FORM 2
THE PATENT ACT 1970 (39 OF 1970)
&
The Patent Rules, 2003 COMPLETE SPECIFICATION (See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A COOLING HOOD FOR ANNEALING BASES WITH HIGHER HEAT TRANSFER RATE AND REDUCED COOLING TIME.
2 APPLICANT (S)
Name : STEEL AUTHORITY OF INDIA LIMITED
Nationality : A Govt. of India Enterprise
Address : Research & Development Centre for Iron & Steel, Doranda, Ranchi -
834 002, State of Jharkhand, India
3. PREAMBLE TO THE DESCRIPTION
COMPLETE:
The following specification particularly descibes the invention and the manner in which it is to be performed.

FIELD OF INVENTION:
The present invention relates to a cooling hood for annealing furnace and in particular to a cooling hood for annealing furnaces adapted for higher heat transfer rate and reduced cooling time of the annealing cycle in batch annealing. The present system of cooling can be used in annealing bases with any type of sealing. This invention also intends to further increase the efficiency of cooling hoods by increasing the heat transfer rate from inner cover to air by adopting jet impingement of air. The cooling time being the longest time period in the total heating-soaking-cooling cycle, the present invention achieves significant improvement in base productivity by shortening the cooling time duration maintaining the end objectives of the predetermined annealing cycle for a given variety of steel, and thus having enough potential for wide industrial application.
BACKGROUND AND PRIO ART:
It is well known in the art of batch annealing of selective steel items in the hood annealing furnace, the cooling time plays an important role in the total annealing cycle to achieve desired properties in the treated steel. The prerequisite for higher productivity in a hood annealing furnace is the shorter heating cycle, exactly required duration of soaking time, short cooling time and optimum charge weight/batch size. The cooling time is usually the longest in annealing cycle and can be as high as twice the combined duration of heating and soaking time. Therefore, the easiest way to increase the base/furnace productivity is to decrease the cooling time. The system of cooling in annealing furnaces are carried out dividing the process in two different categories- (a) firstly through the heat exchangers for cooling of protective gas flowing inside the inner cover and (b) secondly, the protective gas and the coils can be cooled indirectly by cooling the inner cover from outside.
It is a common experience that in the first category of cooling of protective gas through water cooled heat exchanger, the deposition of muck over the walls of the tubes of heat exchanger and blocking of the inner flow passage of the tubes due to deposition of dirt/contaminants flowing along with the industrial water through these tubes, resultantly reduces the heat exchange rate. The maintenance of these heat exchangers and its tubes, attract various problems. The cooling of protective gas and coils by cooling of inner cover from outside is done through cooling hoods which are updraft type. The ambient air is drawn over the face of hot inner cover and exhausted over the top. These hoods cannot be
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used for bases, which have sand sealing as it leads to breakage of sand sealing and as a consequence the coils get oxidized.
There was therefore a continuous need for developing a cooling hood that can be used for cooling of items subjected to batch annealing, with any type of sealing of bases favoring lifting arrangement similar to that of heating furnace to take care of the operational problems and to increase the efficiency of cooling hoods by inducing effective heat transfer rate and thereby to reduce cooling time in the annealing cycle to improve productivity in a hood annealing furnace.
OBJECTS OF THE INVENTION:
This is therefore the basic object of the present invention to provide a cooling hood for the annealing furnace/bases used for batch annealing of steel items adapted to substantially reduce the cooling time and improve the cooling efficiency with higher heat transfer rate and higher productivity of batch annealing process in furnace/bases.
A further object of the present invention is directed to a cooling hood adapted for use with any type of sealing of annealing base without affecting the efficiency of cooling.
A further object of the present invention is directed to a cooling hood for annealing bases adapted to favor increased heat transfer rate from the inner cover to air by jet impingement of air on the inner cover.
A further object of the present invention is directed to a cooling hood for annealing bases favoring faster cooling by inducing improved heat transfer rate, is having the lifting arrangement similar to heating furnaces so as to facilitate ease of operation and eliminate problems of maintenance.
