Method of making the metal coating on one side of previously cleaned metal band and device for executing the same

The invention relates to a method and apparatus for continuously forming a contact coating on only one side of an iron-based metal strip with a molten coating metal, and more particularly to such a method and apparatus, wherein it is not necessary to immerse the strip in the molten coating metal.

The method and apparatus of the invention are intended for the production of an iron-based metal strip coated on only one side with any suitable metal by plating in hot metal such as zinc, zinc alloy, aluminum alloy, aluminum alloy, alloy. lead and tin, lead, etc. Without wishing to limit the scope of the invention, the method and apparatus of the invention are further described with reference to exemplary embodiments in which an iron-based metal strip is formed with only one side coated with zinc or aluminum.

In recent years, there has been a growing demand for iron-based metal strips coated with a protective metal on one side only, such as steel sheet strips only one side galvanized. Such a product is particularly useful in the automotive industry, in the manufacture of apparatus and in the manufacture of building panels. The galvanized side of such. The article shows excellent corrosion resistance, while the uncoated side has excellent ability to be painted and can be easily welded, e.g. In cases where corrosion protection is required on only one side of the article, it will be appreciated that the one-sided coated article will bring substantial savings in the coating metal and will additionally form an uncoated side on which a high gloss coating or other finish can be applied.

In the prior art, a number of methods have been proposed to produce a glandular metal strip coated with a one-sided coating. In one method, the iron-based metal band is coated on one side with a non-wettable masking layer. The strip is usually dipped into molten metal. The masking layer is then scraped or otherwise removed.

U.S. Pat. No. 3,383,250 discloses a process in which the metal strip is suitably cleaned on both sides, brought to the coating temperature and then allowed to oxidize on only one side. The strip is then passed through a bath of molten metal which adheres only to the non-oxidized side.

In another method, the strip is coated on both sides by immersion in molten metal, whereby as much of the coating metal on one side is then removed by an air jet knife. The residual coating metal on the blasted side is removed electrolytically.

Finally, a product coated only on one side can be obtained electrolytically. To this end, the strip to be coated is moved around a cylinder partially submerged in the electrolyte. The exposed side of the strip then has a metal coating deposited thereon, while the other side of the strip remains uncoated because it is protected by a roll around which it moves.

While these known processes can yield acceptable products, they have a number of disadvantages. In general, the known processes are expensive because they require more work processes than the mere coating of molten metal and the use of expensive special equipment. The processes used hitherto produce uncoated marginal quality surfaces in terms of the requirements for producing high quality coating finishes.

A melt of molten metal has been used in the prior art to fully coat tubes and rods as described in German Patent No. 24 06 939. However, this method is not applicable for forming a one-sided coating on an iron-based metal strip.

The present invention is based on a method of forming a metal coating on one side of a previously cleaned iron-based metal strip by using a molten coating metal bath wherein the strip to be coated is guided over the top surface of the coating bath. metal, between the lower surface of the strip and the. a meniscus is formed by the upper surface of the bath, the coating metal contacting such a lower surface of the strip extends along the surface of the moving strip into a continuous coating adhering to the surface of the strip, said one side of the strip to be coated being applied at least at the onset of its contact with said meniscus in an un-oxygenated state, whereupon the coated strip is discharged upwardly away from contact with the meniscus of molten coating metal, and the excess metal on the coated side of the strip is removed by the finishing gas stream.

According to a preferred embodiment of the invention, the strip is guided above the top surface of the bath at a distance of 1.6 to 7.95 mm.

Preferably, the side of the strip to be coated is maintained in an un-oxygenated state with a non-oxidizing protective atmosphere surrounding the strip until the respective side has been coated with the coating metal, and thereafter the coated strip is discharged upwards into the ambient atmosphere.

According to another embodiment of the invention, the strip is maintained in a protective, non-oxygenated atmosphere throughout the coating and surface finishing.

Finishing the coated side with a gas stream can be carried out with air in the ambient air. It is likewise possible to carry out this finishing with a protective, non-oxygenating gas.

According to another feature of the invention, after the meniscus is formed, the coated strip is compressed to the surface of the molten metal bath.

The process thus performed makes it possible to achieve a rapid and continuous process of coating only one side of the iron-based metal strip with the molten coating metal. In this case, the coating thicknesses can be controlled as in conventional two-way dip coating processes.

No cylindrical assemblies immersed in the molten metal are required, eliminating the problems of material ingrowth and maintenance. The invention is cheaper and easier to carry out than the above described industrial methods for forming one-sided coatings. Existing lines for continuous coating of the annealing type can be easily and inexpensively adapted to produce a one-sided coating product, while providing the interchangeability, the same line can be used to produce both a one-sided and a two-sided product. The quality of the product is higher than that achieved with other dip coating methods, both in coated and uncoated areas.

The invention also relates to an apparatus for carrying out the method, comprising a molten metal bath tank, guide rollers for guiding the strip during its coating, at least one work roll for guiding the strip in contact with the molten coating metal, and a jet knife for removing excess coating metal a coated strip which, according to the invention, is characterized in that the working rolls are located above the plane with their entire volume, above which the molten metal bath level is maintained in the tank and at least one of them is. located at a distance of its lowest point of the surface from a plane of not more than · 7,95 mm, with a protective cover attached over at least the part of the tank in which the extended strip guide path to the first working roll extends through the bath surface; supply to the protective atmosphere source. .

Where the equipment includes:. More than one work roll, an intermediate work roll may be positioned between the two outer work rolls to urge the coated strip towards the bath level, located lower than the two outer work rolls.

The protective cover preferably has a ceiling and front, rear and side walls extending below the plane of the bath, and is provided with an outlet for the coated metal strip.

According to a further feature of the invention, the first work roll is spaced from a plane of 3.18 to 6.35 mm which is greater than the distance of the second work roll from this plane.

According to a further feature of the invention, the front wall of the protective cover is located between the first working roll and the second working roll, the first working roll being completely surrounded above the plane of the bath level by the protective cover up to the outlet for the coated strip.

