Claims:We Claim:
1. A run out table (ROT) laminar cooling system for hot strip mill comprising:

array of top and bottom cooling header in run out table comprising top banks and bottom banks ;

each said banks having top and bottom spray arrangements including goose neck type headers for the top banks for smaller stream to break steam barriers and achieve laminar flow.

2. A run out table (ROT) laminar cooling system for hot strip mill as claimed in claim 1 comprising

staggered streams in two types of headers to cover up entire strip width with the pressure (0.1-0.2 bar) inside header maintained above zero for better flow to all streams.

3. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 or 2 comprising

ON/OFF shut off valves provided with spring return such that even during power or air failure the valves can return to close position;.
valve actuator adapted for 5 to 3 bar preferably about 3.5 bar operating pressure.
Input signal to the valves in the range of 0-24 V DC ;.
control valves to control flow rate; and
flow meters for ascertaining flow rate.

4. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1to 3 comprising:

(i) top banks , wherein

each said top bank having goose neck type spray headers wherein each said top header comprising goose-neck type pipes welded on either side of seamless pipe to provide water stream at desired flow rate to cool hot strip from top surface;

each said top header is connected with electro-pneumatically operated butterfly shut off valve for opening/ closing of spray;
a flow control valve along with flow meter provided for flow control;

(ii) bottom banks, wherein

each said bottom bank having plurality of section having plurality of spray headers , to constitute a bottom spray arrangement wherein each said header have plurality of laminar pipes to provide water stream at desired flow rate to cool hot strip from bottom surface;

each said bottom section is connected with electro-pneumatically operated butterfly shut off valve for opening/ closing of spray;

an additional manual butterfly valve provided to control the water flow manually in bottom banks.
(iii) pumping means for supplying water to said top and bottom banks at desired pressure and flow rate.

5. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 4 wherein in said top banks two types of top headers are provided with varying the pitch of the goose-neck pipes to cover entire strip width so that water streams are staggered to cover up entire strip width generating smaller diameter streams which can break steam barriers effectively on strip surface.

6. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 5 wherein the pressure inside top headers is above zero preferably in the range of 0.1-0.2 bar, so that the flow to all streams are better assured.

7. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 6 wherein control valves fitted for top headers are provided with 4-20 ma input signal to control flow rate.

8. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 7 wherein in said bottom headers plugs provided at both end for flushing in case of any clogging of pipe.

9. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyoneof claims 1 to 8 wherein in said bottom headers flanged joint to main headers provided in place of welded joint so that headers can be removed easily if any damage occurs.

10. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 9 wherein in said bottom headers sliding freedom engagement is provided on drive side to arrest lateral movement of headers to ensure aligned water flow and only one fixing bolt provided on operator side for easy removal.
11. A run out table (ROT) laminar cooling system for hot strip mill as claimed in anyone of claims 1 to 10 wherein in said bottom headers seamless pipes are fitted with nozzle at top and said nozzles can be removed for cleaning if any clogging occurs.

Dated this the 23rd day of February, 2016
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
, Description:FIELD OF THE INVENTION
The present invention relates to a modified Run Out Table(ROT) laminar cooling system for conventional Hot Strip Mill. The ROT cooling system modified with goose-neck type headers for top banks and laminar pipes for bottom banks. Since, the pumps of cooling water are not changed, same flow rates were taken to design new headers. The design was changed primarily to achieve laminar flow with improved cooling rate for both top and bottom headers.

BACKGROUND OF THE INVENTION

The Hot Strip Mill (HSM) at Rourkela Steel Plant(RSP) of the applicants, is Semi-continuous mill (1700 mm) with a production capacity of 1.5 million ton HR coils per annum. The finished hot rolled strip coming out of the last finishing stands passes over a long roller table called Run Out Table (ROT) prior to coiling at coilers. On this ROT, both the sides of the strip surfaces are cooled by controlled water spray from top and bottom spray banks to control the grain size, hardness and other mechanical & metallurgical properties of the HR strip.

