Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C11/00—Component parts, details or accessories not specifically provided for in groups B05C1/00 - B05C9/00
  • B05C11/10—Storage, supply or control of liquid or other fluent material; Recovery of excess liquid or other fluent material
  • B05C11/1002—Means for controlling supply, i.e. flow or pressure, of liquid or other fluent material to the applying apparatus, e.g. valves
  • B05C11/1007—Means for controlling supply, i.e. flow or pressure, of liquid or other fluent material to the applying apparatus, e.g. valves responsive to condition of liquid or other fluent material
  • B05C11/101—Means for controlling supply, i.e. flow or pressure, of liquid or other fluent material to the applying apparatus, e.g. valves responsive to condition of liquid or other fluent material responsive to weight of a container for liquid or other fluent material; responsive to level of liquid or other fluent material in a container
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C1/00—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating
  • B05C1/003—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating incorporating means for heating or cooling the liquid or other fluent material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/003—Apparatus
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
  • C23C2/24—Removing excess of molten coatings; Controlling or regulating the coating thickness using magnetic or electric fields
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
  • C23C2/36—Elongated material
  • C23C2/40—Plates; Strips

Definitions

• This invention relates to the pots used to hold baths of molten metal for use in the continuous hot dip coating of metal strip with liquid metal coatings. It was developed for use in the continuous hot dip galvanising of steel strip, wherein the coating metal is essentially zinc. However, it will become apparent that it is applicable to any situation wherein the substrate strip is metal and the coating is a liquid metal, for example, hypereutectic aluminium-zinc alloys and other alloys.
• the invention is directed to electro-magnetic plugging means for preventing the leakage of bath liquid from the pot in those instances in which the pot has an opening in it that is below the surface level of the liquid during normal operation.
• dross is sometimes dragged from the surface of the bath by the strip and may become attached to the sink roll and rough alloy growths tend to form on the roll's surface. That dross and those growths damage the strip requiring frequent shut down of the line for removal and replacement of the sink roll with a new or renovated roll. Thus it would be desirable to eliminate the sink roll.
• the surface of the liquid metal that is supported or otherwise restrained by forces generated by the electro ⁇ magnetic plugging means rather than by a solid component of the pot is referred to hereinafter as the "bare" surface of the liquid metal.
• Prior proposed electro-magnetic plugging means have usually fallen into either of two categories, namely those utilising either poly ⁇ phase energising windings or multiple pole electro-magnets and switching devices which provide moving magnetic fields passing through the liquid or within the space into which the liquid might otherwise leak, and those which are analogous to electric motors utilising either permanent magnets or DC or single phase electro-magnets in combination with a transverse electric current. All such electro ⁇ magnetic plugging devices rely on the interaction of electric currents and magnetic fields, either generated independently or induced one by the other, and the currents are either DC or power frequency and the fields are likewise either steady or oscillating at power frequencies. In both categories of plugging means, the magnetic field and/or the electric current passes through the bath liquid adjacent to the opening to generate restraining forces therein.
• the resisting force is perpendicular to the direction of the flux lines of the field and the bare surface of the liquid, and is proportional to the degree of distortion or compression of the field.
• the situation is inherently stable, in that an adventitious projection of the liquid surface into the field space produces a localised distortion of the field and an accompanying increased localised resistance to further intrusion.
• high frequency plugging means overcome the major deficiencies of zero or low frequency plugging means, but they are subject to their own inherent limitations.
• a high density magnetic field is required if sufficient force is to be generated normal to the bare liquid surface to resist the hydrostatic pressure at the bottom of a liquid metal bath of a depth sufficient to enable a reliable continuous strip coating operation to proceed.
• This in turn requires high energy generating coils and places a premium on the use of pot and pot opening shapes and dimensions that minimise the extent of the bare liquid area to be supported or otherwise restrained.
• a coating pot provided with a conceptually simple form of high frequency electro-magnetic plugging means is disclosed in Japanese patent No.04-099160 (Nippon Steel).
