Several small issues with vacuum drying oven

1The reason for the difference between the instrument reading of the electric 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 vacuum chamber wall 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 located in the vacuum chamber can only accept radiant heat, and the blackness of the glass rod cannot reach1,A considerable portion of the radiant heat has been refracted,Therefore, the temperature value reflected by the glass rod thermometer is definitely lower than the temperature reading of the instrument. Generally speaking,200CThe temperature reading of the instrument during working conditions differs from the reading of the glass rod thermometer30CInside is normal.

If the temperature sensor of the temperature control instrument is arranged inside 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 cannot be eliminated, 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 operational perspective, you can use the display correction function of the temperature control instrument * to solve it.

2The reason why the electric vacuum drying oven does not have a temperature uniformity parameter

General electric heating(blast)The drying oven is equipped with temperature uniformity parameters:The natural convection drying oven is a product of the upper limit of the working temperature and3%The forced convection drying oven has a working temperature upper limit multiplied by2.5%Only*Why does the electric vacuum drying oven not have a temperature uniformity parameter?

The possibility of achieving uniform temperature in the working chamber through the movement of gas molecules in a vacuum drying oven is almost non-existent. Therefore, conceptually, we can no longer consider conventional electric heating(blast)The temperature uniformity defined by the drying oven is applied to the vacuum drying oven.

Setting this indicator under vacuum conditions is also meaningless. The amount of thermal radiation is inversely proportional to the square of the distance. same-an object,Distance from heating wall20cmThe radiation heat received by the location is only at a distance from the heating wall10cmThe location1/4The difference is significant. This phenomenon is similar to the fact that in winter, when exposed to the sun, the side that is exposed to the sun is very warm, while the side that is not exposed to the sun is relatively cold Due to the structure of the vacuum drying oven.It is difficult to make every point in the three-dimensional space of the studio(Garden sphere)Uniform and consistent radiant heat,At the same time, there is also a lack of**The evaluation method may be due to the lack of temperature uniformity parameters in the standard for electric vacuum drying ovens.

3The reason for first vacuuming and then heating up the electric vacuum drying oven

1)The purpose of placing the workpiece in a vacuum box for vacuuming is to remove any gas components that can be extracted from the material of the workpiece. If the workpiece is heated first, the gas will expand when exposed to heat. 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 procedure of heating up 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 a high temperature rise of the vacuum pump and a possible decrease in its efficiency.

3)The heated gas is directed towards 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 indication errors in the vacuum pressure gauge.

The correct usage method should first evacuate and then heat up. When the rated temperature is reached and the vacuum degree is found to have decreased, add some more suction appropriately. This is beneficial for extending the service life of the equipment.