JP4318309B2 - Magnetostrictive element, sensor, and method of manufacturing magnetostrictive element - Google Patents

Description

  The present invention relates to a magnetostrictive element, a sensor using the same, and a method of manufacturing a magnetostrictive element.

Conventionally, magnetostrictive elements have been used for linear actuators, vibrators, pressure sensors, torque sensors, vibration sensors, gyro sensors, and the like.
When this magnetostrictive element is used for a linear actuator, a vibrator, or the like, a driving force is generated by changing the size of the magnetostrictive element by changing the magnetic field to be applied. In addition, when the magnetostrictive element is used for a pressure sensor, a torque sensor, a vibration sensor, a gyro sensor, etc., the size of the magnetostrictive element changes due to the pressure applied from the outside, and by detecting the magnetic permeability that changes with this, Sensing is performed (see, for example, Patent Documents 1 and 2).

JP-A-6-194244 JP 2000-266621 A

As shown in FIG. 8, such a magnetostrictive element 1 may be coated with an epoxy resin or the like on the surface of the magnetostrictive element body 3 for rust prevention of the magnetostrictive element body 3.
However, the outer peripheral edge 2a of the coating layer 2 is raised on the surface of the magnetostrictive element 1 that has been coated due to the surface tension of the epoxy resin.
For example, when a thermosetting epoxy resin is used and a coating having a thickness of 25 ± 10 μm is applied to the magnetostrictive element 1, the outer peripheral edge 2a of the coating layer 2 rises by about 6 to 15 μm with respect to the center 2b. End up.
Then, the pressure applied to the magnetostrictive element 1 at the time of detecting the treading force (pressure) is concentrated on the outer peripheral edge 2a where the epoxy resin swells. Variations in magnetic susceptibility will occur. As a result, a large variation occurs in detection characteristics for each magnetostrictive element 1, and accuracy as a pressure sensor is reduced. In order to avoid this, it becomes necessary to select the magnetostrictive element 1 according to the characteristics, or to adjust the detection characteristics by a circuit, which takes time and cost.

  Further, the magnetostrictive element 1 made of a sintered body has a large number of fine holes formed on the surface of the magnetostrictive element body 3. Even if the coating is applied, it is difficult to reliably block the pores with the coating layer 2 due to the surface tension of the coating agent or the like. For this reason, rust is generated in the magnetostrictive element main body 3, which causes deterioration of magnetostriction characteristics and reliability.

  The present invention has been made on the basis of such a technical problem, and a method for manufacturing a magnetostrictive element capable of flattening the surface of the magnetostrictive element, improving its detection accuracy, and further preventing deterioration in reliability, etc. The purpose is to provide.

The magnetostrictive element of the present invention made for this purpose includes a magnetostrictive element body whose permeability changes when pressure is applied, and a coating layer formed so as to cover the surface of the magnetostrictive element body. The magnetostrictive element body has a first surface and a second surface that are substantially parallel to each other for receiving pressure, and a chamfered portion or an R portion is formed on the outer peripheral edge of the first surface and the second surface of the magnetostrictive element. Is formed. Here, it is preferable that the dimension of the chamfered portion or the R portion formed on the outer peripheral edge portions of the first surface and the second surface is 0.1 to 0.4 mm.
Here, the chamfered portion or the R portion can be formed by chamfering or R processing the outer peripheral edge portion of the sintered body after sintering, or the chamfered portion can be formed at the molding stage of the molded body before sintering. Or you may make it form the molded object of the shape which has R part.
In this way, by forming the chamfered portion or the R portion, the step between the inner peripheral portion and the outer peripheral portion of the coating agent covering the flat portion of the sintered body can be suppressed, and this magnetostrictive element can be used as a pressure sensor or the like. When incorporated, the pressure applied from the outside acts evenly on the flat portion of the sintered body.
Here, the coating layer can be formed mainly for rust prevention of the magnetostrictive element body, but may be for other purposes. The coating layer may be formed of any material as long as the desired purpose can be achieved, but an epoxy resin is suitable from the viewpoint of cost, workability, strength, waterproofness, heat resistance, and the like.