A further object of the present invention is directed to a cooling hood for annealing bases, the present cooling hood is comprising of two parts, the upper part housing the fans and motors for creating forced air draft and the lower part is a double walled cylindrical vessel that constitute the outer and inner shell surrounding the inner cover as compared to the single outer shell in the conventional cooling hoods. Said upper and the lower part of the cooling hood is connected by means of flange connection at top of the outer shell.
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A further object of the present invention is directed to a cooling hood for annealing bases, said double walled shell covering the inner cover facilitate up draft type of air circulation by means of forced draft created by fans operating at the upper part of the hood, by flowing in/impinging air jet through rows of holes/openings favorably circumferentially, in selective numbers on the inner shell at preferred vertical spacing/ distance, on to the inner cover for desired rate of heat transfer and rapid rate of cooling.
A further object of the present invention is directed to a cooling hood for annealing bases, said inner and outer shell of the double walled cylindrical lower part of cooling hood, are favorably spaced maintaining uniform gap between the inner and the outer shells by means of spacers installed at preferred locations, so as to favor turbulent flow of air over the inner cover and thus eliminating formation of thin layer of stagnant air on the inner cover as observed in conventional process, thus favoring increased rate of cooling of the inner cover and the coils.
A further object of the present invention is directed to a cooling hood for annealing bases, having inner/outer shell selectively constructed of diameters adequate to accommodate the inner cover.
A further object of the present invention is directed to a cooling hood for annealing bases, said forced up draft of air is achieved by two numbers of fans placed at diametrically opposite locations at upper part of the hood and driven by electrical motors and belting of suitable ratings or they may be directly couple interfaced with a suitable variable speed drive unit, to deliver air flow rate of around 20,000Nm3/hr or more at a discharge pressure head of around 40mm of WC, to achieve said preferred rate of cooling and reduced cooling time in the total annealing cycle time.
A further object of the present invention is directed to a cooling hood for annealing bases, wherein the efficiency of cooling has been improved such that the cooling time is reduced by about 25 to 45 % and total annealing time has been reduced by about 15 to 30%, depending on either base fan running or not running conditions.
SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention there is provided a cooling hood for annealing bases and the like comprising:
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a double walled cylindrical vessel open from the base defining an inner shell adjacent to the heating coil cover and an outer shell;
said inner shell having plurality of spaced apart holes adapted to allow air to impinge on said cover through said holes and cooperating with a central outlet at the atop for exhaust/vent of the air;
fan means disposed at the top with respect to said inner and outer wall extensions at the top and adapted such as to favor blowing of air through the annular space therebetween the said inner and outer shell and thereafter impinge on the inner cover through said holes in the inner shell whereby the flow of air over the inner cover is turbulent with increased rate of heat transfer from inner cover to air and faster cooling of inner cover and the coils.
A further aspect of the present invention is directed to said cooling hood wherein the said outer shell is joined to the inner shell through flange at the bottom, that provides adequate area for seating of the hood on the base.
A further aspect of the present invention is directed to a cooling hood wherein said inner shell and the outer shell kept together and also are maintained spaced apart from one another through intermittent spacers, preferably made of flanged pipe NB-100 of wall thickness preferably of 5.4 mm, placed at four levels along the height of the hood.
According to a further aspect of said coojing hood for batch annealing wherein said inner
and outer shells are obtained of thick plate of mild steel preferably 6mm thick.
A still further aspect of the present invention of said cooling hood for annealing bases
comprising an upper part of the cooling hood adapted to accommodate and support the fan
means.
A still further aspect of the present invention directed to a cooling hood for annealing bases wherein the upper part of the hood is flanged at the bottom and the said upper and lower part of the cooling hood are assembled through said flanges.
According to a further aspect of the present invention directed to a cooling hood for annealing bases, comprising two numbers of diametrically opposite cylinders fixed in the upper part for mounting of said fans and two numbers of cross channels are provided for
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support of the fans preferably having capacity of around 20,000NM3/hr or more and discharge head of around 40 mm of WC and driven by a squirrel cage induction motor of suitable capacity with said fan and motor coupled through belt and pulley.
