The parts of a vacuum heat treating fixture are determined by the requirements of the application and the materials to be processed. Essential aspects of a fixture design include: Materials: For temperatures up to about 980ºC, stainless steels like Types 304, 309, and 310 are common. For higher tempRead more
The parts of a vacuum heat treating fixture are determined by the requirements of the application and the materials to be processed. Essential aspects of a fixture design include:
Materials: For temperatures up to about 980ºC, stainless steels like Types 304, 309, and 310 are common. For higher temperatures, materials such as Haynes 230, nickel-based alloys like MA 956, or pure molybdenum are used. For some applications, graphite is used due to its strength at high temperatures and good thermal shock resistance.
Design Objectives: Minimizing thermal mass for efficient heating and cooling, ensuring long service life, and minimizing cost are primary design goals. Material choice largely determines service life.
Compatibility: It’s crucial to match the thermal expansion coefficient of the fixture material with the workpiece to prevent distortion.
Maintenance: Regular inspections for damage, such as cracking or distortion, are necessary. Periodic grit blasting might be needed to clean fixtures that become discolored during service. Damaged fixtures should be promptly repaired or replaced to avoid failures.
The design must also consider the reactions between the workpieces and the fixtures, such as high-temperature sintering or eutectic melting, and ensure that the fixture material is compatible with the furnace hearth.
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Hot zones are the hearth of every vacuum furnace. When purchasing a new furnace, you might face with the Hamletic doubt about hot zones: graphite-based or all-metal design hot zone? That’s the question! The graphite wafer is an excellent material. It allows operation at very high temperatures (up toRead more
Hot zones are the hearth of every vacuum furnace. When purchasing a new furnace, you might face with the Hamletic doubt about hot zones: graphite-based or all-metal design hot zone? That’s the question!
The graphite wafer is an excellent material. It allows operation at very high temperatures (up to 3000°C based on the vacuum level), has low density, reduced weight and modest thermal capacity. It creates the ideal black body conditions (emissivity about 1) inside the heating chamber for obtaining high uniformity.
All-metal hot zones are used in high demand industries where sensitive materials are processed, such as aerospace, electronics and medical. There are heat treatments that require a particularly clean environment or extreme vacuum levels. There may be different reasons: in some cases the chamber’s graphite could interfere with the process, resulting in unwanted carburation of the pieces treated. In other cases, the load could be particularly sensitive to the presence of residues in the oxygen or hydrogen atmosphere (which could lead to embrittlement of the pieces), and so graphite wafer degassing during the cycle could be damaging. In these circumstances, the user should opt for all-metal heating chambers (shields and resistor).
If you want more information on this topic and a detailed analysis of the differences, take a look at the following 2 articles:
See lessVacuum furnace hot zone: graphite vs all-metal design [1/2]
Vacuum furnace hot zone: graphite vs all-metal design [2/2]