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Single-chamber HPGQ vacuum furnace with quenching efficiency comparable to oil

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Gas has been expanded as a quenchant with the application of vacuum heat treatment technology. In the present decade, development of gas quenching systems (HPGQ) progressed due to the commercialization of low-pressure carburizing (LPC), which has come into common use. Low-pressure carburizing may gradually replace traditional atmosphere- carburizing technology and oil-quench hardening in twochamber furnaces (sealed or integral quench). In order to achieve the same or better results, vacuum-furnace quenching-system designs must be improved to achieve the same cooling efficiency as oil using gas as a modern and more environmentally friendly medium. Gas-quenching systems outperform oil in almost every aspect. Nonetheless, current technology performance is not as strong as oil quenching given the limitations of carburized-case applications in some steel grades and/or the part dimensions. For the purpose of measurement and comparison, many methods and coefficients help to determine the efficiency of a given system and quenching medium. These include: Grossmann’s Number (H), cooling rate at given temperature (typically at 705°C), λ coefficient and heat transfer coefficient (α) as the most objective. Quenching parameters of typical oil systems were determined with α coefficient within the range from 1000÷2500 W/m2K according to traditional division for slow- (1000÷1500 W/m2K), medium- (1500÷2000 W/m2K) and fast-speed oil (2000÷2500 W/m2K).[1] HPGQ vacuum furnaces may be classified as two types depending on design. Single-chamber furnaces (heat treatment and quenching occurs in one chamber without dislocation of charge) have slower cooling due to construction and material limitations. The more efficient two- and multi-chamber furnaces utilize a separated, dedicated cold quenching chamber. At present with current technology, an average α coefficient of 600÷800 W/m2K can be obtained in HPGQ separated chambers [...]

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