US1706172A - Temperature-responsive magnetic material - Google Patents

Description

March 19, 1929. KlNNARD 1,706,172

TEMPERATURE RESPONSIVE MAGNETIC MATERIAL Filed Nov. 11, 1925 Invemor:

15666. F. Ki nnard,

Hi sArromey t... Man 19,1929 UNITED STATES.

PATENT. OFFICE.

ISAAC I. KINNABD, OF LYNN, MASSACHUSETTS, ASSIGNOR '1'0 GENERAL ELECTRIC ('iOMIE'AlhTY, A CORPORATION 0] NEW YORK.

'IEMFEBATUBE-BESPONSIVE GHETTO IATEBIAL.

Application filed l qovember 11, 1925. serial- No. 88,402.

My invention relates to magnetic material and in particular to magnetic alloys having a substantiall linear negative temperature coefiicient 0 permeability between ordinary temperature limits. Such a material is useful in the construction of temperature responsive magnetic. devices and.

for usein various electromagnetic devices to correct for temperature errors as described, for example, in my co ending apled May 5, 1924, assigned to the same assignee as the present invention, of which the present application is in part a continuation.

The-features, of my invention which-are believed to be novel and patentable --will be pointed outin the claims appended hereto.

invention the alloys in question, properties W111 now be For a better understanding 0 the method of making their composition an explained and reference will be made to-the accompanying drawing which shows in Fig.

1 temperature-permeability curves ofmaterial' pre aredin accordance withmy invention. 1g. 2 1s a curve showing how the transformation point-of the material varies with the copper content; and Figs. 3 and 3 give the results of hysteresis tests on the material.

' I have discovered that certain coppernickel alloys when roperly prepared can be made to have, in a dition to other desirable properties, a substantially linear negative temperature coefiicient of permeability between ordinary temperature limits. and that this characteristic may be controlled and varied by varying the composition of the alloy and the method of preparation.

Most magnetic material has more or less hysteresis loss. That is to say, the magnetism of the material lags behind the force producing the magnetism such that the magnetism. for a given producing force will be less if the force is increasing than it would be if the force were decreasing. This property gives rise to the well known hysteresis loop characteristic of magnetic materials. It will be readily expected that a material having. a negative temperature coeflicient of permeability and having appreciable hysteresis loss would have different values of magnetism at a given temperature when crease or an increase in temperature. However, if such material had a very low or inappreciable hysteresis loss, it would be expected that it would always have the same magnetism under the above conditions irrespect ve of the direction of change in temperature. My investigations have shown the above theory to hol good. In order to utilize the negative temperature coeflicient of permeabilit characteristic ofa magnetic material to t e bestv advantage it. is of course desirable that the rmeability vary with the temperature an be independent of the direction oftemperature chan e as otherwise thematerialwould give di erent results at a given temperature,'depending upon whether the temperature was increasing or decreasing. It is therefore desirable that such material have-zero or negli ible hysteresis and it is one-of the objects 0 my invention to provide amaterialhaving these desirable properties.

adding ,sufiicient additional iron to bring the total percentage up to the value desired. It is possible to obtaindesirable results at a low cost in this manner. An alloy containing approximately the percentages of copper, nickel and iron above specified when prepared as described hereinafter gives a permeability temperature curve as shown in curve A of Fig. 1. It will be noted that the curve is a proximately straight between 0 and 100 and below about C. corresponding to range of temperatures where the material will be ordinarly used, the curveis substantiall straight. Another desirable feature of this material, as may be seen from the curve, is that it approaches unity permeability very gradually. The percenta e of copper used also varies the point of transformation. Thus curve of Fig. 2 shows how the point of transforma- I, have found that the effect of adding a small amount of iron to certain copper tion varies with changes in the per cent of copper, the iron content being maintained constant at about 2.2 per cent and the nickel content varying inversely as the copper. 5 Curve B of Fig. 1 shows the characteristics of an alloy containing approximately 60 er cent nickel and 40 per cent copper. In t is case the permeability becomes negligible at about 14 C.

The heat treatment given during the preparation of the alloys is very important if the desired characteristics and uniformity of product are to be obtained. To obtain an alloy having the characteristics given in 1 curve A of Fig. 1, I prefer to use the following method: The following ingredients are melted in an Ajax high frequency induction furnace:

7 Per cent. 11100 X nickel shot 68.2

Clean copper scrap (pure) 30.

A chemical analysis of the Inco X nickel shot shows the composition to be as follows:

Commercially pure iron pure, the t eoretical composition of the alloy is as follows:

Per cent. Nickel 67.25 Copper 30.12 Iron 2.4

Impurities 0.23

A typical chemical analysis of the finished alloy is as follows:

Per cent.

Nickel 67.35 Copper 30.17 Iron 2.08

Impurities Some of the iron is evidently lost through oxidation. The impurities apparently have no influence on the temperature permeability characteristics.

The alloy is' heated to approximately 1650 C. before pouring. No additional stirring is necessary as the electromagnetic forces acting on the molten metal in this type of furnace produce a stirring action sufiicient to thoroughly mix the alloy. Preferably, immediately before pouring, 0.15% of magnesium wire is added to the melt in order. to deoxidize the alloy. This deoxidation apparently has littleor no effect on the magnetic roperties of the material, but it has the e ect of making the al low malleable, while without deoxidation it would be brittle.

