Besides the screw and barrel, these components are equally important when choosing an extruder!

How do people usually choose extruders? Not only do we need to analyze our own needs, but we also need to have a thorough understanding of our suppliers and extruders.

Most enterprises have a basic understanding of whether to purchase a double screw or a single screw extruder, what materials need to be produced, and the amount of materials used varies depending on the product specifications. They can refer to "screw diameter and product specification size" to first select the diameter of the screw, and then further select the specifications and models of the extruder based on the screw diameter.

After determining the type and specifications of the extruder, it is also important to pay attention to how to find equipment manufacturers. It goes without saying that there are many foreign brands, and there are also many extruder enterprises in China that have established factories for a long time, strong influence, and many years of practical experience. They can choose from multiple perspectives such as product quality and after-sales service.

The rotational speed of the screw

This is the most critical factor affecting the production capacity of an extruder. The screw speed is not only to improve the extrusion speed and amount of materials, but more importantly, to enable the extruder to achieve good plasticization effect while achieving high output.

In the past, the main way to increase the output of extruders was to increase the screw diameter. Although the diameter of the screw increases, the amount of material extruded per unit time will increase. But the extruder is not a screw conveyor. In addition to extruding materials, screws also need to extrude, stir, and shear plastics to plasticize them. Under the premise of constant screw speed, screws with large diameters and grooves have less stirring and shearing effects on materials than screws with small diameters.

Therefore, modern extruders mainly increase production capacity by increasing screw speed. The screw speed of a regular extruder is 60 to 90 revolutions per minute (the same below). And now it has generally increased to 100-120 revolutions. The higher speed extruder reaches 150 to 180 revolutions.

When the screw diameter remains unchanged and the screw speed is increased, the torque borne by the screw will increase. When the torque reaches a certain level, the screw is at risk of being twisted and broken. However, by improving the material and production process of the screw, designing the screw structure reasonably, shortening the length of the feed section, increasing the material flow rate, and reducing extrusion resistance, torque can be reduced and the bearing capacity of the screw can be improved. How to design the most reasonable screw and maximize the screw speed while the screw can withstand it requires professional personnel to obtain a large number of experiments.

Screw structure

The screw structure is the main factor affecting the production capacity of the extruder. If there is no reasonable screw structure, simply increasing the screw speed to increase the extrusion amount goes against objective laws and will not be successful.

The design of high-speed and efficient screws is based on high rotational speed. The plasticizing effect of this screw may be worse at low speeds, but the plasticizing effect gradually improves as the screw speed increases, and the best effect is achieved when the design speed is reached. At this point, there is both high production capacity and qualified plasticizing effect.

Barrel structure

The improvement of the barrel structure mainly involves improving the temperature control of the feeding section and setting up the feeding groove. The entire length of this independent feeding section is a water jacket, which is controlled by advanced electronic control devices for temperature control.

The reasonable temperature of the water jacket is crucial for the stable operation and efficient extrusion of the extruder. If the temperature of the water jacket is too high, it will cause the raw materials to soften prematurely, and even cause melting on the surface of the raw material particles, weakening the friction force between the raw materials and the inner wall of the barrel, thereby reducing the extrusion thrust and amount. But the temperature should not be too low. A machine barrel with a low temperature will cause excessive resistance to screw rotation, and exceeding the bearing capacity of the motor will cause difficulty in starting the motor or unstable speed. By utilizing advanced sensors and control technology, the water jacket of the extruder is monitored and controlled, thereby automatically controlling the temperature of the water jacket within the optimal process parameter range.

Gearbox

On the premise that the structure is basically the same, the manufacturing cost of the reducer is roughly proportional to its external dimensions and weight. Due to the large shape and weight of the gearbox, it means that more materials are consumed during manufacturing, and the bearings used are also relatively large, which increases manufacturing costs.

For extruders with the same screw diameter, a high-speed and efficient extruder consumes more energy than a conventional extruder. The motor power is doubled, and it is necessary to correspondingly increase the base number of the reducer. But high screw speed means low reduction ratio. Compared to those with high reduction ratios, a gearbox of the same size has an increased gear module and a greater ability to withstand loads. Therefore, the increase in volume and weight of the reducer is not linearly proportional to the increase in motor power. If the extrusion amount is used as the denominator and divided by the weight of the reducer, a high-speed and efficient extruder will have a smaller number, while a regular extruder will have a larger number.

