ITMI952165A1 - EQUIPMENT AND PROCESS FOR THE CONTINUOUS COATING OF A SUBSTRATE, ESPECIALLY FOR COLD ROLLED STEEL TAPES - Google Patents

Abstract

Equipment for the continuous coating of cold rolled steel strips comprising several processing stations and a first by-pass section inserted between the first coating station and the second coating station to allow the tape to skip, if required, second coating station to go directly to the third coating station; a second by-pass section inserted between the second coating station and the third coating station to allow the belt to skip, if required, the third coating station to go directly to the output section. A method using such an apparatus is also described.

Description

DESCRIPTION of the industrial invention entitled:

EQUIPMENT AND PROCEDURE FOR THE CONTINUOUS COATING OF A SUBSTRATE, ESPECIALLY FOR COLD ROLLED STEEL TAPES.

TEXT OF THE DESCRIPTION

The present invention relates to an apparatus and a process for the continuous coating of a substrate, particularly for cold-rolled steel strips.

Processes and apparatuses for coating steel surfaces (substrates) with a wide range of metals currently known are commonly known in the art. The equipment and processes conceived for this purpose have various drawbacks. A drawback is the difficulty of being able to quickly change the coating process according to the type of material to be used for the coating, as well as varying the thickness of the coating itself.

A second drawback is the high power required to evaporate the metals in order to carry out the coating.

Another drawback concerns the finished product obtained as a result of the coating, ie the surface appearance and the resistance of the coating to detachment from the substrate. In this regard, for example, with the galvanizing processes currently in use (Sendzmir, electrolytic) during the mechanical processing of the steel strip, the final product has areas where the coating has detached from the substrate to attach itself to the processing tools.

Another problem of today's coating equipment is recognized in the accumulation of large quantities of coating material which is deposited not only on the steel strip to be treated, but also on the walls of the deposition chamber. This drawback is highly limiting in cases where the quantity of material evaporated per minute is very high (for example in the case of zinc). Ideally, it would be desirable to be able to deposit 100% of the evaporated material on the belt to avoid unnecessary material consumption.

Furthermore, the processes of the known art are scarcely ecological due to the correlated emission of fumes or gases, noises, waste water or sludge.

The aim of the present invention is therefore to provide an apparatus and a process for the continuous coating of cold-rolled steel strips which allows to obtain a high production flexibility.

Within this aim, an object of the present invention is to provide an apparatus and a process which allow to coat a substrate using most of the known metals and rapidly changing the type and thickness of the coating.

Another object of the present invention is to provide a coating apparatus and process which allow a better workability of the coated substrate.

Another object of the present invention is to provide an apparatus and a process for coating steel strips capable of producing strips with a surface coating of lesser thickness but of higher resistance.

Another object of the present invention is to provide a steel strip coating equipment that is easily expandable.

A further object of the present invention is to provide an apparatus for coating steel strips which allows the particular desired deposition process to be activated and deactivated separately without having to interrupt the working cycle.

Another object of the present invention is to provide a method for coating steel strips which is ecological from the point of view of emissions.

Not least object of the present invention is to provide an apparatus and a method of high reliability, relatively easy to manufacture at competitive costs.

This task, as well as these and other purposes which will become clearer in the following, are achieved by an apparatus for the continuous coating of a substrate, particularly for cold-rolled steel strips, characterized in that it comprises

- an inlet section adapted to bring the strip from atmospheric pressure to high vacuum;

- at least one pretreatment section connected in cascade to said inlet section and adapted to carry out the cleaning and ionic activation of the two surfaces of said belt;

-a first coating section, connected in series to said at least one pretreatment section and capable of depositing different materials on said belt;

-a second coating section, connected in cascade to said first coating section and suitable for depositing materials on said belt;

-a third coating section, connected in cascade to said second coating section and suitable for depositing further materials on said belt;

-an outlet section, connected in cascade to said third lining section and adapted to gradually bring said belt from the high vacuum condition to atmospheric pressure;

a first by-pass section being inserted between said first lining section and said second lining section to allow said belt to skip, if required, said second lining section to pass directly to said third lining section, and a second by-pass section being inserted between said second lining section and said third lining section to allow said belt to skip, if required, said third lining section to pass directly to said outlet section.