The present invention may also be a sensor including a magnetostrictive element whose permeability changes when pressure is applied, and a coil provided on the outer peripheral side of the magnetostrictive element. The magnetostrictive element of this sensor is made of a sintered body, has a first surface and a second surface that are substantially parallel to each other for receiving pressure, and is provided at the outer peripheral edge of the first surface and the second surface. A magnetostrictive element body formed with a chamfered portion or an R portion, and a coating layer formed so as to cover the surface of the magnetostrictive element body.
The coil may output an electric signal corresponding to an external force in a direction in which the magnetostrictive element is compressed. In such a sensor, the coil outputs an electric signal corresponding to the external force in the direction in which the magnetostrictive element is compressed, whereby external force such as pressure and torque can be detected.

The present invention includes a step of chamfering or R processing an outer peripheral edge portion of a sintered body formed using a magnetostrictive material as a raw material, a step of covering the surface of the sintered body with a thermosetting coating agent, and a coating agent. And a step of thermosetting the magnetostrictive element.
At this time, the step of covering the surface of the sintered body with the coating agent includes the step of covering the surface of the sintered body with the first coating agent and the second coating agent having a higher viscosity than the first coating agent. And a step of covering the surface of the bonded body. In this way, by treating the surface of the sintered body with the first coating agent having a lower viscosity in advance, it is possible to reliably close the fine pores formed on the surface of the sintered body. Become. Since the first coating agent with low viscosity may not be able to secure a sufficient film thickness, after coating with the first coating agent, the surface of the sintered body is coated thickly with the second coating agent with high viscosity. It is preferable to do this.

The present invention includes a step of covering a surface of a sintered body formed using a magnetostrictive material as a raw material with a first coating agent having a predetermined viscosity, and a surface of the sintered body is higher than that of the first coating agent. A method of manufacturing a magnetostrictive element including a step of covering with a second coating agent having a viscosity.
Here, the first coating agent and the second coating agent are preferably made of the same material.

  Thus, in order to treat the surface of the sintered body with the first coating agent having a lower viscosity in advance, the first step is to cover the surface of the sintered body with the first coating agent. It is preferable that the second coating agent is sprayed onto the sintered body in the step of immersing in the coating agent and covering the surface of the sintered body with the second coating agent.

According to the present invention, it is possible to suppress irregularities on the surface of the magnetostrictive element by covering the surface of the magnetostrictive element body whose chamfered or R-processed outer peripheral edge is covered with the coating agent. Thereby, the dispersion | variation in the magnetic permeability detected when a pressure is applied to this magnetostrictive element can be decreased. Further, since the pressure acts uniformly on the entire magnetostrictive element, the obtained magnetic permeability is also increased. That is, the characteristics of the magnetostrictive element can be stabilized and improved.
In this way, a sensor incorporating this magnetostrictive element can be made highly accurate.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
In the present embodiment, magnetostrictive elements used for linear actuators, vibrators, pressure torque sensors, vibration sensors, gyro sensors, and the like are RT _y (where R is one or more rare earth metals and T is one or more types). It is a transition metal, and y preferably represents a sintered body having a composition represented by 1 <y <4.
Here, R represents one or more selected from lanthanoid series and actinoid series rare earth metals including Y. Among these, R is particularly preferably a rare earth metal such as Nd, Pr, Sm, Tb, Dy, and Ho, more preferably Tb and Dy, and these can be used in combination. T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly desirable, Fe, Co, and Ni are more desirable, and these can be used in combination.

In the composition formula RT _y, RT ₂ Laves-type intermetallic compounds formed by the R and T when y = 2, the Curie temperature is high, and since the magnetostriction value is large, most suitable as a magnetostrictive element. Here, when y is 1 or less, the RT phase is precipitated by the heat treatment after sintering, and the magnetostriction value is lowered. When y is 4 or more, the RT ₃ phase or the RT ₅ phase increases and the magnetostriction value decreases. Therefore, in order to increase the RT ₂ phase, the range of 1 <y <4 is desirable. A plurality of types of rare earth metals may be used as R, and it is particularly desirable to use Tb and Dy.

