Title of Invention

"A SYSTEM FOR CONTROL OF ZINC COATING THICKNESS FOR CARRYING OUT CONTINUOUS HOT DIP COATING OF BASE METAL SURFACE"

Abstract A system for carrying out continuous hot dip coating on base metal surfaces especially for use in hot strip galvanizing processes comprising means for maintaining base metal strip centre line at said air knife zone comprising a front stabilizer roll and a rear stabilizer roll positioned alongside the flat surfaces of said metal strip and submerged in said molten metal bath on separate movable rig and means for adjustment of said front and rear stabilizer rolls relative to said base metal strip to achieve necessary base metal strip flatness and shape and control vibrations of the strip and deposition thereon by air pressure at air-knife zone and achieve an uniform deposition of the coat on said base metal strip. It is possible by way of the above system of the invention to reduce strip vibration with respect to pass line at air knife zone by over 50% from a level of 10-15 mm to less than about 5-7 mm. the system also assists in controlling the coating wt. on both sides of the strip within ±5% of target. Also, the system is useful in reducing overall specific con option of zinc by over 2 Kg./T.
Full Text The present invention relates to a system for use in continuous hot dip coating of metal and the like and in particular to hot dip steel strip galvanizing processes wherein the thickness of zinc coating deposition on steel strip is controlled by air pressure at air-knife zone. Process of hot dip galvanizing line operation involves coating of zinc on to the steel surface by hot dipping process for protection of steel surface against corrosion.
The hot dip galvanizing line operation and the process usually followed comprise coating of the base metal by immersion in a molten bath of zinc which is maintained at lower temperature than the melting point of the base metal (steel).
Usually for carrying out such hot dip galvanizing line operation, the system used comprise of a molten metal bath which usually contains the molten metal to be coated on the base metal. The base metal in the form of strip is continuously dipped into the molten bath. During travelling in and out of said molten bath the strip is held inside the bath by means of a sink roll which is positioned inside the molten bath. A stabilizer roll was located in front of the front flat surface of the metal strip and positioned within the molten-bath to stabilize the metal strip against vibrations thereon at air-knife zone during wiping operation. The thickness of zinc coating deposition on the steel strip is basically controlled by air pressure at air knife zone.
It is experienced that use of single stabilizer roll system, a considerable amount of vibration at air knife zone take place which result in variation in coating weights by over 10-15 gm/m2 (both sides) for 120 gm/m2 grade of coating. Moreover, such variation in coating weight result in non-uniform zinc coating on both sides of the strip. Also such non-uniformity in coating was associated with loss of the expensive zinc by way of excessive consumption of zinc during the process.

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It is thus the basic objective of the present invention to provide for a double stabilizer roll system for use in coating of metal strips and the like especially for hot dip galvanizing line which would reduce strip vibration with respect to pass line at air knife zone by over 50% from a level of 10 -15 mm to less than about 5 - 7mm.
Another object of the present invention is to provide for a system for use in coating of metal strips and the like especially for hot dip galvanizing line which would achieve uniformity in zinc coating weight on both sides of strip thereby control the coating wt. on both sides of the strip within ± 5% of target i.e. +5-7 gms/m2 from a level of+ 10 - 15 gms/m2.
Yet another object of the present invention is to provide for a system for use in coating of metal strips and the like especially for hot dip galvanizing line wherein average coating weight could be decreased by over 2% for 120 gms/m2 grade of coating.
Yet further object of the present invention is to provide for a system for use in hot dip galvanizing line which would provide for decrease in overall specific zinc consumption (Kg/T) by over 2 Kg/T.
Thus according to the present invention that is provided a double stabilizer roll system for carrying out continuous hot dip coating on base metal surfaces comprising:
a molten metal bath containing metal to be coated onto the base metal surface ;
means for continuous dipping into and taking out of said molten-bath of the base metal strip for the purpose of said coating ;
means for controlling coating/deposition,thickness on said base metal strip by air pressure means at air knifezone ;

