What is the function of twin-screw extruder barrel?
The extrusion system of the twin-screw extruder is a combined type with the screw is a building block structure, and the barrel is also a combined type (the barrel is also composed of several barrel elements). The length of each twin-screw extruder barrel is about 3- 4D, with each barrel section having a temperature measuring hole and a cooling water channel so that the temperature can be precisely controlled to avoid excessive temperature and material decomposition due to the internal friction heat of the material.
The extrusion process of the twin-screw extruder can be divided into solid-state conveying, melting, melt material conveying (mixing), venting, extrusion and other stages. Thus the twin-screw barrels can be divided into seven parts depending on extrusion processes: Feeding barrel, side feeding barrel, barrel with liquid filling port, exhaust barrel and closed barrel etc.
How to choose the suitable barrel material?
The choice of barrel material is related to the characteristics of the material to be processed and is also closely associated with the machining equipment, heat treatment process and other process equipment. In the past, the material of the barrel usually adopts the overall 38CrMoAlA material as its processing accuracy requirements are relatively low, and it is easy to process and has a high-cost performance. This material has certain corrosion resistance, but its wear resistance is very poor, so it is only suitable for some neutral materials for reactive extrusion, PVC processing, etc.
The barrel used for filling and reinforcing modified materials with greater wear and tear must use with a bimetallic barrel, which is made of a base and an alloy sleeve. Basically, adopt 45# steel and alloy so the sleeve is in contact with the material being processed. As the overall hardness is as high as HRC62, its wear resistance is greatly increased, which greatly increases the service life of the cylinder. Another advantage of using a bimetallic barrel is it can be replaced and repaired once the bushing is worn or corroded, which greatly reduces the equipment maintenance cost.
How should the barrel of a twin-screw extruder be properly used and maintained?
First of all, the buyer must truthfully inform the seller of the materials system that will be processed when buying the twin-screw extruder, whether there are glass fibres, calcium carbonate, acidic or alkaline substances in the raw materials. We can recommend suitable barrel and screw elements according to the raw materials.
For example, regarding to PVC processing, we choose 38CrMoAlA barrel that will avoid material pollution caused by PVC corrosion in the barrel. Referring to the modification of glass fibre reinforced and calcium carbonate toughened materials, we use a bimetallic barrel, with the bushing as a high-hardness alloy sleeve, the whole can improve the service life of the barrel. For the blending of acidic or alkaline materials, we must adopt stainless steel materials such as SUS316 or SUS440 or other corrosion-resistant alloy materials to avoid material pollution caused by corrosion and other problems.
The maintenance of the twin-screw barrel needs the following two aspects:
1. Wear of the barrels
The wear of the barrels that are used for the production line of strengthening, toughening and other high-filling is very serious. We require customers to regularly check the wear of the alloy sleeve of the barrels. A new alloy sleeve must be replaced, If the gap between the inner diameter of the barrel and the screw is too large, it will affect the plasticizing melting of materials.
2. The actual temperature of the barrel is higher than the set temperature
When the temperature control meter shows that the actual temperature of the barrel is higher than the set temperature, we have to check whether the temperature control meter, solid state relay, solenoid valve and other components are damaged. If not, it means that the cooling water channel of the barrel is blocked.
After the cooling water enters the cylinder, fouling may occur due to high temperature, which will cause the blockage of the cooling water channel over time. cause temperature control failure. Therefore, we recommend that customers use distilled water for barrel cooling water and replace it regularly. Refer to the barrel that has been blocked, it can be cleaned with an air pump or a weakly acidic substance. If it still doesn’t work after cleaning, please contact us.
Extruder Screw Barrel Heating and Cooling
How to heat the screw and barrel of the twin screw extruder?
Resistance heating is employed for the machine’s heating, and a thermocouple is used for temperature control. The plastic inside the barrel is heated by a resistance heater, which is also used to generate heat. Cast aluminium heaters, cast copper heaters, strip heaters, ceramic heaters, Far infrared heaters etc. are all examples of resistance heating.
The compact size, simple design, and low maintenance requirements of these heaters are all major pluses. Compared with the traditional cast aluminium, cast copper heater, the far infrared heater has the following advantages: higher heating efficiency, faster heating and lower energy consumption can save about 30% electricity.
Heating power of extruder screw barrel
To guarantee that the barrel of the twin screw extruder machine has a fast enough heating rate, it is important to consider not only the heat needed for plasticization but also the productivity needs of the twin screw machine.
Usually, the machine can only be turned on after the temperature reaches the predetermined set temperature and keeps warm for 30 minutes to 1 hour. For small test machines, the holding time must be longer than 1 hour, because its screw rod is very thin and the torque is also very small. Any illegal operation will cause the screw to be broken.
Cooling of the extruder screw barrel
Due to the working mechanism of the twin screw, the two screws completely mesh, so the materials need to absorb heat quickly after entering the barrel and melting it. The molten material will be extruded by the twin-screw, and the materials will generate internal friction heat to make the temperature of the materials increase, so the barrel needs to be cooled at this time to take away the excessive heat in the materials.
Daily maintenance method for twin screw elements of extruder
Regular upkeep is essential for the smooth operation of any twin screw extruder. After 2500-5000h of nonstop operation, the twin screw extruder is shut down for maintenance. It is necessary to remove the twin screw elements in order to inspect, measure, and appraise the wear of the most critical parts, to replace the parts that have reached the required wear limit in time, and to repair the damaged parts. The gearbox of a twin screw extruder requires the same level of upkeep as any other gearbox.
The oil level in the gearbox should be maintained at the level recommended in the machine handbook and the gearbox should be lubricated with the oil recommended for the machine. If there isn’t enough oil, the lubrication won’t be smooth, the temperature of the gearing parts will rise, and it will damage the bearing or gear parts. reducing the components’ service life.
Nanjing Granuwel Machinery CO., LTD is specializing in the R&D design and manufacture of high polymer extruders, our team of top-level extrusion professionals provides the right extruder for your exact application.
We possess excellent capability of innovation and product development, and desire to provide the best products for our customers through the improvement of equipment structure and reduction of equipment energy consumption through our practical experiences and technical innovation.
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