JPH09106506A - Rotary erasing head for magnetic recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotary erasing head having a structure to obviate the occurrence of breakage, chipping and crazing in magnetic core half bodies in spite of the simple structure which enhances the joining strength of these magnetic core half bodies, facilitates production, contributes to the promotion of a cost reduction and does not allow fused glass layers to exist on both sides of a magnetic gap. SOLUTION: A ferromagnetic metal thin film 33 is formed on the other magnetic core half body side facing at least either of a pair of the magnetic core half bodies 21, 22. A gap film 34 is formed on the ferromagnetic metal film and a joining glass layer 35 is formed on the gap film. Both magnetic core half bodies are joined to each other via the joining glass 35. rojecting lined 27 across both magnetic core half bodies at the same width as a track width are formed on the end faces on the magnetic gap forming side of the magnetic core half bodies. The front surfaces of these projecting lines 27 are used as medium-facing surfaces. The magnetic gap G is composed by the gap film exposed in the central part of the projecting lines and the joining glass layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary erasing head for a video recording / reproducing apparatus in which the magnetic core halves have a high bonding strength and a small number of particles are shattered.

[0002]

2. Description of the Related Art Conventionally, a rotary erasing head for a video recording / reproducing apparatus having a structure shown in FIG. 7 is known. This erasing head A
Is attached to a rotary drum that is in contact with a magnetic tape (magnetic recording medium) for video recording, and erases magnetic information on the magnetic tape. Erasing head A having the conventional structure
Is constructed by abutting the side portions of a pair of plate-shaped polycrystalline ferrite magnetic core halves 1 and 2 with each other, and covering both sides of the abutting portions with a fused glass layer 3.

The structure of the erasing head A will be described in more detail. A protrusion 1a is formed on the side of one magnetic core half 1 on the side of the other magnetic core half 2 and the other magnetic core half 2 is formed. A protrusion 2a is formed on the side of one magnetic core half 1 on the side thereof, and a ferromagnetic metal film 5 is formed so as to cover the protrusion 2a of the other magnetic core half 2. The magnetic core halves 1 and 2 are the protrusions 1a and 2 of each other.
a is abutted, and the fused glass layers 3 filled in the recesses 6 formed on both sides of the abutted portions of the protrusions 1a and 2a are joined and integrated.

Although not shown in the drawing, a gap film is formed on the surface of the ferromagnetic metal film 5 so that the magnetic core halves 1 and 2 actually face each other via the gap film. Has been done. Further, a winding window 7 is formed on the upper side of the joining portion of the magnetic core halves 1 and 2, and the upper portion of the winding window 7 is narrowed to the upper side of the protrusion 1 a of the magnetic core half 1. Forming a yoke protrusion 1 a ′, the protrusion 2 of the magnetic core half 2 is formed.
a narrowed yoke protrusion 2a 'is formed on the upper side of a,
A magnetic gap G is formed by the yoke protrusions 1 a ′ and 2 a ′ facing each other via a gap layer. In addition,
A magnetic head having a structure in which a ferromagnetic metal film 5 is deposited on a magnetic core half body 1 made of a magnetic material and the ferromagnetic metal film 5 is opposed to a magnetic gap G is generally called a MIG (MetalIn Gap) head. There is.

Furthermore, notch-shaped steps 8 are formed on the upper sides of the magnetic core halves 1 and 2 so as to sandwich both sides of the magnetic gap G along the magnetic core halves 1 and 2. A ridge 9 is formed, and the upper surface of the ridge 9 is curved to form a medium facing surface. In the erasing head A having the above structure, the width of the ferromagnetic metal film 5 which is in contact with the yoke protrusion 2a ′ and is exposed on the medium facing surface defines the track width W, and the thickness (width) of the protrusion 9 is set. Is slightly thicker than this track width W (wider)
Is formed.

Next, an example of a method of manufacturing the erase head A having the above structure will be described. In order to manufacture the erase head A, rectangular parallelepiped ferrite blocks 10 and 11 as shown in FIG. 8A are prepared, and notches for track width regulation are provided on the abutting surfaces 10a and 11a of the ferrite blocks 10 and 11. A plurality of grooves 12 and 13 are formed at predetermined intervals along the longitudinal direction of the ferrite blocks 10 and 11,
Further, the grooves 14 and 15 for the winding window are formed in the ferrite block 1
It is formed along the longitudinal direction of 0 and 11.