  In the present embodiment, the magnetostrictive element as described above is a mixture of three kinds of raw material powders having different compositions (hereinafter referred to as raw materials A, B, and C as appropriate) as disclosed in JP-A No. 2002-129274. It is preferable to make them. Moreover, it is preferable that a part of the alloy powder serving as the raw material powder contains a raw material to be subjected to hydrogen storage treatment. By storing hydrogen in the alloy powder, distortion occurs and cracks occur due to the internal stress. For this reason, the alloy powder to be mixed is subjected to pressure when forming a compact, and is pulverized inside the mixed state to become fine, and when it is sintered, a dense high-density sintered body can be obtained. Because.

As the raw material A, a material represented by the formula (1): (Tb _x Dy _1-x ) T _y is used. Here, T of the raw material A is at least one metal selected from the group of Fe, Co, and Ni. In particular, the element T may be Fe alone. This is because Fe forms a Tb, Dy and (Tb, Dy) Fe ₂ intermetallic compound having high magnetostriction characteristics. At this time, a part of Fe may be substituted with Co and Ni. However, Co increases magnetic anisotropy but decreases magnetic permeability, and Ni lowers the Curie temperature. In order to reduce the magnetostriction value at room temperature and high magnetic field, Fe is 70 wt% or more, more preferably 80 wt% or more.
In addition, the raw material A may contain a transition metal that forms an alloy with rare earth metals such as Tb and Dy. Specific examples of the transition metal include Mn, Cr, Mo, and W. A part of Tb of the raw material A may be substituted with rare earth (R ′) excluding Dy. Examples of R ′ include Nd, Pr, Gd, and Y.

In the formula (1), x and y are in the range of 0.35 <x ≦ 0.5 and 1.7 ≦ y ≦ 2.0. When x is a small value of 0.35 or less, the magnetostriction value becomes large, and orientation in the [111] axis direction becomes difficult, and when x exceeds 0.5, the ratio of the raw material A to the whole magnetostrictive material decreases. Therefore, the degree of orientation in the [111] axial direction after sintering becomes low. If y is less than 1.7, the ratio of the raw material A to the entire magnetostrictive material becomes small, and the degree of orientation in the [111] axial direction after sintering becomes low. When y is large, there are many Fe-rich phases such as (Tb, Dy) T _3. For this reason, the degree of orientation due to molding in a magnetic field is lowered, and accordingly the degree of orientation of the magnetostrictive material after sintering is also lowered. Therefore, y is set to 2.0.
Preferred x is 0.3 ≦ x ≦ 0.45, and more preferred x is 0.34 ≦ x ≦ 0.40. Further, preferable y is 1.8 ≦ y ≦ 2.0, and more preferable y is 1.87 ≦ x ≦ 1.92.

The raw material B is represented by the formula (2): Dy _t T _1-t (Dy may contain either or both of Tb and Ho, and t is in the range of 0.37 ≦ t ≦ 1.0). Those having the composition described above are used. When t is within this range, Dy and T have eutectic points. Therefore, when t is outside this range, R ₂ T, which is the eutectic composition, is reduced in the mixing of raw material A and raw material C. It becomes difficult to increase the density.

  Moreover, it is preferable that the raw material B contains hydrogen of 7000 ppm <= hydrogen amount <= 22000 ppm by performing a hydrogen storage process. The raw material B becomes brittle by occlusion of hydrogen, and this is mixed with the raw material A and the raw material C, and is pulverized and refined inside the mixed state by the pressure at the time of forming a molded body. Therefore, it becomes easy to enter between the raw materials A that are responsible for forming the main phase, and when sintered, a dense and dense sintered body is formed.

  The amount of hydrogen stored in the raw material B is preferably in the range of 7000 ppm ≦ hydrogen amount ≦ 22000 ppm. When the amount of hydrogen is less than 7000 ppm, the amount of hydrogen is small, the internal strain of the raw material B is small, the cracks during molding are small, the density is low, and the number of pores (open pores) increases. In addition, the magnetostriction characteristics deteriorate due to long-term use. Moreover, when the amount of hydrogen exceeds 22000 ppm, the refinement | miniaturization of the raw material B will be saturated and there will be no effect which occludes any more.

