WO2008059321A1

WO2008059321A1 - Method and device for the cleaning treatment of metallic strips, drafts and/or draw pieces

Info

Publication number: WO2008059321A1
Application number: PCT/IB2007/000389
Authority: WO
Inventors: Lorenzo Licitra; Fabio Leonardi
Original assignee: Tenova S.P.A.
Priority date: 2006-11-15
Filing date: 2007-02-19
Publication date: 2008-05-22
Also published as: EP2087150A1; ITMI20062189A1

Abstract

A method for the surface preparation of metallic strips, drafts and/or draw pieces comprises the treatment of the surface of the metallic strip, draft and/or draw piece by the ejection onto the strip of jets of fluid, at a high velocity, with a slope of the axis of the fluid jet with respect to the perpendicular to the surface of the strip struck, of less than 60°.

Description

METHOD AND DEVICE FOR THE CLEANING TREATMENT OF METALLIC STRIPS, DRAFTS AND/OR DRAW PIECES

The present invention relates to a method and device for the cleaning treatment of metallic strips, drafts and/or draw pieces, in particular for the surface treatment of metallic strips, drafts and/or draw pieces which are then subjected to subsequent processing phases or directly commercialized.

The production ^• of fine sheets and metallic strips envisages various processing phases which ^■ require cleaning treatment to remove undesired substances which can negatively, influence the final quality of the product or jeopardize its processing in the intermediate phases of the production process. The surface of laminated strips is typically contaminated by oils, greases and previous processing residues such as metallic powders or protective layers. The performances of the types of treatment applied to these strips (pickling, deposition of protective metallic layers, conversion and/or coating) mainly depend on the cleaning degree and surface preparation of the strip.

The surface treatment of metallic^' materials is very widespread in the production technique of numerous sectors. Strips, drafts and draw- pieces, in combined or specific lines, can, as- already mentioned, be subjected not only to mechanical and thermal treatment, but .also to pickling, cleaning, metallic coating or varnishing. These types of treatment are generally effected in production lines which comprise separate sections in which the subsequent treatment phases are carried out with various fluids. In all physico-chemical surface treatment processes of metallic materials there is therefore the necessity, in order to obtain a high-quality product and/or to avoid the excessive consumption of chemical products, to remove, with appropriate cleaning systems, substances from the surface, which can interfere with the subsequent treatment phases in continuous or unacceptable substances on the surface of the end-product.

The role of these preparation sections is critical above all when the production envisages particularly high quality standards of the end-product.

In any case, however, if, on the one hand, specialized preparation is preferable as it potentially induces the best preparation of the metallic surface for subsequent .treatment, on the . other hand, the complications due to different methods inserted in the same line raise the costs of maintenance and consumption materials, make the lay-out of the line more complex and consequently costly and require skilled workers for an optimum^' functioning of the line. The effective cost of these lines with specialized preparation sections is also increased due to the high environmental impact:^' the cleaning and preparation tanks, in fact, often contain solvents, acids, surface-active agents or other products which require particularly complex recovery systems, further increasing the costs indicated above linked to the construction of the line and its management and maintenance.

This has led to the search for an economically convenient surface preparation system, i.e. cleaning and heating, of metallic materials in continuous treatment lines .

For several years now, various attempts have been made at avoiding the above drawbacks . Numerous types of treatment are effected for many processes, such as for example, degreasing, pickling and chemical passivation, using liquid solutions in contact with the surface of the material, the changing of the solution is important and spray treatment extremely effective, even if the less effective immersion system is preferred to this method, above all for reducing the complexity of the installations necessary for preventing the leakage of potentially harmful liquids or vapours.

