GB2139404A - Magnetic Head Core and Manufacturing Method - Google Patents

Abstract

A magnetic head core of Fe-Si-Al alloys (Sendusts) comprising nonmetallic inclusions oriented in a core surface to be contacted with a magnetic recording medium, substantially perpendicularly to the movement of the magnetic recording medium. This magnetic head core may be obtained by slicing an alloy extrude 1 prepared by a hot extrusion method at an angle substantially perpendicular to the longitudinal direction of the extrude. <IMAGE>

Description

SPECIFICATION Magnetic Head Core and Manufacturing Method Background of the Invention (1) Field of the Invention This invention relates to a magnetic head core of an Fe-Si-Al high permeability alloy with improved wear resistance and uniform quality.

(2) Description of the Prior Art Magnetic heads are conventionally made of ferrites, permalloys, Sendusts, Co-base amorphous alloys, etc. Ferrites have permeability y with good frequency characteristics and excellent wear resistance which is an important factor for the reliability of magnetic heads, but they are disadvantageous in low saturation magnetic flux density Bs. Permalloys have good magnetic characteristics and are easily formed into magnetic heads at low costs because of good workability, but they have poor wear resistance. Amorphous alloys do not have a long history as magnetic head materials, so they are still under research to improve their characteristics. There have been proposed so far no amorphous alloys having good magnetic characteristics and wear resistance at the same time.

Contrary to the above materials, Sendust alloys have good saturation magnetic flux density Bs and permeability y as well as excellent wear resistance, so they are suitable for magnetic heads. They have, however, poor workability, which makes it difficult and costly to produce magnetic heads therefrom. As for wear resistance, Sendust alloys are inferior to ferrites, though the former is superior to permalloys. Therefore, further improvement in the wear resistance of Sendust alloys has been desired, because they are to be used for magnetic heads which are operated at high magnetic tape speeds. The wear resistance problem is serious particularly when magnetic heads are operated in the atmosphere of high temperatures and humidities.

Further, because of their brittleness, Sendust alloys are usually machined from cast ingots. In the cast ingot, however, solute atoms tend to segregate when the ingot is cooled. In the process of solidification of a Sendust melt, Si and Al, solute atoms migrate from a solid phase to a liquid phase in the ingot because of difference in their solubility in the liquid and solid phases, resulting in higher concentration thereof in the molten phase. As a result, the segregation of the solute atoms occurs in the range of several hundreds to several microns. Accordingly, magnetic head chips sliced from the cast ingot may have slightly different compositions from each other, resulting in the non-uniformity of magnetic characteristics among the resulting magnetic head cores.Since the Si concentration affects the magnetic characteristics of magnetic head cores more than that of Al, curbing the Si segregation is greatly desired to provide magnetic head cores with uniform magnetic properties.

It is effective to heat the ingot to reduce the Si segregation, but a heat treatment should be carried out at higher than 1 2000C for several to several tens hours to achieve the Si segregation level of within +0.2 wt.%. Such a high-temperature heat treatment of a long period of time, however, produces very large crystal grains, extremely lowering the workability of that alloy.

Summary of the Invention An object of the present invention, therefore, is to provide a magnetic head core having good wear resistance and magnetic characteristics.

Another object of the present invention is to provide a method of manufacturing a magnetic head core of an Fe-Si-Al alloy having good wear resistance and magnetic characteristics.

A magnetic head core of an Fe-Si-Al alloy according to the present invention comprises nonmetallic inclusions oriented in a core surface to be contacted with a magnetic recording medium, substantially perpendicularly to the movement of the magnetic recording medium.

A method of manufacturing such a magnetic head core according to the present invention comprises subjecting the alloy to a hot extrusion under side pressure, and slicing the resultant alloy extrude to form each magnetic head core chip, at such an angle to the longitudinal direction of the extrude that nonmetallic inclusions contained in the alloy extrude are oriented, in a surface of the resulting magnetic head core to be contacted with a magnetic recording medium, substantially perpendicularly to the movement of the magnetic recording medium.

