US3582572A - Transducer head with grain oriented silicon-iron core - Google Patents
Transducer head with grain oriented silicon-iron core Download PDFInfo
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- US3582572A US3582572A US746651A US3582572DA US3582572A US 3582572 A US3582572 A US 3582572A US 746651 A US746651 A US 746651A US 3582572D A US3582572D A US 3582572DA US 3582572 A US3582572 A US 3582572A
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49034—Treating to affect magnetic properties
Definitions
- a microgap magnetic transducer head having a core formed of a binary alloy of silicon and iron (preferably from about 3 percent to 7 percent silicon) provides a sharply PATENTEU JUN H911 3582572 INVliN'IYIN f wry 22 6227221229 IKHZ 101ml 100KHz IMHz w I Z ATTORNEYS TRANSDUCER HEAD WlITllll GRAIN ORIENTED SILICON- IIRON CORE METHOD OF MAKING THE HEAD
- the head core of silicon iron is preferably annealed in an atmosphere ofdry hydrogen, holding at a temperature of at least 2000 F. for minutes or more, and then cooled slowly over a period of several hours.
- the head core is preferably annealed as part of a magnetic circuit corresponding to the one in which it will be ultimately used.
- the cores are preferably strung on a loop of stainless steel wire in the heat treatment chamber so as to subject the cores to a magnetic field during at least part of the annealing process.
- tape recorder head pole pieces is of nickel-iron composition, usually approximately 79 percent nickel, and 21 percent iron and minor constituents. These heads are used for recording, playback, or erasing. Special purpose heads have also been made with ferrites, alfenol, and Sendust; but the special heads are expensive to manufacture because of brittleness, and generally sacrifice efficiency, gap definition and the like to obtain better wear qualities (or high frequency performance in the case of ferrites).
- superior heads can be made of binary alloys of silicon and iron, the silicon being preferably in the range from about 3 percent to 7 percent and the balance being essentially iron, if sugzh alloys are properly fabricated and heat-treated.
- My preferred pole piece fabrication of such binary alloys takes advantage of grain orientation, high temperature heat treatment, heat treatment in a magnetic field, and other features as will be described herein.
- l-Ieads such as disclosed herein give better defined gaps than obtained using Permalloy or the like when the gap size is below 100 microinches as for example 40, 20, or 10 microinches or even smaller.
- the gaps are maintained after long tape usage while gaps of Pennalloy" may smear across and become magnetically short circuited.
- the tape support area of the head acquires and maintains a laterally crowned contour with the pole pieces at the highest point. This insures excellent contact between head and tape at the gap, which is extremely important at short wave lengths. Wave lengths less than 0.000,025 inch long were recorded and played back with these heads.
- the silicon-iron alloy poles remain clean after passage of tape across them and do not have an affinity for metallic and nonmetallic accumulations that separate the tape from the gap.
- Silicon-iron pole pieces have a longer life than those made ofPermalloy by a factor of several times. They can be made with a lesser gap depth while the poles are still adequately supported because the metal is stronger, and will still have a long life before wearing through.
- the heads described herein may be made with a gap depth of one mil (0.001 inch), increasing their efficiency especially at gap lengths of less than 40 microinches (1 micron), which is considered to be the microgap region of special interest in the present specificatron.
- Magnetic saturation densities of 20 kilogauss or more are obtainable with silicon-iron in the lower range of silicon content. Even at the higher limits of silicon content the saturation density exceeds 10 kilogauss. By comparison, the saturation density is 5 to 8 kilogauss in Mumetal" and Permalloy", and with about 1.5 to 3 kilogauss in ferrites. A high saturation density did not prove advantageous in prior art heads and was therefore not considered important. In microgap heads which are to be used for recording it has been found that pole pieces according to this invention allow higher signal levels to be recorded than with prior art heads of the same microgap size.
- the improved heads are especially suitable for economical video recorders of the fixed head longitudinal scan type, since they give high performance in the MegaI-Iertz range, are economical to construct, and have a long life.
- a single head can be used for both recording and playback. At 60 inches per second tape-to-head speed, a response to 2.5 MegaHertz was obtained.
- a further object of the invention is to provide a magnetic head exhibiting superior wear qualities.
- a still further object of the invention is to provide a magnetic head providing improved head-to-tape contact for reliable and efficient transducing of recorded wave lengths below microinches.
- Still another object of the invention is to provide an improved magnetic transducer head especially suitable for economical video recorders of the fixed head longitudinal scan type and which gives a high performance in the MegaHertz range and yet is economical to construct.
