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How to reduce the energy consumption of the extruder, start with the screw combination!

In modified production, electricity consumption is a very large cost, so the current extruder is gradually developing towards energy-saving type. In a co-rotating twin-screw extruder, the extrusion system is the core part, and the consumption of electrical energy also occurs here.

Reducing energy consumption and saving costs is the collective expectation of modified enterprises, and we will take a look at how to reduce the energy consumption of the extrusion system through the selection of screw combinations.

After reading it, you know, what is the most power-consuming component of the twin screw extruder? Which segment has the greatest impact on energy consumption during extrusion?

Energy consumption analysis of twin screw extruders

The energy consumption of twin screw extruder is different from that of single screw extruder, due to the complex mechanical structure and mechanical properties of twin screw extruder, the study of energy consumption is also complex and changeable, and it is necessary to study all aspects affecting the energy consumption of twin screw extruder.

Ordinary twin screw extruder is usually composed of feeding system, metering batching system, extruder host, barrel heating and cooling system, granulation system, etc. According to research, the main motor is the largest part of power consumption, accounting for more than half of the total power, so to study the energy consumption of twin screw extruder, the key is to study the factors affecting the energy consumption of the main motor.

No.Equipment NameEquipment numberPower/kw
1.Twin screw feeder11.5kw
2.Extruder motor190kw
3.Gearbox lubrication system10.55kw
4.Vacuum forced exhaust system11.5kw
5.Soft water circulation system10.55kw
6.Barrel heater13 zones40kw
7.Hydraulic screen changer11.5kw
8.Air knife11.5kw
9.Pelletizer14 kw

CHT-65B TWIN SCREW EXTRUSION MASTERBATCH PRODUCTION LINE EQUIPEMENTS POWER ANALYSIS

In general, the selection of high-efficiency and low-consumption motors is the key to reducing energy consumption, and domestic extruders generally use German high-efficiency energy-saving motors. In the process of barrel heating, the temperature difference between the surface and the inner wall of the barrel will occur too large, in order to improve the heating efficiency, most of the means of electromagnetic heating are now used to improve efficiency and reduce energy consumption.

So what other factors in production affect the energy consumption of the main motor?

The motor mainly provides the driving speed, drives the screw and other parts to rotate, and the screw, barrel and head extrude the material. Therefore, the factors affecting the energy consumption of the motor are mainly as follows: screw combination, screw speed, extrusion amount, screw diameter, head pressure, etc.

Of course, different materials must produce different energy consumption, such as the shear force required to add glass fiber and not add glass fiber. Because this factor is too complex, we will not focus on it this time.

We will study several aspects such as screw speed and extrusion volume, screw diameter, screw combination, etc. under the same production situation, so as to come up with feasible solutions to reduce energy consumption.

1. Extrusion capacity

When the extrusion amount increases, the energy consumption per unit decreases first and then increases. Because the mechanical loss during the extruder operation is the lowest at the optimal extrusion amount, the energy waste is relatively small. After that, as the extrusion volume continues to increase, the energy consumption per unit will increase slightly.

Therefore, when using twin screw extruder mixing or plastic modification, long-term production below the optimal operating capacity should be avoided, and reasonable use of extruder can reduce energy consumption.

2. The combined effect of screw speed and extrusion amount

In actual production, the extrusion amount and screw speed work together. While keeping the speed of the screw unchanged, the output is increased, and the energy consumption per unit will gradually decrease slightly. When the output remains unchanged, with the increase of screw speed, the energy consumption per unit decreases.

3. Screw diameter

As the diameter of the screw gradually increases, the yield energy consumption will gradually become smaller, which indicates that the diameter of the screw has a certain influence on the yield energy consumption.

Now the extruder is gradually developing to large-scale, but if the output of mass production is relatively small, a smaller extruder should be appropriately selected, so that not only low energy consumption, but also the screw, barrel and other components of the large extruder will not cause excessive wear and damage due to the output does not reach the range of its best ability.