Further characteristics and advantages of the invention will become clearer from the description of a preferred but not exclusive embodiment of the apparatus according to the invention, illustrated by way of non-limiting example in the accompanying drawing, in which the only figure is a schematic diagram. blocks of the coating apparatus according to the invention.

With reference to the aforementioned figure, the apparatus according to the invention comprises a section 1 for the entry of the strip consisting of several chambers within which the strip passes; the chambers are pressurized at increasing vacuum values so that the belt passes from an atmospheric pressure (at the inlet of section 1), to high vacuum, at the outlet of the same section. Pressurization is obtained by means of suitable pumps, not shown in the drawing for simplicity. At the entrance and exit of each of these chambers, seals are arranged which are chosen according to the type of tape.

In cascade to section 1 there are four pre-treatment sections 3, 4, 5 and 6 suitable for carrying out the cleaning and ionic activation of the two surfaces of the belt before a subsequent coating process.

This pretreatment takes place by vacuum plasma cleaning and then by bombardment with a beam of ions from an ion cannon. The degree of vacuum in these sections is maintained by suitable pumps (also not shown in the figure).

In cascade to the four pretreatment sections 3, 4, 5 and 6 there are three coating sections in series. The first coating section is divided into four chambers 7, 8, 9 and 10 suitable for depositing different materials, under vacuum, on the steel strip passing through them. The four sections include the use of magnetron / sputtering technology. Also in these chambers the vacuum level is maintained by suitable pumps.

In cascade to this first lining section 7, 8, 9 and 10 there is a first by-pass section 11 suitable to allow the belt to skip, if desired, the subsequent lining section 12 divided into two chambers 12a and 12b.

In this second coating section 12 the deposition technology by means of electric resistances (Resistive-heating Evaporation) is used.

The vacuum level is always maintained by suitable pumps.

In cascade to the second lining section 7, 8, 9, and 10 there is a second by-pass section 13 designed to allow the belt to skip, if desired, the subsequent third and last lining section divided into the chambers 14, 15 , 16 and 17. In this third coating section the technology used is that which uses electron guns.

Also in these chambers 14, 15, 16 and 17 the vacuum level is maintained by suitable pumps.

Finally, in cascade to the third lining section 14, 15, 16 and 17 there is the outlet section 18, also constituted by a plurality of chambers with increasing pressure, where the strip is brought back from a vacuum condition to atmospheric pressure in a way analogous to inlet section 1.

With reference to the aforementioned figure, the use of the apparatus for coating a steel strip according to the invention will be described in conjunction with the process connected thereto.

Before entering section 1, the steel strip undergoes an initial cleaning phase carried out in an ambient atmosphere in order to remove oil, dust and various impurities. The device for carrying out this cleaning is not shown in the figure.

Subsequently the belt enters the inlet section 1 where it is carried by atmospheric pressure progressively to a high vacuum through a series of pressurized chambers. The reasons for bringing the belt to a high vacuum condition are the following:

1. greater control over impurities and contamination that could affect the final product;

2. the possibility of being able to evaporate / sublimate a large variety of metals at a lower temperature than that required at atmospheric pressure.

The level of vacuum required depends on several factors, some of which are the level of control over impurities, the functionality of some devices, the type of metal to be evaporated (this is because each metal has its own evaporation rate mainly proportional to the pressure) .

The desired vacuum level can be created using different types of pumps. Advantageously, the most used pumps for this purpose are the following:

1) mechanical pumps

2) turbine pumps

3) diffusion pumps

4) cryogenic pumps

5) steam jet pumps

In the embodied form of realization, mechanical pumps connected in series will be advantageously used in order to create the required degree of vacuum in successive stages. The vacuum degree is then progressively reduced. Since each pump works effectively only within certain pressure limits, to obtain the required vacuum level starting from atmospheric pressure it is necessary to have a series of pumps connected in series, even of different types. In this way the desired vacuum level is reached by going through a series of stages, where pumps suitable for that given vacuum level are used at each stage.

Advantageously, the following pumps are used in the inlet section 1:

- ring-liquid

- rotating piston

-Rotary Booster

- dry pumps

The vacuum level can be quickly changed according to the type of material to be treated.

