Industrial electric heating furnaces – Arc furnace device – Furnace body detail
Reexamination Certificate
2000-10-26
2001-12-11
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Arc furnace device
Furnace body detail
C373S071000, C373S075000
Reexamination Certificate
active
06330269
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus for metallurgical processing, particularly steelmaking. More particularly, the invention relates to a cooling apparatus for a metallurgical furnace. More specifically, the invention relates to a type of pipe used in a cooling apparatus for an electric arc steelmaking furnace, and the apparatus which incorporates the pipe therein.
BACKGROUND OF THE INVENTION
Steel is made by melting and refining iron and steel scrap in an electric arc furnace (EAF). Today, the EAF is considered by those skilled in the art of steel production to be the single most critical apparatus in a steel mill or foundry. Consequently, it is of vital importance that each EAF remain operational for as long as possible.
Structural damage caused during the charging process affects the operation of an EAF. Since scrap has a lower effective density than molten steel, the EAF must have sufficient volume to accommodate the scrap and still produce the desired amount of steel. As the steel melts it forms a hot metal bath in the hearth or smelting area in the lower portion of the furnace. As the volume of steel in the furnace is reduced, however, the free volume in the EAF increases. The portion of the furnace above the hearth or smelting area must be protected against the high internal temperatures of the furnace. The vessel wall, cover or roof, and duct work are particularly at risk from massive thermal, chemical, and mechanical stresses caused by charging and melting the steel. Such stresses greatly limit the operational life of the furnace.
Historically, the EAF was generally designed and fabricated as a welded steel structure which was protected against the high temperatures of the furnace by a refractory lining. In the late 1970's and early 1980's, the steel industry began to combat such stresses by replacing expensive refractory brick with water-cooled roof panels and water-cooled sidewall panels located in portions of the furnace vessel above the smelting area. Water-cooled panels have also been used to line furnace duct work. Existing water-cooled panels are made with various grades and types of plates and pipes.
Using water-cooled panels has reduced refractory costs and has also enabled steelmakers to operate each furnace for a greater number of heats. Furthermore, water-cooled equipment has enabled the furnaces to operate at increased levels of power. Consequently, production has increased and furnace availability has become increasingly important.
Although water-cooled panels last longer than brick refractory, the panels have problems with wear and are subject to damage. Critical breakdown of one or more of the panels commonly occurs within a few months of furnace operation. When such a breakdown occurs, the EAF must be taken out of production for unscheduled maintenance to repair the damaged water-cooled panels. Since molten steel is not being produced by the steel mill during downtime, opportunity losses of as much as five thousand dollars per minute for the production of certain types of steel can occur. In addition to decreased production, unscheduled interruptions significantly increase operating and maintenance expenses.
To increase the life of water-cooled components, an effort is made to promote slag adherence to the surface of the water-cooled equipment. Adhered slag “freezes”, that is solidifies, to the water-cooled equipment thereby forming a thermal and chemical barrier between the cooling equipment and interior of the furnace.
In prior art furnaces, slag is encouraged to stick to the cooling equipment by welding studs, fins or cup like members onto the surface of the equipment, or by using slag bars or other similar items. For example, U.S. Pat. No. 4,221,922 discloses a fin welded to a water-cooled panel. However, these typical methods cause stress risers, that is, the beginning of cracks at the molecular level within the material of the water-cooled pipes. The stress risers are caused by localized heating differentials or stress differentials during the manufacture of the pipes. As an electric arc furnace cycles, the components expand and contract, further breaking down the grain structure in the material of the pipes and broadening the stress risers, until a pipe in the cooling apparatus fails prematurely. Water leaking from a damaged pipe into the furnace can potentially lead to catastrophic reoxydation of hot metal in the furnace. Hence, a damaged cooling element must be timely replaced.
A need, therefore, exists for an improved water-cooled furnace panel apparatus which remains operable longer than existing comparable panels and continues to operate, despite some structural damage, until scheduled maintenance occurs.
OBJECTS OF THE INVENTION
The present invention is directed to a unitary heavy-walled, steel, iron, or ferrous alloy pipe for use in a cooling panel in an electric arc furnace. According to the present invention, the unitary pipe includes a tubular section, an elongate ridge, and a base section. The ridge and the base section are formed on the exterior surface of the tubular section and oppose each other.
According to another aspect of the present invention, the unitary pipe is formed by extrusion in which the mass of the half of the tubular section which includes the ridge is substantially equivalent to the mass of the other half of the tubular section which includes the base section.
According to a further aspect of the present invention, the pipe includes the following features individually or in combination: a plurality of elongate ridges, radially extending ridges, ridges of varying lengths and segmented ridges.
According to another aspect of the invention, a plurality of unitary pipes are interconnected in serpentine fashion and connected to a plate. The plate is connected to the interior of an electric arc furnace.
According to another aspect of the present invention, a method is provided for cooling the interior wall of an electric arc furnace. The method includes providing a cooling panel having a plurality of extruded unitary pipes. The pipes have a tubular section, an elongate ridge and a base section. The method further includes the steps of attaching the cooling panel to the interior of the electric arc furnace, retaining transient matter from the electric arc furnace on the elongate ridge and removing the tube assembly from the electric arc furnace.
SUMMARY OF THE INVENTION
The invention is a heavy-walled pipe for a cooling panel, the pipe having fin-like structures extending outwardly from the surface of the pipe. An array of the pipes are aligned along the inside wall of an electric-arc furnace above the hearth thereby forming a cooling surface between the interior and wall of the furnace.
The fins, extending from the pipe surface, tend to retain slag and spatter material from the iron/slag mixture in the electric-arc furnace during the refining of molten metal in the furnace. The slag is collected by the fins and retained against the pipe surface. The retained slag acts as an insulating barrier between the molten iron material and the cooling pipes as well as the wall which carries the pipes. This protects the wall and pipes from the extreme heat and chemically reactive conditions within a typical electric-arc furnace and, consequently, increases the longevity of the pipes and the cooling panel apparatus as a whole.
REFERENCES:
patent: 1774150 (1930-08-01), Murray
patent: 1844407 (1932-02-01), Murray
patent: 2239662 (1941-04-01), Bailey
patent: 3294162 (1966-12-01), Loehlein et al.
patent: 4097679 (1978-06-01), Fukumoto et al.
patent: 4122295 (1978-10-01), Nanjyo et al.
patent: 4135575 (1979-01-01), Gersch
patent: 4221922 (1980-09-01), Okimune
patent: 4351055 (1982-09-01), Bick et al.
patent: 4455017 (1984-06-01), Wunsche
patent: 4458351 (1984-07-01), Richards
patent: 4559011 (1985-12-01), Gritsuk et al.
Kincheloe David P.
Manasek Richard J.
Amerifab, Inc.
Hoang Tu Ba
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