METAL WIRE WITH ANTI-CORROSIVE COATING AND INSTALLATION AND METHOD FOR COATING A METAL WIRE

Abstract

An installation for continuously coating wires by means of plasma deposition includes at least one plasma deposition chamber having a pressure-tight inlet and a pressure-tight outlet which are capable of maintaining a reduced pressure inside the chamber when they are passed through by a wire which travels through the chamber. At least one generator of plasma rays is provided in the chamber for the deposition of a target material on the external surface of the wire in a portion thereof which is between the pressure-tight inlet and the pressure-tight outlet. A transport system is provided in the installation in order to progressively draw the wire through the plasma deposition chamber.

Claims

1. An installation for continuously coating wires by means of plasma deposition comprising at least one plasma deposition chamber having a pressure-tight inlet and a pressure-tight outlet which are capable of maintaining a reduced pressure inside the chamber when they are passed through by a wire which is introduced from the pressure-tight inlet and which travels through the chamber as far as the pressure-tight outlet, at least one generator of plasma rays being provided in the chamber for the deposition of a target material on the external surface of the wire in a portion thereof which is between the pressure-tight inlet and the pressure-tight outlet, a transport system being provided in order to progressively draw the wire through the plasma deposition chamber.

2. The installation according to claim 1, comprising at least one decompression chamber upstream of the plasma deposition chamber in order to reduce the pressure differential from ambient pressure to the reduced pressure of the chamber.

3. The installation according to claim 1, wherein each decompression chamber is passed through by the wire which is progressively introduced therein through respective pressure-tight inlets.

4. The installation according to claim 1, comprising at least one compression chamber downstream of the plasma deposition chamber in order to reduce the pressure differential between the reduced pressure of the chamber and ambient pressure.

5. The installation according to claim 1, wherein each compression chamber is passed though by the wire which is progressively discharged therefrom via respective pressure-tight outlets.

6. The installation according to claim 1, wherein an oscillation system allows the oscillation of the wire about the longitudinal axis thereof during the passage thereof through the plasma deposition chamber.

7. The installation according to claim 1, wherein an oscillation system allows the oscillation of the at least one generator of plasma rays about the longitudinal axis of the wire during the passage thereof through the plasma deposition chamber.

8. The installation according to claim 1, comprising three generators of plasma rays which are arranged radially spaced apart by 120° about the longitudinal axis of the wire in the plasma deposition chamber.

9. A method for coating wires by means of plasma deposition, comprising the steps of: supplying a wire inside at least one plasma deposition chamber from a pressure tight inlet to a pressure-tight outlet which are capable of maintaining a reduced pressure inside the chamber, progressively pulling the wire through the plasma deposition chamber with a transport system, activating at least one generator of plasma rays in the chamber for the deposition of a target material on the external surface of the wire in a portion thereof between the pressure-tight inlet and the pressure-tight outlet.

10. The method according to claim 9, wherein the wire and/or the at least one generator of plasma rays is/are caused to oscillate about the longitudinal axis of the wire during the deposition of the target material on the external surface of the wire.

11. A metal wire which is coated with a protective layer which is obtained via a plasma deposition method.

12. The metal wire according to claim 11, wherein the plasma deposition method is a Pulsed Plasma Deposition (PPD) method.

13. (canceled)

14. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Additional advantages and characteristics will be appreciated from the following description of a preferred embodiment with reference to the drawings which are given by way of non-limiting example and in which:

[0014] FIG. 1 is a schematic view of an installation for producing wires which are coated by means of plasma deposition technology,

[0015] FIG. 2 is a schematic cross-section of the plasma deposition chamber in accordance with the line II-II of FIG. 1.

DETAILED DESCRIPTION

[0016] With reference now to FIG. 1, there is schematically illustrated an installation 10 for coating a wire 12, preferably but not exclusively a metal wire, for example, a steel wire or a wire of another metal or metal alloy. Naturally, the installation may be adapted for bringing about the coating of a plurality of wires in a parallel manner. The coating may be a coating of a metal material. For example, the wire 12 may be coated with zinc or zinc alloys.