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means for maintaining base metal strip centre line at said air knife zone comprising a front stabilizer roll and a rear stabilizer roll positioned alongside the flat surfaces of said metal strip and submerged in said molten metal bath on separate movable rig ;
means for adjustment of said front and rear stabilizer rolls relative to said base metal strip to achieve necessary base metal strip flatness and shape and control vibrations of the strip and deposition thereon by air pressure at air-knife zone and achieve an uniform deposition of the coat on said base metal strip.
The above disclosed system of the invention is thus directed to provide for a more controlled hot dip coating of metal strips and the like especially galvanizing line operation by controlled coating of zinc onto the steel surface. In particular, the system of the invention provides for maintaining the strip centre line at air knife zone by the provision of both front and rear stabilizer roll adjacent to both flat surfaces of the coated metal strip. Importantly, the stabilizer roll is positioned horizontally to set the existing pass line of the moving strip at air knife zone. The means for adjusting the relative position of the front and rear stabilizer rolls with respect to said coated metal strip further providing for achieving strip flatness and shape correction.
The details of the invention, its objectives and advantages are explained hereunder in greater detail in relation to the non-limiting exemplary embodiment of the system as shown accompanying figures wherein :
Fig. 1 is an enlarged representation of a conventional system for hot dip galvanizing illustrating the position of the front stabilizer roll.
Rig. 2 is a schematic illustration of the modified system in accordance with the present invention.

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Fig. 3 is an enlarged view of the relevant portion of the modified system of the present invention illustrating the modified construction providing for better stability of the metal strips and uniformly in coating thereon.
Reference is first invited to Fig. 1 which shows the conventional system presently in use of coating of metal strips comprising the molten metal bath (Zn pot) which is identified as (ZP), the sink roll (SR) carrying the base metal steel strip (SS) to be coated. As also illustrated in said figure, the system comprises of only one front stabilizer roll (FSR) for arresting the vibration of the strip at the air knife (A/K) zone. As would be evident from Fig. 1 due to considerable vibration at the air knife zone due to process operating variables, the front stabilizer roll was not sufficient to achieve uniformity in the coating on both sides of the metal strip. Accordingly this resulted in variation in coating weight by over 10 - 15 gms/m2 in use of the existing systems.
Reference is now invited to Figures 2 and 3 which show the modified system in accordance with the present invention. As shown in sad figures the system basically comprises of the molten metal bath (MB) which contains the molten zinc for coating on the base metal. The base metal in the form of a strip preferably having a maximum width of 1250 mm is adapted to be dipped into the molten metal bath and for the purpose is carried out in and out of the said metal bath by means of sink roll (SR). After being dipped into the metal bath (MB) the coated metal strip (SS) is taken out of the metal bath. As discussed above, the thickness of zinc coating deposition on steel strip is controlled by air pressure at air knife zone. Importantly in order to avoid the considerable amount, of vibration experienced at the air knife zone due to-process operating variables, the system of the present invention provides for modification by way of a provision of two stabilizer rolls comprising a front stabilizer roll (FSR) and a rear stabilizer roll (RSR) as clearly illustrated in Fig. 3. As would be evident from Fig." 3 the said front and

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rear roll stabilizer rolls together provide for maintaining strip centre line at air knife zone. In particular, the rear stabilizer roll (RSR) used in the system is submerged in the bath and placed on a separate movable rig. The stabilizer roll is positioned horizontally to set the existing pass line of the moving strip at the air knife zone. The strip flatness and shape correction is possible by means of relative adjustment of the front and rear stabilizers as per requirement.
Air at pressure range between 0.3 kg/cm2 to 0.5 kg/cm2 is allowed to pass through well designed nozzles (air-knife) at the air-knife zone at predetermined distance (25 - 40 mm) from the strips at both sides. The air-knife permits the desired Zn coating thickness to be adhered to the strip and the excess Zn wiped away and flows back to the Zn-pot along the strip surface.
It is thus possible by way of the system of the invention to reduce strip vibration with respect to the base line at air knife zone and thereby achieve uniformity in coating wt. on both sides of the strip. Thus loss of expensive zinc and controlled coating could be achieved. The system therefore is directed to favour more efficient and cost effective method of coating of metal strips.