Ih surface treatment it is suitable and often necessary to preliminarily remove the residual oil of previous processings or applied as a protection, also often containing powders, from the surface of the metallic metal to be subjected to surface finishing treatment. The process traditionally adopted for this purpose uses an aqueous solution of chemical degreasing agents, sent from nozzles assembled on spray ramps on the surface treated, or contained in tanks in which the material is immersed, possibly also subjected to electrolytic treatment. The oil is sometimes removed in various stages, also extremely complex and costly such as for example in the system described in the patent GB 2003181 (1978) where the traditional degreasing section of a strip is preceded by a section in which solvents such as chloro-fluoro-carbides or trichloro-ethane, are used, as well as vapour jets for dispersing the oil and heating the material treated. Complex and onerous preparation, control and recirculation systems of the degreasing solution are necessary for the functioning of traditional systems and an onerous neutralization treatment of the potentially polluting chemical solutions adopted, is also required for environmental compatibility.

Pickling of the oxidized metallic material is necessary for removing the surface layer which is non- homogeneous with the base alloy. In continuous treatment lines, the pickling process is effected with acid solutions at temperatures normally ranging from 40 to 104⁰C, depending on the material treated, the acids used and the duration of the treatment. If the material is cold and dry when it enters the pickling section, for a few seconds during which the surface is still not wet as far as the porosity and the solution in contact with the surface is cold due to contact with the material which has not yet been heated, the chemical pickling reactions are not effectively completed. It is often advantageous to remove substances, such as for example metallic powders, from the surfaces to be treated, which negatively influence the pickling process or react chemically, uselessly consuming costly acids, and it is convenient to heat and humidify the material before the acid treatment to allow the immediate efficacy of the subsequent pickling, as heating the acid pickling solution to a high temperature to bring the material to the useful process temperature, is onerous due to the necessity of using materials which are corrosion- resistant, delicate and expensive.

In continuous surface treatment lines of metallic materials, after treatment with chemically active fluids, a washing section is always present, normally consisting of various feeding steps of washing water in countercurrent with respect to the movement of the material, to reduce the need for water which, as this is polluted after use, must be treated in an effluent neutralization plant. The washing water is normally heated for a better efficacy due to the reduced viscosity as a result of the higher temperature and to facilitate the subsequent drying of the material, normally effected with heated air blown onto the surface.

These surface treatment methods are traditionally effected with spray or immersion systems (even multi- step) which exploit the detergent action of solutions and baths containing chemical agents.

The detergent action of the solutions and baths, generally heated to suitable temperatures, can be assisted by mechanical actions such as brushing. Other methods are based on processes of the electrolytic or ultrasonic type.

Within the iron and steel and metallurgic field, particularly sophisticated methods such as ultrasounds are only occasionally applied due to their . high installation and running costs.

As mentioned above, processes of the chemical type, which are particularly widespread, have a ^' significant associated cost especially .considering the prices of the raw materials necessary for their functioning and all the recycling and abatement systems of the substances with a high environmental impact which are used and/or generated.

In traditional cleaning systems, capable of obtaining excellent results in terms of the removal of contaminants, the complexity of the plant is extremely high, especially if mixed systems are used (for example chemical/electrolytic/mechanical) .

The complexity of the traditional systems, inherent to the technology used, can be only marginally simplified, also against considerable reductions in the performances requested, when only a refining action is desired, with less restrictive • final contamination^' requisites allowed. Methods such as that described in US patent 4252572

(Shaming) start from the use of vaporized water by spraying, vapour-propelled, to which consistent quantities of chemical agents can be added. The system mostly used water in the liquid state. Vapour has the sole function of heating and increasing the pressure of the liquid stream which, accelerated, forms the cleaning medium.

Like all hot water spray cleaning methods, consistent flow-rates are required and there is the disadvantage of having to provide for the discharging and/or recycling of huge quantities of water contaminated by process -oils and possible detergents, consequently without a real saving in the waste treatment sections.

