Injection molding machine barrel temperature control

Update:31 May 2019
Summary:

At present, the injection molding machine barrel is wid […]

At present, the injection molding machine barrel is widely used in the resistance heating mode. The heating device includes a cast aluminum heater, a ceramic heater, a mica heater, etc., and the plastic is subjected to steady-state plasticization by a combination of a heating source and mechanical shearing. The temperature of the cylinder is controlled by segmentation to obtain the temperature distribution in accordance with the process requirements, as well as the rapid heating rate and temperature control accuracy, and meet the energy saving requirements. Generally, when the shear heat of the processed plastic is small, it is approximated that the melt temperature mainly depends on the barrel heating temperature. In recent years, a new method of electromagnetic dynamic plasticization has emerged, which basically requires no external heating in the stable working process, and has the characteristics of high plasticizing efficiency and low energy consumption.

Since the temperature of the injection molding machine barrel and its control effect directly affect the quality of the injection molded product, for example, the residual stress on the surface of the product, the shrinkage rate, and the weight stability of the product, the latter has become an important basis for measuring the quality of precision injection molded products. Therefore, it has attracted the attention of the industry. The reliability of the barrel temperature control device and the accuracy of its temperature control have become the key to achieving precision injection molding. Due to the large inertia of the heating system and the influence of environmental factors such as power supply voltage fluctuations, it is often difficult to obtain the desired quality factor, and corresponding measures need to be taken. Based on the relay type switch control of the injection molding machine barrel heating system, the barrel adopts the front, middle and rear three-stage heating mode, and its performance indicators such as overshoot, transition process time and steady-state deviation are not ideal.

Although the contactless thyristor is an ideal device for controlling high power components, it is also used to control the heating of the cartridge and adjust the output power of the thyristor by changing the conduction angle. Practical applications have confirmed that there are still three obvious defects in this method:

(1) The instantaneous conduction will cause great pollution to the power grid, which in turn will cause strong interference to the control system itself, especially in the case of high power;

(2) The control circuit is more complicated, especially for the trigger pulse circuit, to meet the precise power adjustment requirements;

(3) There is a non-linear relationship between the output voltage and the conduction angle of the control quantity, which brings a lot of inconvenience to the adjustment of the control system, and also deteriorates the performance of the control system.

Therefore, most of todayadays, non-contact zero-crossing solid-state relays are used as high-power control devices, and the heating process is controlled based on various new control strategies, and the temperature is controlled by adjusting the heating power.

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