The screw speed directly affects the output of the plastic blow molding machine and the quality of the product.
The value of the screw rotation speed depends on the size and shape of the screw and the extruded product, and the type of the raw material.
Increasing the speed of the screw can significantly increase the output of the blow molding machine. But the power consumption is also increased accordingly. From the standpoint of increasing production, it is advantageous to use a higher rotational speed. At the same time, due to the enhanced shearing action of the screw on the material, increasing the screw speed can also improve the plasticizing effect of the material and improve the microscopic quality of the product.
However, the increase in screw speed should be limited.
If the rotation speed is too high, the residence time of the plastic in the barrel is short, which may cause the melt temperature to be uneven and the surface quality of the parison to decrease. In particular, the increase in shear rate causes melt fracture of high density polyethylene plastics. Moreover, the large amount of frictional heat generated when the rotational speed is increased causes the plastic to be degraded instantaneously.
Therefore, the speed of the screw should be adjusted according to the actual situation.
In the past, the main method to increase the output of the blow molding machine was to increase the screw diameter. Although the amount of material extruded per unit time increases as the diameter of the screw increases, the blow molding machine is not a screw conveyor. In addition to extruding the material, the screw also extrudes, stirs, and shears the plastic to plasticize the plastic. Under the premise of the same screw speed, the screw speed of the ordinary blow molding machine, the traditional blow molding machine is 60 to 90 revolutions (per minute). Now it has generally increased to 100~120 rpm. The high-speed blow molding machine reaches 150 to 180 rpm (per minute).
When the screw diameter is constant and the screw speed is increased, the torque that the screw is subjected to 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, the screw structure is rationally designed, the length of the feed section is shortened, the flow rate of the material is increased, and the extrusion resistance is reduced, which can reduce the torque and improve the bearing capacity of the screw. How to design the most reasonable screw, under the premise of the screw can withstand, to maximize the screw speed, which requires professionals to obtain a large number of tests.
For the same screw diameter blow molding machine, the high-speed and high-efficiency blow molding machine consumes more energy than the conventional blow molding machine, and it is necessary to increase the motor power.
The same screw diameter blow molding machine is equipped with a larger motor, which seems to be a waste of electricity, but if calculated by production, high-speed and efficient blow molding machines are more energy efficient than conventional blow molding machines. Moreover, this is only a comparison of the energy consumption of the motor. If the power consumption of the heaters and fans on the blow molding machine is taken into account, the difference in energy consumption is even greater.
A large screw diameter blow molding machine is required to have a larger heater, and the heat dissipation area is also increased. Therefore, the two blow molding machines of the same capacity, the high-efficiency new blow molding machine barrel is smaller, the heater consumes less energy than the traditional large screw blow molding machine, and saves a lot of electricity in heating.
In terms of heater power, a high-speed and high-efficiency blow molding machine does not increase the power of the heater due to an increase in capacity compared to a conventional blow molding machine having the same screw diameter. Because the heater of the blow molding machine consumes electricity, mainly in the preheating stage, during normal production, the heat of melting of the material is mainly converted by the consumption of electrical energy of the motor. The conduction rate of the heater is very low, and the power consumption is not Large, this is more obvious in high speed blow molding machines.
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