US2443756A - Magnetic material - Google Patents

Description

June 22, 1948." A. L. w. WILLIAMS ETAL 2,443,756

I I MAGNETIC MATERIAL Filed Dec. 26, 1942 Hm Ha '3 Sheets-Sheet 2 l INVENTORS ALFRED L. W WILL/AMI ATTORNEY June 22, 1948 A; L. w. WILLIAMS ET'AL 2,443,756

MAGNETKIC. MATERIAL Filed Dec. 26, 1942 Y s Sheets-Sheet s IiLl' I INVENTORS AL FRED AIM Mum/14s BY SEM/ JOJLPH BEGU/V ,4 ENE) Patented June 22, 1948 MAGNETIC MATERIAL Alfred 1;.-. w. Williams and Semi Joseph Begun, Cleveland Heights, Ohio, assignors to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio A plication December 26, 1942, Serial N0. 47 0,192

octane-;. (01. 274-4114) Our invention pertains to ail-improved magnetic material and the means and method for producing it. k

t is an object of ouri-nvention to providea magnetic material and the method of making it wherein the material is endless andjointless.

It is another object of our-invention to provide an endless and jointlesspathofmagnetic material.

A further object of ourinvention isv toprovide an endless and jointless path comprised only of magnetic material.

Another object of our invention is to' provide an endless and jointless path oi-permanent magnetic material.

Further objects of ourinvention are: to provide the means and methods for producing improved magnetic materials.-

It is also an object of our invention to provide a magnetic path of continuous solid magnetic material in which the crystallinemagnetic material is held together by intermolecular forces.

An object of our invention-is to provide a magnetic path composed of solidmagnetic material.

A "further object of our invention istoprovide a magnetic material which can be readily formed into difiicult shapes.

It has always been a problem toproduce agood magnetic tape. The chief difiicultyhas been-that good magnetic materials are hard and brittleand therefore cannot be readily and cheaply worked into desired shapes, and soft workable materials which can be readily worked-are usually not good magnetic materials; For exam-ple-ztungsten steel wire is a good magnetic material but it is so hard and tough that Carboloyrollersareused to work the wire intoa flat tapes If softerrollers were used the wire would make; grooves inthe rollers instead of the rollers fiattening the wire into a tape. Obviously when special. rollers have to be used the process becomes veryexpensive. Swedish magnetic tape hasbeen producedby rolling large sheets of the tungsten steel and then cutting from them narrow strips .oftape. It is then necessary to polish-the cut edges to make them smooth. This results in tape which, when obtainable, is very expensive.

Our invention makes possible the production of magnetic tapes. having magnetic qualities which are equal to or better than those of tun sten steel, and which can b'e'readily'w'orked, and which has the further advantage that when an endless tape is desired no tapejoint nee'd. be present.

Other objects and-sinner"understanding of our invention may be had by referring tovth'e following description and drawings in which:

Figure 1 illustrates an endless length of material having a joint.

Figure 2 shows an enlarged view of the joint portion of the'material shown in Figure I after a-magnetic layer has been aifixed to the material.

Figure 3 shows another type of joint.

Figure 4 shows a disk.

Figure 5 shows an enlarged View of a, portion, of the disk of Figure 4' after a magnetic material has been afiixed.

Figure 6 illustrates a'thin endless band of magnetic material such as may be obtained by stripping the base material from the composite tape of Figure 1.

Figure 7 illustrates a method oi treating magnetic material by resistance heating.

Figure Sillustrates a method of treating a magnetic material by induction heating.

Figure 9 illustrates a method of treatihg-amagnetic material by flame'heating.

Figure 10 shows a'process of heat treatingseve eral materials to establish in them the best magnetic characteristics.

Figure 11 shows another process somewhat similar to the-processof Figure 10.

Figure 12 shows another form oimagnetictape material.

Figures 13 and l show a. method of-iormihg an improved magnet, and

Fig. 15 shows a type of tape joint.

With reference to Figures 1 and 2, our-invention comprises providinga leng'th of non-magnetic material Iii;- s'uch' as copper or a copper al1oy.which has been formed into an endless-loop by joining the two free endstogether'atf6, and depositing or otherwise aflixing to the non-magnetic material a permanentlymagnetizable ferromagnetic material ll', such as cobalt or nickel, or a-cobalt nickel alloy, to establish a composite magnetic recording medium. When the joint-l6 is properly made and the magnetic material 11' is properly applied over the joint l-dtherewillbe no tape joint click caused by the joint lfiwhen a record is reproduced from the composite magnetic recording medium. As shown in Figure 2 we prefer to use a diagonal butt joint as this pro: vides a maximum strength due to' a large area of contact between the two ends of the tape 15; and also reduces the physical displacement of the recording and reproducing head pole pieces which lap joints often cause.

While we have shown an endless length of material in Figures 1 and 2 it is to be understood that our invention is not to be limited to endless materials but may just as well be used with a length of material having two free ends.

