AU2023266395A1 - Wiping excess coating from hot dip metal coated strips - Google Patents

Abstract

This invention is a method and an apparatus for uniformly wiping and controlling excess metallic coatings from wide strips in the continuous hot dip coating process through electromagnetic induction and interactions despite the inherent drawbacks, such as crossbows and fluttering, in the running strip. The coated strip is squeezed coaxially through a rectangular loop of electrical conductors carrying an alternating electric current of adequate frequency and magnitude. The conductors are linked by Horseshoe shaped composite soft ferromagnetic cores from outer sides, with their poles facing the strip on either side. Each composite core essentially consists of a closed spatial loop with adequate conductor windings connected to a DC bias circuit. Coating uniformity is achieved by sensing the lateral displacements of the fluttering strip and countering their ill effects through adequately altering the extents of saturation of the composite cores through variations of the DC bias circuit currents online. PLO ~~7\\

Description

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WIPING EXCESS COATING FROM HOT DIP METAL COATED STRIPS INTRODUCTION

[0001] This invention relates to a novel method/technique and an apparatus for wiping and controlling excess liquid metallic coating layers and coat weights on long wide strips with electromagnetic fields. More particularly, the said coat weight control and its uniformity is achieved through controlled saturation of certain ferromagnetic cores stacked along the width of the running strip and used in applying the electromagnetic fields for wiping. While this invention is useful for strips of all dimensions and compositions when coated with all coating metals and alloys thereof, it is herein described with reference to the most frequently employed hot dip galvanizing (Zinc Coating) operations on steel strips in modern manufacturing practice. A metal coated finish is required on the product for reasons like protection against corrosion in normal use, good solderability, and others.

THE BASIC HOT DIP PROCESS

[0002] In normal operations, a surface treated steel strip is longitudinally and continuously run through a molten zinc bath. The strip surface chemically bonds with molten zinc while inside and picks up a layer of liquid zinc as it exits the bath in a vertical planar mode. As the strip runs upward, the coating mass entrained thereon eventually solidifies in surrounding gaseous atmosphere, such as air. By default, in modem manufacturing practice, the resultant amount of coating mass is much in excess than required or specified and is generally not smooth. For product quality and economy, a smooth and uniform coating layer slightly thicker than the specified minimum is desirable on the finish product. Eventually, some mechanism is used to wipe away the excess liquid coating mass and recover it to the bath, and to smoothen the rough surface of the coated strip within acceptable limits.

CONTEMPORARY WIPING SYSTEM & PROBLEMS THEREIN

[0003] By far, the most frequently employed wiping system in modern manufacturing practice consists of a pair of linear gas jets (also known as air or gas knives) impinging onto the running strip from opposite sides immediately after its exit from the bath. The jets are generally quite rigid and are located along the width of the running strip and beyond its both edges. For uniform and accurate coat weight on either side, the running strip needs to be flat and the stand-off distances of the wiping devices (gas jets) from the strip need to be maintained uniform and constant throughout the entire production.

[0004] However, in the manufacturing practice, a wide running strip generally deviates from the absolute flatness and uniform stand-off distances from the wiping jets or devices, due to: - Crossbow or curvature in its horizontal profile, and - Flapping or fluttering.

[0005] As is fairly known, the said deviations have detrimental effects on coat weight control accuracy and uniformity due to change of wiping intensity on either side of the running strip. Then again, in modern manufacturing operations for steel strips, some electro-magnetic stabilizers are fitted in close vicinity of the gas jets. These stabilizers have distance sensors and feedback control systems, which physically rectify the said deviations of the running strip through magnetic attractions, thus regaining its flatness and the coat weight uniformity to some extent. However, owing to the inertia and rigidity of the running strip, the stabilizing action is slow or delayed and, hence, incomplete before the deviated portion of the strip passes through the wiping zone. Eventually, some excess coat weight and its non-uniformity remain on the finish product while maintaining the specified minimum requirement as per quality standards.

