Gas cooling and recirculating device in continuous strip furnaces

A "jet cooler" device for cooling and recirculating the gas forming the protective atmosphere in the cooling chambers of the furnaces for the continuous annealing of steel strips, comprises vertically arranged boxes (4) which extend in the furnace interior between successive vertically extending parallel strip sections, substantially over the whole length thereof, i.e., throughout the height of the furnace, and which have their walls (104) turned toward the facing adjacent strip sections provided with perforations (5). Associated to each vertically arranged perforated box (4) are a plurality of individual protective gas-cooling and recirculating units (6), which are distributed over the vertical extent of the respective box (4) and are attached to the outside of the furnace sidewalls (1). Each cooling and recirculating unit (6) comprises a heat exchanger (13) in form of a group of water-cooling rectilinear tubes, and a fan (11) that draws the protective gas from the furnace inside and cools it by causing the same to flow through the heat exchanger (13) and that blows this gas at a certain pressure into the associated vertically arranged box (4). The protective gas then flows out of the perforations (5) in the vertically arranged box (4) in form of jets directed to the facing surfaces of the adjacent strip sections.

BACKGROUND AND SUMMARY OF THE INVENTION 
The object of the invention is a device for cooling and recirculating the 
gas forming the protective atmosphere in the cooling chambers of furnaces 
for the continuous processing of metal strips, particularly for the 
continuous annealing of steel strips. 
A device of this kind, so-called "jet cooler", comprises vertically 
arranged boxes which extend in the furnace interior between the successive 
vertically extending parallel strip sections, substantially over the whole 
length thereof, i.e. throughout the height of the furnace, and which have 
their walls turned toward the adjacent strip sections provided with 
perforations, to the said boxes there being associated a protective 
gas-cooling and recirculating unit comprising a heat exchanger, and a fan 
that draws the protective gas from the furnace interior and cools it by 
causing the same to flow through the heat exchanger, and that blows this 
gas at a certain pressure into the boxes, so that the cooled protective 
gas flows out of the perforations in the boxes in form of jets directed to 
the facing surfaces of the adjacent strip sections, whereby it causes the 
cooling of the strip. 
In a known device of the above-disclosed kind, a plurality of suction ports 
communicating with the furnace interior, and a plurality of delivery ports 
communicating with the interior of the perforated boxes, are provided in 
the furnace sidewall. To all the perforated boxes, or at least to a number 
of same, there is associated only one cooling and recirculating system 
with only one fan that through suitable tubes draws the protective gas 
from the suction ports and causes the same to flow through only one heat 
exchanger, so that it blows the cooled gas through suitable delivery tubes 
into the vertically arranged perforated boxes. The drawback of this known 
device resides in the fact that big volumes of protective gas will be 
displaced from the furnace interior through suction and delivery tubes 
into an external cooling and recirculating system, which increases the 
risk of this gas becoming polluted owing to any possible leaks in the 
tubes, or to any defect in their tightness. Moreover, the said known 
device has great overall dimensions at the furnace outside, and occupies a 
rather large floor space. 
In another known device for cooling and recirculating the protective gas in 
the cooling chambers of furnaces for the continuous annealing of steel 
strips, instead of the perforated boxes extending vertically over the 
whole height of the furnace, a plurality of individual horizontally 
arranged boxes are provided between the parallel steel strip sections, and 
these boxes extend into the furnace transversely to the longitudinal 
direction of the said steel strip sections, and are distributed at 
predetermined intervals over the furnace height. Each one of these 
individual horizontally arranged boxes is tightly welded to the furnace 
sidewall and partly projects out of the furnace. Associated to each 
horizontally arranged individual box are a heat exchanger and a fan, 
preferably a centrifugal fan, which are housed in the box portion 
projecting out of the furnace. The opposite sidewalls of each horizontally 
arranged individual box, which are turned toward the two adjacent strip 
sections, are perforated. Moreover, each horizontally arranged box has a 
suction chamber containing the heat exchanger and communicating with the 
interior of the furnace through suction ports provided in the upper and/or 
the lower end of the horizontally arranged individual box. The fan of each 
horizontally arranged individual box draws the protective gas through the 
said suction ports and through the said suction chamber in the box, thus 
causing the said gas to flow through the heat exchanger, where the gas is 
cooled. The cooled protective gas is blown by the fan into the respective 
horizontally arranged individual box, and is caused to flow out through 
the perforations in said box, in form of cooling jets directed to the two 
adjacent strip sections. 
