US2779699A

US2779699A - Annealing process for magnetic material

Info

Publication number: US2779699A
Application number: US384616A
Authority: US
Inventors: William P Langworthy
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-10-07
Filing date: 1953-10-07
Publication date: 1957-01-29
Anticipated expiration: 1974-01-29

Description

1957 w. P. LANGWORTHY ANNEALING PROCESS FOR MAGNETIC MATERIAL 2 Sheets-Sheet 1 Filed Oct. 7, 1953 BY W M ATTORNEYS Jan. 29, 1957 w. P. LANGWORTHY 2,779,699

\ ANNEALING PROCESS FOR MAGNETIC MATERIAL Filed Oct. 7, 1955 2 Sheets-Sheet 2 FIG. 3.

INVENTOR ar/-14, LANG Jazz Twy ATTORNEYS ANNEALING PROCESS FOR MAGNETIC MATERIAL William P. Langworthy, Philadelphia, Pa. Application October 7, 1953, Serial No. 384,616

18 Ciaims. (Cl. 148-422) This invention relates to a coating and annealing process for magnetic materials and to a coated magnetic material produced by the foregoing process.

it is well known that magnet cores for use in alternating current machines, such as transformers, must be laminated in order to reduce eddy currents. Laminating the core is not effective unless the laminations are insulated from each other. Moreover, in order to secure best results the laminations must be annealed in a high temperature hydrogen atmosphere. While the effect of insulating the laminations and annealing the material may be determined experimentally in the laboratory, it has been ditiicult to achieve low cost production processes capable of attaining results such as those proved possible by laboratory experiments. One difiiculty encountered in practice is that during the high temperature annealing step the laminations tend to stick and/or weld together. Another difficulty is attaining adequate exposure of the surfaces of the stacked laminations to the hydrogen annealing atmosphere or medium. Still another difiiculty involves obtaining in production at .a low cost a thin insulating coating onthe surface of the laminations that will reduce eddy current. losses without seriously increasing the thickness of the laminations. The principal object of this invention is to overcome the foregoing difficulties.

Another object of this invention is to provide an improved process for producing coated laminations for electrical machines.

A still further object of the invention is .to provide an improved coated lamination for use in electrical machinery.

Other objects and advantages of t the invention will appear as this description proceeds.

Others have discovered prior to my invention that a thick coating of zirconium dioxide may be applied to a metal base by heating the metal base to a temperature of several hundred degrees Fahrenheit and spraying it with a water solution of ammonium zirconyl carbonate. 1 make no claim herein to that process but I claim the series of steps including applying that process to produce an extremely thin film on a metallic base composed of material Whose magnetic properties are improved by a high temperature (about 1000 F. to 2350 .F.) hydrogen anneal, and then exposing thecoated material to such an anneal. The results achieved by this combination of steps are that the high temperature of the annealing step drives oil the last traces of the water in the coating and thus improves it. The coating step improves the annealing step by providing a porous film during the annealing step which separates the laminations sufliciently to allow the hydrogen atmosphere to contact the magnetic material and by separating the laminations to a sufficient extent that they do notstick together. Moreover, after the process is completed the resulting laminations have a very thin film that willinsulate them from each other afterthey are placed into use,

Hydrogen is the preferred atmosphere or-medium esr 2,779,699 Patented Jan. 29, 195.7

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pecially when the metal from which the laminations are stamped is one of the well known magnetic nickel alloys of iron, such as the Permalloys. One of these contains approximately 50% nickel, while the remainder is essentially iron. Another is composed of 79% nickel, 4% molybdenum and almost pure iron to make up the remaining balance of almost 17%. These materials may be annealed in a medium consisting of pure dry hydrogen, or if desired to make the process less expensive, the medium may be cracked ammonia or any other desired mixture of hydrogen with nitrogen. Either of these media may be used in the annealing of the silicon containing magnetic alloys of iron, but to further decrease the cost of these materials they are often annealed in a so called burned-out-air medium, which may contain variable amounts of nitrogen, carbon dioxide, carbon monoxide and perhaps hydrocarbons. Such anneals of the silicon-iron alloys are usually done at a maximum ternperature in the range between about 1000 F. and i800 F., a value of 1450" F. being most common.