In terms of unit output, the motor power of the high-speed and efficient extruder is small, and the weight of the reducer is small, which means that the machine manufacturing cost per unit output of the high-speed and efficient extruder is lower than that of a regular extruder.

motor drive

A high-speed and efficient extruder with the same screw diameter consumes more energy than a conventional extruder, and an increase in motor power is necessary. The high-speed 65 extruder needs to be equipped with motors ranging from 55 kW to 75 kW. A high-speed 75 extruder requires a motor ranging from 90 kW to 100 kW. A high-speed 90 extruder requires a motor ranging from 150 kW to 200 kW. This is one to two times higher than the motor power configured for a regular extruder.

During the normal use of the extruder, the motor drive system and heating and cooling system are constantly in operation. The energy consumption of the transmission parts such as the motor and gearbox accounts for 77% of the overall energy consumption of the machine; Heating and cooling account for 22.8% of the input energy consumption of the entire machine; Instrument electrical accounts for 0.8%.

The extruder with the same screw diameter is equipped with a larger motor, which may seem to consume electricity, but if calculated based on output, a high-speed and efficient extruder is more energy-efficient than a conventional extruder. For example, a regular 90 extruder with a motor of 75 kW and a production capacity of 180 kg consumes 0.42 kWh of electricity per kilogram of material extruded. A high-speed and efficient 90 extruder has a production capacity of 600 kilograms and a motor of 150 kilowatts. It only consumes 0.25 kilowatt hours of electricity per kilogram of material extruded, and the power consumption per unit of extrusion is only 60% of the former. The energy-saving effect is significant. Moreover, this only compares the energy consumption of the motor. If the electricity consumption of the heater and fan on the extruder is also taken into account, the difference in energy consumption will be even greater. The extruder with a large screw diameter needs to be equipped with a larger heater, which also increases the heat dissipation area. Therefore, for two extruders with the same production capacity, the new type of extruder with high rotational efficiency has a smaller barrel, less energy consumption for the heater than traditional large screw extruders, and also saves a lot of electricity in heating.

In terms of heater power, high-speed and efficient extruders do not increase heater power due to increased production capacity compared to ordinary extruders with the same screw diameter. Because the heater of the extruder consumes electricity mainly during the preheating stage, during normal production, the heat of material melting is mainly converted by consuming the electrical energy of the motor. The conductivity of the heater is very low, and the electricity consumption is not high. This is more pronounced in high-speed extruders.

Before the widespread application of frequency converter technology, traditional high extrusion extruders generally used DC motors and DC motor controllers. Because in the past, it was generally believed that DC motors had better power characteristics than AC motors, a wider speed range, and were more stable during low-speed operation. High power frequency converters are relatively expensive, which also limits their application.

In recent years, the development of frequency converter technology has been relatively fast. Vector type frequency converters have achieved sensorless control of motor speed and torque, and low-frequency characteristics have made significant progress. Prices have also decreased relatively quickly. The biggest advantage of frequency converters compared to DC motor controllers is energy efficiency. It makes energy consumption proportional to the motor load, increasing energy consumption when the load is heavy, and automatically lowering energy consumption when the motor load decreases. The energy-saving benefits of this in long-term applications are very significant.

Vibration reduction measures

High speed extruders are prone to vibration, and excessive vibration is very harmful to the normal use of the equipment and the service life of the components. Therefore, multiple measures must be taken to reduce the vibration of the extruder and improve the service life of the equipment.

The most vibration prone parts of the extruder are the motor shaft and the high-speed shaft of the reducer. Firstly, the high speed extruder should be equipped with high-quality motors and reducers to avoid becoming a source of vibration due to the vibration of the motor rotor and reducer high-speed shaft. The second is to design a good transmission system. Pay attention to improving the rigidity, weight, processing, and assembly quality of the frame, which is also an important link in reducing the vibration of the extruder. A good extruder does not need to be fixed with anchor bolts during use, and there is basically no vibration. This depends on the rack having sufficient rigidity and self weight. We also need to strengthen the quality control of the processing and assembly of various components. During processing, control the parallelism of the upper and lower planes of the frame, as well as the perpendicularity between the installation surface of the reducer and the plane of the frame. During assembly, the shaft height of the motor and reducer should be carefully measured, and the reducer pad should be strictly prepared to make the motor shaft concentric with the input shaft of the reducer. And make the installation surface of the reducer perpendicular to the plane of the frame.