Common problems with vacuum drying boxes:

1. There is a difference between the instrument reading of the vacuum drying oven and the reading of the glass rod thermometer in the vacuum chamber

The heating method of an electric vacuum drying oven usually involves heating the wall of the vacuum chamber first, and then radiating heating from the wall towards the workpiece. In this heating method, the temperature sensor of the temperature control instrument can be arranged on the outer wall of the vacuum chamber. Sensors can simultaneously receive conduction, convection, and radiation heat. The glass rod thermometer in the vacuum chamber can only accept radiant heat, and since the glass rod blackness 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 instrument. Generally, under the condition of 200 ℃, it is normal that the difference between the temperature reading of the instrument and that of the glass rod thermometer is within 30 ℃. 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 appropriately reduced, but it is impossible to completely eliminate it. If you want to avoid 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. Reasons for not setting temperature uniformity parameters in vacuum drying boxes

Usually, blast drying boxes are equipped with temperature uniformity parameters: natural convection drying boxes multiply the upper limit of working temperature by 3%, and forced convection drying boxes multiply the upper limit of working temperature by 2.5%. But what is the reason why the electric vacuum drying oven does not have temperature uniformity parameters?

Because the possibility of achieving uniform temperature in the chamber through the movement of gas molecules in the vacuum drying chamber is almost zero. Therefore, conceptually, it is no longer necessary to define the temperature uniformity specified by a general electric blast drying oven as a vacuum drying oven. Because setting this indicator in a vacuum state is meaningless. The amount of thermal radiation is inversely proportional to the square of distance. The radiation heat received by the same object at a distance of 20cm from the heating wall is 1/4 of the temperature at a distance of 10cm from the heating wall. The difference is significant. This phenomenon is the same as being exposed to the sun in winter. The side that is exposed to the sun is very warm, while the side that is not exposed to the sun is colder. The structure of vacuum drying boxes is difficult to achieve uniform and consistent radiation heat at various points in the three-dimensional space of the studio, and there is also a lack of authoritative evaluation methods. This is also the reason why temperature uniformity parameters are not set in the standards for electric vacuum drying boxes.