Description: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 :
ALUZINC COATED STEEL STRIP FOR APPLICATION IN BOTTOM PLATE OF AIR CONDITIONER OUT DOOR UNIT AND A PROCESS TO PRODUCE THE SAME.



2 APPLICANT (S)

Name : JSW STEEL COATED PRODUCTS LIMITED.

Nationality : An Indian Company incorporated under the Companies Act, 1956.

Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,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 INVENTION:
The present invention relates to corrosion resistant coated steel strip and more specifically Aluminium-Zinc alloy(Aluzinc) based coated steel strip. Importantly, the present invention relates to an alternate Aluzinc based coating on a cold rolled, non-skin pass, stretch levelled steel strip of 0.8 to 1.0 mm thickness that meets the mechanical property requirements and salt spray test requirements of a galvanized and powder coated steel requirement which is used as a structural component of Air Conditioner Out Door Unit Bottom plate.The bottom plate gets in contact with the hot gases & water droplets during defrosting cycle 3 times in an hour for 3min. So the SST properties of the component is important for long life of AC out door unit, approximately a life of 10~15 years.

BACKGROUND OF THE INVENTION
Air conditioner outer door unit bottom plate is a steel shell that houses the air conditioner compressor unit. The steel shell is usually made from 0.8 to 1.00 mm thick galvanized steel sheet that is further powder coated. The mechanical properties and corrosion resistance requirement to meet the said application is given in Table 1. The mechanical properties for the functional requirement of the end application is, yield strength of 220 MPa max., tensile strength of 330 MPa max. and a minimum elongation of 35% (in 50 mm Gauge length specimen). Traditionally, the application calls for 220 GSM galvanized coated steel conforming to the coating class designation Z220 with 40microns powder coating on it. The galvanized steel of 220GSM conformed to a salt spray test life of 600 h., as per IS 15961_2012.
Table 1 Target mechanical properties and corrosion resistance properties to be met for intended application.
Mechanical property requirements Coating Class
designation Salt Spray Test(600hr, first red rust)
Minimum coating mass gram per square meter
Total Both Surfaces One Surface
Triple Spot Single Spot Single Spot
Yield Strength - 220 MPa (Max)
Tensile Strength - 330MPa (Max)
Elongation -35 % (Min)
[In 50 mm Gauge Length]
AZ150
(150 GSM) 150

140

70

The aim of the present invention is to develop a cold rolled Aluzinc coated non-skin pass stretch levelled steel strip of thickness 0.8 and 1.0 mm that meets the above mentioned mechanical and salt spray test requirement, which is equivalent to that of Z220 GSM galvanized coating with 40microns of powder coating and its potential demonstration in an application. Applicants herein demonstrates this development in air conditioner out-door unit bottom plate component where the mechanical property and corrosion resistance property as per salt spray test life is demonstrated.This development will eliminate the powder coating process required in traditional galvanized coated material. It will bring down the cost encoring for powder coating.Again it eliminates the chances of emission of Volatile Organic Compounds, called VOCs (likeformaldehyde)which affect the workers’ health and ozone layer..Also the combination of barrier protection provided by the Aluminum network and the galvanic protection of interdendritic zinc provides excellent corrosion resistance.
Aluzinc Coating is a common form of coating technique,that provides a protective aluminum and zinc alloy coating on steel or iron, to prevent it from rusting.The coating is developed by Hot-dip Aluzinc coating process. There is a requirement of Aluzinc coated material with a salt spray test life of 600hrs minimum for first red rust with AZ150 GSM coating by using IF grade HRC for the application of air conditioner out-door unit bottom plate. The current invention is about the challenge to achieve the end requirement of salt spray test life and draw ability that is equivalent to the galvanized zero spanglematerial with Z220GSM and applying powder coating (40 Microns) as given in Table 1. The invention is a test case study where the AluZinc coated product can meet the galvanized product with complete retention of mechanical properties and corrosion resistance requirement measured by salt spray test for 600 h. as per IS 15961_2012.
Not any prior invention related to the product change from galvanized to Alu-Zinc exists for the specific requirement of the mechanical properties, Salt spray Test(SST) life & coating weight as given in Table 1 for the application of AC outdoor unit bottom plate.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to developing the Aluzinc Coated, non-skin pass steel with 0.8,1.0mm thickness, AZ150, using IF grade HRC with specific requirement of 600 hrs. salt spray test life as per IS 15961_2012, using substrate as per IS 277_2018 GPIF Grade.
Further, the object of this invention is to provide the above specific material to the application of air conditioner out door unit bottom plate.
A still further objective of the present invention is to achieve the AZ150 GSM as per specification mentioned herein before.For the present study, the applicants have demonstrated a certain thickness range of steel and the idea as per the invention will enable development of several other similar components like Ac side plate & Front Cover of about 0.6~0.7mm in thickness
The still further objective of the current invention to overcome the possible challenges going to be faced during the trials and making the process smooth to achieve the Mechanical properties suitable for the draw application andsalt spray test life, required for the end application.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to corrosion resistant coated steel strip having steel composition of

