AU2009222514A1 - Wiping Excess Coating From Hot Dip Metal Coated Wires - Google Patents

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT WIPING EXCESS COATING FROM HOT DIP METAL COATED WIRES The following statement is a full description of this invention, including the best method of performing it known to me: WIPING EXCESS COATING FROM HOT DIP METAL COATED WIRES INTRODUCTION This invention relates to a novel method and an apparatus for wiping and controlling excess metallic coating layers and coat weights on long cylindrical products or substrates such as 5 wires and strips in continuous hot dip metal coating operations like galvanising. More particularly, this invention relates to a method of exercising selective coat weight control on individual wires and strips, hereinafter called "wires", in multi-substrate coating operations on a common hot dip metallic bath. The invention is effective and useful in coating operations on wires in various sizes and shapes with metals such as tin, aluminium, zinc, lead, copper and 10 alloys thereof. A metal-coated finish is required on the product for reasons such as protection against corrosion in normal use, improving the soldering capability on the product surface, and others. This invention is basically characterised by mechanical wiping forces arising from i electromagnetic interactions generated within the liquid metallic coating layers on running wires outside the hot dip bath through the process of electromagnetic induction applied in a particular manner. The invention makes use of the good electrical conductivities of coating metals and is further characterised by a method in which all the wires emerging out of a common hot dip bath are subjected to the process of electromagnetic induction with a common 20 apparatus and the intensities of the forces of interactions are further varied and controlled on each wire individually and separately, as required, in a novel manner. Electromagnetic wiping, or wiping with mechanical forces of electromagnetic interactions, as stated above, is well known and well established in continuous hot dip galvanising of steel 25 wires (see prior art list). Such methods or techniques, except one (Indian Patent # 186942), as known to the applicant, are mainly applicable in the manufacturing practice to multi-wire, uniform production wherein all the wires of uniform size and quality are run at uniform speeds on a common zinc bath and require uniform coat weights retained after galvanising. The coat weight control on running wires in such uniform production is achieved normally through a 30 variation of some high frequency current used for the electromagnetic induction process.

However, in modem manufacturing practice, the continuous hot dip metal coating operations consist of mixed product scheduling on a common bath, wherein various wires of different sizes and qualities are simultaneously run at different rated speeds as required and may require 5 different coat weights retained after wiping. This invention is particularly useful for such mixed product scheduling while its usefulness for uniform operations and production is maintained. This invention and its guiding principles described herein are applicable and useful for all 10 kinds of mixed simultaneous operations on wires in all qualities, sizes and cross sectional geometries and of all materials coated with all kinds of coating metals and alloys thereof in the molten or liquid state. However, for brevity, this invention is substantially described herein for the most commonly manufactured galvanised steel wires of circular cross sections, hereinafter called "galvanised wires". The use of zinc as the coating metal is only illustrative. PRIOR ART IN ELECTROMAGNETIC WIPING Prior patents known to the applicant in the field of Electromagnetic Wiping are listed below. 20 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 25 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 30 All the patents listed above, except No. 2, describe suitability for wires in multi-wire uniform operations. No. 2, i.e. Indian Patent # 186942 is suitable for mixed operations but involves mechanical movements of certain ferromagnetic cores for the required individualized coat weight control on running wires in the wiping device, which is close to the bath level whereat the ambient temperature is quite high and handling of wires during initial threading or loading through the wiping device is quite rough. Also, for smooth surface on coated wires, which is a quality requirement on the product, an oxygen-free protective gas blanket is used around the 5 running wires as they pass through the wiping device. The high frequency induction process generates substantial amount of heat in the ferromagnetic cores due to magnetic hysteresis and joule heating, if any, and the cores require good cooling. This invention differs from the said Indian Patent in that the cores required for the selective 10 coat weight control are made immobile or stationary through a particular shape and stacking arrangement or design and use of certain auxiliary electrical circuits, at the same time allowing the user to exercise the said selective coat weight control. The stationary arrangement of the cores makes the wiping device compact without any moving parts thus providing better cooling for the cores and making the wiping device sturdier and the protective gas leakage-proof or free iU of contamination with oxygen from ambient air. Furthermore, the present invention allows purely electronic adjustment for individual coat weight control. This is a great advantage over having to mechanically move the cores. No. 3, i.e. US patent # 4,228,200, claims that the electromagnetic wiping device is at least 20 partly immersed in the molten zinc bath, thereby essentially including part of the bath in the electromagnetic induction and interaction phenomena used for wiping and coat weight control. The present invention differs from this in that the wiping device is located entirely outside and well apart from the molten zinc bath, thereby excluding the bath from the electromagnetic induction and interaction phenomena occurring on the travelling coated wires for wiping and 25 coat weight control. WORKING OUTLINE OF PRESENT INVENTION As per the basic requirement of this invention, each wire in a multi-wire operation with the 30 liquid metal coating layer thereon continuously emerges from the bath, and thereafter travels through a zone of an effectively localised externally applied alternating magnetic field having non-zero components of required strengths parallel to the longitudinal axis of the wire. All the wires emerging out of a common bath travel through their respective individual zones, which are all applied with a common apparatus and electronic power circuit and the magnetic field strengths or intensities in various zones are individually varied at will to suit the wiping requirements on corresponding running wires under stabilized variables and output of the said 5 electronic power circuit. In a preferred embodiment of this invention, such conditions are achieved by having each travelling wire, after its emergence from the bath, run freely or without any physical or electrical contact through two transversely disposed straight and parallel electrical conductors, Ic in which equal and opposite or unlike alternating electric currents of required frequency, waveform and magnitude are maintained. For best results, the conductors are located in such a position that the wire runs centrally through them and at right angles. Under such conditions, substantial alternating currents are induced in the liquid coating layer i; on the wire while in the vicinity of the conductors. The interactions between the existent alternating magnetic flux and the induced currents in the liquid coating layer generate net or effective mechanical forces acting in all directions away from the conductors and this effects rejection, through squeezing and wiping, of the entrained excess coat weight or coating mass on the running wire. The wiped away excess coating mass returns to the bath due to gravity. 21) Again, in the preferred embodiment, the intensity of the wiping forces is further enhanced, through an increase of the magnetic flux density for the same magnitude of the current, by substantially covering the conductors, in the vicinity of the running wire, with magnetically soft ferromagnetic materials or core composites of high electrical resistance to eddy currents on all 25 their outer sides except directly in between the conductors and the said wire. Examples of such cores are Ferrites, Laminations, Tape Wound and Cut Toroids and Iron Powder Compacts stacked or formed in the shapes of 'C' or 'U' or 'Horse Shoe' and rectangular bars or yokes. For reference, the entire assembly of conductors and cores for one wire is termed "wiping device", and the empty space in the wiping device about the wire position is termed "wiping 30 zone" in this specification.