Immediately after the strip rolls out from the last stand of the finishing stands, it enters the run out table cooling zone. Depending on the finishing temperature, mill speed, and the required coiling temperature, the material is cooled by arrays of top and bottom cooling headers in run out table. Further, material is continuously cooled by air convection and radiation until it is wound in the downcoiler. This cooling process cools the strip from ~ 900C to below 700C. The process includes cooling by internal and external conduction, stagnation forced convection, forced boiling convection, air convection and radiation, and heat generation from material phase transformation.

The ROT cooling system was modified based on the design provided by United Engg USA. It had 4 banks, each bank having top and bottom spray. Each top bank had 6 headers with tubular nozzles and each bottom bank had 21 headers with flat spray nozzles. Each bank was fed with 1600 m3/hr water approx. at 0.5 bar.

The ROT cooling system went massive change with the introduction of goose neck cooling top headers. This design was first introduced by SMS. This system gives better cooling rate, more uniform water streams than United design. This design gradually adopted by almost all mill builders at various projects. Today, ROT cooling system of almost all present mills are with this design.

The ROT laminar cooling system at HSM, RSP needed modification in order to achieve high heat transfer coefficient for improved productivity and product quality. The previous design had tubular nozzles at top headers from where water falls under very less pressure and has gravity fall. The water gains speed while falling and attains substantial velocity while reaching strip surface. Such velocity is necessary to achieve desired cooling rate. Since the strip surface is flooded with water, a velocity is required to penetrate through the water pool to reach hot strip surface. There is a steam barrier also present between water pool and hot strip surface hence, only penetrating through water pool is not sufficient. This steam barrier is more difficult to break and without breaking it, desired cooling rate cannot be achieved. The previous system had also laminar streams but bigger in diameter which made difficult to break above barrier. Moreover since water was supplied at negligible pressure at the nozzle the equal flow to all nozzles was difficult to achieve. The gooseneck design have smaller stream which could break barriers effectively and many such streams, staggered well to cover up entire strip width. Since the pressure inside header is slightly above zero, the flow to all streams are better assured.

Shortcomings of previous ROT Cooling System:

(i) Old pneumatic line was with ample water and scales and low pressure.
(ii) The flow meter and flow control valves not operative.
(iii) Bottom headers were welded to pipe and were difficult to remove.
(iv) Water leakage from top header even when not in use and falling on motors causing frequent motor damage.

Limitations of modification as per existing Site Condition:

(i) The pumps were not changed. Hence water flow and pressure available are the same.
(ii) The 12” rotating headers and basic arrangement not changed hence no. of headers in top and bottom banks kept same. Flow available to each header had to be kept same.
(iii) Spacing between headers also kept the same as before.

There has been thus a persistent need in the ROT cooling system of HSM, that both the top and bottom spray headers to be modified, under above stated limitative operating conditions, to suit the requirement of laminar flow and rapid cooling of the hot rolled strip to achieve better and uniform cooling rate so as to ensure better metallurgical properties of rolled sheets than before which will give better pricing in market.
OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for conventional Hot Strip Mill, with goose-neck type headers for top banks and laminar pipes for bottom banks, primarily to achieve laminar flow with improved cooling rate for both top and bottom headers.

The basic object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein top and bottom bank are designed to achieve better and uniform cooling rate, favouring better metallurgical properties of sheets with better pricing in market.

A further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein by effecting improved uniform cooling rate of hot rolled steel sheets ferroalloys consumption can be reduced while achieving the same strength.

A still further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein strip to strip metallurgical properties can be changed irrespective of ferroalloys added in SMS stage just by changing cooling rate.

A still further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein ON/OFF shut off valves provided with spring return, hence even during power or air failure the valves can return to close position.

A still further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein input signal to the valves changed from 0-230V AC to 0-24 V DC to ensure reliability and reduce electrical breakdown of valves.

A still further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill whereinon each nozzle of top/bottom headers, smaller stream is achieved which can break steam barriers effectively.

A still further object of the present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for Hot Strip Mill wherein water leakage from top header is arrested and thereby frequent failure of motor is avoided.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a run out table (ROT) laminar cooling system for hot strip mill comprising:

array of top and bottom cooling header in run out table comprising top banks and bottom banks ;

each said banks having top and bottom spray arrangements including goose neck type headers for the top banks for smaller stream to break steam barriers and achieve laminar flow.

