Open a small hole in the box and heat it from the outside.
The small irradiation holes opened in the box take advantage of the high infrared absorptivity.
The effectiveness of this heating method is proved by the “Stephan-Boltzmann law”.
Using this heating method, a high temperature electric furnace can be manufactured with a simple structure.
The energy input from the irradiation hole can not escape from other than the irradiation hole if the insulation performance of the box is ideal, so the energy is accumulated inside.
If the thermal insulation performance of the wall is good, the theoretical internal temperature of this box may reach about 1800 ° C, which is the upper heating limit of the halogen point heater.
The use of the box has long been used as “kiln,” “furnace,” “oven,” but heating objects with poor infrared absorptivity, heating of relatively large objects, and heating objects with distributed distribution are high. It is a method that can uniformly heat to high temperature with efficiency.
The key to the success of this heating method is the production of highly insulated boxes.
Unlike the common “furnace”, the heat source and the box can be separated, so they can be used inline on the belt conveyor.
Box heating can also be a two-piece structure in which the object to be heated can be taken in and out.
In addition, the shape of the box can be any shape such as a triangle, a sphere or a cylinder, as well as a square as shown in the figure.
The inside wall of the box is ideally a mirror surface with a high reflectance like gold plating, but smoke may be generated from the object to be heated, and a high mirror surface is difficult to maintain.
In that respect, ceramic boards and silica boards are almost maintenance-free because they maintain high reflectivity by self-cleaning when they become hot due to the heat insulation.
In general, as long as the insulation performance is good, the material is not selected.
(It is the same as high reflectivity because it is re-radiated from the wall as the temperature rises).
Since ceramic boards and silica boards require a temperature rise time on the wall, the temperature rise time of the object to be heated will be slightly longer.
The time loss is just rising, and in continuous work the temperature inside the furnace is rising, so there is no time loss.
There is also a method of heating in a vacuum chamber using quartz glass for the irradiation hole.
Since the inside can be made non-oxidative atmosphere, non-oxidative heating processing becomes possible.
Or you can make some kind of chemical reaction in a special gas.
It is particularly convenient for electric furnaces that require cleanness.
There is no heating element inside the furnace, so the inside is not dirty.