US2736957A - Manufacture of copper wire for varnish-insulated wires - Google Patents

Description

MANUFAQTIURE OF COPPER WIRE FOR VARNllSH-WSULATED WERES Harry Hearing, Berlin-Spandau, Germany, assignor to Siemeus-Schuckertwerke Aktiengesellschaft, Berlin Siemensstadt, Germany, a corporation of Germany No Drawing. Application February 20, 1952, fierial No. 272,715

Claims priority, application Germany March 8, 1951 1 Claim. (Cl. 29-528) the blank wire to be insulated is an essential prerequisite.

Various expedients are available for avoiding the occurrence of impurities on the wire surface or removing such impurities prior to enameling.

Besides, it is also known to use for the manufacture of enameled wire a copper raw material free of the customary inclusions of cuprous oxide and free of bubbles or other contaminations and irregularities, i. e. a pure electrolyte copper smelted and cast under the exclusion of oxygen. Such oxygen-free high-conductivity copper is available in the trade, for instance under the trade designation OFHC. Heretofore this type of copper has been cast in the customary manner into rectanguar wire bars, and these bars have been converted into wires by rolling. This process cannot prevent the occurrence of folds or overlaps whose oxidized surfaces are rolled into the soft copper material during subsequent rolling passes but reappear later on the drawn Wire. It is known to subsequently eliminate such impurities by a material-removing operation with the aid of a drawing die or nozzle, a milling cutter, a scraper or the like tool that removes a superficial layer of the drawn wire. Such operations, however, involve an uneconomical loss in material.

It has also been proposed to fabricate copper for enamel wires by a pressing method which does not produce the contamination and surface roughness inevitable with the Wire rolling process. According to this proposal, bars of ordinary electrolyte copper are processed into wires on extrusion presses.

It is an object of my invention to provide a method for the manufacture of varnish or enamel insulated copper wires that results in better and more uniform products than obtainable with the known processes.

The invention is based upon the recognition that for attaining highest quality in enamel insulated wires not only a smooth surface of the copper wire on the one hand, or an oxide-free copper material on the other hand is essential, but that a further improvement is to be expected if these two conditions are jointly satisfied within the same processed wire material so that the resulting blank wire neither contains occluded oxygen nor shows any spots of surface roughness.

ttes Patent 0 According to my invention, therefore, blank copper wire to be used particularly for the manufacture of varnish or enamel insulated electric conductors, is produced from pure electrolyte copper smelted and cast under exclusion of oxygen and is prepared for the final drawing by a pressing or extrusion operation. The use in this process of pure and oxygen-free copper bars has the result of preventing any inclusion of cuprous oxide that might reach the surface during the subsequent final drawing of the wire, while the fabrication of these bars by extrusion also prevents the occurrence of defective or rough spots at the wire surface. The wires thus processed, when drawn to the ultimate sizeand insulated, have uniformly excellent qualities superior to those best expectable from the methods heretofore available.

The method is preferably carried out by smelting and casting oxygen-free electrolyte copper under the exclusion of oxygen, for instance in vacuum, into round ingot bars to form bolt-shaped copper bars which are suitable for insertion into an extrusion press. In the press the bars are heated to a plastic condition and are forced through the extrusion die under heavy pressure to form a wire. After the extrusion step, the Wires are drawn through dies in the customary manner to the desired final measure. It is not necessary to subject the drawn wire to a material-removing operation but suffices, if desired, to etch the wire prior to enameling for final cleaning. The varnish or enamel coating is applied to the wires in the customary manner.

The invention is not limited to the manufacture of wires to be insulated by a coating of varnish or enamel but may be applied with advantage in all cases where Wires, especially fine-size wires, are to be manufactured that are to be given a clean and perfectly smooth surface.

I claim:

The method of producing enamel-insulated electric conductors, which comprises smelting pure electrolyte copper in an oxygen-free environment, casting the copper in said environment into bars, subjecting the bars to heating to plastic condition, hot pressing in an extrusion press to form wire, drawing the wire to size, and coating the drawn wire surface with varnish.

References Cited in the file of this patent UNITED STATES PATENTS Re. 7,913 ONeill Oct. 16, 1877 68,331 ONeill Aug. 27, 1867 662,247 Vinton Nov. 20, 1900 1,432,803 Summey Oct. 24, 1932 1,902,905 Schreiben Mar. 28, 1933 2,023,498 Winston Dec. 10, 1935 2,228,257 Collins Jan. 14, 1941 2,257,535 Rohn Sept. 30, 1941 2,260,914 McGar Oct. 28, 1941 2,264,287 Betterton Dec. 2, 1941 2,286,759 Patnode June 16, 1942 2,371,716 Snell Mar. 20, 1945