Practical skills and methods for precise temperature control of vacuum furnace

1. Control mode selection and parameter setting

1. Control mode adaptation : Common control methods include PID control, advanced PID control and fuzzy control. Conventional PID control can be used for basic application scenarios. For complex processes (such as multi-stage heating and high-precision insulation), it is recommended to use advanced PID or fuzzy control with self-tuning function to reduce overshoot and improve stability.
2. Process curve programming : Through the intelligent temperature control instrument (temperature control accuracy of 0.1%), multiple temperature control curves can be compiled. Each curve can set the heating rate, insulation time and cooling mode in stages, and support multiple curve storage and call. For example, the PID parameter self-tuning can be set in the heating stage to ensure no overshoot.
3. Temperature range and power matching : Determine the heating power based on the material properties (such as thermal conductivity and heat capacity). Materials with high heat capacity require increased power to shorten the heating time. The higher the control accuracy requirement, the greater the heating power required, but avoid power overload that may cause component damage.

2. System debugging and signal transmission optimization

1. Instrument and sensor calibration : Regularly calibrate the temperature controller and thermocouple to ensure that the temperature display error is ≤±1°C. Support the connection of thermocouples with various graduation numbers. During installation, ensure that the thermocouple is in close contact with the sample or heating area to reduce thermal response delay.
2. Signal conversion and execution control : The temperature controller outputs 4-20mA current signal to the trigger unit, which is converted into a voltage signal to control the DC voltage/current of the excitation circuit, and then adjust the magnetic modulation power to achieve heating and insulation according to the set curve. For example, the output current is increased during the heating stage, and the voltage is maintained stable during the insulation stage.
3. Pre-operation test : Before the new program is activated, an empty furnace test is required to simulate the entire process of heating-keeping-cooling. The temperature control curve tracking accuracy and equipment abnormalities must be checked before it can be officially put into use.

3. Key Operation Notes

1. Coordinated control of heating and vacuum : The vacuum atmosphere furnace needs to start heating after the vacuum degree reaches the standard to avoid gas heat conduction affecting the temperature control accuracy; the gas-fired vacuum furnace needs to detect the flame signal before starting, and execute the ignition procedure after pre-purging the furnace to prevent gas leakage.
2. Dynamic monitoring and adjustment : Observe the temperature curve and current changes in real time during operation. If overshoot occurs (such as rapid temperature rise), the proportional coefficient in the PID parameter can be temporarily reduced. During the cooling stage, it is forbidden to suddenly interrupt the cooling system, and the temperature must be gradually reduced to a safe temperature according to the procedure.
3. Equipment cleaning and maintenance : Regularly clean the oxides and impurities on the surface of the heating elements, check the aging of the seals, and keep the furnace cavity clean to reduce the interference of heat radiation. The vacuum system needs to regularly check the valve sealing and replace the aged seals.

4. Common problems and solutions