I. Overview
Hot runner is a kind of temperature control equipment widely used in the plastic mold industry. It is an advanced technical equipment for the pouring runner system of plastic injection molds. It is a hot direction in the development of plastic injection molding technology. Beijing Kaideen Company and a polyester mold factory used the Kinco-K3 series PLC and thyristor voltage regulating module independently developed by Shenzhen Step Technology Co., Ltd. to jointly develop a hot runner control system, which includes 4-channel temperature control And 12 way voltage adjustment.
Second, realize the function
According to process requirements, the control system realizes the following functions:
1. The temperature of 4 channels can be separately set and controlled by PID, with an accuracy of ± 1 ℃.
2. The 12-channel (multi-channel) voltage can be set and controlled separately.
3.4 Alarm when the temperature of No. 4 is out of the specified range.
4. 12 channels (multi-channel) voltage out of the specified range alarm.
5. Output element (SCR) short circuit and open circuit alarm.
6. It can display all actual temperature values and all actual output voltage values.
3. Introduction to SCR Module
Thyristor (SCR) is a voltage controlled power device widely used in industrial automation. Controlling the conduction angle of the SCR makes the output voltage of the SCR continuously adjustable, so it is widely used in temperature control, light adjustment, motor speed control and other fields. The thyristor voltage regulating module (FM351) developed by Step Technology for thyristor control is an extended function module of Kinco-K3 series PLC, which is connected to the expansion bus of the CPU. FM351 has the following characteristics:
1. Each SCR expansion module can control four SCRs;
2. The control method is to write the output voltage value to the SCR module by the program, and the adjustment process is completed by the module itself, which can realize:
·Open loop control
The voltage output by the thyristor changes with the voltage of the external power grid.
·Closed loop feedback control
The output voltage of the SCR will be stable near the voltage value set by the user. It will automatically adjust the trigger time of the thyristor with the change of the external grid voltage, so that the actual output voltage is always stable near the set voltage value.
3. Alarm detection
l Open loop control: "SCR disconnected" alarm, "SCR short circuit" alarm;
l Closed-loop control: "SCR off" alarm, "SCR short circuit" alarm, actual output voltage exceeding the set value ± 10V alarm, communication error alarm between the SCR module and the CPU module;
Four, control system realization
The control core PLC selects Kinco-K3 series PLC.
Kinco-K306-24AR, a host, it has 14 inputs /10 relay outputs.
Kinco-K331-04TC, a thermocouple temperature measurement extension module.
Kinco-K351, 4 multifunctional thyristor voltage regulating expansion modules.
16 BTA40 triacs.
The touch screen serves as a man-machine interface.
1. Temperature feedback control
There are four channels of precise temperature control in the mold, and the Kinco-K331-04TC thermocouple temperature measurement module is used to measure the mold temperature value, and the given value is calculated by the PID in the PLC and adjusted by the FM351 multi-function thyristor voltage adjustment extension module The conduction angle of the thyristor changes the output voltage, thereby controlling the heater power to keep the mold temperature at a specified value.
2. Voltage regulation
There are 12 channels of precise control of heating voltage in the flow channel. The set voltage value is transmitted to the Kinco-K351 thyristor voltage regulation module in the program. The thyristor voltage regulation module adjusts the conduction angle of the thyristor to change the output voltage. Then the temperature in the flow channel can be adjusted. The SCR voltage regulating expansion module automatically completes the voltage detection and feedback functions to stabilize the output voltage.
3. Call the police
When the SCR is short-circuited, open, over-voltage, or the SCR voltage regulating module fails, the SCR voltage regulating module can automatically transmit fault information to the CPU module, display an alarm screen on the touch screen, and notify the fault type for maintenance. (Including temperature tolerance alarm).
4. other
The temperature curve can be displayed on the touch screen as required.
Because the four-way precise temperature control in the mold has a soft start function, the temperature of the mold rises slowly when the mold is turned on, which avoids the thermal shock to the mold and prolongs the life of the mold.
All operations are completed on the touch screen to realize the parameter setting and display, as well as the start and stop of each output. The panel has an emergency stop button.
Five, summary
Actual operation shows that the system fully meets the process requirements. After replacing the traditional instrument system with an advanced PLC control system, it not only greatly improves the reliability and control accuracy of the equipment, simplifies the system wiring, but also improves the beauty of the human-machine interface with the LCD screen, and more importantly, helps the equipment Manufacturers have improved the technical grade of their products and increased their added value.