EP0279803B1 - Installation for continuously manufacturing an extra thin metal foil by electrodeposition - Google Patents

Description

The present invention relates to an installation for the continuous manufacture of an extra-thin metal sheet by electrolytic deposition.

The electroplating technique has been known and used for a long time to form thin metal coatings on substrates having the most diverse shapes. Continuous deposition is particularly suited to elongated products of great length, such as strips or wires, which can pass through the deposition device. This technique makes it possible to produce adhesive coatings, which remain permanently on the surface of the substrate, or non-adhesive coatings, which can be detached from the substrate and thus constitute independent products.

For the purposes of the present invention, it should be understood that the expression “manufacture of an extra-thin sheet” designates the formation of a non-adherent coating on a mobile substrate followed by the peeling of this coating in the form of a sheet. extra-thin which constitutes an independent product.

It has already been proposed to use a mobile substrate constituted by a rotary drum which forms the cathode of the electrolysis system and which rotates in front of an anode of suitable shape. In the narrow space formed between the anode and the cathode, the electrolyte is circulated at high speed and tangentially to the cathode. Thanks to this arrangement, it is possible to reach current densities of the order of 30 A / dm².

By patent LU-A-86.119 (corresponding to EP-A-0222724 document belonging to the state of the art according to Art. 54 (3) EPC) from the same applicant, a device is known for depositing an electrolytic coating , in particular non-adherent, on a rotary cathode. This device comprises an anode which is designed so as to ensure high turbulence of the electrolyte in the space between the anode and the cathode, by practicing an electrolyte supply perpendicular to the plane of the cathode and without using any excessive motor pressures.

However, this device does not make it possible to reach the high level of production required by industrial exploitation.

The realization of an installation capable of ensuring a high production poses problems arising in particular from the continuous nature and the high technicality of the process which is implemented there.

The average thickness and the width of the extra-thin sheet to be produced are determined according to the needs of the users and therefore vary, for a given installation, within relatively narrow limits.

As a result, the increase in production implies an increase in the speed of the substrate which in turn leads to an increase in the length, and therefore in the size, of the deposition device, in order to maintain the same deposition time.

The size of the deposition device can, to a certain extent, be minimized by resorting to some special precautions, such as the use of an anode making it possible to operate with high current densities and the implementation of a electrolyte flow and current density as high as possible. It nevertheless remains necessary to increase the net deposition length, that is to say the length of the zone where the electrodes are actually opposite one another.

This increase is obtained by a simultaneous increase in the length of the anode and the cathode in the direction of travel of the substrate.

The length of the anode can be easily increased by juxtaposing several devices such as those described in patent LU-A-86,119 already cited.

With regard to the rotary drum cathode mentioned above, the desired increase in the net deposition length implies a substantial increase in the diameter of the drum, which is limited, in practice, for reasons of manufacturing, mounting and size.

It is also possible to envisage using several successive deposition devices. However, this arrangement has several serious drawbacks. The sheet leaving an intermediate device has a thinner thickness than the final extra-thin sheet and its handling increases the risks of tearing of the product. Furthermore, such sheets cannot moreover be detached below a "minimum peelable thickness" limiting the running speed. Finally, the proliferation of deposit systems greatly increases the cost and complexity of the installation.

It is also known to use a mobile cathode constituted by a metal belt rotating around two parallel rollers. Such a belt can have a sufficient length for the deposition to be carried out completely on a single belt, regardless of the speed thereof. It overcomes the aforementioned drawbacks of rotary drum cathodes, but it gives rise to other difficulties related in particular to the length and speed of the belt. In particular, one can mention the difficulty of guiding a very long belt and the need to compensate for chain deformation, which are further complicated by the aggressive nature of the environment. Such an installation also faces problems of sealing and braking of the belt linked to the electrical supply of the belt by brushes.

The object of the present invention is to provide an installation for the continuous manufacture of an extra-thin metal sheet by electrolytic deposition of a non-adherent coating on a mobile substrate followed by the detachment of this coating, an installation which makes it possible to avoid various aforementioned drawbacks and ensuring high production of extra-thin sheet.

The installation which is the subject of the present invention is based on the use of anodes of the type described in the aforementioned patent LU-A-86,119 and of a mobile cathode moving opposite these anodes.