In order to achieve satisfactory wiping on the running wire, the entire wiping device is preferably located adequately apart from the bath level in order not to subject the same to an appreciable degree of magnetic induction, which would interfere with the electromagnetic wiping phenomena occurring in the coating layer on the wire while within the said device, as 5 well as unnecessarily waste power. Furthermore, the entire wiping device is located and oriented above the bath level in such a position and manner that the coating layer entraining the travelling wire remains in a liquid state at around the same temperature as that of the bath. Moreover, an inert gaseous atmosphere at around the same temperature as the bath is 10 maintained in the wiping zone in order to avoid rapid oxidation and premature cooling of the coating layer. Examples of suitable inert gases are oxygen-depleted air or nitrogen, argon and other gases that do not cause rapid oxidation of the coating metal at the operating conditions. In multi-wire simultaneous operations, a wiping device with other conditions as above is made 15 available for each running wire at its running position on a common zinc bath and the conductors of all the wiping devices are connected in a suitable series circuit preferably through a variable inductor or choke to form an open loop. The two terminals of the open loop thus formed are connected to a variable electric or electronic power source or circuit, which is stabilized to maintain the current of required frequency, waveform shape and magnitude in the 20 said series circuit to achieve sustained wiping on all the running wires in ongoing operations. The variable inductor or choke is required to compensate for the changes in inductance required for individual coat weight control, as described later. The dimensions and geometries of the wiping devices and their positioning relative to the 2; running wires have marked effects on the wiping intensities that can be achieved. For example, the gap between the opposite conductors, the conductor and core span heights and core widths facing the running wires, and the angles between the conductors and corresponding wires all affect the extent of wiping action. Furthermore, the frequency, waveform shape and magnitude of the loop current also affect the wiping intensity that can be achieved. Increasing the current 31) increases the intensities of wiping forces and thus results in decreasing the retained coat weights on the products. The loop current magnitude thus provides a stable and repeatable control variable for controlling the obtainable coat weights, which is common to all wires.

As per this invention, the coat weight control common to all the running wires is stabilized by stabilizing all the variables and parameters as described above, and the coat weight control on each individual running wire is further exercised as required by selectively taking each of the 5 corresponding composite C cores into a state of partial saturation to a desired or required extent. In order to achieve this, each core mass on either side of each wire is composed of a closed spatial loop of ferromagnetic materials stacked together with minimal air gaps and the said loop is linked with separate conductor windings of several turns in which a variable steady or direct electric current of required magnitude is maintained with the help of another electrical 10 control circuit. In a preferred embodiment, the said spatial loop of ferromagnetic materials is constructed by placing two C shaped sub-cores together with adequate gap to accommodate the windings and joining them together at their legs or poles with two ferromagnetic yokes or bars. Refer to FIG. 4, 7 and 10. As explained further with reference to FIG. 5, 6 and 11, a change in the said direct current changes the average level of magnetization of the complete i. ferromagnetic loop and thus changes the magnitude of the alternating magnetic flux generated in the wiping device for the same magnitude of the alternating current (AC) through the main AC current conductors. This changes the local flux density and induced current density in the liquid coating layer entrained on the running wire. This, in turn, changes the intensity of forces of electromagnetic interactions, which bring about effective squeezing and wiping of the liquid 20 coating layer. The direct current (DC) bias of the ferromagnetic cores thus provides an excellent control variable for controlling the coat weights on individual wires in multi-wire galvanising. It should be noted that this invention makes use of the non-linear magnetization or saturation characteristic of ferromagnetic materials. 23 APPLICATION IN CONVENTIONAL WIRE GALVANISING In the contemporary continuous hot dip wire galvanising process, a long wire is continuously annealed or stress relieved, cleaned and longitudinally drawn through and out of a bath of molten zinc, at a speed mainly determined by the metallurgical and physical properties required 30 on the finish product. The freshly cleaned or nascent wire surface bonds with the zinc metal in the bath, forming a thin Iron/Zinc alloy layer. Depending on the thermal exchange between the wire and the bath, a layer of pure liquid zinc also freezes onto the travelling wire surface within the bath. The bonded layer or the solidified zinc layer exerts a viscous drag on the surrounding liquid free zinc in the onward direction. Once outside the bath, part of the entrained liquid coating mass returns or drains backwards to the bath under gravity while the remaining mass is supported and dragged onward against gravity due to its viscosity. The drag force is generated 5 at the solid/liquid interface and also at the outer surface of the liquid coating layer due to its surface tension. In due course of onward travel outside the bath, the dragged liquid zinc layer freezes onto the running wire. The total mass of zinc retained per unit surface area of the un galvanised product is generally known as the 'coat weight 'or the 'zinc carry' or the 'zinc pick up' or simply the 'pick-up' in the particular galvanising process. The coat weight is also 10 sometimes expressed as the average coating layer thickness on the finish product in solid state. After its exit from the bath, the wire runs in an ascending manner either vertically upwards or at an acute angle to the horizontal, mainly in order to facilitate draining off of the excessively entrained liquid coating mass back to the bath under the action of gravity. In multi-wire 1! galvanising operations, many wires are suitably spaced apart and exit the bath in a planar row either vertically upwards or at an acute angle to the horizontal. Some plants have both the modes of exit in simultaneous operations. In mixed product scheduling on the same galvanise line, different wires of different sizes and qualities have different rated running speeds depending on required physical and metallurgical properties and the line parameters. These 20 wires also may have different coat weights specified as per the product requirements. In modem manufacturing practice, attempts are constantly made to increase the speeds of wires through the hot dip bath for reasons of higher productivity and lower costs of production. It is also known that the zinc 'pick up' on any wire in the hot dip process increases as the speed of 25 the wire increases; and at speeds desirable and otherwise attainable in the manufacturing practice, the obtainable coat weights far exceed the minimum specification. It becomes desirable to wipe off or squeeze off the excess liquid coating metal from the running wire and recover it to the hot dip bath to save material and costs. Also, for enhanced product quality and marketability, uniform and even distribution of the coating mass, giving a smooth surface, is 30 desirable. This invention aims at achieving both of these requirements (accurate coat weight control and its uniform distribution) in the manufacturing practice through suitably designed wiping systems and devices. Furthermore, this invention can be suitably applied to all the existing modes of exit of wires from the zinc bath without having to modify any of the existing set up except replacing the current wiping devices by the wiping devices and systems as per this invention. Until now, some wiping methods involving physical and chemical means have been developed 5 and enjoyed limited success. These include: * Providing additional external heating to the wires exiting the bath * Maintaining inert or oxygen free atmosphere around the exiting wires * Maintaining a bed of crushed charcoal around the exiting wires * Passing the exiting wires through a hot, vibrating bed of gravel and burning gas flames 10 * Blowing nitrogen on the exiting wires e Passing the exiting wires through dies of required openings * Passing the exiting wires through tightened soft insulation pads * Treating the exiting wires with surface active chemical fluxes * Alloying zinc in the bath with other coating metals These methods have been mainly known to break the external surface film of the liquid coating layer outside the bath and transmit the wiping forces onto the running wire through external mediums and material bodies whereby the control capability is limited. Against these, the present invention is distinguished by its unique characteristic that the wiping forces are self 21) generated within the liquid coating layers and not transmitted externally through material bodies. This invention effectively breaks the external surface film of the liquid coating layer outside the bath and also effectively reduces the coating mass supported by both the surfaces (refer to FIG. 2) to any desired extent and at any desired speed of the wire through the bath. 25 This invention is further described and explained with the help of some schematic figures, listed below, relating to some preferred embodiments. However, the drawings herein in no way limit the scope of this invention. Moreover, in the said drawings, same numerals and letters are used to denote the same parts and entities. Also, some objects and parts in the foreground are shown in dashed lines for clarity of concealed significant parts and phenomena, 30 which are shown in continuous lines.