A still further aspect of the present invention of said cooling hood for batch annealing in annealing bases, comprising lifting hook secured preferably by welding to the center of the upper part the cooling hood at the junction of the two channels and a cat ladder provided for the approach to the upper part of the hood for maintenance of said motor and fans.
According to a further aspect of the present invention directed to a cooling hood for annealing bases wherein the speed of the fan is adapted to be varied by a variable frequency drive and said diameter of the double walled cylindrical hood is selectively determined based on the diameter of the inner cover over the coils and said lifting arrangement on the upper part of the hood is adapted according to the lifting arrangement of the furnaces.
The present invention and its objects and advantages are described in greater details with reference to the following accompanying figures and the non-limiting illustrative example.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: is an illustration of the sectional view of the conventional cooling hood for batch annealing having Down Draft type air flow for cooling.
Figure 2: is an illustration of the sectional view of the conventional cooling hood for batch annealing having Up Draft type air flow for cooling.
Figure 3: is the illustration of the sectional view of the cooling hood, demonstrating the Up Draft type air flow pattern through the double walled cylindrical shell of the cooling hood according to the present invention.
Figure 4: is the illustration of the sectional view of the cooling hood according to the present invention, demonstrating the constructional details of the Upper and Lower part, fan-motor drive, base, sand sealing and other optional features.
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DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES:
Reference is first invited to the accompanying figures 1 and figure 2, that illuatrate the constructional and functional aspects of the conventional type of Cooling Hoods used for batch annealing of steel coils/items. These cooling hoods are used for cooling the batch in a controlled manner in an annealing cycle after they have been heated to desired temperature at a desired rate and soaked for preferred time duration at defined temperature. The cooling time being the longest duration in the total annealing cycle time, a reduction in cooling time effectively improves the productivity of the annealing process/furnace. The conventional cooling hoods, as apparent from the accompanying figures, comprise of either a Down Draft Or an Up Draft configuration for forced airflow used for cooling purpose. The figure 1 shows a situation where the cooling hood is haying Down Draft of cooling air through the passage in between the inner cover and the outer single walled shell surrounding the inner cover and the coils inside of it. The fan installed at the top of outer shell and driven by a motor, suck in air from top opening on the outer shell and force it to flow past the surface of inner cover downwards and thereby producing the desired cooling effect of the batch of material inside, and the air being driven out through the gap between the bottom of the shell and the base, provided with suitable sealing with bases except for fragile sand sealing, to prevent the coils from oxidation.
Figure 2 shows the same conventional cooling hood with Up Draft type air circulation, wherein air is sucked in through the gap between the bottom of hood and the base by the induced draft created by adaptive rotation of fan at the top of the outer shell. The cooling air flows past the inner cover from bottom to top and discharged through the vent at shell top. Thus, in the existing hoods, suction or discharge of air is from the base near the sealing and therefore the existing hoods are not capable to be used in bases with sand sealing.
In either of these two flow configurations in the existing conventional cooling hoods for batch annealing, the flow of air over the inner cover is laminar. A thin layer of stagnant air over the inner cover is formed by this process of cooling, forming a heat barrier that decreases the rate of heat transfer through the inner cover to the flowing air. Thus the time taken for cooling of the charge inside the inner cover is much longer and results in low productivity in annealing cycles.
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Reference is now invited to the accompanying figures 3, that illustrate the air flow pattern in the cooling hood according to the present invention, with reduced time required for cooling of charge in batch annealing cycle. The cooling hood of the present invention comprise of two parts-an upper part having housing for the fans and motors and the lower part having a double walled shell, having the inner and the outer shell. The ambient air is sucked in by a pair of fans, installed inside two diametrically opposite cylinders at the upper part of the hood, operatively driven by squirrel cage induction motors of suitable capacity. The fans (FN) and motors(MTR) are coupled through belt and pulley or they are optionally directly coupled. The speed of the fan can also be varied by a variable frequency drive. The capacity of the fan is 20,000IMm3/hr or more and discharge head of 40 mm of WC. The air discharged by the fans flow from top through the annular passage between the inner shell(IS) and the outer shell(OS).