• (a) la cathode mobile est constituée par une courroie métallique tendue entre deux rouleaux parallèles, de préférence horizontaux;
• (b) au moins un desdits rouleaux est motorisé afin de mettre la courroie en rotation autour des deux rouleaux;
• (c) une première pluralité desdites anodes est disposée en face d'une portion de la longueur d'un premier brin de ladite courroie;
• (d) des moyens de raccordement électrique de la plaque de chacune des anodes de ladite première pluralité d'anodes à la borne positive d'une source de courant électrique continu;
• (e) des moyens de raccordement électrique de la dite courroie métallique à la borne négative de ladite source de courant électrique continu;
• (f) des moyens de réglage de la vitesse de ladite courroie métallique, des débits d'alimentation et d'évacuation de l'électrolyte, ainsi que de l'intensité du courant électrique.

To this end, the installation which is the subject of the present invention, for the manufacture of an extra-thin metal sheet by electrolytic deposition on a movable cathode and subsequent separation of the deposit and the cathode, which comprises anodes comprising each a plate pierced with a first series of orifices connected to means for supplying electrolyte and a second series of orifices connected to means for discharging the electrolyte, is characterized in that:

• (a) the mobile cathode is constituted by a metal belt stretched between two parallel rollers, preferably horizontal;
• (b) at least one of said rollers is motorized to rotate the belt around the two rollers;
• (c) a first plurality of said anodes is disposed opposite a portion of the length of a first strand of said belt;
• (d) means for electrically connecting the plate of each of the anodes of said first plurality of anodes to the positive terminal of a source of direct electric current;
• (e) means for electrically connecting said metallic belt to the negative terminal of said source of direct electric current;
• (f) means for adjusting the speed of said metal belt, the flow rates of supply and discharge of the electrolyte, as well as the intensity of the electric current.

According to other characteristics which can be combined, the device of the invention comprises means for rinsing the extra-thin sheet, respectively means for drying this extra-thin sheet, which are located before the device for separating said sheet. sheet and movable cathode; the device may also include an installation for subjecting the sheet to a treatment causing an increase in its carbon content.

According to the invention, said cathode is constituted by a titanium belt, preferably polished. The surface condition of the cathode strongly influences the detachment and the quality of the extra-thin sheet produced, and it is advantageous in this regard that the cathode has an active surface as polished as possible. Within the meaning of the present application, the active surface of the belt is that which receives the electrolytic deposit.

It has also proven advantageous that the second of said preferably horizontal rollers is also equipped with a drive motor.

According to a particularly advantageous characteristic, the device of the invention comprises a second plurality of anodes arranged opposite a portion of the length of the second strand of said belt, the plate of said anodes being electrically connected to the positive terminal of a source of direct electric current.

In an advantageous embodiment of the device of the invention, said first and second pluralities of anodes are arranged opposite portions of substantially equal length of the respective strands of said belt, from a first of said horizontal rollers, the assembly comprising said first roller, said first and second pluralities of anodes and the corresponding portions of the strands of the belt is enveloped by a sealed enclosure, the second of said rollers is located outside of said enclosure and said enclosure comprises liquid-tight means for the entry and exit of said belt.

According to the invention, at least one anode is constituted by a parallelepipedic box whose wall located in front of the cathode is made of an electrically conductive material, preferably graphite, the other walls of said box being preferably made of an electrically insulating and chemically inert material vis-à-vis the electrolyte.

Also according to the invention, the means for electrically connecting an anode comprise copper bars connected to the plate of said anode, preferably on both sides of the width of said plate.

According to yet another feature of the device of the invention, the electrical connection means of said metal belt include brushes, which are preferably immersed in the electrolyte.

Another characteristic of the installation according to the invention resides in the fact that the means for rinsing, respectively drying, the extra-thin metal sheet comprise devices for spraying water, respectively air, in the direction of said sheet.

Other advantages and characteristics of the invention are specified in the description which follows, of a particular embodiment of the installation, schematically illustrated by the accompanying drawings in which Fig. 1 shows a general view of this particular embodiment; Fig. 2 illustrates the circuit of the electrolyte in this embodiment; and Fig. 3 illustrates a particular variant of the installation comprising a carburizing device.

