1. Why does the vacuum drying oven not set the temperature uniformity parameter?
The general electric (blast) drying ovens are equipped with temperature uniformity parameters: the natural convection oven is the upper limit of the operating temperature multiplied by 3%, and the forced convection oven is the upper limit of the operating temperature multiplied by 2.5%. However, the electric vacuum drying oven does not have a temperature uniformity parameter. Why? There is almost no possibility of relying on the movement of gas molecules in the vacuum oven to make the temperature of the studio uniform. Therefore, from the conceptual point of view, we can no longer use the temperature uniformity defined by the usual electric (blast) drying oven to define the vacuum drying oven. It is also meaningless to set this indicator under vacuum. The amount of thermal radiation is inversely proportional to the square of the distance. For the same object, the radiant heat received at 20 cm from the heated wall is only 1/4 of 10 cm from the heated wall. big difference. This phenomenon is warm when the sun is shining in the winter, and the sun is not warm. It is a truth that the sun is not cold. Because the vacuum drying oven is difficult to make the radiant heat of each point (the spherical surface) in the three-dimensional space of the studio uniform, and there is also a lack of evaluation method, it is possible that there is no temperature in the standard of the electric vacuum drying oven. The reason for the uniformity parameter.
2. Why is the difference between the meter reading of the vacuum oven and the glass rod thermometer reading in the vacuum chamber:
In general, the electric vacuum drying oven adopts a method of heating the wall surface of the vacuum chamber first, and then heating the wall toward the workpiece. In this way, the temperature sensor of the temperature control meter can be arranged on the outside wall of the vacuum. The sensor can accept convection, conduction, and radiant heat simultaneously. The glass rod thermometer in the vacuum chamber can only receive 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 is definitely lower than the temperature reading of the meter. . In general, it is normal to have a difference between the temperature reading of the meter and the reading of the glass rod thermometer within 30 °C at 200 °C. If the temperature sensor of the temperature control instrument is placed in the vacuum chamber, the difference between the temperature value of the glass rod thermometer and the temperature reading of the meter can be appropriately reduced, but it cannot be eliminated, and the sealing reliability of the vacuum chamber increases a possible unreliable link. . If you do not want to see this difference from the practical point of view, you can use the display correction function unique to the temperature control instrument.
3. The reason why the vacuum drying box first vacuums and then heats up:
The correct method of use of the vacuum drying box: first vacuum and then heat up. After the rated temperature is reached, if it is found that the vacuum has decreased, then add it appropriately. This is advantageous for extending the life of the device. The specific reasons are as follows:
The vacuum is placed in the vacuum box to extract the gas components that can be removed from the workpiece material. If the workpiece is heated first, the gas expands when heated. Due to the excellent sealing of the vacuum box, the enormous pressure generated by the expanding gas may cause the observation window tempered glass to burst. This is a potential danger. This danger can be avoided by the procedure of first vacuuming and then heating up.
If the heating air is pumped out by the vacuum heating and then the vacuum is pumped out, the heat will be brought to the vacuum pump, which will cause the vacuum pump to rise too high, which may reduce the efficiency of the vacuum pump.
The heated gas is directed to a vacuum gauge and the vacuum gauge produces a temperature rise. If the temperature rise exceeds the operating temperature range specified by the vacuum gauge, the vacuum gauge may cause an indication error.