Classifications

• • 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
  • C23C2/0036—Crucibles
  • C23C2/00361—Crucibles characterised by structures including means for immersing or extracting the substrate through confining wall area
  • C23C2/00362—Details related to seals, e.g. magnetic means

Definitions

• the present invention relates to a method and a device for coating a metal strip with a metal or an alloy with a lower melting point or with liquidus than that of the material constituting the strip, according to which the strip is preheated and entrains it from bottom to top through a bath of said metal or of said alloy brought to a temperature higher than that of preheating the strip, then cools this strip at the outlet of said bath to a temperature lower than that of solidification of said metal or alloy.
• High speed wire coating methods have already been proposed which are passed from bottom to top through a bath of molten metal or alloy. Such methods are described, for example, in US-3,523,815, US-2,565,677, US-3,484,280 and US-4, 169,426.
• the strips are generally thin, ⁇ 1 mm thick and even ⁇ 0.5 mm, most often. Consequently, the edge of the strip, which, given its surface, develops the lowest driving force on the molten metal when moving this strip from bottom to top, is also the part of the strip which is in front of the largest mass of liquid, that is to say all the liquid metal located between the edge of the strip and the edge of the rectangular opening, taking into account the necessary clearance between this edge and this edge.
• the width of the opening will be between 0.7 and ⁇ 20 mm, that is to say a width between approximately 2 and 7 times the width of l edge, with a distance of 2 to 4 mm between the edge and the narrow edge of the rectangular opening, hence the difficulty in solving the problem of leaks.
• Another problem posed by the coating of a strip is that of supplying the layer of liquid which this strip must pass through.
• a cylindrical space is spared which is fed through a lateral opening.
• the volume is divided into two halves by this strip, it is necessary to feed each of the halves of this volume with a substantially equal flow rate, in order to ensure the same height of molten liquid on the part and on the other side of the plan of this strip.
• the problem of homogeneous heating of the strip is also more complex than that of heating a wire. This probably explains why this coating technique was essentially reserved for the wire, or, in the case of bands, to one side only, thus avoiding the problems linked to leaks at the edges of the band, mentioned above.
• the object of the present invention is precisely to propose a solution making it possible to extend the use of this method to a flat strip.
• the subject of the present invention is a process for coating a metal strip with a metal or an alloy with a lower melting point or with liquidus than that of the material constituting the strip, according to claim 1.
• One of the essential advantages of this process is to have a layer of liquid metal in contact with the strip having only a very small volume, of the order of 200 cl per meter of width of the strip.
• the coating of the strip therefore stops very quickly from the moment when the supply of the liquid metal layer which it passes through ceases. This makes it possible to obtain very great flexibility of use, to stop the installation, to change the coating metal or the strip without having large volumes of metal to be removed from the installation, as is the case. with conventional installations where the strip is immersed in a metal bath resulting in the immobilization of very large volumes of metal.
• Another advantage of the process according to the invention is that it allows to obtain homogeneous coatings having small thicknesses between 10-20 ⁇ m depending on the operating conditions.
• Figure 1 is a general sectional elevation view of this embodiment.
• FIG. 2 is a detail view in section along the line II-II in FIG. 1.
• Figure 3 is a sectional view along line III-III of Figure 2.
• Figure 4 is an explanatory diagram.
• Figure 5 is a partial sectional view similar to Figure 3 of an alternative implementation of the method.
• the installation illustrated in Figure 1 includes a crucible 1 surrounded by a copper tube 2 cooled by internal circulation of water, connected to a high frequency source (not shown) for induction heating.
• This crucible contains a piston 3, intended to regulate the level of the liquid metal by immersing this piston more or less deeply in the metal.
• a graphite nozzle 4, formed of two parts 4a, 4b assembled by screws 5, is fixed against the wall of the crucible 1 by screws 6.
• the crucible comprises two supply channels 7a, 7b (FIG. 2), each of them communicating with a channel 8a, 8b of each part 4a, 4b of the nozzle 4.
• each channel 8a, 8b opens into an interior parailissepidédique 10 formed between the parts 4a, 4b of the nozzle 4.
• This space communicates with the outside by two rectangular openings, vertically aligned, 11 and 12, intended to allow the passage of a ribbon 13 to be coated, this ribbon then dividing the interior space 10 into two halves, each supplied by one of the channels 8a, 8b.
• the lower opening 11 and, preferably, also the upper opening 12 are each formed by two inserts 14a, 14b and 15a, 15b arranged on either side of the plane of the ribbon 13.
• These inserts 14a, 14b, 15a, 15b are of rectangular section and are maintained in housings formed at the bottom and at the top of the interior space 10. They are made of non-wettable material by the Zn-Al alloy used, preferably in Mo.
• the presence of the inserts 14a, 14b delimiting the lower opening 11 makes it possible to increase the clearance between the walls of this opening and the ribbon 13, in particular the lateral clearance between the edge of the ribbon 13 and that of the opening, where there has the largest mass of liquid metal for the smallest ribbon drive surface, without detecting any leakage of liquid metal. Thanks to this play, which can reach 2 to 4 mm, the ribbon can move slightly in its plane without touching the edges of the opening.