C – 0.0005 to 0.0025 % by wt. preferably 0.0020 % by wt;
Mn- 0.15 to 0.2 % by wt. preferably 0.15 % by wt;
P-0.0 % to 0.02% by wt. preferably 0.005 % by wt;
S- 0.0 to 0.008 % by wt. preferably 0.006 % by wt;
Si-0.0 to 0.02 % by wt. preferably 0.006 % by wt;
Al- 0.03 to 0.05% by wt. preferably 0.048 % by wt; and
N.- 0.00 to 0.004 % by wt. preferably 0.0035 % by wt;
Ti-0.025 to 0.035 % by wt. preferably 0.03 % by wt;
Nb.- 0.003 to 0.007 % by wt. preferably 0.005 % by wt; and balance iron,
and Al Zinc coating having Yield Strength – 180 MPa to 220MPa preferably about 210 MPa Tensile Strength – 270 MPa to 330 MPa preferably about 290 MPa; and Elongation 30 % to 45% preferably minimum 35% in 50mm gauge length.

A further aspect of the present invention is directed to said corrosion resistant coated steel comprising

Al Zinc coating of thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm & 1.0mm including that of a bottom plate of Air conditioner outdoor unit.
A still further aspect of the present invention is directed to said corrosion resistant coated steel which is non-skin pass and stretch levelled having thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm and 1.0mm and having coating AZ150GSM preferably more than 150GSM having minimum 140GSM for single spot both side and 70GSM for one side, matching requirement of 600 hrs. salt spray test life as per IS 15961_2012.
A still further aspect of the present invention is directed to said corrosion resistant coated steel having finish size of preferably 0.8x1245mm & 1.0x1250mm.

Another aspect of the present invention is directed to a process for manufacture of Aluzinc Coated Deep Drawing steel sheet including:
i)providing HR coil of steel composition having
C – 0.0005 to 0.0025 % by wt. preferably 0.0020 % by wt;
Mn- 0.15to 0.2 % by wt. preferably 0.15 % by wt;
P-0.0 % to 0.02% by wt. preferably 0.005 % by wt;
S- 0.0 to 0.008 % by wt. preferably 0.006 % by wt;
Si-0.0 to 0.02 % by wt. preferably 0.006 % by wt;
Al- 0.03 to 0.05% by wt. preferably 0.048 % by wt; and
N- 0.00to 0.004 % by wt. preferably 0.0035 % by wt;
Ti-0.025to 0.035 % by wt. preferably 0.03 % by wt;
Nb.- 0.003to 0.007 % by wt. preferably 0.005 % by wt; and balance iron,
ii) carrying out HR coil slitting;
iii) subjecting to pickling for removal of the oxide layer;
iv)subjecting to cold rolling including mechanical working of mild steel material to below its recrystallization temperature such as to reduce the thickness at cold rolling mills;
v) subjecting to step of Aluzinc coating involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance of the strip (c) stretch levelling to impart anti-fluting property to Aluzinc coated steel strip and desired shape involving tensile stress and bending stress to thereby provide for the corrosion resistant coated steel strips having yield strength in the range of 180 MPa to 220MPa preferably about 210 MPa;tensile strength in the range of 270 MPa to 330 MPa preferably about 290 MPa; and elongation in the range 30 % to 45% preferably minimum 35% in 50mm gauge length.

