1. introduction
Extrusion Blow Molding Machine is the largest production of blow molding equipment for production containers and hollow products. It can produce a variety of container products ranging from a minimum of 1ml to a maximum of 10000l, such as milk bottles, beverage bottles, washing. Bottles, cosmetic bottles and chemical reagent barrels, beverage barrels, mineral water buckets, etc.
In recent years, the main technical trend of extrusion blow molding has been toward automation, intelligence, high precision and high speed. Therefore, how to improve the overall technical content of traditional extrusion blow molding and adapt it to the technical development trend of the industry is an important issue.
The extrusion blow molding machine described in this paper adopts V80 series PLC developed by Deweisen Technology (Shenzhen) Co., Ltd. as the main electrical control system. The application shows that the system can fully meet the automation, intelligence, high precision and high speed. Technological development trends.
First, the V80 series PLC is highly integrated with electronic technology, automation technology and network technology. With the V80 series PLC as the control system of the blow molding machine, the blow molding machine will have extrusion, clamping, inflation, cooling and opening. The automatic control function of the mold and other processes, as well as the automatic adjustment function of the extrusion parison temperature, extrusion pressure and cooling temperature, is moving towards automation and intelligence.
Second, the high-precision thermocouple module and analog input and output expansion module in the V80 series PLC can meet the high-precision control requirements of parison temperature, extrusion pressure and parison wall thickness, and meet the requirements of product molding. Quality requirements, and accuracy repeatability; CPU module with high-speed hardware analysis technology and its own analog expansion module with CPU chip and dedicated shared data area can greatly improve the melt plasticizing speed, extrusion speed and opening and closing The mold speed shortens the molding cycle and ensures the molding quality of the product.
2. Equipment process
Extrusion blow molding is a molding method for manufacturing hollow plastic articles by inflating a hot parison in a mold into a container by means of gas gas pressure. The extrusion blow molding equipment consists of an extruder, a machine head, a mold, a blowing system and a clamping device. The process is as follows:
(1) The thermoplastic is fed into the barrel from the feed port, and the plastic is melted into a melt fluid by the extruder, and the melt is mixed and uniformly mixed by the extrusion system with a certain capacity and pressure from the head mouth. Mold extrusion to form a parison;
(2) placing the parison that has reached the specified length in a blow mold, and cutting the parison from the cutting edge on the mold;
(3) inflating the parison by a compressed air at a certain pressure by an air inlet on the mold;
(4) Maintain the pressure in the cavity of the mold so that the product and the inner surface of the mold are in close contact, then cool and shape, and open the mold to take out the product.
In the blow molding process, the formation and inflation of the parison is the core of the blow molding process. The quality of the parison formation and inflation directly affects the quality of the container product, and the heating temperature and extrusion pressure of the melt and And the cooling time will directly affect the forming and inflation quality of the parison. If the wall thickness of the parison is not effectively controlled during the blow molding process, the thickness will be uneven after cooling, and the stress generated by the embryo wall will be different, and the thin position will easily break. Therefore, controlling the wall thickness of the embryo is equally important for improving product quality and reducing costs.
In summary, how to control the heating temperature of the extruder, the extrusion pressure, the cooling time of the product and the wall thickness of the preform become several key factors affecting the quality of the container product.
3. Control system design
3.1 System Principles and Configuration
The granular or powdered plastic is plasticized into a molten state by an extruder, and the amount of the extruded melt is controlled by the electronic scale data, and the melt is fed into the handpiece through a predetermined flow rate. When the storage amount reaches a predetermined value, the die control die is opened by the PLC. According to the set parison wall thickness curve, the parison wall thickness control is completed by the PLC. At the same time, the molten material is pressed out to form the product parison, and the mold clamping mechanism of the mold forming machine adopts a four-bar three-plate linkage system, and the moving speed of the clamping machine is automatically controlled according to the set value, and the movement is stable. After the mold is blown, the parison is formed into a hollow product in the mold, and after cooling and shaping, the mold is opened, and the robot is controlled by the robot to take out the product.
The basic configuration of the system's electrical control section is as follows:
(1) The controller adopts V80 series PLC produced by Deweisen Technology (Shenzhen) Co., Ltd. for motion control and 50-point parison wall thickness control.
(2) The temperature measurement adopts the industrial armored thermocouple. The temperature control is completed by the V80 series thermocouple module E5THM. The module itself has a CPU chip and can execute the PID algorithm. After setting the parameters on the power-on, the E5THM module can The on-off control of the solid state relay is controlled by itself, thereby controlling the temperature stability and the fluctuation range is small.
