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 METHOD FOR IMPROVING PRODUCTIVITY OF COLD ROLLING MILLS AVOIDING STICKINESS BETWEEN WRAPS OF COIL.

2 APPLICANT (S)
Name : JSW Steel Limited.
Nationality : An Indian Company.
Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg, Mumbai - 400 026,
State of Maharastra, India.
3 PREAMBLE TO THE DESCRIPTION
COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.


FIELD OF THE INVENTION
The present invention relates to cold rolling mills and , in particular, to a method for improving productivity of cold rolling mills eliminating the problem of stickiness between the wraps of the coils during batch annealing of cold rolled coils due to the high temperature involved. In particular the, invention is directed to modification in the Electrolytic Cleaning Line (ECL), directed to imparting desired degree of roughness to the strip surface prior to annealing. Importantly, the processing proposed in the Electrolytic Cleaning Line (ECL) is directed to improving the mechanical properties, surface roughness and improved flatness of the strip without inducing any downtime for roll change or the like equipments and favoring improved productivity. Advantageously, the present invention provide for benefits like increase in productivity in Cold Compact Mill by about 15% and also increases yield at skin pass mill by about 3%, favoring wide application of such ECL system/lines in steel industry.
BACKGROUND ART
It is well known in the art of steel mill rolling processes that the process of cold rolling of hot rolled coils essentially comprises the steps of pickling, cold rolling and annealing, each having its own contribution interms of properties and quality of the finished CR strip. Pickling is a process whereby the surface oxide layers of HR coils/sheets are removed by passing the strip in dilute hydrochloric acid bath. The pickeld steel product i.e. the descaled sheet is subjected to cold rolling, whereby the thickness of the pickled strip is reduced to the desired level by passing it through a selective number of sets of steel rolls. Due to such cold reduction of thickness by selective roll pass, a substantial amount of stress is locked up in the rolled product. Annealing is the process whereby the stress induced in the steel strip during rolling are relieved by controlled heating to a temperature of around 750°C in hydrogen atmosphere and then controlled cooling.
The strip surface should be clean prior to annealing, as a precondition for the process to achieve desired surface characteristics of the CR coils. For the purpose of cleaning the strip surface, it is passed through electrolytic cleaning line (ECL) wherein oil, grease, iron fines and other dirt and soil on the surface of the strip is removed by spraying, brushing and electrolytic treatment with hot aqueous (Uniclean - 93 as used by JSW) cleaning solutions which ultimately results in bright surface and avoids sooth marks while skin passing.
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Conventionally the ECL line is divided into three main sections:
Entry section: comprising of 2 pay off reels, one welder section and one vertical accumulator. The Pay-off reel is used to receive the coil from the entry coil car to unwind/uncoil and to feed the coil to the subsequent stages of the process. The welder is used for continuous lap seam welding of trailing end of outgoing strip with leading edge of incoming strip to maintain continuity of process and to avoid down-time. The accumulator is used for accumulating the strip for uninterrupted operations of the process while welding the two coil ends together in order to make the strip continuous.
Process section: Comprising 2 alkali cleaning tank, 3 brushing tank, 1 electrolytic cleaning tank, 3 hot water rinsing tank, 2 hot air dryer, 1 air wiper, 2 alkali holding tank, 3 brush holding tank, 1 electrolytic holding tank, sump tank mixing tank and condensate tank. Alkali cleaning tank is used to pre-remove oil off the strip surface by spraying the alkali solution on the both side of the strip. Brushing Tank is used to clean the dirt and grit on the coil surface remaining after the alkali spray cleaning. Electrolytic cleaning tank is used for final removal of oil and remaining iron fines off the strip surface. High current density bipolar system is used in ECL tank. The strip is then rinsed with hot water and then air dried.
Exit section': This section consists of 2 re-coiler unit and 1 flying shear. Flying shear cuts the strip while in motion to match the load requirements at exit re-coiler and belt wrapper. Re-coilers are used to wind the strip for easy handling and dispatch. It consists of belt wrapper, outboard bearing support and pusher plate assembly.
It has been observed despite cleaning of sheet surface carried out by involving the above said conventional Electrolytic Cleaning Line through its various stages, one major problem encountered is the sticker formation during annealing of cold rolled coils and thereby compromising the quality standards of the finished steel products.