A still further aspect of the present invention is directed to said process wherein said Al Zinc coating is obtained of thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm & 1.0mm including configuring as that as structural components of a bottom plate of Air conditioner outdoor unit.

A still further aspect of the present invention is directed to said process wherein the said step of cold rolling is carried out involving coils of sizes 0.74 mm x 1245 mm to 0.78 X 1255mm preferably about 0.76 X 1250mm and 0.94 x 1245mm to 0.98 X 1255mm preferably about 0.96 X 1250mm, each said coil having weight of 24.5 Mt to 30.5 Mt preferably about 24.965 Mt., wherein Input HR sheet thickness is 3.97 mm to 4.03 mm preferably about 4.0 mm, output thickness 0.77 mm to 0.83 mm preferably about 0.8mm and 0.97mm to 1.03mm preferably about 1.0mm, so as to achieve a cold reduction in the range of 75 % to 83 % preferably about 80% min.

Another aspect of the present invention is directed to said process wherein the said step of Aluzinc coating involving a zinc bath comprising of Al 53 % to 57 % preferably about 55 %, Zn % 40 % to 46 % preferably about 43.5 % and Si % 1.4 % to 1.8 % preferably about 1.5 %, Fe % 0.3 to 0.5 % preferably about 0.4%.

Yet another aspect of the present invention is directed to said process wherein said step of Aluzinc Coating is carried out involving selective temperature control in various furnace sections sequentially including select exit temperatures comprising in Non-ox Furnace (NOF) 6000C to 700 0C preferably 6500C to clean the strip surface by burning the impurities, Radiant Tube Furnace (RTF) 720 0C to 780 0C preferably 7500C for being initially annealed by heating the cold rolled strip to its recrystallization temperature and soaked for 1 minute, soaked strip is coated by hot dipping in a AluZinc alloy pot with a layer of Al Zn alloy and proceed through soaking furnace 750 0C to 800 0C preferably 7800C and Jet Cooling Furnace (JCF) 580 0C to 610 0C preferably 6000C.

A further aspect of the present invention is directed to said process wherein said step of Aluzinc Coating involve furnace operative parameters including subjecting coil of size of 0.74 x1245 mm to 0.78x 1255mm preferably 0.76x1250 mm and 0.94 x 1245 to 0.98 X 1255 preferably about 0.96 X 1250mm to line speed of 60mpm to 80 mpm preferably about 70 meters per minute, 30 TPH to 50 TPH preferably about 35 Mt./Hrs, Furnace tension 880 kgf to 1200 kgf preferably about 1000 Kgf , Pot tension 1000 kgf to 1500 kgf preferably about 1200 kgf, Air Knife RPM 1650 to 2500 RPM preferably about 2000 RPM, Air Knife Pressure 60 to 80 Mbar preferably about 75 Mbar and air knife gap 10~15mm preferably about 12mm.

A still further aspect of the present invention is directed to said process wherein said Aluzinc Coating step is followed by a chemical treatment of the Aluzinc Coated surface with a superficial layer of non-chrome thin organic chemical passivation treatment to improve the corrosion resistance characteristic of the Aluzinc Coating.

According to yet another aspect of the invention there is provided the process wherein said non-chrome thin organic chemical passivation treatment is carried out involving pick up rolls which transfer to applicator rolls with said applicator rolls applying the this layer of said Aluzinc coated surface with said coating weight controlled by the pickup roll to applicator roll pressure measured via load ceslls and speed ratio of the applicator rolls with strip speed, followed by drying and finally cooling of the strip.

