JP3419519B2 - Pulse generating magnetic wire and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic wire for pulse generation suitable for applications such as a magnetic sensor which produces a pulsed output voltage due to a change in an external magnetic field, and a method for manufacturing the magnetic wire.

[0002]

2. Description of the Related Art A magnetically sensitive wire having a large Barkhausen effect causes a sharp magnetization reversal in response to a change in an external magnetic field. Therefore, its magnetic properties are expected to lead to various applications. There is.

An example of a well-known magnetically sensitive wire is composed of a central layer and an outer peripheral layer having mutually different coercive forces, and abrupt magnetization reversal is caused by applying an alternating magnetic field. That is, after applying a strong external magnetic field (Hp or more) such that both the central layer and the outer peripheral layer are magnetized in the same direction, a weak reverse external magnetic field (Ha) that reverses the magnetic field only in the outer peripheral layer is applied. Then, a weak voltage pulse (-Vs) is generated in the detection coil wound around the magnetically sensitive wire. When a large external magnetic field (Hp) in the same direction as that of the central layer is applied to the outer peripheral layer again, abrupt magnetization reversal occurs in the outer peripheral layer, and a steep and large voltage pulse (+ Vs) is generated in the detection coil.

Conventionally, as a means for producing a magnetically sensitive wire, a wire made of a ferromagnetic material such as baicalloy (Fe-Co-V alloy) or permalloy (Fe-Ni alloy) has been used.
It is known that the surface layer of the wire is permanently set by twisting or heat treatment.

For example, as in the magnetic wire described in Japanese Patent Publication No. 55-15797 (KOKAI) No. 55-15797, a wire made of a ferromagnetic material is provided with sufficient longitudinal tension so as to be permanently elongated. Those in which a circumferential strain is generated and those in which a wire made of a ferromagnetic material is twisted, such as a magnetic device described in Japanese Patent Publication No. 61-28196 (known art 2), are known. ing.

Further, as described in JP-A-5-159913 (known art 3) and JP-A-5-205958 (known art 4), a large tension is applied to a wire made of a ferromagnetic material in the direction of the wire axis. It is also known that the large Barkhausen effect stably occurs when the magnetic anisotropy in the direction of the linear axis is increased by the stress-magnetic effect.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In both cases, since the manufacturing method for imparting a desired strain to a thin wire is extremely complicated, not only is mass productivity inferior, but it is difficult to perform uniform processing, resulting in a large variation in characteristics. there were. For example, when performing processing such as twisting or untwisting a wire rod, if the hardness of the wire rod (particularly the surface hardness) varies, it becomes difficult to give a uniform strain over the entire length of the wire rod when twisting the wire rod. It is not possible to consistently manufacture a uniform product having the magnetic properties described above. In particular, this tendency is remarkable in a thin wire rod. In addition, there is a problem that the apparatus for twisting is complicated and mass productivity is poor.

Further, since it is a composite magnetic wire in which the coercive force is made different between the central layer and the outer layer by twisting, only the strong magnetic field and the central layer are magnetized in the same direction in both the central layer and the outer layer. It is necessary for pulse generation to alternately apply a weak magnetic field for reversing the magnetization. That is, there is a trouble that the alternating magnetic field applied to the magnetic wire has to be asymmetric.

On the other hand, in the case of the prior arts 3 and 4, since the large Barkhausen effect disappears when the tension is removed, a structure or mechanism for maintaining the tensioned state is required, and the equipment cost becomes high. Will end up. Further, since the tension to be held is extremely large, it is difficult to hold it evenly, and even if it can be held, there is a problem in reliability such as secular change.

Therefore, an object of the present invention is to provide a magnetic wire for pulse generation which is easy to process, can be manufactured efficiently, and can exhibit stable magnetic characteristics, and a manufacturing method thereof.

[0011]

The magnetic wire for pulse generation of the present invention developed to achieve the above object is composed of a core wire made of a magnetic material and a non-magnetic material having a different coefficient of thermal expansion from the core wire. And having a coating layer adhered to the outside of the core wire so as to cover the core wire, strain of tensile or compression is applied to the core wire by the coating layer due to the difference in thermal expansion coefficient between the core wire and the coating layer. In addition, this strain is characterized by being fixed and held by the coating layer.

