Chemistry: electrical and wave energy – Processes and products
Patent
1987-03-19
1988-11-22
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
204 28, 204 40, 204 442, 204 445, 204 44, 204 49, 204 551, C25D 550
Patent
active
047863773
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for electroplating steel wires as well as to the products thus obtained, which products can be employed for the manufacture of reinforcing structures for elastomeric material articles, and more particularly for tires.
More particularly, this invention relates to a process for coating steel wires with a thin layer of an alloy, containing copper, zinc, nickel and lead, by electroplating and subsequent diffusion by Joule effect.
BACKGROUND OF THE INVENTION
In the production of reinforced elastomeric materials, in particular of radial tires, wire cords have been employed up to the present time, as is well known, which cords are made up of steel wires coated by electroplating with brass, preferably of a composition between Cu/Zn=60/40 and Cu/Zn=70/30 (% by weight) at the amounts between 2 and 8 g/Kg of steel and of 1-2 .mu.m thickness for a wire diameter between 0.75 and 1.40 mm. Such wires ar then wet-drawn according to a chipless procedure and employed for the production of said cords.
It it also well known that such cords, in addition to a high ultimate tensile stress and to a high flexibility, also show, during the curing process with a standard mix, an adhesion to rubber (or other elastomeric material) which is much larger than the value of adhesion that can be ascribed to the mere friction effect. At the present time such property is considered to stem substantially from the formation and growth of films of some hundred .ANG. thickness of copper and zinc sulfides at the rubber/brass interface, as a consequence of the chemical reactions occurring during vulcanization.
On the other hand, it has been observed that the adhesion between steel and the coating is also of the same importance. Thus it is clearly evident that any physical or chemical phenomenon, such as for instance corrosion, which alters the state of surfaces, affects the cord/elastomer adhesion negatively.
Such drawback manifests itself frequently, because rubber mixes commercially employed in the production of tires are hardly ever anhydrous, and give rise during vulcanization to the formation of a ZnO film, in addition to sulfides films, and next, owing to material aging, to the formation of hydroxides with the consequent definitive separation of the cord from the rubber. This was shown by a prolonged treatment with overheated steam (120.degree. C. or more), in the presence of chlorides.
In that case the examination of the state of surfaces put into evidence the presence of rust at the interface between steel and coating.
On the other hand, it is well known that car and truck tires are subjected during employment to severe mechanical stresses, especially at the highest speeds or in off-road runs.
As the safety of passengers and of load depends on tire reliability, it is necessary that the cord/elastomer adhesion be particularly strong, not only at the very beginning, but also during the full tire life.
SUMMARY OF THE INVENTION
Thus it is a main object of the present invention to provide a coating for steel wires that results in an improved starting adhesion cord/elastomer and that is stable in time, as a result of the increase in the corrosion resistance. It is another object to provide a coat for a wire which permits mechanical working of the wire and drawing of the wire without producing chips, and with no remarkable changes in the surface composition and in the continuity of the coating itself.
In accordance with the present invention there is provided a coating made up of copper, zinc, nickel and lead electrodeposited as successive layers on steel wires and then transformed into an alloy through solid state diffusion a Joule effect.
It is worthwhile observing that the present invention is not limited to the selection of the components mentioned above and of their percentage amounts in the alloy, but, in the formation of said coating, the present invention also sets forth the order and the manner in which the constituents of the alloy are to be plated onto the steel support. Namely, copper an
REFERENCES:
patent: 1918159 (1932-01-01), Weisberg et al.
patent: 3926749 (1975-12-01), Passal
Ambrosio Leo
De Filippo Domenico
Andrews R. L.
Gencord SpA
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