EP0093681A1 - Process and apparatus for plating great lengths of metallic strip material - Google Patents

Abstract

The invention relates to a method and a device for coating by electrolysis, continuously with a high unwinding speed and a very short residence time in the electrolyte, a long length of metal with a metal layer. It consists in passing the length of metal (2) through a shaving die (3), then in a solution of the coating metal to which an electric voltage is applied by means of a liquid current outlet constituted by a solution of nickel chloride, boric acid and hydrofluoric acid. It finds its application in all the problems of coating a metal with an adherent metal layer and having both a ductility such that it easily lends itself to wire drawing operations and a low and non-evolving contact resistance.

Description

The invention relates to a method and a. device for coating, continuously and at high speed, a large length of metal such as raw wire, round, bar, tube, flat, with a metal layer and which applies in particular to nickel plating of aluminum wires for electrical use.

Numerous processes are known for coating metal parts with another metal intended to improve their surface properties: appearance, resistance to corrosion, electrical contact resistance, for example. These processes are inspired by several principles, among which one can cite deposition by metallization, by plasma, in vapor phase, by chemical route, by coating, by co-laminating or cofiling, by electrolytic route ...

Depending on the nature of the metal to be coated, its surface condition, the nature of the coating, the types of stress imposed by the device for implementing the process, the characteristics required of the finished product, each of these processes has both advantages and disadvantages, and it is therefore necessary to choose according to the desired goal, that which presents the optimum compromise.

In the present case, the applicant has mainly aimed to resolve the problem of coating electrical conductors of aluminum or aluminum-based alloys. Indeed, if, for several years, it has been shown that aluminum and its alloys and, in particular, the alloy designated by the Aluminum Association under the name 6101, can replace copper, both from the point of view electrical resistivity and mechanical characteristics, it has also been found, however, that its use in the form of a wire is poorly connected to the connection systems currently used in electrical installations, in particular in high-stress applications or in aggressive atmospheres. In fact, under these application conditions, it is possible to observe a growth in the contact resistance, a possible source of harmful overheating. the good behavior of this type of driver and the safety of the installations. It was therefore necessary, to fully benefit from the indisputable advantages of aluminum and to impose it definitively in place of copper in the field of conductors, to find an economical process, which gives the wire a contact resistance stable over time and at least equivalent to that of copper.

• - des traitements de cofilage ou de colaminage, mais leur développement a été limité en raison du coût élevé de la mise en oeuvre,
• - des traitements de dépôt électrolytique d'étain, nais ceux-ci n'ont pas connu d'extension importante à cause, d'une part, des gammes de préparation longues du métal nécessitant des sous-couches de bronze et/ou de cuivre obtenues en bain de cyanure, d'autre part, du prix de plus en plus élevé de l'étain devenu métal stratégique.

Admittedly, this desire to see the use of aluminum conductors developed further and to succeed in finally destroying the prejudices of electrician installers who are reluctant to use aluminum, is not the prerogative of the applicant, because other manufacturers or other users of aluminum have sought to develop suitable techniques to solve this problem of contact resistance. This is how it was proposed:

• - cofiling or colaminating treatments, but their development has been limited due to the high cost of implementation,
• - treatments of electrolytic deposit of tin, but these have not known any significant extension because, on the one hand, of the long ranges of preparation of the metal requiring underlays of bronze and / or copper obtained in cyanide bath, on the other hand, from the increasingly high price of tin which has become a strategic metal.

More recently, there has been an orientation both towards the use of nickel coating, a metal much cheaper than tin, and having intrinsically good resistance to aggressive atmospheres, and towards the maintenance of the coating principle. by electrolysis well suited to aluminum.

We have thus seen appear in this field a series of processes in which recourse is had either to cells in which the electrolyte circulates at high speed, or to a more or less complex surface preparation, or to the techniques of intermediate layers used for the 'tinning. As many methods which make it possible to produce a relatively adherent coating, but which all suffer from a major drawback, that of achieving only a relatively low processing speed, most often limited to a few meters per minute and which nevertheless require, in order to have a sufficient residence time in the electrolyte, very long devices, the production of which entails significant investment costs.

This is why the Applicant, aware not only of the advantage of nickel coating by electrolysis, but also of the need to improve its performance so as to make this treatment as inexpensive as possible and thus be able to render the aluminum wire obtained even more competitive with respect to copper, sought and developed a process in which a coating is formed, for a high speed of travel and with a residence time in the relatively short electrolyte thickness and contact resistance such that it meets the various standards in use in the electrical industry.