LIST OF FIGURES ATTACHED FIG. 1 depicts a sectional elevation of the hot dip bath and the row of galvanised wires. FIG. 2 shows a sectional view of a travelling wire and its liquid coating layer. 5 FIG. 3 depicts in section electromagnetic wiping phenomena on a galvanised wire. FIG. 4 depicts a preferred wiping device and DC control circuit shown for one wire. FIG. 5 depicts the magnetic flux loops through one C core composite and wire of FIG. 4. FIG. 6 depicts the effect of DC bias on AC field strength relevant to FIG. 5. FIG. 7 depicts another preferred stacking arrangement to achieve C core composites of FIG. 4. Ic FIG. 8 depicts a preferred AC circuit diagram for the entire multi-wire wiping system. FIG. 9 depicts another preferred AC circuit diagram for the entire multi-wire wiping system. FIG. 10 depicts another preferred wiping device and control circuit for one wire. FIG. 11 depicts the magnetic flux loops through one C core composite and wire of FIG. 10 FIG. 12 depicts a preferred wiping device arrangement in multi-wire operations. 1! FIG. 13 depicts another preferred wiping device arrangement in multi-wire operations. DETAILS OF FIGURES AND RELATED ELECTROMAGNETIC WIPING PHENOMENA 1. Conventional Wire Galvanising 21) FIG. 1 depicts a longitudinal sectional elevation of the hot dip bath and the row of galvanised wires, in the contemporary multi-wire galvanising practice. In this figure, a running wire is shown at '1'. This wire runs through the bath at a constant velocity shown by an arrow marked 'V'. The wire enters the bath level '3' at an entry point, runs through the bath '2' around a 25 sunk roller '40' or skid or a similar such device and exits the bath level 3 either at an exit point 'El' in a vertical take up mode or at another exit point 'E2' in the so called horizontal take up mode. The darkened menisci at El and E2 are indicative of liquid coating mass returning to the bath under the action of gravity. In the vertical take up mode, the exiting wire generally subtends a right angle with the bath level 3; while in the horizontal take up mode, the exiting 30 wire subtends an acute angle with the bath level, as shown at 'a', which is generally less than 30 degrees for operational convenience on the plant.

