The thermal field is the core part of the vacuum resistance furnace, and its quality directly affects the performance of the furnace and its operating costs. There are various designs of thermal fields, and the specific design scheme chosen is mainly based on the specific analysis of the process flow. The thermal field of most vacuum resistance furnaces includes four main components: the heater and its connecting parts, the heat insulation component (or reflective screen), the thermal field support component, and the workpiece-bearing hearth. These accessories often need to be replaced regularly due to material issues or usage time issues. So under what conditions do graphite thermal field accessories need to be replaced, and under what conditions do they need to be cleaned?
1. In principle, if the life span has reached the replacement period, it needs to be replaced (or let an experienced person identify it and decide whether to continue using it). For those that have not reached the end of their life and are not in use temporarily, seal them in a plastic bag, put them in a carton and pack them, indicate the furnace number, number of furnaces, reason for replacement, source, date, and keep them properly.
2. For those that are partially damaged (such as three valves broken and one valve broken) but have not reached the end of life, they can be used or replaced (for new three-valve crucibles with only a few furnaces, the workshop supervisor will decide whether to use them after judging them. Those that can be used and can make up a set will be used, and those that can be used but are not used temporarily will be sealed and kept. When sealing and storing it for reuse, it is recommended to use it in a purification furnace.
3. Every time the furnace is dismantled, clean the oxides in the thermal field and clean the silicon infiltration on the graphite parts. The guide tube and insulation cover should be carefully wiped clean to avoid accidents of debris contaminating the raw materials. When handling graphite parts, in addition to paying attention to personal safety, you must also handle them with care and pay attention to the safety of the graphite parts.
4. Strictly follow the operating procedures for heating, chemical mixing, melting back, furnace shutdown, etc., and protect graphite parts. After each furnace is dismantled, the graphite accessories must be carefully cleaned, the conditions of the seed crystals and various graphite thermal field accessories must be carefully checked, and detailed records must be kept.
5. Check whether there are cracks in graphite accessories, especially graphite crucibles, graphite trays, and graphite crucible rods. If cracks occur, report them to the workshop supervisor immediately and replace them. If there are silicon stains, you should make a judgment or report to the workshop supervisor. The shift leader will be responsible for inspection and review before using the 5 furnaces before the expected service life. After using the 5 furnaces before the expected service life, the workshop supervisor will be responsible for inspection and review.
6. After the service life of graphite accessories expires, the graphite accessories (graphite tray, crucible rod, graphite crucible) and other parts that may cause heavy losses due to overdue use should be removed and replaced with new ones. The replaced graphite accessories should be sealed and processed after joint review by the single crystal workshop, technical department, and production department. Other accessories, such as heaters, insulation cylinders, flow guide cylinders, etc., should be carefully inspected to see if there are microcracks and defects. In principle, these graphite accessories can continue to be used if there are no defects mentioned above. Detailed records must be kept of graphite thermal field accessories that appear to be stuffed.
7. Keep detailed records of graphite thermal field accessories that cause accidents. Detailed records should be kept of problematic graphite accessories and placed in designated locations to prevent confusion.