Method and means for continuously contact-coating one side only of a ferrous base metal strip with a molten coating metal

were:

AT 357 841

No. 357841

The invention relates to a method and a device for one-sided dip coating of a previously cleaned metal strip using a metal bath of the coating metal, in particular a method and a device, according to which the metal strip does not have to be submerged in the bath of molten metal.

The method and apparatus according to the invention can be used to produce an iron-based metal strip which is only coated on one side with a suitable hot dip coating metal such as zinc, a zinc alloy, aluminum, an aluminum alloy, Terneblech (Pb-Sn alloy coating), Lead, a lead alloy or the like. is coated. The invention will be described with reference to an embodiment according to which the method according to the invention and the apparatus according to the invention for producing an iron-based metal strip which is coated on one side only with zinc or aluminum is used.

In recent years, there has been an increasing demand for iron-based metal strips coated on one side with a protective metal, eg, a steel strip galvanized on one side. Such a product is particularly well suited for use in the automotive, household appliance and building board industries. The galvanized side of such a product has excellent corrosion resistance, while the uncoated side is excellent for application of paint and spot welding or the like. suitable is. In those cases where corrosion protection is required on only one side of the product, this one-side coated product can achieve a considerable saving in coating metal,

Various methods for the production of single-sided coated iron-based metal strips are known from the prior art. According to one of these methods, the ferrous metal strip is coated on one side with an inhibiting stop-off agent, ie a barrier layer which is not wettable by the coating metal. The tape is coated by a conventional hot dip method, the barrier layer is subsequently abraded or otherwise removed.

US Pat. No. 3,383,250 describes a process according to which the metal strip is appropriately cleaned on both sides, then brought to the coating temperature and oxidized on only one side. Thereafter, the strip is passed through a bath of molten coating metal which adheres only to the non-oxidized side.

According to another method, the strip is sufficiently coated on both sides in a hot dip process on which the coating is removed on one side by means of a (air) jet knife or nozzles. The remaining coating metal on the jet brush treated side is removed by an electrolytic plating process.

According to another known method, a product coated on one side is produced by an electrolytic coating process. For this purpose, the strip to be coated is passed around a roller which is partially immersed in an electrolyte. A metallic coating is applied to the exposed side of the tape while the other side of the tape remains uncoated since it is protected by the roll about which it is guided.

Although useful products are produced by these known processes, they have certain disadvantages. In general, the processes known from the prior art are expensive, require more process steps than conventional hot dip coatings and require expensive special equipment.

The currently used from cover process yield an uncoated surface of barely sufficient quality for the application of high gloss paint.

From DE-PS No. 2406939 the use of a hot metal meniscus for the full coating of pipes and rods is known. However, the method described in this publication is not applicable to one-sided coating of an iron-based metal strip.

Method and apparatus according to the invention enable the rapid and continuous

Contact coating only one side of an iron-based metal strip with a molten coating metal. The coating thickness can be adjusted as in a conventional two-sided hot dip coating process. There are no roller assemblies within the molten metal

- 3 No.357841, which eliminates material build-up and maintenance issues. The method and apparatus according to the invention are less expensive and the method is easier to carry out than known, commercial, one-sided coating methods. Existing, continuous

Coating coating lines can be modified in a simple and cost-saving manner so that they can produce a single-side coated product according to the invention. If interchangeability of the equipment is provided, one and the same run can be used to produce both a single side coated and a double side coated product. The quality of the products so produced is superior to those produced by other hot-dip processes, both in terms of the coated and uncoated sides.

According to the invention, a method is provided for producing a metal strip, in particular iron-based, which is coated on one side with a coating metal, while the other side of the strip remains free of the coating metal and the metal strip has been pretreated to bring it to the correct coating temperature and to clean its surfaces and rid it of oxide. The method is characterized in that the strip to be coated is guided over the surface of the metal bath at such a distance that due to the wetting properties (surface tension) the molten metal adheres to and is carried by the strip on only one side,

The device according to the invention comprises a coating vessel in which a

Coating metal bath is and is characterized by means which guide the metal strip over the surface of the metal bath at such a distance that due to the wetting properties (surface tension), the molten metal adheres only on one side of the strip, further by finalizing means which remove excess coating metal from the coated one Remove side of the belt and facilities that hold at least one side of the metal strip under nichtoxydieren25 conditions until at least the said one side of the belt is coated with the coating metal. The device for transferring the ferrous metal strip is designed so that it allows a Steüung with respect to the surface of the bath,

Page of the meta tape stands and only this one side of the tape is coated. Further, the apparatus comprises a fining device for finishing the coated side of the tape and means for holding the tape in a protective, non-oxidizing atmosphere at least until the side of the tape facing the surface of the bath is in contact with the meniscus.

According to one embodiment of the invention, the tape is passed over the surface of a bath of molten coating material. The belt is passed over a first roller and the belt surface to be coated is brought close enough to the surface of the molten coating metal bath so that the surface covering and wetting properties of the coating metal allow for the maintenance of a meniscus continuous with the belt surface

Contact stands and these are coated. The initial coating of the strip surface is done inside a hood or door in which there is a non-oxidizing inert gas atmosphere. While the surface to be coated is still in contact with the meniscus of the molten coating, the tape is removed from the door. After leaving the hood or door, the belt is led upwards around a second roller and away from the molten coating meta-bath. The coated surface of the tape is finished by means of jet brushing. A device which prevents the penetration of an oxidizing atmosphere into the door is provided.

Another embodiment of the invention differs from the first only in that a small third roller is provided between the first and second rollers and disposed outside the hood or door. This third roller deflects the path of movement of the belt between the first and second rollers slightly downwards and thereby allows the two rollers slightly further from the

Surface of the molten Metaübades can be arranged so that the spraying or the

Absorption of the molten Metaüs is prevented by the roller. The little third roller is

Normally lesser width than the width of the strip to be coated in order to prevent it from absorbing coating metal.

Furthermore, an embodiment of the invention is provided in which the surface of the tape to be coated is brought close enough to the surface of the molten metal bath to allow the formation of a coating meniscus under the action of a single roller which directs the tape surface to and through the meniscus and thereafter leading up and away from the surface of the molten coating metal bath. Also in this case, the coated surface is finished by means of jet brushing. According to this embodiment, the individual rollers and the jet brushes are arranged inside a spout filled with a protective gas atmosphere, and the nozzle processing is performed with a non-oxidizing or inert gas.