Next, a ferromagnetic metal film and a gap film are formed on the abutting surface 10a of the ferrite block 10,
Then, the two ferrite blocks 10 and 11 are butted to each other through their butting surfaces 10a and 11a as shown in FIG. 8B, and thereafter, the inside of the winding window grooves 14 and 15 is filled with a welded glass to form the ferrite blocks. By joining 10 and 11 and then cutting along the cutting lines 17 ... Orthogonal to the longitudinal direction of the ferrite blocks 10 and 11 as shown in FIG. 8C, the erasing head A having the structure shown in FIG. Multiple products can be manufactured at the same time.

[0008]

In the erasing head A having the conventional structure shown in FIG. 7, the magnetic core halves 1 and 2 are joined by the welding glass layer 3, but the welding glass layer 3 is ,
The recesses 6 and 6 formed by the protrusions 1a and 2a of the magnetic core halves 1 and 2 are filled, and the protrusions 1a and 2a of the magnetic core halves 1 and 2 are sandwiched from the recesses 6 and 6 side so as to be magnetic. Since the core halves 1 and 2 are joined, the magnetic core halves 1 and 2 are joined.
The abutting portions of the protrusions 1a and 2a do not greatly contribute to the joining, and there is a problem that the joining strength cannot be sufficiently increased.

Further, an erasing head A having a conventional structure shown in FIG.
8A to 8C, a large number of grooves must be accurately formed in the ferrite blocks 10 and 11 to complicate the manufacturing process. Therefore, there is a problem that it is difficult to reduce the manufacturing cost.

Further, in the erasing head A, the bonding glass layers 3 are sandwiched on both sides of the magnetic gap G, but the thickness (width) of the ridge 9 should be close to the track width W. When the magnetic core halves 10 and 11 are formed of ordinary polycrystalline ferrite when processed into a thin film, chipping or chipping on the medium sliding surface of the magnetic core halves 10 and 11 due to sliding with the magnetic recording medium. However, there is a possibility that the track width may fluctuate, and cracks may cause fluctuating inductance.

The present invention has been made in view of the above circumstances, and it is possible to increase the bonding strength of the magnetic core halves, to facilitate the manufacture and to reduce the cost, and to weld the glass layers on both sides of the magnetic gap. It is an object of the present invention to provide a rotary erasing head for a magnetic recording / reproducing apparatus, which has a structure that does not cause chipping, chipping, or cracks in the magnetic core half body even with a simple structure in which no magnetic field exists.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is arranged such that a pair of magnetic core halves are butted against each other via a gap film, a winding window is formed at the butted portion of the magnetic core half, and winding is performed. A rotary erasing head for a magnetic recording / reproducing device, wherein a magnetic gap is formed by a projection of a magnetic core half body formed on an end side of a line window and a gap film, wherein at least one of the pair of magnetic core half bodies is provided. On the other hand, a ferromagnetic metal film is formed on the other magnetic core half body facing each other, a gap film is formed on this ferromagnetic metal film, a bonding glass layer is formed on this gap film, and this bonding glass layer is formed. The two magnetic core halves are joined together via a ridge, and a ridge extending over both magnetic core halves with the same width as the track width is formed on the end face of the magnetic core halves on the side where the magnetic gap is formed. As the medium facing surface, It constitutes a magnetic gap by bonding glass layer and the gap film exposed in the central portion, said magnetic core halves, the main component Fe ₂ O ₃ and MnO and ZnO,
Formed from Mn-Zn ferrite formed by adding 0.01 to 0.02 wt% of SiO ₂ , 0.03 wt% or less of CaO, and 0.05 to 0.15 wt% of Ta ₂ O _5. It will be.

In the present invention, a ferromagnetic metal film, a gap film, and a bonding glass layer are formed on one magnetic core half body side of the other magnetic core half body side, and one magnetic core half body side of the other magnetic core half body side is formed. It is also possible to form a structure in which a gap film and a bonding glass layer are formed on the magnetic core halves and the magnetic core halves are bonded to each other via the bonding glass layers. Further, in the present invention, an end portion of the winding window is cut into a central base portion of the protrusion, and a reinforcing glass is filled in a magnetic gap side of the winding window, and a part of the central base portion of the protrusion is filled with the reinforcing glass. It is also possible to adopt a structure in which the reinforcing glass is prevented from wrapping around the side of the magnetic gap and the magnetic core halves are joined and strengthened by the reinforcing glass.

