US3209299A - Resistance metal alloy - Google Patents

Description

Sept. 28, 1965 c. J. GANCI RESISTANCE METAL ALLOY Filed July 2'7, 1962 hit 501 .QRXNUE o .0 .2 a 4 .5 .e .7 .8 .9 1.0 u: m. mm 1.5 t6 \-7 Lsmwu 21276241526 y I E Re 3 m m m m fu p\ M f mm W C W Z r M C m United States Patent 3,209,299 RESISTANCE METAL ALLOY Charles J. Ganci, Bellerose Manor, N.Y., assignor to Ward Leonard Electric 00., Mount Vernon, N.Y., a corporation of New York Filed July 27, 1962, Ser. No. 212,939 3 Claims. (Cl. 338269) This invention relates to electrical resistors and particularly to the composition of the metal alloy forming the resistive element.

The invention is particularly directed to wire wound type resistive elements mounted on a ceramic base and covered by a vitreous enamel coating. For a high quality, high precision, reliable resistor of this type it is desirable that the resistance element have certain characteristics and meet certain standards.

The temperature coefiicient of resistance measuring the change in resistance with temperature should be'zero or nearly zero, so that the resistor may be subjected to high temperatures without a material or, if possible, any

change in the resistance value of the resistive element due to the temperature rise. Further, the alloy should have a high tensile strength in order to form fine, strong wire having a high resistance value.

In the case of enamel coated resistors, the composition of the resistance element should not produce gases during the firing operation in the manufacture of the resistor. Gases that are produced by the resistive element create bubbles in the coating which form pinholes, thereby reducing the eifectiveness of the coating and rendering the resistor unsatisfactory for adverse climatic conditions.

Another desirable and essential characteristic is the ability of the resist-or to maintain the resistance value con stant over sustained periods of high heats. This is known as stability under electrical load life. Recrystallization is produced by sustained high currents heating the wire or by external heat which changes the resistance value of the resistive element.

The copper-nickel alloys containing 55% copper and 45% nickel have a low temperature coefiicient of resistance and moderate tensile strength with good resistivity so that .the Wire may be drawn into small diameters and have the required toughness and ruggedness for winding, bending and welding or soldering to terminals. However, the copper-nickel alloy forms gases on heating, which make it objectionable for coated resistors, and the temperature coefiicient of resistance is still too great for the requirements of precision resistors. These latter disadvantages may be overcome by the addition of small percentages of cobalt to provide a zero or nearly zero temperature coeflicient of resistance and eliminate or reduce the gasing so that it does not affect the coating.

Although these foregoing resistors have many of the desirable characteristics, they fail to have a high stability under electrical load life. Thus under sustained load or heat the resistance Values change.

An object of this invention is to produce a copper-nickel alloy for electrical resistance elements that has a zero or nearly zero temperature coeflicient of resistance and has a high stability under electrical load life while retaining the other desirable characteristics.

By the addition of small amounts of zirconium to a copper-nickel alloy, electrical resistance elements can be made that have all of the foregoing requirements, including high stability to electrical load life. The amount of zirconium may be increased or decreased to provide the resistive element either with a positive temperature coeflicient or with a negative temperature coefiicient, if it is so desired to impart such a characteristic to the electrical resistor. The zirconium-containing copper-nickel alloy eliminates or reduces the formation of gases and also has a high tensile strength providing a wide range of wire sizes and resistance.

The invention is more specifically described in connection with the drawings, in which FIG. 1 illustrates a coated wire wound resistor; and

FIG. 2 is a chart of the percent of zirconium in relation to the temperature coeflicient of resistance of the alloy.

Referring to FIG. 1, the base 10 may be made of a ceramic or other insulating material for supporting the terminals 11 and 12 and the resistive element 13. The base 10 is cylindrical in shape and the terminals are mounted thereon in a conventional manner. The resistance element or wire is helically wound on the base and soldered or welded to the terminals at each end. If a high resistance is required a small size wire is wound with many turns on the core. If a low resistance wire is required, the diameter of the wire is large and fewer turns are formed on the core.

In order to protect the resistive element against physical impact and corrosion a vitreous enamel layer is formed on the resistor by coating a vitreous enamel slurry in paste form on the resistorand then subjecting the resistor to high temperatures to convert the slurry to a hard, solid enamel. Several coats may be applied in order to secure the necessary thickness covering the terminals and the turns of the wire.

