1.  Preheating stage: At this stage, the oven is in a low vacuum state, and the water vapor is used for convective heat transfer, so that the temperature of the coil and iron core can rise evenly and quickly. During the preheating process, evaporation and vacuumizing are continuously performed. Evacuate the water vapor to prevent it condensing on the surface of the workpiece. This reciprocating cycle makes the uniformly warm up, and can continuously evaporate the water in the deep insulation wood.

2.  Main drying stage: After the preheating stage, the temperature of the workpiece reaches a predetermined value, and then it enters the main drying stage. The process is that close the main valve after vacuuming, wait for the temperature and vacuum degree reach the schedule, evacuate and then close the main valve ... so reciprocating cycle. At this stage, when vacuumizing the water vapor is evacuated, and the vacuum degree is raised. When the vacuum valve is closed, the water in the insulation layer is continuously evaporated, so the vacuum is reduced. At this time, these water vapors are involved in convective heat transfer to the workpiece body. The process is not only removes water vapor, but also takes into account the transfer of heat, so that water is continuously evaporated from the deep side.

3.   Final drying stage: In the main drying stage, as a large amount of water is evaporated and pumped out, the vacuum degree of the drying oven will gradually increase. When the degree of vacuum reaches the required value of the process, it enters the final drying stage. At this time, the drying oven is continuously evacuated, and the residual moisture in the insulation layer is continuously removed until the drying is completed.