US patent 4569635 (Nicodemus) also allows a heated and pressurized liquid stream to be obtained, using the propelling action of vapour which is almost completely- condensed into a liquid stream. The device was proposed in US ^Λ635 without any specific indications as to its use for cleaning purposes. Only recently have technical solutions been described, which renounce water in the liquid state as a cleaning medium in favour of vapour. These solutions use vapour mixed with water as cleaning medium, projected onto the strip at a high velocity by means of nozzles. The efficacy of the use of overheated water jets and vapour jets for the cleaning and heating of materials is in fact known, but the use of these means does not normally^' take place in continuous treatment lines due to the difficulty of containing the vapours which are formed. Water vapour jets,^' in fact, entrain with them the adjacent layers of the atmosphere surrounding the jet, with a movement effect of said atmosphere and the vapour diffusion which is difficult to control.

In the traditional^' configuration of systems using fluid jets for the surface treatment of metallic strips, drafts or draw pieces, one or more series of nozzles are arranged in one or more perpendicular planes with respect to the direction of the movement of the material. The jets of fluid which contemporaneously strike the whole width of the surface, are normally tilted with an axis having a component parallel to the surface struck parallel to the direction of the movement of the material. With this configuration, the fluid which reaches the surface of the material flows mainly longitudinally onto the surface struck, accumulating on the surface itself mixed with what is possibly removed, until it falls by the effect of gravity, possibly with the help of mechanical means such as, for example, wiping rolls or the like. The average concentration of the substance removed in the fluid which remains on the surface approximately corresponds to the ratio between the quantity of substance removed and the flow-rate of the fluid which strikes the surface. If the treatment is effected with more than one series of parallel jets, most of the force of the jets of a series must be used for moving the fluid sent onto the surface by the adjacent series of jets. ^■ _. . .

Furthermore, in the traditional configuration, the jets of fluid, orientated with an important component parallel to the direction of the movement of the material, entraining the adjacent layers of the surrounding atmosphere with it, dynamically create in the environmental atmosphere around the material, a pressure difference in the movement direction of the material which is such as to induce the suction of external atmosphere and the respective discharge of vapours at least through the openings for the passage of the material into the containment element of the jets, which are normally not airtight and not very suitable for containing the vapours which tend to be discharged. This ventilation effect is extremely strong in the case of gas or vapour jets, with considerable technical difficulties for containing the vapours used and/or those which are formed during the process; although the efficacy of the use of jets of overheated water and vapour jets is well- known for the removal of oil and for the cleaning and heating of materials, the use of these means is very rarely adopted in continuous treatment lines due to the difficulty of containing the vapours. In the traditional configuration of treatment systems with fluid jets of materials which have a high extension in length, in continuous lines, it is difficult to avoid a difference in treatment between the surfaces depending on their position with respect to the direction of the force of gravity: on the upper sides, the fluid carried by the jets remains much longer and with much higher average thicknesses than on the sides otherwise orientated as the removal of the fluid from the surfaces prevalently takes place by gravity. The objective of the present invention is to identify a more flexible cleaning system, with a reduced environmental impact, capable of adapting its capacities (and operating costs) to the actual requirements of the subsequent processings and quality of the end-product, overcoming the drawbacks of the known art.

A general objective of the present invention is therefore to solve the above disadvantages in a simple, economical and particularly functional way, particularly in the field of processes in continuous for the treatment and/or processing of metallic strips, drafts and/or draw pieces, in which it is necessary or useful, in one or more phases, to clean and/or heat and/or humidify the metallic product in the processing phase.

It has been surprisingly found that, by wisely exploiting an aggressive agent, such as water vapour, possibly with the addition of a detergent product, it is possible to provide a general method for the surface preparation of all types of metallic strips, drafts and/or draw pieces in continuous production and/or treatment lines of metallic strips, drafts and/or draw pieces which require, in one or more phases, the cleaning and/or heating and/or humidification of the surface of the material treated.

An object of the present invention therefore relates to a method for the surface preparation of metallic strips, drafts and/or draw pieces which envisages the surface treatment of the metallic strip, draft and/or draw piece by the ejection onto the strip of a jet of fluid consisting of vapour mixed with water, at a high velocity with a slope of the axis of the jet of fluid with respect to the perpendicular to the surface of the strip struck, of less than 60°.

