As a new type of material, graphite has excellent characteristics, therefore, it is widely used in various fields, and has achieved remarkable resultsGraphite can be used in a high-temperature environment, in a normal temperature environment, the general metal strength is higher than the strength of graphite, but when the temperature changes, the mechanical strength of graphite will continue to increase. Graphite materials have a high melting point and low vapor pressure, and a reaction will occur in the vacuum furnace, thus playing a purification role. In this way, workpiece handling is guaranteed even at low vacuum levels, simplifying the vacuum system and providing significant economic benefits.
There are many types of graphite heating elements in vacuum graphite furnaces, and their structural forms are also distinctive. (1) Single rod.
The current is introduced into the graphite rod from both ends, where L1 is the heating part and L2 is the joint part. When the graphite rod is specially treated, it becomes hollow, the heat generation becomes larger, and the heating time is shortened, so the use of electricity is reduced.
According to the characteristics of the graphite blank, the joint part and the working part cannot be regarded as a whole. In the production process, each part is carried out separately and the nut is used. Due to the defects of the graphite material itself, it is best to use coarse thread connection to effectively control the diameter of the screw, and at the same time, it is necessary to control the length of the engraved thread to ensure that the connection has sufficient conductive area. When the current used is relatively large, in order to ensure effective contact between the threaded connection and the electrode joint, graphite paste can be applied, so that the conductive area will become larger.
2) Tubular heating body.
Tubular heaters include single and triple phases, which are cut from one end of the tube and the other end is not, so that the heating length becomes longer and, therefore, the resistance becomes larger. At the same time, the strength of the heating element can be improved by increasing the thickness of the incision end, the heating part and the thickened part are L1 and L2 respectively, and the resistance of the upper and lower parts is added to the total resistance.
The three-phase tubular heating body, which is very similar in structure to the single item, is also cut from one end of the tube and divided into three parts. After cutting, three gaps will be formed, and these three parts have the same resistance, among which, a, b, and c are the three-phase lead-out ends. In practice, if you need to increase the resistance value, you can make an appropriate number of long seams for each upward direction.
3) Combined rod heating element.
Tubular heaters are generally used in resistance furnaces, but they are only used in small high-temperature vacuum furnaces due to the size of the material. Due to the relatively small size of the material, the tubular heating element cannot be used in a large heat treatment furnace, and the processing requires a large investment, and if the part is damaged during use, the whole will not be usable, so the risk is relatively high.
The combined rod heater, which is a new type of heater that has a specific temperature range for use in vacuum furnaces. The structure was analyzed, and the graphite rod was used as a heating element. Therefore, the size of the raw material does not affect this, which is not only very easy to process, but also relatively low manufacturing cost. When the parts are damaged in use, the parts can be replaced, which is very convenient to repair and avoid unnecessary economic losses.
The whole structure is composed of multiple parts, including graphite heating rods, graphite conical ferrules, etc. Among them, the graphite rod is a heating element, and the graphite conical ferrule can be fixed on the graphite rod by using the graphite conical ferrule, which is located on the graphite conductive ring at the upper and lower ends. Graphite bolts are required to connect the graphite conductive ring and the 99 porcelain insulated connecting ring. Control the graphite heating rod. The number of graphite conductive rings and lay them in a suitable position, so that the graphite heating rod will form a series and parallel circuit, and finally connect the rod with an electrode to obtain external power supply support for effective heating.
4) Plate heating body.
Plate heating body, which is a new heating element, has obvious advantages, mainly reflected in the convenience of manufacturing, large radiation area, etc., and the practical application effect is good.
Square studios are more common flat plate heating bodies, which are generally composed of an appropriate number of blocks in series and parallel according to the area requirements of the effective heating zone. In the whole production process, the graphite blank is first processed to change the original shape, and then the groove treatment is carried out to form a loop. It should be noted that the electrode outlet needs to be thickened. Combined with the requirements of furnace temperature uniformity, plate heating elements are arranged on both sides and tops of the furnace, which will form a square studio, so as to play a multi-surface heating role.
5) Graphite cloth and graphite belt heating element.
With the rapid development of science and technology, the way of making heating elements has also changed, graphite fibers can be woven into graphite cloth or graphite tape, and multiple strips can be effectively processed, which will form single-phase and three-phase power supply. Graphite cloth is better than graphite in practical application, so it has a broad application space in the future. Figure 4 shows a graphite tape fixing method, which is relatively simple and easy to replace the elements. When determining the size of graphite fiber preparation, it is necessary to analyze the resistivity requirements and combine them with the space layout requirements in the furnace to ensure the rationality of graphite fiber preparation.