The type of seals chosen at the inlet of the tape is determined by the type of tape (range of widths and thicknesses). Flat seals have proven to be suitable for tapes over 1mm thick while pressurized roller seals are best suited for moderate thicknesses (0.5-1.5mm) and so-called "wiper" seals are best for very fine materials with pressure sensitive surfaces.

The various vacuum chambers are sized according to the size of the open passages and the pressure difference between one chamber and the next. To facilitate the initial vacuum process, a slight overpressure is created in the first stage of the inlet section 1, where there is the greatest pressure drop, by injecting a neutral gas, thus decreasing the infiltration of air from the outside. At the first stage, where there is the greatest difference in pressure, the flow of gas from the environment is highly turbulent. The gas flow in the initial pumps is instead laminar and determines the amount of pumping (emptying) necessary for this first stage.

The free molecular flow determines the effects in the entry and exit with regard to the medium and high vacuum stages.

The most important factor in these areas is not the flow of gas into the openings but the release of gas from the steel strip. This release can be characterized by two factors: surface release and diffusion.

The surface release rates, mostly of water vapor, are 300-400 mbar / m2 at 20 C and 10-20 mbar / M2 at 100 C for steel.

Diffusion, particularly of hydrogen, is 2-6 mbar / m2.

So, the parameters that determine the gas release rate are:

1) the pressure level at the seals

2) the amount of surface in transit in the section per unit of time

3) the surface temperature of the steel

Furthermore, the gas release rate varies from one type of steel to another. For the design of the vacuum systems it is therefore necessary to measure the two release speeds. These release rates are affected by the cleanliness of the steel. Therefore, the following parameters were taken into account in the design of the vacuum chambers:

- cleanliness level of the belt surface

- dimensions of the belt

- belt speed

- drawing of the vacuum seals between one chamber and another.

After passing through the inlet section 1, the steel strip in continuous motion at 15-135 m / min is transported to the pre-treatment sections 3, 4, 5 and 6 where the strip is prepared in order to activate it.

There are various technologies for preparing the tape for the subsequent restoring phase.

The choice of which technology to use or which combination of them depends on the type of material to be subsequently laid, the quality of the coating and cost factors. Advantageously, the belt is cleaned under vacuum by plasma treatment (sputtering-etching) of the surface to eliminate a slight residue of passive oxide formed on the surface of the belt (20-40 Angstroms per face) and in order to activate the surfaces, i.e. to prepare them. This bombardment has the purpose of removing the atoms and oxide molecules from the surface of the belt and starting to activate the surface making it more suitable for bonding with the coating metals.

Subsequently, this activation, still within the pretreatment sections 3, 4, 5 and 6, is improved by a second ion bombardment procedure. With this treatment, the completely clean belt is further bombarded by a beam of ions from an ion cannon. The vacuum degree in these sections is of the order of 10E-1 mbar and is maintained by the following pumps:

- rotating blades

-Rotary Booster

-to diffusion of oil

This treatment will allow the steel strip to bond optimally with the materials chosen for the coating, avoiding any possibility of delamination.

After the pretreatment sections, the steel strip passes into the three casing sections in series. The tape in these sections can be coated with metals, oxides and nitrites. Furthermore, the coating can be carried out in alloy, multilayer and differentially between the two faces of the strip.

In the first cladding section, divided into four chambers 7, 8, 9 and 10, the use of magnetron / sputtering technology is envisaged.

In this process, positively ionized Argon is accelerated by an electric field towards the cathode covered with material to be deposited (sputtering). The transfer of energy from the ions to the metal (to be evaporated) causes a detachment of the atoms. These detached atoms are subsequently deposited on the substrate to be coated, that is the steel strip.

When using the magnetron, magnetic fields concentrate the flow of electrons on the material to be detached and increase the number of ions, thus increasing the deposition rates. The control over the evaporation rate is mainly carried out by controlling the density of the plasma cloud (ionization level) and the powers of the electric and magnetic fields.

The degree of vacuum varies according to the material used and is of the order of (10E-3) - (10E-6) mbar.

Advantageously, the pumps used are the following:

- to oil diffusion

- Rotary Booster

- with rotating blades.

