Metallurgical apparatus – Means treating solid metal – By contact with gas
Reexamination Certificate
1998-09-25
2001-01-23
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means treating solid metal
By contact with gas
C266S263000
Reexamination Certificate
active
06177044
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a bell-type furnace, particularly for annealing steel coils in a controlled atmosphere, with an inner cover which surrounds the steel coils, with a cooling cover which, forming an intermediate space, concentrically surrounds the inner cover and comprises a cooling-cover shell and a cooling-cover roof, the cooling-cover shell being provided with a plurality of air nozzles in such a way that cooling air in the form of jet streams impinges the inner cover, and with at least one fan for producing a cooling-air flow in the intermediate space.
Such bell-type furnaces are used particularly for the bright annealing of cold-rolled steel in the shape of coils in a controlled atmosphere.
During the annealing process, a heating cover is placed over the inner cover. After annealing, the heating cover is removed and replaced by a cooling cover.
BACKGROUND OF THE INVENTION
WO 95/20058 discloses a cooling cover with air nozzles arranged exclusively in the bottom third of its height. The coils are usually stacked on top of each other, being separated by convector plates. Volumetric flows through the convector ducts are significantly larger for the bottom coils in the stack than for the top coils. Consequently, coils lying at the bottom are at an advantage during cooling, while coils lying at the top are at a disadvantage. This is exacerbated by the fact that cooling occurs only in the bottom region. The cooling process cannot be ended until the temperature in the core of the top coil falls below the maximum temperature set for the end of cooling, which means that the cooling process takes fairly long.
THE INVENTION
It is therefore an object of the invention to enhance a bell-type furnace of the aforementioned kind so that cooling is improved and particularly the cooling time is reduced.
According to the present invention, this object is achieved in a bell-shaped furnace of the kind indicated above by the spacing between adjacent air nozzles increasing from the bottom up, said spacing being 4 to 20 times the nozzle diameter and, in addition, by providing the cooling-cover roof with a second plurality of air nozzles, the spacing between said second plurality of air nozzles being 4 to 8 times the nozzle diameter.
An arrangement wherein the spacing between the air nozzles of the cooling-cover shell continuously increases from the bottom up is particularly easy to design.
It is also possible to reduce the diameter of the nozzles from the bottom up. However, this solution calls for a more complicated design.
Convective heat transfer at the coil sides is determined by the volumetric flow of the circulated controlled atmosphere and the free flow cross-section of the annular gap between the inner cover and the coils. Since part of the controlled-atmosphere flow passes through the convector plates over the coil edges, the controlled-atmosphere speed determining the heat transfer decreases from the bottom up. Therefore, the invention proposed herein also reduces the cooling effect on the inner cover by increasing the spacing of the air nozzles in the cooling-cover shell from the bottom up.
At the topmost point of the inner cover, the controlled-atmosphere flow changes its direction, as a result of which the turbulence and hence the convective heat transfer to the cooling-cover roof is significantly larger than that between the inner cover and the cooling-cover shell in the region of the vertical annular gap between the coils and the inner cover. In addition, an appreciable exchange of radiated heat occurs between the inner cover and the top coil edge. The cooling-cover roof must therefore additionally be provided with a plurality of air nozzles to achieve intensive cooling there.
The advantage of the solution proposed herein is that the cooling of the coils is optimised, thus shortening the cooling process.
Another advantage is that the driving power of the fan can be relatively low. Consequently, the noise level is fairly low.
According to another feature of the invention, the bell-type furnace is characterised by the length of the air nozzles of the cooling-cover shell being 3 to 10 times the nozzle diameter.
This feature is based on the recognition that a very effective jet stream for cooling purposes is created if a fully developed tubular flow occurs in the air nozzles.
In an advantageous embodiment of the invention, the inlets of the air nozzles are rounded. This reduces pressure losses.
According to another feature of the invention, the speed of the cooling air in the air nozzles lies roughly between 10 and 40 m/s and preferably between 20 and 40 m/s.
It is advantageous if the speed of the cooling air in the air nozzles is at least 3 times the speed of the cooling-air flow in the intermediate space. The speed of the vertical flow in the intermediate space must be relatively low so that the cooling-air speed in all air nozzles in the cooling-cover shell is equally large as far as possible. The greatest possible width is therefore chosen for the intermediate space. The upper part of the cooling cover may in addition possess a greater external diameter than the bottom part in order to reduce the flow speed.
REFERENCES:
patent: 5230617 (1993-07-01), Klein et al.
patent: 5249960 (1993-10-01), Monroe
patent: 5290017 (1994-03-01), Hemsath et al.
patent: 32 33 815 (1984-03-01), None
patent: WO 98/33946 (1998-08-01), None
Maschler Frank
Scheuermann Walter
Velten Georg
Fay Sharpe Fagan Minnich & McKee LLP
Kastler Scott
LOI Thermprocess GmbH
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