In the present invention, in the shedding test in which a 1: 1 solution of HF-HNO ₃ is etched for 40 seconds, the shedding number is 2
It is preferably 0 or less.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an erase head B of a first example according to the present invention.
Is attached to a rotary drum that is in contact with a magnetic tape (magnetic recording medium) for video recording, and erases magnetic information on the magnetic tape. In the erasing head B of this example, the side portions of a pair of plate-shaped magnetic core halves 21 and 22 made of Mn-Zn ferrite having a special composition described later are butted against each other via a joining glass layer described later, and the butted portions are A reinforcing glass 23 is provided in the vicinity of the magnetic gap G and is joined and integrated.

The structure of the erasing head B will be described in more detail. A winding window 25 is formed on the upper portion of the magnetic core halves 21 and 22 on the joining side, and the upper portion of the winding window 25 is formed in a triangular shape. A magnetic gap G is formed above the apex portion. Further, on both upper sides of the magnetic core halves 21 and 22, notched step portions 26 and 26 are formed along the magnetic core halves 21 and 22 so as to sandwich both sides of the magnetic gap G, and projecting ridges 27 are formed. The ridge 27 is formed, and the upper surface of the ridge 27 is curved to form a medium facing surface. The width (thickness) of the ridge 27 is formed to be substantially the same as the track width W. The upper side of the front winding window 25 is formed so as to reach the central base side of the protrusion 26, so that the yoke protrusion 28 is provided on the magnetic core half 21 and the yoke protrusion 28 is provided on the magnetic core half 22. Each of the yoke protrusions 29 is formed.

On the other hand, the entire surface of the magnetic core half 21 on the side of the magnetic core 22, that is, the tip surface 28a of the yoke protrusion 28 and the surface of the winding window 25 on the side of the magnetic core 22 and below the winding window 25. On the side surface 21a of the magnetic core half body 21, a gap film 30 and a bonding glass layer 31 as shown in an enlarged view in FIG. 3 are laminated. In addition, the magnetic core 21 of the magnetic core half body 22
3 on the entire surface on the side, that is, on the tip surface 29a of the yoke protrusion 29, the surface of the winding window 25 on the side of the magnetic core 21 and the side surface 22a of the magnetic core half 22 below the winding window 25. Also, a ferromagnetic metal film 33, a gap film 34, and a bonding glass layer 35 are laminated as shown in the enlarged view. Therefore, in detail, as shown in FIG. 3, the magnetic gap G is provided between the yoke protrusion 28 of the magnetic core half body 21 and the ferromagnetic metal film 33 of the yoke protrusion 29 of the magnetic core half body 22. , Gap film 30
Bonding glass layer 31, bonding glass layer 35, and gap film 3
4 is sandwiched therebetween.

The upper portion of the winding window 25 is filled with the reinforcing glass 23, and the upper portion of the reinforcing glass 23 constitutes a part of the step 26 of the magnetic core halves 21 and 22 and the yoke protrusion 28. , 29 to form a part of the base of the ridge 27.

Next, the composition of Mn-Zn ferrite constituting the magnetic core halves 21 and 22 will be described. Mn-Zn ferrite used in this example, the main component Fe ₂ O ₃ and MnO and ZnO, with this, 0.01% by weight or more 0.
02 wt% or less of SiO ₂ and 0.03 wt% or less of Ca
O and Ta _{2 of} 0.05% by weight or more and 0.15% by weight or less
It is preferable to use the one obtained by adding O ₅ .

Mn-Zn ferrite of this composition is Si
By adding specific amounts of O ₂ , CaO and Ta ₂ O ₅ , the grain boundary strength and the specific resistance are increased.
Fe ₂ O ₃ is 45 mol% or more and 55 mol% or less, M
It is preferable that the content of nO is 20 mol% or more and 40 mol% or less, and the content of ZnO is 5 mol% or more and 30 mol% or less.

CaO in the ferrite segregates at the grain boundary portion and is easily eluted in water. By reducing this CaO, the grain boundary portion becomes chemically stable and the grain boundary strength can be improved. That is, if the addition amount of CaO exceeds 0.03% by weight, the grain boundary strength will decrease. On the other hand, if the addition amount of SiO ₂ is less than 0.01% by weight, the specific resistance becomes too small, and if it exceeds 0.02% by weight, the grain boundary strength decreases. The addition of Ta ₂ O ₅ has the effect of increasing the grain boundary strength and increasing the specific resistance.

