FIELD OF INVENTION
The present invention relates to an improved air wiping system. Particularly, the invention relates to an improved air wiping system for arresting carry over on cold rolled strip surface thereby reducing the carry over residue on strip surface by substantial amount improving the surface quality of the strip.
BACKGROUND AND PRIOR ART
Recent trends for production of clean steel which indicates the higher degree of strip surface cleanliness of the post-annealed cold rolled strip coils. The cleanliness of cold rolled strip prior to annealing is primarily dependant upon the amount of oil and iron find residues on the strip surface. An emulsion coolant system used for cold rolling of steel which results in some amount of emulsion are being carried over on the strip surface during rolling. Therefore, it is important that level of emulsion carry over on the strip surface to be kept minimum otherwise potential carryover will impair strip surface quality and the downstream processes. The surface of cold rolled strip is required to be cleaned to facilitate coating, painting and plating of the strip as end uses and give on visual appeal/an aesthetic look for the finished products.
Generally, tandem cold steel mills are equipped with two air wiping header one for the top surface and other for the bottom surface of strip after last stand which are not effective and results to emulsion of carryover on the strip surface in the existing mill. The header is fitted with number of air blow off nozzles aligned in a single row and
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placed after the box roll of the mill stand. The header is connected to industrial air supply line of 3 to 3.5 bar to the mill thus having lots of contaminants in the air like moisture, dirt, oil, etc. But the wiping is not effective resulting to poor and uncleaned bottom strip surface.
In the existing emulsion system with semi-synthetic rolling oil existing air wiping system is found inadequate to arrest the emulsion carryover on the strip surface. As a result of emulsion carryover there is an increasing trend of surface staining and black patch on the strip surface.
Usually wiping system is of two types, one is contact type and other is non-contact type. The problem with contact type wiping system is that it collect dust/debris which gets embedded on the wiping pad and subsequently produces scratches on the strip surface and therefore highly maintenance prone. The second one is the non-contact type wiping system usually provided after finishing operation at the last stand of the tandem cold mill (TCM) to arrest the carryover on the strip surface. After cold reduction process at the TCM, the cold rolled strip carried lot of emulsion both the surfaces. This emulsion get entrapped in between the coil laps leads to oxidation during annealing process in result to surface detect like staining on the strip surface.
To take care of the above problems there is need to provide an efficient and effective air wiping system in the tandem mill such that carryover residues on strip surface may be reduced to substantial amount and resulting in reduction of
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diversion on account of black patch and improvement in surface quality.
The present inventors have found that air wiping header designed in a chevron and ergonomic manner will provide higher blow off power and high impinging force which is efficacious thereby arresting carry over on cold rolled strip surface reducing the carry over residue on strip surface by substantial amount improving the surface quality of the strip.
OBJECTS OF INVENTION
Thus one object of the present invention is to overcome the disadvantages of the prior art and the existing technology.
Another object of the present invention is to provide an improved air wiping system.
Another object of the present invention is to provide air wiping header introduced in the air wiping system.
Yet another object of the present invention is to provide wide spray width with proper overlap of spray pattern.
Yet one more object of the present invention is to provide heatless air dryer for availability of moist free air supply.
Further object of the present invention is to provide easy maintenance and trouble free and cost effective operation.
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SUMMARY OF INVENTION
According to one aspect of the present invention there is provided a air wiping header adapted for high surface quality of strips, said header comprising :
header box means being substantially angular at its middle portion defining plurality of arms extended to a predetermined distance;
plurality of nozzles being located in plural rows on the header box in a chevron manner, said nozzles having appropriate spacings among each other such that spray of adjacent nozzles are suitably overlapped; and
plural flange means operatively placed on the box means almost at ends of the arms.
According to another aspect of the present invention there is provided an improved air wiping system adapted to arrest carryover on cold rolled strip surface, said system comprising:
air dryer means having inlet and outlet, said inlet and outlet include plurality of valve means to draw in and draw out moist/dust free air;
air accumulating means operatively connected to the air dryer means in a manner to provide constant and uniform volume of air in a desired pressure range; and
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air wiping header comprising header box means being substantially angular at its middle portion defining plurality of arms extended to a predetermined distance; plurality of nozzles being located in plural rows on the header box in a chevron manner, said nozzles having appropriate spacings among each other such that spray of adjacent nozzles are suitably overlapped; plural flange means operatively placed on the box means almost at ends of the arms.
According to another aspect of the present invention there is provided a protector means located below box means extending to an appropriate distance in a perpendicular direction of the box means in a manner to protect the nozzle means during rolling operation.
