal depth, and the measuring section is relatively long. This screw is designed for crystalline plastics such as polyphenylamine and polypropylene. Enlarge the mutation zone to around 5D, which is suitable for processing plastics with a wide range of melting temperatures.

4. Torpedo head screw barrel
The torpedo head screw barrel is equipped with a torpedo head at the front end of the measuring section. This type of screw has a high shear force and good plasticizing effect, suitable for granulation and molding of polystyrene, polyethylene, phthalamide, methyl methacrylate, and polyvinylidene diazoxide. Due to the high frictional heat in the torpedo head, a cooling device should be installed.

5. Multi screw extruder
A multi screw extruder usually refers to an extruder with three or more screws in the barrel. The screw can be configured in a straight or V-shape. There is also a planetary multi screw extruder with an active screw and a driven screw.

6. Twin screw extruder
Twin screw extruders are the same as multi screw extruders, so compared to single screw extruders, twin screw extruders are sometimes referred to as multi screw extruders. Twin screw extruders allow for a certain degree of relative motion between the screws in their structure, allowing for better mixing and plasticization of materials during the extrusion process. In addition, twin-screw extruders can also be used to process high viscosity and heat sensitive materials, with unique advantages.