Similar elements which appear in the figures are given the same reference numerals. In addition, the parts of the installation which are not essential to a good understanding of the invention have not been shown.

Figure 1 shows a general view, in length, of a particular embodiment of the installation of the invention. This installation comprises a mobile cathode in the form of a metal belt (1) stretched between two parallel horizontal rollers (2,3). The edges of the belt (1) can be masked, on the anode side, by means of a suitable coating so as to give the extra-thin sheet the desired width. The rollers are driven in rotation by motors, not shown, and their direction of rotation is indicated by a curved arrow. The metal belt (1) thus defines an upper strand (4) which, as will be explained below, is the input strand, and a lower strand (5) or output strand. The installation also includes anodes of the type described in the aforementioned patent LU-A-86,119, in which the wall pierced with two series of orifices is a flat graphite plate. These anodes are divided into two groups, namely an upper group (6) in which the anodes are positioned such that their respective graphite plates are opposite and parallel to the outer face of the upper strand (4) of the belt, and a lower group (7) in which the anodes are positioned so that their respective graphite plates are opposite and parallel to the outer face of the lower strand (5) of the belt.

In such an arrangement, the metal belt (1) is only partially immersed in the electrolyte and it can therefore be considered that the installation for manufacturing an extra-thin metal sheet consists of two distinct parts, despite the physical continuity of the belt (1).

• ― une portion de la courroie (1), ladite portion ayant une longueur constante, mais étant constamment renouvelée par suite du mouvement de la courroie;
• ― les deux groupes d'anodes (6, 7);
• ― le rouleau (3);
• ― les balais assurant l'alimentation électrique de la cathode, dont il sera question plus loin.

The submerged part of the installation includes:

• - A portion of the belt (1), said portion having a constant length, but being constantly renewed as a result of the movement of the belt;
• - the two groups of anodes (6, 7);
• - the roller (3);
• - The brushes ensuring the electrical supply of the cathode, which will be discussed below.

• ― la portion restante de la courroie (1);
• ― le rouleau (2);
• ― les moyens d'essorage, de rinçage, de séchage et de décollement de la feuille extra-mince, qui seront décrits plus loin.

The non-submerged or aerial part of the installation includes:

• - the remaining portion of the belt (1);
• - the roller (2);
• The means of wringing, rinsing, drying and peeling off the extra-thin sheet, which will be described later.

In the embodiment shown in FIG. 1, the submerged part of the installation is surrounded by a sealed enclosure (8), which includes airlocks for entering and leaving the belt.

Opposite the portion of the belt (1) located on the immersed roller (3) is arranged a polarization electrode making it possible to eliminate any chemical attack on the extra-thin sheet by the electrolyte during the passage of the upper group ( 6) to the lower group (7) of the anodes. This arrangement also makes it possible to avoid the manufacture of cylindrical anodes.

This submerged roller (3) must have a diameter large enough to transmit to the belt the torque necessary for its rotation and to minimize the risk of rupture of the belt by fatigue.

The supply of both an electrolyte and an electric current to the anodes of the two aforementioned groups can be carried out either individually or by cells grouping together any number of anodes. For the sake of clarity, the various power supplies will be described with reference to a cell, it being understood that such a cell could have only one anode.

The electrical supply of a cell is ensured by means of a set of copper bars, known per se, connected to the graphite plate, on both sides of the width thereof; this arrangement has the effect of reducing the ohmic losses in the graphite plate and thus minimizing the variations in the current density liable to cause variations in the thickness of the deposit along the width of the belt.

The cathode is supplied with electricity by means of brushes immersed in the electrolyte and distributed over the "internal" surface of the belt (1), opposite the groups of anodes.

The fact that the brushes are submerged eliminates the need to provide tight seals between fixed parts and moving parts. In addition, the electrolyte acts as a lubricant and thus reduces the friction force applied to the belt. Finally, the electrolyte reduces the contact resistance between the cathode and the brushes and thus contributes to improving the electrical efficiency of the installation.

The electrolyte circuit will be described later, with reference to Figure 2.

The non-submerged roller (2) has a diameter equal to that of the submerged roller (3). It ensures the transmission of half of the torque necessary for driving the belt, as well as guiding the belt in the transverse direction.