If the coated tape, while still hot enough, is exposed to an oxidizing atmosphere to produce a visible oxide on its uncoated side, it must subsequently be subjected to acid cleaning and then rinsed and dried to add the visible oxide remove.

As will be described below, this purification by means of an acid can be carried out in various ways.

If the entire coating and finalization process is carried out within a protective gas atmosphere, acid cleaning can be eliminated by keeping the strip under a protective gas atmosphere until it has cooled to a temperature at which no visible oxide forms on its uncoated side, when exposed to an oxidizing atmosphere. As will be described below, a means for accelerating the cooling of the belt within the visual gaseous atmosphere may also be provided.

The invention will be explained in more detail below with reference to the drawings. 1 shows a semi-schematic cross-sectional partial view of the first embodiment of the coating apparatus according to the invention for carrying out the method according to the invention; FIG. 2 shows a cross-sectional view along the section line II-II of FIG. 1; FIG. 3 shows a semi-schematic cross-sectional partial view illustrating FIG Fig. 4 is a semi-schematic cross-sectional partial view similar to that shown in Fig. 3, showing the type of meniscus that can be formed when aluminum is used as the molten coating metal, Fig. 5 a semi-schematic cross-sectional view similar to Fig.l another embodiment of the invention, Fig.5a is a cross-sectional view,

- 5 No.357841

All embodiments of the invention require the application of conventional metal strip or tape preparation techniques prior to coating. For example, the strip can be cleaned in a non-oxidizing preheater and tempered or annealed and cooled in a high-temperature protective gas atmosphere. The pretreatment of the tape is not a limitation of the invention, provided that at the time of coating, the tape has the correct temperature and its surfaces clean and free from. Are oxides. Suitable strip preparation techniques are described in U.S. Patent Nos. 2,110,893, 3,320,085, 3,837,790, and 3,936,543

Figures 1 to 3 illustrate a first embodiment of the invention. A coating container 1- contains a bath of molten coating metal -2-. The ferrous metal strip, one side of which is to be coated, bears the reference numeral -3-. A grommet -4- represents an extension of the partial hood of the conventional belt preparation device. The grommet 4- may be formed integrally with the hood 5, it may also be gas-tightly connected thereto. Preferably, a gas-impermeable seal, generally designated --6-, between spout --4- and hood -5- is provided. The seal -6- may have any shape and is shown, for example, as consisting of two pairs of sealing rolls -7, 8 and 9, 10--.

The spout -4- comprises a front wall -4a, a rear wall -4b-, side walls -4c and 4d- and a top -4e-. From Fig.l and 2 it can be seen that the front and rear walls and the Be tenwände in the molten metal existing bath -2 extend into it.

The front wall -4a is provided with a U-shaped notch or opening -11-, part of which extends above the bath -2- and defines an outlet for the belt -3- from the hood grommet -4-. The outlet -11- should be wide enough to accommodate the widest iron metal band to be coated.

The belt -3- is guided between the sealing rollers -9, 10 and 7, 8- to a roller -12- within the grommet -4-. From the roller -12- the belt is guided to the roller -13- which brings the surface of the belt to be coated close to the surface -2a of the molten metal coating bath. From the roller -13-, the belt is passed through the spout outlet -11- to the roller -14- and thence up and away from the metal plating bath. The rollers -12, 13 and 14- are held by suitable support means, not shown.

The front wall 4a of the grommet -4- may be provided with a support -15- which is adapted to receive an elongated, slab-like block -16- of graphite or other suitable material which serves as a seal to the Closing a majority of Tüllenauslasses -11- is used. The graphite block -16- is freely movable up and down within the support -15- and is supported on the upper or uncoated surface of the ferrous metal strip -3-.

It is important that there is a non-oxidizing atmosphere in the nozzle -4-, so that the surfaces of the tape -3- remain clean and free of oxides before coating. For this purpose, the grommet -4- is provided with an inlet -17-, through which a suitable non-oxidizing gas is introduced into the grommet -4-. Any non-oxidizing gas such as nitrogen, inert gases or the like is suitable. The non-oxidizing atmosphere within the spout -4- must be kept at a slight overpressure so that the oxidizing atmosphere outside the spout does not pass through the spout outlet -11- into the spout, and in particular to those portions -11a and 11b- which are not from the seal -16- are closed, can penetrate (see Fig. 2). Therefore, it is also preferable to have an inlet 18 for the non-oxidizing atmosphere between the seal roller pairs -7, 8 and 9, 10- provided. Another preferred measure is to maintain the non-oxidizing atmosphere in sub-chamber -18a at a pressure slightly higher than the pressures in spout -4- and hood -5-. This ensures that the non-oxidizing atmosphere within the hood -5- can not be contaminated even when the device is turned off while working within the nozzle -4-. Since the pressure of the non-oxidizing atmosphere within sub-chamber 18a is higher than the atmospheric pressure inside hood -5-, this also avoids contamination of the atmosphere within hood -5- by locations at the inlet end of the conventional belt preparing device. Finally, the coated side of the tape -3- is finished by means of jet brush -19-.

The device is operated in the following manner: When the ferrous metal belt -3- is guided between and over the rollers -7, 8, 9, 10, 12, 13, 14- and moves in the direction of the arrow A (Fig.l),

- 6 No. 357841, a slight swell can be produced on the surface of the molten metal coating tape -2-. Thereby, the adjacent side of the ferrous metal strip -3- is brought into contact with the molten coating metal, and the surface tension and wetting property of the coating metal causes the formation of a meniscus which continuously contacts and coats the adjacent strip surface. The meniscus is provided with the reference number -20- in FIGS. Through the meniscus - 20-- the continuous contact coating can only be performed on one side of the belt -3- without having to immerse the belt in the bath -2-. The belt -3- therefore has, as it moves from the roller -14- up,

It will be understood by those skilled in the art that for purposes of clarity of illustration, Figs. 1-3 illustrate the thickness of the belt -3-, the distance between the rollers -13 and 14- from the surface -2a of the bath -2-, and the height of the meniscus were exaggerated. The distance of the surface of the tape to be coated -3- from the surface -2a of the bath -2-, which allows the formation and maintenance of a coating meniscus, depends on the coating metal used, its surface tension and its wetting properties. With most of the coating metals, excellent results were achieved at a distance of about 8 mm or less.

Preferably, the roller -13- is arranged slightly higher above the surface -2a of the molten metal coating bath -2- than the roller -14-. This height difference is also exaggerated in Fig.l for clarity. Consider an actual height difference of about 3 to about 6 mm. The purpose of this difference in height is to ensure that the roller 13, which is inside the grommet 4 and therefore not visible to the operator, is not splattered or pickled with metal.