A further aspect of the present invention is directed to a run out table (ROT) laminar cooling system for hot strip mill comprising
staggered streams in two types of headers to cover up entire strip width with the pressure (0.1-0.2 bar) inside header maintained above zero for better flow to all streams.

A still further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill comprising

ON/OFF shut off valves provided with spring return such that even during power or air failure the valves can return to close position;
valve actuator adapted for 5 to 3 bar preferably about 3.5 bar operating pressure;
Input signal to the valves in the range of 0-24 V DC ;
control valves to control flow rate; and
flow meters for ascertaining flow rate.

A still further aspect of the present invention is directed to a run out table (ROT) laminar cooling system for hot strip mill comprising:

(i) top banks , wherein

each said top bank having goose neck type spray headers wherein each said top header comprising goose-neck type pipes welded on either side of seamless pipe to provide water stream at desired flow rate to cool hot strip from top surface;

each said top header is connected with electro-pneumatically operated butterfly shut off valve for opening/ closing of spray;
each bank is connected with a flow control valve along with flow meter provided for flow control;

(ii) bottom banks, wherein

each said bottom bank having plurality of section having plurality of spray headers , to constitute a bottom spray arrangement wherein each said header have plurality of laminar pipes to provide water stream at desired flow rate to cool hot strip from bottom surface;

each said bottom section is connected with electro-pneumatically operated butterfly shut off valve for opening/ closing of spray;

an additional manual butterfly valve provided to control the water flow manually in bottom banks.
(iii) pumping means for supplying water to said top and bottom banks at desired pressure and flow rate.

Another aspect of the present invention is directed to a run out table (ROT) laminar cooling system for hot strip mill wherein in said top banks two types of top headers are provided with varying the pitch of the goose-neck pipes to cover entire strip width so that water streams are staggered to cover up entire strip width generating smaller diameter streams which can break steam barriers effectively on strip surface.

Yet another aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein the pressure inside top headers is above zero preferably in the range of 0.1-0.2 bar, so that the flow to all streams are better assured.

A further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein control valves fitted for top headers are provided with 4-20 ma input signal to control flow rate.

A still further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein in said bottom headers plugs provided at both end for flushing in case of any clogging of pipe.

A still further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein in said bottom headers flanged joint to main headers provided in place of welded joint so that headers can be removed easily if any damage occurs.

A still further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein in said bottom headers sliding freedom engagement is provided on drive side to arrest lateral movement of headers to ensure aligned water flow and only one fixing bolt provided on operator side for easy removal.

A still further aspect of the present invention is directed to arun out table (ROT) laminar cooling system for hot strip mill wherein in said bottom headers seamless pipes are fitted with nozzle at top and said nozzles can be removed for cleaning if any clogging occurs.

The above and other objects and advantages are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: showsprevious design of top headers having tubular nozzles from where water falls under very less pressure and has gravity fall.
Figure 2: shows water leakage from previous top header even when not in use and falling on motors.
Figure 3: shows the design configuration of goose-neck top header in the modified ROT cooling system according to the present invention.
Figure 4.: shows the smaller diameter water stream generated from goose neck type modified header for top bank.
Figure 5: illustrates the insertion of new plate in Top Header to arrest water leakage.
Figure 6: shows Bottom Headers/banks of Modified ROT cooling system according to the present invention with incorporation of laminar pipe design.
Figure 7: shows the flanged joint to main headers provided replacing earlier welded joint so that headers can be removed easily in case of any damage.
Figure 8: illustrates the end arrangement for bottom headers wherein plugs are provided at both end for flushing in case of any clogging of pipe and also having sliding freedom engagement provided on drive side and only one fixing bolt provided on operator side for easy removal.
Figure 9(a) & (b): shows the previous and modified bottom headers.
Figure 10:shows the modified bottom headers installed in one of the bottom banks.
Figure 11(a) & (b): shows the water flow from (a) previous bottom headers & (b) from modified bottom headers.
Figure 12(a) & (b): shows the water flow from (a) previous top headers & (b) from modified top headers.
Figure 13: shows graphically the comparison of cooling rates of previous and modified ROT cooling system.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to provide a modified Run Out Table(ROT) laminar cooling system for conventional Hot Strip Mill, with goose-neck type headers for top banks and laminar pipes for bottom banks, primarily to achieve laminar flow with improved cooling rate for both top and bottom headers.