  In the present embodiment, a raw material C containing T is used. As described above, T is at least one metal selected from the group consisting of Fe, Co, and Ni, and among these, Fe is most preferable.

The raw material A, the raw material B, and the raw material C described above are mixed, molded in a magnetic field, and sintered to produce a magnetostrictive material represented by the formula (3): (Tb _v Dy _1-v ) T _w . Here, v and w are in the range of 0.27 ≦ v <0.5, 1.7 ≦ w ≦ 2.0. When v is less than 0.27, a sufficient magnetostriction value is not shown in a temperature range lower than room temperature, and when v is 0.5 or more, a sufficient magnetostriction value is not shown in a room temperature range. When w is less than 1.7, there are many rare earth-rich phases, and when w exceeds 2.0, a different phase such as a (Tb, Dy) T ₃ phase is generated and the magnetostriction value is lowered.
Preferred v is 0.27 ≦ v ≦ 0.40, and more preferred v is 0.27 ≦ v ≦ 0.34. Further, preferable w is 1.8 ≦ w ≦ 1.95, and more preferable w is 1.87 ≦ w ≦ 1.92.

The mixing ratio of the raw material A, the raw material B, and the raw material C can be appropriately determined so as to be a magnetostrictive material represented by the formula (3), but it is preferable to follow the following.
When the weight percentage of the raw material A is a, the weight percentage of the raw material B is b, and the weight percentage of the raw material C is c, the raw material A is preferably 50 ≦ a <100, more preferably 60 ≦ a ≦ 95. When a is too small, that is, when the ratio of the raw material A that is oriented in molding in a magnetic field is low, the degree of orientation of crystals after sintering becomes low. On the other hand, when a is too large, it means that the composition of the raw material A is close to the final composition, and the meaning of using the raw material A for facilitating magnetic field orientation is lost.
The raw material B is preferably 0 <b ≦ 40, more preferably 5 ≦ b ≦ 30. Since the raw material B acts as a flux during sintering, if b is too small, sintering is difficult to proceed and it is difficult to obtain a dense magnetostrictive material. On the other hand, if b is too large, a becomes too small, causing the above-mentioned adverse effects.

The above raw materials A, B, and C constitute a magnetostrictive material made of a sintered body through the following steps.
As the raw material A, Tb, Dy, and Fe are weighed so as to correspond to the above formula (1) and melted in an inert atmosphere of, for example, Ar gas to produce an alloy. This alloy can be annealed at a temperature of about 1150 to 1230 ° C. to make the concentration distribution of each metal element uniform during the production of the alloy and to eliminate the precipitated heterogeneous phase. Next, the raw material A is pulverized to an average particle size of about 5 to 200 μm.

  As the raw material B, Dy or an alloy made of Dy and T is prepared and pulverized in the same manner as the raw material A. Next, the pulverized raw material B is held in a hydrogen atmosphere or a mixed atmosphere of hydrogen and an inert gas, and a hydrogen occlusion treatment is performed by allowing hydrogen atoms to enter the crystal lattice of the raw material B or using a hydride. As described above, the amount of hydrogen contained in the raw material B is preferably 7000 to 22000 ppm. The raw material B is cracked by the hydrogen storage treatment. When the raw material B is comprised from the alloy which consists of Dy and T, it refines | pulverizes to about 5-200 micrometers by a crack. When the raw material B is composed of Dy alone, it is difficult to pulverize like an alloy composed of Dy and T due to cracks after the hydrogen storage treatment, and therefore it is preferable to perform a pulverization treatment after the hydrogen storage treatment. This pulverization may be performed with an average particle diameter of about 5 to 200 μm. The temperature at which the hydrogen storage treatment is performed is 100 to 200 ° C. when the raw material B is composed of an alloy composed of Dy and T, and 250 to 450 ° C. when the raw material B is composed of Dy alone. At this temperature, the raw material B can contain the above amount of hydrogen if the holding time is 1 to 20 hours. The hydrogen content depending on the holding time also depends on the size of the raw material B alloy.