The metal alloy forming the resistive element comprises 45% nickel, approximately 1.7% zirconium and 53.3% copper. With this composition the resistive element will have a zero or nearly zero temperature coefiicient of resistance and will provide the element with high stability under electrical load life. As set forth in the following table, the percentage of zirconium may be varied above or below this amount to impart either a positive or negative temperature coefiicient of resistance to the element and still retain the high stability under electrical load life.

1 Interpolated. 2 Range of 20 C. to C.

The alloys set forth in the table will have a resistivity at 20 C. of approximately 290 ohms per c.m.f. and a tensile strength in the order of 6080,000 pounds per square inch and a melting point of approximately 1200 'C. The resistance wires formed with these alloy compositions are easily drawn to wide ranges of Wire sizes down to very small sizes, and are easily worked and formed on supporting bases without breakage and have good aging characteristics.

In the foregoing specific embodiment a cylindrical base has been described and illustrated. The resistive Wire may be mounted on other types of bases and may be formed into other resistive element shapes, such as ribbons.

The most advantageous use of all of the characteristics of the alloy are in an enamel coated type of resistor. Other types of coating such as glazes, silicone cements, epoxy, Teflon or the like may be used. Also, the resist- In the specific embodiments previously described the.

inclusion of other metals has not been taken into account.

It is often desirable to add other metals to meet other conditions that may arise in the manufacture or use of the alloy. For example, in the formation of the alloy at the elevated temperatures oxidation of the metals occurs forming a slag which becomes included in the alloy imparting undesirable properties to the alloy. In the foregoing embodiments it may be assumed that the alloys are formed in an inert atmosphere or a vacuum so as to prevent this oxidation. However, in actual practice deoxidizers such as magnesium, aluminum, manganese, iron, calcium, etc. may be included in small amounts. These amounts may be in the order of from a few tenths of a percent to two percent by weight. These additives will correspondingly alter the percentages of the other metals. The values set forth in Table I and the chart of FIG. 2 are determined without such additives. The additives will slightly alter such values and slightly different percentage of zirconium will result in an alloy having a zero temperature ooefficient of resistivity. The zirconium in the alloys containing such additives will be withinthe 4- range of .5 to 2% to impart to the alloy a zero or low temperature coeflicient of resistance.

I claim:

1. An electrical resistor comprising an insulating base and an electrical resistance element having a long resistance path in relation to its thickness mounted on said base, said element consisting of a copper-nickel alloy of the nickel-% copper type containing 0.5 to 2.1% zirconium having a temperature coefficient of resistivity over a range of -7.5 X 10 to -l-9.0 10 ohms per degree centigrade and a high stability under electrical load life.

2. An electrical resistance element as set forth in claim 1 wherein the copper nickel alloy comprises 45% nickel, 53.3% copper and approximately 1.7% zirconium with a temperature coefficient of resistivity of zero.

3. An electrical resistor as set forth in claim 1 wherein said element is a wire and a vitreous enamel coating is provided embedding said wire element.

References Cited by the Examiner UNITED STATES PATENTS 2,283,246 5/42 Wise 159 X 2,343,039 2/44 Allen 75-11 2,343,040 2/44 Allen 75134 2,425,032 8/47 Deyrup 106-49 2,696,544 12/54 Poch 338302 3,017,269 1/62 Finch et al 75-159 RICHARD M. WOOD, Primary Examiner.

Claims (1)

1. AN ELECTRICAL RESISTOR COMPRISING AN INSULATING BASE AND AN ELECTRICAL RESISTANCE ELEMENT HAVING A LONG RESISTANCE PATH IN RELATION TO ITS THICKNESS MOUNTED ON SAID BASE, SAID ELEMENT CONSISTING OF A COPPER-NICKEL ALLOY OF THE 45% NICKEL-55% COPPER TYPE CONTAINING 0.5 TO 2.1% ZIRCONIUM HAVING A TEMPERATURE COEFFICIENT OF RESISTIVITY OVER A RANGE OF -7.5X10**-5 TO +9.0X10**-5 OHMS PER DEGREE CENTIGRADE AND A HIGH STABILITY UNDER ELECTRICAL LOAD LIFE.

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