By French patent 2,012,592, it knew that it was possible to coat an aluminum wire with a layer of copper of 3 μm by making it scroll at a speed of 30 meters per minute, first through a peripheral planing die, then in a 3 m long electrolyte tank to which an electromotive force was applied by means of an anode contained in this electrolyte and of the wire acting as a virgin cathode. Admittedly, the residence time in the electrolyte was only 6 seconds for a thickness of 3 μm, but the coating was made of copper and that could not foreshadow anything of the results which it could obtain with nickel, in particular in terms of adhesion and contact resistance.

Having tried to transpose this teaching to nickel plating of aluminum without worrying about the mode of rabotaqe, in a 5 m long tank, she experienced difficulties, in particular at the level of the electric current supply of the wire, because all the devices used: rollers, rollers, friction contacts, led to the formation of electric arcs more and more important and more and more harmful for the adhesion of the coating as the speed of movement increased, hence the obligation to reduce The current density and, consequently, to decrease this speed to have a coating layer of sufficient thickness. In fact, it obtained maximum speeds close to 25 m / min, that is to say a residence time of 12 seconds for a thickness of 0.5 pm leading to a nickel-plated wire which did not entirely meet the standards in use.

The Applicant then thought, among other solutions, of replacing mechanical systems with a liquid current outlet, and found during numerous tests, that such a means made it possible to obtain a wire of satisfactory quality at speeds higher than those obtained until now and with relatively short residence times. It also found that this means could even be applied to other metals and other coatings. This is why it proposes, according to the invention, a process for coating, by continuous electrolysis with a high running speed and a very short residence time in the electrolyte, a long length of metal with an adherent metallic layer. , in which the said length is optionally subjected to a surface preparation treatment, then passed through a solution of the coating metal to which an electrical voltage is applied to form the coating, via a liquid outlet .

Thus, the length of metal which may be a wire, a round, a bar, a tube, a flat made of aluminum, copper or other metal, is optionally initially subjected to a conventional degreasing or chemical pickling treatment to remove the surface stains, then it passes into a coating metal solution which is preferably nickel, but can be any other metal capable of being electrolytically deposited and chosen according to the problem to be solved.

To this solution, an electrical voltage is then applied, which can be continuous or pulsed. If the positive pole of the current source is conventionally connected to an electrode immersed in said solution, on the other hand, to close the circuit, we no longer connect the negative pole directly over a part of the length of metal as in the prior art, but via an electrode which plunges into a conductive liquid through which passes said length, and which constitutes the liquid current outlet.

If such a method makes it possible to avoid the drawbacks due to poor mechanical contacts, and therefore to appreciably improve the current densities and, consequently, to increase the speed of travel while reducing the residence time since the length contact with the electrolyte was maintained at 5 m, it was found that performance could be further improved by the judicious choice of the composition of the liquid intended to form the liquid outlet, and that this depended on the composition of the coating solution and the metal to be treated. It is necessary, in fact, that this composition makes it possible to obtain high current densities while maintaining balanced voltages between the liquids constituting the current outlet, and the coating bath.

• - pour la prise de courant liquide, un mélange de chlorures métàlli- ques, de fluorures et d'acide borique tel que, par exemple, le mélange suivant :
  
• - pour le revêtement, les bains de nickelage classiques, et de préférence, celui ayant la composition :
  

Thus, in the case of nickel plating, the applicant has found that the best results are obtained with the following electrolytic solutions:

• - for the liquid current intake, a mixture of metallic chlorides, fluorides and boric acid such as, for example, the following mixture:
  
• for the coating, the conventional nickel-plating baths, and preferably that having the composition:
  

These solutions are used at temperatures enabling equivalent resistivities to be achieved.

For example, for the compositions cited above, these temperatures are respectively around 35 and 50 ° C.

Under these conditions, the plaintiff has already managed to realize nickel plating several µm thick with a running speed of the order of 30 m / minute and a residence time of less than 12 seconds, which constitutes a great improvement compared to the technique with mechanical contact, where, for an equivalent speed and residence time, the thickness was less than 0.5 μm.

However, it then noted the advantage of a particular treatment for surface preparation of the length of metal used. Indeed, by operating on raw wire drawing, it obtained a nickel deposit of good appearance, adherent and low contact resistance, but with the disadvantage of polluting the outlet of liquid current, by surface stains. With a surface preparation by any conventional degreasing treatment, the time necessary to have a suitable action was too long and its integration into the continuous process required limiting the running speed.