Advantageously, an adjustable sealing closure is positioned at the exit surface of the front wall of the protective cover at the outlet, vertically displaceable in contact with the plane of travel of the upper surface of the strip between the work rolls. Furthermore, a contact roller may advantageously be disposed at the bottom of the sealing cap.

According to another embodiment of the invention, the first and the second working roll are encased by the protective cover.

According to a further feature of the invention, if the apparatus comprises a single work roll, the roll is completely surrounded by a protective cover.

According to one embodiment of the invention, the nozzle blade may be located outside the protective cover. According to another embodiment, the nozzle blade is located within the protective housing and is connected to a source of protective non-oxygenating gas.

Further downstream of the protective cover may be a cooling cover whose front end is gas-tightly connected to the protective cover outlet and the other end is provided with an outlet for the coated strip and a lead connected to a source of protective non-oxygenating atmosphere. Inside the cooling covers are cooled cylinders in the path of the coated belt. The cooling cover preferably has at least one outlet for a protective, non-oxygenating atmosphere, and at least one heat exchanger for cooling the vented atmosphere, and at least one cooled atmosphere return connected to the heat exchanger outlet.

The other end of the cooling cover is preferably designed in the form of a downwardly facing throat, which extends below the level of the cooling bath water level in the cooling tank, wherein one cooling roll and cooling water guide are provided in the cooling cover and cooling tank. spa.

According to a further feature of the invention, the nozzle blade is provided with a directional orifice plate for directing the gas away from the uncoated side of the belt.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a first embodiment of the apparatus and method of the invention; FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1; FIG. Fig. 4 is a schematic cutting sectional view, similar to Fig. 4; Fig. 3 is a schematic sectional view similar to Fig. 1 showing another embodiment of the invention; Fig. 5a is a cross-sectional detail showing a combination of a sealing block and a third cylinder; Fig. 5, Fig. 6 is a schematic cross-section similar to Fig. 2 showing the coating device of Figs. 1 or 5 without the use of a sealing block; 7 Fig. 8 is a schematic sectional view of a further embodiment of the method and apparatus of the invention; Fig. 8 is a sectional schematic sectional view showing a first method and apparatus for pickling; Fig. 10 is a schematic sectional view showing a third method and pickling apparatus; Figs. 11-14 are schematic sectional views similar to Figs. 7 illustrating the various methods and means by which the web can be maintained in a protective, non-oxygenating atmosphere until it cools down to a temperature at which a visible oxide film is not formed on exposure to the uncoated side of the web; FIG. an embodiment of a method and means according to the invention, similar to that of FIG. 5, but in which the entire coating and finishing are carried out in a protective atmosphere, FIG. 16 and 17 are a schematic cross-sectional view similar to FIG. 7 and showing an alternative nozzle knife arrangement; and obi. 18 is a sectional plan view of the device of FIG. 17.

All embodiments of the invention require that conventional strip pretreatment be performed prior to coating. For example, the strip may be cleaned in a non-oxidizing preheater, annealed and cooled in a high temperature protective atmosphere. The precise nature of the pre-treatment steps of the web is not a limiting factor for the scope of the invention if, at the time of coating, the web is at the right temperature and its surfaces are clean and free of oxides.

A first embodiment of the invention is shown in Figures 1 to 3, from which a tank 1 containing a bath 2 of molten coating metal is visible. Above this molten metal bath 2 is guided an iron-based metal strip 3 to be coated. Above the bath is a protective cover 4, which is an extension of the cover 5 of a conventional belt preparation device. This protective cover 4 can be integral with the cover 5 or can be connected to it in a gas-tight manner. Preferably, the seal 6 is gas-tight between the protective cover 4 and the cover 5. The seal 6 may have any suitable shape. In order to illustrate an exemplary embodiment, in the drawings this seal 6 is shown to be formed of two pairs of sealing rollers 7, 8 and 9, 10.

The protective cover 4 has a front wall 4a, a rear wall. wall 4b, side walls 4c and 4d and ceiling 4e. OF .' 1 and 2 it is clear that the front, rear. and the side walls extend downwardly into the molten metal bath 2. The front wall 4a has an outlet 11 therein for a coated metal strip, designed as a notch or a U-shaped aperture, a portion of which extends above the surface of the bath 2. The outlet 11 should be of a width corresponding to the widest iron-based metal strip is to be coated.

The belt 3 passes between the sealing rollers 9, 10 and 7, 8 to the guide roller 12 inside the protective cover 4. From the guide roller 12, the belt passes along a path d to a working roller 13 which lists the surface of the belt 3 to be provided. coating, close to the plane 2a on which the molten coating metal bath level is maintained in the tank 1. From working. In the roll 13, the belt 3 passes through the outlet to another working roll 14 and from there upwards and from the bath 2 of the molten coating. metal. The guide roller 12 'and the working rollers 13 and 14' are appropriately supported by conventional means (not shown).

The front wall 4a of the protective cover. 4 may be provided. support. 1S, adapted for insertion. elongated panel seal. a '16 of graphite' closure; or. other suitable material that serves as a seal. for m closing most of the output 11.. Graphite. the sealing closure 16 can move freely upwards. and & quot; down in the abutment 15 & quot; and rests on the top or & apos; uncoated surface of the iron-based metal strip. ·.

It is important that the protective cover 4 is filled with a non-oxidizing atmosphere so that the surfaces of the strip 3 remain clean and free of oxides prior to coating. For this purpose, the orifice protective cover 4 has in it. An inlet 17 is provided by which a suitable non-oxygenating gas is introduced into its interior. Any non-oxidizing gas such as nitrogen, inert gases and the like can be used. The non-oxidizing atmosphere within the protective cover 4 must be maintained at a slight overpressure so that the surrounding oxygenating atmosphere outside the protective cover 4 space cannot penetrate through the outlet 11, and in particular portions 11a and 11b thereof shown in Figure 2 which are not closed by a graphite seal 16. In a similar manner, it is preferable to provide a non-oxidizing atmosphere supply 18 between the pairs of sealing rollers 7, 8 and 9, 10. Furthermore, it is preferred that the non-oxidizing atmosphere branch chamber 18a thus formed has a pressure slightly higher than the pressure inside the protective cover 4 and than. This ensures that the non-oxidizing atmosphere inside the housing 5 cannot be contaminated even when the device is closed when working inside the protective housing 4. Since the pressure of the non-oxygenating atmosphere in the chamber 18a is higher than the atmospheric pressure inside the housing 5, contamination of the atmosphere within the housing 5 by sources at the inlet end of a conventional belt preparation device 3 is also prevented. The nozzle knife 19 is discussed in greater detail below.

