US1726679A - Method of teeating composite wiee - Google Patents

Description

J. H. RAMAGE METHOD OF TREATING COMPOSITE WIRE Fi1ed March 1'8, 1925 INVENTOR JOHN H. RAMAGE Patented Sept. 3, 1929.

UNITED STATES PATENT OFFICE.

, JOHN HUMPHREYS RAMAGE, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

METHOD OF TREATING COMPOSITE WIRE.

Application filed March 1.8, 1925. Serial No. 16,290.

This invention relates to the manufacture of a composite wire and particularly to chromium coated wire and a process for producing the same.

In the manufacture of incandescent electric lamps, it is desirable to rovide electrical conductors in the form 0 wires which may be embedded in a glass portion of an evacuated container. It is essential that wire for the above purpose be of such a character that it will effectively unite or wet with the glass portion through which it passes and thus prevent communication between the interior and exterior of the bulb.

It has been found that a wire having the surface of chromium answers the requirement as to wetting with the glass to furnish a bond and prevent leakage to the detriment of the vacuum within the bulb. Wires or conductors for providing a gas-tight seal have been used heretofore, a preferable composition for such wire being copper coated nickel steel which, however, has certain disadvantages. For example, any oxide on that portion of the leading-in wire within the evacuated vessel is subjected toreduction by the hydrogen therein, causing the formation of water vapor which is deleterious to the operation of a lamp.

It has been proposed to utilize a wire composed of nickel steel which has the proper coefiicient of expansion for a conductor when sealed in a glass and to coat the nickel steel wire with chromium in various ways. One example of such coating may be the deposit of chromium upon a nickel steel wire by electrolysis. The electrolytic or plating deposition of the coating is desirable,

since it provides for a more accurately controlled layer with respect to the thickness and uniformity of the deposit. It has been found, however, that when chromium is electrolytically deposited, it is somewhat brittle and not sufiiciently adherent to the object upon which it is deposited. The plated coating, therefore, has the disadvantage of being subject to cracks and may, in fact, become separated from the object when subjected to heat or the object or core may shrink away from the outside coating. or sheath, depending upon the relative coefiicient of expansions of the plated material and the chromium.

Although chromium wets with glass and bonds properly therewith, it is obvious that in order to efl'ectively provide a gas-tight seal, the chromium itself must bond or unite intimately with the core upon which it is deposited. Ordinarily, a chromium layer plated upon a body is more or less subject to rupture when the body is bent'inasmuch as the layer lacks suflicient ductility to .take a the shape of the body, the consequence being that a loosening of the coating and the body occurs.

An object of the present invention is, therefore, to provide a wire having a suitable core with a ductile nonbrittle chromium layer thereon.

Anotherobject of the invention is to provide a pliable coated wire resistant to rupture when flexed.

A further object of the invention is to provide a wire having a suitable coefiicient of expansion for sealing into a vitreous object and provided with an adherent ductile coating capable of Wetting with the object. A still further object of the invention is to provide a method of ductilizingchromium.

A still .further object of the invention is to provide a method of sintering chromium 4 without embrittling.

A still further object of the invention is to provide an article composed of a. body having an electroplated ductile, coating thereon.

Other objects and advantages of the invention will become apparent as' the de-- scription proceeds.

As above set forth, it has been heretofore proposed to eletroplate a body with a coating of chromium. Such plated bodies have been heat-treated to certain temperatures preferably near the melting point of chromium but limited by the melting point of the body.

Although good results havebeen obtained by the above method, it has been found that certain desirable advantages are possible by the present method. It is necessary that the atmosphere in which the plated object is heated be absolutely free from oxygen or oxidizing gas which I have found tends to cause a brittle coating.

The present invention aims to provide an effective sintering of the platingor chromium coating and tween t e coatin and the body to which it is applied. It as been found that any traces of moisture n the atmos here or heating environment will defeat e sintering operation. For the purpose of obtaining the desiredsintering or proper adherence between the coating and body or core to which it is applied, the

present novel method is employed to remove all traces of moisture in the atmosphere or in a reducing gas. I, therefore, entirely surround or pack a chromium plated wire to be treated in powdered material capable of dissociating water vapor at working temperatures and of forming an irreducible oxide at those temperatures and in the atmosphere used such for example as hydrogen or other gas inert with respect to the material employed. An illustration of the operation of my 'fprocess will be had from the following.