Brief Description of the Drawings Figure 1 is a partial perspective view of a Sendust alloy extrude according to one embodiment of the present invention; Figure 2 is a schematic cross sectional view of an apparatus used for the hot extrusion of a Sendust alloy; Figure 3(a) is a photograph (x 100) of the microstructure of a Sendust alloy extrude in which the arrow shows an extrusion direction; Figure 3(b) is a photograph (x100) of the microstructure of a Sendust alloy casting; Figure 4(a) is a graph showing the Si distribution along the length of a Sendust alloy casting; and Figure 4(b) is a graph showing the Si distribution along the length of a Sendust alloy extrude according to the present invention.

Description of the Preferred Embodiments Figure 1 shows an elongated Sendust alloy extrude 1 having a C-shaped cross section to be used for a magnetic head core according to one embodiment of the present invention. This Sendust alloy extrude 1 has a web 2 and two extensions 3 and 4 projecting from one side of the web 2 at both ends thereof. The projection 3 has an outer surface 5 which may be brought into contact with a magnetic recording medium such as a magnetic tape.

The term "Sendust alloy" used herein includes any alloy having the composition of 3-13 weight % Si, 3-10 weight % Al and balance Fe.

A Sendust alloy contains small amounts of spherical nonmetallic inclusion of Al203, SiO2, etc.

Where it contains Ti, Zr or Cr as additives, however, carbides, nitrides and oxides of these elements are precipitated as non-metallic inclusions. Ti, Zr and Cr may be added in the amounts of 0.1-5.0 wt.%, 0.01-1.0 wt.% and 0.1-10 wt.%, respectively. 0.3-1.0 wt.% Ti, 0.05-0.3 wt.% Zr and 0.3-5 wt.% Cr may be preferably added.

It has been formed that such nonmetallic inclusions can be oriented by plastic working such as hot extrusion. It has also been formed that the nonmetallic inclusions oriented in a particular direction to the movement of a magnetic medium increase the wear resistance of the Sendust alloy head core.

The Sendust alloy extrude having a C-shaped cross section may be manufactured by a hot extrusion method using an apparatus 10. The hot extrusion per se is described in detail in Japanese Patent Publication No. 55-24962 published July 2, 1 980, so it is not within the scope of the present invention.

Referring to Figure 2, the hot-extrusion apparatus 10 comprises a container 12, a die 14 having a nozzle 16, an inner stem 1 8 and an outer stem 20 concentrically surrounding the inner stem 18.

A heated Sendust alloy billet 22 is introduced into the container 12 together with a pressure medium 24. The pressure medium 24 may be solid or powdery materials with good flowability, such as talc, molybdenum disulfide powder and mixtures thereof with pyrophillite, alumina or magnesia. The pressure medium 24 surrounds the Sendust alloy billet 22 in the container 12 so that it can exert pressure on all the side surface of the billet 22 uniformly.

The outer plunger or stem 20 is first pushed to exert uniform pressure P 1 on the billet 22 through the medium 24. The inner plunger or stem 18 is then pushed under pressure PO to perform the extrusion of the Sendust alloy.

The Sendust extrude 1 may have a circular cross section, but preferably has a cross section which is substantially the same as the shape of a magnetic head core chip to be made. The Sendust extrude of a C-shaped cross section is particularly preferable, because it can be formed into magnetic head core chips simply by slicing it, requiring substantially no working which would otherwise have to be done.

For this purpose, the nozzle 16 should have a C-shaped opening.

The resulting Sendust alloy extrude 1 contains nonmetallic inclusions oriented in the longitudinal direction due to hot extrusion. On the other hand, the microstructure of a Sendust alloy casting contains the nonmetallic inclusions which are not oriented in any particular direction.

This extrude 1 is subjected to appropriate surface working and then sliced to provide magnetic head core chips. The core chip is bonded to another core chip of an appropriate shape to provide a magnetic head core in such a manner that the surface 5 constitutes a magnetic medium-contacting surface and that the surface 7 constitutes a gap surface. Since the nonmetallic inclusions are oriented substantially in the longitudinal direction of the extrude 1, they are substantially perpendicular to the lengthwise direction of the surface 5, which means that the nonmetallic inclusions are substantially perpendicular to the movement of a magnetic medium.Such orientation of the nonmetallic inclusions makes a magnetic head core much stronger than those in which nonmetallic inclusions are oriented randomly or in parallel with the direction of a magnetic medium moving on the magnetic head, in terms of wear resistance.

