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Title:
DEVICE FOR THE CONTROLLED REDUCTION OF THE THICKNESS OF METALLIC COATINGS OBTAINED WITH THE TECHNIQUE OF THE HOT BATH IN MOLTEN METAL
Document Type and Number:
WIPO Patent Application WO/2018/025222
Kind Code:
A1
Abstract:
The present invention discloses a machinery for depositing a metal coating on continuous sheet metal, by the hot bath technique, such as for example in hot-dip galvanizing processes. An important peculiarity of this machinery is the ability to fine- tune the thickness of the coating at intervals as wide as possible to effectively cover the widest range of orders. Indeed, actual industrial logic requires that these machines be used with fast and possibly continuous rhythms; and so it is very important that they can be used to carry out the widest range of machining operations, as the requests from the market are not always foreseeable. The machinery described here is therefore innovative as it uses two thickness adjustment stages that operates alternatively. In addition, the stage used for thinner coatings is particularly innovative as it is not based on technology (known in the art) which employs the so-called "air knives". In fact, the workings required to obtain thin thicknesses are carried out by means of a mechanical removal, which is designed to handle the major criticalities associated with this type of machining where a tool is expected to come into contact with the surface to be refined. This mechanical removal is made possible by the provision of a suitable gasket, replaceable when worn or too dirty, with which to make the spatula wire that physically reduces the thickness of the coating. These gaskets are made by means of an interlacement of different types of fibers joined together to form a cord. This is to provide a good grip and strength traction (to be able to stretch it well on the spatula wire), excellent abrasion resistance (in order tο limit wear and tear) and excellent resistance to temperature (since they must be able to be used in contact with the high temperatures of the molten metal). Furthermore, the cord is designed to have a good elastic deformability in the direction of its section, and adequate properties of repellency to the molten coating material, so as to avoid that it adheres on its surface and to facilitate fluid and continuous detachment without spraying in different directions.

Inventors:
BECHERINI MARCELLO (IT)
BECHERINI MARCO (IT)
DEMOZZI ANDREA (IT)
Application Number:
PCT/IB2017/054765
Publication Date:
February 08, 2018
Filing Date:
August 03, 2017
Export Citation:
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Assignee:
MEDEA S R L (IT)
International Classes:
C23C2/00; C23C2/20; C23C2/22; C23C2/40
Domestic Patent References:
WO2013164493A12013-11-07
Foreign References:
US4291074A1981-09-22
US3681118A1972-08-01
US5529816A1996-06-25
US3260577A1966-07-12
US3889018A1975-06-10
Attorney, Agent or Firm:
BRUNI, Giovanni (IT)
Download PDF:
Claims:
CLAIMS

1 , Machinery (100) for the coating of a continuous sheet metal (10) with a layer consisting in a coating material (1 ) which is deposited on both faces of said continuous sheet metal (10) by immersing it in a hot bath of said coating material (1 ) which is maintained in the molten state; and said machinery (100) is characterized in that it incorporates at least a first wiper element for taking away the molten coating material in excess and a second wiper element for taking away the molten coating material in excess; and said machinery (100) is configured to activate alternatively, one at a time, said two wiper elements for the removal of the molten coating material in excess, and the choice about the wiper element which have to remain active is determined as a function of the thickness of said layer of coating material which must remain deposited on said continuous sheet metal (10), and:

said first wiper element, positioned in correspondence of the line of exit of said continuous sheet metal (1 1 ) from said hot bath of coating material (1 ), comprises two "air knife" generators (1 10) facing the two surfaces of said continuous sheet metal (1 1 ), and said "air knives" are long, at least, as the width of said continuous sheet metal (1 1 ), and said two "air knife" generators (1 10) can be adjusted by varying their distance from said surfaces of said continuous sheet metal (1 1 ) and/or varying the pressure of the air jet which constitutes the "air knives" or completely disabling said air jet which constitutes the "air knives";

said second wiper element for taking away the molten coating material in excess is positioned close to said first wiper element for taking away the

1 molten coating material in excess, and it comprises two wiping tools (120), positioned close to said two faces of said continuous sheet metal (1 1 ), and they are long, at least, as the width of said continuous sheet metal (1 1 ), and they are constrained so as to rotate each around its longitudinal axis, placed horizontally and parallel to said faces of said continuous sheet metal (1 1 ), and each of said two wiping tools (120):

- comprises at least two scraping spatulas which protrude from its

lateral surface, and

- the blade of said scraping spatulas is constituted by a movable edge (130), wherein said movable edges (130) are also formed by an interlacement, or a weave, of the type in which different fibers are present: and there are very harsh to traction filamentous fibers, and fibers consisting of lubricant materials, and

- said scraping spatulas are suited to be positioned so as to slide over said faces of said continuous sheet metal (1 1 ), so as to maintain the contact with them and scraping away the molten coating material in excess.

