According to the different production materials, product specifications and material consumption of customers, it is necessary to select the diameter of the screw first, and then further select the specification and model of the extruder. We need to consider many factors when selecting plastic extruder. Only by considering these factors can we ensure that the selected equipment meets the use requirements.
1. Screw
Screw is the main factor affecting the productivity of extruder. The performance of the screw determines the productivity, plasticizing quality, dispersion of additives, melt temperature, power consumption of an extruder. It is the most important part of extruder, which can directly affect the application scope and production efficiency of extruder. The rotation of the screw produces extreme pressure on the plastic, so that the plastic can move, pressurize and obtain part of the heat from friction in the barrel. The plastic can be mixed and plasticized in the moving process of the barrel. When the viscous melt is extruded and flows through the die, it can obtain the required shape and form.
2. Screw speed
Screw speed not only affects the extrusion speed and amount of material, but also makes the extruder achieve high output and good plasticizing effect. In the past, the main way to increase the output of extruder was to increase the diameter of screw. Although the material extruded per unit time will increase with the increase of screw diameter. However, in addition to extruding materials, the screw also extrudes, stirs and shears the plastic to plasticize it. On the premise of constant screw speed, the mixing and shearing effect of the screw with large diameter and large screw groove is not as good as that of the screw with small diameter. Therefore, modern extruders mainly improve production capacity and product quality by increasing screw speed.
If the screw diameter is unchanged and the screw speed is increased, the torque borne by the screw will increase. When the torque reaches a certain degree, the screw is in danger of being twisted and broken. However, by improving the material and production process of the screw, reasonably designing the screw structure, shortening the length of the feeding section, increasing the flow rate of the material and reducing the extrusion resistance, the torque can be reduced and the bearing capacity of the screw can be improved.
3. Barrel structure
The improvement of the barrel structure is mainly to improve the temperature control of the feeding section. Whether the temperature of the water jacket through the barrel is reasonable is very important for the stable work of the extruder and efficient extrusion. If the temperature of the water jacket is too high, the raw material will soften prematurely, and even the surface of the raw material particles will melt, which will weaken the friction between the raw material and the inner wall of the barrel, thus reducing the extrusion thrust and extrusion volume. However, the temperature should not be too low. The barrel with too low temperature will make the screw rotation resistance too large, which will cause difficulty in starting the motor or instability of speed when exceeding the bearing capacity of the motor. Advanced sensor and control technology are used to monitor and control the water jacket of the extruder, so as to automatically control the temperature within the range of the best process parameters.
4. Reducer
On the premise of basically the same structure, the manufacturing cost of the reducer is roughly proportional to its overall size and weight. The large shape and weight of the reducer means that more materials are consumed in manufacturing, and the bearings used are also relatively large, which increases the manufacturing cost.
For extruders with the same screw diameter, high-speed and efficient extruders consume more energy than conventional extruders, double the motor power, and correspondingly increase the base of the reducer. But high screw speed means low reduction ratio. For the reducer of the same size, compared with the reducer with large reduction ratio, the gear module increases and the capacity of the reducer to bear load also increases.
5. Motor drive
Extruders with the same screw diameter, high-speed and efficient extruders consume more energy than conventional extruders, and the motor power also needs to be increased. During the normal use of the extruder, the motor drive system and heating and cooling system are always working. The energy consumption of transmission parts such as motor and reducer accounts for 77% of the energy consumption of the whole machine; Heating and cooling account for 22.8% of the input energy consumption of the whole machine; Instrument electrical accounts for 0.8%.
The extruder with the same screw diameter is equipped with a larger motor, which seems to consume electricity, but if calculated by output, the high-speed and efficient extruder is more energy-saving than the conventional extruder. If the power consumption of heaters, fans and other devices on the extruder is also considered, the difference in energy consumption is also greater. Extruders with large screw diameters should be equipped with larger heaters, and the heat dissipation area will also increase. Therefore, for the two extruders with the same capacity, the new extruder with high conversion efficiency has a smaller barrel, the heater consumes less energy than the traditional large screw extruder, and saves a lot of electricity in heating.
In terms of heater power, the power consumption of the extruder heater is mainly in the preheating stage. During normal production, the heat of material melting is mainly converted by consuming the electric energy of the motor. The conductivity of the heater is very low and the power consumption is not large.
6. Shock absorption measures
High torque extruders are prone to vibration. Excessive vibration is very harmful to the normal use of the equipment and the service life of the parts. Therefore, multiple measures must be taken to reduce the vibration of the extruder and improve the service life of the equipment.
The motor shaft and the high-speed shaft of the reducer are the most susceptible parts of the extruder to vibration. First of all, the high rotation extruder should be equipped with high-quality motor and reducer to avoid becoming the vibration source due to the vibration of motor rotor and reducer high-speed shaft. Secondly, we should design a good transmission system. Pay attention to improving the rigidity, weight and quality of processing and assembly of the frame, which is also an important link to reduce the vibration of the extruder. A good extruder does not need to be fixed with anchor bolts when in use, and there is basically no vibration. This depends on the sufficient rigidity and self weight of the frame. In addition, we should strengthen the quality control of the processing and assembly of various components.
7. Instruments
The production operation of extrusion can only be reflected by instruments. Therefore, precise, intelligent and easy to operate instruments and meters will make us better understand their internal conditions, so that production can achieve better and faster results.