DETAILED DESCRIPTION OF INVENTION
In the present invention the air wiping header comprises a header box means on which plural nozzle means are located having predetermined spacing between each other. The box means is substantially angular at the middle portion defining plurality of arms extended to a predetermined distance. The box means and therefore the nozzle means are guarded by protector means placed below the nozzle rows and extending to a desired distance perpendicularly to the lateral surface of the box so as to cover the nozzles. The wiping header is designed in a chevron manner, fabricated in V shaped where notch of V shape is paced against the rolling direction. This helps to arrest the carry over from central portion of strip with and gradually the arrested carry over is dispersed from central portion towards the
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edges of the strip due to off set of nozzles and spray overlap of adjacent nozzles. The box means comprises 27 nozzles in two rows. The front row consists 13 nozzles and back row consists 14 nozzles. Each nozzles are welded to the header box with proper spacing such that the spray of adjacent nozzles are properly overlapped by at least 20% -25%. The nozzles have higher blow off power and repeated in a chevron manner with proper overlapped of spray. In the next row nozzles are welded at a central line of spacing of previous row nozzles. The header box is provided with two end flanges for opening and cleaning of the nozzles. The nozzles are located on the box header in such a manner that the carry over emulsion on the strip surface are dragged away from the strip surface and dropped outside due to its chevron design such that the arrested carry over emulsions are drained off from the edges of the strip. The spray height is maintained at a distance of 150mm approximately from the strip surface and the impinging angles of the spray are kept at an angle of 30° approximately to the vertical axis of the header.
Two separated inlet connections are provided to the box header for compressed air supply from the top. The inlet connection again also branched to two tapping connection to the header and are placed for an uniform distribution of air supply to spray header box through air receiver/accumulator means. For supply of air at higher and uniform volume, the accumulated is installed on line for storing and supplying air at constant volume and pressure between 3.5 to 5 bars.
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One embodiment of the present invention describes an automatic heatless absorption type air dryer in the air wiping system for supply of moist and dust free air to the spray header. The dryer is equipped with plural gate valves on its inlet side and with a pre-filter of 25 micron to protect the desiccant powder at the outlet. The dryer has been designed under normal standard condition to obtain due point atmospheric pressure of -40°C. Capacity of the air dryer takes care of total air flow of around 980 m3/hr. at 5 bar pressure.
One embodiment of the present invention describes a pipeline laid down from main compressed air line being fitted to the air dryer and air receiver. High volume air receiver delivers moist free air to the spray header in the system for constant volume supply of air without any process interruption.
After being rolled the strips are subsequently processed in continuous annealing line (CAL) for relieving work hardening that takes place during cold deformation. At the entry of CAL, tape test are being carried out for the evaluation of strip surface cleanliness. After completion of rolling, samples of dimension 200mm x 200mm strip is being cut down from the rolled strip for evaluation residual amount of oil and iron fines on the strip surface.
Tape test:
The transparent 20mm cello-tape is pasted on a blank white paper. The reflectance of this tape is calibrated as 100% reflectance with the help of Smoke Stain Reflectometer.
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Then the tapes are pressed on the rolled strip and subsequently pasted on the white paper. The carry over residuals are stuck to the glued side of tape which gives relative reflectance of the strip surface. Higher the reflectance % indicates better and cleaner strip surface and lesser oil and iron fines residual.
Determination of iron fines and oil residue on strip surface :
Taking sheet sample of dimension 200mm x 200mm from the cold rolled strip after tandem cold rolling mill. The sample surface is then immersed into concentrated benzene (CeHe) and washed thoroughly on both the strip surface with brush. Carry over on the strip surface containing residual rolling emulsion and iron fines get washed by benzene. Residual oil will dissolve in benzene and iron fines will be left as residue in the solution. Then the solution is filtered through filter paper (M-41) where the filter will arrest the iron fines and the filtered solution containing dissolved residual oil are collected in a beaker.
For residual oil evaluation : The collected solution in the beaker is being heated upto 140°C where the benzene will evaporate and the left over will be residual oil (as benzene usually evaporates at 120°C-130°C). The empty beaker is pre-weighed. Again the beaker with residual oil is being weighed and difference in weight will give the amount of residual oil on the strip.
For iron fines evaluation : The filter paper with fines are collected in a beaker and concentrated Hydrochloric acid
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(HCL) is being added and diluted to desired extent o match the level. The iron analyzer are added to the solution and the concentration of iron fines is being measured by photometry.
The improvement in the strip surfaces are apparent from the below tables I, II and III.