In the installation according to the invention, the means for rinsing and / or drying the extra-thin metal sheet are located before the device for separating said sheet and the belt (1). This arrangement makes it possible to carry out the important and delicate rinsing and / or drying operations while the extra-thin sheet still adheres to the belt; this reduces the risk of degradation or tearing of this sheet.

The devices used for this purpose are known per se. In addition to the rubber spin rollers, not shown but arranged as close as possible to the outlet of the enclosure (8), the installation comprises rinsing means (9) for example by spraying hot water, possibly followed drying means (10) such as air blowing apparatus, hot or cold.

Peeling of the extra-thin sheet is carried out by means of a small motorized roller (11), placed approximately at the height of the axis of rotation of the non-submerged roller (2).

FIG. 2 illustrates the circuit of the electrolyte in an installation of the type represented in FIG. 1. As indicated above, reference is again made here to an anode cell.

As is known from patent LU-A-86,119 already cited, the electrolyte crosses the graphite plate of the cell through a first series of orifices, travels a short path between the cathode and said graphite plate and crosses again the graphite plate, the other way around. This construction is not shown in detail in FIG. 2. It may be recalled that this type of anode makes it possible to dispense with the side seals, since it does not give rise to any sensitive lateral flow of electrolyte.

In this FIG. 2, which results from a cross section along the plane II of FIG. 1, the upper (4) and lower (5) strands of the belt have been shown diagrammatically, as well as the graphite plate of an anode of each of the upper (6) and lower (7) groups.

To produce, with a high current density, an extra-thin metal sheet having a good surface appearance and sufficient cohesion, it is necessary to produce specific specific flow rates of electrolyte in the narrow space formed between the anode and the cathode. .

The present installation includes an electrolyte circuit in which the pressure drops are low.

Each pair of superimposed cells, one belonging to the upper group (4, 6) and the other to the lower group (5, 7) is supplied with electrolyte by a pump (12) taking the liquid from a collection basin (13 ). The pump (12) sends the electrolyte through the conduits (14) and (15) which supply the first series of orifices of the anodes (6) and (7) respectively.

As shown in Figure 1, the collection basin (13) is located directly below the lower group (7) of anodes and it extends at least over the entire length of the submerged part of the installation.

The electrolyte discharged from the rear face of the cells of the lower group (7) falls directly into the collection basin (13). The electrolyte discharged from the rear face of the cells of the upper group (6) is collected by a channel (16) of large section which runs along the immersed part of the installation over its entire length and which brings the electrolyte back into the basin. collection (13) via a cascade (17) bypassing the submerged roller (3).

The installation also comprises, at the entrance to its submerged part, pinch rollers (18) which make it possible to prevent the belt (1) from twisting in the deposition section.

The device of the invention can advantageously be equipped with means for, after separation of the iron-based sheet and the movable cathode, subjecting said iron-based sheet to a treatment causing an increase in its carbon content; according to the invention, this treatment is advantageously constituted by a gas carburizing operation.

Such treatment by gas carburizing has proved to be particularly advantageous for increasing the carbon content of a sheet. iron-based initial produced by electrolytic deposition. In fact, the tests carried out by the Applicant have shown, in an absolutely unexpected manner, that the rate of cementation of such a sheet was particularly high, provided that the conditions of the treatment are judiciously chosen. This high cementation speed, which could in particular be due to the purity of the initial sheet, makes it possible to achieve the desired degree of cementation in a very short time, perfectly compatible with a continuous manufacturing process.

According to the invention, the means for applying the treatment in question comprise a heating oven up to a temperature between 900 ° C. and 1050 ° C., under a fuel atmosphere, a zone for maintaining in this temperature range and under this atmosphere for a period not exceeding 5 min., and a cooling zone with a speed of 5 ° C / s to 20 ° C / s in the temperature range from 800 ° C to 600 ° C, then a cooling zone down to room temperature.

For this treatment, it is possible to use an oven with a fuel atmosphere known per se, such as CH₄ or a gas mixture rich in CH₄ and / or CO and H₂.

Also in the context of the invention, the installation may also include at least one device for covering said sheet with a protective metal layer, with a flash heating step to cause the formation of an intermediate layer of intermetallic alloy between said sheet and the protective layer.