Above and other aspects of the present invention are described hereunder in greater details with reference to the following accompanying non limiting drawings and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows the graphical plot of Coil No VG4ACJ1047 to VG4ACJ1049 & VG4ACJ1142 to VG4ACJ1144, Showing Strip Temperature at Exit in Deg. Centigrade at different Furnace Sections – Non-ox Furnace, Radiant Tube Furnace, Soaking Furnace and Jet Cooling Furnace.
Figure 2: Samples condition after salt spray test (SST).
Figure 3: shows the roll coater facility for passivation treatment of Aluzinc coated steel sheet.
Figure 4: Air conditioner base Pan component made from Alu-Zinc coated steel passivated with chrome free acrylic coating.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS AND EXAMPLE
The basic aspect of the present invention is directed to AluZinc coated steel comprising of steel composition as in Table 2, which is Al Zinc coated and of thickness in the range of 0.77 mm to 0.83 mm & 0.97 mm to 1.03 mm preferably 0.8 mm & 1.0 mm having yield strength in the range 180 MPa to 220MPa, preferably about 210 MPa; tensile strength in the range 270 MPa to 330 MPa, preferably about 290 MPa; and elongation in the range 30 % to 45%, preferably minimum 35% [in 50 mm gauge length].

Table 2 The chemical composition of EDD Steel grade in wt.%
Elements Min Max. Target
C 0.0005 0.0025 0.0020
Si 0.0 0.02 0.006
Mn 0.15 0.20 0.15
P 0.02 0.005
S 0.008 0.006
Al 0.03 0.05 0.048
N 0 0.004 0.0035
Ti 0.025 0.035 0.03
Nb 0.003 0.007 0.005
A further aspect of the present invention is directed to the said Aluzinc Coated steel which is non-skin pass and stretch levelled having thicknesses as in Table 3.
Table 3 Thicknesses of AluZinc Coating and finish size of the steel strip
Aluzinc Coat thickness, mm Steel Strip
Thickness, mm Steel strip
Width, mm Galvanized coating
0.77 mm to 0.83 mm 0.8 1245 AZ150GSM
>150 GSM & min 140 GSM for single spot both side & 70 GSM for one side
0.97mm to 1.03mm 1.0 1250

EXPERIMENTAL PROCEDURE
The experimental trial involved in this invention was carried out in the Continuous Galvanizing Line. The inventive steel grade was produced as per the process route:
Hot Rolled Coil (HR coil) ? HR Coil Slitting ?Pickling ?Cold Rolling ? Aluzinc Coating? Packing
The process parametric details of the strips processed from hot rolling stage is shown in Table 4. Two hot rolled coils with the chemistry as in Table 4 were slit, pickled and cold rolled with reduction close to about 80%. There were three cold rolled coils from each hot rolled coil as shown in Table 4.
The cold rolled steel strip is thermally processed as shown in Table 5 and Figure 1. This involved cold rolled strip being initially annealed by heating the cold rolled strip to its recrystallization temperature of about 780oC in radiant tube furnace where the strip is soaked for 1 min. Before that Direct heating up to 650°C in NoX furnace to clean the strip surface by burning the impurities. The soaked strip is coated by hot dipping in a AluZinc alloy pot with a layer of Al Zn alloy. The strip travels through Radiant tube furnace, soaking furnace and Jet cooling furnace as in Table 5. The coated material is stretch levelled to achieve anti-fluting property to get desired shape by applying tensile and bending stress. This is followed by a chemical treatment of the Aluzinc Coated surface with a superficial layer of non-chrome thin organic chemical passivation treatment to improve the corrosion resistance as measured by the salt spray test life.
Table 4-Details of the production coils chosen for the invention.
Experimental Coil Coil -1 Coil-2
Hot Rolled Coil No VDNBCI3952 VDNBCI3953
Size (mm) 4.0 X 1280 4.0 X 1280
Grade 41ZAP(JDHIFV2W0F) 41ZAP(JDHIFV2W0F)
Heat No B020911 B020909
Chemistry (wt.%)
C 0.0020 0.0020
Mn 0.184 0.156
P 0.006 0.006
S 0.0060 0.0060
Si 0.004 0.004
Al 0.050 0.050
N 0.0031 0.0028
Cold Rolled Coil No VL1UCJ1467 VL1ACJ1036
Size (mm) 0.78X1250 0.96X 1250
% Cold Reduction 81.2 76.0
Coil No after cold reduction VG4ACJ1142 VG4ACJ1143 VG4ACJ1144 VG4ACJ1047 VG4ACJ1048 VG4ACJ1049