- Certain features of the invention are not limited to the use of silicon-iron and relate to novel oriented core configurations, composite core constructions, and the annealing of a head core in a magnetic circuit corresponding to that which is present in actual use.
- FIG. l is a transverse view showing a magnetic head in accordance with the present invention in end elevation and indicating the tape record medium in cross section;
- FIG. 2 is a somewhat diagrammatic side elevational view illustrating a first magnetic core configuration in accordance with the present invention
- FIG. 3 is an end elevational view of a core piece for the core configuration of FIG. 2;
- FIG. 4 illustrates apparatus for applying a magnetic field to a magnetic core part such as illustrated in FIG. 3 during the annealing of such core part;
- FIG. 5 is a somewhat diagrammatic cross-sectional view taken generally along the line V-V of FIG. 4;
- FIG. 6 is a somewhat diagrammatic side elevational view of a second form of core configuration in accordance with the present invention.
- FIG. 7 represents an end elevational view of one of the core parts of the core configuration of FIG. 6;
- FIG. 8 illustrates a third form of core configuration in accordance with the present invention.
- FIG. 9 illustrates a further form of magnetic transducer head in accordance with the present invention.
- FIG. 10 is an enlarged somewhat diagrammatic detail view showing the gap region of the head of FIG. 9;
- FIG. 11 illustrates a still further form of head construction in accordance with the present invention.
- FIG. 12 illustrates approximate comparative flux densities and permeabilities as a function of frequency for Supermalloy, 6.5 percent silicon-iron and 3 percent oriented siliconiron.
- FIG. 1 illustrates a magnetic transducer head 10 having a tape record medium 11 with its magnetizable surface layer 11a in sliding contact with the head.
- the head is shown as comprising a housing 12 having tape contacting surfaces such as indicated at 120 and having an aperture 12b exposing a magnetic core 13.
- the tape contacting surfaces 130 of the magnetic core 13 are made of my preferred silicon-iron alloy and the housing surface 12a is ofa material that wears more rapidly, the tape support area of the head acquires and maintains a laterally crowned contour as shown in FIG. 1, with the tape engaging surface 13a at the highest point.
- the head core 13 is embedded in insert blocks such as 14 of silver or other highly conductive material.
- the tape contacting surfaces 12a of housing 12 may be ofsilver, brass, Mumetal," or other material that wears more rapidly than the silicon-iron alloy providing the tape engaging surface 13a of core 13.
- FIGS. 2 and 3 illustrate a head core 15 including core pieces 16 and 17.
- each of the core pieces may have a gap defining face 16a and may have a generally channel cross section with integral lateral flanges 16b and l6c.
- the gap defining faces such as 16a define a nonmagnetic gap 17 for coupling of the core with a magnetic record medium traveling successively across the polar surfaces 18 and 19, for example in the same way as contemplated in FIG. 1.
- the core pieces 16 and 17 are made of a 3 percent grainoriented silicon-iron sheet material having a thickness of about 2 to 4 mils (1 mil equals 0.00] inch) obtainable from Allegheny Ludlum Steel Company under the name Silectron.
- the curved portions of the core pieces are in the direction of grain orientation with the preferred direction being indicated by arrows such as 21 and 22 in FIG. 2.
- FIGS. 4 and 5 illustrate apparatus for applying a magnetic field to the corepieces l6 and 17 during annealing treatment.
- the core pieces 16 and 17 may be assembled on a loop 30 of nonmagnetic stainless steel wire of about one-sixteenth inch diameter held inside a heat treatment chamber indicated at 31.
- a gap spacer 32 is inserted between the polar edge faces such as 16a, FIG. 3, and the C-shaped core pieces 16 and 17 are nested inside a ring 34 of nonmagnetic material such as stainless steel, held securely by means of a wedge such as indicated at 35 if necessary.
- One or more of these nests are strung onto the loop 30 as indicated at 37 and 38 in FIG. 4 (the nest shown in FIG. 5 being designated by the reference numeral 37).
- the loop 30 is electrically connected by means of conductors 40 and 41 with an electrical current source 42 which may be capable of supplying an electrical current of8 to 12 amperes as measured by an ammeter 43.
- FIGS. 6 and 7 illustrate a head core 50 made of 6% percent silicon-iron of composition 6.5 percent silicon and the balance iron and minor impurities. Such material is too brittle to be formed as in FIGS. 2 and 3. It is therefore built up by bending strips of silicon-iron into C-shaped side pieces such as indicated at 55 and 58in FIG. 6 and at 55, 56 and 57in FIG. 7. The side pieces are spot welded to the generally arcuate interior surface of core pieces 51 and 52 as indicated at 61, 62, 61 and 62, for example, in FIG. 6. Good welds should be obtained as close to the gap 63 as possible.
