Application and development of induction furnace real-time control system
Modern induction melting furnaces are the result of a combination of high-power semiconductors and microelectronics, especially computer technology. The foundry industry needs high-power, high-power density, continuous high-volume, environmentally-friendly and computer-managed melting equipment, which is proposed by manufacturers of induction melting equipment. With new challenges, various induction furnace manufacturers have done a lot of research and practice in this area. Generally divided into three cases: embedded real-time control system with microprocessor as control unit; real-time control system represented by flat-panel industrial integrated computer; real-time control system represented by industrial computer. The following is an example of the real-time control system of Yingda's induction melting furnace.
1. Embedded real-time control system with microprocessor as control unit
Hardware composition
The hardware of the embedded real-time control system with the microprocessor as the control unit consists of three parts (see Figure 1): 1 microprocessor control board with CPU, memory, input and output interfaces. 2 keyboard. 3-character display.
Figure 1 Microprocessor is an embedded real-time control system for the control unit
2. Input signal
The input signal has operating parameters of the intermediate frequency power supply; the weight of the electric furnace; the temperature signal of the oven.
3. Output signal
The output signal has parameters for monitoring and displaying the operation of the power supply; diagnosing and displaying faults; receiving control signals linked with other devices; and printing output.
4. Several main control methods for electric furnace
(1) Kilowatt hour (kW·h) power consumption control The kW·h melting mode is used to determine when the required kW·h power has been put into the smelting. When this energy value is delivered, the IF power system can automatically reduce the output power to the holding power or turn it off. The operator can directly input the kW·h value or enter the kW·h /t data of the charge. The system can automatically calculate the kW·h count value based on the weight and output the value of the energy required from the melting to the pouring temperature.
(2) Automatic sintering furnace lining The sintering mode is used for the operator to sinter the furnace lining and set the temperature curve. The sintering mode automatically controls the on/off of the VIP power supply. The sintering setting screen allows you to enter the temperature profile.
The temperature curve generally has the following four areas:
First zone: initial heating. Use "temperature rise rate 1" as °C/h and "temperature 1" as the initial target temperature. This stage should take into account the environment or the initial furnace temperature. The time is calculated only in this initial heating phase (temperature rise rate 1 / temperature 1 = time course).
Second region: The "temperature rise rate 2" and "time 2" are used to determine the next target temperature, the temperature rise rate x time = the next target temperature.
Third zone: The "temperature rise rate 3" and "time 3" are used to determine the next target temperature.
Fourth region: The "temperature rise rate 4" and "time 4" are used to determine the next target temperature.
Not all areas are used. Below is an example of a sintering curve using three areas (see Figure 2). 1 The initial temperature is 650 ° C, (1200 ° F, target temperature 1), and the rate is about 95 ° C / h (200 ° F / h, temperature rise rate 1). 2 Maintain the temperature at 650 ° C for 2 h. 3 The temperature was raised at 150 ° C / h (300 ° F / h, temperature rise rate 3), time 4h (time 3), up to 1300 ° C (2400 ° F). The total sintering time was 12 h.
The sintering process uses a "K-type" thermocouple attached to the lining and feeds the thermocouple signal back to the regulator. The output voltage of this regulator is 0~5V, which is connected to the microprocessor control board. If the thermocouple breaks or burns out, the feedback is the full scale of the thermocouple or 1360 ° C (2500 ° F). This allows the microprocessor control board to determine when the thermocouple is damaged or burned and to stop the sintering process.
Figure 2 shows the sintering curve using three regions
(3) Automatic furnace start mode is used to allow the operator to preheat the charge and lining before starting the smelting cycle. The automatic cold start can automatically turn on the VIP device according to the time specified by the operator, and control the power value of the intermediate frequency power supply so that the charge is slowly heated.
If the setting parameters are entered and the automatic furnace start mode is enabled, the IF power will stop and wait until the specified start time arrives. When the specified time has elapsed, this mode will issue a command to turn on the pump system of the intermediate frequency power supply, reset the intermediate frequency power circuit monitor alarm (eliminate the low water pressure alarm of the water system), and then start the intermediate frequency power supply. Once activated, the IF power will increase to the level set by the operator and run within the set time. After this time arrives, the IF power supply unit will automatically turn off, and the audible and visual alarm will start, indicating that the automatic cooling furnace start has been completed.
(4) Trigger pulse control Some manufacturers integrate the pulse control of the intermediate frequency power supply with the microprocessor control system, while others are not integrated.
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