In the erasing head B having the structure shown in FIG. 1, the bonding glass layers 31 and 35 are present at the boundary portion where the magnetic core halves 21 and 22 are in direct contact with each other to bond the two and to reinforce each other. Since the glass 23 is filled in the upper portion of the winding window 25 to bond the magnetic core halves 21 and 22, the bonding strength of the magnetic core halves 21 and 22 can be increased as compared with the conventional structure. Further, since the ridge 27 having the magnetic gap G and the same width as the track width W is formed of Mn-Zn ferrite having the above-mentioned special composition,
Even when the medium facing surface of the upper surface of the protrusion 27 is brought into sliding contact with the magnetic recording medium, chipping or chipping does not occur. Therefore, the track width does not change. Further, since the ridges 27 are made of Mn-Zn ferrite having the above-mentioned special composition, variations in the inductance (erasing rate) due to cracks do not occur.

Next, an example of a method of manufacturing the erase head B having the above structure will be described. To manufacture the erasing head B, rectangular parallelepiped ferrite blocks 40 and 41 as shown in FIG. 4A are prepared, and winding window forming grooves are formed on the abutting surfaces 40a and 41a of the ferrite blocks 40 and 41. 44 and 45 are formed along the longitudinal direction of the ferrite blocks 40 and 41. Next, a gap film and a bonding glass layer are formed on the upper surface of the ferrite block 40, and a ferromagnetic metal film, a gap film and a bonding glass layer are formed on the upper surface of the ferrite block 41, both of which are shown in FIG. As described above, the winding windows 44 and 45 are aligned and brought into close contact with each other, and the winding windows 44 and 45 are filled with the reinforcing glass. For the filling of the reinforcing glass, a method of inserting a glass rod into the winding window and heating and melting the glass rod can be adopted. Then, during this heating, the bonding glass layers on the bonding surfaces of the ferrite blocks 40 and 41 can be welded to each other.

Once both blocks 40 and 41 have been welded,
As shown in FIG. 6, a plurality of grooves 47 are formed at predetermined intervals in a direction orthogonal to the longitudinal direction of the blocks 40 and 41. The gap between the grooves 47 may be formed so that the width of the protrusion 48 formed between the grooves 47 is equal to the track width. Therefore, the predetermined interval is equal to the track width W. Then, as shown in FIG. 6, a plurality of blocks 40, 41 are cut along a cutting line 48 along the center line of each groove 47, whereby a plurality of erasing heads B having the structure as shown in FIG. 1 can be obtained.

If the erase head B is manufactured by the manufacturing method described above, the ferrite blocks 40, 4
Since the number of grooves to be machined in 1 can be markedly reduced as compared with the conventional method described above based on FIG. 8, simplification of the manufacturing process can be promoted and manufacturing cost can be reduced.

In the above example, the winding window 25 is formed in both the magnetic core halves 21 and 22, but the winding window is formed in only one of the magnetic core halves 21 and 22. Can also be formed. In that case, the yoke protrusion formed by the winding window is formed only on one of the magnetic core halves forming the winding window. Again,
In the above example, the gap film and the bonding glass layer are formed on both of the magnetic core halves 21 and 22, but the gap film and the bonding glass layer are formed on only one of the magnetic core halves, and the other magnetic core half is formed. It is also possible to adopt a structure in which these films are not formed on the core half body.

[0027]

【Example】

[Example 1] A Fe ₂ O ₃ (5
2.5 mol%), MnO (30.7 mol%), ZnO (1
6.8 mol%) as the main component, and with respect to this main component, S
iO ₂ (0.15% by weight), CaO (0.02% by weight),
Mn-Zn having a composition to which Ta ₂ O ₃ (0.08% by weight) is added
Ferrite is used, a gap film of SiO ₂ film is used, low melting point lead silicate glass is used as the bonding glass, low melting point lead silicate glass is used as the reinforcing glass, and the thickness of the magnetic core half body is 170 μm. An erasing head having a ridge width of 44 μm was manufactured. Further, as a comparative example, Mn-having the same composition was used.
An erase head having a conventional structure shown in FIG. 7 was also manufactured using Zn ferrite. In this case, the thickness of the magnetic core half is 170
μm, the width of the ridges was 70 μm, and the track width was 44 μm.

