On 2018-08-08 14:48:54
Temperature control of ion nitriding furnace
The temperature control of the ion nitriding furnace is really a difficult task, because there is a certain deviation between the temperature from the thermocouple and the instrument display. Moreover, the deviation is not small, some of which reach more than 100 degrees. The most difficult thing is that the furnace temperature is uneven, and the temperature difference between different parts is also large, so it is more difficult to determine the temperature far away from the thermocouple. Therefore, it is necessary to rely on experience to clear the temperature displayed by the furnace instrument Approximate amount of actual temperature difference, range of furnace temperature dispersion, etc.
The temperature field in the furnace is not uniform. It is recommended to place one near the thermocouple when installing parts. In this way, the measured temperature is close to the temperature of the part Otherwise, it may be more than 100 ° difference.
1. The size of the observation hole on the equipment. Theoretically, the infrared instrument only needs a small opening to detect the object to be measured, but the furnace equipment needs other peripheral equipment to get the working environment, such as the vacuum pump for the vacuum furnace, so the furnace itself will have certain vibration. If the opening of the observation hole is too small, it is likely to cause the infrared radiation deviation when the infrared instrument is vibrated, so the real workpiece temperature cannot be obtained To solve this problem, we need to start at the same time with the size of the observation hole and the fixing method of the infrared instrument. Because the internal temperature of the sealed furnace equipment is very high, the infrared instrument is mostly installed outside the equipment with a bracket, but that bracket will amplify the vibration, so try not to use it as much as possible, and the thread fixing method is not conducive to adjusting the direction of the ray, so we need to choose a suitable one Installation mode.
2. Material and opening of thermal insulation materials in the furnace. A layer of thermal insulation material will be used between the heating body and the furnace wall for high-temperature furnace equipment to reduce power consumption, enhance the thermal insulation performance of the furnace and protect the accessories installed on the furnace wall, such as sealing rings. The thickness of the thermal insulation material will increase with the maximum temperature of the furnace, and the furnace type thermal insulation layer of 2000 ℃ will reach more than 150 mm, so it is necessary to move some to make the infrared ray pass through the thermal insulation layer smoothly Brains. The hole on the insulation layer corresponds to the position of the observation hole on the furnace wall. It doesn't matter if the observation hole on the furnace wall is larger, but if the observation hole on the insulation layer is too large, it will cause temperature run, and it will burn out the observation hole on the furnace wall, so the hole on the insulation layer should not be too large; in addition, the thermal deformation of the insulation material should be considered, sometimes the hole on the insulation material and the hole on the furnace wall In the cold state, it seems to correspond very well, but when the temperature is high, the heat insulation layer will expand and deform due to heating, so that the position of the opening will move, resulting in the radiation that could pass through the opening onto the heat insulation material, and the temperature measured is not correct.
3. Placement of measured objects. The ideal state is to let the infrared ray shine on the surface of the object to be measured. If the object to be measured in the furnace is a whole piece, there is basically no problem. If it is a pile of small pieces and there is a gap between each other when they are placed, we should pay attention to whether the ray will pass through the gap between the workpiece and shine on the opposite heat insulation material, so the measured temperature value deviation is also large.