In the present text, the term ^Mfluid" refers to water vapour mixed with a varying quantity up to a 1:1 weight ratio of water, optionally containing surface- active agents or any other product having a detergent function.

In particular, the method according to the present invention is carried out at a vapour pressure ranging from 1 to 20 absolute bar.

The method according to the present ^■ invention is also preferably carried out at a vapour temperature ranging from 100° to 250⁰C.

The method according to the present invention is preferably effected with a quantity of water ranging from 0 to 100% of the quantity of vapour (mass in kg) .

The rate of the fluid jet preferably varies from 0.2. Mach to supersonic velocities.

In particular, the method according to the present invention envisages that the jet of fluid is preferably biphasic due to the presence of water vapour and drops of liquid.

The jet of fluid, moreover, can be integrated with additives to improve the efficiency of the preparation process, such^' as chemical detergents, chemically active solutions, etc.

In the surface preparation method of metallic strips, drafts and/or draw pieces (long) according to the present invention, the jet of fluid consisting of water vapour mixed with water is used in at least one phase of the continuous production and/or treatment line of metallic strips, drafts and/or draw pieces, as an agent for the heating, cleaning, humidification, degreasing, elimination of surface agglomerates and/or control ^'of the surface humidity.

The present invention essentially consists in the particular distribution mode of the jet of treatment fluid which can be sent by means of blade ejection devices or nozzles which always generate a jet of fluid on the surface of the material in movement. As a result of this distribution, when it is on the surface of the strip it is pushed in a transversal direction with respect to the movement direction, preferably along the shorter run, either beyond the surface edge, or away from this, pushed by the rebounding component of the fluid jet which abandons the surface. The flow should preferably cover the whole width of the surface to be treated of the material in movement. At all moments, the streams of fluid on the surface treated flow directly towards and beyond the edges or the rebounding component of the fluid moves away from the surface. The procedure can be repeated with several jet systems, possibly transversally offset so as to homogeneously immerse the surface for the whole of its width. The areas struck by the jets are preferably partially superimposed, in a transversal direction with respect to the movement direction, to obtain a homogeneous covering of the surface. In the case of a nozzle ejection system, the component of the jet axis, parallel to the surface struck, forms, with respect to the movement direction of the material, an angle which is preferably closer to the right angle, the higher the ratio between the velocity of the jet and that of the material treated. The preferred angle is that whereby the jet fluid diverted by the impact with the surface flows thereon following the shortest run towards the nearest edge. The angular shift of the component of the jet axis parallel to the surface struck from the perpendicular to the movement direction can be up to 60°, but preferably lower than 45°. The direction of the jet axis with respect to the perpendicular on the surface struck is, as already indicated, tilted by an angle ranging from 0° to 60°.

If the impact effect is privileged, for example by the removal of substances adhering to the surface, the angle preferably ranges from 8° to 15°, whereas, if the transporting of the fluid onto the surface is privileged, for example by chemical treatment, rinsing or heating, the angle is preferably higher than 15°.

The flow-rate and velocity of the jet depend on the dimension of the nozzles and their feeding pressure. These parameters, as also the fluid which forms the jet depend on the type of treatment to which the material is subjected, and they are established in relation to the process requirements with the same procedures used for the definition of the traditional spray treatment systems or with vapour or gas jets, respectively.

With the method according to the present invention, the components of the direction of the jet parallel to the movement direction of the material are modest and the containment of the sprays can be effected in a much simpler, economical and effective way than with the traditional configurations of the nozzles where the direction of the jets, prevalently parallel to the movement of the material, inevitably induces, in the containment element, currents in the atmosphere around the material, directed towards the inlet or outlet openings of the material, which are such as to cause external air suction and the leakage of vapours, if complex and onerous sealing and/or suction and vapour abatement systems have not been installed.