The device described can function as follows. By introducing the iron-based base metal strip 3 between the sealing rollers 7, 8, 9, ID, the guide roller 12 and the working rolls 13 and 14, as shown in FIG. 1, and by moving the strip in the direction of arrow A, to form a small wave in the plane 2a of the stratified coating metal bath 2. This causes a touch between. the facing side of the strip 3 and the molten coating metal, and the surface tension and wetting properties of the coating metal will cause the meniscus to progressively contact and coat the adjacent surface of the strip. This meniscus is designated as a meniscus in FIGS. 1 to 3. 20. By means of the presence of the meniscus 20 ', it is thus possible to achieve a continuous contact coating of only one side. belt. 3 without the need to immerse the belt in the bath 2. The belt 3 moving upwards from the bath. 'work roller 14.'. thus, it will have a coated side 3a and an uncoated side 1b. that for the sake of illustration. .giant. 1 to 3, the strip thickness was 3. working distance. The height of the meniscus is intentionally exaggerated. the surface of the strip 3 to be provided. coated, from. - Plane:. on. below. še. maintains the level of bath 2 which. enable creation and maintenance. coating. se. will vary to some extent by:. type ,. used. The coating material and its surface tension and wettability. Properties. . For most. coating metals were achieved. .excellent :. results when. maintaining this distance of about 7.5 mm or less.

'. ... It is 'preferred'. that the first working roll 13 is positioned slightly higher than the plane 2a of the molten coating metal bath 2 than the second working roll 14. The difference is. Referring again to FIG. The actual height difference from. about 3 mm to. about 6 mm. The purpose of this height difference is. only further securing against splashing or collecting metal by the first working cylinder 13, which is located below. 4 and is therefore not visible to the operator.

The nozzle blade 19 can be positioned slightly. below the central axis of the second working cylinder 14. How far below the central axis of the working cylinder 14 the nozzle knife 19 will be located depends primarily on the diameter of the work roller 14 and the belt speed 3. It is important that the nozzle knife 19 does not blow contaminating atmosphere. The nozzle knife 19 may be positioned above the working cylinder 14 as indicated by the dashed position 19a. To ensure proper finishing. by blasting it is important that the transverse profile of the strip 3 remains flat. For this purpose, it is preferred. place a support cylinder 21, indicated by dashed lines in FIG. 1, opposite the nozzle blade at position 19a.

A further embodiment of the invention is shown in FIG. 5. This embodiment is similar to that of FIG. 1 and like parts bear like reference numerals. The embodiment according to FIG. 5 differs only in that the device comprises an intermediate work roll 22 located outside the protective cover 4 between the working rollers 13 'and 14 of the intermediate work roll. 22 will be provided with suitable support means (not shown) and positioned so as to slightly bend the belt 3 between the working rolls 13 and 14 downwards. This allows the working rolls 13 and 14 to rise slightly from the plane 2a of the molten coating metal bath 2, thereby preventing the coating metal from splashing or collecting with these rolls. The intermediate work roll 22 should have a length slightly smaller than the width. As in the case of FIG.

3 to 3, the thickness of the strip 3, the height of the meniscus 20 and the distance of the rollers 13 and 14 from the plane 2a of the molten coating metal bath 2 in FIG. 5 are exaggerated for clarity. Also, the degree of deflection of the belt 3 provided by the intermediate working roller 22 is shown to be intentionally increased. In order to position the work rolls 13 and 14 equidistant from the plane 2a of the bath 2, a deflection of 6 to 12 mm is provided. In all other directions, the apparatus of FIG. 5 and its function may be the same as in the embodiment shown in FIG. 1. The meniscus formed is the same as shown in FIG. 3. This meniscus will be the same using any suitable coating metal. However, it has been found that using aluminum as the coating metal, and the meniscus will normally have the shape shown in Figure 3, the intermediate work roll 22 'can compress the belt 3 slightly' below plane 2a at which the molten coating bath level is maintained. metal, since aluminum forms a meniscus 23 of the type shown in FIG. 4. Thus, using aluminum as the molten coating metal, the strip 3 may pass slightly below the plane 2a of the molten coating metal bath level 2, yet a one-sided coating is still achieved.

The embodiment of FIG. 5 may be provided by fitting the intermediate cylinder 22 onto the sealing cap 1B. This case is illustrated in Fig. 5a where the roller 22a, which corresponds to the roller 22 of Fig. 5, is rotatably mounted on a sealing cap 16a corresponding to the sealing cap 16 in Fig. 5, the fit being shown by conventional means (not shown). A contact roller 22a is disposed along the lower edge of the sealing closure 16a, which touches the uncoated side 3b of the belt 3 and performs the same function as described with respect to the intermediate working roller 22 in Fig. 5. 5 within the protective cover 4, which only requires a suitable bearing of the working rolls 13 and 14 in order to allow this variation.

Giant. 6 is similar to FIG. 2 and the same parts do not have the same reference numerals and this figure can be considered as a cross-section showing the front wall 4a of the protective cover 4 of FIG. 1 or FIG. 5. Giant. 6 differs from-FIG. 2 in that the abutment 15 and the graphite seal 16 are omitted and the lower edge 11c of the exit cover 4 is lowered to a position just above the belt 3 to minimize the exit size. In FIG. 1 Thus, the graphite seal 16 and the abutment 15 can be omitted, and the entry of the oxidizing atmosphere through the outlet 11 prevents the non-oxidizing atmosphere from being maintained in the protective cover 4 at a slight positive pressure.