In the first method for producing a magnetic wire for pulse generation of the present invention, while heating the material for the coating layer outside the material for the core wire to a temperature at which these melt or soften, By stretching the core wire and the coating layer at the same time until they have a desired diameter and then cooling them, the core wire and the coating layer are brought into close contact with each other and strain of tensile or compression on the core wire by the coating layer due to the difference in thermal expansion coefficient between the core wire and the coating layer. And the strain is fixed and held by the coating layer.

In the second manufacturing method, the core wire and the cover layer are formed by coating the outside of the core wire having a predetermined wire diameter with the covering layer under a heated condition and then cooling the core wire. While imparting tensile or compression strain to the core wire by the coating layer from the difference in thermal expansion coefficient with,
It is characterized in that this strain is fixed and held by the coating layer.

If the core wire is a positive magnetostrictive material, glass is preferably used as the coating layer. A positive magnetostrictive material is a magnetic material that expands when magnetized. When glass is used for the coating layer, the coefficient of thermal expansion of the coating layer is smaller than that of the core wire.Therefore, if the coating layer is coated on the core wire while being heated to the melting temperature of the coating layer, the core wire will be pulled when the temperature returns to room temperature. Distortion will occur.

On the other hand, when the core wire is a negative magnetostrictive material, the coating layer may be made of a non-magnetic metal such as an aluminum alloy having a larger coefficient of thermal expansion than the core wire. A negative magnetostrictive material is a magnetic material that contracts when magnetized. If the coating layer is made of a non-magnetic metal having a large coefficient of thermal expansion and the coating layer is coated on the core wire at a high temperature, compressive strain is generated in the core wire when the temperature returns to room temperature.

[0016]

The phenomenon that strain occurs in the magnetic body when the magnetic domain of the magnetic body faces the direction of the external magnetic field, that is, when the magnetic body is magnetized is known as magnetostriction. On the contrary, when the magnetostrictive material is magnetized, if a strain is applied from the outside in the magnetic field direction, the deformation during the magnetization is assisted, and thus the magnetization is facilitated.

For example, if a tensile strain is applied from the outside when magnetizing a positive magnetostrictive material in the direction of the magnetic field, the deformation during the magnetization is assisted and the magnetization becomes easier. That is, the magnetic hysteresis curve (B-H curve) tends to be rectangular,
The change in the magnetic flux density becomes rapid with respect to the change in the magnetic field. The voltage pulse output generated in the detection coil increases in response to this rapid change in the magnetic flux density.

Therefore, in the pulse generating magnetic wire of the present invention, when the core wire made of the positive magnetostrictive material is given tensile strain by the coating layer, or the core wire made of the negative magnetostrictive material is compressed by the coating layer When given, when a critical magnetic field is applied to this magnetic wire, a steep voltage pulse is generated in the detection coil arranged near the magnetic wire.

The pulse generating magnetic wire of the present invention does not generate a pulse output due to the difference in coercive force between the central layer and the outer peripheral layer unlike the composite magnetic wires of the prior arts 1 and 2 described above. It is not necessary to make the applied external magnetic field asymmetrical, and a steep voltage pulse is generated if a magnetic field change greater than the critical magnetic field of the rectangular hysteresis loop is applied.

[0020]

EXAMPLE As shown in FIG. 3, a pulse generating magnetic wire 10 of this embodiment has a core wire 11 made of a magnetic material and a coating layer 1 made of a non-magnetic material having a different coefficient of thermal expansion from the core wire 11.
2 and. The coating layer 12 is in close contact with and fixed to the core wire 11 so as to cover the entire circumference of the core wire 11. Core wire 1
One example is a positive magnetostrictive material such as Fe-Ni alloy (permalloy), and one example of the coating layer 12 is glass such as borosilicate glass (Pyrex).

The magnetic wire 10 for pulse generation has a core wire 11
Due to the difference in the coefficient of thermal expansion between the core layer 11 and the coating layer 12, a tensile strain is applied to the core wire 11, and the strain is fixed and held by the coating layer 12.

As an example of means for producing the magnetic wire 10, a glass-coated spinning method is adopted in which the core wire 11 is spun and the coating layer 12 is coated at the same time. For example, in a manufacturing apparatus 20 schematically shown in FIG. 1, a material 12a for a coating layer is provided outside a material 11a for a core wire, and this manufacturing apparatus 20 integrates the materials 11a and 12a into an axial direction. To the material feeding mechanism 21, a heating device 22 such as a high frequency induction coil that heats the materials 11a and 12a to a temperature at which the materials 11a and 12a melt, and a tension is applied to the materials 11a and 12a to obtain a desired diameter. A cooling device 23 for cooling the stretched product, a winding device 24 for winding the obtained magnetic wire 10 and the like are provided.

