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United States Patent	3,655,428
Bragard	April 11, 1972

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Foreign Application Priority Data

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Jan 02, 1969 [BE]			726,416

Current U.S. Class:	427/567 ; 118/718; 427/251
Current International Class:	C23C 14/56 (20060101); C23C 14/04 (20060101); C23c 011/00 ()
Field of Search:	117/93.3,16R,16A,107.1 118/48,49,49.1,49.5,50,50.1

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References Cited

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U.S. Patent Documents

2879739	March 1959	Bugbee et al.
3019129	January 1962	Walsh

Primary Examiner: Leavitt; Alfred L.
Assistant Examiner: Newsome; J. H.

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Claims

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I claim:

1. A process for coating metal wires with a coating substance in a low pressure enclosure, comprising bombarding at least one auxiliary wire, constituting the coating substance, with electrons so as to raise the auxiliary wire to a temperature at which the coating substance evaporates; passing the metal wires through the enclosure, the metal wires being substantially parallel with the auxiliary wire; and reflecting vapor emitted by the auxiliary wire by means of at least one screen held at a temperature at least equal to the melting temperature of the coating substance, so that vapor is directed towards parts of the metal wires facing away from the auxiliary wire.

2. A process as claimed in claim 1, said screen being constituted by said enclosure, including holding the internal surface of said enclosure at a temperature at least equal to the melting temperature of said coating substance.

3. A process as claimed in claim 2, said enclosure being cylindrical, including feeding said metal wires into said enclosure in an air-tight manner, and withdrawing said metal wires from said enclosure in an air-tight manner.

4. A process as claimed in claim 1 said enclosure containing an array of auxiliary wires and electron emitters for heating said auxiliary wires, including passing said metal wires to be coated through said array of auxiliary wires, and bombarding each auxiliary wire with electrons from at least one electron emitter, in which process:

a. said wires to be coated are substantially parallel to each other;

b. said auxiliary wires are substantially parallel to each other;

c. said wires to be coated are substantially parallel to said auxiliary wires; and

d. said wires to be coated do not meet said auxiliary wires, said emitters, or the electron trajectories, during their passage.

5. A process as claimed in claim 4, in which the direction of motion of said wires to be coated is substantially parallel to said auxiliary wires.

. A process as claimed in claim 4, in which said wires to be coated each lie along an edge of a regular lattice of hexagonal prisms; each auxiliary wire lies along the longitudinal axis of one of said prisms; and said emitters are placed between said auxiliary wires, at a ratio of one emitter per two auxiliary wires.

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Description

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The invention relates to processes for coating metallic materials, and principally metallic materials in elongated form such as, for instance, wires or strips.

At present numerous methods are known for coating metallic materials, in which the substance serving as the coating, after having been atomized or vaporized in an appropriate enclosure, condenses on the material to be coated.

In the case where the metallic materials to be covered are in an elongated form, or occupy a space which is large relative to that of the source of the vaporized substance, it is generally rather difficult to obtain on the material a coating, the thickness of which is accurately uniform. This lack of uniformity in the thickness of the deposit has its origin in the differences of length existing among the paths which the vapor produced has to travel to reach the different parts of the material to be covered, the nearest parts being covered to a greater extent than the more distant parts.

The invention provides a process for coating metallic materials in a low pressure enclosure (for example, of the order of 10.sup.-.sup.1 to 10.sup.-.sup.5 Torr) containing a substance intended to serve as a coating, the substance being at a temperature at which it vaporizes, the material to be coated being disposed near the substance, and at least part of the material being opposite the free surface of the substance, in which process at least one screen intended to serve as a reflector of the vaporized substance, is held at a temperature at least equal to the melting temperature of the substance, and is positioned such that at least part of the vaporized substance coming into contact with the screen is reflected by the screen towards parts of the said material facing away from the said free surface.

The invention will be described further with reference to the accompanying drawings, which illustrate embodiments of the invention by way of example only, and in which:

FIG. 1 is a schematic transverse section through apparatus for putting a process according to the invention into effect;

FIG. 2 is a similar view of a further form of apparatus;

FIG. 3 is a similar view of another form of apparatus; and

FIG. 4 is a diagrammatic transverse section through yet another arrangement for putting a process according to the invention into effect.

In FIG. 1, the material to be coated 1 is disposed above a melting vessel 2 containing a coating substance 7. Screens 3 and 4 are placed obliquely at a higher position than the material 1, and are maintained at a temperature higher than the melting point of the substance 7. By reflection of the vaporized substance 7 from the screens, as indicated in broken line, a uniform deposit is obtained on the upper face 5 of the material 1 to be coated; the assembly of melting vessel 2, covering substance 7, and screens 3, 4 is placed in a enclosure 6 under vacuum.

