Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
104069~
The present invention relates to a roof assembly for an arc
furnace.
Since the temperature inside the arc furnace is higher than
1,600 C, the prior art furnace roof consists of fire bricks laid in the form -~
of a dome. However, the erosion of the fire bricks has recently become very -~
quick because the capacity of the arc furnace is increased; the capacity of
the transformer used i9 increased, thus resulting in the furnace operation
at higher power; auxiliary burners are used; a dust collector system is
employed for directly sucking the furnace gases through the furnace roof;
and the continuous charging of reducing pellets is employed, resulting in
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the exposure of the furnace roof to high temperature heat for an increased
time. As a result, the life of the furnace roof becomes very short, thus
resulting in the increase in cost as well as idle time required for the
repair or replacement of the furnace roof.
In order to reduce the operating cost and to attain the continuous
furnace operation, it is imperative to provide a furnace roof whose service -
life is sufficiently long.
In view of the above, the primary object of the present invention
is to provide a roof assembly for an arc furnace having a semi-permanent
service life.
It is almost impossible at present to increase the life of the
furnace roof only by the improvement of the heat-resisting properties of the
refractory materials. To overcome this problem, there has been devised and
demonstrated a furnace roof which is made of steel and which is provided
with water jackets, but the above furnace roof has thè following defects~
(i) Since the water jackets are formed by welding steel plates, the
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water leakage very often tends to occur through the welded joints.
(ii? When thethickness of the steel plates used is too thick, cracking ~ ;
of water jacket occurs because of the temperature difference between the
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surface exposed to the cooling water and the surface exposed to the high
temperature in the fu~nace. Therefore, the steel plates of a relatively
thin thickness must be used, but when the water jacket made of thin steel
plates is exposed to the sparks which is most frequently produced by the
contact of charged metal scrap with the electrodes in the initial stage of
the melting process, holes are formed through the walls of the water jacket -
so that the cooling water leaks. ;
(iii3 Since the water jackets are made of thin steel plates, a large
quantity of cooling water is required, resulting in the increase in heat -
1~ absorption and consequently reducing the thermal efficiency of the furnace.
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Furthermore, the life of the water-jacket furnace roof is reduced.
To overcome these defects, there has been also devised and
demonstrated a method for cooling the fire-brick furnace roof by circulating
cooling water through the cooling coils or tubes placed within the fire
bricks.
According to this method, the grooves or the like must be formed
in the fire bricks in order to place the cooling coils or tubes so that the
cost becomes very expensive. Furthermore, this method cannot provide a
sufficiently large cooling area so that the cooling efficiency is low. -
As described above, the prior art furnace roofs made of materials `
other than fire bricks have not satisfactorily solved the problem of water
leakage and hence the problem of a long service life.
The present invention was therefore made to provide a water-cooled
furnace roof assembly which may completely eliminate the problem of water
leakage. Briefly stated, the present invention provides a roof assembly
for an arc furnace comprising a furnace ring made of metal and defining the
outer periphery of the roof assembly, and a plurality of sectionalized roof
units assembled together within said roof ring, each sectionalized roof unit
comprising a main body cast from cast iron or copper and a cool-ing coil
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embedded in said main body in such a way that cooling water may be charged
into and discharged from said cooling coil, the inner major surface of said
main body directed toward the inside of the furnace having the high-
temperature and thermal-shock resistance construction.
The present invention will become more apparent from the following
description of some preferred embodiments thereof taken in conjunction with
the accompanying drawings, in which:-
Figure 1 is a schematic top view of a first embodiment of thepresent invention;
Figure 2 is a cross sectional view thereof;
Figure 3 is a cross sectional view of a sectionalized roof unit
thereof; and
Figures 4 and 5 are cross sectional views of sectionalized roof
units of a second and a third embodiments, respectively.
Same reference numerals are used to designate similar parts
throughout the figures.
First Embodiment~ Figures 1, 2 and 3.
Referring to Figures 1, 2 and 3, there is shown a first embodiment
of a furnace roof in accordance with the present invention comprising a ~ -
circular roof top 6~ a plurality (12 in the instant embodiment) of
equiangularly radially sectionalized roof units 1 and a roof ring 8.
m e sectionalized units 1 are similar in construction so that only
one of them will be described in detail. The unit 1 comprises a main body
2 cast from cast iron or copper and a hairpin type cooling coil 3 which has
i been embedded in the main body 2 when the latter was cast. The paralleled
~ adjacent sections of the cooling coil 3 are spaced apart by a suitable dis-
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tance~ and the ends 4 and 4', which serve as an inlet and an outlet,
respectively, of cooling water as well as the 180 return bend sections of
the cooling coil 3 are extended out of the upper major surface of the main
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body 2 as best shown in Figure 2. A plurality of fire bricks 5 are partially
embedded in the lower or inner surface of the main body 2 as best shown in ~ ~
Figure 3. The trapezoidal-shape sectionalized furnace roof units 1 with the -
above construction are assembled with the roof top 6 and the roof ring 8 ~ -
as shown in Figures 1 and 2.
m at is, the arcuated longer base sides of the units 1 are ; `-
positioned along the inner wall of the roof ring 8 which is made of metal
and defines the outer periphery of the furnace roof assembly~ and the side
walls of the roof units 1 are abutted against each other so that the roof
units 1 are assembled and securely held in position by their own weights in
the form of a truncated cone as best shown in Figure 2. Thus, the semi-
permanent substructure of the furnace roof assembly is provided, and the ~; -
inner arcuated shorter bases of the roof units 1 define a circular top
opening having the inverted frustoconical cross sectional configuration as
best shown in Figure 2. The roof top 6, which is made of electrically
insulating refractory materials, is a consumable substructure and has
three electrode holes 7~ closely is fitted into the top opening. mus~ the
furnace roof assembly is completely assembled. -
In the instant embodiment, in order to minimize the weight of the
furnace roof assembly, the sectionalized roof units 1 are abutted against -
each other, but any suitable means may be used for securely holding them
together.