It has also been found that the Sendust alloy member prepared by the above-mentioned hot extrusion method has a uniform Si distribution along the length of the Sendust alloy extrude. The Si segregation is within ~0.2 weight % along the length of the extrude. Such an uniform Si distribution ensures that magnetic head core chips manufactured from the same Sendust alloy extrude have very uniform Si content, and thus very uniform magnetic characteristics.

The present invention will be illustrated in further detail by the following Examples.

EXAMPLE 1 Alloys having compositions as shown in Table I were melted and cast to form about one-kg ingots. Each ingot was cut to form a billet of 20-mm diameter and 30-mm length. The resulting billet was heated at 11 500C and introduced into the apparatus as shown in Figure 2. Pyrophillite was used as a pressure medium, and the outer stem 20 and the inner stem 1 8 were pushed at 24 tons and 20 tons, respectively. Hot extrusion was conducted to form a Sendust alloy extrude having a cross section as schematically shown in Figure 1. The extrude 1 had the following dimensions: 8 mm between the outermost parts of the two extensions 3 and 4, 4 mm between the top surface 7, 8 and the web bottom, 1.5 mm between the top surface 7, 8 and the upper surface of the web 2, 1.5 mm width of the top surface 7 and 2 mm width of the top surface 8.The extrude 1 was sliced at a thickness of 0.2 mm.

The resulting core chip was subjected to heat treatment at 1 0000C after grinding, and three pieces of the core chips were laminated to form a sample magnetic head core. A lower surface of the resulting head core, which is to be brought into contact with a magnetic tape, was ground to have a desired surface curve and then lapped with an Al203 tape.

TABLE I Sample No. Composition (wt.%) 1 9.6 Si~6.0 Al-Bal. Fe 2 9.6 Si~6.0 Al~0.8 Ti-Bal. Fe 3 9.6 Si~6.0 Al~0.1 Zr-Bal. Fe 4 9.0 Si~6.7 Awl~1.5 Cr-Bal. Fe EXAMPLE 2 Photomicrograph was taken at the magnification of 100 on the Sendust alloy extrude of Sample No. 2 prepared in Example 1. Photomicrograph of the same magnitude was also taken on a Sendust alloy casting of Sample No. 2, for the purpose of comparison. The results are shown in Figure 3(a) and Figure 3(b), respectively.Figure 3(a) clearly shows that the Sendust alloy extrude prepared by the hot extrusion method contains nonmetallic inclusions oriented in parallel with the direction of extrusion as indicated by the arrow. On the other hand, Figure 3(b) shows that the Sendust casting contains nonmetallic inclusions oriented randomly.

EXAMPLE 3 Each of the magnetic head cores produced in Example 1 was subjected to a 1000-hour wear test with a r-Fe2O3 tape. Cast ingots of the same alloys as shown in Table I were also cut into magnetic head cores, each of which was then subjected to the same wear test.

In addition, ring samples of a 5-mm outer diameter, a 3-mm inner diameter and a 0.2-mm thickness were prepared from the above Sendust alloy extrudes and cast ingots, respectively. These ring samples were heat treated at I 0000C for two hours and then measured with respect to magnetic properties; effective permeability, coercive force and magnetic flux density at 10 Oe. The results are shown in Table II.

TABLE II 1000-Hour 0.2 t Sample No. Wear (#) Me 1 KHz Hc (Oe) B10 (KG) 1 P* 7 15,000 0.035 9,600 C** 12 14,000 0.035 9,600 2 P 3 14,000 0.040 9,400 C 7 14,000 0.040 9,400 3 P 3 12,000 0.050 9,100 C 7 13,000 0.045 9,100 4 P 4 11,000 0.040 9,000 C 10 11,000 0.045 8,900 Note: *... Present invention alloy in which nonmetallic inclusions are oriented perpendicularly to the prospective movement of a magnetic tape.

Conventional cost alloy in which nonmetallic inclusions are oriented randomly.

it is clear from Table II that the magnetic head cores of the present invention are much superior to the conventional counterparts in respect to wear resistance, while maintaining the magnetic characteristics substantially on the same level.