The magnetic layer depositing of the invention includes electroplating, vacuum sputtering, evaporation, chemical plating, or any other process which produces a continuous layer of permanently magnetizable ferro-magnetic material, such as cobalt, nickel, ortheir alloys, and thereafter, if necessary, heat treating the deposited material to improve its magnetic properties. Some materials which are deposited on the base material need no heat treatment.

Figure 3 illustrates a butt joint it which is covered, by a magnetic layer on the order of several mils thick, and which has a connecting plate 22 for providing a more secure joint. The plate 22 is preferably glued or otherwise affixed to each end of the base material l5 prior to depositing the magnetic layer IT. This arrangement is particularly adaptable for use with magnetic recording and reproducing heads which contact only one side of the magnetic record track.

Our invention may also be utilized with disks is of material as is shown in Figures 4 and 5. The disk 18 is composed of non-magnetic material such as paper, plastic, or metal, and the layer ll of magnetic material is deposited on it in any of the aforesaid manners. One of the chief reasons for plating a. non-magnetic disk with magnetic material instead of using a disk of rolled magnetic material is to obtain a more uniform signal response. The process of rolling a magnetic material results in imparting to the material a preferred magnetic direction. For this reason a disk which has been rolled will not exhibit uniform magnetic characteristics throughout a given path around its center. Our process of depositing the layer ll of magnetic material on a nonmagnetic disk results in a composite magnetic disk which will exhibit uniform magnetic characteristics throughout a given path around its center.

Figure 6 illustrates an endless and jointless magnetic tape consisting only of magnetic material. It is formed by the plating process de scribed in connection with Figure 2, and then re moving the base material. If the base material is inflammable, it may be burned ofi if care is taken to keep the temperature below the melting point of the magnetic material. In? the base-is wax it may be removed by heating or by dissolving it in a solvent. tricity such as paper is used as a base material upon which the magnetic material is to be deposited, it is necessary to first coat one side of the paper with a conductor such as graphite. The magnetic material will then be deposited on the graphite coating. After a suitably thick coating has been obtained and the paper base removed, most of the graphite can be wiped or scraped ofi of the magnetic material.

Figure 7 illustrates a method of heat treating the magnetic tape [9 if it is made of an alloy whose magnetic properties are improved by heating. This heating method comprises rotating the tape over rollers which are connected to a source of current such as the transformer 20. The temperature to which the tape will be heated depends upon the current passed through it, the resistance of the tape, and the rate of rotation. By proper design these factors can 'be established to result in the amount of heat in the tape which will,

If a non-conductor of elecupon cooling, give the tape its best magnetic characteristics.

Another method of heating the tape is by induction as is shown in Figure 8. The tape I9 is driven about rollers by the motor, and passes an induction coil 2| which is connected to a source Of high frequency alternating current. For best results the axis of the coil 2| should be normal to the plane of a broad face of the tape IS. A particularly valuable feature of induction heating is that for thick magnetic materials the depth to which the tape is heated can be accurately controlled. This advantage is most fully realized when a thick composite magnetic recording medium is heat treated, and where the base material cannot withstand the high temperature to which it is desired to heat the surface of the magnetic material. For instance; the base material may be beryllium-containin copper in order to give the composite magnetic recording medium strength and resistance to fatigue, and the magnetic material maybe platinum-containing cobalt. This base material cannot withstand temperatures much in excess of 800 degrees centigrade, while it is necessary to heat this particular magnetic material to about 1100 degrees centigrade in order to realize its maximum magnetic characteristics. By using induction heating and controllin the depth of penetration of the heat it may be practical to use the combination of a base which cannot withstand high temperatures and a magnetic material which must be heated to a high temperature. There is now available a new type of steel which has a high melting point, and which has a mu between 1.2 and 1.5. This steel also has relatively poor electrical conductivity, is machinable, and, has good fatigue resisting qualities which makes it an ideal base material.

A third method of heating the tape is by an open flame such as is shown in Figure 9. In using this method, care must be exercised to assure a constant heating of the tape or different portions might have different magnetic characteristics. By applying the heat at one of the rollers, it is possible to maintain the base material l5 at a lower temperature than the magnetic layer l1.

Figures 10 and 11 show two methods of continuously heat treating composite magnetic recording mediums. In Figure 10, two layers of permanently magnetiz-able materials 25 and 26 are deposited on a base material 21 by electroplating or by chemical plating. It may be necessary, in order to deposit two or more layers of material, to run the base material 21 through several successive plating processes, one for each material deposited. The two layers 25, 26 may be formed of cobalt and nickel, respectively, and the base material 21 may be copper or a copper alloy. Sputtering or evaporation could be used for simultaneously depositing two or more different materials. After the two materials have been deposited the tape is run over two rollers 28, 29 to which is connected a battery 30 or other current source suitable lfOI establishing a high temperature in the tape between the rollers 28, 29. The temperature established must be sufficient to cause the two plated materials 25, 26, such as cobalt and nickel, to diffuse into each other and form one or more alloy materials, such as a cobalt nickel alloy. After the plated materials have been fused into an alloy, the composite tape is quenched in the tank 3|. If the alloy is one which requires further heat treating to establish its best magnetic qualities, we provide a subsequent heat anew-e treatingistep which is percformed by resistance heatingv of. thetapebetween the. rollers .32, tit-by the. battery. 34.. Immediately after the. tape. is heated itisquenched in the. tank 35. A coil 3% isplacedaround the tape at the. surface of the quenching fluidfor establishingin the successive portions ofrthe tape a uniform magnetization at the :instanttlre portion is quenched.