• the "pot” is a hollow, rectangular prismatic cell of silicon carbide some 100 mm wide with a slot some 20 mm wide in its floor.
• a steel sheet moves upwardly through the slot and through a galvanising bath contained in the cell.
• the lower part of the cell is surrounded by a solenoid coil that is energised at 20 kHz and has a vertical centre plane coinciding with that of the cell.
• the slot is set to one side of that centre plane. This is described as causing the lower part of the bath liquid to be pushed towards the centre plane of the cell clear of the slot but leaving the upper part of the bath unaffected.
• a steel strip to be coated is shown travelling upwardly through the slot and through the upper part of the bath.
• An object of the present invention is to provide a hot dip coating pot with high frequency electro-magnetic plugging means that overcomes at least the above mentioned deficiency (i) of prior proposed high frequency electro-magnetically plugged pots, and in preferred embodiments alleviates deficiency (ii) thereof.
• the invention achieves that object by providing plugging means of the high frequency type which provide stabilising forces on the strip tending to prevent it from deviating from its intended pass line through the plugged opening, and which are more effective to prevent leakage of the liquid metal in the absence of a strip than prior known plugging means of that type.
• the invention consists in a hot dip coating pot having a strip inlet passage and electro-magnetic plugging means to prevent leakage of bath liquid from the pot through that passage, wherein: the plugging means comprise two magnetic field generators disposed one on each side of the passage; each generator projects an oscillating magnetic field into the passage from at least two poles of opposite polarity that are adjacent the passage and spaced apart in the through direction of the passage; the said at least two poles of each generator are respectively in substantial alignment with the corresponding poles of the other in the transverse direction of the passage; the magnetic fields projected by the generators have flux patterns which are substantially mirror images with reference to a plane of reflection coinciding with a centre plane of the passage; and both generators operate at a frequency of more than three kiloHertz.
• the projected fields provide identical repulsive forces on opposite sides of a centrally positioned strip, if one be present in the passage. If the strip deviates from the centre of the passage the additional compression of the field on one side and the expansion of the field on the other increases and decreases the repulsive forces respectively to produce a restoring force tending to return the strip to the centre position.
• any magnetic field generator necessarily has at least two spaced apart magnetic poles.
• the poles are necessarily of opposite polarity at any instant and the projected field extends from one to the other along part of an endless flux path.
• Those poles may be real (solid bodies from which the field emanates) or virtual (a spatial location from which the field emanates). Therefore, to project mirror image fields into the passage in accordance with the invention each generator must have at least two poles of opposite polarity closely adjacent the passage, spaced apart in the through direction of the passage, and in alignment with the corresponding poles of the other generator, as aforesaid.
• the combined field extends transversely of the passage and is ideally positioned to plug the passage when it is open for its full width due to the absence of the strip.
• the fields extending along the passage on each side of the strip not only respectively plug the narrow passage spaces on each side of the strip but also react with the strip to maintain it central of the inlet passage as a whole, thus enabling a narrow inlet passage to be used along with low tension in the strip.
• the invention also extends to a continuous, hot dip, strip galvanising line or like metal coating apparatus, wherein the coating pot is a pot according to the invention.
• pot In conventional coating lines the pot is necessarily large enough to house the sink roll and allow it to be partly or fully submerged in the liquid coating metal.
• An advantage of the present invention is that the pot may be made very much smaller than has been possible hitherto.
• pot as used hereinafter includes small but elongated trough-like containers somewhat different in shape and size from the normal concept of a conventional prior art pot, although fulfilling the same function as before.
• Figure 1 is a diagrammatic sectional view of a bottom portion of a coating pot according to the invention showing a magnetic field pattern established in the absence of a strip to be coated.
• Figure 2 is a view similar to figure 1 showing the subject matter of that figure and the magnetic field pattern established when a strip is present.
• Figure 3 is a perspective view of a pair of electromagnetic field generating coils, being components of the pot of figure 1.
• Figure 4 is a view similar to figure 3 of an alternative pair of coils.
• Figure 5 is a diagrammatic sectional view of a bottom portion of a coating pot according to another embodiment of the invention showing a magnetic field pattern established in the absence of a strip to be coated.