- the core pieces 51 and 52 provide polar end faces such as indicated at 510 in FIG.
- the core pieces 51 and 52 may be of identical construction and are preferably filled with laminations 70, FIG. 7, whose configuration corresponds to that of the side pieces such as 55 and 58, FIG. 6.
- the laminations 70 are of high permeability material such as Supermalloy" having a composition of 5 percent molybdenum, 79 percent nickel and the remainder iron and minor constituents. The material of the laminations has the lowest possible coercive force and the laminations are insulated with magnesium oxide from each other and from the silicon-iron material.
- the core pieces 51 and 52 may be formed from grain oriented sheet material such as the silicon-iron binary alloy above described, having a thickness of 4 mils and having a rolling direction as indicated by the arrows such as 72 and 73, so that when the core pieces are bent into the generally arcuate shape the preferred direction follows the circumference of the core (which is in conformity with the direction of the working magnetic flux path in the core).
- the side pieces such as 55 and 58 may also be formed from oriented sheet material with a preferred direction as indicated by arrows such as 75 and '76.
- FIG. 8 illustrates a head construction wherein core pieces and 81 are formed from the aforementioned oriented silicon-iron sheet material with preferred directions as indicated by arrows such as 82 and 83.
- the core pieces 80 and 81 may be built up from a series of C-shaped laminations of identical configuration having respective extremities such as indicated at 85 and 86 defining gap 87 and across which a tape record medium moves in sliding contact with surfaces such as indicated at 850 and 86a as in the previous embodiments.
- the polar portions 85 and 86 have a width dimension (in the vertical direction as viewed in FIG. 8) which progressively increases in the direction away from the gap 87.
- the core pieces have intermediate portions as indicated at 90 and 91 which are of substantially greater width (here measured in the horizontal direction as viewed in FIG. 8) in comparison with the width dimension ofthe extremities 85 and 86.
- the preferred direction indicated by arrows 92 and 93 is crosswise to the direction of the working magnetic flux path of the core, and electric windings 95 and 96 are preferably located on the intermediate portions 90 and 91 of the core pieces 80 and 81.
- FIGS. 9 and 10 illustrate a further head construction wherein core pieces 101 and 102 define a coupling gap 103 and having pole pieces 104 and 105, FIG. 10, across which a tape record medium 107 moves in the direction of arrow 108.
- the tape 107 has a magnetizable layer 108 which is in sliding contact with polar surfaces of the pole pieces 1M and M in the vicinity of the gap 103.
- the layer 108 may be formed of iron oxide particles in a nonmagnetic binder and exhibiting a coercivity of at least 200 oersteds.
- the tape may move in the direction of the arrow 108' at a speed of 30 inches per second or at a speed of 60 inches per second.
- the gap 103 is considered to have a depth which is measured in the vertical direction as viewed in FIG. 10 and is determined by the vertical dimension of the gap defining faces 104a and 105a of the pole pieces 1M and 105.
- the direction of the working magnetic flux path of the core in the gap region is indicated by the flux line 100, FIG. 10.
- the core pieces I01 and 102 may be formed from a series of generally C-shaped laminations which are stamped from grain oriented flat sheet silicon-iron material.
- the preferred direction of magnetization is at an oblique angle, for example about 45 to the horizontal as viewed in FIG. 9, and pointed toward the gap edges as indicated by arrows 115 and 116, for example.
- the working magnetic flux path in the pole tips 104 and 105 generally conforms with the preferred direction of magnetization as indicated by arrows 115 and 116, and the direction of arrows 115 and 1116 is in close conformity with the magnetic field direction inside the record medium as indicated by flux line 110.
- the core pieces 101 and 102 may be made of 3 percent grain oriented silicon-iron and may comprise a stack of identical laminations one mil thick with the direction of orientation as indicated by the arrows 115 and 116.
- the exterior perimeter of the core formed by the assembly of core pieces 101 and 102 may have an outer perimeter 121 which is circular, and may have an inner perimeter as indicated at 122 which is also circular that is offset in the direction towards the gap 103 relative to the circle defined by outer perimeter 1121.
- the result is a configuration with a base region 123 of substantially greater cross-sectional area and flux carrying capacity than other portions of the core, the preferred direction as indicated by arrows 124 and 125 in the base region being generally transverse to the direction of the working magnetic flux path.