A further embodiment of the invention is shown in Fig. 7. The tank 24 shown in Fig. 7 comprises a bath 25 of molten coating metal. The protective cover 26 forms a continuation of the cover 27 of the belt preparation device, of which only a portion is shown in FIG. 7. The protective cover 26 may again be integral with the cover 27 or may be gas-tightly connected thereto. A seal 28 is disposed between the protective cover 26 and the cover 27. The gasket may have any suitable shape and for the purpose of the example is again shown in the form of two pairs of sealing rollers 29, 30 and 31, 32. A non-oxygenating atmosphere supply 33 is disposed between the pairs of sealing rollers. The protective cover 26 has a front wall 26a, a rear wall 26b, and side walls 26c. The front, rear and side walls of the protective cover 26 extend downwardly into the molten coating metal bath 25.

The iron-based metal strip is again indicated by the reference numeral 3 and passes between the sealing rollers 31 and 32 and the sealing rollers 29 and 30 of the seal 28. It then passes around the guiding 'roller 34 downwards' and around the working roller 35 which indicates the surface of the belt 3, to be coated near the bath level plane 25a of the molten coating metal. The work roll 35 then directs the coated strip upward from the molten coating metal bath 25 and the strip 3 exits through the outlet 36 in the protective cover 26.

The protective cover 26 is provided with a non-oxidizing atmosphere inlet 37 and the non-oxidizing atmosphere is maintained within the protective cover 26 by slight overpressure, so that the surrounding oxygen-containing atmosphere outside the protective cover 26 cannot enter through outlet 36. Seal 28 and its non-oxidizing supply 33 the atmosphere may serve the same purpose as described in connection with the seal 6 and the lead 18 of FIG. 1. Again, seal 28 and lead 33 are of particular importance during stoppage of the guard. In the embodiment of FIG. 7, the nozzle knife 38 is located within the protective housing 26. The nozzle knife 38 will operate with a non-oxidizing gas, which may be the same as the non-oxidizing atmosphere within the protective housing 26.

The function of the embodiment of FIG. 7 differs from that of FIGS. 1 and 5, in particular in that the entire coating and finishing is carried out within the protective housing 26 and in its protective non-oxidizing atmosphere. During the introduction of the iron-based metal strip 3 as shown in FIG. 7 and as it moves in the direction of arrow B, a small wave at the surface of the molten coating metal bath 25 will again result in a meniscus 39, which will continuously and contact the surface of the strip facing the bath 25 continuously and contact the molten metal as it passes The mounting means (not shown) for the rollers 34 and 35 in the protective cover 26 and for the jet knife 38 can be of conventional design. The iron-based base web that moves upwardly toward the outlet 36 will be coated on side 3a and is uncoated on side 3b. The coated side will be finished with a jet knife 38, which can again be placed in any position as long as it does not violate the meniscus 39 and the bath level 25 of the molten coating metal. If it is desired to position the nozzle blade 38 upwardly away from the working roll 35 so that the transverse shape of the strip 3 could be twisted, a support roll as described in connection with FIG. 1 may be used to provide the cross-section. which remains flat during the finishing operation.

In all the embodiments described so far, the strip 3 is exposed to ambient air at a temperature high enough to form a visible oxide layer on its uncoated side 3b. At short exposure times, the visible oxide coating is formed from oxide layers or films, the base metal film being predominantly made of ferrous oxide, on which a layer of ferric iron oxide FesCU is deposited, followed by a layer of ferric oxide FezOa. When the temperature of the web when exposed to the oxidizing atmosphere is below about 570^,OC, a layer of iron oxide is not formed, which is usual when the coating metal is zinc. If the coating metal is aluminum, the strip temperature is usually above 570 ° C and a layer of iron oxide is formed.

The visible oxide coating can be removed by acid pickling as mentioned above. The difference between pickling as used herein and normal pickling is a matter of the degree of this surface treatment, where normal pickling usually involves intensive surface treatment to remove scale from the blank. The first stage of pickling of the oxide coating by pickling is purely chemical and consists of dissolving the oxide films. Oxygen films dissolve at different rates, and the dissolution rate of the iron-iron oxide film is decisive as this oxide dissolves most slowly. Thin porous oxide films can be removed by acid penetration and direct attack of the parent metal. The rate of oxide removal can be increased in various ways.

In particular, the removal rate may be increased by increasing the temperature of the acid bath or increasing the acid concentration. In addition, the rate of removal of oxide by penetration can be increased by introducing an electric current. This increases the dissolution of the parent metal and the local shaking of the surface by generating hydrogen.

The pickling of the base metal strip with a one-sided coating presents a particular problem in that it is desirable to remove the oxide from the uncoated side. at the same time, the etching on the coated side is minimized. Electrolytic pickling is most preferred.

The pickling comprises a number of variable and interrelated parameters that provide an almost infinite number of specific combinations, each capable of adequately removing the oxide film from the uncoated side of the web. However, it is possible to establish basic principles for the most advantageous method of contaminating a metal strip with a one-sided coating.

The basic variable pickling parameters are the acid used, the acid concentration, its temperature, the electrode-strip distance, the dip immersion time, and the electrode current density. In order to minimize etching of the coated side of the web, it is most advantageous to use a dilute acid solution, usually industrial acid, at a concentration of 1% by volume or less. The type of acid used will be determined by its efficiency, affordability price, pollution control and ventilation requirements. Sulfuric, phosphoric, hydrochloric and nitric acids can be effectively used from the usual acids for this purpose. Sulfuric and phosphoric acid are slightly more effective and sulfuric acid is most advantageous not only because of its efficacy but because of its reduced susceptibility to smoke.

The acid temperature should be kept low (below about 38 [deg.] C.) if the etching and rusting of the coated side of the coated strip is to be minimized, but the distance between the electrode and the strip should be kept to a minimum to increase efficiency. as required, to avoid contact between the strip and the electrode during continuous passage of the strip. The immersion time of the strip should also be reduced to the minimum necessary for the time needed to remove the visible oxide layer in the particular case.