• Each part 4a, 4b of the nozzle has two more cylindrical housings intended to receive heating bodies 61a, 16b respectively 17a, 17b to maintain the metal in the liquid state inside the nozzle 4.
• the ribbon 13 passes through a tubular conduit 18 supplied with reducing gas N 2 + H 2 by conduits 21.
• a flattened segment 18a of the tubular conduit is surrounded by a copper tube 20 (FIG. 1) internally cooled with water, and connected to a second high frequency source (not shown) intended for preheating the ribbon 13 by induction.
• the total current was initially set at 15A (0.96A / dm 2 ) and the contact time of the tape in the bath at 5 sec. Teflon spacers were used to prevent the tape from coming into contact with the stainless steel anode.
• the ribbon was then rinsed with tap water, then with demineralized water at 80 ° C and, finally, dried with hot air previously degreased.
• This ribbon preparation step takes place horizontally.
• the rest of the process, i.e. preheating, heating and cooling of the ribbon, takes place vertically and the height necessary for these operations is of the order of 3 m to 4 m, of which 1.5 m at the speed of 10 to 30 m / min are necessary to ensure the solidification of the coating after exiting the strip from the nozzle 4.
• the ribbon 13 is maintained in the conduit 18-18a supplied with gas [N 2 (50) + 10% H 2 (45)] at a pressure of 20 mm Hg and at a flow rate of 1, 5 1 / min, before entering space 10, supplied with metal or a liquid alloy from crucible 1.
• gas [N 2 (50) + 10% H 2 (45)] at a pressure of 20 mm Hg and at a flow rate of 1, 5 1 / min, before entering space 10, supplied with metal or a liquid alloy from crucible 1.
• the tests were carried out with pure zinc (99.998) and with a zinc alloy comprising 0.15% in Al weight (purity 99.98).
• the HF supply used for preheating the ribbon was of the EMA HG 255 type at a frequency of 375 kHz and with a maximum power of 25 kVA.
• the HF power supply used for heating the crucible by induction was of the PlusTherm-IG113W5 type at a frequency of 700 kHz and a maximum power of 10.9 kVA-5kW.
• the role of the lower inserts is to make it possible to provide an opening large enough for the strip 13 never to come into contact with the wall of the opening.
• the upper inserts 15a, 15b are in particular intended to allow the thickness of the coating to be reduced considerably. Other functions of these upper inserts will be discussed later.
• the ribbon 13 had a section of 0.3 x 30 mm: two types of inserts 14a, 14b were used to form the lower opening, namely inserts having an opening length 1 of 32 mm and others, whose length 1 was 34 mm.
• the width d of this same opening varied from 0.4 to 2 mm passing through 0.66; 1, 2; 1, 55 and 1.7 mm.
• the height h of these inserts was 2 to 4 mm.
• the upper inserts 15a, 15b some were made of graphite, with a width d of 0.8 mm, others in Mo, with a width d of 0.4 mm, the latter serving to reduce the thickness of the coating.
• the width d of the upper openings formed by the inserts 15a, 15b made of molybdenum, intended to limit the thickness of the coating was generally smaller than that of the lower openings, up to 5 times, that is, 0.4 versus 2 mm.
• the feed channels 8a, 8b had sections of 1 mm x 32 mm, 0.8 mm x 34 mm and 1.5 mm x 34 mm.
• the cooling was carried out using a simple fan blowing air up and down over a distance of 1.5 m. This cooling proved to be sufficient for coating speeds of 40 m / min.
• the preheating of the ribbon 13 was preferably of the order of 410 "C, although tests were carried out between 390 ° C and 470 ° C, while the temperature of the molten alloy was generally of the order of 510 * 0.
• the coating thicknesses essentially varied, as has already been said, depending on the presence or not of the upper inserts 15a, 15b.
• the minimum thickness obtained under these conditions was 12 ⁇ m; without insert, this minimum thickness was 20 ⁇ m.
• the parameters influencing the thickness of the coating are the preheating temperature of the strip and its speed of movement.
• the thickness of the coating is dependent on the preheating temperature of the tape and the space between the tape and the inserts. No significant influence was found in the two cases with regard to the temperature of the molten metal or the coating alloy.
• the maximum coating thicknesses measured were of the order of 80 ⁇ m.
• FIG. 4 shows the influence of the dimension e (FIG. 3) corresponding to the horizontal surface of the lower molybdenum inserts 14a, 14b on the leaks of molten metal as a function of the height of the bath h in the interior space 10.
• Two curves are plotted on this diagram, one corresponding to a total space (on both sides) between the strip and the width of the lower opening 11 of 1.2 mm and the other to a space of 2 mm. These curves represent the limit from which a bandless metal leak occurs for an opening 11 34 mm in length.
• FIG. 5 illustrates a ribbon 13 ′ U-shaped.
• the inserts 14 ′ a, 14 ′ b must have grooves 22 to allow the passage of the parallel branches of the profile 13 ′.
• the preheating of the strip can be obtained by means other than induction heating. This is how it could be heated by passing it through a bath of molten metal which does not react with the metal of the strip.
• a bath of molten metal which does not react with the metal of the strip.
• bismuth or silver as a preheating bath.
• the preheating temperature was a big influence on the appearance of the coating.
• the coating did not have good adhesion and several small holes were observed in the coating .

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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)

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• 1996
  • 1996-05-17 JP JP8536072A patent/JPH11505885A/ja active Pending
  • 1996-05-17 EP EP96913420A patent/EP0828864A1/de not_active Withdrawn
  • 1996-05-17 WO PCT/CH1996/000191 patent/WO1996038599A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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