This known device with a plurality of horizontally arranged individual 
boxes provided in a superposed aligned relation between every two 
successive vertically extending strip sections, has the drawback that the 
entire perforated useful area through which the cooled protective gas jets 
are directed to the strip, is only a fraction of the area directly facing 
the strip, owing to the vertical spacing apart of the superposed 
horizontally arranged individual boxes from one another. This remarkably 
decreases the useful cooling area and--with the available spaces being 
equal, proportionally decreases the installable cooling power. Therefore, 
this known device does not satisfactorily meet the requirements of the 
continuously operated modern furnaces, in which a specific high cooling 
power needs to be installed. 
Another drawback of the said known device with horizontally arranged 
individual boxes resides in the fact that when one or more of the 
individual protective gas-cooling and recirculating units, respectively 
associated to the horizontally arranged individual boxes forming part of 
the same vertically extending file of these boxes, should stop owing to a 
failure, a local unbalance in the pressures acting on the strip might be 
produced whenever all the cooling and recirculating units in the 
next-adjacent vertically extending file of individual horizontally 
arranged boxes continue to be regularly operated, so that they tend to 
push the strip toward the individual horizontally arranged boxes 
comprising the cooling and recirculating units affected by a failure, and 
the strip is then caused to rub against the structure of these individual 
boxes. By such a rubbing, the surface of the strip may be damaged, and the 
final quality of the strip may be inevitably deteriorated. In order to 
reset a pressure balance and avoid the said rubbing of the strip, in the 
instance of a breakdown and a stopping of a certain number of cooling and 
recirculating units, respectively associated to the individual vertically 
arranged boxes in the same vertically extending file, the cooling and 
recirculating units of the facing horizontally extending boxes in the 
opposite file might be intentionally excluded, but this would determine a 
further important reduction in the overall cooling capacity. 
A further drawback of the known device with individual horizontally 
arranged boxes arises from the fact that the heat exchanger of each 
protective gas-cooling and recirculating unit consists of a water-cooled 
finned tube group extending into, and out of the respective individual box 
with a recumbent U-shaped or horse shoe-shaped path. In this embodiment, 
the protective gas to be cooled tends to flow only through the arcuate 
inner part of the cooling tube group, while the rectilinear parts of said 
U-shaped cooling tube group are scarcely utilized, since they are situated 
in a fluid-dynamically calm zone of the suction chamber in the respective 
horizontally artranged individual box. Consequently, the actual efficiency 
of the heat exchanger is considerably reduced, whereby it produces, with 
the same overall dimensions, a further reduction in the specific cooling 
capacity. 
The object of the invention is to eliminate the drawbacks of both of the 
above-disclosed kinds of known devices, and for this purpose the invention 
provides a cooling and recirculating device of the kind as disclosed at 
the beginning, substantially characterized in that a plurality of 
individual cooling and recirculating units are associated to each 
perforated vertically arranged box extending throughout the furnace 
height, and are distributed over the vertical extent of the respective 
box, and are attached to the outside of the furnace sidewalls. 
In one preferred embodiment of the invention, each individual cooling and 
recirculating unit associated to one perforated vertically arranged box 
consists of a sealed case element, tightly attached to the outside of the 
furnace sidewall, and which is comparted into a suction chamber containing 
a heat exchanger and communicating with the interior of the furnace 
through the side of the respective perforated vertically arranged box, and 
into a delivery chamber containing a fan and communicating with the 
interior of the said perforated vertically arranged box, the suction inlet 
of the fan being connected to the said suction chamber, and the delivery 
outlet of the fan being in communication with the said delivery chamber. 
