Heating – Work chamber having heating means – Combustion products heat work by contact
Patent
1998-02-10
1999-09-28
Walberg, Teresa
Heating
Work chamber having heating means
Combustion products heat work by contact
432179, 432180, F27D 1700
Patent
active
059576847
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an atmosphere gas heating method and apparatus for continuously heating and supplying an atmosphere gas necessary to heat an object to be heated. The present invention is particularly suitable for when an object to be heated (a tundish body in the case of a tundish) must be heated in a non-oxidizing or reducing atmosphere, as required for tundishes used in heating furnaces, annealing furnaces, heat-treating furnaces and continuous casting for, e.g., blooms and strips.
BACKGROUND ART
Hitherto, there are known the following methods for heating steel materials in various furnaces such as heating furnaces, annealing furnaces and heat-treating furnaces, for example, under a non-oxidizing condition. edited by The Iron and Steel Institute of Japan, (1983), p. 31)
According to this method, a radiant tube is disposed in a heating furnace, etc., a high-temperature combustion exhaust gas from a burner unit or a gas having high temperatures raised by the exhaust gas is supplied to the radiant tube, and a steel material is heated with heat radiating from an outer wall of the radiant tube toward the interior of the furnace. Because a furnace atmosphere contacting the steel material can be freely set, it is easy to bring the furnace atmosphere into a non-oxidizing state. Gijutsu Koza (Nishiyama Memorial Technology Lecture), (1983), p. 75)
According to this method, a reducing flame formed in an outer portion of a flame produced by a burner unit is directly put into contact with a steel material to heat it in a reducing atmosphere. No. 120 (1988), p. 24)
According to this method, a steel material is heated with such a two-layer atmosphere adjustment that a steel material is surrounded by a non-oxidizing atmosphere produced by imperfect combustion, and at the same time secondary combustion is performed in a not-yet-burnt gas area outside the non-oxidizing atmosphere.
Although the above heating methods are adapted for use with heating furnaces, etc. for steel materials, similar methods are also employed in heating nonferrous metals such as aluminum and copper.
The conventional heating methods stated above however have problems as follows.
This method is very superior in that an oxidizing gas containing H.sub.2 O produced by combustion, extra O.sub.2 during combustion, etc. can be completely isolated from the furnace atmosphere.
But the following problems are encountered in this method.
a) When the temperature of a heating furnace is as high as 1200.degree. C., for example, there is no effective tube endurable against such a high temperature. In other words, the radiant tube itself is broken due to thermal stresses and high-temperature creep; hence the life of the radiant tube at the high temperature is short.
b) Because the burner unit performs combustion in a narrow space of the radiant tube, there is a limit in combustion capacity of a burner itself.
This method requires the reducing atmosphere to be formed near the steel material. The following problems are therefore encountered in this method.
a) From the point of operation, there are restrictions in, e.g., the surface temperature (900.degree. C. or below) of the steel material and combustion conditions (load, air/fuel ratio, burner capacity), etc.
b) From the point of equipment, there are restrictions in, e.g., the distance from the surface of the steel material to the burner.
c) Thermal efficiency is poor because only part of combustion heat available from fuel is utilized. For the above reasons, this method cannot be applied to, e.g., heating furnaces for rolling steel materials.
The following problems are encountered in this method.
a) Because of forming a two-layer atmosphere, burner layout in the furnace suffers from restrictions in, e.g., that a roof burner and a side burner cannot be used in a combined manner. This raises a problem in evenness of the heating temperature when large-size steel materials are to be heated.
b) A heating ability per unit volume of the furnace is smaller than conventional burners. The
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patent: 4666403 (1987-05-01), Smith
patent: 4671346 (1987-06-01), Masters et al.
patent: 5431147 (1995-07-01), Tanaka et al.
patent: 5839894 (1998-11-01), Schedler et al.
Kawasaki Steel Corporation
Lu Jiping
Walberg Teresa
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