BRIEF DESCRIPTION OF THIS INVENTION

[0006] The basic electromagnetic wiping system, relevant to this invention, is fairly known in "prior art" (Indian Patent # 156939 dated 24/12/1983). The problems associated with the deviations, which are mainly due to crossbow and fluttering of the running strip, exist for the basic electromagnetic wiping system also. This invention is an advancement of the basic system and tackles or circumvents the said problems in a radically different manner altogether. Despite the crossbow and fluttering, it continuously monitors the strip's deviation at every spot and counters its detrimental effect on wiping intensity and uniformity through feedback-controlled saturation of certain ferromagnetic cores used in the wiping system. The control action is through electronic circuits and can be very much faster than mechanical or physical stabilization of the strip; thus, regaining the coat weight control accuracy and uniformity to maximum possible extent in modem technology. The basic electromagnetic wiping system and its advancements as per this invention are briefly described and explained with reference to Figure 1 next:

THE BASIC ELECTROMAGNETIC WIPING SYSTEM

[0007] In the drawings/figures of this specification, various system components and parts are duly identified and indicated by bold numerals and letters, followed through along lines ending on the respective objects in dots. Electrical conductors and signal cables are drawn in continuous or broken lines in various thicknesses as appropriate. Dots are also used to indicate spots anywhere, and physical connections and contacts of electrical conductors and signal cables with objects as appropriate, and applicable. Figure 1 schematically depicts the entire setup in an isometric view at the strip's exit out of the hot dip bath. For clarity and transparency, the main/basic wiping system and zinc bath are drawn using continuous lines, and the running strip and the auxiliary control equipment and related circuits as per this invention are drawn in broken lines. Cartesian coordinates or axes are used, and are shown as 'XX', 'YY', and 'ZZ'. The perfectly flat strip with liquid coating thereon is shown running vertically upwards in the axial plane 'XY' of a horizontal wiping device located entirely above the bath level. The strip is entirely drawn in broken outlines for clarity, as mentioned, and indicated by '1' at two places. The bath is indicated by '2' at two places, and the bath level is shown at 'BL' at the strip's line of emergence from the bath at one end. After emerging, the strip travels vertically upwards with a velocity shown by arrow 'V', against gravity, which is indicated by arrow 'g' pointing downwards. The prevalent gaseous atmosphere thereat in the entire set up is preferably inert (e.g., Nitrogen), as indicated by 'N' at two random spots marked by dots.

[0008] The wiping device basically consists of a rectangular, single-turn electrical circuit loop or coil around the coated strip in a horizontal plane. The circuit loop is preferably and mainly formed by two straight, slender, and adequately flexible electrical conductors of rectangular cross sections, marked 'FC'. The conductors are located parallel to, and one on either side of the running strip; and extend well beyond its both edges. To form the said circuit loop, the conductors are electrically connected to each other beyond the strip's edge at one end; and are connected to a variable electronic power source, marked 'EPS', and located beyond the edge at the other. The output power of EPS is varied and stabilized for maintaining the required alternating current, marked 'If, at required frequency through the circuit loop thus formed for sustained wiping process. The horizontal axis of the loop along the width of the strip is coincident with the 'XX' coordinate for reference purpose.

[0009] Further, each conductor FC is linked by a series of 'Horseshoe' or 'C' shaped, soft ferromagnetic cores from the outer sides with their inner profiles closely matching the outer profile of the conductor on three sides, except the inner side facing the coated strip. These cores are stacked along the entire width of the strip and beyond its both edges. Each conductor is located parallel to the coated flat strip with an equal and uniform stand-off distance on either side along 'ZZ' direction, as shown at 'd', in its normal position. The assembly is preferably and adequately cooled with coolants like water circulating through suitable bores in the conductors, as shown at 'Br'. Under such conditions, the running strip with liquid zinc coating layers thereon is subjected to electromagnetic induction in the localized wiping zone or device as substantially formed by the conductors, and the linking 'C' cores on both sides of the strip together.