The jet brush 19- may be disposed on or slightly below the centerline of the roller -14-. How deep the jet brush is located below the center line of the roller 14 depends mainly on the diameter of the roller and the speed of the belt. It is important that the blasting brush does not blow any contaminating atmosphere through the spout outlet or disturbing the meniscus. The jet brush 19- can be arranged above the roller -14-, as shown by dashed lines at -19a. In order to ensure a satisfactory finalization by means of the jet brush, it must be ensured that the cross section of the belt -3- is absolutely flat. For this purpose, a back roll is preferably provided opposite the jet brush -19a (shown dashed at -21-).

Fig.5 shows another embodiment of the invention. This embodiment is similar to that shown in Fig.l. Similar parts have been given the same reference numerals. The embodiment of Figure 5 differs only in that a roller -22- outside the door -4- and between the rollers -13 and 14- is provided. The roller -22- is provided with respective support means (not shown) and arranged to slightly deflect the trajectory of the belt -3- between rollers -13 and 14- downwards. This allows the rollers -13 and 14- to stand out slightly from the surface 2a of the molten metaU coating bath -2-, thus ensuring that they are not splashed or absorbed with MetaU. The roller -22- should be slightly shorter than the width of the belt -3-. As in Fig.l to 3, the thickness of the belt -3-, the height of the meniscus -20- and the distance between the rollers -13 and 14- from the surface of the MetaUbeschichtungsbad -2a- was also in Figure 5 for reasons of German exaggerated. Also, the amount of deflection provided to the belt -3- by the roller is exaggerated. The actual deflection is about 6 to about 12 mm, thereby the rollers -13 and 14- can be located just this distance further from the surface -2a of the bath, as it is in the embodiment of Fig.l FaU. In all other respects, the device of Figure 5 and its operation is substantially identical to that shown in Figure 1. The meniscus is the same as that shown in FIG. It is the same when using any appropriate suitable metering device. It has been found, however, that when aluminum is used as the coating material - although the meniscus normally has the shape shown in Fig. 3 - the roller -22- actually the belt -3- slightly below the surface -2a of the molten MetaU coating bath Since aluminum forms a meniscus, as shown at -23- in FIG. When using aluminum as a molten BeschichtungsmetaU, the band 3 - the roller -22- can actually depress the belt -3- slightly below the surface -2a of the molten metaU coating bath - 2--, since aluminum forms a meniscus, as at -23.degree Fig.4 is shown. When using aluminum as a molten BeschichtungsmetaU, the band 3 - the roller -22- can actually depress the belt -3- slightly below the surface -2a of the molten metaU coating bath - 2--, since aluminum forms a meniscus, as at -23.degree Fig.4 is shown. When using aluminum as a molten BeschichtungsmetaU, the band

In fact, it is true that they are conducted slightly below the surface of the molten metal plating bath, still achieving only one-sided coating.

The embodiment of Figure 5 can be modified by supporting the roller -22- on the sealing block -16. This is illustrated in Fig. 5a where the roller -22a (corresponding to the roller -22- in Fig. 5) on the sealing block -16a (corresponding to the sealing block -16- in Fig. 5) by means of (Fig. not shown) of conventional devices is rotatably supported. The roller -22a is disposed along the lower edge of the sealing block -16a and contacts the uncoated side -3b- of the belt -3- to serve the same purpose as described with respect to the roller -22- in FIG. 5 is described. Within the scope of the invention, the roller -22-10 in Fig. 5 can also be placed inside the grommet -4-; this change requires only a corresponding position of the rollers -13 and 14-.

Fig. 6 is similar to Fig. 2 (like parts are numbered alike) and may be considered as a cross-sectional view of the front wall -4a of the grommet -4- in Fig. 1 or 5. Fig. 6 differs from Fig. 2 in that the carrier -15- and the graphite gasket -16- are not present and the notch forming the spout outlet - 11c has been lowered to a position just above the belt -3- to reduce the outlet opening to a minimum. In the embodiments of Figs. 1 and 5, therefore, the graphite gasket -16- and the support -15- may be omitted since the penetration of an oxidizing atmosphere through the outlet -11c by maintaining a slight overpressure of the oxygen-free atmosphere within the grommet - 4- is avoided.

Fig.7 shows another embodiment of the invention. A coating container -24- contains a molten metal coating bath -25-. A grommet -26- represents an extension of the belt pretreatment hood -27-, which is shown only partially. Also in this case, the spout can either be integral with the hood -27- or connected to this gas-tight 25. A seal generally designated -28- is provided between spout -26- and hood -27-. The seal may be of any shape, for example, it is made up of two seal roller pairs -29, 30 and 31, 32-. An inlet for an oxidation-free atmosphere may be provided between the rollers at -33-. The hood -26- has a front wall -26a, - a rear wall -26b- and side walls, one of which is shown at -26c. The front and rear walls and the side walls of the hood extend down into the molten metal coating bath.

The ferrous metal strip is here also designated -3- and is passed between the rollers -31 and 32 and 29 and 30- of the seal. Then it is passed over the down-roller -34 and roller -35- which brings the surface of the belt to be coated close to the surface -25a-35 of the molten metal coating bath. The roller -35- then leads the coated tape upwards away from the coating bath -25-, the tape is led out of the nozzle -26- through an outlet slot -36-.

The nozzle -26- is provided with an inlet -37- for a non-oxidizing atmosphere; this is maintained within the spout at a slight overpressure, so that the oxygen-containing atmosphere from outside the spout can not penetrate through the outlet slot -36-.

The non-oxidizing atmosphere seal -28- and its inlet -33- serve the same purpose as described with respect to the gasket -6- and the inlet -18- in Fig.l. Also in this case, seal -28- and inlet -33- are particularly important during shutdown of the spout -26-. In the embodiment of Figure 7, a jet brush -38- is provided within the nozzle -26-45. The jet brush -38- is operated with a non-oxidizing gas which may be the same as the non-oxidizing atmosphere within the nozzle.

The operation of the embodiment of Fig. 7 differs from the embodiments of Figs. 1 and 5 mainly in that all coating and finalization steps are taken within the nozzle and its non-oxidizing inert gas atmosphere. Since the iron metal band -3- is guided around the rollers in the manner shown in FIG. 7 and moves in the direction of the arrow B, a weak wave formation of the surface -25a of the coating bath -25- consisting of molten metal also results in this Case for forming a meniscus -39-, by means of

- 8 No. 357841 which shows the surface of the strip facing the surface of the molten metal bath

- 3 "is continuously contact-coated while being passed around the roller -35-.