Machinery (100) as in the preceding claim wherein said movable edges (130), which constitute the blade of said scraping spatulas, are also formed, inside them, of a material which gives them the majority of the thickness, and said material is characterized in that it is compressible in elastic way in the thickness sense.

Machinery (100) as in the preceding claim wherein, when said second wiper element for taking away the molten coating material in excess is active, said

2 movable edges (130) are compressed against said faces of said continuous sheet metal (1 1 ) as a function of the thickness of said layer of coating material (1 ) which must remain deposited on said continuous sheet metal (10), and the they are more compressed, the thinner said layer of coating material (1 ) results.

4. Machinery (100) as in the preceding claim, wherein said interlacement, or weave, of the type in which different fibers are present, forms the external covering of said movable edges (130).

5. Machinery (100) as in claim 5, wherein said interlacement, or weave, of the type in which different fibers are present, also comprises aramid or vitreous fibers.

6. Machinery (100) as in claim 5, wherein said interlacement, or weave, of the type in which different fibers are present, also comprises graphite filaments, or Teflon, or fibers containing mineral oils.

7. Method for the coating of a continuous sheet metal (10) with a layer consisting in a coating material (1 ) which is deposited on both faces of said continuous sheet metal (10) by immersing it in a hot bath of said coating material (1 ) which is maintained in the molten state; and said method is characterized in that it is put into practice by means of said machinery (100) indicated in the preceding claim 1 , and it comprises at least the following phases:

setting of the desired coating thickness, by providing instructions to the control elements (101 ) of said machinery (100) indicated in claim 1 , choosing, as a function of the set thickness, of one wiper element for taking away the molten coating material in excess, which have to be activated for machining,

3 activation of the wiper element for taking away the molten coating materia in excess, chosen at the preceding stage, and deactivation of the other wiper elements for taking away the molten coating material in excess which are incorporated into said machine (100) as indicated in claim 1

4

Description:
TITLE:

DEVICE FOR THE CONTROLLED REDUCTION OF THE THICKNESS OF METALLIC COATINGS OBTAINED WITH THE TECHNIQUE OF THE HOT BATH IN MOLTEN METAL

DESCRIPTION

The invention disclosed herein finds its specific field of application in industrial systems in which continuous sheets made of a first material, generally metallic or predominantly metallic, are coated with a layer consisting of a second coating material; also the composition of said second coating material is generally metallic or predominantly metallic. This coating process is carried out by means of a hot bath of said continuous sheets immersed on said second coating material which is in the molten state.

The so-called hot-dip galvanizing of metal sheets is one of the most typical processes of the type mentioned above and it will be taken as the reference application for the illustration of the present invention.

However, it is to be understood that the teachings of the present invention are generally applicable also in other applications where a thin metal coating is to be applied on continuous sheets of another material, using the technique of the hot bath. The hoi-clip galvanizing of metal sheets, of various thickness and width, is a mature industrial process that is carried out with techniques that have been consolidated in many years of application.

In summary, the hot-dip galvanizing of continuous metal sheets takes place, at the current state of the art, by sliding a continuous sheet which have to be coated along a path, generally driven on rollers; and this path comprises a section where the sheet to be coated is dipped in a tub containing the coating material kept in the molten state.

Such molten coating material, during the immersion, adheres to the surfaces of such metal sheet. The sheet metal then emerges vertically from the molten bath, so that, after the emersion, the surfaces of said metal sheet are covered, generally unevenly, by the coating material (which, as said, is normally a metal, or an alloy, in the molten state).

Just above to the level of emersion from the molten metal bath (typically a distance of a few tens of centimeters or few centimeters) the sheets undergo a first finishing treatment of the coating.

This first finishing treatment of the coating provides that excess molten metal is removed to obtain a homogeneous coating as well as to adjust its thickness.

The first systems that was developed to perform this first finishing treatment were based on the use of a pair of opposing rollers between which the sheet was forced to slide through after its exit from the bath, by performing a sort of calendering of the sheets just emerging from the hot bath.

Thus, the thickness of the coating was regulated by the distance between these opposed rollers, and the molten metal was then removed mechanically by contact. However, this procedure had the severe contraindication that molten metal got dirty the rollers, compromising the accuracy of the treatment. The need for excessively frequent cleaning of the rollers ended up to result in slowdowns in the processing; as well as the production of washing waters containing metal residues, requiring proper disposal, was another contraindication.

Finishing treatments by calendering, and more generally those methods based on the mechanical removal of excess coating metal, have been replaced by pneumatic finishing processes based on the use of the so-called "air-knives".

At present, such "air-knives " are the technology that is more widely used to perform the first finishing treatment of hot-dip galvanizing of continuous metal sheets.

The "air-knives" are high pressure air jets, emitted by nozzles consisting of long narrow openings. Such nozzles, in the considered application, are positioned horizontally, parallel to the surfaces of the metal sheets just emerging from the bath in the molten metal, and at a short distance (millimeters or centimeters) from said surfaces.

