US3419958A - Magnetometer core and process of making the same - Google Patents

Description

1969- A. w. OBENSCHAIN 3,419,958

MAGNETOMETER CORE AND PROCESS OF MAKING THE SAME Filed Nov. 29, 1963 ARTHUR W. OBENSCHAIN INVENTOR.

15 P BY ATTORNEY ,[ZMAXLQ AGENT United States Patent 6 Claims The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This application is a continuation-in-part of application, Ser. No. 211,454, filed July 20, 1962, now abandoned.

This invention relates to a magnetometer core and to the process of making the same including a novel annealing process. More particularly, the invention relates to a magnetometer core which in use exhibits a lower noise characteristic than has heretofore been obtained, to the annealing process responsible therefor, and to a method of maintaining the noise characteristic at the low value.

In magnetic cores heretofore employed with sensitive stationary magnetometers it has been found that such stationary magnetic field measuring instruments of the fundamental frequency saturable core type exhibit a noise associated with the magnetic core under a no-signal condition which is often of higher intensity than the magnetic signal to be sensed thereby. While the cause of this magnetic noise is not positively known, it is thought to be molecular in nature as a result of jumping of the magnetic domain within the core material forming small sharp peaks of maxima similar to the well known Barkhausen effect.

In the heat treatment of magnetic core material heretofore employed it has been the usual practice to:

(a) Furnace heat the material to 1250 plus or minus 10 C. and hold at this temperature for two hours.

(b) Furnace cool the material to 1090 C. and hold at this temperature for one hour.

(c) Furnace cool the material again to a temperature of 400520 C. and hold at this temperature for twelve hours.

(d) Cool rapidly (250 C./hr.) to 200 C.

This old method possesses several disadvantages, for example, the high temperature used (1250 plus or minus 10 C.) results in very soft cores that are shock sensitive and easily damaged by rough handling. Another disadvantage is the twelve hour hold at 400-520 C. which results in an overly long annealing cycle. The greatest disadvantage of this old method, however, is that the annealed cores consistently exhibit the high noise level mentioned above.

The magnetometer cores of the present invention possess all of the advantages of the cores heretofore devised and none of the foregoing disadvantages.

One of the objects of the present invention is to provide a magnetometer core having a magnetic noise characteristic not in excess of 50% of the cores annealed in accordance with the annealing process set forth hereinbefore.

Another object is to provide a core of magnetic material for use in a magnetometer having a noise level of about 50% or less than that of cores heretofore produced and which possesses the desirable characteristic of ruggedness and resistance to change as the result of a shock applied thereto.

3,419,958 Patented Jan. 7, 1969 Other objects and advantages of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevation, partly in section, of a magnetometer core made in accordance with the present invention; and

FIG. 2 is a cross-section taken on line 22 of FIG. 1.

Referring now to the drawings, the magnetometer core 10 of the preferred embodiment of this invention is seen to comprise a magnetic scroll 12 composed of conventional high-permeability magnetic material mounted within a protective ceramic tube 14. The magnetic material employed may be a material known in the trade as Permalloy having approximately 4% molybdenum, 79% nickel, 0.50% manganese and the remainder iron and a small amount of impurities, or a material known as Supermalloy containing 5% molybdenum, 79% nickel, 0.50% manganese and the remainder iron together with a small quantity of impurities. Another suitable material is that known as HyMu-80 manufactured by the Carpenter Steel Company. The selected core material is first formed into a ribbon .0007 inch thick having a length of 1% inches and a width of inch. The ribbon is then rolled to form scroll 12, 1% inches long, .064 inch in diameter and having approximately 1 /4 turns. Scroll 12 is disposed within ceramic tube 14 which is slightly longer than the length of the scroll and secured therein in the following manner. Tube 14 is provided near its mid portion with an opening 16, through which a blunt tool is inserted to contact scroll 12 and to form a depression 18 therein. Care should be taken here to avoid tearing or perforating the core material. Opening 16 and depression 18 are then filled with cement 20 to secure the scroll in the tube. The cement may, if desired, be trimmed down so as to be flush with the exterior surface of tube 14.

The forming operations which have been performed on the scroll, such as the rolling operation and the forming of the depression 18, introduce stresses within the material which stresses are ordinarily relieved by a heat treatment such as the process described above. The annealing process of the present invention, now to be de scribed, has been found to be highly superior in that the resultant cores exhibit the lower noise characteristic as discussed above.

A number of the core assemblies to be annealed are stacked horizontally in a container suitable for transporting them through the heat treatment and for storing them until they are to be assembled into the magnetometers. The assemblies, in their container, are placed in a furnace and annealed in a pure dry hydrogen atmosphere in accordance with the following cycle:

(a) Heat at a rate of 400 C. to 500 C. per hour to 1,000 plus or minus 10 C. and hold at this temperature for three hours.

(b) Turn off the furnace and cool the cores in the furnace, maintaining an average cooling rate of 30 to 40 C. per hour over the temperature range of 600 C. to 300 C.

(c) When the cores have cooled to 200 C. or less turn off the hydrogen and open the furnace.

