GB2170640A

GB2170640A - Magnetic head

Info

Publication number: GB2170640A
Application number: GB08502397A
Authority: GB
Inventors: Tsunehiro Tsukagoshi; Kazuhiko Sato; Satoshi Miyaguchi; Yutaka Takasu; Akira Yokoi
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1985-01-31
Filing date: 1985-01-31
Publication date: 1986-08-06
Also published as: GB2170640B; DE3503286A1; GB8502397D0

Abstract

A magnetic head for use in a VTR or magnetic disk unit providing a frequency response of several megahertz, superior wear resistance, good frequency response and high reliability is formed with a magnetic core block composed of two shaped core halves (1a,2a) of Sendust magnetic material, each having a track width regulating groove (5) and a winding groove (7,8) and which are joined together with a gap of predetermined width therebetween. A glass filler is inserted into the track regulating grooves (5), the glass having a working temperature range of not higher than 500 DEG C, there being no intermediate layer between glass and core. Fabrication procedures are detailed (Figs. 2a et seq) the core parts being provided with non- magnetic layers (4) (Figs. 3A,B), and a foil of Ag brazing alloy between mating surfaces where no non- magnetic layer is present. <IMAGE>

Description

SPECIFICATION Magnetic head and method of manufacture The present invention relates to a magnetic head which is capable of satisfactorily recording onto and reproducing from a recording medium having a high coercive force.

Ferrite materials have been extensively used in VTR or magnetic disk head cores because of their high permeability at frequencies higher than several megahertz and their superior wear resistance. However, the recent tendency in the art is toward achieving a higher recording density with media of higher coercive force. A magnetic head constructed of such materials, which include magnetic materials made of powder alloys, plated or evaporated films, and ferritic materials having relatively low saturated magnetic flux densities, is unable to accomplish satisfactory recording on a medium whose coercive force exceeds 1000 Oe. For this reason, head manufacturers have again lately been investigating Sendust, an alloy composed of Fe-Si-Al and having a high saturated magnetic flux density.Sendust has already been used in applications such as a material for VTR heads in professional broadcasttype VTR's but one major problem with the Sendust head is its relatively high wear rate.

The wear of a Sendust head may be reduced by filling the tracking part of the head with a hard material, typically glass. However, glass does not have a strong adherence to Sendust and must be supplemented with an oxide material such as SiO2 or Al2O3 inserted between the glass and the Sendust core.

However, the oxide insert and glass have different degrees of hardness and hence the magnetic head has a tendency to wear unevenly, which may lead to a deterioration in head performance over an extended period of service.

The present invention has been accomplished in order to solve this problem. A principle object of the invention is to provide a magnetic head which is capable of satisfactorily recording onto and reproducing from a recording medium of high coercive force, and which has high wear resistance and reliability, is free from uneven wear, and has good frequency characteristics.

In accordance with the present invention a magnetic recording/reproducing head has a magnetic core block comprised of two shaped core halves of Sendust, each having a track width regulating groove and winding groove, joined together with a predetermined gap width therebetween and a glass filler in the track regulating groove having a working temperature range no higher than 500 C. The track width regulating grooves in the core halves are filled with glass having a strong adherence to Sendust, and no intermediate layer is disposed between the core and the glass. The resulting head has satisfactory wear resistance at the track-forming portion and the head gap. Additionally, this head is free from uneven wear.Therefore, the magnetic head according to the present invention has high reliability and retains good frequency characteristics over an extended period of service.

The invention also includes a method of manufacturing a magnetic recording/reproducing head, comprising the steps of cutting first and second coil receiving grooves on opposite sides of a first block of magnetic material made of Sendust; cutting a coil receiving groove in a second block of Sendust magnetic material; cutting a plurality of track width regulating grooves in both the first and second blocks, the track width regulating grooves extending in a direction generally perpendicular to the coil receiving grooves; providing a nonmagnetic layer having a thickness equal to approximately half the width of a desired head gap on predetermined portions of first surfaces of the first and second magnetic blocks; placing the first surfaces second magnetic blocks together with a foil of a silver brazing alloy inserted between portions of the first surfaces having no non-magnetic layer; heating the first and second blocks under pressure to integrally join the blocks by molten silver alloy; filling the track width regulating grooves with a glass having a melting temperature lower than a melting temperature of the silver brazing alloy and a working temperature range no higher than 500 C; lapping the gap-forming side of the integrally joined first and second blocks to form a rounded surface; cutting the integrally joined first and second blocks into sections to produce a plurality of magnetic head cores; and winding a coil around each half of each of the magnetic head cores in the coil receiving grooves.

A head constructed in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a magnetic core block of the invention; Figures 2A to 5 are perspective views illustrating a process of fabricating this magnetic core block; and Figure 6 is a graph showing frequency response characteristics of a magnetic head of the invention and a conventional magnetic head.

