Extruder feeding device

Most of the feed materials are granular materials, but ribbon materials or powder materials can also be used. The loading equipment usually uses a conical hopper with a capacity that can provide at least one hour's supply. There is a cut-off device at the bottom of the hopper to adjust and cut off the material flow, and a viewing hole and a calibration and measurement device are installed on the side of the hopper. Some hoppers may also be equipped with a pressure reducing device or heating device to prevent the raw materials from absorbing moisture from the air, or some barrels may also have a stirrer that can automatically feed or add materials.
1. Hopper
Hoppers are generally made in a symmetrical form. There is a window on the side of the hopper to observe the material level and feeding situation. There is an opening and closing door at the bottom of the hopper to stop and adjust the feeding amount. Add a cover above the hopper to prevent dust, moisture and impurities from falling in. When selecting hopper materials, it is best to use materials that are light, corrosion-resistant and easy to process. Aluminum plates and stainless steel plates are generally used. The volume of the hopper depends on the size of the extruder and the feeding method. Generally, it is the extrusion amount of the extruder in 1 to 1.5 hours.
2. Loading materials
There are two feeding methods: manual feeding and automatic feeding. Automatic feeding mainly includes spring feeding, air blast feeding, vacuum feeding, conveyor belt feeding, etc. Generally, small extruders use manual loading, and large extruders use automatic loading.
3. Classification of feeding methods
① Gravity feeding:
Principle - Materials enter the barrel by their own weight, including manual feeding, spring feeding, and blast feeding.
Features - simple structure and low cost. However, it is easy to cause uneven feeding, thus affecting the quality of the parts. It is only suitable for small size extruders.
② Mandatory feeding:
Principle - Install a device in the hopper that can exert external pressure on the material to force the material into the extruder barrel.
Features: It can overcome the "bridging" phenomenon and make the feeding even. The feeding screw is driven by the extruder screw through the transmission chain, so that its rotational speed adapts to the screw rotational speed. The overload protection device can be activated when the feeding port is blocked, thereby avoiding damage to the feeding device.
barrel
It is generally a metal barrel, made of alloy steel or a composite steel pipe lined with alloy steel. Its basic characteristics are high temperature and pressure resistance, strong wear resistance and corrosion resistance. Generally, the length of the barrel is 15 to 30 times its diameter, and its length is based on the principle that the material can be fully heated and plasticized evenly. The barrel should have sufficient thickness and stiffness. The inside should be smooth, but some barrels are carved with various grooves to increase friction with the plastic. The outside of the barrel is equipped with electric heaters, temperature automatic control devices and cooling systems that are heated by resistance, inductance and other methods.
1. There are three structural forms of barrels:
(1) Integral barrel
Processing method - processed on the whole material.
Advantages - It is easy to ensure high manufacturing accuracy and assembly accuracy, it can simplify assembly work, the barrel is heated evenly, and it has many applications.
Disadvantages - Due to the large length of the barrel, the processing requirements are high, and the requirements for processing equipment are also very strict. It is difficult to repair the inner surface of the barrel after it is worn.
(2) Combination materials
Processing method - process the barrel into several sections, and then connect the sections with flanges or other forms.
Advantages - simple processing, easy to change the aspect ratio, mostly used in situations where the screw aspect ratio needs to be changed.
Disadvantages: The requirements for machining accuracy are very high. Due to the large number of segments, it is difficult to ensure the coaxiality of each segment. The flange connection destroys the uniformity of barrel heating and increases heat loss. The setting and maintenance of the heating and cooling system are also complicated. more difficult
(3) Bimetal barrel
Processing method - Inlay or cast a layer of alloy steel material inside the matrix of general carbon steel or cast steel. It can not only meet the material requirements of the barrel, but also save precious metal materials.
① Bushing barrel: The barrel is equipped with a replaceable alloy steel bushing. Precious metals are saved, the bushing is replaceable, and the service life of the barrel is improved. However, its design, manufacturing and assembly are more complex.
② Casting barrel: A layer of alloy about 2mm thick 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 combined with the matrix of the barrel, and the bonding is relatively uniform along the axial length of the barrel. It has no tendency to peel off and will not crack. It also has sliding properties, high wear resistance and long service life.
(4) IKV barrel
1. A longitudinal groove is provided on the inner wall of the feeding section of the barrel.
In order to improve the solid conveying rate, according to the solid conveying theory, one method is to increase the friction coefficient of the barrel surface, and another method is to increase the area of the cross-section perpendicular to the screw axis that the material at the feeding port passes through. Setting up a longitudinal groove on the inner wall of the feeding section of the barrel and making a section of the inner wall of the barrel close to the feeding port of the feeding section into a tapered shape are the embodiments of these two methods.
2 Forced cooling feeding section barrel
In order to increase the solid transport capacity, there is another method. It is to cool the barrel of the feeding section. The purpose is to keep the temperature of the transported material below the softening point or melting point, avoid the appearance of melt film, and maintain the solid friction properties of the material.
After adopting the above method, the conveying efficiency is increased from 0.3 to 0.6, and the extrusion volume is less sensitive to changes in die pressure.