From a practical point of view, however, the immersion time of the belt is determined by the tank dimensions and the belt operating speeds. A certain minimum current density will be required for the device. Amounts from 2200 to 4400 A / m2 are found to be quite adequate. Using a current density above the practical minimum would be completely unnecessary and would be a waste of energy.

Giant. 8 illustrates a modified galvanic cell solution for pickling. A bath 40 containing a dilute sulfuric acid bath 41 is shown. The strip 3 with the coated side 3a and the uncoated side 3b is passed through the bath 41 around a roller 42 carried in the bath by a conventional means (not shown). The waste metal block 43 is electrically connected to the iron-based metal strip by a guide 44 with a roller 42. Although the rate of attack of the parent metal does not increase, the rapid generation of hydrogen on the surface of the uncoated strip 3 helps to shake off the oxide from that surface. Hydrogen is also generated on the scrap metal block 43 from where it rises and aids the shaking of the oxide on the uncoated side 3b of the belt 3. Other scrap metals such as magnesium or aluminum may be used.

Both 0.5% sulfuric acid and 0.5% phosphoric acid are used in the test runs as a dilute acid bath 41 and maintained at a temperature of about 32 ° C. The strip 3 is coated with zinc on the side 3a and has an oxide coating on the side 3b formed as a result of the strip 3 leaving the protective atmosphere at a temperature of about 480 ° C. A zinc depletion block 43 is used, and is maintained at approximately 3 mm. from the surface 3b of the belt 3. The oxide coating is removed from the uncoated side 3b in approximately 3 seconds without showing any etching of the zinc coating on the coated side 3a of the belt 3.

Giant. 9 shows another method and apparatus for pickling a strip 3 provided with a hot metal coating on side 3a and an oxide coating on side 3b. In this embodiment, a bath 45 comprising a dilute acid bath 46 is used. The strip 3 'is passed around the submerged roller 47 and an electrode 48 is placed on the uncoated side 3b of the strip 3.

It has been found that instead of connecting the current source 49 with a conductor 51 to the roll 47 (or sliding contact or contact rollers, as is known in the art), a molten coating metal bath can be used to supply current to the strip 3 and thereby eliminate possible surface damage For this purpose, the conductor 51 from the power source 49 can be connected to the coating metal tank 1, if the tub is metal, for example, this connection has been illustrated in Fig. 1. Alternatively, the conductor 51 may be connected to an electrode 51a immersed in a bath of molten coating metal. By way of example, this case has been illustrated in Fig. 5. It will be appreciated that the conductor connections 51 shown in Figs. 1 and 5 may be used in any embodiments of the coating apparatus when using acid pickling of the type described with respect to P0. Fig. 9.

The embodiment of Fig. 9, in which the current is supplied from an external source 49, has been shown to be more efficient than the embodiment of Fig. 8.

The dissolution of the iron below the oxide layer is accelerated by some hydrogen evolution that does not assist in shaking the base metal oxide based on the iron strip 3. The power source 49 can be either AC or DC current, with AC being more preferred with pickling accelerating current. The electrode 48 may be of any suitable material that is conductive and is not supplied with dilute acid. Stainless steel is an excellent electrode material. Other materials that may be used as the electrode 48 are platinum or lead.

In the experimental operation, a dilute acid bath 46 of 0.5% sulfuric acid is used, which is maintained at a temperature of about 32 degrees Celsius. The power source 49 is a DC generator. current generating a current of 110 A, the strip 3 forming a cathode of stainless steel anode 48. The strip 3 has an oxide film formed on the side 3b resulting from the strip leaving the non-oxidizing protective atmosphere used to form the zinc coating and comes into contact with air at a strip temperature of about 480 ° C. Deň: 32 ° C. The oxide film is stripped off in less than 6 seconds with rapid hydrogen evolution as at electrode 48, flow even on the uncoated web 3b of the strip. There is no formation of rust on the 3o side when immersed for no more than 4 seconds. Some slight rust formation and zinc coating etching are observed at a dip time of 6 seconds. The stainless steel electrode is located about 12.5 mm from the uncoated web 3b of the belt 3.

In another experimental operation, the dilute acid bath 46 is again 0.5% sulfuric acid, maintained at a temperature of about 26.5. ° C, o the electrode is again made of stainless steel. The strip 3 has a zinc coating on side 3o of an oxide coating on side 3b, formed by the strip 3 leaving the protruding otmosphere used in forming the zinc coating and coming into contact with air at a strip temperature of about 480 ° C. The power source 49 is a no-current source providing approximately 9A current. The electrode 48 is held approximately 25 mm from the surface 3b of the strip 3. From these conditions, the oxide film is removed in approximately 2 seconds. No etching of the zinc coating on the coated strand 3o of the belt 3 is observed.

FIG. 9 shows a variation of the embodiment of FIG. 9. In this embodiment, the belt 3 passes through the support cylinder 52 and the bath 46 of FIG. 9 is threatened with a sponge 53 saturated with dilute acid. The sponge 53 is supported by a support means 54 which is made of stainless steel or other material not attacked or embrittled by the action of dilute acid. The sponge 53 and its holder 54 are connected to the power source 55 by a conductor 56. The belt 3 is also connected to the power source 55 by a conductor 57 by means of a support roller 52. The power source 55 may be either alternating current or direct current. In the holder 54 of the sponge 53 an acid supply 58 is provided, which can be used to replenish the acid. The embodiment of FIG. 10 is characterized by the advantage that no tubs are required, and the sponge provides a scraping action to remove oxides. However, the replacement of the sponge should be borne in mind as it results from its wear or from the collection of a sufficient quantity of particles retained in its body which constitutes a risk of scratching · the belt 3.

All of the staining procedures described above must be followed by suitable rinsing and drying (procedures well known to those skilled in the art) to reduce acid attack on both sides of the strip. dilute acids is well known to those skilled in the art. The dilute acids may contain conventional additives such as surface tension agents, inhibitors, antifoams, and the like, as is well known to those skilled in the art.