A further object of the present invention relates to an ejection device of a jet of fluid for the surface preparation of metallic strips, drafts and/or draw pieces, by means of nozzles and/or blade ejection devices, which comprises a fluid feeding system, consisting of a feeding collector, the feeding collector being equipped with at least one vapour inlet, at least one liquid inlet, and at least one feeding opening of the fluid to an accelerating duct which has at least one outlet opening.

The device envisages that one or more liquid inlets are preferably equipped with distributor nozzles capable of vapourizing the liquid in the form of droplets within the vapour stream. The accelerating duct is also delimited by beaks and side closing elements.

The structural and functional characteristics of the present invention and its advantages with respect to the known art will appear even more evident from the following description and enclosed drawings, in which:

Figure 1 represents an embodiment of the device according to the present invention in a schematic perspective view, whereas Figure 2 is a schematic section. Figure 3 represents a detail of figure 2 seen from A.

Figure 4 shows a simplified flow chart relating to the installation of the device according to the applicative form of figures 1 and 2. Figures 5 and 6 relate to embodiments of the device according to the present invention, whereas figure 7 shows a cleaning example obtained on the test bench using samples of cold laminated steel sheet.

With reference to figures 1 and 2, the device (20) consists of a vapour feeding system (21) , consisting of a feeding collector (1) , preferably having a circular section. Said feeding collector (1) is equipped with one or more vapour inlets (2) and one or more liquid inlets (3), preferably equipped with distributor nozzles (4) capable of vapourizing the liquid in the form of droplets inside the vapour stream. The feeding collector (1) is also equipped with one or more openings (5) through which the fluid is fed into an accelerating duct (6) delimited by two beaks (7) and side closing elements (8) . The beaks (7) and side closing elements (8) can be fixed in various ways to the collector, and equipped with blocking and registration elements for guaranteeing the correct assembly and regulation of the reciprocal position (see Figure 3, view "A") . In the accelerating duct (6) , there is a strong increase in the fluid rate. As the fluid crosses through the duct, in fact, it passes from the pressure value inside the feeding collector (1) to the lower pressure value in force in the outside environment. An expansion takes place with the consequent transformation of the enthalpic jump into kinetic energy of the fluid. The accelerating duct (6) can be conformed so as to allow supersonic velocities of the fluid to be reached on the outlet opening (9) of the same duct (6) .

The jet (10) , which is preferably biphasic due to the presence of liquid droplets, coming from the outlet opening (9) strikes the strip (16) at a high velocity, thus effecting its cleaning, rinsing and heating action.

The device represented in Figures 1 and 2 can be housed inside treatment chambers having a horizontal or vertical development, equipped with guiding and supporting elements for the moving strip (preferably rolls) both inside and outside the chamber itself. Said chambers can be equipped with openings for the inlet and outlet of the moving strip, as well as specific ducts for the suction of the vapours to be evacuated, and ducts for the draining of the liquid phase which is formed in the chamber during functioning.

Depending on the installation requirements, it is possible to select various positioning modes of the device according to the present invention in the space, for example with a longitudinal axis having an angulation different from 90° with respect to the running direction of the strip.

Furthermore, as specified above, the orientation of the jet can be such as to strike perpendicularly with respect to the surface of the strip to be cleaned or washed, or form an angle therewith which is less than

90°, as in the example of Figure 2, or greater than 90°.

The chamber in which one or more devices are inserted can be subjected to appropriate vapour suction. Furthermore, septa can be introduced into the chamber, which are shaped so as to suitably convey the streams which are abandoning the surface _. of the strip, facilitating their evacuation. In Figure 4, a possible simplified flow-chart is represented, relating to the installation of the device of figures 1 and 2.

The vapour fluid is fed to the circuit by means of the interception valve (11) and the flow-rate of the vapour fed can be verified by means of a flow-rate meter

(12) . The regulation unit (13) allows the pressure of the fluid to be varied inside the feeding collector (1) .