The fasteners (not shown) within the spout -26- for the rollers -34 and 35- and for the jet brush -38- may be conventional. When the iron metal band is led up to the output slot -36-, it is coated on one side -3a and remains uncoated on the other side -3b-. The coated side is finished by means of a jet brush -38-, which can be arranged at any point if it does not disturb the meniscus -39- and the surface -25a- of the molten metal coating bath -25-. If, for practical reasons, the jet brush -38- above the roller -35- must be arranged at such a distance that they could cause the distortion of the cross-sectional shape of the belt -3-, a return roller can be provided

In all embodiments described so far, the belt -3- is exposed to the atmosphere while still having a sufficiently high temperature to cause the formation of a visible oxide on its uncoated side -3b-. For short exposure times, the visible oxide coating consists of thin oxide films or films, the layer adjacent to the base metal being predominantly FeO, superimposed by a layer of Fe₃O₄, in turn, of a location Fe₂O₃ followed. When the temperature of the belt is below 568 ° C at the time of exposure to an oxidizing atmosphere, no FeO layer is formed. This is usually the case when zinc is used as the molten coating metal. When aluminum is used as the molten coating metal, the temperature of the belt is usually above 568 ° C and a FeO layer is formed.

As already mentioned, the visible oxide coating can be removed after an acid cleaning process. The term "acid purification process" is used deliberately here, unlike "acid immersion". The difference between acid cleaning and acid immersion is a gradual difference, with "acid soaking" usually being a very sweeping treatment for removing mill scale from a semi-finished product. The first phase of an acid purification process is purely chemical and involves the dissolution of the oxide layers. The oxide layers dissolve at different speeds, the dissolution of the Fe₃O4 layer is crucial here because this layer is the slowest soluble. Thin, porous oxide layers can be removed by acid penetration and direct attack of the base metal. The rate of oxide removal can be increased in several ways. First, the chemical reaction rate can be accelerated by increasing the temperature of the acid bath or increasing the acid concentration. In addition, the rate of oxide removal by penetration, by supplying electric current, can be increased. As a result, the solution of the base metal and the local surface movement is increased by hydrogen formation.

The acid cleaning of a one-side coated base metal tape poses a unique problem because it seeks to simultaneously remove the oxide from the uncoated side of the ferrous metal strip and to minimize etching of the coated side thereof. It has been found that an electrolytic acid purification process is preferable.

Acid cleaning involves a number of cooperative variables that yield an almost unlimited number of specific combinations of these variables, each of which is suitable for satisfactorily removing the visible oxide layer from the uncoated side of the belt. Nonetheless, basic guidelines for the preferred acid cleaning of a one-side coated metal strip can be established.

The basic variables of acid cleaning include the acid used, the concentration and temperature of this acid, the distance between the ribbon and the electrode, the period of immersion of the ribbon, and the current density through the electrode. In order to minimize the etching of the coated side of the belt, a dilute acid solution is preferred, generally 1% by volume or less of a commercial acid. The type of acid used depends on its effectiveness, cost, accessibility, environmental regulations and ventilation requirements. For this purpose, sulfuric, phosphoric, hydrochloric and nitric acid can be used with good success. Sulfuric and phosphoric acid are slightly more effective, also is the

- 9 No. 357841

Sulfuric acid is preferred not only because of their effectiveness, but also because of their lower vapor evolution tendency.

The temperature of the acid should be kept low (ie, below 37 ° C) if the etching and staining on the coated side of the belt should be reduced to a minimum. To increase the effectiveness of the distance between the electrode and the band should be kept as low as possible. However, the distance of the electrode from the belt is determined by the requirements of the continuous movement of the belt to avoid contact between belt and electrode. Also, the period of immersion of the band should be kept to a minimum necessary to remove the visible oxide. However, for practical reasons, the immersion of the tape is determined by the dimensions of the container and the speed of movement of the tape. Each system requires a certain minimum current density.² was found to be sufficient. Increasing the current density above the practical minimum would be pointless and wasteful.

8 shows a modified galvanic cell is shown, with which the acid cleaning can be performed. FIG. 8 shows a vessel containing a dilute acid bath. The tape -3- with the coated side -3a and the uncoated side -3b- is passed through the bath -41- around the roller -42- which is stored inside the bath on conventional means (not shown). A sacrificial metal block -43- (such as zinc) is disposed near the uncoated side -3b- of the ferrous metal strip -3- and is held in place by corresponding retainers (not shown). The sacrificial metal block -43- is electrically connected to the ferrous metal strip at -44- via the roller -42-. Although the speed at which the base metal is attacked is not increased, The rapid evolution of hydrogen on the uncoated surface of the ribbon helps to remove the oxide from it. Hydrogen also forms at the sacrificial metal block -43- and rises to contribute to the movement of the oxide on the uncoated surface -3b- of the band -3-. Other sacrificial metals such as magnesium and aluminum may also be used.

In series of experiments, both dilute acid bath and sulfuric acid 0.5% and 0.5% phosphoric acid were used and maintained at a temperature of 32 ° C. The tape -3- was coated on the side -3a with zinc and had on the side -3b- on an oxide coating, which was formed by the fact that the tape on exiting the protective gas atmosphere of the coating process at a strip temperature of 482 ° C the Air was exposed. A sacrificial metal block -43- of zinc was inserted and kept at a distance of about 3 mm from the strip surface -3b-. The oxide coating is removed from the surface -3b- within about 3 seconds, without any visible etching of the zinc coating on the tape side -3a observed.

Fig. 9 illustrates another method and apparatus for the acid cleaning of the belt -3- with a hot metal coated side -3a and an oxide coated side -3b-. According to this embodiment, a vessel 45 is provided contains diluted acid bath -46-. The belt -3- is passed around a submerged roller -47- and an electrode -48- is placed adjacent to the uncoated side -3b-- ​​of the belt -3-. The electrode and ribbon (via roll -47-) are connected to a current source -49- as shown at -50 and 51-, respectively.

It has also been found that instead of connecting line -51- from power source -49- to roller -47- (or to a sliding contact or contact rolls as known in the art), the molten metal plating bath is used therefor be added to the tape electrical power so that possible damage to the tape surface is avoided by scratching or arcing. For this purpose, the line -51- from the power source -49- can be connected to the coating vessel -1-, if this consists of metal. This has been shown for example in Fig.l. An alternative measure is to connect line -51- to an electrode -51a immersed in the molten metal plating bath. This is illustrated for example in FIG.

