The graphite heating unit is the electric furnace heating heater parts which are made of the graphite materials.
The graphite has excellent electrical conductivity and thermal conductivity. In the special industrial furnace, graphite is used as a heating unit. In the early selection of industrial furnace , the graphite electrode is the heating unit, the high density of high power electrode is used as heating unit later (smelting quartz glass also use graphite electrode as the heating unit). Along with semiconductor industry development, the heating furnace which refine silicon, single crystal germanium, gallium, indium, indium and other materials select high purity ,fine structure graphite and isotropic graphite for heating. Some special industrial furnace and experimental furnace used carbon cloth or graphite cloth as the heating unit.
As the graphite heating unit in heating furnace should generate stable thermal field, so the requirements of graphite is uniform texture, stable electrical resistivity. For the graphite heating unit which manufacture single crystal, it require special graphite clean to avoid the effect of impurities for crystal purity and the total ash content should be less than 20 * 10 - 6, and some require up to 5 x 10 - 6.
The heating furnace unit has a variety of body shape, cylindrical shape, disc shape ,square canister shape, square disk shape, rectangular plate shape etc..
The graphite heating unit often appear deformation phenomenon in the process of using , this is due to the creep caused by graphite. At room temperature, the graphite creep is very small, when the temperature rises to 1700 degrees Celsius or higher, after a few hours, the creep can be observed, the residual strain in the material after the stress is eliminated and resulting in plastic deformation of graphite heating unit. Reflected in the actual use of graphite deformation caused by thermal field is not uniform, the larger the size , the deformation the smaller, the smaller particles graphite is in larger deformation than the bigger particle size graphite.
The way to prevent the graphite heating unit deformation : before use it , empty burning the (first ohmic heating) heating unit which is supported by bracket , the air sintering temperature should be greater than the actual use temperature of 100 to 200 DEG C. In order to eliminate the thermal stress cause the graphite heating unit deformation, some manufacturers will use the graphite which the maximum grain size is changed from 0.075mm to 0.5 ~ 1mm to make the graphite heater unit , and it has achieved good results.
