In the extruder, in general, the most basic and most versatile is a single screw extruder. It mainly includes six parts: transmission, feeding device, barrel, screw, machine head and die.

Transmission section

The transmission part is usually composed of an electric motor, a reduction gear box and bearings. During the extrusion process, the screw speed must be stable and cannot change with the change of the screw load, so as to maintain the uniform quality of the obtained product. However, in different occasions, the screw can be required to be shifted to achieve the requirement that one device can extrude different plastics or different products. Therefore, this part generally uses AC commutator motor, DC motor and other devices to achieve stepless speed change, the general screw speed is 10~100 rev / min.

The function of the drive system is to drive the screw, which supplies the torque and speed required by the screw during the extrusion process, usually consisting of a motor, a reducer and a bearing. Under the premise that the structure is basically the same, the manufacturing cost of the reducer is roughly proportional to its external dimensions and weight. Because the shape and weight of the reducer are large, it means that there are many materials consumed during manufacturing, and the bearings used are also relatively large, which increases the manufacturing cost.

In the same screw diameter extruder, the high-speed and high-efficiency extruder consumes more energy than the conventional extruder, and the motor power is doubled. It is necessary to increase the frame number of the reducer. But a high screw speed means a low reduction ratio. The same size of the reducer, the low reduction ratio compared to the large reduction ratio, the gear modulus increases, the reducer's ability to withstand the load also increased.

Therefore, the increase in the volumetric weight of the reducer is not linearly proportional to the increase in motor power. If the derivation is used as the denominator, the speed of the reducer is divided, the number of high-speed and high-efficiency extruders is small, and the number of ordinary extruders is large. In terms of unit output, the motor power of the high-speed high-efficiency extruder is small and the weight of the reducer is small, which means that the unit production cost of the high-speed and high-efficiency extruder is lower than that of the ordinary extruder.

Feeding device

Most of the feedstocks are made of pellets, but strips or powders can also be used. The charging equipment usually uses a conical hopper with a volume requirement of at least one hour. There is a cut-off device at the bottom of the hopper to adjust and cut the flow, and a sight hole and a metering device are installed on the side of the hopper. Some hoppers may also have a pressure relief device or heating device that prevents the feedstock from absorbing moisture from the air, or some of the cartridges may also have their own agitator for automatic loading or feeding.

Hopper

The hopper is generally made in a symmetrical form. A window is opened on the side of the hopper to observe the material level and the feeding condition, and the bottom of the hopper has a opening and closing door to stop and adjust the feeding amount. Cover the top of the hopper to prevent dust, moisture and impurities from falling into it. When selecting the material of the hopper, it is best to use lightweight, corrosion-resistant and easy-to-machine materials, generally using aluminum and stainless steel. The volume of the hopper depends on the size of the extruder and the loading method. Generally, the extruder has an extrusion amount of 1 to 1.5 hours.

2. Feeding

There are two types of feeding methods: manual feeding and automatic feeding. The automatic feeding mainly includes spring feeding, blast feeding, vacuum feeding, conveying belt conveying and the like. In general, small extruders are manually loaded and large extruders are automatically loaded.
3. Classification of feeding methods

1 Gravity feeding:

Principle - The material enters the barrel by its own weight, including manual feeding, spring feeding, and blasting.

Features - simple structure and low cost. However, it is easy to cause uneven feeding, which affects the quality of the parts. It is only suitable for small size extruders.

2 Forced feeding:

Principle - Install a device in the hopper that applies external pressure to the material, forcing the material into the barrel of the extruder.

Features - can overcome the "bridge" phenomenon, so that the feeding is even. The feed screw is driven by the extruder screw through the drive chain to adjust its speed to the screw speed. The overload protection device can be activated when the feed port is blocked, thereby avoiding damage to the feeding device.

Cartridge

Generally, it is a metal material barrel made of alloy steel or composite steel pipe lined with alloy steel. Its basic characteristics are high temperature and pressure resistance, strong wear and corrosion resistance. Generally, the length of the barrel is 15 to 30 times its diameter, and the length is such that the material is sufficiently heated and plasticized uniformly. The barrel should have sufficient thickness and rigidity. The interior should be smooth, but some of the barrels are engraved with various grooves to increase the friction with the plastic. Electric heaters, temperature control devices and cooling systems are provided on the outside of the barrel with resistors, inductors and other means of heating.

1. There are three forms of material in the barrel:

(1) integral barrel

Processing method - processed on the whole material.

Advantages - easy to ensure high manufacturing accuracy and assembly accuracy, can simplify the assembly work, the cylinder is evenly heated, and more applications.

Disadvantages - Due to the large barrel length and high processing requirements, the requirements for processing equipment are also very strict. The inner surface of the barrel is difficult to repair after being worn.

(2) Combination material

Processing method - the barrel is processed in several stages, and then the sections are connected by flanges or other forms.

Advantages - simple processing, easy to change the aspect ratio, mostly used to change the aspect ratio of the screw.

Disadvantages - high processing precision requirements, due to many segments, it is difficult to ensure the coaxiality of each segment, the flange connection breaks the uniformity of barrel heating, increases heat loss, heating and cooling system settings and maintenance More difficult

(3) Bimetallic barrel

Processing method - Inlay or cast a layer of alloy steel material inside the base of ordinary carbon steel or cast steel. It not only meets the material requirements of the barrel, but also saves precious metal materials.

1 Bushing cartridge: The cartridge is fitted with a replaceable alloy steel bushing. Save precious metal, the bushing can be replaced, increasing the life of the barrel. But its design, manufacturing and assembly are more complicated.

2 Casting barrel: A layer of approximately 2 mm thick alloy is centrifugally cast on the inner wall of the barrel, and then the required inner diameter of the barrel is obtained by grinding. The alloy layer is well bonded to the base of the barrel, and the bonding along the axial length of the barrel is relatively uniform, has no tendency to peel off, does not crack, has excellent sliding performance, and has high wear resistance. long life.

(4) IKV barrel

1) The longitudinal groove of the inner wall of the barrel feeding section is opened

In order to increase the solids transport rate, one method is to increase the coefficient of friction of the surface of the cylinder by solid transport theory. Another method is to increase the area of ​​the material at the feed port through the cross section perpendicular to the screw axis. The formation of a longitudinal groove in the inner wall of the barrel feeding section and the taper of the inner wall of the section of the feeding section near the feeding port are the embodiments of the two methods.

2) Forced cooling feed section barrel

There is also a method to increase the amount of solids transported. It is to cool the feeding section barrel, the purpose is to keep the temperature of the material to be conveyed below the softening point or melting point, to avoid the appearance of the melt film to maintain the solid friction property of the material.

With the above method, the conveying efficiency is increased from 0.3 to 0.6, and the amount of extrusion is less sensitive to changes in head pressure.

Dongguan Pinyang Cable Machinery Co., Ltd. is a professional manufacturer of wire and cable equipment for professional development, design and production. It specializes in: optical fiber extruder, ultra-fine winding machine, earphone wire special machinery and other products, optical fiber extruder, very fine winding Machine, earphone line dedicated mechanical consultation hotline: 13731224526 / Lu Jianjun