Table 5 -Furnace Parameters used for hot dip Aluzinc coating.
Parameters Units Reading
Avg. Line Speed m / min 75
Avg. t/h. 35
Avg. DFF Deg. Centigrade 650
Avg. RTF Deg. Centigrade 750
Avg. Soaking Deg. Centigrade 780
Avg. Exit Deg. Centigrade 600
SPM load Ton Nil
Parameters Units Reading
SPM Elong. % Nil
TLL Elong. % 0.4
Spencer Blower Air % Top: 66; Bot : 66
Air knife Pressure RPM 2000
Air knife gap mm 12~15
Finish size, mm 0.8 X 1245 mm & 1.0 x 1250 mm 0.8 X 1245 mm & 1.0 x 1250 mm

Figure 1 shows Furnace preheating thermal condition used for preheating the coils for hot dip Aluzinc process for cold rolled and annealed coils [VG4ACJ1047 to VG4ACJ1049 & VG4ACJ1142 TO VG4ACJ1144]
The Aluzinc coated steel strip after coating were sampled and analyzed for their mechanical and corrosion properties evaluated by salt spray testing as shown in Table 6. The results show that the property target as in Table 1 could be established. The typical air conditioner out-door unit bottom plate component stamped from the sheet so produced is shown in Figure 2.

Table 6 Mechanical Properties of AluZinc coated steel strip
Cold Rolled full hard
coil No. VL1ACJ1036 VL1UCJ1467
Galvalume Coil No VG4ACJ1047 VG4ACJ1048 VG4ACJ1049 VG4ACJ1142 VG4ACJ1143 VG4ACJ1144
Thick (mm) 1.0 1.0 1.0 0.8 0.8 0.8
Width (mm) 1250 1250 1250 1245 1245 1245

Mechanical Properties
Yield Strength (MPa)
Required 220 max 216 216 200 215 211 211
Tensile Strength (MPa)
Required 330 max 302 302 297 301 290 290
Elongation (%)
Required 30 % min. 44 44 46 38 38 38

Alu Zinc Coating Results
Minimum coating mass gram per square meter Total Both Surfaces Triple Spot 160 158 158 180 183 178
Single Spot 150 148 145 165 164 160
One Surface Single Spot 75 73 72 81 80 78

Table 7: SST Results
Reference Standard: ASTM B117
Equipment Used:Q-FOG, Q-Lab Corporation
Testing Hr. Observation for Samples Result
VG4ACJ1049 VG4ACJ1142 VG4ACJ1144 VG4ACJ1147
24 No Red Rust No Red Rust No Red Rust No Red Rust No Red rust observed up to 900SST Hr.
100 No Red Rust No Red Rust No Red Rust No Red Rust
200 No Red Rust No Red Rust No Red Rust No Red Rust
300 No Red Rust No Red Rust No Red Rust No Red Rust
400 No Red Rust No Red Rust No Red Rust No Red Rust
500 No Red Rust No Red Rust No Red Rust No Red Rust
600 No Red Rust No Red Rust No Red Rust No Red Rust
700 No Red Rust No Red Rust No Red Rust No Red Rust
~900 No Red Rust No Red Rust No Red Rust No Red Rust

Accompanying Figure 3 shows the roll coater facility for passivation treatment of Aluzinc coated steel sheet.
Facility Used: Vertical Roll Coater
Passivation Used: Non Chrome Organic Coating
Mechanism: The Pickup rolls (Steel rolls) picks the ready to use solution from drip pan & transfer it to Applicator rolls (Polyurethane) and at last the applicator roll transfer the thin solution layer on Aluzinc Coated surface. The coating weight controlled by the Pickup roll to applicator roll pressure measured by load cells and Speed ratio of applicator rolls with strip speed.
After the passivation coating the thin layer is dried by induction heater and at last the strip cooled to room temperature by air blowers.
Speed Ratio(%) Drying Temp.
(°C) Pressure(Kg) Direction(Ref. to Strip Direction)
Pickup Roll Applicator Roll Strip Temp. Load cell Pickup Roll Applicator Roll
50 140 90°C 8~15 Forward Reverse

Accompanying Figure 4 shows the Air conditioner base Pan component made from Alu-Zinc coated steel passivated with chrome free acrylic coating.