Design of screw combination

When ultrafine calcium carbonate powder with a mass fraction of 30% is used to fill PP, the screw speed is constant at 300r/min, the feed volume is 130kg/h, and the temperature is set to 190°C in the first section and 220°C in the 2nd-10th section, the following conclusions can be drawn.

1. Effect of kneading disc thickness

According to the thickness of the 45° kneading disc (30, 40, 50mm), three screw combinations are set, numbered 1#, 2#, 3# in turn.

Effect of kneading disc thickness 1
Effect of kneading disc thickness 2

The tensile strength of calcium carbonate PP specimen under 1#~3# screw combination and the yield energy consumption of extruder.

The tensile strength of calcium carbonate PP specimen under 1#~3# screw combination and the yield energy consumption of extruder.

It can be seen that as the thickness of the kneading disc increases, the tensile strength of the specimen decreases sequentially and the energy consumption of the co-directional twin screw extruder increases sequentially. This is because with the increase of the thickness of the kneading disc, the dispersed mixing components per unit mixing length increase, and the distributed mixing components decrease, that is, the filling effect of calcium carbonate powder in PP is weakened, resulting in a decrease in mechanical properties.

At the same time, when the thickness of the kneading disc increases, the energy consumption of the extruder under the screw combination increases significantly, and the torque required by the screw increases.

It can also be seen from Figure 1 that when the thickness of the 45° kneading disc is 30mm and 40mm, the tensile strength of the specimen and the energy consumption of the extruder are not much different, so the thickness of the 45° kneading disc can be selected 30mm or 40mm.

2. The influence of the wrong angle of the kneading disc of the plasticizing section

On the basis of the 2# screw combination, a set of kneading discs with different misalignment angles is added before the 45° kneading disc of the plasticization section, and according to the wrong angle of the kneading disc of different plasticizing section (30°, 45°, 90°), 3 screw combinations are set, numbered 4#, 5#, 6# in turn.

The influence of the wrong angle of the kneading disc of the plasticizing section 1
The influence of the wrong angle of the kneading disc of the plasticizing section 2

The tensile strength of calcium carbonate PP specimen under 4#~6# screw combination and the yield energy consumption of extruder.

It can be seen from this that changing the wrong angle of the kneading disc of the plasticizing section, the mechanical properties of the specimen under the 5# screw combination are the highest, 4# is slightly lower, and 6# is the worst; The energy consumption per unit yield of the extruder increases sequentially with the increase of the angle of the kneading disc in the plasticizing section, among which the energy consumption of the 4# and 5# screw combination is not much different, but the energy consumption of the 6# screw combination increases significantly.

This is because when the material enters the plasticizing section from the feeding section, it has not yet melted, because the kneading block of the 6# screw combination has a wrong angle of 90°, the shear force is too large, the leakage is too large, the screw conveying capacity is reduced, the local residence time is increased, the material filling of the screw conveying part is too high, resulting in poor material mixing effect, increased energy consumption, and rough surface of the extruded.

When the malalignment angle of the kneading disc of the plasticizing section is 30° and 45°, the tensile strength of the specimen and the energy consumption of the extruder are not much different, so the misalignment angle of the kneading disc of the plasticizing section can be selected by 30° or 45°.

3. Influence of rotor threaded element position on energy consumption

To further enhance the mixing effect, a set of kneading discs can be replaced with rotor-like threaded elements.

screw combination

It differs from conventional high-helix threaded elements in that it creates a large gap between the threaded element and the inner wall of the barrel, its screw edge top is narrower, and the contours of the threaded guide and trailing edges are different. Its helix consists of 2 segments, 1 left-handed and 1 right-handed. The element is installed on both screws, and the spiral direction of the parts meshing with each other is the same. When this element rotates, the material is “squeezed before and after pressing” to achieve the purpose of enhancing the mixing effect.