Also in FIG. 1, the liquid coating layer on the galvanised wire is shown at '4', and arrows marked 'Bk' and 'Fr' respectively show the backward and forward directions on the galvanising line. The gaseous atmosphere covering the bath and exiting wires is marked '5' and the action of gravity is indicated with arrows marked 'g'. As can be expected, the coating 5 layer 4 remains in a liquid state for some time from the exit of the wire from the bath and all the wiping needs to be carried out during this time. The spatial zone above the bath wherein the coating layer remains liquid is shown by the broken outlined rectangular region marked 'R1'. As per this invention, the wiping device needs to be located anywhere in the region RI. In the vertical take up mode, the liquid coating layer 4 on the exiting wire is acted upon by 1C, gravity g directly in the backward direction along the running wire and in the horizontal take up mode, a component of gravity acts on the liquid coating layer in the backward direction along the running wire, which component is shown by the arrow marked 'gc'. Both g and gc act to facilitate draining off of excess liquid coating back to the bath on all the running wires in the multi-wire galvanising process. 15 The horizontal and vertical take up modes are basically similar, as far as wiping and recovering the excess coating mass to the bath is concerned. Therefore, for brevity, reference will be made mainly to the vertical take up mode in the rest of this specification, assuming that similar action can be expected in case of the horizontal take up mode. Also in FIG. 1, the onward and 21) backward directions of travel of the wire are shown by arrows marked 'Ow' and 'Bw' respectively. 2. Details of Zinc Pick Up Phenomena 25 FIG. 2 shows a partial sectional elevation of a vertically oriented coated wire at an arbitrary region marked 'R2' in FIG. 1, wherein the coating layer is in a liquid state. In this figure, the interface between the constituent wire I or the chemically bonded or the solidified zinc layer and the liquid coating layer 4 is shown at '1/4' and the interface between the coating layer 4 and the surrounding atmosphere 5 or the coating layer outer surface is shown at '4/5'. The 30 coating outer surface 4/5 behaves like an elastic sack or membrane under tension. The tension is generally known as surface tension and is shown by arrows marked 'ST' at some arbitrary surface point marked 'SP'. Depending on its reaction with the atmosphere 5 and the prevalent temperature, the tension on the coating layer outer surface 4/5 changes from place to place in its course of onward travel. In this figure, the velocity distribution in the liquid zinc layer 4 dragged or entrained by the 5 travelling wire 1 is shown at an arbitrary line 'M-N' which is normal to the onward travelling wire and coating layer. The outer surface 4/5 and the wire/coating or solid/liquid interface 1/4 together support and drag the liquid coating mass 4 within against gravity in the onward direction by virtue of the liquid coating viscosity. It can be envisaged that the pattern of velocity within the free zinc layer is of a magnitude 'Vs', which is equal to or less than V, at 10 the outer surface 4/5, which progressively attenuates to a certain minimum, shown by arrow 'Vm', from the surface inwards and again progressively increases to V at the interface 1/4. This velocity distribution flattens as the wire and the liquid coating mass travel onwards (due to increased viscosity as the coating mass cools) and eventually all the coating mass attains the velocity V upon solidification. 13 Before solidification, at a height or distance where the weight of the supported liquid coating column exceeds the surface tension ST, the coating surface 4/5 ruptures, shedding off its supported coating mass, which tends to return to the bath under gravity. Depending upon the cooling and oxidising conditions outside the bath, which mainly control the coating outer 23 surface tension ST and which can be heterogenous or unsteady, the rupturing and reformation of the coating outer surface 4/5 can happen in an unsteady but repetitive manner in steady state operations of wire galvanising, resulting in an array of coating mass lumps on the galvanised product. This phenomenon is commonly known as "Bambooing Effect". 25 As per this invention, a considerable amount of heat is generated in the substrate and the coating mass in the vicinity of the Electro-Magnetic Wiping device due to eddy current heating and magnetic hysteresis. As a result, the temperature of the coating layer and its outer surface 4/5 is higher within the wiping zone. This, together with the atmosphere 5 around the coating being neutral and oxygen free, results in lowering of tension on surface 4/5 within the wiping .o zone. Therefore, the coating outer surface 4/5 is preferentially created after the wiping action is complete (where surface tension is lowest) and hence does not create any support for additional coating pick-up from the bath. This avoids the "Bambooing Effect" and renders the final coating surface smooth. 3. Details of Electromagnetic Wiping Action/Phenomena 5 FIG. 3 depicts a sectional elevation of the entire basic wiping device 'WD', mainly consisting of conductors marked '6' and '7' and C shaped composite cores marked '8' and '9', the zinc bath 2 and a galvanised wire 1, centrally located in the device and oriented and running along its axial direction 'YY', the section being axial through the wire and perpendicular to the 10 conductors. The conductors preferably have rectangular cross sections, as shown, to snugly fit the inner profiles of the C cores for better heat transfer and also preferably have through bores, shown at 'Br', in order to facilitate passage of a coolant like water, which provides cooling for the conductors as well as the cores and their control windings in normal use. 15 'If' denotes the alternating current in the conductors 6 and 7. Likewise, 'J' denotes the induced current density at any point of interest in the liquid coating layer. The directions of If and J are indicated using the well known "Dot and Cross" notation system for vectors and phasors, wherein a dot in a circle indicates a vector normal to the paper and coming out towards the viewer, and a cross in a circle indicates a vector normal to the paper and going away from the 20 viewer. Arrow 'V' indicates the velocity of the running wire. The currents If in conductors 6 and 7 set up substantial and adequate alternating magnetic flux in the surrounding space including the cores 8 and 9, the gaseous atmosphere 5 surrounding the travelling wire, the liquid coating layer 4 and the substrate 1. Such flux is shown by solid line closed loops with arrows marked 'flx-l'. In a similar manner, the induced currents also set up alternating 2:5 magnetic flux through the surrounding space, which is shown by dashed line closed loops with arrows marked 'fix-2'. Such alternating magnetic flux can be said to exist in the entire wiping zone of the wiping device WD, and the resultant vector sum of flx-1 and flx-2 maintains the alternating magnetic flux in the said zone as required for the squeezing and wiping action in the liquid coating layer 4. 3 D Important dimensions on the wiping device to achieve efficient wiping are shown in FIG. 3. These are: " 'G' - the gap between the conductors 6 and 7 or cores 8 and 9, allowing a rectangular prismatic passage for the coated wire to pass through 5 * 'HI' - the height of conductors 6 and 7 facing the running wire * 'H2' - the span height of composite C cores facing the wire The squeezing and wiping action within the liquid coating layer 4 is schematically shown in FIG. 3 at two arbitrary points below the central plane of conductors 6 and 7, which cuts the 10 sectional elevation along the axis 'ZZ'. These are marked 'P1' and 'Qi' and are symmetrically situated on opposite sides of the axis YY within the wiping zone. J denotes the alternating induced current densities at points P1 and QI. 'Bz' denotes the components of the existent alternating magnetic flux densities along ZZ at P1 and Q1. 'By' denotes the components of the existent alternating magnetic flux densities along YY at P1 and Ql. Interactions between By is and J at P1 and QI generate effective mechanical forces, marked 'Fz', which are normal to the wire surface and act from outside inwards, cumulatively developing pressure in the liquid coating layer 4. Owing to the configuration of the wiping device about the running wire, both, By and J increase in intensity along YY from the bath level up to the central plane or the axis ZZ, and so does the said pressure due to Fz, which is the product of By and J. The incremental 20 pressure in 4 along YY effectively causes a differential force acting on the liquid mass in the YY direction but away from the central plane, and this differential force is marked 'dFz'. The interactions between the horizontal components of the magnetic flux densities Bz and the current densities J at P1 and Qi create effective mechanical forces, as marked 'Fy', which act 25 along YY and away from the central plane and directly contribute to the wiping action below the said plane. Both, dFz and Fy are vibratory or pulsatory, with their net impulsive actions in directions as shown, and substantially act around the entire periphery of the coated wire in cross section for all frequencies, waveform shapes and magnitudes of the alternating currents If. The resultants of forces dFz and Fy, marked 'Fl' at the points P1 and Q1, retard the onward 30 motion of the entrained liquid coating mass under the central plane, causing effective squeezing and wiping. Similar analysis of the electromagnetic phenomena at arbitrary points, marked 'P2' and 'Q2', in the liquid coating layer above the central plane shows that the resultant forces of electromagnetic interactions thereat, marked 'F2', act away from the said plane and hence in the onward direction. However, since the liquid coating layer is free of any contact with solid or rigid bodies on the outside, the forces F l and F2 cannot nullify each other, and squeezing and wiping progresses smoothly and unhindered below the central plane of the 5 wiping device. FIG. 3 depicts a symmetrical set up for a wire of round cross section, with the two conductors at the same distance from the wire. However, wire of non-circular cross section or asymmetrical placement of the conductors does not alter the effectiveness of the invention. 1C Since the zinc layer is in a molten state, asymmetrical wiping forces still result in a substantially smooth and uniform coating mass distribution owing to the pulsatory nature of the forces of electromagnetic interactions as described above and as the coating outer surface always tries to follow the profile of the inner substrate to minimise surface energy. Therefore, the above and the following discussions apply equally well to asymmetrical configurations and V; to non-circular wires and strips. The flow of liquid coating mass is indicated by arrows marked 'lf'. FIG. 3 depicts the liquid mass flow pattern in the vicinity of the wiping device WD. Below the central plane, the liquid layer close to the running substrate flows in the onward direction while the wiped away liquid 20 coating mass flows backwards on the outer sides and eventually returns to the zinc bath. Above the central plane, the liquid mass flow is only onwards. This indicates that the wiping action occurs completely below the central plane of the wiping device. The backward flowing coating mass causes the coating outer surface 4/5 also to travel backwards, which, in turn, marginally enhances the wiping action below the plane, by virtue of its surface tension. 25 Owing to the elevated temperature of the coating mass travelling through the wiping device, its viscosity reduces. This reduces the onward viscous drag exerted by the running wire on the coating mass and indirectly enhances the wiping action by forces of electromagnetic interactions as described above. 30 The force of gravity on the entrained coating mass acts downwards and supports the wiping action by the forces of electromagnetic interactions below the central plane.

The actions of forces F 1 and F2 are pulsatory, which further help in smoothing out the coating layer by distributing it uniformly all over the surface of the running wire. 5 Since the returning coating mass flows along the coating outer side, the surface tension on the coating/atmosphere interface 4/5 plays an important role in the wiping phenomena under the central plane, and also in smoothing the coating layer, which is an important quality requirement on the finish product. Oxygen, if present in the atmosphere 5, readily attacks the pure zinc surface to form zinc oxide, which, being in solid state, has higher surface tension 10 compared to pure liquid zinc at the operating temperatures. As explained above in subsection 2 on "details of zinc pick up phenomena", higher surface tension increases its support to the coating mass within and reduces the wiping action, thus resulting in thickening of the coating layer due to inefficient or inadequate wiping. Oxygen in any form, either free or in the combined forms such as water vapour, carbon dioxide, carbon monoxide, sulphur dioxide etc. 1,; readily and preferentially combines with pure zinc to form zinc oxide at the operating temperatures. The speed of zinc oxide formation depends on the form and concentration of oxygen in the atmosphere 5. The oxidation of zinc is progressive over time and disturbs the stabilized wiping action in a cyclic manner, thereby causing lump formation in the coated layers on the finish products. As per this invention, the best way to avoid lump formation and 23 achieve smooth finish on the wiped product is to eliminate the presence of oxygen as much as possible in the atmosphere surrounding the running wire during the wiping action in the wiping zone. While complete elimination of oxygen is not practicable, reducing its concentration to below 20 parts per million gives good finish on the electromagnetically wiped product. 25 All of the forces and effects as discussed above tend to support and actuate effective retardation or backward motion of the onward travelling liquid coating mass under the central plane of the wiping device. This effectively causes wiping of the excess pick up from the bath. The aim of this invention is to achieve individual control of magnetic flux density locally at .o each wire in order to control the extent of wiping. This is achieved by varying the incremental magnetic permeability of each core as required separately through DC biased partial saturation.

