US2123778A - Electric wire - Google Patents

Description

July 12, 1938. HElLMANN 2,123,778

ELECTRIC WIRE Filed March 22, 1935 jig-i :1 T

Patented July 12, 1938 UNITED STATES ELECTRIC WIRE Josu Heilmann, Clichy,

ciete Alsacienne de Clichy, France Application March 22,

France, assignor to Sonatructions Mecaniques,

1935, Serial No. 12,497

In France December 12, 1934 15 Claims.

Finished products in which the conducting core is insulated from the outer metallic sheathing by means of a solid pulverulent body have already been produced. In such processes a work-piece having an initial size which will give the final size desired is subjected to drawing to produce a wire of a given diameter and length.

The manufacturing processes heretofore used failed to secure conducting-or resistance wires of high electrical properties and particularly failed in producing a perfectly homogeneous dielectric material having an exactly centered core (either with a single integral or stranded core or with a core comprising a plurality of conductors) and a high kilometric insulating resistance.

The present invention has for its object a manufacturing process overcoming the above mentioned disadvantages and producing a product materally different from the products heretofore manufactured.

The invention first of all comprises a complete dehydration of the dielectric to remove all water whether of composition, crystallization or suspension. The work pieceis then preferably tightly sealed before being subjected to the metallurgical treatments. In fact, the inventor has ascertained that complete dryness of the dielectric permits reaching insulating resistances of much higher range than those obtained with the same but not completely dehydrated dielectric. Consequently a new type of electric wire is produced.

Such dehydration causes a new stability of the wire involving the new and very useful feature of high temperature resistance. This feature means, first, that the electric wire can withstand, without any disadvantage, a high temperature at which the presence of vaporized water in ordinary wires entrapped in the compressed insulating material, which becomes impervious due to its considerable length, would involve the danger of explosion of the sheathing, and second that it is practically possible, without danger or any disadvantage to subject the wire to a temperature beyond which the metals constituting the sheathing and the core are burnt or molten ordinarily. The new wire can withstand a temperature at which electric wires or cables heretofore manufactured would be destroyed.

Another feature of the invention consists in arranging the dielectric within the metallic sheathing under a homogeneous, isotropic and compact form and to this end said dielectric is reduced to a fine powder and compressed under a proper pressure.

Such pressure is sufliciently high to secure a compactness hereinafter called limit compactness so that external stresses applied to the sheathing are completely transmitted to the core through the dielectric.

In one example of the process, the insulation, 5 prior to its insertion in the sheathing, is shaped into compressed elements by moulding under high pressure. Such elements are then arranged by hand in the work-piece.

In another example, the insulation in the form 10 of a powder is directly compressed within the sheathing of the work-piece under suitable pressure.

The work-piece thus obtained is subsequently subjected to metallurgical treatments comprising is shrinking and drawing in several courses, to secure a very considerable length.

Electric conducting or resistance wires are secured comprising a continuous metallic sheathing, a single integral or stranded conductor or a plurality of conductors and having an intermediate insulation such as magnesia or steatite, which is completely dehydrated, homogeneous and compact. The insulating resistance and thermal conglictivity of such electric conductors are both very 25 By way of example and in order to facilitate the understanding of the invention, an example thereof will be hereafter described.

The apparatus intended to com sulation in pulverulent form will with reference to the accom which:

Figure 1 is a longitudinal sect work piece during the filling. 35 Figures 2 and 3 are respectively plan and-eleva tional views of a tup-hammer for a single conductor work-piece.

Fig. 4 is a cross sectional view of the completed wire. 40 The insulating material used is pulverulent magnesia but other materials such as steatite could as well be used.

The said insulating material, either in the form of powder or of compressed elements of such powder,'is subjected to a complete dehydration, which will be continued until the last traces of water, whether composition, crystallization or suspension, has disappeared. Practically, drying will be continued until after the weight of the 5 material ceases to vary.

A thermal cycle which gives good results for magnesia consists in heating at 1112 F. for 3 hours.

In inserting the insulation in the sheathing,

press the in- 30 be described panying drawing in ional view of a care must be taken to avoid re-hydration. To this end the work-piece may be heated during such operation.

The finished work-piece is heated for some minutes in a high temperature kiln and the piece is preferably tightly closed in order to avoid any alteration during subsequent treatments.