The previous design had tubular nozzles at top headers as illustrated in Fig.1 from where water falls under very less pressure and has gravity fall. Moreover, in the existing ROT cooling system, water leakage from top header even when not in use and falling on motors as shown in Fig.2 caused frequent motor damage.
Modified ROT cooling system

The ROT cooling system at HSM, RSP is divided into 4 banks, each bank having top and bottom spray arrangement. The ROT cooling system modified with goose-neck type headers for top banks and laminar pipes for bottom banks. Since, the pumps of cooling water are not changed, same flow rates were taken to design new headers. The design was changed primarily to achieve laminar flow with improved cooling rate for both top and bottom headers.

Flow Rate of ROT cooling system:
a) Flow rate of each Top header = 132.2 m3/hr
b) Total Flow Rate when all top headers open = 132.2 x 24 ? 3175.2 m3/hr
c) Flow rate of each Bottom headers = 37.8 m3/hr
d) Total Flow Rate when all bottom headers are open = 37.8 x 84 ? 3175.2 m3/hr
e) Total flow rate of the system (Top+ Bottom) = 3175.2 + 3175.2 ? 6350.4 m3/hr

Modification in Top Banks:

Each of the 4 top banks has 6 goose neck type spray headers. So, there are 24 headers in top spray arrangement. Each top header has 69 goose-neck SS pipes welded in 200NB seamless pipe. 35 pipes are welded on one side and 34 pipes on other side. Further two types of top headers (type-1 & type-2) have been used with varying the pitch of the pipe to cover entire strip width. Each top header is connected with one 6’’ electro-pneumatically operated butterfly shut off valve for opening/ closing of spray. Two banks were changed in phase manner during HSM weekly/ monthly shutdown. A flow control valve along with flow meter has been provided for flow control system.

The modifications done in top banks are summarized as follows:
(i) ROT cooling system design with incorporation of goose-neck type top headers. Basic design of gooseneck header designed for this case is shown in Fig.3.
(ii) Since, the pumps are not changed, flow rate for headers kept same.
(iii) With gooseneck type design system, smaller stream is achieved which can break steam barriers effectively as shown in Fig.4.
(iv) Many such streams are staggered by providing two types of headers to cover up entire strip width.
(v) Since the pressure (0.1-0.2 bar) inside header is above zero, the flow to all streams are better assured.
(vi) The new ON/OFF shut off valves provided with spring return, hence even during power or air failure the valves can return to close position.
(vii) The valve actuator designed for 3.5 bar operating pressure compared to 5 bar for earlier valves.
(viii) Input signal to the valves changed from 0-230V AC to 0-24 V DC to ensure reliability and reduce electrical breakdown of valves.
(ix) Water leakage from top header arrested by inserting a new flat plate as shown in Fig.5 since the old flat surface was damaged beyond repair.
(x) New control valves fitted for top headers with 4-20 ma input signal to control flow rate.
(xi) New flow meters were fitted to know flow rate in each top bank.

Modification in Bottom Banks:

Each of the 4 bottom banks has 3 sections, each section having 7 spray headers. So, there are 84 headers in bottom spray arrangement. The modified bottom header has 35 laminar pipes compared to 24 nozzles in previous headers. Further, flushing arrangement has been provided in end connection for cleaning headers during any pipe clogging. Each bottom section is connected with one 8’’ electro-pneumatically operated butterfly shut off valve for opening/ closing of spray. An additional 8” manual butterfly valves are also been provided to control the water flow manually in bottom banks.