4. Electromagnetic Wiping Device and Control System FIG. 4 is an isometric view of a preferred embodiment of a wiping device and coat weight control system as per this invention for a single wire exiting the zinc bath in a vertical take up 5 mode. The wiping device consists of two electrical conductors marked '6' and '7', and a pair of substantially 'C' or 'U' or 'Horse Shoe' shaped soft ferromagnetic composite cores, marked '8' and '9', which substantially and adequately cover the conductors 6 and 7 on their outer sides except directly in between the conductors and the running wire. The conductors 6 and 7 are disposed parallel to each other and are symmetrically located on opposite sides of the wire 10 running normal to the axial plane of the conductors. Each of the composite C cores 8 and 9 further consists of a closed ferromagnetic loop or path. Each closed loop is formed with a pair of C shaped sub-cores placed or stacked apart around the conductor and further magnetically stacked together by placing two rectangular soft I:J ferromagnetic pieces or bars in between as shown. As shown in FIG. 4, the cores 8 and 9 consist of four pieces of soft ferromagnetic cores each. These are marked '8-l', '8-2', '8-3' and '8-4' (concealed in the figure) for composite core 8 and '9-', '9-2', '9-3' and '9-4' for composite core 9. Of the eight core pieces, 8-1, 8-2, 9-1 and 9-2 are C shaped in profile and have rectangular cross sections. The remaining core pieces, i.e., 8-3, 8-4, 9-3 and 9-4 are 2') prismatic in shape and have rectangular cross sections. All the core pieces preferably have identical cross sections. The C-shaped sub-cores are linked with equal and adequate number of turns of conductor windings, shown at 'N-8' for core 8 and at 'N-9' for core 9, N denoting the total number of 25 turns of windings for the respective composite core. The location of the windings can be chosen as convenient and does not appreciably affect the circuit operation. The conductor windings N-8 and N-9 are connected to separate control circuits 'CC8' and 'CC9' respectively. Alternatively, both the windings can be connected to a common control circuit 'CC8+9' as shown with partly broken lines representing cables. 30 Each of the control circuits primarily consists of a DC voltage source of control voltage 'Vc', a variable control resistance 'Rc', and a control inductor or choke 'Lc', which are connected in series with the windings N-8 or N-9 or both, when together in series as shown. The chokes Le are required to prevent large alternating voltages, induced by the main AC current 'If', from appearing across the DC voltage source and short-circuiting it. In order to minimise the induced AC voltage to begin with, the conductor windings N-8 and N-9 preferably should be 5 evenly divided between the C-shaped sub-cores in a symmetrical manner. All electrical connections are indicated by prominent dots in the circuit diagrams. Adequate electrical insulation is to be provided on all the parts and components of the circuits to prevent unwanted leakage currents and short circuits in any and all of the electrical systems used in this invention. For the winding senses and control currents 'Ic' as shown, the sizes of the required chokes Lc IC are small and practicable. For preference, integral conductive fins (formed either by cutting slots or by welding) are provided on conductors 6 & 7 on both sides of the composite cores. These fins are shown at 'Fn' with broken outlines for clarity and help provide better cooling for the core composites i; and also act as flux barriers to confine the generated alternating magnetic flux to the corresponding wire, and not the neighbouring wires, if any. The whole assembly of conductor, composite core, insulations and windings on each side is preferably strengthened with adequate glue, resin and other suitable binding materials to form a compact body in order to have good strength, cooling and long service life, and also to prevent oxygen leakage into the inert 20 atmosphere surrounding the coated wires running through the wiping devices. The entire assembly of conductors 6 and 7 and composite cores 8 and 9 along with their windings as described above constitutes a wiping device for a single wire. This is shown at 'WD' in various relevant figures in this specification. For best performance, the wiping device 25 should be located symmetrically about the wire position. For convenience of reference, the entire wiping device has three mutually perpendicular axes, namely, 'XX', 'YY' and 'ZZ', all passing through the centre point. XX is horizontal and parallel to the two conductors 6 & 7, YY is vertical and coincides with the wire axis or position, and ZZ is horizontal and perpendicular to conductors 6 & 7. 30 Depending on the inter-wire spacing or pitch on the zinc bath and other operational requirements, one such wiping device is located in a suitably oriented position for each wire position on the bath, and main conductors 6 and 7 of all the wiping devices are electrically connected in a simple series circuit to form an open loop. This is schematically shown in FIG. 4 with partly broken lines in the left side top corner. In a preferred embodiment, a variable inductor, shown at 'Lfv', is effectively connected in series with the said loop. The entire open 5 loop has two terminals, shown at 'Ti' & 'T2', which are connected to a suitable electronic power circuit or source, which maintains a variable alternating voltage 'Vf between TI & T2 in order to maintain the alternating current 'If' of required frequency, waveform and magnitude in the said loop. In order to match the load consisting of all the wiping devices together to the output of the electronic power source, and for practicable construction of the variable inductor 10 Lfv, use of suitable transformers is preferable. In yet another preferred embodiment, all the DC control circuits of the wiping devices on a common bath would have their individual control resistances Rc and all such circuits would be connected in parallel to a common control inductor Lc and a common control voltage source 1!; Vc in series. In yet another preferred embodiment, all the DC control circuits of the wiping devices on a common bath would have their individual control resistances Rc and control inductors Lc, and all such circuits would be connected in parallel to a common control voltage source Vc. 21) 5. Flux patterns in Operation for Wiping Device in FIG. 4 FIG. 5 shows the relevant DC and alternating (AC) magnetic flux patterns for the running wire 25 1 and one composite core 9 on one side relevant to FIG. 4. Similar patterns exist for composite core 8 and wire 1 also. It should be noted that the DC flux generated in the composite core due to the direct current in the windings is substantially confined to the core itself, since there is provided a closed loop flux path of uniform cross section throughout. The DC flux is indicated with single headed arrows in the closed loop substantially along the sequential path formed by 30 the core pieces 9-1 + 9-4 + 9-2 + 9-3 + back to 9-1. The DC flux is marked 'fix-c'.