[0010] Under conditions as described above, the running strip and the entrained coating layers thereon are electromagnetically or inductively "coupled" in the said circuit loop while passing through the localized wiping device. Eventually, alternating magnetic flux and induced or eddy currents in the coating layers therein effectively interact to cause mechanical squeezing onto each coating layer from outer side. In net effect, restricted amount of coating metal is allowed to pass through the said wiping zone. The squeezed away or wiped away liquid coating metal runs back to the bath under gravity and is thus recovered.

[0011] With good electromagnetic coupling, the alternating magnetic flux causing the mechanical squeeze onto the coating layer at any spot on any side of the strip is substantially confined to the magnetic circuital path in the YZ plane, i.e., around the corresponding conductor 'FC' on the same side, through the 'C' shaped core, air gap (as shown at 'd'), zinc layer and the running strip. Under stabilized alternating current 'If' and its frequency, the wiping intensity of the said squeeze is mainly governed by the average magnetic permeance of the entire circuital path in every alternating cycle of If. This, in turn, is substantially governed by the peak magnetic permeability of the core material, dimensions and geometry of the conductor/core assembly in cross section, the standoff distance 'd', the coating layer thickness and peak magnetic permeability of the strip material and its thickness.

[0012] When the wiping device of uniform and opposite linear structure about the XY plane is laid along the width of the strip with constant standoff distances 'd' on either side, the degree of electromagnetic coupling with the strip is substantially constant or uniform along the strip width.

Eventually, for stabilized current 'If, the controlled coat weight after wiping is uniform along the width, and length of the entire strip on either side when running at constant speed.

[0013] However, the deviations of the running strip from its absolute flatness and central position on either side along the ZZ axis, which are mainly due to "crossbow" and "fluttering", can be detrimental to the coat weight uniformity. As stated earlier, this invention is an advancement to the basic wiping system and aims at rectifying or countering the detrimental effects without having to stabilize the running strip or regaining its flatness, as described further.

ADVANCEMENTS TO THE BASIC ELECTROMAGNETIC WIPING SYSTEM

[0014] As per this invention, the deviation of the running strip from its central flat position at every spot is continuously detected and/or estimated, and a change in the average permeance in the local magnetic circuital loop thereat is countered through feed-back controlled saturation of the relevant 'C' core/s, as required, through adequate electronic control circuits. The surest practicable way for the controlled saturation, as known to the inventor, is through variable direct current (DC) bias or magnetization of each 'C' core, spatially split into a closed magnetic loop, as described further in the following steps with reference to Figure 1:

[0015] Each 'C' shaped core is substantially composed of or effectively split to form an internal closed magnetic circuital loop. In a preferred embodiment, each core is formed of four components, as shown, and marked 'C1', 'C2', 'B1' and 'B2' for a pair, as an example. C1 and C2 are substantially 'C' shaped, and rectangular in cross section; and B1 and B2 are rectangular prisms. For convenience, this assembly of four core components is termed "Composite Core" and denoted as 'CC' in this specification. The magnetic circuital loop is sequentially formed as C1--B1--C2--B2--C1, or in the reverse order if convenient. Adequate conductor windings (not shown in Figure 1) are provided over the said magnetic circuital loop and the two terminals of the windings are brought out for connecting to a variable direct current (DC) control circuit. (The direct current is used and varied to substantially maintain the composite core 'CC' in a state of partial saturation and vary its incremental magnetic permeability as required.) Between neighbouring composite cores, non-magnetic spacers, marked 'Sp', of adequate thickness are provided to prevent or reduce any DC magnetic flux from crossing over, as much as possible.

[0016] Besides each conductor/core (FC/CC) assembly, a control processing unit, drawn in broken lines and marked 'CPU', is located, and performs some essential tasks through adequate electronic components and circuits, as described next.