I the method is to be employed to produce lead-in wires for incandescent lamps, nickel steel wire of a suitable size may be plated electrolytically with chromium to a predetermined thickness in a' proper that by raising the temperature to 1100 C.

and maintaining such temperature for a period of about 10 minutes and then cooling the contents of the'furnace in a flowing hydrogenor other inert gas to normal temperatures, that good results are obtained.

Wire produced by the foregoing method was found to have a bright appearing'metallic ductile and adherent layer of chromium of'such quality that the wire could be repeatedly bent back upon itself until fracture occurred without cracking or chipping the coating' Microscopic examinations showed that although an apparentline of division remained between the chromium layer and the core, that the layer was adherently united to the core by a sinterin action. The process is not, however, limited to wire since, other objects may be readily electroplated with chromium and subjected to the steps of the present method.

Apparatus of the character employed to carry out my method is shown diagrammatically in the accompanying drawings in which. v

Fig. 1 is an .elevational view, of several units such as a plating tank, furnace, etc., in proper arrangement to permit a progressive treatment of a wire, and

Fig. 2-shows a sectional view of a tray f containing a spool of plated wire covered with a powdered material ready to be placed in a furnace.

Good results have been attained when employing a tray containing chromium powder 8. in which a spool -9 of chromium pla-ted wire is embedded, and positioning the traywithin a furnace and heating in an inert atmosphere such as hydrogen.

When desirable the steps of the present method may be progressive in which case the wire may be coated continuously by being drawn slowly through a plating bath. It may then be passed through washers and driers into a heated tube through mercury seals provided at each end and finally wound on a spool.

The accompanying drawing is a schematic illustration of an apparatus by means of which wire may be coated and rendered due tile by a continuous operation. In the drawing it will be noted that a nickel steel "or other suitable wire 10 may be led over a pulley 11 from a suitable source of supply on a spool 12. The wire 10 may pass into an electrolytic bath 13 and out over pulley 14.

When the wire has been plated, the same may be led through a furnace 15 in which a suitably prepared atmosphere is provided. The furnace 15 maybe entirely closed and the inlet and outlet for the wire may be provided. with seals 16 and 17 respectively in the form of, U-shaped tubes containing mercury through which the, wire passes. After having passed through the furnace. the wire may be wound upona spool 18.

The heat-treatment to which'the wire is subjected as above set forth must be performed in a suitable environment in the absence of oxygen or such gasesas will have a detrimental efiect upon the chromium coating of the wire and after all traces of moisture have been removed.

It has been found preferable to use hydrogen which may be passed through a suitable drier 21 and thence through powdered chromium which may be contained in a chamber 22 heated by burners 23 to a suitable temperature. After passage through the chromium the hydrogen may be permitted to flow into the chamber through an inlet 24 and out therefrom throughoutlet 25.

The outlet line may be provided with a chamber 26 containing powdered chromium and heated by burners 27, and an additional drier 28 may also be provided. The drier and powdered chromium on the outlet line of the apparatus prevent the return of impure gases by diffusion.

It: is obvious that materials may be used other than chromium powder as a protecting agent during the sintering operation. For

. e'xample,'tantalum powder, thorium powder,

aluminum, silicon, etc, may be used and suitable temperatures employed during heating. depending upon the action of the material on the water vapors at the temperatures selected. Although any suitable powdered substance maybe used, it has been found desirable to use a powder of the same material as that of the layer to be rendered ductile for the reason that the passage of the gas over such material results in a removal of any impurities forming stable compounds inthe treating atmosphere which would otherwise form on the material treated.

It has been found that although such other powdered materials as for example tantalum give very satisfactory results, that the use of chromium powder is more effective inasmuch as it acts to dissociate Water vapor from the inert gas and appears to absorb gases that would be detrimental if permitted to come in contact with the layer of chromium being ductilized upon the body of other metal.

When practicing the present invention the resultant product is a body having a ductile firmly adherent layer of chromium thereon.