  By subjecting the raw material B to hydrogen storage treatment, the oxidation resistance of the raw material B can be improved. Since Dy, which is a rare earth element, is easily oxidized, an oxide film having a high melting point is formed on the surface even with a slight amount of oxygen. This oxide film suppresses the progress of sintering. For this reason, the density of the obtained sintered body is low and the number of pores increases. When the number of holes increases, the oxidation of Dy further proceeds during long-term use, and the magnetostrictive characteristics are lowered accordingly. Therefore, a high sintered density can be obtained by subjecting the raw material B to hydrogen storage treatment to produce a sintered body, and deterioration of the magnetostrictive characteristics over time can be suppressed.

  The raw material C is preferably crushed in the same manner as the raw material A and the raw material B and then subjected to a reduction treatment for removing oxygen adhering to the surface. For example, the reduction treatment may be held in a hydrogen atmosphere at 300 to 600 ° C. for about 1 to 3 hours.

  The raw material A, the raw material B, and the raw material C obtained as described above are weighed and mixed so as to finally have a desired composition, and then pulverized. In the pulverization treatment, a pulverizer such as a wet ball mill, an attritor, or an atomizer can be appropriately selected. In particular, an atomizer is preferable. This is because impact and shear can be applied at the same time, preventing aggregation of the powder and high productivity. The average particle size after pulverization is 1 to 100 μm, preferably 5 to 20 μm. If the particle size is too small, oxidation tends to proceed during the manufacturing process, degrading the magnetostrictive properties. If the average particle size is too large, sintering is difficult to proceed, the sintering density is not increased, and the number of pores increases.

The mixed raw material A, raw material B, and raw material C are formed into a desired shape before sintering. By performing this molding in a magnetic field, the raw material A is mainly aligned in a certain direction, and the sintered magnetostrictive material is oriented in the [111] axial direction. The applied magnetic field is 2.4 × 10 ⁴ A / m or more, preferably 4.8 × 10 ⁴ A / m or more. The direction of the magnetic field may be perpendicular or parallel to the direction of pressure. The molding pressure is 4.9 × 10 ⁴ Pa or more, preferably 2.9 × 10 ⁵ Pa or more.

The molded body obtained by molding in a magnetic field is sintered. Sintering conditions are 1100 degreeC or more, Preferably it is 1150-1250 degreeC and it is good to carry out for 1 to 10 hours. The sintering atmosphere is preferably a non-oxidizing atmosphere, and is preferably an inert gas such as Ar gas or in a vacuum.
The sintered body produced in this way has the formula (3): (Tb _v Dy _(1-v) ) T _w (where v and w are 0.27 ≦ v <0.5, 1. 7 ≦ w ≦ 2.0)), and is oriented in the [111] axial direction in which the magnetostriction is greatest. The average grain size of crystal grains of the magnetostrictive material is 10 μm or more. If the average grain size of the crystal grains is small, the grain boundaries increase and the magnetic susceptibility due to the external magnetic field decreases. The upper limit of the average grain size of the crystal grains is not particularly limited. However, if the grain size is 200 μm or more, the magnetostriction value is almost saturated and does not need to be increased any more.

The sintered body produced as described above is preferably coated in order to improve rust prevention.
As shown in FIG. 1, the magnetostrictive element 10 is formed of a magnetostrictive element body (sintered body) 11 formed as described above and a coating layer 15 that covers the entire surface of the magnetostrictive element body 11.
The magnetostrictive element body 11 is a plate having a predetermined thickness, and has a pair of pressure surfaces (first surfaces) 12 and pressure surfaces (second surfaces) 13 parallel to each other, and an outer peripheral surface 14. Is formed. As shown in FIGS. 1B and 1C, the outer peripheral edge portions 12a and 13a of the pressurizing surfaces 12 and 13 of the magnetostrictive element body 11 are chamfered or rounded to be chamfered or rounded. . A preferable dimension range of chamfering or R processing is 0.1 to 0.4 mm. When the thickness is 0.1 mm or less, the height difference (step) on the surface of the coating layer 15 becomes large (ΔH ≧ 9 μm), and the flatness of the coating layer 15 cannot be obtained. If it is 0.4 mm or more, the effective area of the pressurizing surfaces 12 and 13 is reduced, so that the load pressure acting on the magnetostrictive element body 11 is increased and the pressure measurement range is reduced. Further, in the case where the diameter of the magnetostrictive element body 11 is small, if the contact pressure becomes large, the mechanical load on the magnetostrictive element body 11 tends to be excessive, and the substantial pressure measurement range becomes small.