The problems involved and the desirability of a coating for magnetic laminations are (llSC'dSSfidilIl U. S. Patent 2,410,220 to William P. Langworthy, dated October '29, 1946. The present invention describes certain improvements upon the basic teachings described and claimed in that patent.

In the drawings:

Figure 1 illustrates one form of the process constituting my invention.

Figure 2 illustrates a coated lamination according to the invention.

Figure 3 illustrates a box of stacked laminations.

Figure 4 is a sectional View taken along line 4-4 of Figure 3.

Figure 5 is a photomicrograph of thecoated lamination following step C of Figure l.

Figure 6 isa photomicrograph of the coated lamination after step E of Figure 1.

Referring now .to Figure 1, step A involves stamping, a lamination of suitable magnetic material to proper shape and heat cleaning it at 800 degrees, F. Other cleaning methods may of course be used. The material is of a type Whose magnetic properties are improved by annealing it in a high temperature hydrogen atmosphere. One such material is Permalloy which is a well known 'steel having about 50% nickel therein.

Step B involves heating the laminations singly or in groups to a temperature preferably between 300 and 600 degrees, Fahrenheit. The laminations are heated in a gas-fired or electric oven. An electrical induction heater may also be used. if burning gas is used to heat the laminations the products of combustion should not be allowed to contact the laminations to avoid poisoning them. Step C involves passing the heated laminations one at a time through a mist or fog composed of an aqueous solution of ammonium zirconyl carbonate (hereinafter referred to as AZC). The mist of AZC solution may be produced, for example, by directing a spray toward the passing laminations. Preferably the AZC solution is dilute but it maybe within the range of 0.l% to 12% by Weightof the equivalent contained zirconia (ZrOz}, 12% being the saturation value. When the dilute mist strikes the hot laminations the AZC solution breaks down leaving a thin coating of a refractory metal oxide (ZrOz) on the surfaces of the laminations. The laminations remain at the aforesaid 300 to 600 degree temperature during the coating operation. The chamber or zone in which the mist or fog is created .may encounter :an elevated temperature due to the heated laminationsipassing therethrough.

.Step D involves stacking the .laminations after-they have cooled. Figure 3 illustrates how thezlaminations may be stacked in a tray preparatory for the annealing step. The tray has separators 11 and 12, and the laminations are stacked in rows as shown in Figure 4. Preparatory for the annealing step a number of trays of the type shown in Figure 4 may be placed on top of each other. These stacks of trays, so to speak, are placed in a heated hydrogen atmosphere for purposes of annealing. Step E involves annealing the stacked laminations at a high temperature in an annealing atmosphere or medium. In the case of Permalloy, step E is carried out at 1800 to 2350 degrees Fahrenheit in a hydrogen atmosphere. In order for the annealing to have maximum beneficial effect the hydrogen gas must permeate the pores of the laminations. This is possible in the present case since the thin coating separates the laminations enough to allow hydrogen to enter between the laminations. Moreover, the coating is rather spotty or discontinuous thus allowing the hydrogen gas to actually contact a very large percentage of the total surface. The thickness of the coating and the extent of its coverage can be controlled somewhat by varying the concentration of the solution in step C and also by varying the time period that the laminations remain in the mist or fog of AZC solution.

The high temperature annealing step accomplishes the additional function of driving off any remaining water of crystallization in the coating and thus improving it.

When the laminations have been annealed they are ready for use in a transformer or other electrical machine in the usual Way. Figure 2 is an illustration of the final product. The thin coating of zirconium dioxide crystals insulates the laminations from each other. However, the coating is so thin that it does not substantially increase the height of a stack of laminations. In technical language this means that the stacking factor of the laminations is very favorable. For example it is possible for me to produce Permalloy laminations 0.006 inch thick with a controlled coating thickness of from 1 to 1000 micro inches, as required.

There are other coating steps per se that may replace step C. These alternate coating steps per se are not my invention and are hereinafter claimed only in combination with other steps. It may be stated as a fundamental proposition that the coating step or material must not poison the magnetic material or adversely affect its properties. Some of the substitutes for AZC may be defined by the following formula:

wherein X is a metal of group IV-A. In the event the metal is titanium, for example, the fog or mist would be a solution of ammonium titanyl carbonate. The corresponding analogs of aluminum (ammonium aluminum carbonate) or magnesium (ammonium magnesium carbonate) may be used. In fact, the ammonium metal carbonate salts which may be used include beryllium, thorium, magnesium, calcium, barium, strontium, aluminum, titanium, zirconium, hafnium, and cerium.

