As a type of constant temperature drying oven, vacuum drying oven is especially suitable for drying heat-sensitive, easy to decompose, easy oxidation and other high-temperature resistant samples, as well as complex and precise mechanical parts, porous samples, etc., and the principle of use is that the boiling point of water or solvent becomes low under negative pressure, and the water can be volatilized at low temperature, to achieve the purpose of drying.
Therefore, the vacuum drying oven has the advantages that ordinary drying ovens do not have: it can quickly dry samples that are not easy to dry, eliminate the possibility of sample oxidation or even thermal explosion in vacuum conditions or inert gas environment, and there will be no loss in the drying process of powdery samples.
The vacuum drying oven is not a motor blower, its heating method is to heat the inner tank, which uses heat radiation to bake the items in the box, the radiation of heat is inversely proportional to the distance, so how to achieve a uniform temperature inside the vacuum drying oven is particularly important. Kenton's KZ series of vacuum drying ovens has the original inner cavity preheating technology and separator heat transfer technology, which increases the contact area between the separator and the preheating chamber so that the temperature of the separator and the preheating chamber is consistent.
At present, the small vacuum pump on the market is simply divided into two types: oil-containing and oil-free, with 1L, 2L, 4L to choose from, and it is generally recommended to choose an oil-free vacuum pump. When using the oil-impregnated vacuum pump, it should be noted that when the vacuum oven does not need continuous pumping, the vacuum valve on the oven should be closed first, and then the power supply of the vacuum pump motor should be turned off, otherwise the vacuum pump oil would be leaked into the oven. In order to prolong the service life of the vacuum pump and avoid corrosion of the inside of the vacuum pump after some solvents are pumped out, it is recommended to install an adsorption filter device in the oven and in the middle of the vacuum pump.
There are several points to note when using a vacuum drying oven:
Vacuum first and then heat up, avoid heating first and then open the vacuum pump, and then add a moderate pump when you find that the vacuum value has a certain decrease after reaching the set temperature value.
In the same way, at the end of the experiment, the vacuum valve should be turned off first, then the power of the vacuum pump, and finally the temperature control switch.
After the vacuum drying oven is used, it should be deflated and depressurized first, otherwise the door will not be opened.
Take out the sample in time to avoid re-contamination of the sample by the condensed liquid on the inner wall of the chamber.
Therefore, when choosing a vacuum drying oven, the tightness of the vacuum drying ovenis the first factor to be considered. GB/T 29251-2012 stipulates that after the ultimate pressure of the vacuum drying oven with a studio volume of 0.1m³ and above reaches 0.3kPa, the ultimate pressure at the ambient temperature for 24h should not be greater than 8kPa. The second factor is the thickness of the plate. Due to the vacuum environment in the vacuum drying oven, in order to prevent the atmospheric pressure from crushing the oven, the thickness of the shell should be slightly larger than that of the air blast drying oven. Then, according to the application, choose the size, material, accessories, etc. The price of vacuum drying ovens for different purposes is also different. The desk-top vacuum drying oven on the market is relatively small, with thousands of yuan, which is more suitable for laboratory use. The low-temperature vacuum drying oven used in the food and drug industry is more expensive according to the size and material requirements.
Finally, it should be noted that the vacuum drying oven does not have the parameter index of temperature uniformity, which is different from the ordinary electric constant temperature drying oven. The temperature displayed and set on the vacuum drying oven meter is the temperature at which the inner tank wall is heated, and is not the actual temperature inside the oven.