Depending on the rotor type threaded element position, two screw combinations are used, numbered 7# and 8#, as shown in Table 4.

NO.Screw combinationScrew total lengthMaterials status
Feeding sectionPlasticizing sectionMixing sectionExtrusion section
7#24/24,48/48×636 /36×324 / 24 x345°/5/40×248 /48×2,36 / 36 x224/24×245°/5/40×2,48 /48 x236 /36×2,24 /24 x2,160 /40,160/40Left48/48×636/36×336/18,24 /24×51698The extrusion is normal, and the surface is smooth
8#24/24,48/48×636 /36×324 / 24 x345°/5/40×248 /48×2,36 / 36 x224/24×2160/40,160 /40 Left48/48×236/36×224 /24 x2,45°/5/40×248/48×636/36×336/18,24 /24×51698Extrusion is normal, the surface is rough

7# and 8# screw combination and its material extrusion status

Influence of rotor threaded element position on energy consumption 1
Influence of rotor threaded element position on energy consumption 2

The tensile strength of calcium carbonate PP specimen under 7#~8# screw combination and the yield energy consumption of extruder.

As can be seen from the above figure, the tensile strength of the specimen under the 7# combination is higher than that of 8#, and the energy consumption of the extruder is lower than that of 8#

This is because the rotor element of the 8# combination is placed behind the first group kneading disk, and the material is not completely melted, and the shear and reflow at this time are of little significance to its dispersion and distribution mixing, and it is easy to cause increased energy consumption. The rotor element of the 7# ore combination is arranged behind the kneading disc of the second group, and the material has been completely melted, so the mixing effect and energy consumption are better.

4. The effect of the continuous arrangement of multiple sets of kneading disks

The screw combination of some foreign extruder manufacturers is a continuous arrangement of multiple groups of kneading discs, and the extruded materials have good performance. This combination differs from the previous 8 combinations in that all the conveying elements between the three groups of 45° kneading discs are replaced with kneading disc elements, forming a combination of multiple groups of kneading discs arranged continuously.

Screw combinationScrew total lengthMaterials statusTensile strength /MPaEnergy consumption per unit production /Kw.h.kg-1
Feeding sectionPlasticizing and mixing sectionExtrusion section
24/24,48/48×636 /36×324 / 24 x345°/5/40×290°/5/40,45°/5/54,30°/7/55,45°/5/40,90/5/40×230°/7/5548/48×636/36×336/18,24 /24×41698The  surface is rough,there is foaming27.93 0.307

The combination form of continuous arrangement of multiple kneading discs and their material extrusion status, specimen tensile strength and extruder yield energy consumption.

Compared with the above eight combinations, after replacing all the conveying elements of the plasticizing and mixing sections with multiple sets of kneading discs with strong shear force, the energy consumption does not increase significantly, and the tensile strength of the specimen does not decrease significantly. This screw combination is therefore suitable for practical production applications and can be used in extrusion production where high shear materials are required.

  1. The thickness of the 45° kneading disc is selected as 30mm or 40mm, which can effectively reduce the energy consumption of the extruder under the condition of maintaining the high tensile strength of the sample.
  2. The wrong angle of the kneading disc of the plasticizing section is preferably 30° or 45°. 
  3. In the case of rotor elements, the position of the rotor elements has a great influence on the tensile performance of the specimen and the energy consumption of the extruder, and it should be placed after the plasticizing mixing section, which can effectively reduce energy consumption.
  4. Using the continuous arrangement of multiple groups of kneading discs, the energy consumption of the extruder has not increased significantly, and the tensile strength of the specimen has not decreased significantly, so it has certain applicability and can be applied to the extrusion production of materials requiring high shear. 
  5. The screw combination has a great impact on the energy consumption of the extruder, and the focus should be on the plasticizing area, which has a significant impact on the energy consumption of the host.

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