At the exit of the first cladding section 7, 8, 9 and 10, the steel strip, whose path within the various sections that make up the cladding equipment is indicated in the figure, passes to the first cladding section. by-pass 11. This section allows you to select which path to take the steel strip, according to your needs.

At the exit from the first by-pass section 11, the steel strip therefore has the possibility of following two paths. The first path leads directly to the second lining section 12 divided into the two chambers 12a and 12b. In these two chambers, where a zinc deposition is carried out in the present embodiment, this deposition is performed using electrical resistances. The zinc is heated through said resistances until the atomic vibrations, that is the energy acquired by the atoms, is such as to make these atoms detach and evaporate.

Zinc is continuously introduced into the chambers and into the appropriate crucible from the outside. The material is first melted in an external oven with electric resistances and then, by virtue of a pressure difference between the oven and the chamber, rises and fills a special crucible (not shown in the figure) and then evaporates. The amount of zinc in the crucible is continuously measured by controlling the rate of replenishment of new material from the outside. The evaporation rate is controlled by varying the height of molten zinc in the external furnace and the degree of opening of the crucible.

The degree of vacuum maintained in the chambers 12a and 12b is of the order of 10E-3 mbar; the pumps used for this purpose are the following:

- Rotary Booster

- with rotating blades.

At the exit from the second coating section 12, the steel strip passes to the second by-pass section 13. This second section 13 has the possibility of allowing the steel strip to reach the third coating section 14, 15, 16 and 17 or to bypass said third cladding section to reach directly the outlet section 18. The connection with the third cladding section can occur directly from the first by-pass section 11 or from the second cladding section 12 through the second by-pass section 13.

The third coating section is composed of a series of modular chambers 14, 15, 16 and 17. In each chamber a deposition takes place by means of electron guns (Pierce type).

The electron gun is a known technology for evaporating and helping to deposit layers on a wide belt, given the possibility of being able to use multiple guns in parallel. In this case the crucible width corresponds to the belt width. Normally water-cooled copper crucibles are used, to ensure evaporation not contaminated by other materials. By oscillating the electron beams, the cannon can heat the material in a crucible until the desired evaporation temperature is reached.

The type of crucible chosen for the third lining section 14, 15, 16, and 17 has the particularity of having adjustable screens. By varying the degree of opening of these screens it is possible to direct the steam flow towards the substrate. This is very important both because it is possible to limit the amount of steam that is deposited on the walls of the crucible, and because it is necessary to be able to regulate the flow of steam according to the width of the steel strip.

The vapor, in passing through a smaller opening created by the screen, will acquire a greater speed, thus increasing its adhesion to the steel strip.

One of the characteristic data that are measured during an evaporation cycle is the efficiency of use of the molten material, that is the ratio between the quantity of evaporated material and the quantity of material deposited on the belt.

This efficiency depends on the shape of the screens, on the geometry that the tape has inside the chamber and on the distribution of the vapor density over the sources of this vapor.

These peculiarities, in combination with a series of heated barriers for the direct recovery of the material deposited on the walls, give great control over the evaporation itself with an efficiency of 98% of evaporated metal that is deposited on the substrate.

The material to be evaporated or sublimed is bombarded by a beam of electrons. These electrons, coming into contact with the atoms that make up the material in question, cause a vibration (thermal agitation) and an energy purchase of the latter high enough to be able to detach and then evaporate. Given the energy involved, this evaporation method is the most flexible in order to evaporate a wide range of metals.

Free electrons are produced in the cannon's cathode. The electron beam is formed by means of special electrostatic fields and focused and directed by means of electro-magnetic fields.

The characteristics of the electron gun are as follows:

- thermal energy is produced at the surface of the molten bath - energy consumption is very limited

- the control of the electron beam is carried out by means of electromagnetic fields

- the magnetic density is very high

- the material to be evaporated is not contaminated by the energy source (i.e. the cannon)

- efficiency is approximately 95%

- no thermal inertia

The control to guide the electron beams is done with a series of magnetic coils. The evaporation rate, and therefore the deposition rate, can be controlled constantly and quickly through the emitted radiation and energy density.