The connections of the line -51- shown in Figs. 1 and 5 can be used in any of the above-described embodiments of the coating method and those used therefor

Devices are used when the acid cleaning as described for Fig.9, performed.

Nr.357841

The embodiment of Figure 9, after which a current is supplied from an external source -49-, has proved to be more effective than the embodiment of Fig..8. The dissolution of the iron under the oxide layer is accelerated by hydrogen formation to remove the oxide from the iron metal band -3-. The power source -49- may be an AC or DC power source. Alternating current is preferred because of the pulsation of the current, which speeds up the rate of the acid purification process. The electrode -48- can be made of any suitable material that is conductive and unaffected by the dilute acid bath -46-. Stainless steel is an excellent electrode material. Other metals such as platinum or lead could also be used for the electrode.

In one of the experiments, a dilute acid bath of 0.5% sulfuric acid at a temperature of about 32 ° C was used. The current source -49- formed a DC welding generator with a current of about 110 A, wherein the band -3- represents the cathode and the electrode -48- a stainless steel anode. The tape -3 had a layer of oxide on page -3b, which had been formed by exposing the strip emerging from the non-oxidizing inert gas atmosphere of the 482 ° C coating process to air. The oxide layer was removed in less than 6 seconds with vigorous evolution of hydrogen at the electrode -48- and the ribbon surface -3b-. No staining of the zinc coating on the tape side -3a was observed at immersion times less than 4 seconds. At a dip time of 6 seconds, there was a slight staining and etching of the zinc coating. The stainless steel electrode was located at a distance of about 12 mm from the strip side -3b-.

In another experiment, the dilute acid bath -46- was also 0.5% sulfuric acid at a temperature of about 26 ° C and the electrode was also stainless steel. The tape -3- had a zinc coating on the side -3a and an oxide coating on the side -3b-, the latter was caused by the tape was exposed from the inert gas atmosphere of the coating process at a strip temperature of about 482 ° C the air atmosphere , From the DC power source -49- about 9 A were supplied. The electrode -48- was held about 2.54 cm from the tape surface -3b-. Under these conditions, the oxide layer was removed in about 2 seconds. There was no etching of the zinc coating on the belt surface -3a observed.

A variant of the embodiment according to FIG. 9 is shown in FIG. 10, in which the band is also designated -3-, its metal-coated side -3a and its oxide-coated side -3b-. According to this embodiment, the belt -3- is passed over a back-up roller -52-. The band -46- in Figure 9 was replaced by a sponge soaked in dilute acid. The sponge -53- is supported by a holding device -54- which may be made of stainless steel or other material that is not attacked or embrittled by the dilute acid used. The sponge -53- and its holder -54- are connected to a StromqueRe -55-. The belt -3- is also connected via the roller -52- over -57- with the StromqueRe. The current Re -55- may be either a DC or an AC Re. In the sponge holder -54- an inlet device -58- is provided, through which acid can be nachgefüUt. The embodiment of Fig. 10 has the advantage that no vessel is required and that the sponge 53 has an oxide scouring action. Care must be taken to replace the sponge in case of heavy wear or in the presence of a large accumulation of particles embedded therein, otherwise there is a risk of scratching the strip.

The acid cleaning procedures described above must be followed by appropriate rinsing and drying steps (well known in the art) to limit acid attack on both sides of the belt. Any other suitable dilute acid may be used as desired by those skilled in the art. The dilute acids used can with conventional additives such as surfactants, inhibitors, antifoams or the like. be offset.

Acid cleaning, rinsing and drying can be switched off if the coated on one side EisenmetaUband is kept in an oxygen-free inert gas atmosphere until its

Temperature has dropped so far that no visible oxide can arise on its uncoated side. This method and an apparatus for carrying it out are shown in FIG. 11. The

- 11 No. 357841

Coating method and device used in Fig. 11 are the same as those shown in Fig. 7, and like reference numerals are used for like parts. The embodiment of Figure 11 differs from that of Figure 7 only in that on the spout -26- in the region of Tüllenauslasses -36- a cooling hood -59- has been placed. The cooling hood -59- is provided with an outlet -60-. The cooling hood is of such a length that the belt -3-, when passed through the hood outlet -60-, has a temperature of only about 149 ° C, ie a temperature at which no visible oxide is present on the uncoated one Page -3b- of the band forms. Of course, the cooling hood -59- is provided with a non-oxidizing atmosphere which is introduced into the cooling hood -59- through the spout outlet -36. If desired, an additional inlet for such a non-oxidizing atmosphere may be provided in the cooling hood -59 at 61-. For example, although the cooling hood -59- is shown as simply attached to the grommet -26-, the portion -26e- of the spout top -26d- disposed under the hood -59- and including the spout outlet -36- may be omitted , With the exception of the measure that the coated strip is kept in a protective atmosphere until it has cooled sufficiently to avoid the formation of a visible oxide on its uncoated side, the operation in the embodiment of Fig. 11 is identical to that in relation to FIG on Fig.7 described. For example, although the cooling hood -59- is shown as simply attached to the grommet -26-, the portion -26e- of the spout top -26d- disposed under the hood -59- and including the spout outlet -36- may be omitted , With the exception of the measure that the coated strip is kept in a protective atmosphere until it has cooled sufficiently to avoid the formation of a visible oxide on its uncoated side, the operation in the embodiment of Fig. 11 is identical to that in relation to FIG on Fig.7 described. For example, although the cooling hood -59- is shown as simply attached to the grommet -26-, the portion -26e- of the spout top -26d- disposed under the hood -59- and including the spout outlet -36- may be omitted , With the exception of the measure that the coated strip is kept in a protective atmosphere until it has cooled sufficiently to avoid the formation of a visible oxide on its uncoated side, the operation in the embodiment of Fig. 11 is identical to that in relation to FIG on Fig.7 described.

The length of the cooling hood required to hold the coated tape in an inert gas atmosphere until it has cooled sufficiently to prevent the formation of visible oxide on its uncoated side can be reduced by providing means for increasing the cooling rate of the tape become. In Fig. 12, an embodiment is shown which is substantially identical to that shown in Fig. 7, also in this case, like reference numerals have been used for the same parts. The cooling hood -62- in FIG. 12 is similar to the cooling hood -59- shown in FIG. It has an outlet -63- and an additional inlet -64- for an optionally required non-oxidizing atmosphere. In this embodiment, however, the belt -3- is guided around (ice) cooled rollers -65 and 66-, which cause a reduction in the temperature of the belt, whereby the cooling hood -62- can be shorter. In this case as well, the portion -26e- of the upper tube part -26d-, which is arranged under the cooling hood -62- and which comprises the outlet -36-, can be omitted.