  The coating layer 15 is formed of, for example, a thermosetting epoxy resin (coating agent). The coating layer 15 preferably has as small as possible surface irregularities (difference in height of the outer peripheral edge with respect to the center: step). More specifically, although depending on the film thickness of the coating layer 15, in order to apply pressure evenly to the pressure surfaces 12 and 13, the unevenness of the surface of the coating layer 15 is generally within 6 μm, and further within 3 μm. Is preferred. Of course, this numerical value may vary depending on the material forming the coating layer 15 and the film thickness of the coating layer 15, but it is within 25% or even within 15% of the film thickness of the coding layer 15. preferable.

  At this time, as described above, since the outer peripheral edge portions 12a and 13a of the pressurizing surfaces 12 and 13 of the magnetostrictive element body 11 are chamfered or rounded, the coating layer 15 is formed at the outer peripheral edge portions 12a and 13a. Is formed without excitement.

FIG. 2 shows a flow of steps for forming the coating layer 15.
(Chamfering process)
Prior to the formation of the coating layer 15, a barrel (polishing) / chamfering process and an etching process are performed as pre-processing of the magnetostrictive element 10 (step S101).
At this time, as shown in FIG. 1B, if the outer peripheral edge portions 12a and 13a of the pressurizing surfaces 12 and 13 of the magnetostrictive element body 11 are chamfered by chamfering, after barrel processing, by a rotating grindstone or the like, As shown in FIG. 3A, the outer peripheral edge portions 12a and 13a are chamfered by a predetermined dimension of 0.1 to 0.4 mm, and then etched. Further, as shown in FIG. 1C, if the outer peripheral edge portions 12a and 13a of the pressing surfaces 12 and 13 of the magnetostrictive element body 11 are R-processed, this can be performed by barrel processing. The R machining dimension is set to a predetermined dimension of 0.1 to 0.4 mm by barrel machining.

(Ground treatment process)
Thereafter, as a base treatment, the magnetostrictive element body 11 is immersed (dipped) in a thermosetting epoxy resin solution (step S102). At this time, the preferable viscosity of the epoxy resin liquid is preferably 0.01 to 0.03 Pa · s, for example, 0.02 Pa · s (20 Cp). Thereby, as shown in FIG. 3B, a coating layer 15 having a thickness of about 5 μm or less is formed on the surface of the magnetostrictive element body 11.

(Coating process)
Thereafter, a plurality of magnetostrictive elements 10 are placed on a wire mesh, and a thermosetting epoxy resin is sprayed from above with gun spray on one of the pressure surfaces 12 on the upper surface side in that state. Thereby, an epoxy resin adheres to the pressurization surface 12 and the outer peripheral surface 14 (step S103). The preferable viscosity of the epoxy resin at this time is preferably 0.25 to 0.40 Pa · s, for example, 0.3 Pa · s (300 Cp).

(Curing process)
Next, the magnetostrictive element 10 is heated to a temperature higher than the temperature at which the curing reaction (polymerization) of the thermosetting epoxy resin sprayed on the magnetostrictive element body 11 starts (step S104).

Thereafter, the upper and lower sides of the magnetostrictive element 10 are inverted (step S105), and the coating process and the curing process are performed on the pressing surface 13 in the same manner as described above (steps S106 to S107).
As a result, as shown in FIG. 3C, the coating layer 15 made of epoxy resin is formed so as to cover the entire surface of the magnetostrictive element body 11.