Pickling, rinsing and drying may be omitted if the iron-based parent metal strip, coated on one side with the inventive coating, is kept in a protective, non-oxygenating atmosphere until it reaches a temperature sufficiently low to prevent the formation of visible oxide coating on its uncoated side. This method, and the apparatus for carrying it out, are shown in Fig. 11. the coating process and apparatus of FIG. 11 identical to the method and apparatus of FIG. 7 and the same parts carry the same reference numerals. The embodiment of FIG. 11 differs from the embodiment of FIG. 7 only in that a cooling cover 59 is attached to the protective cover 26 in the region of the outlet 36. The cooling cover 59 is provided with an outlet 80 and is of such a length that the belt 3 passes through the outlet 60, is cooled to a temperature of about 150 degrees Celsius, a temperature at which a visible oxide layer is not formed on the uncoated side 3b of the belt 3. The cooling cover 59 is, of course, filled with a non-oxidizing atmosphere that will enter this cover 59 through the outlet 36. If desired, a further non-oxidizing atmosphere supply 61 is provided in the cooling cover 59. Although for the purpose of this example, the cooling cover 59 is shown simply attached to the protective cover 26, it is understood that the ceiling portion 26e of the protective cover 26d located below the cooling cover 59 and including the outlet 36 can be omitted. Except that the coated strip is maintained in a protective atmosphere until it is sufficiently cooled to prevent the formation of a visible oxide layer on the uncoated side, the function of the embodiment of FIG. 11 is identical to that described in relation to FIG. 7.

The length of the cooling cover required to hold the coated strip in a protected atmosphere until a visible oxide layer appears on the uncoated side can be reduced by using a means for accelerating belt cooling. Giant. 12 shows an embodiment substantially identical to FIG. 7, with the same parts again bearing the same reference numerals. Na ob. 12 shows a cooling cover 62 similar to the cooling cover 59 of FIG. 11, and · provided with an outlet · 63 · and an additional inlet 64 of a non-oxygenating atmosphere if desired. In this embodiment, however, the belt 3 is passed around the cooled rollers 65 and 66, which causes the temperature of the belt 3 to be reduced and allows the cooling cover 62 to be shorter. The ceiling portion 26e of the protective cover 26, which lies below the cooling cover 62 and has an outlet 36 formed therein, can again be omitted.

Another way in which the strip can be protected from the formation of a visible film is shown in FIG. 13. The device is again substantially the same as that of FIG. 7 and the coating is carried out in the same manner. In this embodiment, the protective cover 26 is provided with a cooling cover 67 with an outlet 68. In the cooling cover 67, there is a protective atmosphere behind the protective cover 26, and the cooling cover 67 may be provided with an additional inlet 69 if necessary. In this embodiment, a portion of the protective atmosphere is removed from the cooling housing through the outlet 70 to a heat exchanger 71 provided with a fan or the like. The cooled protective atmosphere from the heat exchanger 71 is returned to the cooling cover 67 via a nozzle-shaped return line 72 which causes the cooled protective atmosphere to strike the strip 3. A second heat exchanger 73 having an inlet 74 and a nozzle 75 diametrically opposed to the return inlet nozzle 72 can be used to increase the cooling effect of the strip. The use of diametrically opposed nozzles ensures that the flat cross-sectional shape of the strip 3 is maintained. This allows the cooling cover 67 to be shortened compared to the cover 59 of FIG. 11, since cooling of the strip 3 is accelerated.

Yet another cooling means is shown in FIG. 14. In this embodiment, the coating method and apparatus for carrying out this method are again the same as in FIG. 7, and like parts bear the same reference numerals. The embodiment according to FIG. 14 is based on the fact that the one-sided coated strip is quenched in a water bath. without forming a visible oxide film on its uncoated side. For this purpose, the device is provided with a cooling cover 76 extending from the ceiling 26d of the protective cover 26. At its upper end, the cover is provided with a guide cylinder 77 and terminates downwardly · the neck 78. · The neck 78 is located below the water surface. bath 79 in the cooling tank .80. The belt exits the protective cover 26 through the outlet 36 and enters the cooling cover 76. In the cooling cover 76, the belt passes around the guide roller 77 and exits the neck 78 into the water bath 79. The strip 3 is guided through a water bath 79 and is directed upwardly out of the bath by a submerged roller 81. The neck 78 of the cooling housing 76 is provided with an outlet 82 for a non-oxidizing protective atmosphere from the cooling housing 76 and water vapor produced by dipping the strip 3 into the water bath 79. 82 is provided with a control valve 83 and a flow through the outlet 82, can be recorded by an outlet meter 84 of a well known type. Barriers 78a and 78b may be disposed within the throat 78 to reduce backward diffusion of water vapor into the cooling housing 76 to a minimum. Obviously, a non-oxygenating, protective atmosphere inside the cooling. 11 to 13, the protective atmosphere in the cooling housing must be maintained at a pressure sufficient to prevent the surrounding oxidizing atmosphere from entering the cooling housing through the housing. an outlet from this cooling cover.

Giant. 15 illustrates a variation of the embodiment of FIG. 5 in which both coating and finishing processes are carried out in a protective atmosphere. To this end, the apparatus comprises a molten metal tank 85 in which a molten coating metal bath 86 is disposed. The protective cover 87 is attached to, or integrates with, the pretreatment cover 88. A seal 89 serving for the same purpose as the seal 6 in Fig. 5 can again be placed between the protective cover 87 and the precooking cover 88. Again, for the purposes of the example of the seal 89, it is shown to be formed of pairs of sealing rollers 90, 91 and 92, 93 with a non-oxygenating atmosphere inlet 94 disposed therebetween serving the same purpose as the inlet 18 of FIG. 5. The iron-based base metal strip 3 again passes around the guide roll 95, bending the strip downwardly, which corresponds to the guide roll 12 of Figure 5. The strip 3 also extends below the work rolls 96, 97 and 98 which correspond to the work rolls 13, 14. and 22 of FIG. 5 and serve the same purpose. The protective cover 87 has a front wall 87a, a rear wall 87b, and side walls 87c. These front, rear and side walls extend partially into the molten coating metal bath 86 as shown. The protective cover ceiling 87d is provided with a non-oxidizing protective atmosphere inlet 99 and a belt outlet 100

3. A nozzle knife 101 is disposed within the protective cover 87, and may be positioned in any position within the cover as long as it does not interfere with the meniscus 102. The apparatus may further comprise a support roller or other nozzle knife (not shown) with respect to the nozzle knife 101. 1.