- the circular window defined by inner perimeter 1122 accommodates a doughnut-shaped winding 127 which is of larger volume at the region thereof within the inner perimeter 122 than the volume of the pole pieces 11M and 105 considering the volume of the pole pieces which is directly above the cross section of the winding 127 as viewed in FIG. 9.
- a channel-shaped piece may be added as indicated in dash-outline at 130 in FIG. 9.
- the channel-shaped piece 130 would have a bight portion conforming in contour to the external perimeter 121, and would have respective planar portions extending vertically as viewed in FIG. 9 at opposite sides of the core and in contacting relation with the outer faces of the respective end laminations forming the core pieces 10]! and 102.
- the channel-shaped piece 130 may bridge across the back gap 132 between core pieces M11 and 102, or it may be cut and lapped so as to provide a gap corresponding in configuration with the back gap 132 of the core.
- the core pieces 101 and 102 may each be mounted in a cavity such as indicated at 140 in an electrically conductive mounting block M1.
- the generally arcuate face 1410 of the block M1 has the same radius of curvature as the outer perimeter of 121 so as to provide a layer of electrically conductive material in close conforming relation to the exterior perimeter of the core piece 101, the core surface being insulated to avoid excessive eddy current loss.
- the lateral surfaces such as l41b may also be disposed in close conforming relation with the core particularly at the upper portion thereof at each lateral side of the core piece 101.
- the mounting block M1 may be suitably recessed as indicated at 1410 to accommodate the winding 127 and the channelshaped piece 130.
- the portion of the mounting block 141 indicated at 145 may be removed during the final finishing operation so as to expose the tape engaging surfaces of the pole pieces 104 and 105.
- FIG. 11 illustrates diagrammatically a single pole piece having a polar extremity 151 for coupling with a magnetic tape record medium 152 moving in the direction of arrow 153.
- the pole extremity 151 has a polar tape-engaging surface in sliding contact with the surface of the magnetizable layer of the record medium 152.
- the core piece of 150 may be made of a flat strip of oriented silicon-iron, the preferred direction of orientation being in the direction of arrow 155.
- the properties may be further enhanced by heat treatment in a linear magnetic field also in the direction of arrow 155 using an alternating current magnetic field with a frequency of 60 cycles per second and providing an R.M.S. value of magnetizing force of about 15 oersteds. Substantially higher frequencies may be used instead, or direct current magnetic field may be applied to provide a direct current of magnetizing force of about 15 oersteds.
- FIG. 12 compares typical magnetic characteristics of Supermalloy," 6.5 percent silicon-iron, and 3 percent oriented silicon-iron, at various frequencies useful in magnetic heads.
- the measurements were taken using flat washerlike samples of the material which were stamped from flat sheet material having a thickness of 4 mils.
- the permeability (;1.) measurements were taken at a field of 0.1 oersted R.M.S. in all cases, and the B readings represent the highest level (in kilogauss) where an undistorted output was obtained.
- the oriented 3 percent silicon-iron sample had an orientation somewhat analogous to that indicated by the arrows associated with side pieces 55 and 58in FIG. 6.
- a curve 161 shows the permeability variation of the Supermalloy sample; curve 162 shows the permeability variation for 6.5 percent silicon-iron; and curve 163 shows the permeability variation for 3 percent oriented silicon-iron.
- Curve 164 shows the B variation for Supermalloy"; curve 165 shows the B variation for 6.5 percent silicon-iron; and curve 166 shows the B variation for 3 percent oriented silicon-iron.
- silicon-iron heads having a relatively high magnetic saturation are of best advantage when used with high coercive record materials as represented by modern oxide surfaces with coercive forces above 200 oersteds, for example 225 oersteds or higher, and make it possible to record efficiently on record materials with coercive forces above 350 oersteds which have not been practical except in very thin coatings.
- Iron-cobalt alloys of 50 percent iron and 50 percent cobalt composition, and improved versions containing 49 percent iron, 49 percent cobalt, and 2 percent of vanadium also have exceptionally high magnetic saturation, but are more expensive and difficult to produce than are silicon-iron.
- the following Table I gives some properties of silicon-iron alloys, the values being intended to be typical for the percentages of silicon indicated. It is notable that the resistivity is a 7 maximum at about 11 percent silicon content; a high resistivity being advantageous for low eddy current losses.