On the other hand, the AC flux in the wire is generated due to the alternating current If in conductor 7, and takes a closed loop path substantially around conductor 7. The AC flux is marked 'flx-f, and its closed loop path is shown by double headed arrows through the sequential path substantially along (9-1 and 9-2 in parallel) + 9-3 + 5 + 4 + 1 + 4 + 5 + 5 9-4 - back to (9-1 and 9-2 in parallel). 6. Magnetization of Composite Cores FIG. 6 shows the plots of magnetic induction of a composite core with DC and AC ic magnetization. The DC flux generated in the closed loop path of the composite core (flx-c) when plotted against the total magnetizing force due to control DC current {N.Ic or N multiplied by Ic} is along the continuous curve KAOCDEFG, where points K and A correspond to some negative values of the magnetizing force, point 0 is the origin corresponding to zero value of Ic, and points C, D, E, F and G correspond to progressively is; increasing values of Ic. For small values of N.Ic around the origin, the magnetic permeability of the core material is very high and the DC flux generated (flx-c) in the closed magnetic loop is proportional to the magnetizing force. As the DC control current Ic is progressively increased, the permeability of the composite core material progressively decreases and so does the increment in flx-c until the core material gets practically saturated of flux, which is indicated 2') by the broken line marked 'fix-s'. Induction of the composite core with AC magnetization is shown by broken line hysteresis loops at relevant DC control points. When the alternating current If is stabilized at some value as shown by the range marked 'If-r' on the abscissa and the control current Ic is zero, i.e., at the 25 origin, the incremental permeability (AC) of the core loop is maximum and the magnetic flux change in the composite core is also maximum, as between the points A and C shown at 'dflx 0' on the ordinate. This flux change is available for the induction of the wire and coating layer in the vicinity of the wiping device, and causes wiping of the liquid coating layer to the maximum extent. 30 When the DC magnetization control point is moved to some positive value corresponding to the point 'E' on the induction curve, the core material gets partially saturated and its incremental permeability decreases, and for the same AC magnetization range If-r, the magnetic flux change in the composite core decreases, as between the points D and F shown at 'dflx-E' on the ordinate. This reduces the flux change as available for the induction of the wire and coating layer in the vicinity of the wiping device; and hence reduces the intensity of the 5 wiping forces of electromagnetic interactions under the stabilized alternating current If. 7. Alternate Stacking Arrangement for Cores in FIG. 4 FIG. 7 shows an alternate stacking arrangement for composite C-cores in FIG. 4. Instead of 10 short bars between the C shaped sub-cores, longer bars are abutted to the ends of the sub-cores to complete the ferromagnetic loop. This arrangement works in the same way as that in FIG. 4. 8. AC Current Circuits Including Power Supply 15 FIG. 8 and FIG. 9 show two preferred embodiments of the AC circuit and power supply. In both cases, 'Lf' and 'Rf' are the total load inductance and resistance respectively. The load inductance is the sum of the AC effects of all wiping devices, while the load resistance is the sum of all the lossy elements. Lfv is a variable inductor or choke that is needed to compensate for changes in Lf as individual coat weight controls are exercised. Lfv is adjusted such that (Lf 20 + Lfv) remains constant. 'Tr' is a load-matching transformer in both figures, with its secondary terminals at TI and T2 and primary terminals at 'T3' and 'T4'. FIG. 8 shows a parallel resonant circuit, where the tank capacitor bank 'Cb' is placed in parallel with the primary winding of Tr. FIG. 9 shows a series resonant circuit where Cb is 25 placed in series with the primary winding of Tr. Such series and parallel resonant circuits are commonly used in industry. Electrical power is provided to either of the circuits, when used, at the terminals T5 and T6 by a suitable high-frequency power supply shown at '100'. It should be noted that Cb and Tr could both be integrated into the power supply 100. 3D 9. Alternate Core Arrangement FIG. 10 shows an isometric view of an alternate core arrangement. Instead of side-by-side sub cores, an arrangement of concentric sub-cores is used, with rectangular bars or yokes abutted to 5 their pole faces to complete the ferromagnetic loop. Various parts of the figure are labelled using the same symbols as in FIG. 4. This arrangement works in much the same way as that in FIG. 4, except that, preferably, a common control circuit is used for the two halves of the wiping device. This is because the AC voltage induced in the DC control circuit cannot be made small by symmetric placement of windings in the inner and outer sub-cores. 10 10. Flux Patterns in Core Arrangement of FIG. 10 In FIG. 11, the DC and AC magnetic flux is indicated by single-headed and double-headed arrows respectively, as in FIG. 5. The magnetic saturation of the core happens in a similar manner, as shown in FIG. 6, and this is used to control the wiping action on individual wires. 15 11. Multi-Wire Wiping Device Arrangement FIG. 12 shows a multi-wire wiping device arrangement that allows independent coat weight control on individual wires in simultaneous multi-wire operations. It is composed of a row of 20 wiping devices lying in a horizontal plane. The main AC conductors for all the wiping devices (6 and 7) are formed by two common straight lengths, naturally in successive series connections. Individual wires are numbered 1-1, 1-2, 1-3, ... for clarity with vertical axes YIYl, Y2Y2, Y3Y3, ... and the corresponding wiping devices are denoted by WD-1, WD-2, WD-3, ... The XX axis is common for all the wiping devices and the ZZ axes are separate at 23 the same horizontal level and denoted as ZIZI, Z2Z2, Z3Z3, ... The wires are run at their respective speeds denoted by Vl, V2, V3, .... The other parts are as shown on previous diagrams. The DC control circuits are not shown for clarity. The variable inductor Lfv is as shown and the load matching transformer Tr and the capacitor bank Cb are assumed to be integrated into the power source 100. 30 12. Alternate Multi-Wire Wiping Device Arrangement An alternate arrangement for wiping devices, as shown in FIG. 13, is especially suitable in multi-wire simultaneous operations on thick and stiff wires, which are difficult to thread or 5 load through the wiping devices shown in FIG. 12. In this arrangement, all the wiping devices are rotated by 90 degrees in the XX-ZZ plane with respect to FIG. 12. In each device, conductors 6 and 7 are joined together on the backside of the row of wires (shown by arrow Bk), and the same are joined to the conductors of adjacent wiping devices on the front side (shown by arrow Fr), for making the series loop as required. Where the wire pitch or inter-wire to spacing is too small to allow a single row of wiping devices as in FIG. 12, the said wiping devices are staggered by placing them alternately of two horizontal planes. Note that FIG. 13 shows the staggered arrangement, but a non-staggered arrangement in a single plane is merely a simplification (not shown for brevity). i!; In FIG. 13, the odd numbered wiping devices (WD-I, WD-3, ...) are in one horizontal plane and their ZZ axes (ZIZl, Z3Z3, ...) lie in the same line, while the even numbered ones (WD-2, WD-4...) are in another horizontal plane and their ZZ axes (Z2Z2, Z4Z4, ...) lie in another line. The XX axes for various wiping devices are all different due to the 90 degree rotation (denoted by XIX I, X2X2,...). Each wire is made to pass through two tiers of wiping devices, 20 and if this causes some interference or nuisance, the same can be avoided by adequately separating the two rows of wiping devices at two levels horizontally, i.e., in the forward and backward directions by providing alternate grooves on the sunk roller 40 or skid deeper. However, for the sake of brevity, this further modification of the alternate arrangement is not shown in this specification. 25 The alternate arrangement as shown in FIG. 13 is particularly suited to easy loading/threading of the wires since all wiping devices are open at the front and wires can be easily slotted into the wiping devices. If, depending on the line or plant design, backside loading of wires is convenient, the same can be achieved by reversing the arrangement of connections of 30 conductors 6 and 7 for all the wires, as described above.