After the materials 11a and 12a are heated to a predetermined temperature by the heating device 22, the core wire 11 and the coating layer 12 are stretched so as to have a desired wire diameter near a portion 11b where the core wire material 11a is melted. , And is cooled by the cooling device 23. Magnetic wire 10 thus obtained
In comparison with the shrinkage of the core wire 11 during the cooling process, the coating layer 1
Since the shrinkage amount of 2 is small, a tensile strain is applied to the core wire 11 by the coating layer 12 due to the difference in thermal expansion coefficient between the core wire 11 and the coating layer 12, and this strain is applied to the coating layer 1 as well.
It is fixed and held by 2.

As a means for providing the coating layer 12 on the outside of the core wire 11, the coating device 30 shown in FIG.
As described above, the core wire 11 having a predetermined wire diameter may be coated on the outside with the material 12a for the coating layer that has been heated to the softening or melting temperature and then cooled. The coating device 30 includes a core wire feeder 31.
And a heating device 32, a winder 33, and the like. Also in this case, due to the difference in the coefficient of thermal expansion between the core wire 11 and the coating layer 12, the coating layer 12 gives a tensile or compressive strain to the core wire 11, and this strain is applied to the coating layer 12 as well.
It is fixed and held by. The above-mentioned coating device 30 may be directly connected to the equipment for spinning the core wire 11, or the once wound core wire 11 may be coated with the coating layer 12 by the coating device 30.

Since the magnetic wire 10 has tensile strain applied and fixed to the core wire 11 made of a positive magnetostrictive material by the coating layer 12 having a small coefficient of thermal expansion, when a critical magnetic field is applied from the outside, A steep voltage pulse is generated in the detection coil. Since this voltage pulse does not have a pulse output as seen in a composite magnetic wire having different coercive force between the central portion and the surface portion, it is not necessary to make the alternating magnetic field to be applied asymmetrical, and as shown in FIG. A steep voltage pulse is generated when a magnetic field change greater than the critical magnetic field of the loop is applied. Therefore, it can be easily applied to a magnetic field sensor and a rotation sensor.

FIG. 6 compares the pulse output of the magnetic wire 10 of the above embodiment with the pulse output of the conventional magnetic wire (permalloy wire). The magnetic wire 10 of this embodiment has a larger pulse than the conventional product. The output is obtained.

The magnetic wire 10 of this embodiment is not a torsional strain but a strain due to the difference in the coefficient of thermal expansion between the core wire 11 and the coating layer 12. Therefore, a stable strain can be continuously applied over the entire length of the core wire 11. . Therefore, the pulse output is stable, and the magnetic wire 10 having a small variation can be obtained. In this case, by covering the core wire 11 with the coating layer 12, tensile or compressive strain can be easily applied to the core wire 11,
Moreover, since the strain is fixed simultaneously by the coating of the coating layer 12, the productivity is high and the cost can be reduced.
Moreover, it has little deterioration over time and is highly reliable.

In addition to the above Fe-Ni alloy (permalloy) as the core wire 11, for example, Fe ₂ O ₃ (ferrite), Fe-Ni-Mo alloy (supermalloy), F
An e-Co-V alloy (Baicalloy), a Fe-Si-Al alloy (Sendust), etc. may be used. Permalloy has a melting point of about 1440 ° C, Baicalloy has a melting point of about 1460
Since the melting point of C. and Sendust is about 1480.degree. C., an appropriate one may be selected from the above magnetic alloys in relation to the softening point of the coating layer 12. The coefficient of thermal expansion of these magnetic alloys is
It is (10 to 15) × 10 ⁻⁶ . The diameter of the core wire 11 is preferably several μm to several hundred μm. The cross-sectional shape of the core wire 11 is preferably a perfect circle, but may be an ellipse, a polygon, or the like.

When the coating layer 12 is glass, 96% silica glass (Vycor) may be used. Vycor softening point 1550 ° C, coefficient of thermal expansion (0.8-15) x 1
0 ^-6. In the case of Pyrex, the softening point is 820 ° C. and the coefficient of thermal expansion is (3.2 to 15) × 10 ⁻⁶ . Coating layer 12
When such a glass is used, the coefficient of thermal expansion is smaller than that of the core wire 11, so that the core wire 11 is pulled. Therefore, it is applied when the core wire 11 is a positive magnetostrictive material.

