Twin Screw Barrel Overview

Extruder twin screw barrel normally consist of two screws and one barrel, according to the shape there are 2 types, one is conical screw barrel, another is parallel screw barrel. The tooth shape of the screw is irregular and cannot form a closed meshing line, belonging to the non sealed type. The screw is self-locking and driven by gears, without direct contact between the master and slave screws. The barrel has properties such as heat resistance, wear resistance, and corrosion resistance. The combination of the barrel and screw enables the mixing, gelatinization, and maturation of materials.

The function of the transmission system is to drive the screw and supply the torque and speed required by the screw during the extrusion process, usually composed of an electric motor, gearbox, and bearings. The axial force generated by twin-screw during extrusion is similar to or higher than that generated by single screw during extrusion. Such a large axial force should be borne by larger sized bearings. However, due to the limitation of the working arrangement of twin-screw, there are multiple bearing arrangements.

Twin Screw Barrel Characteristic

1. Compact structure. The conical rolling wheel and twin-screw gear adopt a center symmetric structure, with four studios of balanced size and layout

2. Simple structure. Due to the lack of hydraulic and electronic control units, maintenance and upkeep are relatively easy

3. Smooth transmission. Due to the rolling meshing of gears, the axial force and bending moment are small, and the transmission is stable and reliable

4. Wide applicability. The cone double flat twin screw machine barrel is suitable for various materials, especially those with high viscosity and poor fluidity

Application Field of Twin Screw Barrel

Twin screw extruder is a common plastic processing equipment widely used in the plastic processing industry and related fields. It heats and melts plastic columns through the rotation and movement of twin screws, and extrudes them into the desired shape through molds, which has the advantages of high efficiency, precision, and strong controllability.

1. Plastic products production

Twin screw extruders have a wide range of applications in the production of plastic products. It can be used to produce various plastic products such as plastic pipes, plastic sheets, plastic films, etc. Twin screw extruders can produce plastic products of different specifications and shapes by adjusting the operating parameters of the extruder, meeting market demand.

2. Plastic modification processing

Plastic modification is a method of improving the properties of plastics by adding modifiers. Twin screw extruders can mix and melt modifiers and plastic raw materials, making the modifiers evenly dispersed in the plastic and improving its performance. This modification method is applicable to many plastics, such as polymers, engineering plastics, etc., and can improve the mechanical properties, heat resistance, corrosion resistance, and other characteristics of plastics.

3. Rubber product processing

Twin screw extruders can be used for rubber processing. Rubber is a highly elastic material that typically requires heating and extrusion to form the desired shape. Twin screw extruders can efficiently melt rubber columns and extrude them into desired rubber products such as rubber tubes, rubber sheets, etc. through molds. This processing method can improve the production efficiency and quality of rubber products.

4. Food processing

Twin screw extruders also have important applications in the food processing industry. It can be used to make various shapes of food, such as noodles, cookies, candies, etc. Twin screw extruders can melt food raw materials and extrude them into the desired shape through molds, which is efficient and fast, suitable for large-scale food production.

5. Medical Industry

Twin screw extruders are also widely used in the field of medical device manufacturing. It can be used to make medical instruments such as pipes, syringes, infusion sets, etc. Twin screw extruders can produce high-quality medical devices in a high-precision and highly controllable manner, meeting the requirements of the medical industry for product quality and safety.

What Plastic Twin Screw Barrel Can Process? 

Polyethylene (PE): including high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE).

Polypropylene (PP): Suitable for polypropylene blocks, polypropylene fibers, polypropylene films, etc.

Polyvinyl chloride (PVC): including rigid PVC and soft PVC.

Polystyrene (PS): suitable for polystyrene foam, polystyrene sheet, etc.

ABS plastic: widely used in electronic product casings, toys and other fields.

Polyamide plastics, such as nylon (PA) and polyamide composite materials

Twin Screw Barrel Components

- Conical Screw

Conical twin screw is a combination of two screws used for melting and extruding plastics. The screws can rotate in the same direction or in opposite directions, with the screw edges meshing with each other but maintaining a certain distance. The outer diameter of the screw is larger for feeding and smaller for discharging. Commonly used in PVC material processing, as wear is concentrated in the discharge section, it is advisable to choose to spray weld the alloy layer on the outer diameter of the screw edge to increase wear resistance.

- Conical Barrel

The conical twin barrel is matched with a screw to provide heat and support. There are two connected apertures in the barrel for assembling the screw, and the center distance is consistent with the center distance of the screw. The conical twin barrel is also large at one end

Conical Twin Screw Barrel Specification

Twin Screw Barrel Material & Design Theory 

Twin screw extruder is a commonly used equipment for producing polymer materials. Its working principle is to melt and mix solid materials through the two rotating screws of the twin screw extruder, ultimately forming continuous plastic films, pipes or profiles.Specifically, the solid material to be processed is first fed into the hopper of the twin-screw extruder, and the screw begins to rotate, bringing the material into the barrel of the extruder. In the cylinder, while the screw rotates, it also needs to be heated or cooled according to the characteristics of the material to melt or solidify it.After a certain distance between the screws, the material begins to mix and shear, causing the bonding between the material molecules to break and recombine, thus forming a uniform mixture. During this process, pressure is continuously applied outward to squeeze the material to the outlet of the extruder.The final product shape depends on the mold of the extruder. For example, if it is a twin-screw extruder used for producing plastic film, the outlet of the extruder will be installed on a cylindrical mold, forming an infinite length of plastic film. If it is producing plastic pipes or profiles, the mold will be designed according to the required shape.

Material Use for Twin Screw Barrel

- 38CrMoAla (SACM645) Gas Nitrided

38CrMoAlA is a well-known nitrided steel with high wear resistance, high fatigue strength, and high strength characteristics. Mainly used for nitrided parts with precise dimensions after heat treatment, or various nitrided parts with high wear resistance due to low impact load. It has high wear resistance, high fatigue strength, and high strength characteristics. Mainly used for nitrided parts with precise dimensions after heat treatment, or various nitrided parts with high wear resistance and low impact load, such as screws and barrels

- Stellite Ni60 Alloy Powder

Ni60 is one alloy powder which can be processed as regular welding or PTA processing. it's of high hardness and wear resistance performance, and commonly used as screw barrel armor material

- SKD61

SKD61 is a medium carbon and high chromium alloy tool steel, which has high hardness and wear resistance after heat treatment, strong hardenability, and good dimensional stability. It is suitable for making high-precision and long-life cold working molds and thermosetting plastic molds. Can be used to make screw barrel components

- SKD11

SKD11 is a universal cold working die steel with high wear resistance and toughness, a high carbon and high chromium alloy tool steel, and a vacuum degassed refined steel. The steel is pure and has good hardenability with good hardenability and small quenching deformation. This steel has undergone spheroidization annealing and softening treatment, with good machinability and small and uniform carbide particles. There is no need to worry about the special addition of quenching cracking strengthening elements such as molybdenum and vanadium. And for high wearing situation screw barrel can have good resistance also.