The air jet emitted by such narrow nozzles is therefore very thin and it invests, roughly along a line, the metal sheet while it is rising vertically, blowing away part of the molten material that is not solidified yet.

By adjusting the air jet pressure, the distance of the nozzle from the surface to be treated and the sliding speed of the sheet, you can adjust the thickness of the resulting coating on the metal sheet.

Various physical limitations, concerning the minimum nozzle distance from the sheet, and the air jet pressure, determine both the minimum thicknesses obtainable for coatings and the speed of the processing. Obviously, thicker coatings require less material removal, and therefore metal sheet can flow faster, so thin-films coatings generally require a slower processing.

Known techniques, which are more commonly used in practical applications, are driven from the achievement of machine simplicity and efficiency. The main purpose consists in making reliable industrial hot-dip galvanizing lines requiring reduced maintenance. Consequently, and considering the remarkable maturation of these pneumatic techniques based on the use of "air knives " , said known techniques can be considered to be satisfactory for hot-dip galvanizing with thicknesses in which the contribution of coating material is approximately between 100 g/m 2 and 600 g/m 2 . Typically, lines active in the industry are able to process about 150 linear meters per minute, with thinner thicknesses (hence in the slower cases).

It should be noted that these data are indicative and they are cited for the sole purpose of providing some realistic quantitative references about the performance obtainable by means of the actual techniques, which are more commonly used in the real industry.

As mentioned, the widespread hot-dip galvanizing techniques favor the simplicity and maintainability of the lines. However, performance improvements can be achieved, always remaining within the known solutions, using more sophisticated nozzles that can be operated at smaller distances from the metal sheet, and which use gas jets other than air, for the purpose to drastically reduce metal redox processes: processes that are one of the reasons for the above-mentioned physical limits, regarding the possibility of further reductions of coating thicknesses and increases of machining speeds.

For example, EP1586672 A1 "Liquid wiping apparatus", Yoshikawa IVfasashi et ai, teaches to make a nozzle able to create an "air knife" that can flow faster on the surface to be treated by removing the excess coating metal, and that it may operate nearer to the surface. This new type of nozzle includes, in addition to the "air knife", a solid blade that runs in contact with the surface just treated with a suitable inclination. An essential function of this additional solid blade is to protect the surface, just treated with the "air knife", from sketches of the material just removed with the "air knife" itself. Said sketches are formed as the air jet is generated very close to the metal sheet, and runs over it at quite high speeds. The so conceived system for metal coating reduction allows to achieve the result of thinner coatings and faster machining.

It is noted that, from the point of view of the industrial economy, there is a strong interest in making coatings as thin as possible, as there is a saving in the

consumption of the coating material which is usually the most valuable.

In order to provide an idea of the magnitude of the savings that can be obtained, it should be noted that in the very frequent case of sheets intended for subsequent painting it is sufficient to provide zinc coatings in which the contribution of coating materia! is no more than 30 g/m 2 : Therefore, it is clear that the coating metal consumption may be reduced by more than two-thirds, in the event of being able to carry out such thin coatings at sustained speeds.

It is not clear what performance can be achieved with the apparatus made according to the teachings disclosed in EP1586672 A1 , but this apparatus can certainly remove more coating material than the known "air knives" and it can operate at speeds of sliding sufficiently high.

The apparatus according to the teachings disclosed in EP 1586672 A1 , however, appears to be quite complex and so requiring significant maintenance, at least to clean it.

It is recalled that in industrial environments, where large quantities of galvanized metal sheet are produced, the requirements of simplicity, reliability and minimal maintenance, are the prevailing requirements; at the point that it is still convenient to accept waste of coating metal, making thicker coatings than needed, since they can be processed reliably, fast, and substantially defects-free.

Nevertheless, zinc waste in galvanizing processes is a very heavy compromise to accept in the perspective of improving efficiency.

In addition, the techniques of coating metal removal based on "air knives", which are still widely widespread, involve a fast oxidation of the metal removed, compromising part of the reuse, thus increasing waste and making it necessary to set up suitable processes for waste disposal.

A new approach to the problem of an efficient execution of this first finishing treatment, to which said metal sheets must be subjected as they emerge from the hot bath in the molten metal used for their coating, is disclosed in WO 2013/164493 A1 "Device for reducing the thickness of a metallic coating on a metallic sheet ",

Becherini M..

The solution disclosed in WO 2013/164493 A1 teaches to return to the mechanical removal of excess coating metal by sliding a kind of spatula on the surface emerging from the hot bath, and said spatula scrapes an adjustable amount of newly deposited coating metal.