It was then that by associating scalping with the electrolytic coating treatment with liquid current outlet, she realized that this new combination made it possible to achieve the goal which she had proposed, that is to say high running speed - short residence time - adherent deposit - low and non-evolving contact resistance.

For this, it passed the length of wire through one or more floating mounted dies, which allows to continuously remove the peripheral part of the length of metal to a thickness of 1 to 2/100 mm and to eliminate thus the oxide layer and the lubricant residues.

Under these conditions, the results achieved exceeded all his expectations, since it was already possible to reach the maximum speed allowed by the experimental installation which is 300 m / minute with thicknesses between 1 and 3 µm, this value being limited, in his opinion, by the installed electrical power. The quality of the nickel-plated wire thus obtained was checked according to the electrical standards in use and was recognized as very satisfactory. In particular, the applicant having carried out winding tests of ten turns on diameter, has found a quite remarkable ductility of the nickel layer and, in particular, its surprising ability to wire drawing. Thus, in a first test, a wire of aluminum alloy 6101 of diameter 1.78 mm, coated according to the invention, with a layer of nickel of 3 μm could be drawn to a diameter 0.78 mm, without any detachment or tearing of the nickel coating. In a second test, a 1350 aluminum wire, 5.67 mm in diameter, could be drawn up to 0.78 mm in 16 passes with conservation of the adhesion of the nickel deposit while keeping, after each pass low contact resistance.

To implement this method, the applicant has designed an experimental device of great simplicity, of short length, comprising in the direction of travel of the length of metal successively at least one circular shaving die, a liquid current outlet constituted by a tank only 5 m long containing an electrolyte in which a negatively charged electrode is immersed, a coating tank of the same length containing the coating solution and in which a positively charged electrode is immersed, the two tanks possibly being separated by a system rinse.

This device is represented by the attached figure in which there is a coil (1) unwinding the length of metal (2), a shaving die (3), a tank (4) for taking a liquid current with an electrode. (5) connected to the negative pole of the current source (6) and immersed in the solution (7), a washing compartment (8), a tank (9) of coating containing the solution (10) in which is immersed l 'electrode (11) positively charged. At the exit from this tank, a rinsing (12) and drying (13) system is provided before winding the length of metal on the coil (14).

The invention can be illustrated with the aid of table n ° I in which appear a series of 18 tests carried out on an aluminum alloy wire 6101, of diameter 1.78 mm having as mechanical characteristics for tests 1 to 11 :

For tests 12 to 18, these characteristics are respectively the following: .215 MPa - 226 MPa - 3.4%

• - préparation de surface :
  • . Essais 1 à 5 - pas de traitement de surface préalable
  • . Essais 6 à 18 - traitement préalable de rasage ;
• - la température du bac I (prise de courant liquide) et du bac II (solution de revêtement) ;
• - les conditions électriques : tension de courant en volts appliquée aux deux électrodes, densité de courant ayant traversé le système en A/dm² ;
• - la vitesse de défilement du fil en m/min, puis, les résultats d'essais obtenus avec le fil traité ;
• - résistance de contact en m/Ω déterminée par la méthode des fils en croix sur lesquels repose une masse de 1 kg ;
• - l'épaisseur du revêtement de nickel en µm obtenue par détermination du poids de nickel recueilli par dissolution du revêtement dans l'acide nitrique ;
• - des observations sur la tenue du fil au vieillissement électricrue, contrôlée en soumettant ce dernier jusqu'à 200 cycles thermiques sous 30 A environ.

Are grouped in a series of columns, first, the wire processing conditions:

• - surface preparation:
  • . Tests 1 to 5 - no prior surface treatment
  • . Tests 6 to 18 - pre-shaving treatment;
• - the temperature of tank I (liquid outlet) and tank II (coating solution);
• - the electrical conditions: current voltage in volts applied to the two electrodes, current density having passed through the system in A / dm ² ;
• - the wire running speed in m / min, then the test results obtained with the treated wire;
• - contact resistance in m / Ω determined by the cross-wire method on which a mass of 1 kg rests;
• - the thickness of the nickel coating in µm obtained by determining the weight of nickel collected by dissolving the coating in nitric acid;
• - observations on the resistance of the wire to electric aging, controlled by subjecting it to up to 200 thermal cycles at around 30 A.