By the cooling and recirculating device of the invention the advantages are 
maintained of the perforated vertically arranged boxes extending 
throughout the furnace height, but the drawbacks are eliminated of the 
known constructions using these vertically arranged boxes, since in place 
of only one cooling and recirculating system associated to all or to a 
number of the perforated vertically arranged boxes, a plurality of cooling 
and recirculating units are provided, which are associated to each 
perforated vertically arranged box and are distributed over the height of 
the same, and which contain each their own cooling and recirculating unit 
with a heat exchanger and a fan, and are applied to the outside of the 
furnace sidewall. Thus the piping of the protective gas over a long 
conveyance path outside of the furnace is avoided, and the risk of the 
said gas becoming polluted is then eliminated. Moreover, the device of the 
invention also has reduced overall dimensions as compared with the 
above-disclosed known construction having only one cooling and 
recirculating system, and these overall dimensions are however limited to 
the furnace sidewalls, and do not occupy any floor space. Consequently, 
the device of the invention also has a higher specific cooling capacity in 
relation to the occupied volumes. 
With regard to the known constructions comprising perforated individual 
boxes horizontally arranged in a superposed aligned relation, the cooling 
and recirculating device of the invention affords the advantage of 
avoiding any local pressure unbalance in the case of a breakdown and a 
stopping of one or more of the individual cooling and recirculating units 
associated to the same vertically arranged perforated box. In fact, in 
such a case, the pressure decrease within the perforated vertically 
arranged box connected to the broken down cooling and recirculating unit 
or units is not limited to a localized relatively short section, but will 
spread through the respective vertically arranged perforated box, i.e. 
throughout the height of the furnace, so that a relatively small decrease 
of the total pressure in the said vertically arranged box will be 
produced. This decrease of the total pressure within the vertically 
arranged perforated box connected to the cooling and recirculating unit or 
units affected by a breakdown, is unlikely to become so great as to cause 
the strip to be rubbed against the structure of said box under the action 
of the protective gas jets being directed against the opposite face of the 
strip, and flowing out of the opposite respective vertically arranged 
perforated box having all its associated cooling and recirculating units 
working properly. 
Besides this automatic balancing of the pressure in the interior of the 
perforated boxes, the device of the invention compared to the known 
construction with perforated horizontally arranged individual boxes, 
naturally affords all the advantages typical of the perforated vertically 
arranged boxes, particularly a higher cooling efficiency, since for the 
cooling protective gas jets directed against the strip it is taken 
advantage of all the furnace height, and not of only one portion thereof. 
According to a further characteristic feature of the invention, the heat 
exchanger in each cooling and recirculating unit consists of a rectilinear 
water-cooling tubes group preferably vertically passed through the 
respective suction chamber. Thanks to this feature of the invention, the 
efficiency of the heat exchanger with equal overall dimensions is 
considerably improved with respect to the known construction with 
perforated horizontally arranged individual boxes and with a heat 
exchanger consisting of a recumbent U-shaped or horse shoe-shaped cooling 
tube group. 
In comparison to the known constructions, the device of the invention 
furthermore affords the advantages of a simpler construction and a lower 
cost with reference to the attained performances, as well as the 
advantages of being very strong and of requiring practically no 
maintenance, or anyhow very little maintenance. The device of the 
invention is of a reduced weight, whereby it can be more easily 
disassembled and reassembled.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the Figures, numeral 1 denotes the two opposite sidewalls of 
the final cooling chamber of a furnace for the continuous annealing of 
steel strips. The steel strip N is alternately led around upper and lower 
guide rollers 2, 3, so that it presents spaced apart, vertically extending 
parallel sections therebetween. In the interior of the furnace vertically 
arranged boxes 4 are provided between the vertically extending sections of 
the strip N; these boxes are rectangularly shaped in horizontal 
cross-section, and extend substantially over the whole length of the said 
vertically extending strip sections, i.e., practically throughout the 
height of the furnace. The two opposite longitudinal sidewalls 104 of 
boxes 4, which are turned toward the strip N, are provided with 
perforations 5. 