[0017] Several stationary distance sensors are preferably evenly distributed and arranged above the flexible conductor/core assembly 'FC/CC' on either side and along the entire width of the strip and beyond both the edges. As an example, two such sensors or sensor probes, located one on either side of the strip, are schematically shown in broken lines and marked 'Sn'. Each sensor continuously detects and monitors the stand-off distance 'd' from the closest spot on its side on the coated running strip as required. In modern technology, certain coat weight sensors are also available, which can sense the coat weight at the respective closest spot and monitor it in an ongoing manner. These, and any other types of sensors, which can detect the stand-off distance accurately, can also be used if suitable. The sensors/probes are suitably extended and located facing towards the central position of the strip to accurately sense and monitor the standoff distance 'd' or spot coat weight. Each sensor is electronically connected to the respective control processing unit (CPU) through signal cable/s, marked 'SC', as shown in broken lines, at a convenient spot.

[0018] For each composite core CC, a variable direct current (DC) bias control circuit is provided and located in the CPU on the same side. This is shown in broken lines and marked 'BC'. The output terminals therein are brought out and connected through cables to the input terminals of conductor windings of the corresponding composite core. The cables are drawn in broken lines and the DC bias control current therein is shown with arrows and marked 'Ic'.

WORKING OUTLINE OF THIS INVENTION

[0019] Modern strip galvanizing process is a continuous, "round the clock", and stabilized operation. Accordingly, this invention also works round the clock and in an overall stabilized manner. The invention works in the following essential steps.

[0020] The galvanized strip runs at its unrestricted pre-set and stabilized speed V, as required on the operating plant. The electronic power source EPS and control processing units CPU of the electromagnetic wiping system independently draw the required power from mains power supply and work together to achieve the specified minimum coat weight and its uniformity over the entire strip as required.

[0021] The coat weight control and uniformity in the wiping system is excellent in absence of DC bias control of the CC cores when the strip is perfectly flat and runs in the XY plane. As a first step in initializing the wiping system, all the composite cores are set to a uniform degree of partially saturated state through adequate DC biases, whereby the magnetic permeability of each composite core reduces from high value (peak permeability) to a convenient lower value (incremental permeability), thus providing adequate leeway for countering the strip's pre estimated deviations or displacements due to crossbow and fluttering on either side in practice.

[0022] In the initialized state as above, power from EPS is varied and stabilized at a level to set the required current If and its frequency to achieve the wiping intensity for the minimum required coat weight all over the flat strip. Under such conditions, each CPU controls the coat weight uniformity on its side continuously in an ongoing manner by simultaneously performing following essential tasks through suitable electronic control circuits.

- Detect and monitor strip's deviation/displacement or shift from its pre-set position or change in stand-off distance 'd' at every sensor probe on its side. - Based on this displacement data, determine the close-fitting horizontal profile/curve of the strip's surface (due to crossbow and fluttering). - Further work out the strip's deviation/displacement at each spot against every composite core on the close-fitting profile. - Based on the worked-out displacement thereat, alter the DC bias current 'Ic' for the respective composite core CC to counter the relevant change in the wiping intensity through an appropriate change in its incremental permeability as governed by the magnetic induction curve/data of/on the composite core or its material.

SALIENT FEATURES AND ADVANTAGES OF THIS INVENTION

[0023] Salient features and advantages of this invention are briefly enumerated as under: - The problems of non-uniform and excessive coat weights get significantly reduced.