The electron gun deposition control principle is such that not only the evaporation rate but also the coating thickness can be measured. Finally, the times and the correlation between the latter and the thickness of the coating are analyzed. These signals are analyzed by a microprocessor which controls the power distribution and the deflection of the beam. Furthermore, the depth of the liquid bath, i.e. the quantity of molten material, is controlled by constantly feeding new material to be evaporated. The power required for each gun can vary between 60 kW and 500 kW.

Also in the third coating section the vacuum inside the different chambers, depending on the type of material to be treated, is maintained by the following pumps:

- with rotating blades

- Rotary Booster

- to oil diffusion

- turbomolecular.

The material, i.e. the evaporant, must be continuously introduced into the chambers of the first, second and third coating sections. This entry takes place mainly according to two methods:

- in solid blocks or bars

- in material already melted outside the chambers

As for the second method, it has already been mentioned for the zinc replenishment in the second coating section 12.

Instead, for all other metals, the metals will be introduced in solid bars or blocks.

At the outlet of the third lining section 14, 15, 16 and 17 or from the second by-pass section 13 there is the outlet section 18 equipped with the same sealing system as the inlet section 1. the tape passing through this section of output 18 gradually returns to atmospheric pressure.

The three distinct coating sections can be activated and deactivated independently of each other so as to achieve the desired type of coating on the steel strip or even coatings of different types on the same strip.

The possible options provided by the apparatus according to the invention are the following:

- no coating of the steel strip

- coating in the first coating section 7, 8, 9, and 10 with magnetron / sputtering technology

- coating in the second coating section 12 with magnetic induction technology

- coating in the third coating section 14, 15, 16 and 17 with electron gun technology

- cladding in the first cladding section and cladding in the second cladding section

- cladding in the second cladding section and cladding in the third cladding section

- cladding in the first cladding section and cladding in the third cladding section

- lining in the first lining section and lining in the second lining section and lining in the third lining section.

Throughout the process, a temperature control is carried out that reaches the web during the process (cleaning / pre-treatment with plasma and coating). During the deposition processes described above, the temperature of the web will increase due to several factors, the most influential of which is the heat of condensation. During the condensation of the vapor, each metal will give the steel strip a different amount of energy (mainly thermal). This of course could change the mechanical characteristics of the tape. In order to have a control over the temperature of the belt, many of the rollers 2 used to drag the belt through the different sections of the equipment (especially the rollers in the chambers of the coating sections) are equipped with internal liquid cooling, precisely to transfer the heat from the tape to the liquid thus avoiding the presence of internal tensions and / or deformations of the tape itself. The equipment provides for the use of large diameter rollers suitably cooled internally and with an adequate contact angle between steel strip and rollers. In this way it will be possible to have the desired temperature reduction for each roller and to control the temperature increase caused by the absorption of the condensation heat of the evaporant on the surface of the belt.

The different coating sections are electronically controlled through computerized systems for continuous monitoring of all the functions inherent to the different coating processes.

In practice it has been found that the apparatus and the method according to the invention fully accomplish the intended aim as they allow to coat a substrate using most of the known metals and rapidly changing the type and thickness of the coating.

Furthermore, with the apparatus and the method according to the present invention it is possible to obtain a coating thickness of a steel strip which is smaller than that obtained from existing apparatuses and processes, but with greater resistance, thus improving the workability of the coated substrate. . Another purpose of the present invention is to provide an apparatus and a coating process that allow better workability of the coated substrate.

The possibility of activating and deactivating the particular desired deposition process separately without having to interrupt the working cycle and the possibility of skipping unwanted process phases in order to shorten the process times give a high degree of flexibility both to the apparatus and to the process according to the invention. Furthermore, the apparatus and the method according to the invention are ecological since the process takes place under high vacuum and therefore there are no emissions of noxious fumes or gases, noises, waste water or sludge.

the device thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; furthermore, all the details can be replaced by other technically equivalent elements.

