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What Are the Common Problems in the Use of Vacuum Drying Ovens?

There will be different problems during the use of the vacuum drying ovens. Here is a summary of several common problems and their solutions.


Ⅰ. The reason why the electric heating vacuum oven does not have temperature uniformity parameters


General electric heating (blast) drying ovens are equipped with temperature uniformity parameters: natural convection drying ovens are 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%. Why only the electric heating vacuum drying oven does not set the temperature uniformity parameter?


There is almost no possibility that the temperature of the working chamber can reach a uniform temperature by relying on 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 uniformity and consistency of the radiant heat of the spherical surface and the lack of evaluation methods may be the reason why the temperature uniformity parameter is not set in the standard of the electric heating vacuum drying oven.


Ⅱ. The reason for the difference between the meter reading of the electric heating vacuum oven and the reading of the glass rod thermometer in the vacuum chamber


Generally, the electric heating vacuum drying ovens adopt 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, and radiant heat. 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 lower than 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 potentially unreliable link. If you don't want to see this difference from a practical perspective, you can use the unique display correction function of the temperature control instrument to solve it.

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