During each of these cycles, in various sets of connections, the treated wire is brought to 120 ° C. under the effect of the overcurrent which passes through it, then cooled to ambient temperature. It is considered that the resistance is good if the contact resistance R and the temperature of the connection do not change.

Le tableau II ci-après donne pour un fil d'alliage aluminium 6101 de diamètre 1,75 mm, correspondant à l'essai N°8 du tableau I, les résultats de mesures de résistance de contact initiale Ro et aorès 200 cycles R200 effectuées sur des bornes à plaquettes au cours de 8 essais repérés de 1 à 8. Il donne également les mesures de températures de contact après 1 cycle 81 et après 200 cycles 8200, et les compare à la température de contact de référence θ' . Ces essais ont été réalisés en se plaçant dans 2 cas différents de couples de serrage : 0,33 et 0,5 mN qui n'ont pratiquement pas évolués au cours des cycles, à une température ambiante voisine de 20°C et sous une intensité de 31,5 A.

We can see from these results the efficiency of the claimed process, and the surprising results of the increase in the electrolysis yield as a function of the speeds (cf. tests 17 and 18 where for running speeds of 200 and 300 m / mm, practically similar coating thicknesses are obtained).

Table II below gives, for an aluminum alloy wire 6101 with a diameter of 1.75 mm, corresponding to test No. 8 of Table I, the results of initial contact resistance measurements Ro and after 200 cycles R200 carried out. on pad terminals during 8 tests marked from 1 to 8. It also gives the contact temperature measurements after 1 cycle 81 and after 200 cycles 8200, and compares them to the reference contact temperature θ '. These tests were carried out by taking place in 2 different cases of tightening torques: 0.33 and 0.5 mN which practically did not change during the cycles, at an ambient temperature close to 20 ° C and at an intensity 31.5 A.

On constate que le fil d'alliage d'aluminium nickelé à 60m/mn se comporte mieux que le fil de cuivre de résistance linéique équivalente.Table III on the next page repeats the same tests on a copper wire of 1.5 mm ² in cross section.

It can be seen that the aluminum alloy wire nickel-plated at 60 m / min behaves better than the copper wire of equivalent linear resistance.

Table IV reproduces the tests in Table II, but using a coated wire at a running speed of 300 m / min. There are comparable results.

The present invention finds its application in all the problems of coating a long length of metal with an adherent metal layer and having both a ductility such that it easily lends itself to wire drawing operations, and a low contact resistance. and not scalable.

It is more particularly suitable for nickel plating electrical conductors in aluminum or its alloys with the diameter of use.

This is the case of wire for domestic or industrial use, the diameters of which are most often between 1.5 and 3 mm. However, taking into account the wire-drawing ability of the nickel-plated wire by the process, nickel-plating can be carried out on supply diameters, that is to say greater than the use diameter, believed to be reduced by the continuation, which makes it possible to extend the application of the method to other fields such as the fine wires of telephone wires, flexible cables and winding wires ...

Claims (9)

1. Process for coating by electrolysis, continuously, and with a high running speed and a very short residence time in the electrolyte, a large length of aluminum or one of its alloys with an adherent metallic layer, in which said length is optionally subjected to a surface preparation treatment, then it is passed through a solution of the coating metal to which an electrical voltage is applied by means of a plug, of liquid current, characterized in that the liquid outlet consists of a solution of nickel chloride, boric acid and hydrofluoric acid 2. Method according to claim 1, characterized in that the surface preparation treatment consists in passing the length of metal through at least one scalping system. 3. Method according to claim 2, characterized in that the scalping system is at least one shaving die. 4. Method according to claim 1, characterized in that the length of metal consists of a continuous wire. 5. Method according to claim 1, characterized in that the length of metal is for electrical use. 6. Method according to claim 1, characterized in that the metal layer is formed of nickel. 7. Method according to claim 1, characterized in that the coating metal solution contains nickel sulfamate, nickel chloride and boric acid. 8. Device for implementing the method according to claims 1 and 2, characterized in that it comprises in the direction of circulation of the length of metal a scalping system and a liquid current outlet constituted by a tank containing a electrolyte in which a negatively charged electrode is immersed, a coating tank containing the solution of the coating metal in which dives a positively charged electrode, these two tanks possibly being separated by a system for rinsing the length of metal. 9. Device according to claim 8, in which the running speed of the metal length is greater than 100 m / minute, characterized in that the coating tank has a very reduced length of 5 meters maximum.

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