• Figure 6 is a view similar to figure 5 showing the subject matter of that figure and the magnetic field pattern established when a strip is present.
• Figure 7 is a diagrammatic sectional view of a yoke and strip, being components appearing in figures 5 and 6 drawn to a larger scale, showing dimension indicia as referred to elsewhere in the description.
• Figure 8 is a view similar to figure 6 oif another embodiment of the invention. BEST MODE OF CARRYING OUT THE INVENTION
• a hot dip coating pot in a continuous strip coating line contains a bath 1 of a molten metallic coating material, for example zinc or an aluminium-zinc alloy.
• the pot has a floor 2 with a downwardly directed duct 3 of generally rectangular cross-section defining a strip inlet passage 4 providing clearance for the entry into the pot of a metal strip 5 that is to be coated.
• the strip 5 is guided by rolls (not shown) to enter the pot from below and travel upwardly through the bath 1. Prior to reaching the passage 4 the strip 5 may be cleaned and otherwise conditioned in conventional manner to receive the coating.
• a steel strip for example, would normally be pre-conditioned and fed in a conventional manner from a heating furnace having a controlled reducing atmosphere, through a hood (not shown) likewise containing a reducing or at least inert atmosphere 6, into the passage 4.
• the strip 5 Having emerged from the bath 1 , the strip 5 would be treated, also in a completely conventional manner, to become finished product. Therefore, apart from the provision of rolls to bring the strip to the pot from below and the shape of the mentioned hood, the line equipment downstream and upstream of the coating pot may be conventional in all respects.
• the pot may be made from a ceramic or other refractory material, for example a titanium stabilised alumina, silicon carbide or boron nitride.
• Two high frequency magnetic field generators comprising coils 7 are respectively disposed on opposite sides of the duct 3.
• Those coils may, for example, be optionally one or other of the coils illustrated in figures 3 and 4. They are shown in section in figures 1 and 2, the section being taken on line X-X appearing in figures 3 and 4.
• each coil 7 is a single turn comprising an upper coil side conductor 8, a lower coil side conductor 9 and a coil end conductor 10.
• the coils are connected together by interconnecting conductors 11 and are fed by supply conductors 12 extending to terminals 13.
• the interconnecting conductors 11 are such that the two coils are in series, whereas in the figure 4 arrangement the coils are in parallel.
• the coils preferably extend rigidly as self supporting cantilevers from the terminals 13.
• the coils may be fabricated from copper tube, preferably tube of non-circular cross section such that each of the coil side conductors 8 and 9 presents a broad flat face towards the adjacent surfaces of the pot and duct.
• the coils may be fabricated from hollow rectangular section (HRS).
• HRS hollow rectangular section
• the joints between conductors in the coils are preferably brazed with bronze alloy.
• the terminals 13 may be lengths of copper tube adapted to be clamped by pipe clamp formations in or on rigid supply bus-bars extending to a high frequency power supply transformer.
• the terminals may be internally threaded at their lower ends, as indicated at 14 in figure 3 where a part of the terminal has been cut away, to receive coolant supply hoses (not shown) whereby coolant may be circulated through the coils 7 while they are in operation.
• each coil 7 may be regarded as having three virtual poles that are spaced apart in the longitudinal direction of the passage 4, namely the region 15 immediately above the upper coil side 8, the region 16 immediately below the lower coil side 9, and the region 17 at the centre of the coil.
• the fields from virtual poles 15 and 16 will always be in a common direction (say, at a specific instant, towards the passage 4) and field from virtual pole 17 will be in the opposite direction (at that instant, away from the passage 4), as indicated by arrows on the flux lines shown in figures 1 and 2.
• Virtual pole 17 may be regarded either as a single pole having twice the strength of each of virtual poles 15 and 16 or as two closely adjacent poles which are the respective counterparts of poles 15 and 16.