It should be noted that the conductors 6 and 7 are shown symbolically connected by thick lines in order to complete the series loop. In reality, the tubular cross section should be maintained throughout. Design of the whole assembly is more complicated compared to that shown in FIG. 12 and the total power consumption may increase due to greater conductor length. 5 PRACTICAL DESIGNS & APPLICATION OF ELECTROMAGNETIC WIPING SYSTEM Electromagnetic wiping systems described in this specification are workable for all contemporary wire galvanising operations and for all design and control parameters and 10 variables of the wiping systems. However, control stability, accuracy and uniformity and system practicability and efficiency are some of the important aspects to be considered in designing a wiping system for any application. While designing the electromagnetic wiping and control systems, following important system, wire and line parameters need to be incorporated: 1. Vibrations on the running wires at the exit from the bath i! 2. Bath temperature and cooling conditions immediately outside the bath 3. Nature of the take up from the bath - vertical or horizontal 4. Running speeds and coat weight requirements on various wires 5. Geometries of individual wires or strips in cross sections 6. Electrical conductivities and magnetic permeabilities of the substrate and the 21) coating metal at the operating conditions 7. Physical properties of the coating metal, such as, density, viscosity and surface tension at the operating conditions 8. Waveform shape and frequency of AC current 9. Various dimensions on the wiping devices 25 For various applications, AC current frequencies in the range 50 Hertz to 2 Mega Hertz are useful and practicable. For efficient wiping, such frequencies should be chosen after due considerations to all the parameters listed above. 30 Additional external heating can be suitably provided on the wires running between the bath and the wiping device in order to prevent premature freezing of the liquid coating metal layers before undergoing wiping. Solid heat and electrical insulation can be provided around the running wires but without possible physical contacts with the liquid coating layers. It should also be noted that due to inevitable asymmetry of the wiping devices about the wires 5 in reality, certain ferromagnetic substrates might develop residual magnetism due to the DC bias control. Such residual magnetism can be eliminated by having suitable demagnetisers down the galvanise line. Such demagnetisers are commonly used in the manufacturing practice for other applications. ic GENERAL WIPING AND CONTROL PROCEDURES IN ONGOING OPERATIONS 1. Coat Weight Control on Individual Wires Having installed the wiping system on the galvanising plant, the loop current (If) is varied and 15 stabilized as required to achieve adequate maximum wiping intensities on all the wires, when running at their rated speeds, while the control currents (Ic) for all the core composites are set to zero. The wires are run in their normal course of operation and the control current Ic is varied for 20 each running wire to partially saturate the corresponding core composites in order to vary and adjust the obtainable coat weight after wiping. It is worthwhile to note here that some continuous coat weight measurement systems for individual running wires already exist in contemporary metal coating operations. Suitable feed 25 back control systems can be developed using such measurement systems to control the coat weights on individual running wires through continuous monitoring of control currents. 2. Stabilizing AC Current (If) in the Power Circuit 30 For good and efficient wiping action, frequency requirements on the AC current are generally much higher than supply line frequencies of 50 Hertz. Referring to FIG. 8 and 9, the power circuit resonates at a characteristic frequency governed by the product of total inductance (Lf + Lfv) and total capacitance (Cb) in the series loop. At the resonant frequency, large reactive power circulates in the loop compared to the total real power, which is dissipated through the total resistance Rf (because Rf is very small compared to the total inductive reactance at high operating frequencies). Thus, the AC current (If) can be large and stable at the resonant 5 frequency, its magnitude being adjustable anywhere at will by controlling the supply feed at the terminals 'T5' and 'T6'. In the power circuit loop, the required frequency of the current If is initially adjusted as the resonant frequency by selecting proper values of Lfv and Cb. The power is then switched on 1C and the magnitude of the current If is adjusted to the maximum required and stabilized. In on going operations, the resonant frequency in the power circuit loop is constantly measured and stabilized through a proper feed-back control system, which varies the variable inductance Lfv 'on-line' to counter any change in the load inductance Lf in order to maintain the total inductance in the loop (Lf + Lfv), and hence, the resonant frequency and current If constant. IS~ ADVANTAGES OF THE INVENTION IN WIRE GALVANISING 1. Effective for mixed product scheduling - optimum plant utilization when running different size and quality wires with different coat weight requirements 2) 2. Electronic control system - no mechanical movements required on the wiping device 3. Accurate and arbitrarily controllable excess coat weight reduction 4. Accurate and reliable coat weight control 5. Smooth and uniform coatings - enhanced quality control & product marketability 25 6. Effective on any wire geometry in cross section 7. Effective at any galvanising speeds 8. Reduced wastage of coating metals resulting in substantial cost savings 9. Reduced rejection of finished product 10. Reduced environmental pollution 30 11. Effective wiping of vibrating wires 12. Suitability for all production conditions and product requirements.

WIPING SYSTEM DESIGN AND PERFORMANCE IN WIRE GALVANISING Following examples provide some details of electromagnetic wiping system design and performance in wire galvanising. 5 Example 1. Wire Parameters: Wire Size 0.7 millimeter 10 Material : Low Carbon Steel Galvanising Parameters: Zinc Bath Temperature : 455 degrees Celsius Take-up from Bath : Vertical 15 Galvanising Speed :150 Meters/Minute Wiping Device Parameters: Ref. FIG. 3 and 4 Passage for Running Wires (G) :10 mm Cross Section of Conductors 6 & 7 : HI = 10 mm by Width =20 mm (Rectangular) 20 Total Span Height of C Cores (H2) : 30 mm Cross Section of Ferromagnetic Loop: 10 mm by 10 mm (Square) Inert Gas Atmosphere : Pure Nitrogen AC Current Parameters: 25 Waveform of Current If in 6 & 7 : Simple Sinusoidal Frequency of Current If : 200 kilo Hertz Magnitude of Stabilised If : 350 Amperes Wiping Performance Through DC Bias Control (Coat Weight Vs Incremental Permeability): 3D Incremental Relative Permeability of Composite Core: 100 50 20 10 5 3 Coat Weight After Wiping (Grams/Square Meter) : 60 62 65 78 100 140 Example 2. Wire Parameters: Wire Size :2.0 mm 5 Material : Low Carbon Steel Galvanising Parameters: Zinc Bath Temperature : 455 degrees Celsius Take-up from Bath Vertical 10 Galvanising Speed : 50 Meters/Minute Wiping Device Parameters: Ref. FIG. 3 and 4 Passage for Running Wires (G) :30 mm Cross Section of Conductors 6 & 7 : HI = 30 mm by Width =45 mm (Rectangular) I!, Total Span Height of C Cores (H2) : 90 mm Cross Section of Ferromagnetic Loop: 30 mm by 15 mm (Rectangular) Inert Gas Atmosphere : Pure Nitrogen AC Current (If) Parameters: 20 Waveform of Current in 6 & 7 Simple Sinusoidal Frequency of Current 100 kilo Hertz Magnitude of Current : 300 Amperes Wiping Performance Through DC Bias Control (Coat Weight Vs Incremental Permeability): 23 Incremental Relative Permeability of Composite Core: 100 50 20 10 5 3 Coat Weight After Wiping (Grams/Square Meter) :160 165 180 220 275 380 30