Another way to protect the tape from the formation of a visible oxide is shown in FIG. Also, this device is substantially identical to that shown in Fig. 7 and also the coating operation is carried out in the same manner. According to this embodiment, the spout -26- is provided with a cooling hood -67- which has an outlet -68-. A protective gas atmosphere is introduced into the hood -67- of the nozzle -26-, an additional inlet for such an atmosphere may be provided as needed at -69-. According to this embodiment, a part of the protective gas atmosphere is withdrawn from the cooling hood through the outlet -70- and fed to a heat exchanger, which is shown schematically at -71- and a blower or the like. includes. The cooled inert gas atmosphere from the heat exchanger -71- is again introduced through the nozzle -72-, which causes the impact of the cooled inert gas atmosphere on the band -3-, in the cooling hood -67-. To increase the effect of the belt cooling, a second heat exchanger -73- may be provided which has an inlet -74 and a nozzle -75- disposed diametrically opposite the nozzle -72-. The diametrically arranged nozzles -72 and 75- ensure that the flat cross-section of the belt -3- is maintained. The heat exchangers -71 and 73- allow shortening of the hood -67-, compared to the hood -59- in Fig. 11, since the cooling of the belt -3- is accelerated. To increase the effect of the belt cooling, a second heat exchanger -73- may be provided which has an inlet -74 and a nozzle -75- disposed diametrically opposite the nozzle -72-. The diametrically arranged nozzles -72 and 75- ensure that the flat cross-section of the belt -3- is maintained. The heat exchangers -71 and 73- allow shortening of the hood -67-, compared to the hood -59- in Fig. 11, since the cooling of the belt -3- is accelerated. To increase the effect of the belt cooling, a second heat exchanger -73- may be provided which has an inlet -74 and a nozzle -75- disposed diametrically opposite the nozzle -72-. The diametrically arranged nozzles -72 and 75- ensure that the flat cross-section of the belt -3- is maintained. The heat exchangers -71 and 73- allow shortening of the hood -67-, compared to the hood -59- in Fig. 11, since the cooling of the belt -3- is accelerated.

Another belt cooling device is shown in FIG. 14. According to this embodiment, coating methods and apparatus are also identical to those shown in Fig. 7, and therefore like reference numerals are also used for like parts. The embodiment of Figure 14 is based on the recognition that the coated on one side of the band can be quenched in water to prevent the formation of a visible oxide on its uncoated side. To this end, a hood -76- is provided which extends upwardly from the top -26d- of the grommet -26-. At its upper end, the hood is provided with a guide roller -77-, and opens into an outlet spout -78-. The spout -78- is located below the surface of a water bath -79- in a corresponding vessel -80-. The tape -3- is fed out through the spout outlet -36- out of the spout -26- and into the hood -76-. Inside the hood --76-- the strap is passed around the guide roller -77- and enters from the spout -78- into the water bath -79-. The tape is passed through the water bath -79- and by means of a submerged roller -81- from the water bath upwards. The spout section -78- of the hood -76- is provided with an outlet -82- for the non-oxidizing inert gas atmosphere inside the hood -76- and the steam formed by submerging the belt -3- in the water bath -79-. The outlet -82- is provided with a control valve -83-, and the flow through the outlet -82- can be monitored by means of a (known) flow meter, generally designated -84-. Baffles -78a and 78b- may be provided in spout portion -78- to minimize back diffusion of the water vapor into hood -76-. The non-oxidizing inert gas atmosphere in the hood -76- is introduced via the Tüllenauslaß -36- from the nozzle -26-.

In all embodiments of Figs. 11 to 13, the inert gas atmosphere within the cooling hood must be maintained at a high enough pressure to prevent the penetration of the surrounding oxidizing atmosphere into the cooling hood via the cooling hood outlet.

Fig. 15 illustrates a modification of the embodiment of Fig. 5, in which both the coating and finalization steps are performed within a protective gas atmosphere. For this purpose, there is provided a molten metal container -85- containing a molten metal plating bath -86-. A grommet is connected to or integrally formed with the pretreatment hood (fragmentarily shown at -88-). Also in this case, a seal generally designated by -89- may be provided between the door -87 and the hood -88-, this seal serves the same purpose as the seal -6- in Fig.5. Again, for example, the seal -89- consisting of seal roller pairs -90, 91 and 92, 93-, dargesteUt, between the pairs of rollers there is provided an inlet 94 for the non-oxidizing atmosphere serving the same purpose as the inlet 18 in FIG. The EisenmetaUband is also designated here -3- and is passed over a down roller -95-, which corresponds to the roller -12- in Figure 5. The belt -3- is also performed under the rollers -96, 97 and 98- which correspond to the rollers 13, 14 and 22- shown in Fig. 5 and serve the same purpose. The hood -87- has a front wall -87a, a rear wall -87b and side walls, one of which is labeled -87c. The front and rear walls and the side walls extend partially, as shown, into the molten MetaU coating bath. The top door -87- is provided with an inlet 99- for the non-oxidizing atmosphere and an outlet -100 for the belt -3-. A jet brush -101- is mounted within the hood -87- and may be located on any occupied portion of the hood, provided that it does not interfere with the meniscus -102-. A return roller or jet brush (not shown) may be provided for the jet brush -101-, as described with reference to FIG.

The embodiment according to FIG. 15 corresponds to that shown in FIG. 5, the band -3- is provided with a coated side 3a and an uncoated side 3b. The embodiment according to Fig. 15 differs from the embodiment according to Fig. 5 mainly in that both the coating step and the finalizing step are carried out with the jet brush inside the protective atmosphere and thus the sealing block -16- Fig.5 is unnecessary. The unilaterally coated tape can be passed through the door outlet -100 into the outside atmosphere whereupon it is subjected to a corresponding acid cleaning and rinsing and drying operations as described above. Alternatively, the tape may be kept in an inert gas atmosphere until it has cooled sufficiently, to avoid the formation of a visible oxide on its uncoated side -3b-. This can be done by any one of the devices shown in FIGS. 11 to 14. In the embodiment of Fig. 15, the roller -98- could be omitted. The result would be an embodiment similar to that shown in Fig. 1, but in which both the coating and fining steps are performed within the door.