Table - I
Surface Reflectance Test :

Average Reflectance (in %)
With Existing Air Wiping System 48
With Improved Air Wiping System Of Present Invention 60
Table - II
Measurement of Residual Oil and Iron fines:

Oil (mg/m2) Iron (mg/m^)
With Existing Air Wiping System 145 95
With Improved Air Wiping System Of Present Invention 125 67
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Table - III
Diversion due to black patch:

Diversion due to Black Patch
With Existing Air Wiping System 48
With Improved Air Wiping System Of Present Invention 60
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates a schematic view of the air wiping system of the present invention.
Figure 2A and 2B illustrates a schematic plan and front views of the air wiping header.
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
In figure 1, the pipeline (6) laid down from main compressed air line (7) is fitted to the air dryer (2) and air receiver (3). Air from supply (7) passes through the gate valves (1) and enters into the dryer (2) . Non return valve (4) is connected in the air line on the outlet side
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of the air receiver (3) . Two separated inlet connections (8,9) are provided to the box header (5) for compressed air supply from the top.
In figures 2A and 2B, the box header (5) is illustrated in details. Box means (10) comprises nozzle means (11). Box (10) and nozzles (11) are guarded by protector means (12) . The header box (10) is provided with two end flanges (13) for opening and cleaning nozzles (14) . Protection guard (15) is located in the back lateral side of the box (10) protecting all the components.
The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The air dryer and air receiver herein describes can be replaced by its technical equivalence and yet the invention can be performed. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials, dimensions and parameters may be any according to the requirements, which will still be comprised within its true spirit.
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WE CLAIM
1. Air wiping header adapted for high surface quality of
strips, said header comprising :
header box means being substantially angular at its middle portion defining plurality of arms extended to a predetermined distance;
plurality of nozzles being located in plural rows on the header box in a chevron manner, said nozzles having appropriate spacings among each other such that spray of adjacent nozzles are suitably overlapped; and
plural flange means operatively placed on the box means almost at ends of the arms.
2. An improved air wiping system adapted to arrest
carryover on cold rolled strip surface, said system
comprising:
air dryer means having inlet and outlet, said inlet and outlet include plurality of valve means to draw in and draw out moist/dust free air;
air accumulating means operatively connected to the air dryer means in a manner to provide constant and uniform volume of air in a desired pressure range; and
air wiping header comprising header box means being substantially angular at its middle portion defining
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plurality of arms extended to a predetermined distance; plurality of nozzles being located in plural rows on the header box in a chevron manner, said nozzles having appropriate spacings among each other such that spray of adjacent nozzles are suitably overlapped; plural flange means operatively placed on the box means almost at ends of the arms.
3. Air wiping header as claimed in claims 1 and 2,
wherein the nozzles are located on the header box such
that nozzles of one row being placed in the central
line of the two adjacent nozzles of the other row such
that the spray of adjacent nozzles are properly
overlapped by at least 20% - 25% adapted to provide
higher blow off power.
4. Air wiping header as claimed in claims 1 to 3, wherein
the nozzles are located on the header box such the
impinging angle of the spray to the strip surface is
approximately 30° angular to the vertical axis of the
header box.
5. Air wiping header as claimed in claims 1 to 4, wherein
the nozzles comprises a vertical distance of
approximately 150mm from the strip.
6. Air wiping system as claimed in claim 2, wherein the
air accumulating means comprises air receiver adapted
to provide constant volume of air supply to the header
box.
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7. Air wiping system as claimed in claim 6, wherein the
air receiver is adapted be worked in pressure ranging
from 3.5 bar to 5 bar.
8. A protector means located below box means extending to
an appropriate distance in a perpendicular direction
of the box means in a manner to protect the nozzle
means during rolling operation.
9. Air wiping system and air wiping header as herein
substantially described and illustrated with reference
to the accompanying figures.


Dated this day of 2nd February 2007.
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The present invention relates to an air wiping header adapted for high surface quality of strips. The header (5) comprises header box means (10) defining plurality of arms extended to a predetermined distance, plurality of nozzles (11) located on the header box (10). The nozzles (11) have appropriate spacing among each other such that spray of adjacent nozzles (11) are suitably overlapped. Plural flange means (13) are operatively placed on the box means (10) almost at ends of the arms. The invention also relates to an improved air wiping system to arrest carryover on cold rolled strip surface. The air wiping system comprises the header (5).The present invention relates to an air wiping header adapted for high surface quality of strips. The header (5) comprises header box means (10) defining plurality of arms extended to a predetermined distance, plurality of nozzles (11) located on the header box (10). The nozzles (11) have appropriate spacing among each other such that spray of adjacent nozzles (11) are suitably overlapped. Plural flange means (13) are operatively placed on the box means (10) almost at ends of the arms. The invention also relates to an improved air wiping system to arrest carryover on cold rolled strip surface. The air wiping system comprises the header (5).