Metallurgical apparatus – Means treating solid metal – By contact with gas
Reexamination Certificate
2000-12-13
2004-02-03
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means treating solid metal
By contact with gas
C432S127000
Reexamination Certificate
active
06685879
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates generally to steel production, and more particularly, but not necessarily entirely, to a steel heating furnace with particular use in reheating previously cast steel.
In the steel making industry, it is known to produce steel and store it in slabs in sizes required by the provider. This is often accomplished by (i) dispensing newly formed steel from a continuous caster in the form of slabs, during which the steel slabs unavoidably cool to a temperature below the desired working temperature of the steel, (ii) feeding the slabs of steel through a reheat furnace to thereby heat the steel slab to a working temperature, and then (iii) compressively rolling the steel slabs into a reduced thickness. This type of steelmaking system is thus summarized briefly as comprising a caster, reheat furnace, and roll line, utilized in sequence in that order.
A newly cast continuous slab of steel is initially quite thick as it is dispensed from the caster. The slab might for example be 25.4 cm (10 inches) thick. Although the steel has a temperature of perhaps 815° C. (1500° F.) when it is dispensed from the caster, it generally requires a working temperature maintained above 982° C. (1800° F.) while it is rolled into the desired thickness. Naturally, the hotter the steel, the easier it can be rolled, such that a temperature of 2200° F. is preferred. The newly cast steel slab can either be stored somewhere to be reheated and rolled later, or it can be heated immediately to the higher working temperature and rolled right after casting. Naturally, less energy is required to heat the steel slab from 815° C. (1500° F.) to a working temperature above 982° C. (1800° F.) directly after casting than would be required if the steel is stored temporarily after casting and allowed to cool to ambient temperature prior to rolling. It is therefore desirable, in steel casting operations, to utilize the caster, reheat furnace, and roll line in direct succession.
It is futile to attempt to roll steel unless the slab of steel is heated to a working temperature well above 982° C. (1800° F.), such that the temperature of all portions of the steel is maintained above 982° C. (1800° F.). When the steel slab is heated to the working temperature, it is fed through the rollers in the roll line, which roll and compress the steel to a reduced thickness using roll line machinery and processes known to those having ordinary skill in the field. For example, a slab of steel cast at 25.4 cm (10 inches) thick can be reheated and rolled to a reduced thickness of 0.16 cm (1/16 of an inch) or thinner.
Several attempts have been made to construct a steel heating furnace that works efficiently. Many such attempts are described in the following U.S. patents, which are incorporated herein by reference: U.S. Pat. No. 1,539,833; U.S. Pat. No. 1,791,166; U.S. Pat. No. 1,833,132; U.S. Pat. No. 2,883,172; U.S. Pat. No. 2,929,614; U.S. Pat. No. 3,770,103; U.S. Pat. No. 4,243,378; U.S. Pat. No. 5,441,407; and U.S. Pat. No. Re. 19,205.
The known steel reheat furnaces generally burn natural gas or a hydrocarbon fuel within the furnace to provide the heat. The gas or fuel combusts to form super-heated water vapor and carbon dioxide. The water vapor reacts with the steel to form a magnetic iron oxide (Fe
3
O
4
) on the surface of the steel being reheated, in the form of an undesirable crusty, abrasive surface scale. The iron oxide scale must be removed before rolling, otherwise, the iron oxide scale becomes rolled right into the steel surface during rolling and becomes a defect in the steel, such defects sometimes being referred to as “pits.” Sometimes slivers of the iron oxide are rolled into the steel.
The prior art reheat furnaces are not sealed from the atmosphere, and in fact have openings along their sides. To prevent the gas-burning flames from venturing through the open sides and outside the furnace, a pressure monitoring system is utilized in which the pressure within the furnace matches the surrounding atmospheric pressure. This pressure matching system of operation, when utilized in a reheat furnace having side openings, carries the risk of leaking some gas into the atmosphere because the matching pressure varies and therefore cannot be completely reliable.
Common types of reheat furnaces include a “pusher furnace,” a “walking beam” furnace, and a “roller hearth” or “tunnel” furnace. In the walking beam furnaces and in the pusher-type furnaces there is a high degree of surface contact of the steel slabs with the slab supports, particularly in the pusher-type furnaces. Such surface contact causes the slab supports to absorb heat from the steel, often undesirably scoring the slab and producing “cold spots” on the steel slab. These cold spots can result in an inconsistent thickness in the rolled steel. Although the conventional roller hearth type furnace has the advantage of uniformly heating the steel slabs without damaging or marking the surface, it also has the disadvantage of causing excessive heat loss, and the rollers are highly expensive.
The prior art reheat furnaces are thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
In view of the foregoing, it will be appreciated that a steel heating furnace that can significantly reduce oxidation of the surface of the steel, and provide for a controlled atmosphere during reheating, and reduce cold spots and thus increase the consistency of thickness of rolled steel, and improve efficiency of reheating steel, and avoids damaging or marking the surface of the steel, would be a significant advancement in the art.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a steel heating furnace that is simple in concept.
It is another object of the present invention to provide such a steel heating furnace that minimizes the occurrence of iron oxide forming in the surface of the steel.
It is a further object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which the use of hydrocarbon fuel, such as natural gas, is avoided during operation.
It is an additional object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which the occurrence of water vapor within the furnace is minimized.
It is yet another object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which a carbon monoxide atmosphere is maintained within the furnace during operation.
It is a still further object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace capable of enabling steel to be heated with an unoxidized finish.
It is an additional object of the present invention, in accordance with one aspect thereof, to provide a steel heating furnace in which steel within the furnace is more evenly heated.
The above objects and others not specifically recited are realized in a specific illustrative embodiment of a steel heating furnace, comprising:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
means for supplying carbon monoxide into the interior furnace space and maintaining a carbon monoxide atmosphere within the interior furnace space.
Another illustrative embodiment of the invention comprises:
a furnace housing for receiving steel thereinto, the furnace housing defining an interior furnace space;
means for heating the interior furnace space and the steel residing within the furnace; and
means for substantially sealing the furnace housing from the atmosphere.
Still another illustrative embodiment
Clayton Howarth & Cannon, P.C.
Kastler Scott
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