Fig. 16 shows one of the embodiments shown in Fig. 7 similar embodiment, same Teüe are the same

Provided with reference numerals. The coating process in the embodiment of FIG. 16 is again the same as that described in FIG. Fig. 16 differs from Fig. 7 in that the front wall -26- of the door -26- has an opening -103- of such dimensions that it just exposes the jet brush

- 13 No. 357841 -104-, so that its front end is mounted within the spout -26- and its rear end extends outside the spout. The opening -103- may be provided with a hinge closure -105- which snaps onto the top of the jet brush -104- when the spout is in the correct position and the opening -103- closes to prevent the ingress of an oxidizing atmosphere to prevent the opening -103- when the jet brush -104- is removed for cleaning purposes. Conventional additional support means (not shown) may be provided for the jet brush -104-. The opening -103- may be provided with a sealing washer (not shown) or other sealing means, to prevent the contamination of the protective gas atmosphere within the spout by an oxidizing atmosphere penetrating from the outside through the opening -103- and around the jet brush. If the dimensions of the opening -103- are closely matched to the circumferential dimensions of the jet brush -104-, these sealing devices can be replaced by the overpressure of the inert gas atmosphere inside the spout. The arrangement of Figure 16 may be applied to any of the embodiments described above in which the jet brush is disposed within the spout. This arrangement considerably facilitates the periodic cleaning of the jet brush. If the dimensions of the opening -103- are closely matched to the circumferential dimensions of the jet brush -104-, these sealing devices can be replaced by the overpressure of the inert gas atmosphere inside the spout. The arrangement of Figure 16 may be applied to any of the embodiments described above in which the jet brush is disposed within the spout. This arrangement considerably facilitates the periodic cleaning of the jet brush. If the dimensions of the opening -103- are closely matched to the circumferential dimensions of the jet brush -104-, these sealing devices can be replaced by the overpressure of the inert gas atmosphere inside the spout. The arrangement of Figure 16 may be applied to any of the embodiments described above in which the jet brush is disposed within the spout. This arrangement considerably facilitates the periodic cleaning of the jet brush.

In those embodiments of the coating method in which the jet brush is disposed within the spout, the problem may sometimes arise that arise during the finalization step with the jet brush metal vapors and thereby metal dust from the coating is obtained. Also, metal particles can pass from the coating to the uncoated side of the belt. These particles also fall during the finalization process, they are blown away from the strip edges. FIGS. 17 and 18 show a jet brush arrangement in which these problems are eliminated. In Fig. 17, a coating apparatus is shown, which is identical to that shown in Figure 7, again with like parts are provided with the same reference numerals. The spout assembly of FIGS. 17 and 18 can be applied to the coating apparatus of Fig. 15 in exactly the same way (with or without roller -88-). In Figs. 17 and 18, the outlet slot -36- of the hood -26- is surrounded on three sides by walls or baffles -106, 107 and 108-. The jet brush -109- is located outside the grommet -26-, its forward end extending through the baffle plate -107-. With this arrangement and using a non-oxydizing gas in the jet brush -109-, the zinc coating on the side 3a of the belt -3- can be finished before the belt is exposed to the ambient air atmosphere. The metal dust originating from the coating can be blown away from the uncoated side -3b- of the belt. If environmental conditions require it, For example, another baffle plate or top plate (not shown) may extend across the top edges of the baffle plates -106 to 108-. Such an upper plate is provided with a slot for passing the tape -3-. This top plate eliminates any unwanted downward currents that may be caused by the finalization process. The side of the baffle system facing the uncoated side -3b of the belt remains open so that dust or tarnishes from coating metal can be blown away from the uncoated side -3b of the belt. downward flows that may be caused by the finalization process. The side of the baffle system facing the uncoated side -3b of the belt remains open so that dust or tarnishes from coating metal can be blown away from the uncoated side -3b of the belt. downward flows that may be caused by the finalization process. The side of the baffle system facing the uncoated side -3b of the belt remains open so that dust or tarnishes from coating metal can be blown away from the uncoated side -3b of the belt.

In all the coating methods and devices described above, the temperature of the strip depends on the molten metal used as the coating bath. The bath must be maintained at a high enough temperature to ensure that the coating metal melts and remains molten until it is finished by a jet brush. Unlike conventional hot-dip coating processes in which the strip to be coated (on both sides) is submerged in the bath, it can not be expected in the single-sided coating processes according to the invention that the strip itself brings the coating bath consisting of molten metal to a sufficiently high temperature. The practice of adjusting the bath temperature should be substantially the same as the two-sided coating process and should be kept as constant as possible to minimize the formation of sludge. In all the embodiments described above, especially if they depend on the formation of a meniscus, the level of the bath must be kept constant. For this purpose, a known from the prior art pneumatic displacement chamber or a mechanical displacement piston can be used. Preferably, automatic bath level control devices are used (also known from the prior art). especially when they depend on the formation of a meniscus, the level of the bath must be kept constant. For this purpose, a known from the prior art pneumatic displacement chamber or a mechanical displacement piston can be used. Preferably, automatic bath level control devices are used (also known from the prior art). especially when they depend on the formation of a meniscus, the level of the bath must be kept constant. For this purpose, a known from the prior art pneumatic displacement chamber or a mechanical displacement piston can be used. Preferably, automatic bath level control devices are used (also known from the prior art).

- 14 No. 357841

The molten metal plating bath may be heated in any conventional manner, including the use of electrical resistance elements, induction heating, dip tube heating, or the like. Of course, the volume of the molten metal coating bath may be much less than that required for a typical double-sided hot dip coating process. Since according to the invention the contact between the tape and the bath is greatly reduced, the rate of dissolution of the tape can be such that the bath does not become saturated with iron and the sludge formation compared to the rate at which molten metal must be replenished in the bath reduced to a minimum or switched off completely. This leads to a defect-free coating.

In all of the embodiments described above, the temperature of the ferrous metal strip as it exits the conventional pretreatment hood and enters the coating spout depends on the molten metal used as the coating material and can be readily determined by those skilled in the art. The strip temperature should be high enough to prevent solidification (throwing) of the molten coating metal on the strip. On the other hand, the temperature of the strip should not be so high that an alloy is formed between the coating metal and the base metal.

In all the embodiments described above, a non-oxidizing atmosphere within the spout must be obtained. Any non-oxidizing atmosphere including nitrogen or an inert gas is suitable for this purpose. The non-oxidizing atmosphere within the spout must be maintained at a pressure sufficiently high to prevent the penetration of an oxidizing atmosphere into the spout through the spout outlet. This of course also applies to the cooling hood, as described in connection with FIGS. 11 to 14. The dew point inside the spout should be maintained at a level that is appropriate for common (two-sided) coating processes.