There has been therefore a continuing need to develop a process for the surface treatment of the CR sheet/strip, apart from removing the oil, grease, iron fines and other dirt and soil on the surface of the strip by various stages of the ECL line as already explained, such as
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introducing a skin pass mill selectively sequenced, in order to impart through said process certain roughness to the strip surface on one hand and on the other hand improve mechanical properties and flatness which helps avoiding stickiness problem during annealing process. The compound cleaning and skin pass process also favours achieving improved yield of skin pass mill and overall productivity in Compact Cold Mill.
OBJECTS OF THE INVENTION:
The basic object of the present invention is thus directed to a process and system for eliminating /reducing the problem of stickiness between successive wraps of the coil during the annealing carried out at fairly high temperature in the range of 750°C to thereby favour the productivity of the rolling mill.
A further object of the present invention is directed to a process and a system to impart some roughness to the surface of the strip prior to annealing attended in cold rolling mills to avoid occurrences of sticker formation during batch annealing.
A still further object of the present invention is directed to a process of surface treatment of CR coils prior to batch annealing by incorporating a step of working to impart roughness to the strip surface prior to the processing section of the ECL, to improve mechanical properties and flatness while imparting desired surface roughness such as to eliminate the problem of stickiness during annealing.
According to yet another object of the present invention is directed to a process of surface treatment of CR coils prior to batch annealing which is capable of providing consistently good finished product quality by adopting in-line skin pass of CR coils, selectively sequenced prior to processing section in ECL line, and thus ensuring increased yield at skin pass mill, reducing down time of mills due to changing of finishing rolls or problems of sticking of layers and also increased productivity in the Compact Cold Mill by about 15%.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a method for improving productivity of cold rolling mills comprising:
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subjecting the strip surface prior to electrolytic cleaning to passage through skin pass mill to impart surface roughness such that the strip after the electrolytic cleaning and during annealing is free of problems of stickiness and thereby favour improving productivity of the cold rolling mill.
In the above disclosed method for improving productivity of cold rolling mills the said step of passing the strip through skin pass mill comprise passing the strip through two pass line rolls, one deflector roll, two anti crimp rolls, one pair of back up rolls and one pair of work rolls.
Importantly, it is found by way of the present invention that the passage of the strips prior to electrolytic cleaning through said skin pass mill improved productivity by about 15 % and the yield at skin pass mill by about 3 %.
In the above method of the invention the passage of the strip through the electrolytic cleaning line after said desired surface roughness, improved mechanical properties and flatness is done to remove oil, grease, iron fines and other dirt and soil on the surface of the strip by spraying , brushing and electrolytic treatment with hot aqueous cleaning solution.
According to a preferred aspect the method for improving productivity of cold rolling mills
of the invention comprises :
allowing the coils through an entry section comprising receiving the coils from an entry coil car /subjecting to continuous lap seam welding of trailing end of outgoing strip with leading edge of incoming strip to maintain continuity, accumulating the strips in an accumulator;
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processing for electrolytic cleaning by passing the strips from said accumulator through said skin pass mill and processing for said electrolytic cleaning of the strip; and
recoiling in an exit section for subsequent annealing and completion of the cold rolling process.
According to another aspect of the present invention there is provided a system for carrying out the method for improving productivity of cold rolling mills as disclosed above comprising:
an electrolytic cleaning line comprising a skin pass mill adapted to impart surface roughness such that the strip after the electrolytic cleaning and during annealing is free of problems of stickiness and thereby favour improving productivity of the cold rolling mill.
In accordance with a preferred aspect the system includes said electrolytic line comprising:
an entry section ;
a 4HI skin pass Mill section ;
a processing section for electrolytic cleaning ; and
an exit section.
Preferably, in the above system includes:
said entry section comprises pay off reels, welder section and vertical
accumulator;
said skin pass mill section comprises preferably two pass line rolls, one deflector
roll, two anti-crimp rolls, one pair of back-up rolls and one pair of work rolls;
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said process section comprises alkali cleaning tank, brushing tank, electrolytic cleaning tank, hot water rinsing tank, hot air dryer, air wiper, alkali holding tank, brush holding tank ,electrolytic holding tank, sump tank, mixing tank and condensate tank; and
said exit section comprises (i) re-coiler unit including belt wrapper, outboard support and pusher plate assembly and (ii) flying shear.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: is the illustration of the general Process Flow Diagram for the Cold Rolling Mill.
Figure 2: is the schematic representation with line and block diagram of the conventional Electrolytic Cleaning Line of CR coils.