It is thus possible by way of the present invention to provide cold rolled Aluzinc coated Steel and more specifically to Aluzinc coated non-skin pass stretch leveled, 0.8 &1.0 mm thick steel sheet that was subject to further Zinc Coating 150 GSM, and passivated for the application of Air conditioner out Door Unit Bottom plate. The Aluzinc coated steel so produced having YS:220Mpa (Max), TS:330MPa(Max) and Elongation:35%(min) comply with the requirements of IS 15961_2012, mechanical properties & SST Hr. life suitable for the end application of air conditioner out door unit bottom plate.
, Claims:We Claim:
1. Corrosion resistant coated steel strip having steel composition of

C – 0.0005 to 0.0025 % by wt. preferably 0.0020 % by wt;
Mn- 0.15 to 0.2 % by wt. preferably 0.15 % by wt;
P-0.0 % to 0.02% by wt. preferably 0.005 % by wt;
S- 0.0 to 0.008 % by wt. preferably 0.006 % by wt;
Si-0.0 to 0.02 % by wt. preferably 0.006 % by wt;
Al- 0.03 to 0.05% by wt. preferably 0.048 % by wt; and
N.- 0.00 to 0.004 % by wt. preferably 0.0035 % by wt;
Ti-0.025 to 0.035 % by wt. preferably 0.03 % by wt;
Nb.- 0.003 to 0.007 % by wt. preferably 0.005 % by wt; and balance iron,
and Al Zinc coating having Yield Strength – 180 MPa to 220MPa preferably about 210 MPa Tensile Strength – 270 MPa to 330 MPa preferably about 290 MPa; and Elongation 30 % to 45% preferably minimum 35% in 50mm gauge length.

2. The corrosion resistant coated steel as claimed in claim 1 comprising

Al Zinc coating of thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm & 1.0mm including that of a bottom plate of Air conditioner outdoor unit.
3. The corrosion resistant coated steel as claimed in anyone of claims 1 or 2 which is non-skin pass and stretch levelled having thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm and 1.0mm and having coating AZ150GSM preferably more than 150GSM having minimum 140GSM for single spot both side and 70GSM for one side, matching requirement of 600 hrs. salt spray test life as per IS 15961_2012.
4. The corrosion resistant coated steel as claimed in anyone of claims 1 to 3 having finish size of preferably 0.8x1245mm & 1.0x1250mm.

5. A process for manufacture of Aluzinc Coated Deep Drawing steel sheet as claimed in anyone of claims 1 to 3 including:
i)providing HR coil of steel composition having
C – 0.0005 to 0.0025 % by wt. preferably 0.0020 % by wt;
Mn- 0.15to 0.2 % by wt. preferably 0.15 % by wt;
P-0.0 % to 0.02% by wt. preferably 0.005 % by wt;
S- 0.0 to 0.008 % by wt. preferably 0.006 % by wt;
Si-0.0 to 0.02 % by wt. preferably 0.006 % by wt;
Al- 0.03 to 0.05% by wt. preferably 0.048 % by wt; and
N- 0.00to 0.004 % by wt. preferably 0.0035 % by wt;
Ti-0.025to 0.035 % by wt. preferably 0.03 % by wt;
Nb.- 0.003to 0.007 % by wt. preferably 0.005 % by wt; and balance iron,
ii) carrying out HR coil slitting;
iii) subjecting to pickling for removal of the oxide layer;
iv)subjecting to cold rolling including mechanical working of mild steel material to below its recrystallization temperature such as to reduce the thickness at cold rolling mills;
v) subjecting to step of Aluzinc coating involving (a) annealing (b) coating of cold rolled steel strip to increase corrosion resistance of the strip (c) stretch levelling to impart anti-fluting property to Aluzinc coated steel strip and desired shape involving tensile stress and bending stress to thereby provide for the corrosion resistant coated steel strips having yield strength in the range of 180 MPa to 220MPa preferably about 210 MPa;tensile strength in the range of 270 MPa to 330 MPa preferably about 290 MPa; and elongation in the range 30 % to 45% preferably minimum 35% in 50mm gauge length.
6.The process as claimed in claim 5 wherein said Al Zinc coating is obtained of thickness in the range of 0.77 mm to 0.83 mm & 0.97mm to 1.03mm preferably 0.8 mm & 1.0mm including configuring as that as structural components of a bottom plate of Air conditioner outdoor unit.