- The basic electromagnetic wiping system (Indian Patent # 156939 dated 24/12/1983) has a feature, wherein, each sensor 'Sn' is connected through adequate feed-back control system to an actuator, which physically moves the flexible conductor 'FC' to maintain the stand-off distance 'd' constant. This feature is good and can be complimentary to the present invention for greater advantages in enhanced quality and power efficiency. - The existing electromagnetic stabilizers can also be used separately and as complimentary for greater overall power efficiency and economy. - Total power consumption of the wiping system is minimal, and much economical when compared to sizable amount of saving in excess coating metal, which is quite dearer. - The invention can be used on non-magnetic substrates also, e.g., tinned copper strip. - Differential coat weight specifications (two sides of the strip specified for different minimum coat weights) are also achievable for magnetic as well as non-magnetic strips. - Smooth surface finish - cold rolling operation on coating ripples can be eliminated. - No self-imposing restrictions in wiping action or on wiping capability. All standard coat weight specifications can be complied with in modern manufacturing operations. - Silent operation - reduced noise pollution and industrial deafness. - Clean operation - total elimination of "top dross" or oxide formation on the zinc bath. - Normal, but undesirable thickening of coated strip at the edges can be eliminated.

PRIOR ART IN GALVANIZED STRIP WIPING WITH ELECTROMAGNETIC FIELD

[0024] Relevant patents known in the field of Electromagnetic Wiping of strips are listed below: 1. Indian Patent # 156939 dated 24/12/1983, 2. Indian Patent # 186942 dated 12/06/1997, 3. United States Patent # 4,228,200 dated 14/10/1980, 4. United States Patent # 4,273,800 dated 16/06/1981, 5. United States Patent # 3,518,109 dated 30/06/1970, 6. United States Patent # 4,033,398 dated 05/071977, 7. German Patent # 2202764 dated 11/01/1972, 8. German Patent # 3008207 dated 11/09/1980, 9. Belgian Patent # 739,130 dated 19/09/1969.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A detailed description of a preferred embodiment will follow, by way of example only, with reference to the accompanying figures of the drawings, in which:

Figure 1 illustrates a schematic isometric view of the complete embodiment of this invention; Figure 2 is a vertical sectional view of Figure 1 illustrating how the wiping forces are generated through electromagnetic induction and interactions; Figure 3 illustrates how the wiping force intensity is altered through progressive saturation of the composite ferromagnetic cores with a DC bias; Figure 4 illustrates a preferred embodiment or arrangement showing soft ferromagnetic core pieces stacked together to form a composite core loop with relevant conductor windings and DC bias circuit for controlled saturation; Figure 5 illustrates the high frequency alternating and steady (DC) magnetic flux loops generated with arrangements of Figure 4; Figure 6 illustrates yet another preferred embodiment or arrangement showing soft ferromagnetic core pieces stacked together to form a composite core loop with relevant conductor windings and DC bias circuit for controlled saturation; Figure 7 illustrates the high frequency alternating and steady (DC) magnetic flux loops generated with arrangements of Figure 6; Figure 8 illustrates four preferred arrangements of forming/stacking together long straight electrical conductors in cross section for improved cooling and lateral flexibility, namely: A. Single bar of rectangular cross section with rectangular bore to pass coolant, B. Many bars of rectangular cross sections with rectangular bores to pass coolant, C. Many bars of rectangular cross sections with circular bores to pass coolant, D. Many bars of square cross sections with circular bores to pass coolant, and Figure 9 illustrates a preferred schematic arrangement of control components in plan for the entire width of the running strip with deviations, such as crossbows and fluttering.