Figure 3: is the schematic illustration with line and block diagram for the modified Electrolytic Cleaning Line of CR coils, incorporating in-line skin pass Mill prior to process section in ECL line, according to the present invention .
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
The present invention is thus directed to a process of introducing skin pass mill in the Electrolytic Cleaning line of the CR coils prior to annealing to eliminate/reduce the problem of stickiness between successive wraps of the coil during the batch annealing carried out at fairly high temperature in the range of 750°C, and ensure consistent good quality of the finished rolled product and also higher productivity of the Cold Rolling mill.
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Reference is first invited to the accompanying Figure 1, illustrating the flow chart for cold rolling process of hot rolled coils, comprising in general the process steps of:
(i) Pickling, whereby the surface oxide layers are removed by passing the strip in
dilute hydrochloric acid bath; (ii) Cold rolling, whereby the thickness of the pickled strip is reduced to the
desired level by passing it through steel rolls and preferably a Compact Cold 6-
Hi Twin stand; (iii) CR coils are then send to Electrolytic Cooling Line for cleaning of oil, grease or
dust from sheet/strip surface; (iv) Annealing of CR coils is then carried out in HPH cooling furnace, whereby the
stress induced in the steel strip during rolling are relieved by controlled heating
to a temperature of around 750°c in hydrogen atmosphere and then controlled
cooling; (v) The coils are then further rolled through the 4-Hi skin pass mill for finishing and
then they are recoiled and sent for automatic final packaging.
Reference is now invited to the accompanying Figure 2, which illustrates schematically the Conventional Electrolytic Cleaning Line wherein 2 pay off reels or uncoilers are placed at the entry section followed by pinch roll cum flattener and entry shear to be sent next to one welder section and one vertical accumulator. The Pay-off reel is used to receive the coil from the entry coil car to unwind/uncoil and to feed the coil to the subsequent stages of the process. The welder unit performs continuous lap seam welding of trailing end of outgoing strip with leading edge of incoming strip to maintain continuity of process and to avoid down-time. The accumulator is used for accumulating the strip for uninterrupted operations of the process while welding the two coil ends together in order to make the strip continuous.
In the processing section of the ECL line, there exist alkali cleaning tank, brushing tank, electrolytic cleaning tank, hot water rinsing tank, hot air dryer, air wiper, alkali holding tank, brush holding tank, electrolytic holding tank, sump tank mixing tank and condensate tank, in selective numbers and sequence. Alkali cleaning tank is used to pre-remove oil away from the strip surface by spraying the alkali solution on the both side of the strip. Brushing Tank is used to clean the dirt and grit on the coil surface remaining after the alkali spray cleaning. Electrolytic cleaning tank is used for final removal of oil and
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remaining iron fines off the strip surface. High current density bipolar system is used in ECL tank. The strip is then rinsed with hot water and then air-dried.
Finally in the exit section of the Conventional Electrolytic Cleaning Line, there exist 2 re-coiler units and 1 flying shear. Flying shear cuts the strip while in motion to match the load requirements at exit re-coiler and belt wrapper. Re-coilers are used to wind the strip for easy handling and dispatch. It consists of belt wrapper, outboard bearing support and pusher plate assembly.
Such conventional ECL systems suffer from the limitations of occurrences of sooth on the strip surface during annealing and the frequent break down and consequent loss of productive time for repair and resumption tends to lower productivity and yield and also quality of end product is not satisfactory due to either presence of sooth marks at skin pass or sticking of wraps of the coil during annealing.
It has also been observed that providing some roughness to eliminate the problem of stickiness during annealing possible to be achieved by the alternative means such as by having rolls with matte finish in rolling mill. But this would have resulted in an increase in the number of passes due to increased load requirements and thus increasing production time and reducing productivity of the mill.
Another alternative is to achieve desired degree of surface roughness by changing the rolls in the mill with matte finish roll before the final pass; but again such changing of rolls each time before the final pass would have resulted in much increased downtime and unnecessarily decreasing the productivity and thus seemed unviable.
Reference is now invited to the accompanying Figure 3, that schematically illustrates the modified Electrolytic Cleaning line incorporating the skin pass stage prior to the process section of the ECL and also preventing surface sticking of wrappings during annealing, while ensuring improved mechanical properties, flatness in resulting finished product. The process according to the invention also help improving the yield of the skin pass mill by about 3% and productivity improvement by at the Compact cold rolling Mill by about 15%.
