Conclusions
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1.
Large muffle-free furnaces can be used for gas nitriding in batch operations; the hardness and depth of the case are not inferior to those produced in muffle furnaces.
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2.
Muffle-free electric furnaces are lined with standard refractories and insulating materials with a low humidifying capacity.
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3.
With sufficient blower power no reverse of the blower or the gas flow is necessary.
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4.
Fairly rapid and dependable stabilizing of the gas composition during nitriding can be achieved under the following conditions: reliable sealing of the furnace; refractory and insulating materials with a low humidifying capacity; complete chemical reduction of the lining in the start up period; low humidity of the gas supplied to the furnace; no long intervals between nitriding cycles; keeping the lining temperature at 100–120°C at the lowest.
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Literature cited
É. N. Marmer and D. M. Fershter, Calculating and Designing Vacuum Systems for Electric Furnaces [in Russian] Gosénergoizdat, Moscow (1960).
N. A. Zakatova, N. M. Boguslovich, et al., Elektrotermiya, No. 11 (1963).
L. V. Beloruchev, V. V. Dembovskii, et al., Nitriding with Dilute Ammonia [in Russian], LDNTP, Leningrad (1966).
A. G. Hotchkiss and H. M. Webber, Protective Atmospheres [Russian translation], Mashgiz, Moscow (1959).
Additional information
Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 56–60, November, 1968.
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Matin, Y.I. Muffle-free electric furnace for gas nitriding. Met Sci Heat Treat 10, 904–908 (1968). https://doi.org/10.1007/BF00649222
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DOI: https://doi.org/10.1007/BF00649222