The adjustment of the thickness of coating material that must remain on the metal sheet can be made according to the pressure exerted by the spatula on the surface. This solution, as taught in WO 2013/184493 A1 , allows to obtain very thin

thicknesses (with optimum results for coatings between 25 g/m 2 and 70 g/m 2 ), with fine precision and fast machining; and the removed material, which falls into the melting tank, can be completely recovered.

However, as is immediately apparent, the device disclosed in WO 2013/164493 A1 , coming into contact with the metal to be removed, becomes dirty, as was the case of the roll machines used in the first hot galvanizing systems. Moreover, these devices may also be subject to usury, in fact, the higher the pressure and the sliding speed, the greater the wear to which the spatula is subjected to.

WO 2013/164493 A1 provides a solution based on the use of replaceable edge to be attached to the spatula wire. These edges can be removed when they are too dirty or worn. To facilitate the replacement of the spatula edge, it is also expected to make machines with a number of such spatulas.

WO 2013/164493 A1 discloses an implementation in which there is provided a tool carrying three spatulas, which may alternate in the action of scraping excess coating material. These spatulas are radially mounted on the lateral surface of a rotating support (this is a kind of shaft of approximately cylindrical or prismatic shape) that can rotate along its axis so that while a spatula is operative, and it is scraping exceeding metal, the other two are accessible on the opposite side of this rotating support, and therefore their edges can be replaced, possibly, without stopping the operation of the machine.

The device shown in WO 2013/184493 A1 appears to be very easy to implement, it is easy to maintain and, among other things, also makes it possible to greatly reduce the acoustic noise in the working environments by improving working conditions of workers.

Therefore, it would appear to be a very promising solution to address the efficiency problems currently present in industrial hot-dip galvanizing lines.

However, this is a solution that still has important needs for refinements; in fact, some improvements are essential so that such solution can be applied successfully in the real industry, which imposes, as a priority requirement, production efficiency,

!n particular, defects in production must be kept strictly to the minimum. In fact, in the presence of defects in the galvanization, the customer may refuse an entire supply roll: corresponding to tons of product. Surface processing control must therefore be very efficient. The edge on the spatula should therefore always be in good condition; for example, it should not be worn and it must always be sufficiently clean (as residuals of coating material that remain attached to the spatula's edge may modify the contour) so as not to have a significant negative impact on the quality of the manufacturing.

In addition, the control of the coating thickness, as mentioned above, takes place by adjusting the pressure of the spatula on the metal sheet, and this control can be done with due precision just if the elasticity of the edge remains constant throughout the utilization period. In addition to these aspects concerning the manufacturing quality, hot galvanizing lines have to support very flexible production programs, and therefore said hot-dip galvanizing lines should be able to perform galvanizing with very variable

thicknesses, depending on the order; and the machining must be always controllable with the utmost precision. Moreover, it should not be necessary to have long production halts for machine reconfiguration.

The requirement of production flexibility, as well as important, is also not easy to achieve. In fact, this requirement can be limited by the fact that certain edges can be optimized to achieve a certain quality and precision, only within limited pressure ranges.

Therefore, the main scope of the present invention is to indicate a machinery for the coating of a continuous sheet metal, by means of the hot bath technique, in which it is possible the fine-tuning of the coating thicknesses in the widest possible range, so as to effectively cover the widest range of orders.

At the same time, it is required that these machineries can operate with substantial continuity even when the settings are varied. The machinery working is expected to guarantee speed of manufacturing and very high precision of machining, controllable with stability.

It should be noted that the above-described purpose has a remarkable economic value since the machinery in question is a considerable investment, the cost of which depends just in a marginal way on the tool employed to perform the first surface machining after the sheet emerges from the hot bath; in fact, the other stages of the processing line are far more expensive. Therefore, the industrial logics require that these machines work following fast and possibly continuous rhythms. It is clear that, having to keep working the most of these machines, it is very important that they can be used to carry out the widest range of manufacturing, as market demand is not always foreseeable.

On the other hand, it is equally clear that machining defects are extremely harmful from the economic point of view, and therefore, in the absence of machines able to guarantee the quality of over the complete range of thickness that is required for coatings, normally the industry opts to use machines that offer quality assurance, even if the machining supports just thicker coatings, which are then carried out even when not needed.

It is therefore evident that the aim of flexibility in machining must be pursued together with a further aim which consists in having a machinery in which it is easy to manage and reduce the occurrence of defects in surface machining.

Obviously, the prior art does not yet offer satisfactory solutions to the problem of flexibility, therefore, coatings thicker than necessary are commonly widespread. In fact, entrepreneurs normally choose to investment in machines that give the best guarantees in the machining quality.

Finally, a further object of the present invention, equally important, is to indicate a reliable machine that allows simple and easy maintenance, in which the need to stop the plant, for maintenance purposes, is minimized.