Second Embodiment, Figure 4.
The second embodiment shown in Figure 4 is substantially similar
in construction to the first embodiment except that instead of the fire
bricks 5, amorphous refractory material 9 such as magnesia, high alumina
or the like is stamped into the grooves formed in the lower or inner
surface of the sectionalized roof unit 1 in order to improve the resistance
to heat of the furnace roof assembly.
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Third Embodiment, Figure 5.
The third embodiment shown in Figure 5 is also substantially
similar in constuction to the first embodiment except that no refractory
material such as fire brick 5 or amorphous refractory material 9 is used
and that the inner surface of the roof unit 1 is corrugated as shown at 10.
The arcuate convex portion of the corrugated inner surface 10 is coaxial
with the corresponding cooling tube or coil section 3, and the spacing or
distance between the arcuate convex portion and the cooling tube section is
so selected that the temperature of the inner surface of the furnace roGf
assembly may be maintained at a temperature lower than the melting point of
the roof unit 1, but higher than the solidifying point of molten charge in
the furnace.
As a variation of the third embodiment, amorphous refractory ~ .
materials may be stamped into the corrugated inner surface of the roof unit
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In operation, cooling water is charged into the inlet 4 of the
cooling coil 3, flows therethrough and is discharged out of the outlet 4'
so that not only the main body 2 but also the roof top 6 may be sufficiently ~:
cooled. Since the inner surface of the roof unit 1 is provided with the . -:
fire bricks 5 (See Figure 3) or amorphous refractory material 9 (See Figure 4) .: :
or is corrugated as shown at 10 (See Figure 5), there is no fear that the -
cooling coil 3 of the roof unit 1 is cracked due to the thermal stresses :
produced by the temperature difference between the cooling water flowing
through the cooling coil 3 and the cooling coil 3. ~ven if the cooling coil
3 should be cracked, there is no fear at all of the water leakage because the
cooling coil 3 is embedded in the main body 2. Therefore, the long life of
the furnace roof assembly may be ensured, and there is no fear that the ~ .-
water leakage will induce the explosion of the furnace even when the sparks
are produced by the shortcircuits between the electrodes and the scrap in
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the initial stage of the melting process.
The different types of the sectionalized roof units 1 may be
selected depending upon the thermal conditions within the furnace and other
operating conditions. For instance, the roof units 1 of the first
embodiment may be used when the thermal conditions of the furnace are severe,
but when the thermal conditions are not so severe, the roof units 1 of the --
type shown in Figure 4 may be used. When the thermal conditions are too
severe so that the life of refractory used is expected to be very short, the
roof units 1 of the type shown in Figure 5 may be used. However, in the
furnace operation the splashes of the molten charge tend to adhere to the
inner surface of the furnace roof assembly and are solidified to form a :
sort-of protective layer so that the quantity of heat dissipated through ~
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the furnace roof assembly may be reduced. Consequently, the longer service
life of the roof assembly may be ensured, and the thermal efficiency is
very high in furnace operation.
So far only the exemplary embodiments of the present invention
have been described, but it will be undorstood that the present invention is
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not limited thereto and that various modifications may be effected within
the true spirit of the present invention. `
The features and advantages of the furnace roof assemblies in
accordance with the present invention may be summarized as follows: ;
(I) Since the cooling coil is cladded or embedded inthe main body, ~ ~
there is no fear of the water leakage even if the cracks should be started 1~;
in the main body due to the thermal fatigue thereof.
(II) Since the main body of the roof unit has a large thermal capacity,
and the cool;ng water flows through the cooling coil embedded in the main
body, there is no fear that the water leakage induces the explosion of the
arc furnace even when the sparks are produced.
(III) The heat resisting ability of the sectionalized roof units is much
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improved because the fire bricks are partially embedded, the amorphous
refractory is stamped into the inner surface of the unit or the inner
surface is corrugated so that the adhesion to the inner surface of the
splashes is much facilitated, resulting in the easy formation of the
protective layer. As a result, the heat loss may be minimized, and the
service life may be increased. The distinctive features of the corrugated
inner surface are that the cracking of the sectionalized roof units due to
the thermal stresses caused by the temperature difference may be
substantially eliminated and that the cost is low.
(IV) Because of the above features (I), (II) and (III), the furnace -
roof assembly in accordance with the present invention has a semi-permanent
service life.
(V) The spare roof tops may be provided so that the repair of the -~ -
furnace roof as~embly may be accomplished simply by replacing the furnace
roof top. Since the life of the furnace roof assembly except the roof top
is semi-permanent, it is not necessary at all to keep in hand the spare
furnace roof assembly.
(VI) Since the sectionalized roof units are not suspended, there is no
additional weight. Therefore, the furnace roof assemb b in accordance with
the present invention has the weight substantially similar to that of the
prior art furnace roof made of firebricks so that the modifications of the
existing arc furnaces and of the furnace operations are not necessary.
(VII) Since the life of the roof assembly is semi-permanent and the idle
time for replacing the roof top is short, the furnace operation effïciency
may be remarkably increased, thus resulting in the reduction in operating
cost.
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