According to an advantageous variant of this process, a coating can be applied to a filament or a strip, by making the material to be covered to pass, at an appropriate speed, between the screens and the substance intended for the coating. The screens can be plane or curved, according to the local geometric necessities. This process is shown diagrammatically in FIG. 2. Parallel wires 1a, pass continuously above the melting vessel 2 containing the substance 7 to be vaporized and below a curved screen 3a. The whole assembly is again situated in an enclosure 6 under vacuum.

The screens may be a part of the enclosure itself, or may be constituted by this enclosure itself, the internal face of the enclosure being taken to a temperature at least equal to the melting point of the coating substance.

In this latter case, the enclosure can be cylindrical and contain a receptacle for the coating substance; the material to be coated is to pass above the receptacle, the entry of the material into the enclosure and its exit therefrom being performed in an air-tight manner by appropriate means known per se.

Particularly in the case of coating wire, the enclosure can be a cylindrical enclosure in which is mounted a longitudinal element constituting the coating substance; the material is made to pass near the covering substance, the path of the material through the enclosure advantageously being parallel to the said element constituting the covering material. The entry of the material into the enclosed space and its exit therefrom is again made in an air-tight manner.

FIG. 3 shows diagrammatically the mode of operation where the material to be coated 1a, is a number of parallel metallic wires introduced into the enclosure 6 under vacuum; these wires are disposed around an auxiliary wire 8 constituting the coating substance. By bombardment of this auxiliary wire 8 with the aid of an electron gun, the coating substance is vaporized and deposits itself on the wires 1b, either directly or after reflection from the internal wall of the enclosure 6 which serves as a cylindrical screen 3b. The enclosure 6 is maintained at a temperature at least equal to the melting temperature of the auxiliary wire 8.

The arrangement of wires to be covered, auxiliary wires constituting the coating substance, and electron guns, can be made in any manner and it is only purely by way of an example that there will be described hereinafter a particularly advantageous arrangement to attain a uniform coating.

In this arrangement, an aggregate of wires to be coated is passed through a network constituted by auxiliary wires and electron emitters, each auxilliary wire being submitted to the bombardment of at least one electron emitter;

the wires to be coated are parallel to each other, and are preferably regularly spaced in relation to each other;

the auxiliary wires are parallel to each other, and are preferably regularly spaced in relation to each other;

the wires to be coated are substantially parallel to the auxiliary wires;

the wires to be coated do not melt the auxiliary wires, the electron emitters, or the electron trajectories, during their passage.

In this manner, the vapors produced by the electron bombardment of one or the other of the auxiliary wires will be able to condense on each portion of wire to be coated, while, during its passage, each portion of wire will remain in the network of auxiliary wires and emitters.

According to an advantageous variant of this particular process, the direction of movement of the wires to be coated is made parallel to the auxiliary wires, which allows the wires to be coated to pass through continuously, and consequently allows continuous working of the process.

There are many ways of conceiving the arrangement of the wires to be covered, the auxiliary wires and the emitters. There is, however, a technical and economic advantage in using the minimum of auxiliary wires and emitters, while attaining a uniform covering of the greatest number of wires. In this respect, the wires to be coated are each disposed at the edges of a network of hexagonal prisms; the auxiliary wires are placed along the longitudinal axes of the said prisms; and each emitter is placed between two auxiliary wires, at the ratio of one emitter per two wires. It will be appreciated that, due to this arrangement, each wire to be coated (except the outermost wires of the network) is on the longitudinal axis of an equilateral triangular prism, each edge of which is occupied by an auxiliary wire.

In order to attain an equal possibility of coating for all the wires, auxiliary wires are also disposed outside the network of wires to be coated, in such a manner that the outer wires of this network are also situated on the longitudinal axis of an equilateral triangular prism each edge of which is occupied by an auxiliary wire.

In this manner one can attain, for example, the simultaneous coating of 42 wires with only 30 auxiliary wires and 15 electron emitters, as shown in FIG. 4, which shows a transverse section through the network. A lattice of 14 hexagons has 42 peaks each of which is occupied by the trace of a wire to be coated 1c. The center of each of these hexagons is occupied by the trace of an auxiliary wire 8c, that is to say 14 wires. The lattice of hexagons is itself surrounded by the traces of 16 auxiliary wires 9 which allow the outermost wires to be coated evenly. The 30 auxiliary wires 8,9 are acted on by 15 electron emitters 10, each disposed between two auxiliary wires. The whole lattice is placed in a circular sheath 6 the internal wall 3c of which is at a temperature greater than the vaporization temperature of the coating substance and serves as a reflecting screen.

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