In Fig. 1, reference numerals 1a and 2a represent head core halves, each of which is made of a magnetic alloy material such as Sendust. These halves la and 2a are combined to form a magnetic head block. The rear parts of the halves are butt-jointed together with a silver brazing alloy 3. A non-magnetic layer 4 which forms a head gap has a thickness equivalent to the head gap length. A pair of track width regulating grooves 5 for establishing the head gap width are formed in the front parts of the halves 1a and 2a where they are butt-jointed together. These grooves are filled with glass 6.The glass used as a filler in the present invention should not have a working temperature range higher than 500 C. The term "working temperature range" as used herein means the range between the temperature at which the glass being shaped is about to leave the feeder and the softening point of the glass. Glass having a working temperature range not higher than 500 C has a very good adherence to Sendust alloy and provides an adequate bonding strength.

One head core half la (in the embodiment shown in Fig. 1) has a generally V-shaped groove 7 formed in the surface butt-jointed to the other half 2a for accommodating a winding. This groove has a side inclined at an angle of approximately 45 . Other winding grooves 8, which form pairs with the groove 7, are formed on opposite sides of the core halves 1a and 2a. Turns of coils (not shown) are wound around the respective core halves fitted in the grooves 7 and 8.

The process of fabricating the core of the magnetic head shown above is illustrated in Figs. 2A to 4. The process starts with cutting groove 8 in a magnetic block 2 made of Sendust, and grooves 7 and 8 in another magnetic block 1 also made of Sendust (See Figs.

2A and 2B). One side of each block is provided with a plurality of track width regulating grooves 5 extending in a direction perpendicular to the longitudinal direction. The grooves may be cut with a wire saw, a dicing machine, or a slicing machine. The grooved surfaces are then polished to provide a smooth finish.

In the next step, a non-magnetic layer 4 with a thickness equivalent to half the width of the head gap is formed on part of the surface of each magnetic block, as shown in Figs. 3A and 3B, by a suitable technique such as evaporation or sputtering. Thereafter, as shown in Fig. 4, the non-magnetic layer 4 on the magnetic block 1 is united end to end with the non-magnetic layer 4 on the other magnetic block 2 with a foil of silver brazing alloy inserted between that part of the mating surfaces of the blocks where no non-magnetic layer is formed. While care is taken to minimize any mismatch between the track-forming portions of the blocks, the assembly of the blocks is heated under pressure so that the blocks are integrally joined together by the molten silver alloy.

Subsequently, the track width regulating grooves 5 are filled with glass 6 that melts at a temperature lower than the melting point of the silver brazing alloy. As already mentioned, the glass filter is such that it has a working temperature range not higher than 500 C.

The above procedure provides a magnetic core block 10 (see Fig. 5). After lapping the gap#forming side of the block (the side which contacts the recording tape) to produce a rounded surface, the block is cut into sections with a blade or wire saw along the broken lines shown in Fig. 5. This produces a plurality of magnetic core blocks, one of which is illustrated in Fig. 1. Turns of coils are then wound around the head core halves la and 2a with the grooves 7 and 8 being used as guides.

Fig. 6 is a graph showing the frequency response characteristics of a head of the invention and a head employing a glass having a working temperature range around 570 C.

As may easily be appreciated from the graph of Fig. 6 the head of the invention provides an output level about 2 dB above that of the conventional head over a wide range of frequencies.

With the magnetic head constructed as discussed above, a satisfactory wear resistance is achieved at the track-forming portion of the head gap. Also, the head wears evenly over long period of use. Accordingly, the magnetic head of the present invention attains a high reliability and provides good frequency response characteristics.

Claims

1. A magnetic recording/reproducing had comprising a magnetic core block comprising two shaped core halves of Sendust alloy, each having a track width regulating groove and a winding groove and which are joined together with a gap of predetermined width therebetween, and a glass filler in the track reguiating groove having a working temperature range no higher than 500 C.

2. A method of manufacturing a magnetic recording/reproducing head, comprising the steps of cutting first and second coil receiving grooves on opposite sides of a first block of magnetic material made of Sendust; cutting a coil receiving groove in a second block of magnetic Sendust material; cutting a plurality of track width regulating grooves in both the first and second blocks, the track width regulating grooves extending in a direction generally perpendicular to the coil receiving grooves; providing a non-magnetic layer having a thickness equal to approximately half the width of a desired head gap on predetermined portions of first surfaces of the first and second magnetic blocks; placing the first surfaces of the first and second magnetic blocks together with a foil of a silver brazing alloy inserted between portions of the first surfaces having no non-magnetic layer; heating the first and second blocks under pressure to integrally join the blocks by molten silver alloy; filling the track width regulating grooves with a glass having a melting temperature lower than a melting temperature of the silver brazing alloy and a working temperature range no higher than 500 C; lapping the gap-forming side of the integrally joined first.and second blocks to form a rounded surface; cutting the integrally joined first and second blocks into sections to produce a plurality of magnetic head cores; and winding a coil around each half of each of the magnetic head cores in the coil receiving grooves.

3. A method according to claim 2, further comprising the step of polishing the grooved surfaces of the first and second blocks.

4. A method according to claim 2 or claim 3, wherein the non-magnetic layers on the first and second blocks are deposited by evaporation.

5. A method according to claim 2 or claim 3, wherein the non-magnetic layers on the first and second blocks are deposited by sputtering.

6. A magnetic recording/reproducing head substantially as described with reference to the accompanying drawings.

7. A method of manufacturing a magnetic recording/reproducing head, substantially as described with reference to the accompanying drawings.