The cavity heating method of the vacuum pretreatment equipment is divided into two types: internal heating and external heating. The external heating is heating outside the cavity, and then the heat is transmitted through the cavity wall. Finally, heat is transferred through heat radiation. The internal heating is performed directly inside the chamber. Compared with the internal heating method, the external heating method has hysteresis, and the internal heating method is more accurate in controlling the temperature than the external heating, so the internal heating method is selected.
The selection of the heater is also very important. The plate-type heating plate that is easy to install is used for internal heating. The surface of the heating plate is a mirror-finished stainless steel, which is more advantageous in terms of flatness than polishing directly by the wall of the cavity, which is more conducive to the conduction of heat by heat radiation.
Because the interior of the equipment cavity is a regular rectangular solid body, the use of one side of the heat radiation method is not ideal, and heat conduction can not reasonably cover the internal space of the entire cavity. After trial and error, a heating plate is installed directly above, directly below, on the left side, and on the right side of the equipment cavity to heat the inside of the cavity by means of surface heat radiation.
Because the equipment adopts the four-way heating method of upper, lower, left, and right sides in a vacuum state, it is much more complicated than simply heating all the way. This is a difficulty in temperature control. Therefore, PID is used for temperature control adjustment, and the temperature control thermocouple is set inside the cavity so that the temperature in the cavity can be better controlled.
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