In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims (23)

CLAIMS 1. Apparatus for the continuous coating of a substrate, particularly for cold rolled steel strips, characterized in that it comprises - an inlet section adapted to bring the strip from atmospheric pressure to high vacuum; - at least one pretreatment section connected in cascade to said inlet section and adapted to carry out the cleaning and ionic activation of the two surfaces of said belt; -a first coating section, connected in series to said at least one pretreatment section and capable of depositing different materials on said belt; -a second coating section, connected in cascade to said first coating section and suitable for depositing materials on said belt; -a third coating section, connected in cascade to said second coating section and suitable for depositing further materials on said belt; -an outlet section, connected in cascade to said third lining section and adapted to gradually bring said belt from the high vacuum condition to atmospheric pressure; - a first by-pass section being inserted between said first lining section and said second lining section to allow said belt to skip, if required, said second lining section to pass directly to said third lining section, and a second by-pass section being inserted between said second lining section and said third lining section to allow said belt to skip, if required, said third lining section to pass directly to said outlet section. 2. Apparatus according to claim 1, characterized in that said inlet section comprises one or more pressurization chambers within which said belt passes. 3. Apparatus according to claim 2, characterized in that said one or more pressurization chambers are pressurized to increasing vacuum values, said pressurization being obtained by means of pumps connected in series. 4. Apparatus according to claim 2, characterized in that seals are arranged at the inlet and outlet of each of said chambers. 5. Apparatus according to claim 1, characterized in that four pretreatment sections are arranged in cascade to said inlet section. 6. Apparatus according to claim 1, characterized in that said first lining section is divided into four chambers, said chambers being kept under high vacuum by means of pumps. 7. Apparatus according to claim 1, characterized in that said second lining section is divided into two chambers, said two chambers being maintained under vacuum by pumps. 8. Apparatus according to claim 1, characterized in that said third lining section is divided into four chambers, said chambers being kept under high vacuum by means of pumps. 9. Apparatus according to claim 1, characterized in that said outlet section is constituted by a plurality of chambers with increasing pressure, adapted to bring said belt from the condition of high vacuum to atmospheric pressure, said chambers being each equipped, at the inlet and at the exit, of seals. 10. Apparatus according to claim 1, characterized in that said inlet section, said pretreatment section, said first, second and third lining sections and said first and second by-pass sections are internally equipped with rollers adapted to dragging the belt within said sections, said rollers being equipped with liquid cooling. 11. Apparatus according to claim 1, characterized in that it further comprises control means for said coating sections. 12. Apparatus according to claim 11, characterized in that said control means comprise a computer adapted to continuously process the functions inherent to said first, second and third coating sections. 13. Apparatus according to one or more of the preceding claims, characterized in that it comprises one or more of the characteristics described and / or illustrated. 14. Process for the continuous coating of a substrate, particularly for cold rolled steel strips, characterized in that it comprises the steps which consist of: - cleaning said belt at atmospheric pressure; -injecting said tape into an inlet section to bring it to a high vacuum condition; introducing said tape into a pretreatment section in order to clean it and ionically activate it; introducing said tape into a first covering section; introducing said tape into a second covering section; introducing said tape into a third covering section; and introducing said tape into an outlet section adapted to bring it back to the condition of atmospheric pressure; the passage of said tape in said first and / or second and / or third coating section being determined on the basis of the type of coating desired for said tape. 15. Process according to claim 14, characterized in that it comprises the step which consists in passing said tape in a first by-pass section inserted between said first lining section and said second lining section, so that said belt jumps said second coating section to pass directly to said third coating section. 16. Process according to claim 14, characterized in that it comprises the step which consists in passing said belt through a second by-pass section inserted between said second lining section and said third lining section, so that said belt jumps said third lining section to be directly injected into said outlet section. 17. Process according to claim 14, characterized in that in said pretreatment section said belt is subjected to plasma treatment and ionic bombardment. 18. Process according to claim 14, characterized in that the magnetron / sputtering coating technology is used in said first coating section. 19. Process according to claim 14, characterized in that in said second coating section the coating technology by means of electrical resistances is used. 20. Process according to claim 14, characterized in that electron gun coating technology is used in said third coating section. 21. Process according to claim 14, characterized in that the material for carrying out the coating of said strip in said first, second and third coating sections is fed into said sections in solid blocks or bars. 22. Process according to claim 14, characterized in that the material for carrying out the coating of said strip in said first, second and third coating sections is melted before being fed into said coating sections. 23. Process according to claim 14, characterized in that it comprises one or more of the steps described and / or illustrated.