WE CLAIM :
1. A system for carrying out continuous hot dip coating on base metal surfaces comprising.
a molten metal bath containing metal to be coated onto the base
metal surface ;
means for continuous dipping into and taking out of said molten bath of the base metal strip for the purpose of said coating ;
means for controlling coating/deposition thickness on said base metal

strip by air pressure means at air knife zone ;

means for maintaining base metal strip centre line at said air knife zone comprising a front stabilizer roll and a rear stabilizer roll positioned alongside the flat surfaces of said metal strip and submerged in said molten metal bath on separate movable rig ;
means for adjustment of said front and rear stabilizer rolls relative to said base metal strip to achieve necessary base metal strip flatness and shape and control vibrations of the strip and deposition thereon by air pressure at air-knife zone and achieve an uniform deposition of the coat on said base metal strip.
2. A system as claimed in claim 1, wherein the stabilizer roll is
positioned horizontally to set the existing pass line of the moving strip
at the air knife zone.
3. A system as claimed in any one of claims 1 or 2 for hot dip galvanizing
line operations comprising.


said molten bath containing molten zinc maintained at a lower
temperature than the melting point of the base metal steel strip ;
sink roll positioned inside the said zinc bath carrying said moving strip by base metal in and from said metal bath ;
said front and rear stabilizer rolls positioned horizontally to maintain the pass line of the moving strip at air-knife zone ;
means for adjusting the relative position of said front and rear stabilizer roll with respect to said base metal strip to achieve uniformity in coating on the said strip.
4. A system as claimed in anyone of claims 1 to 3 wherein said means for
relative adjustment of the said front and rear stabilizer rolls comprise :
rolls mounted on separate support arms, hinged from a separate movable rig. The roller arm movement (to & fro) is controlled by a mechanical (rack & pinion) arrangement by the operator for setting the existing pass line at a fixed position as desired.
5. A system for carrying out continuous hot dip coating on base metal
surfaces substantially as herein described and illustrated with
reference to the accompanying figures.
A system for carrying out continuous hot dip coating on base metal surfaces especially for use in hot strip galvanizing processes comprising means for maintaining base metal strip centre line at said air knife zone comprising a front stabilizer roll and a rear stabilizer roll positioned alongside the flat surfaces of said metal strip and submerged in said molten metal bath on separate movable rig and means for adjustment of said front and rear stabilizer rolls relative to said base metal strip to achieve necessary base metal strip flatness and shape and control vibrations of the strip and deposition thereon by air pressure at air-knife zone and achieve an uniform deposition of the coat on said base metal strip. It is possible by way of the above system of the invention to reduce strip vibration with respect to pass line at air knife zone by over 50% from a level of 10-15 mm to less than about 5-7 mm. the system also assists in controlling the coating wt. on both sides of the strip within ±5% of target. Also, the system is useful in reducing overall specific con option of zinc by over 2 Kg./T.

Documents:

00144-cal-2000-abstract.pdf

00144-cal-2000-claims.pdf

00144-cal-2000-correspondence.pdf

00144-cal-2000-description (complete).pdf

00144-cal-2000-drawings.pdf

00144-cal-2000-form 1.pdf

00144-cal-2000-form 18.pdf

00144-cal-2000-form 2.pdf

00144-cal-2000-form 3.pdf

00144-cal-2000-letter patent.pdf

00144-cal-2000-pa.pdf


Patent Number 210288
Indian Patent Application Number 144/CAL/2000
PG Journal Number 39/2007
Publication Date 28-Sep-2007
Grant Date 26-Sep-2007
Date of Filing 08-Mar-2000
Name of Patentee STEEL AUTHORITY OF INIDA LIMITED
Applicant Address RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA,RANCHI 834002,STATE OF JHARKHAND.INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 PRUSTY PRAMOF KUMAR Research & Development Centre for Iron and Steel, Steel authority of India Ltd.,Doranda, Ranchi 834002,State of Jharkhand.India.
2 PANDEY KEDAR NATH Research & Developement Centre for iron and steel, Steel Authority of India Ltd, Doranda, Ranchi 834002,State of Jharkhand, India.
3 PATHAK ASHISH Research & Developement Centre for iron and steel, Steel Authority of India Ltd, Doranda, Ranchi 834002,State of Jharkhand, India.
4 KRISHNA BINOD Research & Developement Centre for iron and steel, Steel Authority of India Ltd, Doranda, Ranchi 834002,State of Jharkhand, India.
5 GANTI MAHAPATRUNI DAKSHINI MURTY Research & Developement Centre for iron and steel, Steel Authority of India Ltd, Doranda, Ranchi 834002,State of Jharkhand, India.
6 JHA SUDHAKER Research & Developement Centre for iron and steel, Steel Authority of India Ltd, Doranda, Ranchi 834002,State of Jharkhand, India.
PCT International Classification Number C21D 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA