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Suggestions for optimization of atmosphere furnace on temperature controller

Time:2020-11-13 09:35

   Atmosphere furnace, also known as ladle furnace, atmosphere protection furnace, usually includes a container that can be vacuumed and filled with atmosphere and a box furnace that can be placed in it. The atmosphere furnace has a wide range of uses in the industrial field, especially suitable for the sintering of magnetic cores in the magnetic material industry, and is mainly used for laboratory trials and small batch production. The sintering process of the magnetic core has certain requirements on the partial pressure of oxygen, and it is usually sintered by vacuuming and filling with nitrogen.

The traditional atmosphere furnace uses silicon carbon rods for heating, and the high working temperature is 1350℃. The disadvantage is that the life is short and there are aging problems. If a broken one requires a complete replacement, the temperature control of the atmosphere furnace is labor-intensive; in addition, the heating elements are on both sides Evenly distributed, the optimization on the furnace door and the instrument suggests that the furnace tail temperature is obviously lower, which leads to poor consistency of the sintered product. In the optimized scheme, the heating element adopts silicon molybdenum rods. Its normal working temperature is 1450℃, which meets the temperature requirements of sintered high-performance magnetic cores. The service life is about 1 year. There is no aging problem, and only one needs to be replaced. , Easy to operate; heating elements are installed at the end of the furnace to heat on three sides, and at the same time move forward by the thermocouple of the furnace door,

  The temperature controller of the traditional atmosphere furnace can only set the temperature-time curve. For the resistive load with a certain resistance value, as long as the appropriate PID (proportional, derivative, integral) value is set, the set temperature curve can be obtained. The heating element of the atmosphere furnace in the optimized design is a silicon-molybdenum rod whose resistance changes with temperature. Especially the cold resistance value of the silicon molybdenum rod is extremely small. When the initial temperature rises, even if the voltage regulator triggers the small conduction angle of the thyristor, the current reflected on the load may be large, so that the fast fuse or the Thyristor. The traditional method is to install a 10k potentiometer on the voltage regulator to limit the standard signal sent by the temperature controller to the voltage regulator to reduce the current on the load. However, as the temperature increases, the resistance of the silicon molybdenum rod increases rapidly, which requires manual increase of the output of the 10k potentiometer. Only when the resistance of the silicon molybdenum rod changes little, can the 10k potentiometer be adjusted to a large value. , In order to ensure the set temperature curve, this will not achieve the purpose of fully automatic heating.

In the optimization plan of the atmosphere furnace temperature controller, the temperature controller can automatically limit the standard signal sent to the voltage regulator through the program, and each program segment adds a limiter (F) parameter, so as to ensure Automatic heating. Of course, the ideal temperature control method is to limit the large current value from beginning to end, which requires the use of closed-loop control and additional hardware, which is more complicated.


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