Three aspects of performance of microwave vacuum drying equipment

- May 06, 2019 -

The performance of microwave vacuum drying equipment is described in three aspects: (1) Under vacuum condition, microwave vacuum drying chamber reduces the breakdown field strength of air due to the reduction of vacuum degree, which makes gas molecules easy to be ionized by electric field, resulting in gas breakdown and arc discharge. This phenomenon is most likely to occur at the microwave feed coupling port and the concentration of field strength in the chamber, which will not only consume microwave energy. It can also damage parts and produce larger microwave reflection, shortening the service life of magnetron. Under the given range of vacuum degree and microwave power, the structure and size of microwave vacuum drying chamber should be reasonably designed to ensure that the air breakdown field strength in the chamber is within the safe range. The structure of microwave vacuum drying chamber should also ensure the uniformity of microwave field to avoid overheating due to strong electric field in one part of the material medium and insufficient heating due to weak electric field in the other part. At the same time, the structure of microwave vacuum drying chamber should also meet the design requirements and specifications of pressure vessels. According to the above design principles, the main structure and size parameters of microwave vacuum drying chamber were determined.

(2) The microwave vacuum sealing structure in the microwave vacuum drying equipment connection, need to simultaneously carry out microwave and vacuum double sealing, microwave leakage control in the safety standard range, vacuum should also meet the corresponding design requirements. Therefore, at the interface of microwave vacuum drying chamber and energy feeding device, flanges and inlet and outlet ports, suitable microwave sealing materials should be used to prevent microwave leakage, and rubber rings should be used for vacuum sealing to prevent the vacuum degree from decreasing due to system leakage. According to the different structural types of joints, conductive rubber strips, conductive metal rings and soft ferrites were used as microwave sealing materials.

(3) Continuous feeding and discharging structure of continuous feeding and discharging structure can ensure continuous production of equipment. Because of frequent feeding and discharging actions, this structure needs better sealing to maintain the vacuum of the whole system and prevent microwave leakage, so sealing is the key of this part. The traditional vacuum feeding and discharging structure adopts the rotating air shutter structure, which has good continuous transmission and uniform feeding, but is easy to plug, so that the sealing parts wear seriously. After the sealing parts wear, the vacuum system will leak and the vacuum degree will be unstable. At the same time, microwave radiates outward along the wear gap of the seal, which leads to microwave leakage exceeding the safety radiation standard. In this study, the material was fed into the microwave drying chamber from the feeding hopper, and then discharged from the chamber to the atmospheric pressure environment.

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