(3) The pressure sensor adopts the PT124 type pressure sensor, and the data acquisition work is completed by the 8-channel analog input module E8aD1 of the V80 series.
(4) Wall thickness control The length of the parison is fed back to the PLC by the electronic ruler of the barrel, and then the servo actuator is driven by the 4-channel analog output module E4Da1 of the V80 series.
(5) The control panel adopts the touch screen to complete the setting, modification and screen display of various process parameters such as parison temperature, extrusion pressure, parison wall thickness and cooling time of the whole machine. It adopts menu-type program control and is easy and reliable to operate. It can keep the equipment in good working condition and ensure the safe production of man and machine.
3.2 temperature control system
During the extrusion blow molding process, heating and heat dissipation work are required in an equilibrium state to achieve a certain dynamic equilibrium of the extruded melt temperature. Therefore, the temperature of the extrusion process needs to be measured and controlled in real time. The temperature of the extruder is collected into the thermocouple module E5THM through the thermocouple. The module itself has a built-in CPU chip. It has 5 thermocouple inputs and 5 transistors PWM output. The PID control algorithm can be completed in the module. The control accuracy is ± 1 ° C. The temperature signal collected by the E5THM is compared with the set temperature to obtain a deviation signal. If the measured temperature is greater than the set value, the module controls the solid state relay by the PWM pulse width adjustment technique according to the PID algorithm of the time cycle duty cycle, so that the extruder The heating device stops heating, and vice versa, performs a cooling control operation. The barrel temperature setting and real-time temperature display can be done through the touch screen.
3.3 Pressure Control System
The extrusion pressure is also an important factor influencing the rheological properties of the melt. If the extrusion process is stable, the processing temperature and the screw speed are constant, the viscosity is a constant. According to the activity equation of the viscous fluid, the extrusion amount of the extruder is proportional to the screw rotation speed, and the barrel pressure is inversely proportional.
Therefore, the pressure of the extrusion process is very important, and it needs to be measured in real time to ensure the quality of the formed parison, thereby ensuring the quality of the finished product.
3.4 parison wall thickness control
The melt is extruded from the die in a viscous state for a period of time. Since the raw material characteristics, extrusion temperature and extrusion flow change nonlinearly with time, the parison wall thickness changes during the extrusion process. In order for the extruded blow molded article to meet the wall thickness requirements, effective measures must be taken to control the thickness of the parison wall.
The wall thickness control system is a system that controls the opening and closing of the core slot, that is, the position servo system, which is composed of a controller, an electro-hydraulic servo valve, an action actuator, and an electronic ruler as position feedback. When the die is opened, the PLC reads the parison length fed back by the electronic ruler of the barrel, and then outputs a voltage signal of ±10V to the electro-hydraulic servo valve through the high-precision analog output module E4Da2 according to the parison wall thickness curve. The valve directly drives the actuator to control the core to move up and down, adjust the gap between the die and the core mold to complete the control of the die opening degree, and then complete the closed-loop control of the parison wall thickness. At this time, the wall thickness parison is set in a digital manner, and the 50-point parison wall thickness control is set by the operation panel. The ordinate of the parison wall thickness curve shows the parison length, and the abscissa shows the die opening degree.
3.5 cooling time control
Cooling time is an important process parameter for controlling the appearance quality, performance and production efficiency of the article throughout the blow molding process.
Controlling the appropriate cooling time can prevent the deformation of the parison due to elastic recovery, so that the shape of the product is regular, the surface is clear, and the quality is excellent. However, if the cooling time is too long, the toughness and transparency are lowered due to an increase in crystallinity of the product, the production cycle is prolonged, and the production efficiency is lowered. If the cooling time is too short, the blown container will generate stress and voids, which will affect the quality of the product. Therefore, more precise control of the cooling time is required in extrusion blow molding.
In this system, the time timer of the V80 series PLC can reach 1 millisecond resolution, and the precise cooling time can be set by the touch screen, so that the production efficiency of the blow molding can be effectively improved while ensuring the appearance quality and performance of the product.
4 Conclusion
This paper gives the control scheme of V80 series PLC in extrusion blow molding system, focusing on the control characteristics of PLC in parison temperature, extrusion pressure, cooling time and parison thickness, which shows that the control system can be completely Meet the current technical requirements of automation, intelligence, high precision and high speed of blow molding machines.
The system has been used in an extrusion blow molding machine manufacturer in South China. After nearly one year of use, the system is running well, effectively improving the parison temperature, extrusion pressure, cooling time and parison. The control precision of wall thickness, in turn, improves production efficiency and product quality, and has good engineering application and marketing value.
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