Why is the vacuum oven first vacuumed and then heated?

Why does the vacuum oven first vacuum and then heat the vacuum oven? Why do you have to vacuum and then heat up, instead of heating up and then vacuuming? 1) The product is placed in a vacuum box to draw vacuum to remove the material of the product. Gas composition. If the product is first heated, the gas expands when heated. Due to the excellent sealing of the vacuum box, the enormous pressure generated by the expanding gas may cause the observation window tempered glass to burst. This is a potential danger. This can be avoided by pressing the vacuum first and then heating up the heating procedure. 2) If the heating air is pumped out by the vacuum heating and vacuuming process, the heat will be brought to the vacuum pump, which will cause the vacuum pump to rise too high, which may reduce the efficiency of the vacuum pump. 3) The heated gas is directed to a vacuum gauge, and the vacuum gauge produces a temperature rise. If the temperature rise exceeds the operating temperature range specified by the vacuum gauge, the vacuum gauge may cause an indication error. The correct method of use should first vacuum and then heat up. After the rated temperature has been reached, if it is found that the degree of vacuum has decreased, then add it appropriately. This is advantageous for extending the life of the device.