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Several small questions about the vacuum drying oven

by:Sure     2021-08-18
1. The reason for the difference between the meter reading of the electric heating vacuum drying oven and the glass rod thermometer in the vacuum chamber. Generally, the electric heating vacuum drying oven adopts the method of heating the wall of the vacuum chamber first, and then the wall facing the workpiece for radiant heating. In this heating method, the temperature sensor of the temperature control instrument can be arranged on the outer wall of the vacuum, and the sensor can also accept convection, Conduction, 1. The reason for the difference between the meter reading of the electric heating vacuum drying oven and the glass rod thermometer in the vacuum chamber. Generally, the electric heating vacuum drying oven adopts the method of heating the wall of the vacuum chamber first, and then the wall facing the workpiece for radiant heating. In this heating method, the temperature sensor of the temperature control instrument can be arranged on the outer wall of the vacuum, and the sensor can accept convection Conduction, and radiant heat, and the glass rod thermometer in the vacuum chamber intelligently accepts radiant heat, and because the blackness of the glass rod cannot reach 1, a considerable part of the radiant heat is refracted, so the temperature value reflected by the glass rod thermometer must be low Regarding the temperature reading of the meter, generally speaking, it is normal that the difference between the temperature reading of the meter and the reading of the glass rod thermometer at 200 degrees is within 30 degrees. If the temperature sensor of the temperature control instrument is arranged in the vacuum chamber, the difference between the temperature value of the glass rod thermometer and the temperature reading of the instrument can be reduced, but it is impossible to eliminate, and the sealing reliability of the vacuum chamber adds a possible unreliable link . If you don't want to see this difference from the perspective of practical operation, you can use the unique display correction function of the temperature control instrument to solve it. 2. The reason why the electric heating vacuum drying oven does not have a temperature uniformity parameter The general electric heating (blast) drying oven is equipped with a temperature uniformity parameter: the natural convection drying oven is the upper limit of the working temperature multiplied by 3%. The forced convection drying oven is the upper limit of the working temperature multiplied by 2.5%, but the electric heating vacuum drying oven does not have a temperature uniformity parameter. Why? There is almost no possibility that the temperature of the working chamber can reach uniformity by the movement of gas molecules in the vacuum drying box. Therefore, conceptually, we can no longer apply the definition of temperature uniformity stipulated by the usual electric heating (blast) drying oven to the vacuum drying oven, and it is meaningless to set this index in the vacuum state. The amount of heat radiation is inversely proportional to the square of the distance. The same object is 1/4 of 10cm away from the heating wall. The difference is very large. This phenomenon is the same as that when you bask in the sun in winter, the side that is exposed to the sun is warm and the side that is not exposed to the sun is relatively cold. Because the structure of the vacuum drying oven is difficult to achieve the points in the three-dimensional space of the studio ( The radiant heat of the spherical surface is uniform, and there is no authoritative evaluation method. This may be the reason why the temperature uniformity parameter is not set in the standard of the electric heating vacuum drying oven. 3. The reason why the electric vacuum drying oven is first vacuumed and then heated up and heated 1) The workpiece is put into the vacuum box and vacuumed to remove the gas components that can be extracted from the material of the workpiece. If the workpiece is heated first, the gas will expand when heated. Because the vacuum box is very tightly sealed, the huge pressure generated by the expanding gas may burst the tempered glass of the observation window. This is a potential hazard. This hazard can be avoided by first vacuuming and heating up the program. 2) If you operate according to the procedure of first heating up and heating and then vacuuming, when the heated air is pumped out by the vacuum pump, the heat will inevitably be lifted up by the vacuum pump, which will cause the vacuum pump temperature to rise too high, which may reduce the efficiency of the vacuum pump. 3) The heated gas is directed to the vacuum pressure gauge, and the vacuum pressure gauge will generate a temperature rise. If the temperature rise exceeds the specified temperature range of the vacuum pressure gauge, it may cause the vacuum pressure gauge to produce value errors. The correct method of use should first vacuumize and heat up. After the rated temperature is reached, if the vacuum is found to decrease, then add a suitable vacuum. This is beneficial to prolong the service life of the equipment.
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