The foregoing objects for this invention are achieved by means of a machinery for coating of a continuous metal sheet with a layer consisting of a coating material which is deposited on both faces of said continuous sheet metal by immersing it in a hoi bath of said coating material which is maintained in the molten state; and said machinery incorporates at least two elements of reduction of the thickness of the coating, which work in alternative depending on the thickness of the coating to be obtained: in fact, the machining which must be performed for the thickness reduction generally requires different tools, depending on the thickness.

In particular, in the proposed solution, the machining which is required to obtain thin thicknesses are not carried out with the so-called "air knives", which are efficient, and therefore used, for larger thicknesses of the coatings; but they are carried out by means of a mechanical removal, and some considerable criticaiities associated to this last machining can be handled by setting up a suitable replaceable edge for the spatula by which the thickness of the coating is reduced.

Therefore, the machinery according to the present invention comprises:

a first wiper element for taking away the molten coating material in excess that is deposited on the faces of said continuous metal sheet when emerging from said hot bath, positioned in correspondence of the line of exit of said continuous sheet metal from said hot bath of coating material, which comprises two "air knife" generators facing the two surfaces of said continuous sheet metal, and said "air knives" are long, at least, as the width of said continuous sheet metal, and said two "air knife" generators can be adjusted by varying their distance from said surfaces of said continuous sheet metal, and/or varying the pressure of the air jet which constitutes the "air knives", or completely disabling said air jet which constitutes the "air knives";

v a second wiper element for taking away the molten coating material in excess that is deposited on the faces of said continuous metal sheet when emerging from said hot bath, also positioned in correspondence of the line of exit of said continuous sheet metal from said hot bath of coating material, and said second wiper element is positioned close to said first wiper element for taking away the molten coating material in excess. However, said second wiper element has some major criticisms, therefore, it is crucial that it is achieved by providing some essential arrangements, and in turn it includes:

a) two support structures for the wiping tools, constrained so as to rotate each around its longitudinal axis, which is horizontal and parallel to said faces of said continuous sheet metal, and said two support structures are positioned close to said two faces of said continuous sheet metal, and they are long, at least, as the width of said continuous sheet metal;

b) at least two scraping spatulas which protrude from the lateral surface of said two support structures, and the blade of said scraping spatulas is constituted by a movable edge, and said scraping spatulas are suited to be positioned so as to slide over said faces of said continuous sheet metal, so as to maintain the contact with them and scraping away the molten coating material in excess; and said machinery for the coating of a continuous sheet metal is configured to activate aiternativeiy, one at a time, said two wiper elements for the removal of the molten coating material in excess.

An essential feature of said second wiper element for taking away the molten coating material in excess is that said movable edges, which constitute the wires of the scraping spatulas are also formed by an interlacement, or a weave, of the type in which different fibers are joined together to make a cord. This to allow you to obtain a sort of gasket with:

- good tensile strength (to be able to stretch it well on the spatula wire), - excellent resistance to abrasion (in order to minimize the wear and tear),

- excellent resistance to temperature (since they must be able to be used in

contact with the high temperatures of the molten metal) and

- good compressibility, in the elastic field, with the return of the section, so as to appropriately dose the amount of molten metal removed from the sheet, as a function of the compression of the cord in the direction of its thickness (to be remembered that this cord must be rather rigid in traction).

In addition, the cord should have a repeilency property of the molten coating material so as to avoid that parts of coating material remain attached to the cord itself, and in order to favor the detachment as fluid and continuous as possible without spraying in different directions.

Ail these essential requirements for achieving said cord serving as a gasket to be attached as a removable element to the scraping spatula are obtained by using different fibers weave, such as aramid or glass fiber (which give high tensile strength) braided or woven with lubricating materials, such as graphite, teflon or fibers containing mineral oils. The cord composition has to be designed to guarantee the mechanical strength necessary for the system, while maintaining deformability along the direction of its thickness. The deformability is necessary for the regulation of the coating material which have to remain deposited on the metal sheet, which depends precisely on the deformation of the cord when it is pushed on the metal sheet.

The fact that a machinery as the one taught by the present invention is endowed with a plurality of machining tools, to be used alternately, and with precise adjustments, requires that it is associated with a control unit which allows to execute configurable machining programs with sufficient flexibility. Therefore, in some preferred embodiments, such a machinery will also comprise a numeric controller and appropriate interfaces with which it can load processing programs, whether received from other computing machines, or by direct programming by an operator, acting through a man-machine interface.

The main advantage of the present invention is that machinery for the coating of a continuous sheet metal with a layer consisting in a coating material, metallic or predominantly metallic, made according to the teachings of the present invention meets the main purposes for which it is was conceived.

This invention also has further advantages which will be made more apparent from the following description of a practical example of implementation which discloses further details (including the characterization of the removable element of the scraping spatula, which is of particular importance), from the attached claims which form an integral part of the description itself and from the illustration of some examples of practical embodiment, which are not intended to limit the invention. The attached drawings also help to illustrate the invention and some relevant embodiments and precisely:

V Figure 1 shows some elements of the machinery according to the invention;

V Figure 2a shows a detail of the scraping spatula in non-operating conditions; ·/ Figure 2a shows a detail of the scraping spatula in operating conditions;

V Figure 3 shows some real examples of cords of which the removable elements constituting the edge of the scraping spatulas are made.