Another example of a suitable starting compound is a solution of zirconium nitrate in anhydrous ethanol. Such a solution gives superior results, using temperatures of 400 to 1200" F.

Hence, step C involves a metal compound that breaks down when heated and releases a compound (usually the oxide) of the metal. The starting metallic compound should be in a solution or in essentially sub-colloidal (less than 0.5 micron size) form in the solvent or vehicle which is removed by one or more of the heating steps of the whole process. I

In all cases, the process is workable when the metal oxide content of the solution is between 0.1% and 10% by weight, and the temperature in step C is sufficient to cause the oxide to bond itself to the base metal, usually several hundred degrees.

The zirconia coating is an improvement over the prior art since it does not poison or otherwise injure the magnetic materials.

Laminations produced by this process have an improved permeability of about 20% over laminations produced by present day prior art commercial processes. This is true over a wide range of flux density, for example from 40 to 4000 gausses. In the prior art the permeability of stacks of laminations varied substantially more from the overall average than is true with the process herein claimed.

Moreover, the same size of tray will hold more laminations coated by my process than it will hold of prior art laminations since the coating is thinner. In fact it is possible in some cases to more than double the quantity of laminations that may be placed in an annealing furnace or container of any given size. It has also been found that notwithstanding the increased number of laminations placed in the tray the heat is conducted to the innermost parts of the tray quicker than in the prior art, this being due to the fact that coating is thinner than in the prior art. Hence, it is possible to carry out the process in a shorter time than has heretofore been customary.

Figures 5 and 6 are photomicrographs showing the thin discontinuous zirconia coating (which is white in color) on the magnetic base metal (which has dark color). Figure 5 was taken prior to step E and Figure 6 after that step.

I claim to have invented:

1. The process of producing a part of an electrical machine, said part having magnetic properties, which includes, heating the part, passing it through a mist of a volatile substance containing an ammonium metal carbonate salt that upon striking the heated part breaks down and leaves a thin discontinuous refractory metal oxide coating on the surface of the part, and then annealing the coated part at a temperature above that used during the coating step, the annealing being carried out in the presence of an annealing medium.

2. The process of producing coated laminations of material whose magnetic properties are improved by a high temperature annealing in a suitable medium which includes stamping a lamination of said material, heating the lamination to a temperature in excess of 300 degrees Fahrenheit, passing the heated lamination through a mist of a dilute solution of ammonium zirconyl carbonate, stacking the laminations, and annealing the stacked laminatrons at a temperature higher than the one to which the laminations were subjected during the hereinabove mentloned heating step, the annealing being carried out in the presence of an annealing medium.

3. The process of producing coated laminations of Permalloy which includes stamping the Permalloy laminatlons, cleaning them, heating the laminations to a temperature in the range of 300 to 600 degrees Fahrenheit, exposing the laminations while thus heated to a mist of an aqueous solution of ammonium zirconyl carbonate, the solution having between 0.1% to 12% by weight of zirconia content, stacking the laminations, and annealing the stacked laminations in a hydrogen medium at a temperature in the range of 1800 to 2350 degrees Fahrenheit.

4. The process defined in claim 3 in which the solution is so dilute and the time of exposure of the laminations to the solution is so short that the coating formed on the laminations is discontinuous and of a thickness less than 0.0005 inch.

5. The process of producing coated laminations which are composed of material whose magnetic properties are improved by a high temperature annealing step which includes passing the laminations into a heated zone, exposing the laminations while in said zone to a vehicle carrying a compound of zirconium which breaks down under the heat prevailing in said zone and deposits a refractory oxide of zirconium on a surface of the laminations, and annealing the laminations at a still higher temperature.

6. The process defined in claim 5 in which the laminations are in the form of a stack during the annealing step.

7. The process of producing coated laminations of material whose magnetic properties are improved by a high temperature annealing in a suitable medium which includes stamping a lamination of said material, heating the lamination to a temperature in excess of 300 degrees Fahrenheit, passing the heated lamination through a mist of a dilute solution of ammonium zirconyl carbonate while the lamination is at such a high temperature that the ammonium zirconyl carbonate will. be broken down leaving a coating of zirconium dioxide bonded to the lamination, stacking the laminations, and annealing the stacked laminations at a temperature higher than the one to which the laminations were subjected during the hereinabove mentioned heating step, the annealing being carried out in the presence of an annealing medium.