Claims (19)

1. A method of wiping and controlling excess liquid metallic coating layers carried on substrates in the forms of wires, strips or the like, hereinafter called 'wires', in the 10 continuous, multi-wire hot dip metal coating process, wherein several coated wires exit the hot dip bath in a substantially planar row, interalia comprising the steps of; [i] continuously drawing each wire through and out of the hot dip bath, and then through an effectively localised zone of externally applied alternating magnetic field 1! outside the said bath, said magnetic field having components substantially parallel to the running wire and also having some stationary or non-moving ferromagnetic elements in its magnetic circuits; [ii] varying the intensity of the said alternating magnetic field about each wire through 20 varied saturation of the said ferromagnetic elements in its magnetic circuits, for controlling the metal coating to be retained on the said wire after wiping.

2. A method as claimed in claim I wherein; 25 [i] two straight and parallel electrical conductors, which are substantially symmetrically and transversely disposed on opposite sides of the said coated wire without physical or electrical contact and which are covered on all outer sides, except those facing the running wire in its vicinity, with substantially Horseshoe or C shaped soft, 30 ferromagnetic composite cores and which carry equal alternating electric currents in opposite directions generate and maintain the said localized zone of externally applied alternating magnetic field about the running coated wire, and further wherein; [ii] each of the said composite cores is in the form of a spatial closed ferromagnetic loop linked by conductor windings that carry a variable direct or steady electric current which controls the intensity of the said alternating magnetic field about the running 5 coated wire by controlling the saturation of the core and thus the reluctance of the associated magnetic circuit.

3. A method as claimed in claims I and 2 wherein the said electrical conductors are 10 tubular through which a coolant is circulated.

4. A method as claimed in claims I thru 3 wherein the said electrical conductors have transverse integral conductive fins covering the sides of the composite C shaped cores. If

5. A method as claimed in claims I thru 4 wherein the coated wires are surrounded in the vicinity of the conductor/core assemblies by an inert gaseous atmosphere that does not appreciably chemically react with, or oxidise, the coating metal at the operating 20 conditions.

6. A method as claimed in claims 1 thru 5 wherein the conductors for all wires are located parallel to the plane of the row of wires and connected to form a series circuit loop that 2: is connected to an electronic power source that maintains an alternating electric current through the said loop.

7. A method as claimed in claims I thru 5 wherein the conductors for all wires are located 30 perpendicular to the plane of the row of wires and connected to form a series circuit loop that is connected to an electronic power source that maintains an alternating electric current through the said loop.

8. A method as claimed in claims I thru 5, and either or both of claims 6 and 7, wherein; the wires on a common hot dip bath exit the said bath in one or more planar rows and the conductors for all the wires are connected to form a series circuit loop that is 5 connected to an electronic power source that maintains an alternating electric current through the said loop.

9. A method as claimed in claims I thru 5, 8 and either or both of claims 6 and 7, wherein; 10 the wires on a common hot dip bath exit the said bath in one or more planar rows and the conductors for all the wires are connected to form a series circuit loop that is connected through a variable series inductor or choke to a stabilized electronic power source that maintains a stable alternating electric current through the said loop; and where the total inductance of the entire series circuit loop across the electronic power 15 source is controlled and maintained constant through a variation of inductance of the said variable inductor or choke in ongoing operations.

10. A method of continuously wiping and controlling excess liquid coating metal carried on 20 hot dip metal coated wires as substantially described hereinabove and in the accompanying drawings.

11. An apparatus for wiping and controlling excess liquid metallic coating layers carried on 2:; substrates in the forms of wires, strips or the like, hereinafter also called 'wires', in the continuous, multi-wire hot dip metal coating process, with several coated wires exiting the hot dip bath in a substantially planar row, wherein; [i] each wire is continuously drawn through and out of the hot dip bath and then 30 through a pair of straight and parallel electrical conductors, which are substantially symmetrically and transversely disposed on opposite sides of the said coated wire without physical or electrical contact and which are covered on all outer sides, except those facing the running wire in its vicinity, with substantially Horseshoe or C shaped soft, stationary ferromagnetic composite cores in the form of closed spatial loops, [ii] equal and opposite alternating electric currents are maintained through the said 5 conductor pair with a known apparatus, [iii] the spatial closed loop of each of the said composite cores is linked with conductor windings and a variable, direct or steady electric current is maintained through the said windings with a known apparatus. 10

12. An apparatus as claimed in claim 11 wherein, the said electrical conductors are tubular through which a coolant is circulated. 15

13. An apparatus as claimed in claims 11 and 12 wherein, the said electrical conductors have transverse integral conductive fins covering the sides of the composite C shaped cores. 20

14. An apparatus as claimed in claims 11 thru 13 wherein, the coated wires are surrounded in the vicinity of the conductor/core assemblies by an inert gaseous atmosphere which does not appreciably chemically react with, or oxidise, the coating metal at the operating conditions. 2.1

15. An apparatus as claimed in claims 11 thru 14 wherein the conductors for all wires are located parallel to the plane of the row of wires and connected to form a series circuit loop that is connected to a known electronic power source that maintains the said 31) alternating electric current through the said loop.

16. An apparatus as claimed in claims 11 thru 14 wherein the conductors for all wires are located perpendicular to the plane of the row of wires and connected to form a series circuit loop that is connected to a known electronic power source that maintains the said alternating electric current through the said loop. 5

17. An apparatus as claimed in claims 11 thru 14 and either or both of claims 15 and 16 wherein the wires on a common hot dip bath exit the said bath in one or more planar rows and the conductors for all wires are connected to form a series circuit loop that is 1( connected to a known electronic power source that maintains the said alternating electric current through the said loop.

18. An apparatus as claimed in claims 11 thru 14, 17 and either or both of the claims 15 and i 16, wherein the wires on a common hot dip bath exit the said bath in one or more planar rows and the conductors for all the wires are connected to form a series circuit loop that is connected through a variable series inductor or choke to a known stabilized electronic power source that maintains a stable alternating electric current through the said loop; and where the total inductance of the entire series circuit loop across the 20 electronic power source is controlled and maintained constant through a variation of inductance of the said variable inductor or choke in ongoing operations.

19. An apparatus for continuously wiping and controlling excess liquid coating metal 25 carried on hot dip metal coated wires as substantially described hereinabove and in the accompanying drawings. Vijay Yeshwant Moghe I October 2009 20