Finally, the device of the invention as just described in the above variant can also be equipped with means for coating the sheet with a protective film consisting of an oxide such as chromium oxide or an organic substance such as a lacquer, a resin or a varnish.

Fig. 3 shows a variant of the installation of FIG. 1, in which a device is provided for cementing the extra-thin metal sheet, after it has been detached from the movable cathode.

Downstream of the installation (1) described in detail above, is located a device (19) intended to cause an increase in the carbon content of the extra-thin sheet. In the embodiment illustrated here, this device (19) consists of a gas carburizing furnace, where the extra-thin sheet is exposed to a fuel atmosphere, for example CH₄, at a high temperature.

This device (19) can be followed by other coating installations such as a dip galvanizing installation (20) or a tinning installation (21). Finally, a finishing device (22), such as an installation for depositing a protective coating by chromating, lacquering or the like, can also be installed downstream.

The installations 20, 21 and 22 are, in themselves, well known in the art and do not require a detailed description. It is nevertheless advisable to limit the tensile force exerted in these installations, in order to take account of the relatively low tensile strength of the extra-thin sheet.

Claims (10)

1. Installation for the manufacture of an extra-thin metal foil by electroplating on a movable cathode and subsequent separation of the deposit and the cathode, which comprises anodes each comprising a plate pierced with a first series of orifices connected to electrolytesupply means (14, 15) and with a second series of orifices connected to electrolyte-removal means (16, 17), characterised in that:

(a) the movable cathode consists of a metal belt (1) tensioned between two parallel, preferably horizontal, rolls (2, 3);

(b) at least one of the said rolls (2, 3) is motorised so as to cause the belt to rotate about the two rolls;

(c) a first plurality of the said anodes (6) is arranged opposite a portion of the length of a first side (4) of the said belt (1);

(d) means for electrical connection of the said plate of each of the anodes of the said first plurality of anodes (6) to the positive terminal of a source of direct electrical current;

(e) means for electrical connection of the said metal belt (1) to the negative terminal of the said source of direct electrical current;

(f) means for adjusting the speed of the said metal belt (1), the rates of supply and removal of the electrolyte (12), and the intensity of the electric current.

2. Installation according to Claim 1, characterised in that it comprises means for rinsing (9) and/or drying (10) the extra-thin foil, which means are situated before the apparatus (11) for separating the said foil and the movable cathode.

3. Installation according to either of Claims 1 and 2, characterised in that the cathode consists of a belt (1) made from titanium, preferably polished titanium.

4. Installation according to any one of Claims 1 to 3, characterised in that it comprises a second plurality of anodes (7), arranged opposite a portion of the length of the second side (5) of the said belt (1), the plate of the said anodes being connected electrically to the positive terminal of a source of direct electric current.

5. Installation according to Claim 4, characterised in that the said first and second pluralities of anodes (6, 7) are arranged opposite portions of substantially equal length of the respective sides (4, 5) of the said belt (1), extending from a first one (2) of the said preferably horizontal rolls, in that the assembly comprising the said first roll (2), the said first and second pluralities of anodes (6, 7) and the corresponding portions of the sides (4, 5) of the belt is enveloped by a leaktight enclosure (8), in that the second (3) of the said rolls is situated outside the said enclosure (8), and in that the said enclosure (8) comprises liquidtight means for the entrance and the exit of the said belt (1).

6. Installation according to any one of Claims 1 to 5, characterised in that at least one of the said anodes consists of a parallelepipedal box, the wall of which situated facing the cathode is made from an electrically conductive material, preferably from graphite, and the other walls of which are preferably made from a material which is electrically insulating and chemically inert with respect to the electrolyte.

7. Installation according to any one of Claims 1 to 6, characterised in that the means for the electrical connection of an anode comprise copper bars which are connected to the plate of the said anode, preferably on either side of the width of the said plate.

8. Installation according to any one of Claims 1 to 7, characterised in that the means for electrical connection of the said metal belt (1) comprises brushes, preferably immersed in the electrolyte.

9. Installation according to any one of Claims 1 to 8, characterised in that it is equipped with means (19) for applying a treatment which results in an increase in the carbon content of the extra-thin metal foil.

10. Installation according to any one of Claims 1 to 9, characterised in that it comprises at least one device (20, 21) for coating the said foil with a protective layer.

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