The cooling hood of the present invention, the construction and functional aspects being illustrated in the sectional view of the cooling hood in figure 4, advantageously comprising a double walled shell at the bottom part of the hood that functionally favor an air flow pattern that increases the heat transfer rate from the inner cover to the flowing air and thereby reducing desired time for cooling in the annealing cycle for a batch. The double walled cylindrical vessel that constitute the lower part of the cooling hood of the present invention, comprising an inner shell(IS) and an outer shell(OS). A flange(BFL) has been provided at the bottom that closes the annular opening between the bottom edge of the inner and the outer shell(OS) walls and provide adequate area for sitting of hood. The inner shell(IS) is fabricated from 6mm thick plate of mild steel of specification IS 2062-1992. It has perforations (PS) made by drilling 24 holes of diameter 25mm at one level circumferentially. There are eight such rows at a vertical spacing of 500mm. Air will impinge on the inner cover (IC) over the coils, through these holes on inner shell wall. The outer shell(OS) wall is fabricated from 6mm thick plate of mild steel to IS 2062-1992. The outer shell(OS) is joined to the inner shell through flange at the bottom and spacers(SPS) at four levels. The spacers(SPS) are provided to keep both the shells together. These spacers are made from flanged pipe NB-100 with wall thickness 5.4mm. The outer shell has flange of 16mm thickness on the top through which upper part of cooling hood will be joined. The upper part of the cooling hood is fabricated from 6mm thick plate as per IS:2062-1992. It will be flanged at the bottom. The upper and the lower part of the hoods are assembled together through the flanges, having 24 number holes of diameter 17mm. Two numbers of cross channels of section ISMC-200 are provided for the support of the fans. One lifting
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hook(LH) is welded to the center of the upper part of cooling hood at the junction of two channels to favor lifting of the hood in a way similar to the heating furnace. A cat ladder (CL) is provided for approach to the upper part of the hood for maintenance of motor and fans.
In the cooling hood of the present invention with improved heat transfer rate and reduced cooling time, the two fans suck the ambient air which flows through the annular space between two shell walls and impinges on the inner cover through the holes provided on the inner shell wall. The flow of air over the inner cover in Up Draft circulation is turbulent in nature, and thereby not allowing the formation of thin layer of stagnant air that acts as a deterrent to convective heat transfer to air in conventional process. This turbulent flow of air and jet impingement on the inner cover surface through the perforations provided in the inner shell wall surrounding the inner cover, enable the present cooling hood to increase the rate of heat transfer and results in faster cooling of inner cover and the coils. Moreover, as the suction and discharge of air in this new type of cooling hood take place at the upper part of the hood and much away from the place of sealing of the hood with the base, the cooling hood of the present invention is versatile and capable to be used with any kind of sealing, including sand sealing (SS) without any chance of breakage.
EXAMPLE:
In a particular embodiment of the cooling hood of the present invention the improved cooling efficiency was observed through conducting repeated trials for different batches on the cooling hood of the present invention at different annealing bases under conditions of either with Base fan running or with Base fan not running and the resultant reduction in cooling time for the cooling operation as well as the reduction for the total annealing time in percentage was significant, as detailed in the following Table-I.