The erase heads of these examples and comparative examples are
0 pieces were produced, and the bending strength was measured by pushing the joint portion of both magnetic core halves in the core thickness direction with a core chip bending strength measuring device. As a result, the bending strength of the erasing head of each example structure was 79 to 132 g and the average bending strength was 104.0 g, while the bending strength of the erasing head of the comparative example was 15 to 71 g. The average bending strength is 47.
6g was shown. Therefore, it was found that the erasing head of this example is about twice as strong as the comparative example.

"Example 2" Below, M of the above-mentioned special composition is used.
The result of having performed the shedding test of the magnetic core half body formed by n-Zn ferrite is shown. The addition amounts of SiO ₂ , CaO, and Ta ₂ O ₃ are M and M, respectively, as shown in Table 1 below.
An n-Zn ferrite block was prepared, and the specific resistance of the Mn-Zn ferrite block, the number of PCT particles, and HF-HNO ₃
The number of shed particles was measured.

Here, the PCT grain-removal number is a value obtained by wrapping a ferrite block for 3 μm and then treating it at 120 ° C. and 2 atm for 5 hours using a pressure cooker tester. The HF-HNO ₃ shredding number is a more severe test method than the pressure cooker test.
This is an evaluation of the number of particles removed when etching was performed for 40 seconds with a 1: 1 HNO ₃ solution. As a comparative example, the measurement results of the sample to which Ta ₂ O ₃ was not added are also shown.

[0031]

[Table 1]

From the results shown in Table 1, the amount of SiO ₂ added was 0.015% by weight without adding Ta ₂ O ₃ and the conventional Mn was used.
-Comparative sample N with a reduced composition than Zn-Zn ferrite
In No. 8 of PCT, the number of PCT shatters is as large as 20 / 0.1 mm ² . In addition, Comparative Example No. 9 and Comparative Example No. 1
At 0, the PCT shedding number was almost 0 by reducing CaO.
However, the specific resistance value is 10 (Ω · cm)
It has become the following. However, the Mn of this example containing Ta ₂ O _{3 in an amount} of 0.05 to 0.100% by weight was used.
-In the Zn ferrite block, the number of PCT shedding is 0
Met. In addition, almost no HF-HNO ₃ deficiency was observed, indicating that the erasing head of this example has an extremely high grain boundary strength. Further, the resistivity value can be made higher even though the added amount of CaO is 0.021% by weight or less. Further, addition of Ta ₂ O ₃ also has an effect of stabilizing the residual magnetic flux density Br to a low level in terms of magnetic characteristics. Furthermore, in the case where ZrO ₂ is added instead of Ta ₂ O _3, the number of HF-NO ₃ particles is 20 to 50 / 0.1 mm ²
It could only be reduced to a certain degree.

[Embodiment 3] 30 erase head samples using Mn-Zn ferrite having the same composition and composition as in Embodiment 1 were used, and the relationship between the number of HF-HNO ₃ grain removal and the inductance variation and HF-NO. ₃ The relationship between the number of shedding and the fluctuation of track width was measured. The inductance variation was obtained by measuring the inductance of the head after PCT (pressure cooker test). Also, like the track width variation,
The track width after T was measured and obtained. Fluctuations in the track width occur because the track width is narrower than the ridge width due to grain breakage near the gap.

The results are shown in FIGS. 5 and 6. 5 and 6
The triangles shown in indicate that the data were scattered in this range. From the results shown in FIGS. 5 and 6, HF-HNO ₃
It was found that the sample with a large number of shed particles had large variations in inductance and track width, and the sample with a small number of shed HF-HNO ₃ had small variations in inductance and track width. From the above, if the magnetic head according to the present invention,
It was clarified that it is possible to obtain a magnetic core half body having a small inductance fluctuation, a small number of particles falling off, and a high magnetic core half strength.

[0035]

As described above, according to the present invention, the bonding glass layer is arranged on the surface directly abutting the magnetic core halves,
Moreover, since the upper portion of the winding window is filled with the reinforcing glass to join the magnetic core halves together, it is possible to provide an erasing head having high bending strength. Further, by forming the magnetic core half body using the Mn-Zn ferrite having the above-mentioned special composition, it is possible to reduce the number of grain shedding even under a severe test, and the inductance variation is small and the number of grain shedding is small. A head can be provided. Further, in the case of the magnetic head having the structure of the present invention, in the case of manufacturing by cutting from a ferrite block, the number of grooves processed on the ferrite block can be significantly reduced as compared with the conventional one, so that simplification of the manufacturing process can be promoted and It has the advantage that it can be manufactured at a lower cost than the structure.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an erasing head according to the present invention.