The alloy is cast in green sand molds and as soon as the castings have solidified, they are seized with tongs and plunged into cool water.

A test piece of standard size weighing about 5 grams is cut from one of the castings from a temperature lower than the original quenchlng temperature.

Material having a releasetemperature higher than 105 C. may have its release point lowered by heating to 1050-1100 C. and quenching in oil.

The same general rocedure is followed in making other alloys aving different release points, the characteristics being varied as desired by varying the percentage composi tion of iron, copper and nickel as previously pointed out. When thus prepared the materials are malleable and have a negligible hysteresis loss and ver low retentivity. The curves of Fi, 3 give the results of hysteresis test of an alloy having the properties shown in curve A, Fig. 1. It will be noted that the hysteresis loss is so small that it can be hardly detected on this curve. The lower part of the curve is enlar ed in Fig. 3. This mate rial has a specific resistance of about 49 microns per centimeter cube. Another unusual characteristic is its low retentivity which is only about 8 per cent of the maximum induction.

The importance of uniform temperature treatment to obtain a uniform product cannot be overelnphasized. For example I have found that the alloy which gives the characteristics of curve A, Fig. 1, when prepared as previously described is very sensitive to heat treatment both before and after solidifying in the mold. If this same material is poured in a graphite mold instead of a sand mold, the resulting material is practically non-magnetic at 20 C. If poured in a mold of zirconium silicate, it becomes substantially non-magnetic at 60 C. If this last mentioned sample is then heated for two hours at 700 .C. and cooled in air, its release point is raised to 98 C.

It will be seen therefore that in order to obtain uniformity in results it is necessary to very carefully control the conditions un der which-the alloys are made as well as the percentage composition of the alloy. I believe the linear temperature-permeability relationship of these materials is due to the non-homo eneous manner in which the copper is hel in solution, which givestlie ef fect of the summation of a large number of alloys, each having a different transformation point. They differ from Monel metal in this respect. Monel metal is a natural alloy of copper and nickel which has a negative temperature coefiicient of permeability over a short range of temperature, but which does not have the desirable straight line characteristics shown in Fig. land is not suitable for many purposes because its permeability drops very abruptly as it approaches zero.

It is believed that the, desirable magnetic ,characteristics of the alloys which I have described and the manner in which the characmethod of preparation but seek claims cominensurate with the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An alloy containing between 60 and 80 per cent nickel and between and 20 per cent copper and having substantiall a linear negative temperature coefficient o permeability which gradually becomes less'as the permeability of the material approaches that of air at some temperature between .10 and 110 0.

2. A malleable, magnetic'alloy containing between 60 and 80 per cent nickel and between 40' and 20 per cent copper having a negligible hysteresis loss and having a substantial negative temperature veo'efiicient of permeability which gradually becomes less as the permeability of the alloy'approaches that of air.

3. A magnetic alloy containing between and.80 per cent nickel, between 40 and 20 per cent copper, and approximately 2 per cent iron having a substantial and approximately a linear negative temperature coefiicient of permeability between 0 and 100 C. and having a permeability which approximibtesC that of air in the neighborhood of 10 9 4. A malleable magnetic material contain-- gible hysteresis loss and having a substantialand approximately a linear negative temperature eoefiicient of permeability between unity in the neighborhood of 100 C.

5. A heat treated east magnetic'alloy having a predetermined negative tem erature coefficient of permeability formed A .7 mixing approximately 68 parts of hit el, 30 parts of copper, and 2 parts of iron in the molten state, casting said alloy in-a sandmold and quenching in water as soon as the alloy solidifies.

6. A magnetic material having a temperature crmeability characteristic which ap proac ies unity at about 100 C. and which Increases substantially uniformly with de-- crease in teinperature below about 100 C. over a wide range-of temperature, consisting 0 and 100 C. which gradually reduces to of a copper-nickel alloy containing between 40 and 20 per cent copper, between (SO'aiid per cent nickel, and a small amountiolf iron.

7. A cast material containing between 20 and 40 percent copper and between 60 and 80 percent nickel which is quenched from a temperature sli htly below that at which the material solidi es and in which the permeability ofthe material approaches unity at I some temperature point above 15 C. and in-v creases substantially uniformly with a de creas'ein temperature from such po nt down-' gvbam over a temperature range of at least 8. A magnetic copper-nickel alloy containing between 60 and 80 per cent nickel and between 40 and 20 a negligible hysteresis loss and having a substantia and approximately linear negative temperature coefiicient of permeability over a temperature range in excess of 40 centigrade degrees.

.9. A magnetic copper-nickel alloy having a negligible hysteresis loss and having a substantial and approximately linear negative temperature coefiicient of permeability over a wide temperature range, the copper content of said alloy being between 20 and 40 er cent and being held in solution in a nonomogeneous manner.

:10. A magnetic copper-nickel alloy containing a small percentage of iron having a negligible hysteresis loss and having a substantial'and ap roximately linear negative temperature coe a wide tem erature range, the copper content of said alloy being between 20 and 40 cient of permeability over per cent copper, having er cent and being held in solution in a nonomogeneous manner.

In witness whereof, I have hereunto set my hand this ninth day of November, 1925.

ISAAC F. KIN NARI).

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