The operation of the embodiment of FIG. 15 proceeds as in FIG. 5 and the belt 3 has a coated side 3a and an uncoated side 3b. The embodiment of FIG. 15 differs from that of FIG. 5, in particular in that both the coating and the nozzle finishing are carried out in a protective housing 87 and its protective atmosphere, thereby eliminating the need for the sealing cap 16 of FIG. 5. The one-sided coated strip 3 can pass through the outlet 100 into the ambient air and is then subjected to suitable pickling, rinsing and drying as described above. Alternatively, the strip 3 may be maintained in a protective atmosphere until it reaches a temperature at which no visible oxide layer is formed on the uncoated side 3b by any means shown in FIGS.

14. In the embodiment of FIG. 15, the intermediate work roll 98 may be omitted. This results in an embodiment similar to that of FIG. 1, but with both coating and finishing within the mouthpiece.

Giant. 16 shows an embodiment similar to that of FIG. 7, and like parts bear like reference numerals. The coating of the embodiment of FIG. 16 is again performed in the same manner as described with reference to FIG. 7. FIG. 16 differs from FIG. 7 in that the front wall 26a. The protective cap 26 is provided with an aperture 103 sized such that a nozzle knife 104 can be easily inserted into it with its front end positioned within the protective cap 26 while its rear end extends out of the cover. The aperture 103 may be provided with a hinged closure 105 resting on the top of the nozzle knife 104 when the knife is inserted into the aperture 103 and closing the aperture when the nozzle knife 104 is removed for cleaning, thereby preventing the oxidant entry The nozzle knife 104 may be provided with an additional support means (not shown) of conventional design. The aperture 103 may be provided with a sealing profile (not shown) or other sealing means to prevent contamination of the protective atmosphere of the protective housing outside the orifice 103 and around the nozzle knife 104. If the aperture 103 is sized so closely to the peripheral dimensions of the nozzle knife 104, the need for such a seal can be eliminated by the positive pressure of the protective non-oxidizing atmosphere maintained within the protective cover 26. The arrangement of FIG. 16 may be used in any of the other embodiments described above, wherein the nozzle blade is located within the protective cover. This arrangement greatly facilitates the periodic cleaning of the jet knife.

In the above-described embodiments, in which the nozzle blade is located within the protective housing, there may be under certain circumstances the problem of generating coating metal dust arising from the coating metal vapors during nozzle finishing. There may also be tiny dots of coating metal on the uncoated side. The dots of the coating metal are again the result of the finishing process, when the tiny pieces of the coating metal are blown from the edges of the strip. Giant. 17 and 18 show a nozzle blade arrangement which avoids these problems. By way of example, FIG. 17 illustrates a coating apparatus as in FIG. 7, wherein the same parts bear the same reference numerals. It will be appreciated that the protective cover arrangement of FIGS. 17 and 18 may be used for the apparatus of FIG. 15, with or without intermediate work roll 98, in the exact same manner.

In Figures 17 and 18, the outlet 36 of the protective cover 26 is surrounded. The nozzle knife 109 is mounted outside the protective cover 16 with its front end extending through the partition. 107j: With this arrangement and using a non-oxidizing gas in the jet knife 109, the zinc coating on the side 3a of the belt 3 will be completed before being exposed to the ambient air. Any coating metal dust - or tiny particles will be blown away from the uncoated side 3b of the strip 3 without negative consequences. Where the ambient conditions warrant it, the baffles 106 to 108 may be provided with another baffle (not shown) positioned over their upper edges. The top baffle will then be provided with a slot through which the belt 3 can pass. The bulkhead will eliminate any downward tensile flow that may occur during the - finishing process. The side of the bulkhead system opposite the uncoated side 3b will still be open and will allow the dust or coating metal particles to be blown away from the uncoated side 3b. belt 3.. and

In all of the coating methods and compositions for their performance as described above, the bath temperature will depend on the molten metal used. The bath must be maintained at a sufficient temperature to ensure that the coating metal remains in the molten state until complete with a jet knife. - In contrast to conventional methods of forming coatings by immersion in molten metal; in which the strip to be coated (needle · both sides) is immersed in the bath, in the one-sided coating of the invention the sufficient amount of heat supplied to the molten coating metal bath cannot depend on the strip itself. The procedures for controlling the temperature of the bath should be substantially the same, as for the coating on both sides, and the temperature should be kept as constant as possible in order to minimize scale formation. In all the embodiments described, especially since it depends on the formation of the meniscus, an adequate bath level must be kept constant. For this purpose it is possible to use a precise level adjustment by means of a pneumatic sliding chamber or a mechanical sliding plug, as is known to those skilled in the art. It is preferred that automatic means be used to control the level of the bath (as is well known in the art).

The molten coating metal bath can be heated in any conventional manner, including the use of electrical resistance elements, induction heating, immersion tube heating, and the like. Those skilled in the art will appreciate that the molten coating metal bath volume may be much smaller than required for typical forming processes. by dipping, ie on both sides. Since the contact between the web and the bath is greatly reduced in accordance with the invention, the rate of dissolution of the web when compared to the desired coating metal addition rate will be such that the bath is not saturated with iron and formation is reduced to a minimum or completely eliminated. This will in turn result in a perfect coating. For this purpose, it is preferred that the molten coating metal tank be lined with a suitable ceramic material.

In all the embodiments described above, the temperature of the iron-based metal strip with which the strip exits the conventional precoating cover and enters the protective cover will again depend on the molten coating metal used and is readily determinable by those skilled in the art. The temperature of the strip should be - sufficiently high to prevent the molten coating metal from pouring onto its surfaces. Likewise, it should not be high enough to cause excessive alloying between the coating metal and the parent metal.

