Composition of Singe Screw Extruder

The most basic and versatile of an extruder is the single screw extruder. It mainly includes six parts: transmission, feeding device, material barrel, screw, machine head, and extrusion die head&mould.

1. Transmission part

The transmission part usually consists of an electric motor, a gearbox, and bearings. During the extrusion process, the screw speed must be stable and cannot change with changes in screw load, in order to maintain a uniform and consistent quality of the resulting product. However, in different situations, it is also required that the speed of screw can be variable to meet the requirement that an extruder can extrude different plastics or products. Therefore, AC motor, DC motor and other devices are generally used in this part to achieve stepless speed change. Generally, the screw speed is 0~250 rpm.

2. Feeding device

Generally, granular materials are used for feeding, but strip materials or powder materials can also be used. The loading equipment usually uses a conical hopper with a capacity requirement of at least one hour of usage. There is a cut-off device at the bottom of the hopper for adjusting and cutting off the material flow, and a sight hole and calibration measuring device are installed on the side of the hopper. Some hoppers may also have pressure reducing or heating devices to prevent raw materials from absorbing moisture from the air, or some barrels may also come with their own agitators that can automatically feed or charge them.

3. Barrel

Generally, it is a metal bucket made of alloy steel or composite steel pipes lined with alloy steel. Its basic characteristics are high temperature and pressure resistance, sturdy, wear-resistant, and corrosion-resistant. The length of a general material barrel is 15-30 times its diameter, and its length is based on the principle of fully heating and uniformly plasticizing the material. The material barrel should have sufficient thickness and stiffness. The interior should be smooth, but some barrels are engraved with various grooves to increase friction with the plastic. There are electric heaters, temperature control devices, and cooling systems attached to the external part of the material barrel that are heated by resistors, inductors, and other means.

4. Screw

The screw is the heart of an extruder and a key component. The performance of the screw determines the productivity, plasticizing quality, dispersion of fillers, melt temperature, power consumption, and other factors of an extruder. It is the most important component of an extruder, which can directly affect the application range and production efficiency of the extruder. The rotation of the screw produces extreme pressure on the plastic, which allows it to move, increase pressure, and obtain some heat from friction in the material barrel. During the movement of the plastic in the barrel, it is mixed and plasticized, and the viscous flow of the melt is squeezed and flows through the mold to obtain the desired shape and form. Like the barrel, the screw is also made of high-strength, heat-resistant, and corrosion-resistant alloys.

5. Extrusion die head & bush

The die head and bush are usually a whole and are commonly referred to as the machine head; But there are also cases where the die head and bush are separated. The function of the die head is to transform the plastic melt in rotational motion into parallel linear motion, further homogenizing the plastic, and allowing the melt to be evenly and smoothly introduced into the bush. It also provides necessary molding pressure, making the plastic easy to form and the resulting product dense. The bush is a channel with a certain cross-sectional shape. When plastic melt flows in the bush, it obtains the desired shape and is formed by cooling and hardening by the shaping device and cooling system outside the bush. The components of the extrusion die head and bush include filter screen, porous wrench, splitter (sometimes combined with the mandrel to form a component), mandrel, bush, and neck.

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