This embodiment of the present invention as illustrated in the accompanying Figure 3 includes a 4-Hi skin pass roll stand located prior to process section of ECL, comprising two
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pass line rolls, one deflector roll, two anti crimp rolls, one pair of back up rolls and one pair of work rolls. Processing through this section improve mechanical properties, surface roughness and improve flatness which helps in reducing stickiness problem during annealing process. The in-line skin pass feature of the present electrolytic cleaning line installed and tried out at the plant scale has shown significant improvements in quality and productivity as compared to the conventional ECL line.
It is thus possible by way of the present invention to providing a process for treatment and cleaning of the surface of cold rolled sheets/strips obtained from the HR coils by incorporating a selectively configured and sequenced skin pass stage in the Electrolytic Cleaning line prior to batch annealing, whereby the occurrences of sticking between wraps of coils is avoided during annealing at elevated temperature. The process according to the present invention also helps maintaining consistently good quality of the finished product and also enabling improvements in the mechanical properties of the CR strips, its flatness in a reliable and cost effective manner, reducing the downtime of the rolling mills and achieving enhanced overall productivity and yield of the CCM plant.
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WE CLAIM:
1. A method for improving productivity of cold rolling mills comprising:
subjecting the strip surface prior to electrolytic cleaning to passage through skin pass mill to impart surface roughness such that the strip after the electrolytic cleaning and during annealing is free of problems of stickiness and thereby favour improving productivity of the cold rolling mill.
2. A method for improving productivity of cold rolling mills as claimed in claim 1 wherein said step of passing the strip through skin pass mill comprise passing the strip through two pass line rolls, one deflector roll, two anti crimp rolls, one pair of back up rolls and one pair of work rolls.
3. A method for improving productivity of cold rolling mills as claimed in anyone of claims 1 or 2 wherein the passage of the strips prior to electrolytic cleaning through said skin pass mill improved productivity by about 15 % and the yield at skin pass mill by about 3 %.
4. A method for improving productivity of cold rolling mills as claimed in anyone of claims 1 to 3 wherein the passage of the strip through the electrolytic cleaning line after said desired surface roughness, improved mechanical properties and flatness is done to remove oil, grease, iron fines and other dirt and soil on the surface of the strip by spraying, brushing and electrolytic treatment with hot aqueous cleaning solution.
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5. A method for improving productivity of cold rolling mills as claimed in anyone of
claims 1 to 4 comprising :
allowing the coils through an entry section comprising receiving the coils from an
entry coil car, subjecting to continuous lap seam welding of trailing end of outgoing
strip with leading, edge of incoming strip to maintain continuity, accumulating the
strips in an accumulator;
processing for electrolytic cleaning by passing the strips from said accumulator
through said skin pass mill and processing for said electrolytic cleaning of the
strip; and
recoiling in an exit section for subsequent annealing and completion of the cold
rolling process.
6. A system for carrying out the method for improving productivity of cold rolling mills
as claimed in anyone of claims 1 to 5 comprising:
an electrolytic cleaning line comprising a skin pass mill adapted to impart surface roughness such that the strip after the electrolytic cleaning and during annealing is free of problems of stickiness and thereby favour improving productivity of the cold rolling mill.
7. A system as claimed in claim 6 wherein said electrolytic line comprises:
an entry section ;
a 4HI skin pass Mill section ;
a processing section for electrolytic cleaning ; and
an exit section.
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8. A system as claimed in anyone of claims 6 or 7 wherein
said entry section comprises pay off reels, welder section and vertical
accumulator;
said skin pass mill section comprises preferably two pass line rolls, one deflector
roll, two anti-crimp rolls, one pair of back-up rolls and one pair of work rolls;
said process section comprises alkali cleaning tank, brushing tank, electrolytic cleaning tank, hot water rinsing tank, hot air dryer, air wiper, alkali holding tank, brush holding tank ,electrolytic holding tank, sump tank, mixing tank and condensate tank; and
said exit section comprises (i) re-coiler unit including belt wrapper, outboard support and pusher plate assembly and (ii) flying shear.
9. A method for improving productivity of cold rolling mills and a system for carrying
out such method substantially as hereindescribed and illustrated with reference to
the accompanying figures.

Dated this 10th day of June, 2008 Anjan Sen
Of Anjan Sen & Associates (Applicants Agent)
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