In Figure 1 , the number 100 indicates, as a whole, the machinery according to the invention. Since it is a very articulated machinery, with the function of coating a continuous metal sheet with a layer of a coating materia! which is deposited on both sides of said continuous metal sheet, actually it constitutes a real Industrial processing line. Figure 1 shows, in a very schematic way, just few elements of said machinery 100: those that are useful in highlighting the inventive details that characterize the machinery 100 with respect to prior art, which, as it has been anticipated, is based on mature technologies.

Starting from the elements that are also present in the machines according to the prior art, Figure 1 shows, with the number 140, a tank containing the molten coating material, indicated by the number 1 . The number 10 shows the metal sheet which must be coated and immersed in molten coating material 1 . Said metal sheet 10 is guided by a roller system that slides it; In Figure 1 , with the number 141 , there is shown a roller guiding the sliding of the sheet metal 10 so that it follows a path which includes a section where it is well immersed in the bath of molten material 1 . Continuing its sliding, the sheet metal re-emerges vertically, covered by the coating material 1 , In FIG. 1 , the sheet metal, after its emersion, is indicated by the number 1 1 , since it is composed of the metal sheet 10, and the coating layer constituted by the coating material 1 , which remains "attached" to the sheet metal surfaces when it exits the bath in the molten coating material 1 .

The sheet metal 1 1 then undergoes some treatments. The first one, essential in this industrial process, consists of a first finishing treatment of the coating, which also includes the thickness adjustment.

The number 1 10 indicates two "air knives", each acting on one face of the sheet metal 1 1 . Said " air knives " 1 10 are tools typically present in machineries according ίο the prior art and, for the purpose of this description, they have already been briefly described above. They can operate according to adjustable parameters to a certain extent; in fact, the number 1 1 1 indicates an element connecting said "air kinfe" 1 10 with the rest of the machinery 100, synthetically indicated with the number 101 .

The machinery 100, and in particular its part 101 , is not shown in detail in this description; evidently, it will include all the automatic control elements that are necessary for the proper operation of machinery as a whole.

In fact, an important regulation that must be possible is the adjustment of the thickness of the coating of the metal sheet 1 1 . It is clear that the amount of coating material 1 that will remain permanently deposited on the faces of the sheet metal 1 1 will determine the coating thickness. Such amount of coating material, in turn, depends on a combination of parameters, among which the most important are: the sheet metal sliding speed, the air pressure of the "air knives" 1 10 and the proximity of said "air knives" 1 10 to the metal sheet. The last two parameters relating to the position and operation of the "air knives" 1 10 can be adjusted by means of the connecting element 1 1 1 which may be suitable for adjusting the position of the "air knife" 1 10 and for transmitting a control command about the air pressure. The sliding speed of the sheet metal, on the other hand, is determined by the rolling speed of the rollers.

Ail this can be adjusted, within certain intervals, by the overall control system of the machinery 100.

It should be noted that, in the machinery 100 according to the teachings of the present invention, the connecting element 1 1 1 may also provide for the exclusion of "air knives" 1 10. For example, turning them away from the surfaces of the metal sheet 1 1 and turning off the air jet. Indeed, as mentioned in the first part of this description, there are limits within which the adjustments, related to the "air knives" 1 10, allow to obtain an adequately good quality on the sheet metal coated surface.

For example, the sliding speed cannot exceed certain speeds in order to guarantee the correct bath time, but it cannot be too slow, because the excess coating material 1 must be blown / removed when it is still well fluid, so very hot, and just after the emersion from the bath.

In general, the "air knives" 1 10 processing time are also subject to the constraints associated with the state of coating material 1 that remains deposited on the sheet metal and, when exiting the bath, cools down (so it tends to solidify) and, in contact with the air, oxidizes, modifying its chemical state.

Ail the above considerations refer to the processing technology by the use of "air knives", and thus they are aspects that relate to the prior art. They have been reported only to argue that the flexibility of processing with the use of "air knives" is limited. For example, in the case of hot-dip galvanizing of continuous sheets, satisfactory results can be obtained for coatings with a quantity of coating material (i.e. zinc) in the range of 100 g/mq to 600 g/mq.