[0017] The installation 10 may comprise a plasma deposition chamber 14 in which the method is carried out for plasma deposition according to generally known characteristics which are described, for example, in the document EP2936538 which is cited above. The chamber 14 may be maintained at a known level of reduced pressure which is suitable for the deposition of plasma. The chamber 14 may be passed through centrally by the wire 12. The wire 12 may be introduced into the chamber 14 through a pressure-tight inlet 16. The wire 12 may be discharged from the chamber 14 via a pressure-tight outlet 18. The pressure-tight inlet 16 may be produced, for example, by means of a membrane with a hole through which the wire 12 passes in a pressure-tight manner. The pressure-tight outlet 18 may also be produced by means of a membrane with a hole through which the wire 12 passes in a pressure-tight manner. Other pressure-tight solutions of the known type may be provided for, alternatively or additionally to the membrane, in order to obtain a pressure-tightness on the wire 12 in the pressure-tight inlet 16 and/or in the pressure-tight outlet 18. For example, there could be provision for a calibrated hole through which the wire 12 passes.

[0018] Another solution is that of a labyrinth-like tightness. Other sliding tightness solutions may be used at the pressure-tight inlet 16 and/or the pressure-tight outlet 18.

[0019] The pressure-tight inlet 16 and the pressure-tight outlet 18 may allow a reduced pressure to be maintained inside the chamber 14. In each case, the pressure-tight inlet 16 and the pressure-tight outlet 18 may limit the losses of negative pressure inside the chamber 14 in such a manner that the maintenance of a predetermined constant negative pressure requires a reduced supply of energy.

[0020] In order to limit the pressure differential between ambient pressure and the reduced pressure of the chamber 14, there may be provided at the inlet side of the wire 12 one or more decompression chambers 20a, 20b, 20c. In the decompression chambers 20a, 20b, 20c, the pressure in a predetermined decompression chamber is greater than the pressure in the following chamber. For example, the pressure in the first decompression chamber 20a is less than atmospheric pressure, but is greater than the pressure in the subsequent decompression chamber 20b. If there is provision for a single decompression chamber, the internal pressure thereof will be less than atmospheric pressure, but greater than the pressure of the plasma deposition chamber adjacent thereto.

[0021] Each decompression chamber 20a, 20b, 20c is passed through by the wire 12 which is introduced progressively therein through pressure-tight inlets 22a, 22b, 22c which are identical, equivalent or functionally similar to the pressure-tight inlet 16 of the chamber 14.

[0022] Similarly, in order to limit the pressure differential between the reduced pressure of the chamber 14 and ambient pressure, there are provided one or more compression chambers 24a, 24b, 24c. In the compression chamber 24a, 24b, 24c, the pressure in a predetermined pressure chamber is greater than the pressure in the preceding chamber. For example, the pressure in the third compression chamber 24c is greater than the pressure in the second compression chamber 24b. The pressure in the compression chamber 24c is therefore less than atmospheric pressure. If there is provided a single compression chamber, the internal pressure thereof will be less than atmospheric pressure, but greater than the pressure of the plasma deposition chamber adjacent thereto.

[0023] Each compression chamber 24a, 24b, 24c is passed through by the wire 12 which is discharged progressively therefrom through pressure-tight outlets 26a, 26b, 26c which are identical, equivalent or functionally similar to the pressure-tight outlet 18 of the chamber 14.

[0024] At the outlet of the compression chambers 24a, 24b, 24c, the wire 12 may be drawn by means of a transport system 40 of known type, for example, comprising drawing rollers, pincers, etc. The drawing system of the wire 12 may also be produced, alternatively or additionally to the transport system 40, with other systems or equivalent systems, which are arranged internally with respect to the compression chambers and/or the decompression chambers of the installation and/or inside the plasma deposition chamber 14 and/or upstream of the decompression chambers.