The magnetostrictive element 10 thus coated with the epoxy resin is incorporated into a pressure sensor (sensor) 100 as shown in FIG. The pressure sensor 100 includes a magnetostrictive element 10 and a coil 102 disposed on the outer peripheral side of the magnetostrictive element 10 in a housing 101 that also serves as a yoke. The housing 101 integrally includes contact portions 101a and 101b provided so as to be in contact with the pressing surfaces 12 and 13 with the magnetostrictive element 10 interposed therebetween. The one contact portion 101a is integrally formed with an input portion 103 that receives pressure (torque) input from the outside.
When the pressure sensor 100 presses the input portion 103 with an external force, the contact portion 101 a is pressurized, the housing 101 is elastically deformed, and the pressure surface 12 of the magnetostrictive element 10 is pressed. As a result, the magnetostrictive element 10 is contracted and deformed in the direction connecting the pressing surfaces 12 and 13, and the magnetic permeability changes, so that the pressure can be detected by detecting this with the coil 102 and outputting it as an electrical signal.

As described above, since the coating layer 15 is formed on the magnetostrictive element body 11 having the chamfered outer peripheral edge portions 12a and 13a of the pressing surfaces 12 and 13, the coating layer 15 is formed on the outer peripheral edge portions 12a and 13a. It can be formed without swell. Thereby, the variation in the magnetic permeability detected when pressure is applied to the magnetostrictive element 10 can be reduced. Further, since the pressure does not concentrate only on the outer peripheral edge portions 12a and 13a of the magnetostrictive element 10 and acts equally on the whole, the obtained magnetic permeability is also increased. That is, the characteristics of the magnetostrictive element 10 can be stabilized and improved. As a result, the pressure sensor 100 incorporating the magnetostrictive element 10 can be made highly accurate. In addition, by stabilizing and improving the characteristics of the magnetostrictive element 10, it is not necessary to select the magnetostrictive elements as in the prior art or to adjust the detection characteristics of the pressure sensor with a circuit, thereby reducing labor and cost. Therefore, the yield of the magnetostrictive element 10 can be improved.
Moreover, when forming the coating layer 15, after immersing the magnetostrictive element main body 11 in the low viscosity epoxy resin, the high viscosity epoxy resin was sprayed. As described above, by immersing the magnetostrictive element body 11 in the epoxy resin having a low viscosity, the epoxy resin enters the fine holes formed on the surface of the magnetostrictive element body 11 and can reliably close the holes. . As a result, the magnetostrictive element body 11 can be reliably covered with the coating layer 15, the rust prevention effect of the magnetostrictive element body 11 can be enhanced, and the magnetostrictive characteristics and the reliability of the magnetostrictive element 10 are deteriorated. It becomes possible to prevent.

Here, since the effect by chamfering the outer peripheral edge parts 12a and 13a of the pressurizing surfaces 12 and 13 of the magnetostrictive element main body 11 was confirmed, the result is shown.
First, the magnetostrictive element body 11 was formed as follows.
As raw material A, Tb, Dy, and Fe were weighed and melted in an inert atmosphere of Ar gas to produce an alloy having a composition of Tb _0.4 Dy _0.6 Fe _1.95 . Then, the raw material A is subjected to a heat treatment for annealing at 1170 ° C. (stabilization time 20 hours), the concentration distribution of each metal element at the time of manufacturing the alloy is made uniform, and the precipitated heterogeneous phase disappears. To obtain a coarse powder. The obtained coarse powder was passed through a sieve having an opening of 2 mm to remove coarse powder having a particle diameter of 2 mm or more.
As raw material B, Dy and Fe were weighed and melted in an inert atmosphere of Ar gas to produce an alloy having a composition of Dy _2.0 Fe. And this alloy was heat-treated in a hydrogen atmosphere (concentration 80%) at 150 ° C. (stabilization time 1 hr) and occluded about 18000 ppm of hydrogen, whereby the alloy was pulverized to obtain pulverized powder. This pulverized powder was passed through a sieve having an opening of 2 mm to remove coarse powder having a particle diameter of 2 mm or more.
As the raw material C, Fe powder was used, and this Fe powder was subjected to reduction treatment (300 ° C., stabilization time 1 hr) for removing oxygen in a hydrogen gas atmosphere.