In particular, the lower limit is, from an industrial point of view, very penalizing, as zinc plating would often be sufficient with much thinner thicknesses. Thicknesses in the order of 30 g/mq, which, however, are not easily obtainable with the "air knives" as they would require too low sliding speeds, with consequences on the quality of the work due to the non-optimal oxidation or to fluidity phenomena (solidification) of the coating material. Alternatively, they would require too high pressure for the air jets or a positioning of the "air knives" too close to the sheet, generating, even in this case, problems with the quality of the workmanship. The machinery 100 according to the invention, therefore, in order to meet flexible processing requirements, also includes a further working tool which is activated in alternative of the "air knives" 1 10 when very thin thickness machining is required. Said alternative tool consists of a system comprising a tool equipped with scraping spatulas, inspired by the one disclosed in WO 2013/164493 A1 (previously cited above). Such "spatula-tool" is shown in Figure 1 with the number 120. As with the "air knives" 1 10, two of these "spatula-tools" 120 are usually needed to work on both sides of the coated metal sheet 1 1 .

Compared to the "spatula-tools" indicated in WO 2013/164493 A1 , "spatula tools" 120 according to the teachings of the present invention are provided with a special gasket which constitutes the spatula edge, and which is referred to by numbers 130 in the example of Figure 1 depicting six spatulas (three for each of the two tools),

!n fact, even the coating processes for thin thicknesses require that it is possible to guarantee an appropriate machining quality, and such "spatula tools" 120 have significant criticality to be employed with the required performance. Such critical issues regard the machining control, and they require a technical solution that is neither indicated nor suggested in WO 2013/164493 A1 .

The "spatula-tools" 120 are also driven by means of a connecting element, which is shown in FIG. 1 by the number 121. By means of the element 121 , it is possible to adjust the pressure that the spatula edge exerts on the coated metal sheet 1 1.

Additionally said element 121 provides for rotating the "spatula-tool" 120 to put a new spatula in operation when the one in use has lost its optimal characteristics.

As mentioned above, the quality of surface processing that is obtained by sliding a spatula onto the metal sheet 1 1 requires that the spatula edge, which scrapes the metal sheet 1 1 , has precise characteristics. Figs. 2, show a detail of this edge: Figure 2a refers to the case when it is detached from the sheet metal and is therefore not in operation; Figure 2b, instead, refers to the case where the spatula edge is pressed on the sheet, and is therefore scraping the excess coating material. The view shown in Figures 2 is a top view, in which the sheet is represented only in a portion of its width. The detail of the representation allows to distinguish the actual sheet metal, indicated by the number 10, and the coating material layer indicated by the number 1 . In addition, given the purely explanatory purpose of Figures 2, coating is represented only on one side, being the machining similar to the one performed on the other side.

!n Figure 2a, there is also a piece of "spatula-tool" 120, and with the number 130 it is again indicated the movable edge section placed on the spatula wire and which must be positioned in contact with the sheet to scrape the coating material 1 in

!n a typical embodiment, the edge 130 consists of a kind of cord suitable to be applied along the entire wire of each spatula of the "spatula tool" 120. Such a cord, when is in a rest position, i.e. when it is not squeezed against the sheet, as in Figure 2a, has a thickness "Sr" that depends on how it was built, !n Figure 2a, the thickness "Sr" is indicated next to a spring symbol, indicating that, at least within a certain compression range, this cord is elastic and can be compressed, in the direction of the squeeze, as a spring with elastic coefficient K.

Figure 2b clearly illustrates the operation of the "spatula tool" 120 when a spatula is squeezed against the metal sheet. In this case, the edge 130 is compressed, and in fact the spring is shorter, and the thickness "Sc" of the compressed edge will be less than the resting thickness "Sr". To the extent of the elastic compression behavior of the edge 130, this model describes the reality; the pressure exerted by the spatula on the sheet will be proportional to the extent of the squeezing ("Sr" - "Sc"). And, the greater the pressure, the thinner will be the thickness of the coating material 1 which will remain on the surface of the sheet after the spatula passage.

With the aid of Figures 2, a feature that must be guaranteed by the edge 130 has been illustrated. The edge must be a done with a sort of gasket which exhibits an elastic behavior in the direction of its squeezing, so that it is possible to adjust with sufficient precision the pressure of scrape exerted by the spatulas.

It should be noted that if the spatula edge was too rigid and non-deformabie, the pressure control should be exercised with force commands directly at the points of support of the "spatula tool" 120, with greater control complexity and with significant limits of precision.

Obviously, also the edge 130 cannot act as a perfect spring, and it is also subject to wear and deterioration. This is why the worn edges are replaced when necessary, and why the pressure control will not necessarily be an open chain control, based solely on compression of the gasket; but it will be performed availing a feedback command. However, the presence of an elastic element in the control function is certainly indispensable for obtaining a controllable transfer function with the precision required by the application.

The elasticity in the sense of the squeezing of the gasket (i.e. the cord which constitute the edge 130) is therefore an essential prerogative of the edge 130.

However, said edge 130 must also have other essential features. In fact, in the longitudinal direction, the edge 130 has to be particularly rigid in order not to produce any shaking effects during use, in other words said edge 130 must be elastic in the direction of the squeezing, but a rigid object in an orthogonal direction (traction). Therefore, it is not advisable to make this object with a homogeneous or isotropic material.