Different vapour flow-rates correspond to different pressures, read on the pressure meter (14). The liquid, which must be available under higher pressure conditions with respect to the operating values of the feeding collector (1) , is admitted to the circuit of the device by means of the interception valve (15) . The regulation unit (16) allows the pressure to be varied in one or more liquid inlets (3) through which the .liquid is introduced into the feeding collector (1) . The pressure in the liquid inlet (3) can be read on the meter (18) . The liquid inlets (3) can be equipped with one or more vapourizing nozzles (4). The flow-rate at the liquid inlets (3) , and consequently at the feeding collector (1) can be read on the meter (17) . Example

As operating example, an experimental test bench was developed in which various ejection solutions were tested, with both nozzles and blade ejection devices (see Figure 5) .

A blade-type vapour ejection device on the test bench is illustrated in Figure 6.

The subsequent Figure 7 shows a cleaning example obtained on the test bench using samples of cold laminated steel sheet.

The particularly effective and uniform effect of the blade ejection on the area treated, can be observed.

The method and device according to the present invention therefore adopt the vapour-mixed-with-water technology as cleaning, heating and rinsing means, ejected onto the strip by means of a fluid blade.

They have the fundamental advantage of obtaining a high cleaning uniformity of the strip by exploiting the high impact energy of the water droplets inserted under thermodynamic conditions of disequilibrium inside the ultra-high velocity vapour stream.

A further advantage consists in the fact that the possible detergents can be added in minimum quantities, reducing the problem of environmental impact.

Furthermore, the device according to the present invention, without moving parts, without parts in contact with the strip and which does not require recirculation plants and solution treatment, is extremely simple and economical, reducing both investment costs and operating and maintenance costs.

The system according to the present invention, moreover, operates under stable conditions (temperature and vapour pressure, quantity of water and possible detergents added) and defined only by velocities and dimensions of the strip. This implies a reduction in the controls necessary for the functioning, expertise and number of line operators assigned thereto. c Furthermore, the absence of significant liquid accumulations, together with the reduced dimensions and weight, give the system according to the present invention the further advantage of being able to be applied to any plant configuration (also vertical) . This reduces space requirements of the whole line in new embodiments and, in the case of modernization, it is possible to introduce a cleaning section having a reduced encumbrance capable of exploiting the spaces available. The limited weight reduces interventions on the supporting carpentry and civil works. The method and device according to the present invention allow considerable advantages to be obtained in producing cleaning and degreasing systems, substituting current systems which adopt chemical solutions or integrating these as pre-treatment, with a saving of chemical products with respect to both the process and neutralization treatment of the chemical solutions contaminated by oil and the necessity of heating the chemical solution.

The method according to the present invention, inserted upstream of the chemical pickling, cleans, heats and humidifies the surface of the material, allowing an effective and immediate action of the pickling solution in the subsequent section. As a result of the reduced necessity of heating the material, the other conditions remaining the same, the temperature of the pickling solution, which is chemically extremely aggressive, can be lower making it chemically less aggressive with respect to the plant components and reducing the loss of acid by evaporation. The method and device according to the present invention, inserted upstream of an existing pickling section allows, with the same chemical pickling conditions, an increase in the process rate with a consequent increase in the productivity.

The method according to the present invention can advantageously substitute or integrate the traditional washing of the material after any treatment, also effectively heating the material to facilitate its drying. In many cases it can also avoid the use of costly demineralized water for the washing. The method and device can also be advantageously applied for treating surfaces with chemical solutions or with water, when a high skimming rate extended over the treated surface is useful, with a rapid change of the fluid used. This is the case for example of the pickling, with an acid solution, of strips made of different steel alloys which, by using the method and device according to the present invention, can be effected with the same efficiency in more reduced spaces or with the same space with a higher rate^' or respectively with a less aggressive chemical solution, with respect to the traditional spray or immersion systems.

By applying the method according to the present invention, on the other hand, the impacting fluid moves away what has been removed, with the jet of fluid which progressively brushes the surface transversally beyond the edges of the material treated, or removes it from the same surface using the rebounding action of the fluid.