The work-piece may be closed by means of asbestos washers and a metal washer secured thereto in any desired manner.

According to the invention, the insulation is inserted in the work-piece sheathing under such compactness or limit compactness that the external pressures applied to the sheathing are completely transmitted to the core and consequently it is not necessary to subject the workpiece to a shrinking treatment before being able to obtain a homothetic lengthening after drawing.

According to the materials being tested, the value of the pressure which gave the best results was 57,000 lbs. per square inch for magnesia and 14,200 lbs. per square inch for steatite.

The insulating material may be brought to the compact state in various ways, either in the form of compressed elements obtained under high pressure or by pressing it directly in the work-piece or in any other convenient way.

When the pulverulent insulation is introduced in the form of compressed elements, said elements are agglomerated by a press capable of exerting a pressure which corresponds to the above mentioned values. The blocks thus obtained are subsequently dehydrated and successively introduced within the work-piece.

When the pulverulent insulating material is to be directly compressed into the sheathing the device shown in the accompanying drawing may be used.

The sheath-tube of the work-piece T is arranged vertically upon a bearing of convenient form and is provided at its lower part with a metallic washer forming a complete closure. The core passes through the washer and is firmly secured to the same.

In order that the insulating material may be rapidly compressed into the sheathing, the lower part of the tube should be clamped in a vise or like device E, in order to withstand all the stresses and particularly the tensile strength applied by a spring to the core for maintaining its rectilinear shape.

At the top of the sheath tube is arranged a funnel K in order to facilitate the flow of the insulating material.

Prior to securing the core to the spring R a tup-hammer M is inserted between the wire or wires of the core and the tube, said tup hammer being intended to compress the material. Its shape is determined for compressing the powder introduced between its surface and the tube and for centering the wires.

Good results have been obtained with the type shown in Figures 2 and 3. The tup hammer is fitted to the end of a tube D, which is of suflicient length so that the hammer may reach the lower end of the sheath-tube. In said position, the upper end of the tube D will sumciently extend from the sheath tube so as to secure at O a machine (not shown) which operates the hammer in the manner of a pile driver.

The funnel K is supplied by a device v(not shown) which is filled with pulverulent material treated as explained above. The tup hammer carrier tube is subjected to a positive ascending motion and then to a free fall or controlled motion. The magnesia falls between the front part of the tup hammer and the sheath-tube and is compressed. In the meanwhile the core is exactly centered and the level of the insulating material gradually rises in the work-piece. The ascending and falling motion of the hammer is combined with a rotating motion intended to produce a uniform compacting. Further, in order to facilitate the operation of the tup hammer carrier tube the latter may be made in several sections connected by threaded sleeves.

The finished work-piece is then subjected to drawing in successive courses. Due to the properties obtained by the above mentioned treatments, it will be possible to considerably increase the length of the electric wire, the respective dimensions of sheathing, insulation and core remaining homothetic.

The electric wires thus obtained distinguish from those heretofore produced by their structure as well as by their properties. They are provided with a completely dehydrated, highly compact dielectric constituted by grains of very small size, compressed under high pressure for attaining the limit compactness of the dielectric, and consequently very homogeneous and isotropic.

The kilometric insulating resistance of such electric wires is of a much higher range than those heretofore manufactured. Said resistance is much higher than 10 megohms and for a type of cable in which the internal diameter of the sheath tubing is in. and the core diameter in. the resistance will be higher than 2000 megohms.

In a more general way, the resistivity of the insulation at 68 F. (for magnesia) is higher than 6 x 10 megohms per square centimeter section of insulation and per centimeter of length. For the above mentioned cable the resistivity reached 12 x 10 megohms per square centimeter and per centimeter.

Furthermore, the insulation has a very homogeneous state and a very high degree of compactness or limit compactness giving for magnesia a density of about 2,3.

Finally the thermal conductivity of the insulation reaches and even goes beyond watt per centimeter of length and per degree C. For the example given above the thermal conductivity was higher than watt.

As a new industrial product, the invention also relates to the work-piece provided with agglomerated and dehydrated dielectric. The workpiece is preferably tightly closed at its ends in order to avoid any introduction of water during subsequent treatments.