• poles 15 ensures that a portion of the field extends from one to the other transversely of the passage to provide a barrier to the descent of liquid from the bath through the passage. This may be seen in figure 1 , wherein, although the relevant flux lines are seen to be bowed downwardly where they cross the passage in response to the liquid pressure, the repulsive force on the bare surface of the liquid is still primarily upwards.
• the coils are disposed so that at least their upper coil side conductors are in register with each other in the direction of strip travel, that is to say, assuming the strip travels vertically through the duct the upper coil sides lie in the same horizontal plane.
• the lower coil sides could be more remote from the passage, for example they might lie in the same horizontal plane as the upper sides if desired.
• the arrangement may be further varied to maximise the field at the lower position of poles 17 and to use the field from these poles for levitation of the liquid.
• the coils 7 are energised from a preferably constant magnitude, alternating voltage source at a frequency of at least 3 kHz and preferably in excess of 7 kHz.
• the field from each generator coil is substantially restricted to that part of the passage and strip on its side of the centre plane of the strip.
• the generated fields then adopt the mirror image patterns shown in figure 2, wherein the field from each pole 15 enters the passage more or less transversely and then turns to extend longitudinally of the passage and strip for a distance before turning again to depart more or less transversely from the passage to pole 17.
• poles 15 and 17 serve to plug the passages on each side of the strip.
• the field penetrates the strip, albeit to a very small depth, so that the strip and field together provide for the complete containment for the liquid.
• the magnitude of the energising voltage needed to plug the passage in any instance depends on the physical parameters of the installation, (for example, passage width, strip width, number of turns in energising coil etc.) and on the liquid pressure. The last mentioned depends on the density of the coating material and the depth of the bath.
• the frequency of the power supply is chosen to produce an optimum balance between conflicting effects.
• the so called skin depth of the coil conductors that is to say the thickness of the surface layer to which the current is largely confined, is reduced and the coil resistance becomes higher. This leads to higher resistive losses.
• the repulsive force on a conducting body, in this instance the coating liquid rises as the eddy currents in it become more nearly confined to its surface, that is as the frequency rises.
• the cross over point between attraction and repulsion of the steel strip occurs at a frequency within the range of from 3 to 7 kHz. Thus frequencies in excess of that up to about 100 kHz are preferable.
• the coils 7 may be effectively in air or other non-magnetisable medium as illustrated.
• the generator coils may be partly externally enclosed in C-sectioned magnetisable shells.
• Such shells increase the magnetic flux for a given energising current which is advantageous, but also increase the inductance of the coil, which requires a higher energising voltage and is disadvantageous.
• a design balance has to be struck to optimise the efficiency of the plugging means.
• FIGS 5 to 7 illustrate another preferred embodiment of the invention, wherein each of the field generators is in the nature of an electromagnet comprising an energising coil wound upon a ferro ⁇ magnetic, preferably G shaped, core.
• the pot may have a floor 20 that is thick enough to enable two, high frequency magnetic field generators 21 to be housed within elongated recesses formed in the confronting faces of the floor 20 that define the pot's strip inlet passage 22.
• Each of the generators 21 comprises an energising coil 23 encircling the web of a C- or G-sectioned ferro- or ferri-magnetic core 24 and, preferably, copper or other non-ferrous electrically conductive shields 25 and 26.
• Those shields constrain the high frequency magnetic field, so that virtually all of the fields generated by the coils 23 emerge from the elongate end faces 27 and 28 of the cores 24. Those faces 27 and 28 are therefore the poles of the field generators 21.
• Each of the coils 7 is energised from a preferably common, preferably constant magnitude, alternating voltage source at a frequency in excess of 7 kHz. They are connected to the source so as to produce the preferred polarity, such that when one pole 27 is a north pole the other is a south pole and vice versa.
• Each side of the passage 22 is lined with a non-metallic refractory or other heat resistant, insulatory face plate 30, that provides a barrier between the molten metal of the bath 31 and the upper parts of the shields 25 and cores 24.
• Each core 24 is made of a low loss material having a high permeability and high saturation magnetisation.
• a low loss material having a high permeability and high saturation magnetisation.