- the Curie point is useful in specifying the temperature below which the magnetic field must be applied, for example with the apparatus of FIGS. 4 and 5 during the magnetic anneal process; for example 1380 F. for 3 percent silicon material, and 1270 F. for 6%percent silicon material. Also the annealing temperature should be above the Curie point for the material. Saturation magnetization (for an applied direct current magnetizing force) decreases with increasing silicon content, but is high in all cases compared to previously used 79 percent nickel material such as "Permalloy Values not specified in Table I can be interpolated.
- Permalloy are a resistivity of 55 microhm-centimeters, a Curie point of l l F., a B,,,,. of 7300 gauss and a Rockwell Hardness of 30.
- nonoriented silicon irons are AISI types M-IS, M-19, M-22, M-27 and M-36.
- Filler laminations such as indicated at 25 in FIG. 3, and 70 in FIG. 7 may range from 0.5 mil to 4 mils in thickness and are helpful in reducing residual magnetization and improving the flux carrying capacity. They may be omitted for economy.
- the gap spacer may be of a nonmagnetic stainless steel or of platinum, or oflnconer (which has a composition of approximately 80 percent nickel, 14 percent chromium, and 6 percent iron), so as to withstand the high annealing temperatures.
- the silicon iron having a low carbon content of less than 0.05 percent, and preferably about 0.02 percent or below.
- a typical winding for the illustrated core constructions would have a top portion with 50 turns of No. 40 AWG wire, and a bottom portion of 150 turns of No. 42 AWG wire, both wound together in a doughnut shape such as shown at 127 in FIG. 9.
- the improved heads are especially suitable for economical video recorders of the fixed head longitudinal scan type, since they give high performance in the MegaHertz range, are economical to construct, and have a long life.
- a single head such as those illustrated in any of the embodiments herein, can be used for both recording and playback. At 60 inches per second tape to head speed, a response to 2.5 MegaHertz was obtained.
- Heads made according to the following examples give better defined gaps than Permalloy" when the gap size is below microinches as for example 40, 20 or I0 microinches or even smaller.
- the gaps are maintained after long tape usage while gaps ofPermalloy” may smear across the gap so as to provide a magnetic short circuit between the pole pieces.
- Wavelengths less than 0.000,025 inch (25 microinches) long were recorded and played back with the heads described herein.
- the core 15 comprises core pieces 16 and 17 of 3 percent grain-oriented silicon-iron 4 mils thick obtainable from Allegheny Ludlum Steel Company under the name Silectron.
- the curved portions of the core pieces 16 and 17 are in the direction of grain orientation with the preferred direction as indicated by arrows 21 and 22 and have an outer diameter of I10 mils and inner diameter of 70 mils.
- the 3 percent silicon material is quite malleable and is readily shaped to the channel cross section as shown in FIG. 3.
- the inner portion of the channel is filled with crescents of Supermalloy" as indicated at 25 of 1 mil thickness insulated from each other by thin layers of magnesium oxide. In the same way the channels themselves are also insulated on all surfaces.
- the filled core pieces 16 and 17 are then annealed in an atmosphere of dry hydrogen, holding at a temperature of 2000 F. for 15 minutes or more, and cooled slowly over a period of several hours.
- the core pieces 16 and 17 are cemented into close fitting cavities such as indicated at in FIG. 9 provided by insert blocks such as indicated at 141 in FIG. 9 made of silver.
- the silver insert blocks may in turn fit into recesses in mating mounting blocks of brass which in turn may be enclosed within a one piece housing shell of magnetic material similar to that indicated at 12 in FIG. 1 with a separate bottom closure part.
- the silver insert blocks corresponding to the material 14 in FIG. 1 may be recessed below the tape engaging surfaces 12a and 13a.
- the core pieces 16 and 17 are secured in separate mounting blocks with the mating faces lapped to an optical finish, then assembled with a beryllium copper gap spacer at 17, FIG. 2, having a thickness of approximately 18 microinches and placed between the upper gap defining faces such as indicated at 16a, FIG. 3, with a coil of 200 turns placed around the lower extremities of the core pieces 16 and 17 generally as indicated for the winding 127 in FIG. 9.
- the assembly is mounted in a casing which may be of Mumetal corresponding to casing 12, FIG. 1, the projecting tape engaging surfaces 18 and 19 of the pole pieces being lapped to expose the gap 17' to the active surface such as indicated at 11a of the tape record medium 11 indicated in FIG. 1.
- a head made with two side-by-side cores each 21 mils wide, to provide a 42 mil wide track has an inductance of about 2 millihenries with a 200-turn coil when measured at a frequency of l kiloHertz. This is one-half the inductance of a similar head made of Supermalloy," yet the output of this head equals or exceeds that of the Supermalloy" head under conditions of bias and signal optimized for Supermalloy.” More turns can thus be used on the silicon-iron head for increased output without exceeding limitations caused by head resonance.