The power of the jet is mostly available for removing substances from the surface rather than for moving the fluid of parallel jets, as occurs in the traditional system. The velocity with which the fluid, together with what is possibly removed, abandons the surface, is close to the velocity of the jet, when the ratio between the mass flow-rate of the jet and the mass removed from the surface is high, as is normally the case. The method according to the present invention is therefore much more efficient than the traditional system for cleaning the surface treated or for heating, exploiting the vapour condensation heat, or respectively causes a higher rate of the chemical reactions between the fluid and surface due to the rapid removal of the reaction products, which tend to inhibit the chemical reaction when they are contained in a high concentration in the limit layer of solution adhering to the surface. With the method according to the present invention, the fluid jet produced by nozzles is orientated so that the component parallel to the surface covered is prevalently transversal with respect to the movement direction of the material. This configuration has the advantage that the streams, which are formed in the environment surrounding the jets, tend to form closed rings in transversal planes and the vapours and rebounding sprays can be easily withheld with simple containment and conveyance elements. Furthermore any possible detergent products added can exploit this "stagnation" condition to exert their action better.

Both for the nozzles, and to a greater extent for the blade ejection device, it may occur that the removal of the fluid takes place in the rebounding direction of the jet on the surface, removing the pollutants therefrom.

The nozzle device may consequently in some cases be more suitable for effecting a chemical treatment or application of detergent, whereas the blade ejection device may be more appropriate for effecting energetic washing operations.

The method and device according to the present invention therefore fully exploit the efficiency of the use of a jet of fluid for the surface treatment of materials in continuous lines, with the economical advantage of lower investment, management and maintenance costs, and they also provide a better production quality obtained with the greater treatment uniformity.

As already specified, the dimensions of the device according to the present invention can also be reduced to allow it to also be inserted in existing production lines, to improve the efficacy of the treatment processes and/or with a significant saving of chemical products, improving the environmental compatibility due to a smaller charge of polluting products.

The main advantage of the method according to the present invention is consequently the versatility of the system. It is in fact used in practically the whole production cycle. The high-velocity vapour, in particular not completely dry vapour, does in fact allow an excellent removal of solid residues such as dirt, metallic powders, scraps and protective waxes attached to the surface. The combined effect of the temperature and water also allow the fats, viscous materials and liquids to be dissolved and/or washed away.

The vapour heat also allows the surface preparation method according to the present invention to be used as a preheating method of the metallic strip, draft and/or draw piece when, in order to accelerate the subsequent process, the metallic product being treated must be heated.

The particular application of water vapour, according to the method of the present invention, on the surfaces of the material treated allows the vapour condensation heat to be effectively exploited for the heating and mechanical energy of the vapour and' water contained in the vapour sent onto the material moving through the nozzles positioned and orientated in a specific way for progressively brushing the surfaces transversally with respect to the movement direction, thus effectively removing what is present on the surface.

Finally, the control of the vapour humidity degree and the control of the heat transferred, allow the surface to be optimized preparing it for both processings in wet phase, such as pickling or electrolytic depositions of elements such as tin or zinc, and also for processings where the surface must be strictly dry such as the deposition in molten phase of the same elements or other components. The method according to the present invention is also extremely advantageous from the point of view of pollution both in the operating zone and, more generally, with respect to environmental pollution: the water- vapour-based solution is in fact particularly environmentally friendly. The method according to the present invention does not require the neutralization of particular "added" chemical agents, but only of those extracted from the surface of the metal treated, which are in any case present. The selection of possible additives to the water vapour is also effected in relation to the environmental tolerability of these.

A further advantageous aspect of the method according to the present invention is that it allows the surface preparation/cleaning process to be standardized, in practice, for each phase of the finishing process of metallic strips, drafts and/or long draw pieces in continuous production lines and/or treatment. The standardization thus obtained improves the optimization of the line configuration, it allows savings in consumption materials, maintenance procedures, environmental retreatment plants, in the investment cost associated with the purchasing of the overall line. Finally, the standardization of the surface preparation method allows the line to be run with less specialized personnel and exposed to a healthier environment.