DETAILED DESCRIPTION OF EMBODIMENTS

[0026] The complete embodiment of this invention, as illustrated in Figurelis fairly described in adequate details in the brief description of this invention, relevant prior art, its advancement, and overall working outline in paras [0006] thru to [0022]. Figure 2 depicts a vertical section of the wiping device in Figure 1, and schematically shows wiping action through electromagnetic induction and interactions therein. The alternating currents If in the flexible conductors FC are shown with "dot & cross" as per international convention. These maintain alternating magnetic flux in closed loops 'FL' through the composite cores CC, air gaps d, coating layers 3 and the running strip 1 on its two side, as shown. This causes electromagnetic induction and interaction phenomena at two arbitrary points 'P' and 'Q' in the zinc layers 3 on either side of the strip in the lower half of the wiping device, whereat, 'B' is the induced magnetic flux density in the direction of FL, 'J' is the induced current density, as shown with "dot & cross" again, and 'F' is the induced mechanical force density, acting in a direction perpendicular to B and J, toward the strip as shown. Such forces F substantially cause mechanical squizzing of the liquid coating layer 3 on either side in the lower half of the wiping device, thus causing wiping. The wiped away liquid coating mass eventually returns to the bath under the action of gravity. Figure 3 shows a typical saturation phenomenon of the ferromagnetic composite core CC in Figure 2 when composed of a closed loop formed with core pieces C1, C2, B Iand B2, and progressively magnetized with DC bias control current Ic through suitable windings. As Ic increases from zero to high, the relative incremental permeability of the composite core CC progressively reduces from high to 1, thus causing the induced flux density in CC to saturate at a maximum value 'BS'. For constant alternating current If, the change of flux density per cycle in the composite core CC (shown at BX) through hysteresis from high value at the origin (for Ic= ) progressively reduces, and so do B and J for wiping at points P and Q in Figure 2, and eventually the force F or wiping intensity. This is shown at three consecutive points, namely, X at the origin, X1 and X2, the corresponding BX values being BXO, BX1 and BX2. Figure 4 shows a preferred embodiment of a composite core CC formed with two C cores stacked side by side with conductor windings 'W' and associated DC bias control circuit BC across to maintain and vary the required control current Ic. The bias circuit preferably consists of a battery source with fixed voltage 'Vb', a variable resistor 'Rc', a control inductance 'Lc' and a variable voltage source 'Vc (+/-)' controlled by control signal current 'CSC'; all connected in a series circuit across the windings W. For the arrangements in Figure 4, Figure 5 schematically shows the DC flux density BX in the closed loop "C1-*B1-C2-B2-C1" as shown in broken lines with double head arrows, and the two AC flux densities B in closed loops "C1-*B14341434B24C1" and "C24B19*34143-*B2-C2", as shown in broken lines with single head arrows. Figure 6 shows another preferred embodiment of a composite core CC formed with two C cores stacked one outside the other with conductor windings 'W' and associated DC bias control circuit BC across to maintain and vary the required control current Ic. The bias circuit preferably consists of a battery source with fixed voltage 'Vb', a variable resistor 'Rc', a control inductance 'Lc' and a variable voltage source 'Vc (+/-)' controlled by control signal current 'CSC'; all connected in a series circuit across the windings W.

For the arrangements in Figure 6, Figure 7 schematically shows the DC flux density BX in the closed loop "C14B1-9C2-B2C1" as shown in broken lines with double head arrows, and the two AC flux densities B in closed loops "C14B191*3 14 3-*B2-C1" and "C2+1933B24C2", as shown in broken lines with single head arrows. Figure 8 has already been described adequately in "BRIEF DESCRIPTION OF THE DRAWINGS". Figure 9 shows the entire control arrangement in plan. The arrangement mirrors about the horizontal axis XX of the flat running strip with stand-off distance from either of the flexible conductors FC marked d. 'XcXc' denotes the horizontal curvature of the axis XX due to crossbow and fluttering at any instant; whereat the stand-off distance d on the left is marked 'dl', and that on the right is marked 'dr'. The control arrangements are: 1. Several stand-off distance or coat weight sensors/detectors and associated actuators are arranged on either side of the strip. One pair is described here for brevity and clarity. 'Sn' denotes a sensor/detector of d, 'Ac' denotes an actuator to move the flexible conductor FC "towards and away from" the strip as shown with a two-sided arrow, and SC denotes the signal cable/s to carry the appropriate signal of change in d, i.e., "d - dl" or "d - dr" from Sn to the control processing unit CPU. CPU subsequently processes all the signals delivered by the signal cables on its side and determines the change of d at each spot and suitably varies the control signal current CSC for each spot. 2. All over the flexible conductors FC, suitable composite cores CC are arranged with non magnetic spacers Sp to magnetically isolate each CC from the neighbouring. Each composite core CC has a DC bias control circuit BC, which derives its control signal current CSC from CPU and varies the control current IC to maintain the wiping intensity constant through variation of incremental permeability of CC to counter the variation of d due to crossbow and fluttering.

