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Effect of Screw Speed on Blow Molding Machine

The screw speed directly affects the output of the blow molding machine and the quality of the product parison, and its value depends on the size and shape of the screw and extruded products, as well as the type of raw materials. Increasing the screw speed can significantly increase the output of the blow molding machine, but the power consumption also increases accordingly. Considering the purpose of increasing production, it is advantageous to adopt a higher rotational speed. At the same time, increasing the screw speed can also increase the plasticizing effect of the material and improve the microscopic quality of the product due to the enhanced shearing effect of the screw on the material. However, the increase of the screw speed should be limited. If the speed is too high, the plastic stays in the barrel for a short time, which may cause uneven melt temperature and decrease the surface quality of the parison. In particular, the increase in shear rate may cause melt fracture of high-density polyethylene plastics. Moreover, when the speed is increased, a large amount of frictional heat is generated to cause the plastic to be in danger of instant degradation. Therefore, the screw speed should be adjusted according to the actual situation.


In the past, the main way to increase the output of blow molding machines was to increase the diameter of the screw. Although the screw diameter increases, the material extruded per unit time will increase. But a blow molding machine is not a screw conveyor. In addition to extruding the material, the screw also needs to squeeze, stir and shear the plastic to make the plastic plastic. On the premise that the screw speed remains unchanged, the screw speed of the ordinary blow molding machine, the traditional blow molding machine is 60 to 90 rpm (per minute, the same below). Now it has generally been increased to 100~120 rpm. A blow molding machine with a higher speed reaches 150 to 180 rpm. It is reported that the screw speed of the blow molding machine produced by a certain blow molding machine manufacturer is above 200 rpm.


If the screw diameter remains unchanged and the screw speed is increased, the torque on the screw will increase. When the torque reaches a certain level, the screw may be twisted. However, by improving the material and production process of the screw, rationally designing the screw structure, shortening the length of the feed 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. How to design the most reasonable screw to maximize the screw speed under the premise that the screw can withstand it requires professionals to obtain through a lot of experiments.


For blow molding machines with the same screw diameter, high-speed and high-efficiency blow molding machines consume more energy than conventional blow molding machines, and it is necessary to increase the power of the motor.


Blow molding machines with the same screw diameter are equipped with larger motors, which seem to consume electricity, but if calculated according to output, high-speed and high-efficiency blow molding machines are more energy-efficient than conventional blow molding machines. And this is just a comparison of the energy consumption of the motor. If the power consumption of the heater and fan on the blow molding machine is taken into account, the difference in energy consumption will be even greater. A blow molding machine with a large screw diameter needs to be equipped with a larger heater, and the heat dissipation area is also increased. Therefore, for two blow molding machines with the same production capacity, the barrel of the new high-speed and high-efficiency blow molding machine is smaller, and the energy consumption of the heater is less than that of the traditional large screw blow molding machine, which also saves a lot of electric energy in heating.


In terms of heater power, compared with ordinary blow molding machines with the same screw diameter, the high-speed and high-efficiency blow molding machine does not increase the power of the heater due to the increase in production capacity. Because the power consumption of the heater of the blow molding machine 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 conduction rate of the heater is very low, and the power consumption is not high. Large, which is more obvious in high-speed blow molding machines.

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