" A body treated in accordance with my method is capable of withstanding repeated heating and cooling without cracking or chipping and may be drawn, making the article pliable and applicable for many uses, particularly as the leading-in wires for incandescent electric lamps.

Although it has been found preferable to employ hydrogen, it will'be appreciated that other inert gases may be used. The invention contemplates the treatment of a wire having a core covered with an applied layer of another metal, in an atmosphere in which the sheath or coated wire may be treated in the absence of gases which may cause oxidation or contamination of the treated metal.

It is known that a metallic layer applied by an electrolytic method is comparatively brittle and the degree of brittleness is proportional-to the amount of gas, such as hydrogen occluded during the plating operation. I have found that in my method in which the plating is subjected to sintering temperatures, that the crystalline structure of the plating is rendered similar to that of a metal which has been fused. It is thought that the forces of crystallization induced by the high temperature are sufiicient to cause a movement or readjustment of the crystal or grains of the metal to bring them into close proximity or in a state of better coherence. This action results in the expulsion of the occluded gas.

Although it was generally presumed that the brittleness of a plating was due to the adsorbed or occluded gases, I have found that the ductility attainable by my method is. attributable to the complete sintering of the layer or platin and that the removal of gas which results rom the sintering operap "tion is merely incidental and the ductility is a result of effecting a complete sintering of the plating.

It will be understood that my invention contemplates the production of a ductile adherent coating of one metal upon. another by sintering or heat-treating; that in attaining the desired result I provide as part pf my invention a method of rendering a normally contaminated atmosphere of such purity as to serve as an environment for the metallic coated article during the heat-treatment thereof.

While I have described what I now consider a preferred method of practicing my invention, it is to be understood that the same is merely illustrative and that my invention is limited only by the scope of the appended claims.

What is claimed is: i

1. The method of making a composite body which comprises plating a metal body with a metal, covering the plated body with a layer of a material and heating in the presence of a gas inert with respect to said material, said material beingcapable of yielding 7 compounds irreducible in the said gas to prevent impurities from reaching the plated body during the heat treatment.

, 2.. The method of making a composite body which comprises providing a body of one presence of a gas with respect to said mate- I rial, said material being capable of yielding compounds irreducible in said gas to avoid contamination of the body during the heat treatment.

4. The method of making a composite body which comprises plating a metal body with 3 chromium, covering the plated body with chromium powder and heating in the presence of a gas inert with respect to chromium. 5. The method of making a composite body which comprises plating an alloy with chro- I mium, covering the plated body with chromium powder and heating in the presence of a gas inert with respect to chromium.

6. The method of manufacturing chromium coated metal bodies which comprises electroplating the bodies and ductilizing the plating by heating to annealing temperature under a layer of chromium powder.

7; The method of manufacturing chromium coated wire which comprises electrolating the wire with chromium and sintermg the plating to the wire by heat-treating the wire under a layer of chromium powder. 8. The method of treating a wire electroplated with chromium to render the plating 1 sufiicient to cause the'plating to sinter with the wire and in carrying on the heat-treatment while the wire is embedded in chro- Y mium powder.

.9. The method of making a composite body which comprises plating a body with a metal, covering the body with a powdered substance of the same material of which the' body is composed and heating in the presence of agas inert with respect to said material.

10. The method of making a composite body which comprises plating a metal with another metal, covering the body with a powdered layer of the second mentioned metal andheating in the presence of a gas inert with respect to said layer. 7

11. The method of manufacturing chromium coated metalbodies, comprising electroplatin'g the bodies with chromium and ductilizing the plating by annealing under a 12. The method of treating a wire electroplated with chromium to render the plating ductile and not liable to separation from the wire, comprising heating the same to a temperature to cause the plating to sinter to.

the wire and in carrying on the heat treatment while the plated wire is embedded in a materal in the presence of a gas inert with respect to said. material, said material being capable of yielding compounds irreducible in said gas to prevent impurities from reach ing the plated body during the sinteri'ng operation.

In testlmony whereof, have hereunto subscribed my name this 17th dayof March,

JOHN HUMPHREYS RAMAGE.

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