Claims (19)

WIPING EXCESS COATING FROM HOT DIP METAL COATED STRIPS CLAIMS

1. A method of uniformly wiping excess metallic coatings from long, wide strips in the continuous hot dip process, inter alia comprising the steps of;

[i] continuously drawing the strip longitudinally through and out of the hot dip bath; and then centrally through an effectively uniform localized zone of alternating magnetic field, as externally applied from either side, having components substantially in the longitudinal direction, and also having some soft ferromagnetic elements in its magnetic circuit loops outside the bath;

[ii] continuously detecting, determining and monitoring the lateral displacement or deviation of every spot on the strip from its neutral flat position, and further;

[iii] countering the effect of said displacement/deviation through continuously governing and varying the intensity of the said magnetic field at every spot on the running strip through continuously varying the degree of saturation of the ferromagnetic elements in the vicinity, as required to maintain the expected coat weight control and uniformity on the running strip when fluttering and/or having crossbows.

2. A method as claimed in claim 1, wherein;

[i] the running strip, with liquid coating thereon, coaxially threads through a substantially flat, rectangular loop or coil of electrical conductor/s located outside the bath, having two sides parallel to the strip in its normal flat position and extending beyond its width on both sides;

[ii] the said conductors are linked from outer sides by "Horseshoe" or 'C' shaped, composite soft ferromagnetic cores with their poles facing the strip;

[iii] the said localized magnetic field zone is created around the running strip with a stabilized alternating electric current of required frequency and magnitude maintained in the said conductor loop by connecting it to an external electronic power source;

[iv] each composite core substantially consists of a closed spatial loop of soft ferromagnetic materials with linking conductor windings that are connected across to a variable DC current bias circuit or source.

3. A method as claimed in claims 1 and 2, wherein;

[i] several known distance sensors are located along the width of the strip on either side, which detect the strip's lateral displacements at the closest spots and send signals to a control processing unit on the same side, and;

[ii] each said control processing unit processes all the signals received from the said sensors on the same side and further;

[iii] determines the relative deviation of each composite core from the running strip due to crossbows and fluttering and further;

[iv] regulates the magnetic saturation of each composite core through a variation of the DC bias current to maintain the wiping intensity at the spot in its vicinity on the running strip constant and uniform.

4. Claim as per claims 1 thru 3, wherein, the said DC bias current circuit for each composite core is an open loop current source having in series connections, a. A stabilized voltage battery source of irreversible polarity or its electronic equivalent, b. A variable resistor or its electronic equivalent to preset the relative incremental permeability of the composite core to a suitable level, as required, through variation of the DC control current, c. An inductor or choke or its electronic equivalent to effectively block any stray high frequency alternating currents induced in the conductor windings through magnetic linkage with the alternating current in the rectangular coil, and d. A variable voltage source of reversible polarity, such as a capacitor or its electronic equivalent, whose magnitude and polarity is varied by the control processing unit through appropriate known signal and electronic circuit to regulate the magnetic saturation of the composite core and maintain the wiping intensity at the spot in its vicinity on the running strip constant and uniform.

5. Claim as per claims 1 thru 4, wherein, non-magnetic spacers are provided between adjacent composite cores to substantially reduce leakage of DC magnetic flux across.

6. Claim as per claims 1 thru 5, wherein, a composite core consists of two C cores stacked side by side around a conductor with two rectangular core bars abutting the C cores, one at the top of and one underneath the conductor, thus forming the required closed loop magnetic circuit.

7. Claim as per claims 1 thru 5, wherein, a composite core consists of two C cores stacked one outside the other around a conductor with two rectangular core bars abutting the C cores, one at the top of and one underneath the conductor, thus forming the required closed loop magnetic circuit.

