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Screw speed for extrusion blow molding machine

Views: 1     Author: Site Editor     Publish Time: 2021-09-17      Origin: Site

The screw speed directly affects the output of the blow molding machine and the quality of the product parison, and its value is determined by the size and shape of the screw and the extruded product, and the type of raw materials. Increasing the speed of the screw can significantly increase the output of the blow molding machine, but the power consumption also increases accordingly. Considering the purpose of increasing output, it is advantageous to use a higher speed. At the same time, increasing the screw speed due to the enhanced shearing effect of the screw on the material, increasing the screw speed can also increase the plasticizing effect of the material and improve the microscopic quality of the product. 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 in high-density polyethylene plastics. Moreover, a large amount of frictional heat is generated when the speed is increased, so that the plastic is in danger of instant degradation. Therefore, the screw speed should be adjusted according to the actual situation.


In the past, to increase the output of blow molding machines, the main method was to increase the screw diameter. Although the screw diameter increases, the material extruded per unit time will increase. But the blow molding machine is not a screw conveyor. In addition to extruding the material, the screw also squeezes, stirs, and shears the plastic to plasticize the plastic. Under the premise that the screw speed is constant, the screw speed of the ordinary blow molding machine, the traditional blow molding machine is 60 to 90 revolutions (per minute, the same below). And now it has generally increased to 100~120 revolutions. The higher speed blow molding machine reached 150 to 180 revolutions. Foreign reports have reported that the screw speed of the blow molding machine produced by a blow molding machine manufacturer is above 200 rpm.


If the diameter of the screw is constant and the screw speed is increased, the torque that the screw bears will increase. When the torque reaches a certain level, the screw may be broken. 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 and maximize the screw speed under the premise that the screw can bear it, this requires professionals to obtain through a large number 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 motor power.

The blow molding machine with the same screw diameter is equipped with a larger motor, which seems to be a waste of electricity, but if calculated according to the output, the high-speed and high-efficiency blow molding machine is more energy-saving than the conventional blow molding machine. And this is just a comparison of the energy consumption of the motor. If the electricity 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 the two blow molding machines with the same capacity, the new high-rotation and high-efficiency blow molding machine has a smaller barrel, and the heater consumes less energy than the traditional large screw blow molding machine, and also saves a lot of electricity in terms of heating.


In terms of heater power, high-speed and high-efficiency blow molding machines do not increase heater power due to increased production capacity compared with ordinary blow molding machines with the same screw diameter. Because the heater of the blow molding machine consumes electricity, it is mainly in the preheating stage. During normal production, the heat of material melting is mainly converted from the electrical energy of the motor. The conduction rate of the heater is very low, and the electricity consumption is not Large, which is more obvious in high-speed blow molding machines.



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