• high density ferrites, magnetic metallic glass or iron powder may be used.
• the yoke preferably has a G shape so that the window occupied by the coil 23 may be made arbitrarily large, independent of the pole separation S, whilst maintaining a reasonably compact cross-sectional shape for the coil.
• a large window for the coil allows larger conductors to be used for a given number of turns, this permits lower current densities which, in turn, gives lower resistive power loss in the coil 23.
• increasing the coil size by increasing its conductor size increases the leakage field inside the coil, so that a higher proportion of the field generated does not pass through the upper pole face 27. A balance between these two competing effects has to be reached when determining the size and shape of the core 24.
• the pole separation S is reduced the reluctance of the magnetic path is reduced, so that, for a given number of ampere turns in the coil 23, the total field passed is increased.
• the pole separation S should be about, and preferably not less than, three times the air gap G.
• the spacing between the poles in the through direction of the passage should be within the range of from two to ten times the width of the air gap between the strip being coated and the side of the passage.
• the shields 25 and 26 are made from high conductivity material, for example, copper, aluminium or silver. If the energising coil is very large, additional shielding may be placed between the conductors of the coil to reduce internal flux leakage. Such an embodiment is illustrated by figure 8 wherein such additional shields are shown at 32 and 33. Eddy currents will be induced in the shields. This will cause heating in the shields and of course they are in a hot environment. Thus forced cooling of the shields may be required, for example by passing a cooling liquid through tubes brazed or other wise joined to the shields in a thermally conductive manner.
• the figure 8 embodiment includes such tubes referenced 34 in that figure.
• the number of conductor turns in each coil 23 is small, for example no more than ten, preferably from one to four, depending on the frequency of operation, the geometry of the components and the characteristics of the power supply.
• a multi-filament conductor of the same cross-sectional area as a single filament conductor is more efficient than the single filament conductor at high frequencies. That is to say, other things being equal a multi-filament conductor has a lower power loss than a single filament conductor. This is because high frequency current is largely restricted to the surface skin of the conductor and the multi-filament conductor has a greater surface to cross-sectional area ratio than the single filament conductor.
• each turn of the coil 23 comprises a plurality of tubular conductors in parallel. Those conductors are preferably cooled by means of cooling fluid pumped through their bores.
• the field frequency is preferably within the range of from 7 kHz to 100 kHz although even higher frequencies are quite feasible.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Coating With Molten Metal (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Crucibles And Fluidized-Bed Furnaces (AREA)
• Glass Compositions (AREA)

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Publications (1)

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Cited By (12)

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Citations (3)

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• 1995
  • 1995-07-24 IN IN1383DE1995 patent/IN191638B/en unknown
  • 1995-07-26 ES ES95925672T patent/ES2160170T3/es not_active Expired - Lifetime
  • 1995-07-26 CN CNB951944002A patent/CN1147616C/zh not_active Expired - Fee Related
  • 1995-07-26 CA CA002196056A patent/CA2196056C/en not_active Expired - Fee Related
  • 1995-07-26 DE DE69521135T patent/DE69521135T2/de not_active Expired - Lifetime
  • 1995-07-26 JP JP50531996A patent/JP3811817B2/ja not_active Expired - Fee Related
  • 1995-07-26 WO PCT/AU1995/000458 patent/WO1996003533A1/en active IP Right Grant
  • 1995-07-26 KR KR1019970700518A patent/KR100337725B1/ko not_active Expired - Fee Related
  • 1995-07-26 NZ NZ289790A patent/NZ289790A/en not_active IP Right Cessation
  • 1995-07-26 BR BR9510681-2A patent/BR9510681A/pt not_active IP Right Cessation
  • 1995-07-26 EP EP95925672A patent/EP0776382B1/en not_active Expired - Lifetime
  • 1995-07-26 BR BR9408603A patent/BR9408603A/pt unknown
  • 1995-07-26 AT AT95925672T patent/ATE201718T1/de active
• 1997
  • 1997-01-27 FI FI970334A patent/FI119326B/fi not_active IP Right Cessation

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