In all the embodiments described above, the roller (s) located in the vicinity of the coating bath of molten metal should preferably be provided with a surface which is not easily wetted by the molten coating metal. This facilitates the removal of coating metal inadvertently picked up or sprayed from the rolls by the rolls. If desired, the roller or rollers may be crowned or otherwise shaped near the molten coating metal so that the unused portions taper slightly beyond the edges of the tape to be coated, slightly tapering away from the surfaces of the bath. As a result, the tracking of the band is further facilitated.

The invention has been described with reference to the above embodiments. The choice of a particular embodiment or a combination of embodiments depends on a number of factors, including the existing equipment, the coating metal used, the desired properties of the single-side coated end product, and the like. This selection presents no difficulty to the skilled person. For example, those of the embodiments described above in which the jet brush final treatment is performed using a non-oxidizing gas within the spout, such as in the embodiment of Figure 7, have a number of advantages. These include the lack of ribs in the coating even at slow speeds, no occurrence of problems associated with the formation of oxide on the bath surface, a reduction in the defects caused by sludge fatigue, no formation of oxide layers on the finished coating, and virtually the elimination of foam on the surface. On the other hand, in this process, the operator must pay attention to the build up of coating metal vapors and metal dust and the possibility of transferring metal kitchenware from the coating to the uncoated side of the belt.

In an embodiment such as that shown in Figs. 17 and 18, according to which the jet brush finalization is done using a non-oxidizing gas outside the chamber but before contacting the belt with air, all of the aforementioned advantages of jet brush finalization can be achieved the spout can be achieved. Also, according to this method, the accumulation of metal dust from the coating within the spout is greatly reduced and the transfer of metal coatings from the coating to the uncoated side of the belt

- 15 No.357841 switched off. On the other hand, the non-oxidizing gas used for jet brush finalization can not be used to create overpressure in the spout.

In an embodiment such as shown in Fig.l, according to which the finalization by means of radiation brush in the room atmosphere outside the spout is made, the finalization step is made for reasons of labor relief outside and there are no originating from the coating metal vapors, no metal dust and no transmission from metal kitchen utensils to the uncoated side. Also, the consumption of non-oxidizing atmosphere is reduced. On the other hand, almost none of the advantages that can be achieved in finalizing with a non-oxidizing atmosphere within the spout are achieved, although these drawbacks may be partially offset by a non-oxidizing atmosphere such as nitrogen after exposure of the belt to the ambient air atmosphere is used.

The single-roller arrangement embodiments (such as Fig. 7) are characterized by the simplicity of the device, the minimization of tape forming problems, and the minimum tape-to-meniscus contact time, thereby avoiding the accumulation of iron in the bath. However, the single roll arrangement requires great care to avoid the uptake of zinc by this single roll, and the reduced meniscus area requires control of the jet brush machining so as not to disturb the meniscus by finish machining.

The use of a two roller arrangement allows for air finalization (as in FIG. 1) or within the spout of FIG. 15. The longer meniscus-to-belt contact time ensures that the meniscus is not easily disturbed. On the other hand, this prolonged contact between the band and the meniscus increases the risk of dissolving the iron present in the band. The two-roller arrangement is a complicated device and more attention must be paid to the shape of the belt.

The arrangement comprising three rollers according to FIGS. 5 and 15 has all the advantages of the arrangement with two rollers, moreover, with this arrangement, the distance of the large rollers from the bath surface can be increased. This arrangement also has all the drawbacks of the two-roller arrangement, moreover the device is even more complicated and care must be taken that the intermediate roller does not mark or otherwise damage the belt, especially if the belt to be coated is very wide ,

The invention will be explained in more detail with reference to the examples.

Example 1: A ferrous metal strip was zinc-coated on one side using the apparatus and method of FIG. At a belt speed of 12.1 m / min, the belt was inserted into the grommet at a belt temperature of about 465-471 ° C. The temperature of the belt was kept at 460 ° C.

A non-oxidizing nitrogen blanket gas atmosphere was introduced into the nozzle at a speed of 19.8 m³/ h introduced. At the downstream roller -12- a dew point of -22^ÖC recorded with 120 ppm oxygen.

The jet nozzle -19 had a nozzle opening of 0.7 mm and was supplied with air at an overpressure of 3.8 mbar. The nozzle was held at a height of about 15.24 cm above the surface of the bath and directed upward at an angle of about 2 to 3 °. The roller -14- had a diameter of 30.48 cm. The nozzle was held at a distance of about 0.47 cm from the coated side of the belt.

By the method described above, the iron-based metal strip was coated on one side with a zinc coating at a coating weight of 5 mg / cm² Provided.

The zinc coating thus prepared was subjected to conventional quality tests including adhesiveness tests and proved to be excellent. The uncoated side of the strip had a light oxide layer and no overlapping zinc coating.

Example 2: A ferrous metal strip was produced using the method shown in FIG

Device and the method shown there coated on one side with aluminum. At a belt speed of 15.2 m / min, the belt was introduced into the spout at a temperature of about 704 ° C. The molten metal plating bath was heated to a temperature of

687 ° C held.

- 16 No. 357841

A non-oxidizing inert gas atmosphere (N₂) was in the spout at a speed of

8,4 m³/ h introduced. At the down roll -12-, a dew point of -23 ° C was recorded along with less than 100 ppm oxygen.

The jet nozzle -19 had a nozzle opening of 0.07 cm and was supplied with air with an overpressure of 3.2 mbar. The nozzle was held at a height of about 10 cm above the surface of the bath and directed upward at an angle of about 10 °. The roller -14- had a diameter of 30 cm. The die was held at a distance of about 0.3 to about 0.4 cm from the coated side of the belt.

Following the procedure described above, the ferrous metal strip was unilaterally coated with an aluminum coating having a coating weight of 5 mg / cm² Provided. In the conventional quality inspection including adhesiveness, the aluminum coating thus prepared proved to be excellent.

Within the scope of the invention and without departing from the spirit of the invention, changes and modifications are possible. For example, in the embodiments in which an oxide layer is formed on the uncoated side of the iron-based metal tape, it is not necessary to remove this oxide layer by means of acid cleaning. The oxide film adheres and may be easily subjected to pretreatment for the paint such as phosphating. Under these conditions, the uncoated side with a pretreated oxide layer is excellent for applying a paint.

In the embodiments described above, the finishing treatment is performed using an air brush. But there may be other finalization using an asbestos brush or the like. be used.