2 is a plan view of the erase head shown in FIG. 1. FIG.

FIG. 3 is an enlarged view of a magnetic gap portion of the erase head shown in FIG.

FIG. 4 shows an example of a method of manufacturing an erase head according to the present invention. FIG. 4 (A) is a perspective view showing a state where a ferrite block is grooved, and FIG. 4 (B) is a ferrite. FIG. 4 is a plan view showing a state before the blocks are joined.
(C) is a plan view showing a state in which a ferrite block is joined and cut.

FIG. 5 is a diagram showing the relationship between the inductance value and the number of particles shed in the erase heads of the example and the comparative example.

FIG. 6 is a diagram showing the relationship between the track width and the number of grain removals of the erase heads of Examples and Comparative Examples.

FIG. 7 is a perspective view showing an example of a conventional erasing head.

8A and 8B show an example of a conventional method for manufacturing an erase head. FIG. 8A is a perspective view showing a state where a ferrite block is grooved, and FIG. 8B is a perspective view showing the ferrite block. FIG. 8C is a plan view showing a joined state, and FIG. 8C is a perspective view showing a state in which the ferrite block is joined and cut.

[Explanation of symbols]

 B Erasing head G Magnetic gap 21, 22 Magnetic core half body 23 Bonding glass 25 Winding window 26 Step 27 Protrusion 28, 29 Yoke protrusion 30, 34 Gap film 31, 35 Bonding glass layer 33 Ferromagnetic metal film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Kihara 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Tomoaki Hamano 1-7 Yutaya-Otsuka-cho, Ota-ku, Tokyo Alp Su Electric Co., Ltd.

Claims (4)

[Claims] 1. A pair of magnetic core halves are butted against each other via a gap film, a winding window is formed at the butted portion of the magnetic core half, and a yoke end is provided on at least one of the magnetic core halves by the formation of the winding window. A magnetic erasing head for a magnetic recording / reproducing apparatus, wherein a magnetic gap is formed by a yoke projection of the magnetic core half body and a gap film, the relative erasing head being provided in at least one of the pair of magnetic core halves. A ferromagnetic metal film is formed on the side of the other magnetic core half which faces, a gap film is formed on this ferromagnetic metal film, and a bonding glass layer is formed on this gap film. While joining the magnetic core halves, a ridge extending over both magnetic core halves with the same width as the track width is formed on the end face of the magnetic core halves on the side where the magnetic gap is formed. And, it constitutes a magnetic gap by the bonding glass layer gap film exposed to the protrusion center portion, said magnetic core halves, the main component Fe ₂ O ₃ and MnO and ZnO, from 0.01 to 0 0.02% by weight of SiO ₂ , 0.03
CaO of less than wt% and Ta of 0.05 to 0.15 wt%
_A rotary erasing head for a magnetic recording / reproducing apparatus, which is formed from Mn-Zn ferrite to which ₂ O ₅ is added. 2. A ferromagnetic metal film, a gap film and a bonding glass layer are formed on one magnetic core half body on the other magnetic core half body side, and a gap is formed on the other magnetic core half body side on one magnetic core half body side. 2. The rotary erasing head for a magnetic recording / reproducing apparatus according to claim 1, wherein a film and a bonding glass layer are formed, and the magnetic core halves are bonded via the bonding glass layers. 3. An end portion of the winding window is cut into the central base portion of the ridge, reinforcing glass is filled in the magnetic gap side of the winding window, and a part of the central base portion of the ridge is filled with the reinforcing glass. 3. The rotation for a magnetic recording / reproducing apparatus according to claim 1, wherein the reinforcing core glass joins and strengthens the magnetic core halves with each other in a state where the reinforcing glass does not wrap around the side of the magnetic gap. Erase head. 4. The rotary erasing head for a magnetic recording / reproducing apparatus according to claim 3, wherein the grain removal number is 20 or less in a grain removal test in which a 1: 1 solution of HF-HNO _{3 is used} for etching for 40 seconds.