7. The process as claimed in anyone of claims 5 or 6 wherein the said step of cold rolling is carried out involving coils of sizes 0.74 mm x 1245 mm to 0.78 X 1255mm preferably about 0.76 X 1250mm and 0.94 x 1245mm to 0.98 X 1255mm preferably about 0.96 X 1250mm, each said coil having weight of 24.5 Mt to 30.5 Mt preferably about 24.965 Mt., wherein Input HR sheet thickness is 3.97 mm to 4.03 mm preferably about 4.0 mm, output thickness 0.77 mm to 0.83 mm preferably about 0.8mm and 0.97mm to 1.03mm preferably about 1.0mm, so as to achieve a cold reduction in the range of 75 % to 83 % preferably about 80% min.

8. The process as claimed in anyone of claims 5 to 7 wherein the said step of Aluzinc coating involving a zinc bath comprising of Al 53 % to 57 % preferably about 55 %, Zn % 40 % to 46 % preferably about 43.5 % and Si % 1.4 % to 1.8 % preferably about 1.5 %, Fe % 0.3 to 0.5 % preferably about 0.4%.

9. The process as claimed in anyone of claims 5 to 8 wherein said step of Aluzinc Coating is carried out involving selective temperature control in various furnace sections sequentially including select exit temperatures comprising involving Direct Fired Furnace (DFF) including Non-ox Furnace (NOF), 6000C to 700 0C preferably 6500C to clean the strip surface by burning the impurities ,Radiant Tube Furnace (RTF) 720 0C to 780 0C preferably 7500C for being initially annealed by heating the cold rolled strip to its recrystallization temperature and soaked for 1 minute, soaked strip is coated by hot dipping in a AluZinc alloy pot with a layer of Al Zn alloy and proceed through soaking furnace 750 0C to 800 0C preferably 7800C and Jet Cooling Furnace (JCF) 580 0C to 610 0C preferably 6000C.

10. The process as claimed in anyone of claims 5 to 9 wherein said step of Aluzinc Coating involve furnace operative parameters including subjecting coil of size of 0.74 x1245 mm to 0.78x 1255mm preferably 0.76x1250 mm and 0.94 x 1245 to 0.98 X 1255 preferably about 0.96 X 1250mm to line speed of 60mpm to 80 mpm preferably about 70 meters per minute, 30 TPH to 50 TPH preferably about 35 Mt./Hrs, Furnace tension 880 kgf to 1200 kgf preferably about 1000 Kgf , Pot tension 1000 kgf to 1500 kgf preferably about 1200 kgf, Air Knife RPM 1650 to 2500 RPM preferably about 2000 RPM, Air Knife Pressure 60 to 80 Mbar preferably about 75 Mbar and air knife gap 10~15mm preferably about 12mm.

11. The process as claimed in anyone of claims 5 to 10 wherein said Aluzinc Coating step is followed by a chemical treatment of the Aluzinc Coated surface with a superficial layer of non-chrome thin organic chemical passivation treatment.

12. The process as claimed in anyone of claims 5 to 11 wherein said non-chrome thin organic chemical passivation treatment is carried out involving pick up rolls which transfer to applicator rolls with said applicator rolls applying the layer of said Aluzinc coated surface with said coating weight controlled by the pickup roll to applicator roll pressure measured via load cells and speed ratio of the applicator rolls with strip speed, followed by drying and finally cooling of the strip.
Dated this the 7th day of March, 2024
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199