When the core wire 11 is a negative magnetostrictive material, the coating layer 12
By using a non-magnetic metal such as aluminum having a thermal expansion coefficient larger than that of the core wire 11, a compression strain is generated in the core wire 11. In the case of the coating layer 12 made of a non-magnetic metal, copper, zinc or the like may be used in addition to aluminum. Aluminum has a melting point of 660 ° C and a coefficient of thermal expansion of 29 ×
It is 10 ^-6 . The melting point of copper is 1086 ° C and the coefficient of thermal expansion is 20.
It is × 10 ^-6 . Zinc has a melting point of 420 ° C and a coefficient of thermal expansion of 3
It is 0 × 10 ^-6 .

When a non-magnetic metal having a coefficient of thermal expansion larger than that of the core wire 11 is used for the coating layer 12 as described above, the shrinkage amount of the coating layer 12 is larger than the shrinkage amount of the core wire 11 in the cooling process. Therefore, the coating layer 12 imparts a compressive strain to the core wire 11, and the strain is fixed and held by the coating layer 12.

[0032]

According to the magnetic wire for pulse generation of the present invention,
Since it is not necessary to make the applied alternating magnetic field asymmetrical and a sharp voltage pulse is generated by giving a simple magnetic field change above the critical magnetic field of the rectangular hysteresis loop, application to a magnetic field sensor or a rotation sensor is easy. Further, according to the present invention, since it is easy to uniformly apply strain to the core wire, a magnetic wire having uniform and stable pulse output characteristics can be manufactured at low cost, and mass productivity is extremely good. The magnetic wire for pulse generation of the present invention has little deterioration over time and has high reliability.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an apparatus and a material for producing a magnetic wire for pulse generation of the present invention.

2 is an enlarged view of a portion of the apparatus and material shown in FIG.

FIG. 3 is a sectional view of a magnetic wire for pulse generation showing an embodiment of the present invention.

FIG. 4 is a cross-sectional view schematically showing an apparatus for coating a core wire with a coating layer.

FIG. 5 is a diagram comparing magnetic hysteresis curves of a magnetic wire of the present invention and a conventional magnetic wire.

FIG. 6 is a diagram comparing pulse outputs of the magnetic wire of the present invention and a conventional magnetic wire.

[Explanation of symbols]

10 ... Magnetic wire for pulse generation 11 ... Core wire 12 ... Coating layer 20. Magnetic wire manufacturing device

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Claims (5)

(57) [Claims] 1. A core wire made of a magnetic material, and a coating layer made of a non-magnetic material having a different coefficient of thermal expansion from the core wire and being closely adhered to the outside of the core wire so as to cover the core wire. A magnetic wire for pulse generation characterized in that a tensile or compressive strain is applied to the core wire by the coating layer due to a difference in thermal expansion coefficient between the coating layer and the coating layer, and the strain is fixed and held by the coating layer. 2. The magnetic wire for pulse generation according to claim 1, wherein the core wire is a positive magnetostrictive material and the coating layer is glass. 3. The pulse generating magnetic wire according to claim 1, wherein the core wire is a negative magnetostrictive material, and the coating layer is a non-magnetic metal having a coefficient of thermal expansion larger than that of the core wire. 4. An outer surface of a core material made of a magnetic material,
With the material for the coating layer made of a non-magnetic material having a different coefficient of thermal expansion from the material for the core wire, while heating to a temperature at which these two materials melt or soften, the core wire and the coating layer simultaneously. By stretching and cooling to a desired diameter, the core wire and the coating layer are brought into close contact with each other and a tensile or compression strain is applied to the core wire by the coating layer due to the difference in thermal expansion coefficient between the core wire and the coating layer. A method for producing a magnetic wire for pulse generation, characterized in that strain is fixed and held by the coating layer. 5. A coating layer made of a non-magnetic material having a coefficient of thermal expansion different from that of the core wire is coated on the outside of the core wire made of a magnetic material having a predetermined wire diameter in a heated state and then cooled. By applying a strain of tensile or compression to the core wire by the coating layer from the difference in the coefficient of thermal expansion of the core wire and the coating layer, and this strain is fixed and held by the coating layer pulse Method of manufacturing magnetic wire for generation.