- a high saturation value is noted, with permeability as a function of magnetizing force still rising at an excitation of 4 ampere-tums.
- the above head with a 50 turn tap on the ZOO-turn winding to provide a SO-turn recording winding gives excellent response to signal frequencies up to 2 MegaI-lertz and up to bias frequencies of 7 MegaHertz using quarter-inch tape at 60 inches per second tape-to-head velocity.
- EXAMPLE [I (FIGS. 6 and 7)
- a head of overall dimensions the same as in Example l is made of an alloy of 6.5 percent silicon, and 93.5 percent iron and minor constituents which is 4 mils thick, obtainable from Westinghouse Electric Corp. This material is not malleable enough to form as illustrated in FIG. 3. It is therefore built up by welding as described in connection with FIGS. 6 and 7 heretofore.
- the rolling direction of the core pieces SI and 52 is as indicated by the arrows such as 72 and 73, the core pieces being bent to their curvature with the preferred direction following the circumference.
- the inner C-shaped side pieces such as indicated at 55 and 50 in FIG.
- the inductance of this head is higher and its saturation flux density lower than than of Example I, but still considerably better than for a comparable head of Supermalloy.”
- High resistivity improves the loss factor at high frequencies.
- the extra hardness improves gap definition and wear resistance. Response is to 2.5 MegaHertz at 60 inches per second headto-tape velocity.
- the various forming operations are preferably carried out before annealing, except for the final polishing or lapping.
- Good welds should be obtained as close to the gap 63 as possible, so as to give maximum support to the gap defining surfaces such as indicated at Ma, FIG. 7.
- the laminations 70 for Example ll preferably have the lowest possible coercive force, for example, as provided by Supermalloy" material.
- the gap spacer providing the gap 63 is of beryllium copper having a thickness from 60 microinches down to 12 microinches or less in Example II.
- This silicon-iron material is close enough to that of Supermalloy so that performance of the Example II silicon-iron head in the video range is completely satisfactory.
- the head gives better results than Supermalloy when extremely small gap spacers are used. This is attributed to the freedom from mushrooming or smearing of the core material at the defining faces, causing the gap to be bridged where the tape rides over it.
- Soft materials such as Permalloy are susceptible to this effect when the gap is very small. Microscopic observation confirmed these effects.
- Example ll A range of heat treatment temperatures was tried for the materials of Example ll, above and below the specific temperature of 2000 F., but the results were optimum at 2000 F. It is advantageous to cool the core while a magnetic field is applied to it in the direction of magnetization of the working flux as described in connection with FIGS. 4 and 5. This may be accomplished by supplying a direct current of about 10 amperes to conductor loop 30, FIG. 4, while the core cools from l500 F. in a hydrogen atmosphere.
- Examples I and II utilize the magnetic tapes with oxide surface layers having a coercive force on the order of 225 oersteds.
- EXAMPLE I The pole piece material and procedure are the same as in Example ll, except that for the annealing of the core parts they are nested inside a ring of nonmagnetic stainless steel as indicated at 34 in FIG. 5, and held securely with a wedge 35 if necessary.
- the stainless steel is type 302 18 percent chromium, 8 percent nickel and the balance iron).
- the loop of stainless steel wire has a cross section about one-sixteenth inch in diameter and is held within the heat treatment chamber 31 as illustrated in FIG. 4.
- Sixty cycle per second alternating current having an R.M.S. value of 8 to 12 amperes as measured by ammeter 43 passes through the loop 30, especially during the cooling cycle until the core parts have cooled to below 500 F. This gives a magnetizing force of about 15 oersteds R.M.S. in the pole pieces, the exact value being noncritical.
- Annealing by this procedure gives a higher magnetic permeability than in Example II where the magnetic field treatment is omitted. High frequencies may also be used for the current source 42 with beneficial results.
- EXAMPLE IV The same process is used as in Example III but with a direct current having a value of the order of 8 to 12 amperes. A higher magnetic permeability is also obtained, in comparison to the results in Example ll without the magnetic field treatment.
- a head structure is made having laminations of configura tion corresponding to that of side pieces 55 and 58 in FIG. 6, with the preferred directions of magnetization in successive laminations arranged generally at right angles to each other, such that preferred directions as illustrated by arrows 75 and 76 in FIG. 6 for one lamination are generally horizontal, while the preferred directions for the adjacent laminations on either side are generally vertical, so that the permeability of the overall assembly is improved at the intermediate portion of the core parts where the orientations 75 and 76 are crosswise to the direction of the working magnetic flux path.
