Aozhen Instrument DZF-6050B Vacuum Drying Oven Laboratory Electric Thermostatic Vacuum Oven

1. The reason for the difference between the instrument reading of the vacuum drying oven and the reading of the glass rod thermometer in the vacuum chamber:

The general electric vacuum drying oven adopts the method of heating the wall of the vacuum chamber first, and then radiating heating from the wall to the workpiece. In this way, the temperature sensor of the temperature control instrument can be arranged on the outer wall of the vacuum chamber. Sensors can simultaneously receive convection, conduction, 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 speaking, it is normal that the difference between the temperature reading of the instrument and the reading of the Glass rod thermometer is within 30 ℃ under the condition of 200 ℃. 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, and the sealing reliability of the vacuum chamber adds a possible unreliable link. If you do not 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.

2. The reason for vacuum drying oven to be vacuumed first and then heated up

1) The purpose of vacuuming the workpiece in a vacuum box is to remove the gas components that can be extracted from the workpiece material. If the workpiece is heated first, the gas will expand when heated. Due to the excellent sealing of the vacuum box, the enormous pressure generated by the expanding gas may cause the tempered glass of the observation window to burst. This is a potential danger. By following the procedure of vacuuming first and then heating up, this danger can be avoided.

2) If the program of heating first and then vacuuming is followed, when the heated air is pumped out by the vacuum pump, the heat will inevitably be carried to the vacuum pump, resulting in an excessively high temperature rise in the vacuum pump, which may lead to a decrease in the efficiency of the vacuum pump.

3) The heated gas is directed to the vacuum pressure gauge, which will generate a temperature rise. If the temperature rise exceeds the specified operating temperature range of the vacuum pressure gauge, it may cause an indication error in the vacuum pressure gauge.

The correct method of use should first vacuum and then heat up. After reaching the rated temperature, if it is found that the vacuum degree has decreased, add an appropriate amount of suction. This is beneficial for extending the service life of the equipment.

3. Reasons for not setting temperature uniformity parameters in vacuum drying boxes

General electric heating (air blast) drying oven is equipped with temperature uniformity parameter: Natural convection drying oven is the upper limit of working temperature multiplied by 3%, and Forced convection drying oven is the upper limit of working temperature multiplied by 2.5%. Only the electric vacuum drying oven does not have a temperature uniformity parameter, because the possibility of relying on the movement of gas molecules in the vacuum drying oven to achieve uniform temperature in the studio is almost non-existent. Therefore, conceptually, we can no longer define the temperature uniformity specified by the usual electric (blast) drying oven as a vacuum drying oven. Setting this indicator in a vacuum state is also 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 only 1/4 of that at a distance of 10cm from the heating wall. The difference is significant. This phenomenon is the same as when exposed to the sun in winter, where the side that is exposed to the sun is very warm and the side that is not exposed to the sun is relatively cold. Due to the difficulty in achieving uniform and consistent radiation heat at various points in the three-dimensional space of the studio in the structure of the vacuum drying oven, and the lack of authoritative evaluation methods, this may be due to the lack of temperature uniformity parameters in the standard for electric vacuum drying ovens.