A plurality of units 6 for the cooling and recirculation of the gas (such 
as, for example, HNX) forming the protective atmosphere in the furnace, 
are provided on the furnace outside, along each vertically arranged box 4. 
Preferably, the superposed successive cooling and recirculating units 6 
which are associated to each vertically arranged box 4, are alternatingly 
provided on both of the furnace opposite sidewalls, and the vertically 
extending file of the spaced apart cooling and recirculating units 6, 
which are associated to one vertically arranged box 4, is vertically 
offset from the vertically extending row of the cooling and recirculating 
units 6 which are associated to the adjacent vertically arranged box or 
boxes 4. Thus the access will be facilitated to every one of the cooling 
and recirculating units 6, as well as their fitting up and their removal. 
Each protective gas-cooling and recirculating unit 6 consists of a sealed 
case element 7 which is tightly attached, such as by welding, onto the 
outside of the respective furnace sidewall 1, and which by means of an 
internal vertical partition 8 substantially perpendicular to the furnace 
sidewall 1, is comparted into a suction chamber 9 and into a delivery 
chamber 10 lying therebeside. Through a delivery port 110 in the 
corresponding sidewall 1 of the furnace, the delivery chamber 10 
communicates with the interior of the box 4 that is associated with the 
appertaining cooling and recirculating unit 6. Through one side of the 
associated vertically arranged box 4 the suction chamber 9 communicates 
with the interior of the furnace, through a suction port 109 in the 
corresponding furnace sidewall 1. Both the suction port 109 and the 
delivery port 110 are situated on the inner side of the edge by which the 
case 7 is tightly attached to the furnace sidewall 1. 
The suction chamber 9 and the delivery chamber 10 are in communication with 
each other through a port provided in the partition 8, and forming the 
suction inlet of a preferably centrifugal fan accomodated in the delivery 
chamber 10. The delivery outlet of said fan 11 opens into the delivery 
chamber 10 itself. The fan 11 is driven by an electric motor which is 
flange-mounted directly onto the case element 7 of the respective cooling 
and recirculating unit 6. In the suction chamber 9, between the port 109 
communicating with the interior of the perforated vertically arranged box 
4, and the suction inlet of fan 11, there is provided a heat exchanger 
consisting of a group of rectilinear finned tubes 13 tightly passed 
through the suction chamber 9 of the case element 7 in the vertical 
direction, and in which cooling water flows. 
From the foregoing it appears evident that the fan 11 of each cooling and 
recirculating unit 6 draws the protective gas from the furnace interior 
through the suction chamber 9 and the suction inlet 108, thus causing the 
said gas to flow between the water cooling tubes 13 of the heat exchanger 
provided in the said suction chamber, and so suitably cooling this gas. 
The fan 11 blows with a certain pressure the thus cooled protective gas 
through the delivery chamber and the delivery port 110 into the associated 
vertically arranged box 4. This gas flows out of this vertically arranged 
box 4 through the perforations 5 in its opposite sidewalls 104, in form of 
jets directed to the facing surfaces of the two vertically extending 
sections of strip N, to cool the said strip. 
The cooling and recirculating units 6 are of perfectly tight construction, 
whereby it is reliably excluded any inflow of ambient air which would 
inevitably pollute the protective atmosphere in the furnace interior, and 
would result in the surface of the strip N being oxidated, and in the 
subsequent tinning thereof being impossible. 
Of course the invention is not limited to the just described and shown 
embodiment, but the same may be widely changed and modified, the more so 
in construction, and may be applied to any kind of furnace for the 
continuous processing of any metal strips, in which it is required to cool 
and recicle the gas forming the atmosphere inside the furnace, at least in 
one strip-cooling section thereof, however without departing from the 
leading principle as set forth hereinabove, and as claimed hereinafter.