- the laminated head of this Example is similar to the head of FIG. 9 except for the exact configuration of the laminations. Twenty laminations of 2 mil thickness are used to form each core piece.
- the laminations are of 6.5 percent silicon-iron and have a thin surface layer of magnesium oxide for insulation and are annealed in hydrogen at 2050 F. When cool they are transferred to a block such as indicated at 141, FIG. 9, having a close fitting cavity such as 140 of high electrical conductivity, the cavity being coated on its surface with a thin layer of epoxy resin, suchthat the laminations are held at their outer edge and are not subjected to stresses that occur when the sides of the laminations are adhered together.
- a pair of blocks such as 141 are finished as indicated previously, using an 18 microinch gap spacer. The head made in this way is very efficient at high bias frequencies exceeding 7 MegaHertz, and gives excellent signal response at 2 MegaI-Iertz.
- the overall permeability is improved by increasing the cross section of the core pieces at the intennediate regions 90 and 91.
- the coils 95 and 96 are preferably associated with the core pieces at the intermediate regions 90 and 91 where the direction of orientation as indicated by arrows 92 and 93 is transverse to the working magnetic flux path of the core, so that the magnetomotive force loss of these poorer regions 90 and 91 is supplied by the immediate source of magnetomotive force; while the best permeability portions are used at the pole pieces 85 and 86 so as to channel the magnetic flux to the working gap 87 with minimum loss.
- the directional properties are used to advantage in the construction of FIG. 9 where the preferred direction of magnetization is at an oblique angle (as for example about 45) as indicated by arrows 115 and H6 which as indicated in FIG. 10 are pointed toward the gap edges of pole pieces 104 and 105. As shown in FIG. 10 the arrows 115 and 116 have direction which is in close conformity with the magnetic flux path 110 inside the magnetizable layer 108.
- EXAMPLE VI The head core pieces are made of 3 percent grain oriented silicon-iron Silectrons in laminations 1 mil thick, with the direction of orientation as indicated in FIGS. 9 and 10. The procedure is generally as in Example V. The result is a head with exceptionally good resolution at short wavelengths, and with superior efficiency at megacycle frequencies. Annealing is effected with the direct current magnetic field applied to the core as described in Example IV.
- the nested assemblies such as 37 may be removed and replaced from the loop by disconnecting the leads 40 and 41 from the ends of the loop 30, and removing the ends of the loop 30 from the end seal indicated at the right-hand end of chamber 31.
- the seal also has a duct extending therethrough to provide an atmosphere inlet and outlet.
- Transducer heads made of other materials may also benefit by a magnetic anneal as taught herein.
- Such heads may be made of ferrites, the various materials such as Permalloy," and cobalt iron materials such as Supermendur.”
- Permalloy this is the 65 percent nickel, percent iron range.
- cobalt iron an alloy of 49 percent cobalt, 49 percent iron and 2 percent vanadium is optimum.
- silicon-iron a preferred composition is 6.5 percent silicon, and the balance iron and minor impurities.
- a magnetic head comprising:
- a magnetic core piece having a polar extremity with a gap defining edge face and a relatively broad under surface, means comprising said core piece defining a coupling gap having said edge face as one boundary thereof, and a side piece of flat sheet configuration secured in supporting relation to said polar extremity at said under surface thereof.
- a head according to claim 1 with said polar extremity having a record medium engaging surface of silicon-iron opposite said under surface and having a depth dimension between said surfaces at said gap defining edge face of not more than about 1 mil.
- a head according to claim 1 with said core piece being formed from grain oriented silicon-iron sheet material having a preferred direction corresponding to the direction of the working magnetic flux path in said polar extremity.
- a magnetic head having a magnetic core with a coupling region for coupling the core to a traveling magnetic record medium, said magnetic core being formed of a grain-oriented hydrogen-annealed silicon-iron alloy having a hardness of at least 50 Rockwell (B2 Scale).
- a magnetic head wherein, said silicon-iron alloy has been annealed by heating in a dry hydrogen atmosphere to a temperature above the Curie point of said alloy and during cooling from said temperature has been sub- 3 jected to a magnetic field applied in the direction of the working flux path of said core.
- said silicon-iron alloy has a silicon content of at least about 6.5 percent silicon with the balance iron and minor impurities, and
- said alloy has a resistivity of at least 80 microhm-cms.