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TABLE -I
No. Of
trial Base No. Charge No. Charge Wt.(tons) Heating time (Hrs) Tl Soaking time (Hrs) T2 Cooling Time(Hrs) Decrease (%) Rem arks





Without Hood T3 With Hood T4 Cooling Time Anneal time
1 62 4948 58.75 12 29 90 52 42% 29% BFNR
2 59 5039 60.00 16 28 65 49 25% 15% BFR
3 69 5120 61.90 14 30 90 53 42% 28% BFNR
4 70 5184 59.22 09 22 65 43 34% 23% BFR
5 69 5924 64.86 14 30 95 52 45% 31% BFNR
6 68 6321 59.84 14 30 90 54 40% 27% BFNR
Following terms and relations relate to the compilation of the above tabular presentation of trial data:
BFNR: Base Fan Not Running BFR: Base Fan Running
% Decreasing in Cooling time =(T3-T4)xl00
% Decrease in Annealing time=[(Tl+T2+T3)-(Tl+T2+T4)]/ (Tl+T2+T3)xl00
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WE CLAIM:
l.A cooling hood for annealing bases and the like comprising:
a double walled cylindrical vessel open from the base defining an inner shell adjacent to the heating coil cover and an outer shell;
said inner shell having plurality of spaced apart holes adapted to allow air to impinge on said cover through said holes and cooperating with a central outlet at the atop for exhaust/vent of the air;
fan means disposed at the top with respect to said inner and outer wall extensions at the top and adapted such as to favour blowing of air through the annular space therebetween the said inner and outer shell and thereafter impinge on the inner cover through said holes in the inner shell whereby the flow of air over the inner cover is turbulent with increased rate of heat transfer from inner cover to air and faster cooling of inner cover and the coils.
2. A cooling hood as claimed in claim 1 wherein the said outer shell is joined to the inner
shell through flange at the bottom.
3. A cooling hood as claimed in anyone of claims 1 or 2 wherein said inner shell and the
outer shell kept together and also are maintained spaced apart from one another through
intermittent spacers, preferably made of flanged pipe of wall thickness preferably of 5.4
mm, along the height of the hood.
4. A cooling hood as claimed in anyone of claims 1 to 3 wherein said inner and outer shells
are obtained of thick plate of mild steel preferably 6mm thick .
5. A cooling hood as claimed in anyone of claims 1 to 4 comprising an upper part of the
cooling hood adapted to accommodate and support the fan means.
6. A cooling hood as claimed in claim 5 wherein the upper part of the hood is flanged at the
bottom and the said upper and lower part of the cooling hood are assembled through said
flanges.
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7. A cooling hood as claimed in anyone Of claim 1 to 6 comprising two numbers of
diametrically opposite cylinders are fixed in the upper part for mounting of said fans and
two numbers of cross channels are provided for support of the fans preferably having
capacity of 20,000NM3/hr and discharge head of 40 mm of WC and driven by a squirrel cage
induction motor of suitable capacity with said fan and motor coupled through belt and
pulley.
8. A cooling hood as claimed in anyone of claim 1 to 7 comprising lifting hook secured
preferably by welding to the center of the upper part the cooling hood at the junction of the
two channels and a cat ladder provided for the approach to the upper part of the hood for
maintenance of said motor and fans.
9. A cooling hood as claimed in anyone of claim 1 to 8 wherein the speed of the fan is
adapted to be varied by a variable frequency drive and said diameter of the double walled
cylindrical hood is selectively determined based on the diameter of the inner cover over the
coils and said lifting arrangement on the upper part of the hood is adapted according to the
lifting arrangement of the furnaces.
10. A cooling hood substantially as herein described and illustrated with reference to the
accompanying figures 3 and 4.


Dated this 8th day of January, 2007.

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A cooling hood for annealing bases, adapted to decrease the cooling time of the annealing cycle in batch annealing. The present system of cooling can be used in annealing bases with any type of sealing. This invention also intends to further increase the efficiency of cooling hoods by increasing the heat transfer rate from inner cover to air by adopting jet impingement of air through perforations provided on the inner shell wall by means of Up Draft created by fans. The cooling time being the longest time period in the total annealing cycle, the present invention achieve significant improvement in base productivity by shortening the cooling time duration and a resultant decrease of total annealing time, maintaining the end objectives of the predetermined annealing cycle for a given batch of steel item, and thus having enough potential for wide scale industrial application.