8. The process of producing coated laminations of Permalloy which includes stamping the Permalioy laminations, cleaning them, heating the laminations to a ternperature in the range of 300 to 600 degrees Fahrenheit, exposing the laminations while thus heated to a mist of an aqueous solution of ammonium zirconyl carbonate, the temperature of the laminations while exposed to the ammonium zirconyl carbonate being so high that when contacted by the ammonium zirconyl carbonate the latter breaks down and leaves a coating of zirconium dioxide bonded to the laminations, the solution having between 0.l% to 12% by weight of zirconia content, stacking the laminations, and annealing the stacked laminations in a hydrogen medium at a temperature in the range of 1800 to 2350 degrees Fahrenheit.

9. The process defined in claim 8 in which the solu tion is so dilute and the time of exposure of the laminations to the solution is so short that the coating formed on the laminations is discontinuous and of a thickness less than 0.0005 inch.

10. The process of producing coated laminations which are composed of material whose magnetic properties are improved by a high temperature annealing step which includes passing the laminations into a heated Zone, exposing the laminations while in said zone to a vehicle carrying a compound comprising an ammonium metal carbonate salt which breaks down under the heat prevailing in said zone and deposit a refractory metal oxide on a surface of the laminations, and annealing the laminations at a still higher temperature, said compound being one characterized by the fact that it will not poison the magnetic material or adversely afiect its properties during the carrying out of said process.

11. The process defined in claim 10 in which the laminations are in the form of a stack during the annealing step.

12. The process of claim 10 in which the compound is ammonium zirconyl carbonate.

13. The process of claim 10 in which the compound is ammonium aluminum carbonate.

14. The process of claim 10 in which the compound is ammonium magnesium carbonate.

15. The process of claim 10 in which the compound is ammonium calcium carbonate.

16. The process of claim 10 in which the compound is ammonium titanium carbonate.

17. The process of producing coated laminations of material whose magnetic properties are improved by a high temperature annealing in a suitable medium which includes forming a lamination of said material, heating the lamination, passing the lamination while in a heated state through a mist of a dilute solution or" ammonium zirconyl carbonate, said heating step raising the lamination to such a high temperature that the heat of the lamination will break down the ammonium Zirconyl carbonate mist which contacts it leaving a coating of zirconium dioxide bonded to the lamination, said mist being so dilute that the coating which is formed will be discontinuous, and annealing the coated laminations at a temperature higher than the one to which the laminations were subjected during the hereinabove mentioned heating step, the annealing being carried out in the presence of an annealing medium.

18. The process defined in claim 17 which includes the additional step of stacking the laminations before annealing them, the laminations remaining in stacked form during the annealing step.

References Cited in the file of this patent UNITED STATES PATENTS 1,842,162 Gifford Jan. 19, 1932 1,924,311 Frey Aug. 29, 1933 2,124,446 Detwiler July 19, 1938 2,132,557 Bobrov Oct. 11, 1938 2,354,113 Gould July 18, 1944 2,410,200 Langworthy Oct. 29, 1946 2,475,601 Fink July 12, 1949 2,515,788 Merrill July 18, 1950 2,540,623 Law Feb. 6, 1951

Claims

1. THE PROCESS OF PRODUCING A PART OF AN ELECTRICAL MACHINE, SAID PART HAVING MAGNETIC PROPERTIES, WHICH INCLUDES, HEATING THE PART, PASSING IT THROUGH A MIST OF A VOLATILE SUBSTANCE CONTAINING AN AMMONIUM METAL CARBONATE SALT THAT UPON STRIKING THE HEATED PART BREAKS DOWN AND LEAVES A THIN DISCONTINUOUS REFRACTORY METAL OXIDE COATING ON THE SURFACE OF THE PART, AND THEN ANNEALING THE COATED PART AT A TEMPERATURE ABOVE THAT USED DURING THE COATING STEP, THE ANNEALING CARRIED OUT IN THE PRESENCE OF AN ANNEALING MEDIUM.