- a magnetic head having a magnetic core with a coupling region for coupling the core to a traveling magnetic record medium, a polar region adjacent said coupling region presenting a surface of a binary silicon-iron alloy of from about 3 percent to 7 percent silicon and the balance essentially iron for slidable contacting engagement by said record medium, said magnetic core being characterized by having a gap of a thickness of not more than about 1 micron.
- a head according to claim 8 wherein said magnetic core has a material thickness of 4 mils or less, said gap has a thickness less than 1 micron, and a layer of electrically conductive material having a resistivity less than 2 microhm-centimeters is disposed in close conforming relation to exterior surfaces of said magnetic core except at such coupling region.
- a head in accordance with claim 8 with mounting means for the core having a record medium engaging surface generally flush with the record medium engaging surface of the magnetic core but being of a material subject to substantially more rapid wear in response to sliding contact with the record medium than the material of said record engaging surface of said core.
- a head in accordance with claim 10 wherein said mounting means comprises a layer of electrically conductive material disposed in close conforming relation to the said magnetic core except at said record engaging surface and side pieces are fastened to said core at opposite sides of said magnetic core adjacent said coupling region.
- said core includes said silicon-iron alloy in the form of a C-shaped side pieces with the grain of the silicon-iron alloy at said polar region oriented substantially at right angles to the plane of said gap.
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Magnetic Heads (AREA)
- Soft Magnetic Materials (AREA)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US74665168A | 1968-07-22 | 1968-07-22 |
Publications (1)
Publication Number | Publication Date |
---|---|
US3582572A true US3582572A (en) | 1971-06-01 |
Family
ID=25001754
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US746651A Expired - Lifetime US3582572A (en) | 1968-07-22 | 1968-07-22 | Transducer head with grain oriented silicon-iron core |
Country Status (3)
Country | Link |
---|---|
US (1) | US3582572A (de) |
DE (1) | DE1936817A1 (de) |
GB (1) | GB1235402A (de) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4086639A (en) * | 1975-09-29 | 1978-04-25 | Canon Kabushiki Kaisha | Magnetic head which minimizes the effect of minute variations in the head gap |
US4240121A (en) * | 1978-02-02 | 1980-12-16 | Robert Bosch Gmbh | Broadband magnetic tape transducer head |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1809197A (en) * | 1929-08-06 | 1931-06-09 | Jr William Fendrich | Method of production of generator armatures |
US2489977A (en) * | 1946-12-03 | 1949-11-29 | Harry F Porter | Laminated core |
US2694754A (en) * | 1950-06-12 | 1954-11-16 | Lawrence H Connell | Magnetic recording apparatus |
US2991511A (en) * | 1955-12-20 | 1961-07-11 | Clevite Corp | Method of making multichannel magnetic transducer heads |
US3311711A (en) * | 1963-07-29 | 1967-03-28 | Mach Tronies Inc | Resilient core holder for pressing head sections into alignment |
-
1968
- 1968-07-22 US US746651A patent/US3582572A/en not_active Expired - Lifetime
-
1969
- 1969-06-26 GB GB32416/69A patent/GB1235402A/en not_active Expired
- 1969-07-19 DE DE19691936817 patent/DE1936817A1/de active Pending
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1809197A (en) * | 1929-08-06 | 1931-06-09 | Jr William Fendrich | Method of production of generator armatures |
US2489977A (en) * | 1946-12-03 | 1949-11-29 | Harry F Porter | Laminated core |
US2694754A (en) * | 1950-06-12 | 1954-11-16 | Lawrence H Connell | Magnetic recording apparatus |
US2991511A (en) * | 1955-12-20 | 1961-07-11 | Clevite Corp | Method of making multichannel magnetic transducer heads |
US3311711A (en) * | 1963-07-29 | 1967-03-28 | Mach Tronies Inc | Resilient core holder for pressing head sections into alignment |
Non-Patent Citations (1)
Title |
---|
Magnetic Materials In The Electrical Industry, by P. R. Bardell, Copyright 1960, Published by MacDonald & Co. (Publishers) Ltd., London, pp. 108 109. * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4086639A (en) * | 1975-09-29 | 1978-04-25 | Canon Kabushiki Kaisha | Magnetic head which minimizes the effect of minute variations in the head gap |
US4240121A (en) * | 1978-02-02 | 1980-12-16 | Robert Bosch Gmbh | Broadband magnetic tape transducer head |
Also Published As
Publication number | Publication date |
---|---|
DE1936817A1 (de) | 1970-01-29 |
GB1235402A (en) | 1971-06-16 |
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