In all embodiments, a non-oxygenating atmosphere must be maintained within the protective housing. Any suitable non-oxidizing atmosphere, such as nitrogen or inert gas, may serve for this purpose. - The oxidizing atmosphere inside the enclosure must be maintained at a pressure sufficient to prevent the oxidizing atmosphere from entering the enclosure through its outlet. The same applies of course to the cooling cover as described - in connection with Figures 11 to 14. The dew point inside the shroud should be maintained at a level comparable to that maintained at a level comparable to that permissible for ordinary (two-sided) coating processes. This amount depends on the temperature of the belt and the percentage of hydrogen in the atmosphere in preparing the belt, as is well known in the art.

In all of the embodiments described above, it is preferred that the roll or rollers located near the molten coating metal bath are provided with a surface that does not wet easily with the molten coating metal. This will facilitate the removal of any amount of coating metal on the rollers that has been received there by accidentally trapping the metal with the roll or spilling it off. If desired, the roller or rollers in the vicinity of the molten metal may be provided with a rim or otherwise shaped such that unused portions beyond the edge of the coated strip are slightly tapered away from the surface of the bath. This will further facilitate belt guidance.

The invention has been described above in a number of embodiments. The choice of a particular embodiment or combination thereof will depend on a number of factors, such as the type of equipment already available, the type of metal used, the desired properties of the end product. with a one-sided coating or the like. For example, in the embodiments described above, in which the jet knife finishing is performed with a non-oxidizing gas within the protective housing (for example, the embodiment of Figure 7), a number of advantages are achieved. These advantages include the absence of corrugation in the coating even at very low speeds, without the presence of problems. the surface of the bath, the scale problems are reduced, the oxide film does not form on the final coating, and the formation of surface slag is eliminated. In contrast, in this procedure, the operator must monitor for evaporation and dust formation of the coating metal, which can lead to the formation of dots of the coating metal on the uncoated side of the belt.

In the embodiment as shown in Figs. 17 and 18, where it is used to complete the stream of non-oxidizing gas outside the protective housing, but before the web comes into contact with the air atmosphere, all of the above advantages for jet knife finishing within the protective knife are achieved. cover. This process also reduces the problem of coating metal dust collection. inside the orifice extension and avoids the formation of spots of coating metal on the uncoated side of the strip. In contrast, the non-oxidizing gas used in nozzle finishing does not provide an overpressure in the protective cap.

In the embodiment of Fig. 1, using jet knife finishing outside the protective cover, the finishing process is thus exposed for ease of execution, and there will be no coating metal vapor and dust problems and dots on the uncoated side . Consumption of a non-oxygenating atmosphere will also be reduced. In contrast, most of the advantages achieved in finishing in a non-oxidizing atmosphere within the protective cover are not achieved, although this disadvantage can be partially reduced by using a non-oxidizing atmosphere, such as nitrogen, after the belt has been exposed to ambient air.

Embodiments employing a single cylinder, such as those of FIG. 7, are characterized by simplicity of the apparatus, minimize problems with poor belt shape, and minimize contact length between the belt and meniscus, which has the best prospects to avoid insertion of iron into the bath. When using a single work cylinder, care should be taken to prevent zinc from collecting on the surface of the cylinder and that the reduced meniscus area will require tighter nozzle finishing that requires inspection to prevent meniscus being disrupted.

Use. two working sets. 1 or within a protective cover, such as FIG. 15. A longer contact between the meniscus and the belt will make the meniscus less easily disruptible. However, this longer contact with the meniscus also provides greater opportunity for dissolving iron from the strip. The two - cylinder assembly is more complicated in terms of equipment and needs more care with respect to. belt shape.

The three-cylinder assembly, as shown in Figs. 5 and 15, will have the advantages of a double cylindrical assembly, including the ability to increase the distance of large work rolls from the bath surface. This shape will also have the disadvantages of a two-cylinder assembly along with being even more complex in terms of equipment and need. ensure that the intermediate slave roller does not label or otherwise damage the belt, especially when coating on very wide strips.

Example I

The base sheet of iron-based metal sheet is coated on one side with zinc at. using the apparatus and procedure described in connection with FIG. 1. The web is allowed to enter at a speed of 12 m / min. into the protective cover at a strip temperature of about 465 to 471 ° C. The bath temperature is maintained at 460 ° C.

A non-oxidizing protective nitrogen atmosphere is introduced into the shield at 18.9 m³/throw. A dew point temperature of -23 ° C was detected on the guide roller along with 120% oxygen.

The orifice of the nozzle knife 19 has a slot of 0.75 mm width and is supplied with an overpressure air of 0.63 N / cm². The jet knife is held at a height of approximately 12.5 cm above. and is directed upwards at an angle of up to about 3 degrees. The second working roller 14 has a diameter of 30 cm. The mouth of the jet knife is kept at a distance of about. 4.7 mm from the coated side of the belt.

As a result of the process described, an iron-based metal strip with a one-sided zinc coating having a coating weight of 34.55 g / m 2 is obtained. When subjected to the usual quality tests, including the adhesion tests, it turns out that the zinc coating is of manufacturing quality. The uncoated side of the belt has a weak oxide film and does not show zinc coating on the edges.

Example II

Base metal band. on the one hand, they are provided with an aluminum coating using the apparatus and method described in connection with FIG. 1.

The web is allowed to enter the guard at 15 m / min at a web temperature of approximately 704 ° C. The molten coating metal bath is maintained at 688 ° C.

A protective, non-oxygenating nitrogen atmosphere is introduced into the mouthpiece at a speed of 8.1 m³/throw. For the guide roller 12, a dew point of -23.5 ° C is recorded along with less than 100 ° / oo oxygen.

The jet knife 19 has a slot width of 0.75 millimeters and is supplied with air at an overpressure of 0.52 N / cm². The mouth of the nozzle knife 19 is maintained at a height of about 10 cm above the surface of the bath and is directed upward from the horizontal at an angle of about 10 degrees. The second work roll 14 has a diameter of 3 (3 cm). The mouth is maintained at a distance of about 3 millimeters to about 4.7 mm from the coated side of the belt.

As a result of the described procedure, it is obtained