[0025] There may be provided in the chamber 14 plasma deposition groups 30. The plasma deposition groups 30 each emit a plasma ray 32. As known, each plasma deposition group 30 may comprise a target 34 of the material which is used to coat the wire 12. Each plasma deposition group 30 may further comprise an annular focusing electrode 36 in which there is conveyed the flow of electrons which are from a transport cone 38, in accordance with a technique which is known and not described herein in detail.

[0026] There may be provided around the wire 12, in the chamber 14, one or more plasma deposition groups. Preferably, but in a non-limiting manner, as can be seen in FIG. 2, there may be provided, for example, three plasma deposition groups 30 which are arranged around the wire 12. Each plasma deposition group may be arranged so as not to be struck by a plasma ray of another plasma deposition group. In the specific but non-limiting embodiment of FIG. 2, the three plasma deposition groups 30 are distributed radially at 120° from each other in the chamber 14. The respective plasma rays 32 can be directed radially towards the centre of the chamber 14 and therefore towards the space which exists between the other two plasma deposition groups 30 so as to prevent the deposition of material on another plasma deposition group which is opposite.

[0027] The uniformity of deposition of material on the wire 12 is ensured by the spatial distribution of the plasma rays 32 in the chamber 14 which are arranged radially around the wire 12. In order to improve the uniformity of coating on the wire 12, it is possible to impart to the wire 12 itself an oscillation about the individual longitudinal axis thereof, as indicated by the arrow R in FIG. 2. Preferably, in the embodiment illustrated in FIG. 2, there is imparted to the wire 12 a rotational oscillation of approximately 60° during the throughput time of the plasma rays 32 so as to expose the whole of the external surface of the wire 12 to the deposition brought about by a respective plasma ray 32. There may be imparted to the wire 12 a periodic alternating oscillation in the two directions of rotation about the individual longitudinal axis thereof. Alternatively, it is possible to mount the plasma deposition groups 30 on an internal oscillating drum which is concentric with the chamber 14 and to impart the rotational oscillation to the plasma deposition groups 30 and to the wire 12. In a variant, it is possible to reduce the extent of oscillation of the wire 12 and the groups 30 by imparting an oscillation both to the wire 12 and, in the opposite direction, to the plasma deposition groups 30.

[0028] In order to coat the wire 12, it is possible to proceed initially by inserting the wire 12 inside the installation 10. The wire 12 may pass through the pressure-tight inlets 22a, 22b, 22c, 16 in order to arrive at the chamber 14. The wire 12 may pass from the chamber 14, through the pressure-tight outlets 18, 26a, 26b, 26c. The wire 12 may be engaged by the transport system 40 for the movement thereof inside the chamber 14. The decompression chambers 20a, 20b, 20c, the compression chambers 24a, 24b, 24c and the chamber 14 can be brought to the predetermined negative reference pressure. Subsequently, one or more plasma deposition groups 30 can be ignited. The transport system 40 can pull the wire 12. The drawing of the wire 12 may be brought about at a constant or variable speed, or with portions in accordance with spaced-apart time periods, in accordance with the characteristics of the installation, of the coating material and the characteristics of the metal wire to be coated. Preferably, the wire 12 and/or the plasma deposition groups 30 can be caused to oscillate about the longitudinal axis of the wire 12 in order to allow the uniform deposition of the coating material on the surface of the wire 12.

[0029] There may be provided a number of variants with respect to the installation described above. There may be provided a plurality of plasma deposition chambers. The plasma deposition chambers can be arranged in series in order to carry out a coating with a thickness which is progressively greater and which is formed by a plurality of layers of the same coating material or by a plurality of layers of different coating materials.

[0030] There may be less than or more than three plasma deposition groups. For example, there may be provided a single plasma deposition group in the plasma deposition chamber. In that case, it is possible to provide for rotation of the wire and/or the plasma deposition group so as to cover the entire arc of 360° in order to coat the entire external surface of the wire with the coating material.

[0031] Before or after the plasma deposition chamber(s), the wire may pass through preparation or finishing work stations, for example, for drawing, pickling, degreasing, washing, varnishing, annealing, quenching, polishing, etc.

[0032] Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention.