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Versatility in hot-press furnace system design is key to handling high-temperature processing, such as hot compacting of oxides, nitrides, borides, carbides, sulfides and their mixtures; sintering ceramics and powder metals and diffusion bonding, which is carried out in extreme environments of high temperatures and pressures.
Hot press furnace systems are used to process ceramic, ceramic/metal matrix, and intermetallic composites. Typical applications include diffusion-bonding studies; hot compacting of oxides, nitrides, borides, carbides, sulfides and their mixtures to near theoretical densities; and sintering ceramics and powder metals. A hot-press furnace system typically is capable of operating temperatures from 500 to 2500°C (930 to 4530°F), up to a maximum temperature of 3000°C (5430°F). Because of the extremely high operating temperatures, system design is critical to ensure safe, reliable operation and long service life.
Furnace system design criteria include type of atmosphere in which the load is processed, including inert gas, such as helium, argon and hydrogen and reactive (reducing) gases and vacuum partial pressure. The system also includes a mechanical vacuum pump to evacuate and backfill with process gas or to maintain an operating vacuum level of 10^sup -10^ torr. High vacuum pumps are available for an operating vacuum level up to 10^sup -10^ torr. The heat zone design is based on temperature rating. Generally, three major components make up a hot press furnace system including a controlled-atmosphere furnace, hydraulic press system and vacuum pumping and process-gas control systems.
Controlled-atmosphere furnace
The controlled-atmosphere furnace consists of a furnace chamber, heat zone, power supply package and control instrumentation cabinet. The chamber assembly is a double-wall, water-cooled configuration with water-cooled full opening, hinged door access.
The heat zone is the most vital component of the furnace, consisting of heating elements, insulation or heat shields, and a water jacket for additional cooling if operating temperatures exceed 2000°C (3630°F). Proper selection of element, insulation and heat shield materials (based on temperature and process requirements) is critical for proper operation, as shown in Table 1. Maximum operating temperature varies depending on hot zone materials and process gas. The compatibility of these combinations is shown in Table 2.
Geometry of the heat zone and heating-element location also are critical to proper operation. For example, a cross section of a furnace designed with graphite...