In making flexible magnetic recording tracks, such as tapes, with a base or core of substantially non-magnetic metal of high tensile strength, a thin layer or the magnetic material of the requiredhigh coercive force is deposited by plating on the core, and thereafter an additional thin layer of magnetic material is deposited on the firstlayer, and so forth, until the desired overall thickness of the. magnetic layer is reached.

Theprocess of Figure 11 differs from the process of Figural!) in that it is designed to heat treat only the magnetic materials and not the base material. This .processmay. be used if it is not practical to use. .a base material which will withstand the. high temperatures. necessary to cause the layers 25, 26 to fuse or where the temperature necessary to cause fusion is high enough to cause some of the base material to enter into the alloy and thereby spoil its magnetic characteristics. A knife 31 is shown for separating the deposited layers and the base. It is to be understood, however, that any of the aforementioned methods of separation can be used. After the alloy has been treated by the battery 34 and quenched in a magnetic field established by the coil 36, the same base 21, or a different base, can be joined to the magnetic alloy to establish once again a composite magnetic tape.

Figure 12 illustrates a composite magnetic tape which is cformed of a base material 15 upon which two or more magnetic layers 38, 39 are formed. A tape of this kind is particularly adapted for push-pull magnetic recording and reproducing such as is shown in the co-pending Begun application Serial Number 596,481, filed May 29, 1945, or for multi-channel recording.

Figure 13 illustrates a plurality of thin magnetic strips formed according to any of the previously described methods, and positioned face-toface with respect to each other with each of the strips above the bottom strip slightly longer than the underneath one. Thus, when the plurality of strips are bent into a horseshoe, as is shown in Figure 14, the ends will be even and a laminated magnet will be formed in which there is a continuous magnetic path from one end to the other. This same process can be used to form a magnet of practically any difficult configuration. It may also be used for making transformer cores. Each lamination may be solid magnetic material, or may be magnetic material connected to a base material as has been described previously,

Figure 15 shows a type of joint in a magnetic material which produces much less tape joint discontinuity than existing tape joints. It is formed by butting two free ends of the tape together and connecting them together with the plate 22, without using any welding or soldering material between the ends of the tape or between the tape and the connecting plate. The only magnetic discontinuity in the signal will be occasioned by the very small air gap 4| between the ends of the tape. If welding or soldering had been used the magnetic discontinuity in the signal would be much greater due to the heating of the ends of the tape. Even very carefully controlled heating using heat conductive material in contact with the tape to reduce-heattransmission back along the tape results in a relatively long portion of the tape which has been heated and cooled. This heating and cooling establishes amagnetic discontinuity which results in a click in a reproduced audible signal which is considerably greater than any click caused by a solderless butt-joint such as is shown in Figure 15. In accordance with the James-Miller application Serial No. 43?,350 issued on March--21, 1944, as Patent No. 2,344,615,11he joint-can also be a diagonal butt or a lap joint.

The expression magnetic record transducing as used hereinin the-specification and claims is intended to mean either the operation of magnetically recording signals on --a magnetic recording medium, orthe operationof reproducing magnetically recorded signals, or the operation of erasing magnetically recorded signals, orany combination of twoor more or these operations.

Although we'havedescribed-our invention with a certain degreeofparticularity, it is to be understood that thepresentdisclosure has been made only by wayof example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

We claim:

1. In a magnetic record transducing system for transducing signals on an elongated permanently magnetizable record track by magnetic fiux linkage between magnetic record transducing structure and successive elements of a record member contacting the structure: a record member comprising an elongated flexible and thin core having a joint at which end portions of the core are secured together to form an endless core structure and a permanently magnetizable record-receiving coating adherently affixed to the core and over the joint forming a continuous endless magnetic record track extending smoothly and continuously thereover and free of irregularities that vary the magnetic linkage with the transducer structure along the region of the joint.

2. A magnetic transducing system as recited in claim 1 in which the core is metallic.

3. A magnetic transducing system as recited in claim 2 in which the record member is in the form of a fiat tape.

4. A magnetic transducing system as recited in claim 1 in which the coating is a mixture of cobalt and nickel.

5. A magnetic transducing system as recited in claim 4 in which the record member is in the form of a fiat tape.

6. A magnetic transducing system as recited in claim 1 in which the core is metallic and the coating is a mixture of cobalt and nickel.

'7. A magnetic transducing system as recited in claim 6 in which the record member is in the form of a fiat tape and the coating is an electrolytically deposited mixture.

8. A magnetic transduoing system as recited in claim 1 in which the record member is in the form of a flat tape.

9. A magnetic transducing system as defined by claim 1, in which the core joint is provided with a smoothly continuous record track engaging surface to which the record track is affixed.

ALFRED L. W. WILLIAMS. SEMI JOSEPH BEGUN.

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

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