Cores treated in accordance With this annealing process using various high-permeability materials including 4-79 molybdenum Permalloy, Supermalloy, and HyMu- 80 have exhibited a low noise core characteristic of 1-2 gamma, in contradistinction to a minimum of 4 gamma noise level of magnetometer cores heretofore devised. It was found, however, that the low noise characteristic so obtained was lost after a short time, apparently because the shocks incident to normal handling reintroduced stresses into core material. This additional problem was solved by vacuum impregnating the cores with hydraulic fluid, such as that conventionally employed in power transmission systems. A suitable fluid is one which meets the requirements of Military Standard MIL-L-17111, although others may be used. The fluid is shown for illustrative purposes in FIG. 2 at 22. In this process, a quantity of hydraulic fluid suflicient to just cover the cores is poured into the containers of core assemblies as soon as the last step of the heat treatment is completed. The container is placed into a vacuum chamber which is evacuated to a suitable low value and continuously pumped for a time suflicient ot cause evacuation of the cores, about an hour having been found to be suitable. Air within the cores is drawn out and bubbled up through the fluid until the pressure within the cores is substantially in equilibrium with the zone above the fluid. The vacuum is then released, the resulting higher pressure on the surface of the fluid causing the fluid to be forced into the interior of the cores.

The fluid serves to support or cushion the core material and protect it from shock, thus preserving the low noise characteristic achieved in the heat treatment. To prevent loss of the fluid due to leakage or evaporation, the cores should be left submerged in the fluid until they are to be assembled into the magnetometer. As an incident to assembly, the fluid may be sealed in, in any desired manner, but such is not part of the present process.

Whereas the invention has been described in detail with reference to three particular types of magnetic core materials, it will be apparent to one skilled in the art, after understanding the invention, that other types of highpermeability core material may be employed without departing from the spirit and scope of the invention and it is intended, therefore, in the appended claims to cover all such types of high-permeability material in the process of the present invention. What is claimed is: 1. The process of reducing and maintaining low the core noise of high permeability magnetometer core material which has previously been formed into a thin ribbon, rolled into a scroll and secured within a tube to form a core, which comprises the steps of:

heating the core in a furnace in a pure dry hydrogen atmosphere to a temperature of 1,000 plus or minus C.,

turning the heat off the furnace and cooling the core in the furnace at a rate of 30 to 40 C. per hour over the temperature range of 600 C. to 300 C.,

when the core has cooled to 200 C., turning off the hydrogen and removing the core from the furnace, and

vacuum impregnating the core with hydraulic fluid.

2. The process according to claim 1 which includes the additional step of storing the annealed core in hydraulic fluid until it is assembled in a magnetometer.

3. The process of reducing and maintaining low the core noise of a magnetometer core comprising a thin ribbon of high permeability magnetic material, rolled into a scroll and secured within a tube, comprising the steps of:

heating the core in a furnace in a pure dry hydrogen atmosphere to a temperature of 1000 C.,

turning off the furnace and slowly cooling the core in the furnace to 200 C.,

removing the core from the furnace,

vacuum impregnating the core with hydraulic fluid, and

storing the core in hydraulic fluid until use.

4. The process of claim 3 wherein the 1000 C. temperature is maintained for three hours.

5. A process as set forth in claim 3, in which said vacuum impregnating step is performed by:

immersing the core in hydraulic fluid in a vacuum chamber,

drawing a vacuum on the surface of the fluid and maintaining said vacuum for a time sufficient to cause evacuation of said core, and

releasing said vacuum whereby hydraulic fluid is caused to enter said core.

6. A method of making a magnetic core for a magnetometer, which core exhibits a low noise characteristic, comprising the steps of:

rolling a flat strip of high-permeability magnetic material into a scroll,

inserting said scroll into a tube having an opening therein near the mid portion thereof, inserting a blunt tool through said opening to make a depression in said scroll, and removing said tool,

placing a quantity of cement in said opening in engagement with said depression to secure the scroll in the tube and thus form said core, heating the core in a furnace in a pure dry hydrogen atmosphere to a temperature of 1000 C.,

turning off the furnace and slowly cooling the core in the furnace to 200 C., and then removing the core from the furnace,

immersing the core in hydraulic fluid in a vacuum chamber,

drawing a vacuum on the surface of said hydraulic fluid to thereby draw a vacuum on the inside of said core, and

releasing said vacuum to thereby force hydraulic fluid into the core.

References Cited UNITED STATES PATENTS 1,270,969 7/1918 Parker 264-101 2,102,683 12/1937 Dixon 148-122 2,656,290 10/1953 Beberich et al. 264101 3,018,455 l/1962 Brandon et al. 336-213 X 3,127,559 3/1964 Legg et al 336--213 X CHARLIE T. MOON, Primary Examiner.

C. E. HALL, Assistant Examiner.

US. Cl. X.R.

Claims (1)

1. THE PROCESS OF REDUCING AND MAINTAINING LOW THE CORE NOISE OF HIGH PERMEABILITY MAGNETOMETER CORE MATERIAL WHICH HAS PREVIOUSLY BEEN FORMED INTO A THIN RIBBON, ROLLED INTO A SCROLL AND SECURED WITHIN A TUBE TO FORM A CORE, WHICH COMPRISES THE STEPS OF: HEATING THE CORE IN A FURNACE IN A PURE DRY HYDROGEN ATOMOSPHERE TO A TEMPERATURE OF 1,000 PLUS OR MINUS 10*C., TURNING THE HEAT OFF THE FURNACE AND COOLING THE CORE IN THE FURNACE AT A RATE OF 30* TO 40*C. PER HOUR OVER THE TEMPERATURE RANGE OF 600*C. TO 300*C., WHEN THE CORE HAS COOLED TO 200*C., TURNING OFF THE HYDROGEN AND REMOVING THE CORE FROM THE FURNACE, AND VACUUM IMPREGNATING THE CORE WITH HYDRAULIC FLUID.

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