EXAMPLE 4 Sample alloy 2 (9.6 Si~6.0 Al~0.8 Ti-Bal. Fe) was hot-extruded in the same manner as in Example I to form a Sendust alloy extrude. The extrude was cut to form these types of magnetic head cores in which nonmetallic inclusions were oriented in three directions; 00,450 and 900, respectively to the movement of a magnetic tape. The wear resistance and magnetic characteristics of these magnetic head cores were measured. The results are shown in Table Ill.

TABLE Ill Inclusions' Direction to 1000-Hour 0.2 t Tape Movement Wear(,u) He 1 KHz Hc(Oe) B10 (KG) 00 10 1,400 0.040 9,400 450 6 1,400 0.038 9,400 900 3 1,400 0.040 9,400 It is clear from Table Ill that the wear resistance of a Sendust alloy magnetic head core is maximum when the nonmetallic inclusions are perpendicular to the movement of a magnetic tape.

EXAMPLE 5 The sample No. 2 alloy was melted and cast to form an about one-kg ingot. A billet of about 20 mmf x30 mmi was prepared from this ingot, and then hot-extruded by means of the apparatus as shown in Figure 2 at 1 2000C to form an extrude having a rectangular cross section of 10 mmx5 mm.

100 ring samples of 5 mmXx3 mm#x0.2 mm were prepared from this extrude, heat treated at 1 0000C for two hours, and then measured with respect to magnetic properties. The same measurement was repeated on 100 ring samples of the same size prepared from the cast ingot of the same alloy. The number of ring samples in each ,ue range is shown in Table IV.

TABLE IV 0.2 t He 1 KHz 9000- 11000- 13000- 15000- 17000- 11000 13000 15000 17000 19000 Extrude 0 2 10 81 7 Casting 6 14 26 43 11 These results show that the extrude is much more uniform than the cast ingot in respect to ye.

EXAMPLE 6 The same extrude and cast ingot as in Example 5 were measured with respect to the segregation of an average Si composition. The results are shown in Figures 4(a) and (b). Figure 4(a) shows the Si distribution along the length of the cast ingot, and Figure 4(b) shows the Si distribution along the length of the extrude. It is evident that the extrude prepared by hot extrusion is much more uniform in the Si distribution than the cast ingot.

The present invention has been described by specific examples, but it should be noted that the present invention is not restricted to them. Any modification and change may be made to the present invention unless they depart from the spirit and scope of the present invention.

Claims (9)

1. A magnetic head core of an Fe-Si-Al alloy comprising nonmetallic inclusions oriented in a core surface adapted to be contacted with a magnetic recording medium, in a particular direction relative to the moving direction of the magnetic recording medium.

2. A magnetic head core according to claim 1, wherein said nonmetallic inclusions are oriented in a direction substantially perpendicular to the movement of the magnetic recording medium.

3. A magnetic head core according to claim 1, wherein said alloy further comprises Ti, Zr and/or Cr.

4. A magnetic head core according to claim 3, wherein said nonmetallic inclusions comprise oxides, nitrides and/or carbides of one or more of Si, Al, Ti, Zr and Cr.

5. A magnetic head core according to claim 1, wherein said alloy has a uniform Si distribution within +0.2 weight % of segregation.

6. A method of producing a magnetic head core of an Fe-Si-Al alloy, comprising subjecting said alloy to a hot extrusion under side pressure, and slicing the resultant alloy extrude to form said core at such an angle to the longitudinal direction of the extrude that nonmetallic inclusions contained in said alloy are oriented in a core surface to be contacted with a magnetic recording medium, in a particular direction to the movement of said magnetic recording medium.

7. A method according to claim 6, wherein said nonmetallic inclusions are oriented substantially perpendicularly to the moving direction of the magnetic recording medium.

8. A method according to claim 6 or 7, wherein said alloy extrude has a uniform Si distribution within +0.2 weight % segregation.

9. A method according to claim 7, wherein the hot extrusion of said alloy comprises providing solid pressure medium around an alloy billet heated to more than 9000 C, and extruding said alloy while exerting pressure onto said solid pressure medium.