The invention applies to the manufacture of wires or cables of all types, provided with one or more conductors whether for high or low currents, high or low tension, energy transmission or heating purposes. The electric wires thus obtained are highly resistant to heat; their overall thermal conductivity is very high and consequently avoids the danger of burning due to overload; the insulation is practically indestructible (the perforation of the insulation following accidental excess voltage leaves the insulation practically untouched), and consequently a high security is provided against excess voltages; the insulating resistance is very high and the dielectric features of such electric wires are absolutely stable.

According to the above mentioned process the wires may be made in sections of considerable length.

Having now particularly described and ascertained the nature of my invention and in what manner the same is to be performed, I declare that what I claim is:

1. A process of manufacturing fireproof electric wires comprising a conducting core, a refractory insulation and a metal sheath, by drawing an initial work-piece composed of such elements, characterized by the fact that before the said metallurgical drawing treatment, the insulation is subjected to a complete dehydration in order to eliminate all the water physically and chemically bound which is contained in the insulation, and preserved from all rehydration until the metallurgical treatments.

2. A process according to claim 1, in which the insulation is subjected to a complete dehydration by the elimination of all the water physically and chemically bound, which it contains and is then immediately inserted in the sheath of the workpiece whereupon said work-piece is subsequently subjected to the metallurgical drawing treatments.

3. A process of manufacturing fireproof electric wires comprising surrounding a conducting core located in a metallic sheath with refractory material, subjecting said refractory material to a complete dehydration in order to eliminate all water physically and chemically bound therein and then subjecting said core, sheath and refractory material to a metallurgical drawing treatment.

4. A process as set forth in claim 3 in which said refractory material is subjected to a complete dehydration for the elimination of all water physically and chemically bound prior to the insertion of said refractory material about said core.

5. A process as set forth in claim 3 in which said refractory material is subjected to a complete dehydration at the temperature of at least 600 C. for a period of about three hours prior to the insertion of said material about said core.

6. A process according to claim 1, in which before the metallurgical drawing treatment the insulation is subjected to a complete dehydration in order to eliminate all the water physically and chemically bound it contains and to a compression corresponding to the state of limit compactness of the said insulation.

7. A process as set forth in claim 3 in which said refractory material is subjected to high pressure when being disposed about said core.

8. A process as set forth in claim 3 in which said refractory material is essentially magnesium oxide and in which said magnesium oxide is subjected to a pressure above 4000 kg/cm'.

9. A process according to claim 1 in which the insulation is magnesium oxide and is subjected before the metallurgical drawing treatment to a complete dehydration in order to eliminate all the water physically and chemically bound which is contained in said insulation and to a compression above 4000 kg./cm

10. A process according to claim 3 in which said refractory material is essentially steatite and in which said steatite is subjected to a pressure in excess of 1000 kgs/cm 11. A process as set forth in claim 3 in which said refractory material is compressed in the form of moulded blocks under high pressure and in which said blocks are subjected to a complete dehydration in order to eliminate the water physically and chemically bound therein prior to their insertion about said conducting core within said sheath.

12. A process according to claim 1 in which the insulation is compressed in the form of blocks moulded under a pressure which is corresponding to the state of limit compactness of the insulation, the said blocks being subsequently subjected to a complete dehydration in order to eliminate the water physically and chemically bound, then inserted into the sheath of the workpiece, said work-piece being subsequently subjected to the metallurgical treatments in order to reduce its diameter to the required size.

13. A fire proof electric wire comprising an external metallic sheath, a conducting metallic core located within said sheath and parallel to the axis and a pulverulent insulation inserted between said sheath and said core, said insulation being under pressure and having a physically and chemically anhydrous state and the kilometric insulating resistance of said wire being in excess of 2000 megohms. I

14. A fireproof electric wire comprising a continuous external metal sheath, a conducting metal core parallel to the axis and a pulverulent insulation inserted therebetween, said insulation being in the state of limit compactness, in a physically and chemically anhydrous state and the resistivity of the insulating being, at the ordinary temperature, higher than 6 x 10 megohms per square centimeter section of insulation and per centimeter of length.

15. A process as set forth in claim 3 in which said refractory material is magnesium oxide and is subjected to a complete dehydration at a temperature of at least 600 C. for a period of about

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