Major modifications done in Bottom Banks are as follows:
(i) ROT cooling system design with incorporation of laminar pipe design as shown in Fig.6.
(ii) The seamless pipes fitted with nozzle at top. Nozzle can be removed for cleaning if any clogging occurs.
(iii) Flow rate for headers kept same as previous.
(iv) Streams staggered by providing two types of headers to cover up entire strip width.
(v) Flanged joint to main headers provided in place of welded joint as shown in Fig.7. Thus headers can be removed easily if any damage occurs.
(vi) Sliding freedom engagement provided on drive side to arrest lateral movement of headers and ensure aligned water flow as shown in Fig.8. Only one fixing bolt provided on operator side for easy removal.
(vii) Plug (Fig.8) provided at both end for flushing in case of any clogging of pipe
(viii) The new ON/OFF shut off valves provided with spring return, hence even during power or air failure the valves can return to close position.
(ix) The valve actuator designed for 3.5 bar operating pressure compared to 5 bar for earlier valves.
(x) Input signal to the valves changed from 0-230V AC to 0-24 V DC to ensure reliability and reduce electrical breakdown of valves.
(xi) New manual throttle valves added to make flow variable manually as per requirement.

Installation of Modified System:

(a) Two banks were changed in phased manner during HSM weekly/ monthly shutdown. Further remaining two banks were changed during capital repair of HSM.
(b) The previous and modified bottom headers are shown in Fig.9.a & 9.b. The modified bottom headers installed in one of the banks is shown in Fig.10. The comparison of flow between previous and modified bottom headers is shown in Fig.11. Laminar flow can be clearly seen with modified headers compared to previous header.
(c) The modified goose-neck type top headers were installed in phase manner. Two top banks (bank#3, bank#4) were changed during weekly/monthly shutdown. Remaining two top banks (bank#1, bank#2) were changed during capital repair of HSM. The 6” ON/OFF control valves were also changed along with top headers. An additional 20mm plates were provided between modified header and face of the top banks to take care of any leakages due to uneven surface. The comparison of flow between previous and modified bottom headers is shown in Fig.12. Laminar flow can be clearly seen with modified headers compared to previous header.
(d) Trials were carried out with modified system for different thickness of coils rolled at HSM to evaluate its cooling efficiency. Further, cooling rates were compared with the coils processed before innovation as shown in Fig.13. The cooling rates found to be 3.5-7% higher than previous system. With higher cooling rates (increased by 3.5-7.0%), thicker HR coils can be processed at a higher speed leading to higher mill productivity.

The solutions provided in new modifications:
(i) The new valves were provided with spring return, hence with power or air failure the valves would return to close position of it’s own. The valve actuator were also designed for 3.5 bar.
(ii) Filter regulator was fitted with all valves with auto drain. That means dirt are filtered and free water would drain automatically when a certain water level is accumulated in bowel. But it is advised to inspect it time to time for proper operation for dirt removal / filter cleaning.
(iii) New control valves fitted with 4-20 ma input signal
(iv) New flow meters were fitted to know flow going to each top bank
(v) Bottom headers were designed for easy removal with inlet water flanged joint and only one fixing bolt for removal at operating side.
(vi) Water leakage from top header arrested by inserting a new flat plate since the old flat surface was damaged beyond repair.
(vii) Since for bottom headers, the control valves were not changed, new manual throttle valves were added to make flow variable manually as per desire.
(viii) Old solenoid valve voltage were changed from 230V AC to 24VDC. Such voltage is not hazardous to human and goes well with water / humid condition. Such change would reduce solenoid failures.
(ix) The new valve actuators and solenoid valves are also compatible with air mixed with some stray water. No oil lubrication is required.

It is thus possible by way of the present invention to provide modified ROT cooling system for HSM having the following salient advantageous features:
(a) The new system is aimed to be changed to latest type system in order to achieve better and uniform cooling rate.
(b) By effecting higher cooling rate, better metallurgical properties of product is achieved than before which will give better pricing power in market.
(c) Bottom headers are designed for easy removal with inlet water flanged joint and only one fixing bolt for removal at operating side.
(d) The top headers designed, so that it can be retrofitted in the existing system. Water leakage from top header arrested by inserting a new flat plate since the old flat surface was damaged beyond repair.

The above stated modified ROT cooling system can be utilized for upgrading any existing ROT laminar cooling system of any old Hot Strip Mill to increase their cooling efficiency, with improved operational benefits and product quality.