In short, for illustrative purposes, the method and surface preparation device according to the present invention can be used in the following applications: in a pickling plant of continuous metallic strips, drafts and/or draw pieces, where a metallic material heated and humidified as far as the porosities has a much higher reactivity, at the beginning of the chemical treatment, with respect to a dry and/or cold material. The application of the method according to the present invention, upstream of the chemical treatment, allows a reduction in the pickling temperature and consequently a lower loss of acid due to evaporation and/or a greater pickling rate with the same treatment length. The inlet of the already hot material also correspondingly reduces the heating capacity of the acid solution, which is normally effected with costly and relatively delicate plant installations.

The surface preparation method and device according to the present invention can also be used in a surface treatment plant of continuous strips, drafts and/or draw pieces, wherein the process envisages a final washing. The use of the method according to the present invention is in fact convenient as it allows an optimum cleaning of the surfaces with the condensate of the vapour used, which normally has better characteristics than the washing water, and a good heating of the material which facilitates the subsequent drying, with an overall lower cost, giving the same result. The surface preparation method and device according to the present invention can also be used in a plant where it is necessary to remove substances deposited on the surface which can interfere in subsequent treatment phases . The use of the method according to the present invention does in fact allow good removal in a reduced space and with a modest cost with respect to traditional systems which obtain an analogous result.

Finally, it should also be noted that, by availing of different sections which can be equipped with nozzles and/or blade ejection devices, the various cleaning sections can be adapted according to the requirements of the production cycle (for example: hot or electrolytic zincing, varnishing, continuous annealing and/or pickling), for the production of a specific product.

Claims

1) A method for the surface preparation of metallic strips, drafts and/or draw pieces which comprises treatment of the surface of the metallic strip, draft and/or draw piece by the ejection of jets of fluid onto the strip, at a high velocity, with a slope of the axis of the fluid jet with respect to -the perpendicular to the surface of the strip struck, of less than 60°.

2) The method according to claim 1, characterized in that it is carried out at a vapour pressure which varies from 1 to 20 absolute bar.

3) The method according to claim 1, characterized in that it is carried out at a vapour temperature ranging from 100° to 250⁰C. 4) The method according to claim 1, characterized in that it is carried out with a quantity of water ranging from 0 to 100% of the quantity of vapour (mass in kg) . ^"5) The method according to claim 1, characterized in that the jet of fluid is biphasic due to the presence of water vapour and liquid droplets.

6) The method according to claim 1, characterized in that the velocity of the jet of fluid varies from Mach = 0.2 to supersonic velocities.

7) The method according to claim 1, characterized in that the fluid jet is integrated with additives such as chemical detergents, chemically active solutions, etc. 8) The method according to any of the claims from 1 to 7, characterized in that the fluid jet of vapour mixed with water is used in at least one phase of a continuous production and/or treatment line of metallic strips, drafts and/or draw pieces, as an. agent for heating, cleaning, humidification, degreasing, the elimination of surface agglomerates and/or control of the surface humidity. 9) An ejection device of a jet of fluid for the surface preparation of metallic strips, drafts and/or draw pieces, by means of nozzles and/or blade ejection devices, which comprises a fluid feeding system, consisting of a feeding collector, the feeding collector being equipped with at least one vapour inlet, at least one liquid inlet, and at least one feeding opening of the fluid to an accelerating duct which has at least one outlet opening.

10) The device according to claim 9, characterized in that it envisages that one or more liquid inlets be equipped with distributor nozzles for the vapourization of the liquid in the form of droplets inside the vapour stream.

11) The device according to claim 9, characterized in that the accelerating duct is delimited by beaks and side closing elements.

12) The device according to claim 9, characterized in that the accelerating duct is shaped so as to allow supersonic velocities of the fluid to be reached on the outlet opening of the same duct.