In addition, said edge 130 must have a contacting surface with the metal sheet:

V resistant to abrasion,

V flexible, so as to absorb the deformations due to squeezing, and

v composed of materials repellent to the coating material 1 , in order to prevent this clinging to the gasket itself and soiling it, and in order to favor the drainage of the coating material 1 removed, and its full recovery thereof

Figure 3 is an image of some real samples of cords with which it is possible to realize the removable element, which is the edge of the spatulas apt to process coated sheet 1 1.

The details seen in Figure 3 allow to highlight the technical solution according to the invention. Indeed, such cords must exhibit some features so that the edge 130 can adequately guarantee the satisfaction of all the above-mentioned performance.

These are therefore essential constructive details conceived for the particular application.

The edge 130 thus appears as a cord of a certain thickness, which is necessary to give it a sufficient margin of compressibility. In Figure 3, it is noticed that a homogeneous, non-filamentous material, in which an isotropic structure is visible, constitutes the inside part of the pieces of the cords: the thickness is therefore due to the fact thai these cords may be predominantly made of a deformabie material with excellent elastic properties.

The inner part of the cord, which in terms of volume clearly represents the major part, is therefore essentially dedicated to the implementation of elastic deformabiiity features.

There are many materials that can guarantee this feature, also because it is possible to choose materials whose only further feature is to be resistant to high temperatures. In fact, the other essential features for the cord can be obtained by adding other materials with which to realize the outside of the cord.

In Figure 3, it is very evident how the outer part of the cord samples is made up of a layer made of filament fibers suitably woven, or interlaced. This outer layer is therefore very flexible so as to be able to support the squeezing of the cord, but at the same time it can give the cord the other required features.

In fact, the weave or interlacement that constitutes the outer layer of the cord include very rigid to traction fibers, highly abrasion resistant, and fibers made up of

lubricating materials.

For example, aramid or glass fibers give traction and abrasion resistance, while the use of graphite or teflon filaments, or fibers containing mineral oils, favors the reciprocal slide of the filaments, the good drainage of the coating material 1 which has to be removed (which does not easily cling to the cord), and its full recovery thereof.

The cord samples shown in Figure 3 are just examples and they show how gaskets with excellent elastic properties in the direction of squeezing can be made, using suitable materials that would be not sufficiently abrasion-free and rigid to traction (in fact, their isotropy would make them elastic even in traction). But such additional essential features can then be provided to the gasket by means of a suitable coating layer.

It is evident that, in some variants, it is possible to provide resistance to traction deformation by providing also one or more central rigid filaments placed within the cord. This is a possible variant, although the outer coating made of rigid materials is preferable since the latter is also necessary to confer wear resistance to abrasion. In addition, the outer layer of the cord, made with a variety of fibers of various materials, allows to obtain coatings in which it is also possible to optimize the repellency to the coating material 1 .

A machinery 100 for the coating of a continuous sheet metal with a layer consisting of a metallic or predominantly metallic coating material made according to the teachings of the present invention has all the prerogatives necessary to make it broadly successful in the industrial landscape as if allows to perform a wide variety of workmanships. In fact, such workmanships, in the variety of thicknesses and in size, are present in a number of industrial chains, and they are often an important part of such industrial chains. Therefore, the machining lines must be capable of satisfying many types of orders with very good quality (hopefully better than the qualities obtainable by the known techniques), reducing the times and the risks associated with the occurrence of defective realization as much as possible.

Ultimately, the machinery 100 for the coating of a continuous sheet metal with a layer consisting of a metallic or predominantly metallic coating material made according to the teachings of the present invention, when compared with known systems, appears ίο be an improvement over the main criteria of comparison: speed, quality of result, economy, flexibility and reliability of the process.

The invention described above can be implemented in many variants, which may be especially related to technological evolution, both in terms of materials, and as regards the technology for the controls. Such variants may offer further advantages over the aforementioned ones and may be implemented by the man skilled in the art without thereby departing from the invention as it results from this description and from the appended claims herein.

!n addition, each element can be developed in different shapes or sizes; and the invention itself can be implemented in a partial manner as many of the details described are replaceable by technically equivalent elements.

Specifically, and as already mentioned, particular technologies relating to the use of specific materials are not a characterizing part of the present invention. Therefore, if in the future materials more advantageous than those indicated in preferred implementations are available, or if current control-related technologies would evolve to better apply the various required controls (better performance or better value-for- money), further improvements could be introduced in the implementation of the present invention without altering its inventive nature and the principles that have inspired it.

Finally, the disclosed invention lends itself to incorporating and supporting further arrangements aimed at further enhancing the described machineries, making them more robust, increasingly cost-effective and capable of producing continuous coated sheets with ever-improved quality; such arrangements, which are not dealt with in this description may be described in further patent applications associated with this invention.