8. Claim as per claims 1 thru 7, wherein, the gaseous atmosphere within the localized zone of magnetic field surrounding the coated strip is maintained adequately inert to minimise its reaction/attack on the liquid coating layer, such as oxidation.

9. Claim as per claims 1 thru 8, wherein, the entire conductor loop is formed of one or many tubular conductors stacked together, and further cooled with a coolant, such as water, circulating through the bores for adequately cooling the conductor/core assembly.

10. A method of continuously wiping and controlling excess liquid coating metal carried on hot dip metal coated strips as substantially described hereinabove and in the accompanying drawings.

11. An apparatus as per claims 1 and 2, wherein;

[i] the running strip, with liquid coating thereon, coaxially threads through a substantially flat, rectangular loop or coil of electrical conductor/s located outside the bath, having two sides parallel to the strip in its normal flat position and extending beyond its width on both sides;

[ii] the said conductors are linked from outer sides by "Horseshoe" or 'C' shaped, composite soft ferromagnetic cores with their poles facing the strip;

[iii] the said localized magnetic field zone is created around the running strip with a stabilized alternating electric current of required frequency and magnitude maintained in the said conductor loop by connecting it to an external electronic power source;

[iv] each composite core substantially consists of a closed spatial loop of soft ferromagnetic materials with linking conductor windings that are connected across to a variable DC current bias circuit or source;

12. An apparatus as per claims 1 thru 3, and 11, wherein;

[i] several known distance sensors are located along the width of the strip on either side, which detect the strip's lateral displacements at the closest spots and send signals to a control processing unit on the same side, and;

[ii] each said control processing unit processes all the signals received from the said sensors on the same side and further;

[iii] determines the relative deviation of each composite core from the running strip due to crossbows and fluttering and further;

[iv] regulates the magnetic saturation of each composite core through a variation of the DC bias current to maintain the wiping intensity at the spot in its vicinity on the running strip constant and uniform.

13. An apparatus as per claims 11 and 12, wherein, the said DC bias current circuit is an open loop current source having in series connections, e. A stabilized voltage battery source of irreversible polarity or its electronic equivalent, f. A variable resistor or its electronic equivalent to preset the relative incremental permeability of the composite core to a suitable level, as required, through variation of the DC control current, g. An inductor or choke or its electronic equivalent to effectively block any stray high frequency alternating currents induced in the conductor windings through magnetic linkage with the alternating current in the rectangular coil, and h. A variable voltage source of reversible polarity, such as a capacitor or its electronic equivalent, whose magnitude and polarity is varied by the control processing unit through appropriate known signal and electronic circuit to regulate the magnetic saturation of the composite core and maintain the wiping intensity at the spot in its vicinity on the running strip constant and uniform.

14. An apparatus as per claims 11 thru 13, wherein, non-magnetic spacers are provided between adjacent composite cores to substantially reduce leakage of DC magnetic flux across.

15. An apparatus as per claims 11 thru 14, wherein, a composite core consists of two C cores stacked side by side around a conductor with two rectangular core bars abutting the C cores, one at the top of and one underneath the conductor, thus forming the required closed loop magnetic circuit.

16. An apparatus as per claims 11 thru 14, wherein, a composite core consists of two C cores stacked one outside the other around a conductor with two rectangular core bars abutting the C cores, one at the top of and one underneath the conductor, thus forming the required closed loop magnetic circuit.

17. An apparatus as per claims 11 thru 16, wherein, the gaseous atmosphere within the localized zone of magnetic field surrounding the coated strip is maintained adequately inert to minimise its reaction/attack on the liquid coating layer, such as oxidation.

18. An apparatus as per claims 11 thru 17, wherein, the entire conductor loop is formed of one or many tubular conductors stacked together, and further cooled with a coolant, such as water, circulating through the bores for adequately cooling the conductor/core assembly.

19. An apparatus for continuously wiping and controlling excess liquid coating metal carried on hot dip metal coated strips as substantially described hereinabove and in the accompanying drawings.

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