Subsequently, the obtained raw materials A, B, and C were weighed, mixed, and then finely pulverized with an atomizer in Ar gas to obtain an alloy powder having a composition of Tb _0.34 Dy _0.66 Fe _1.88 .
The obtained alloy powder was put into a mold and molded at a molding pressure of 5 ton / cm ² in a magnetic field of 12 kOe to obtain a molded body. At this time, when filling the alloy powder with the mold, the alloy powder was moved through the pipe filled with N ₂ gas. The magnetic field was applied in a direction perpendicular to the pressure direction (so-called transverse magnetic field). The shape and dimensions of the molded body were 8.6 diameter × 34 mm length.

  The obtained molded body was placed in a sintering vessel, heated in a furnace, fired in a mixed atmosphere of 35 vol% hydrogen gas and 65 vol% Ar gas in a stable temperature zone of 1150 to 1230 ° C., and sintered body A magnetostrictive element body 11 was obtained. The obtained sintered body is cut into a predetermined thickness.

The magnetostrictive element body 11 was subjected to barrel etching. During the barrel treatment, the outer peripheral edge portions 12a and 13a of the pressurizing surfaces 12 and 13 of the magnetostrictive element body 11 were chamfered so that the chamfer dimension was 0.20 ± 0.10 mm (Example).
Thereafter, the magnetostrictive element body 11 is immersed in a thermosetting epoxy resin having a viscosity adjusted to 0.02 Pa · s. Further, the magnetostrictive element body 11 is thermoset to a viscosity adjusted to 0.30 Pa · s. The epoxy resin was sprayed by a spray method to form the coating layer 15 to obtain the magnetostrictive element 10. The epoxy resin used was made by Nagashima Special Paint Co., Ltd., S-No. 6 super rust preventive primer C-7261 gray. Moreover, the epoxy resin was sprayed on the magnetostrictive element body 11 so that the film thickness was 25 ± 10 μm.

  For comparison, the coating layer 15 was formed in the same manner as described above without chamfering the outer peripheral edges 12a and 13a of the pressure surfaces 12 and 13 of the magnetostrictive element body 11 (comparative example).

And about each of an Example and a comparative example, the obtained magnetostrictive element 10 was heated at 165 degreeC for 25 minutes, and the epoxy resin was hardened.
Thereafter, for each of the example and the comparative example, the height difference (step) of the outer peripheral edge portions 12a and 13a with respect to the central portion of the magnetostrictive element 10 was measured with a laser displacement meter.

  As a result, in the comparative example in which the outer peripheral edge portions 12a and 13a of the pressure surfaces 12 and 13 of the magnetostrictive element body 11 were not chamfered, the step of the coating layer 15 made of epoxy resin was 12 μm, and the chamfering process was performed. In the example, the step of the coating layer 15 was 3 μm or less. Thereby, it was confirmed that the coating layer 15 can be planarized by chamfering the outer peripheral edge portions 12a and 13a of the pressure surfaces 12 and 13 of the magnetostrictive element body 11.

Further, for each of the example and the comparative example, after the epoxy resin is cured, the change in the magnetic permeability when a load of 80, 250 kgf is applied to the magnetostrictive element 10 is expressed as an inductance change amount ΔL.
As measured.
FIG. 5 shows the result, and FIG. 6 further shows the distribution of inductance variation ΔL.

As is clear from these results, the σ value of the inductance change ΔL was 0.0208 in the magnetostrictive element that was not chamfered, whereas the σ value was higher in the magnetostrictive element that was chamfered. 0.0154. In this way, it can be confirmed that by performing chamfering, the variation in the amount of change ΔL in inductance is small and the σ value is small. Further, in the magnetostrictive element that was not chamfered, the average value of inductance was 0.4423, whereas in the magnetostrictive element that was chamfered, the average value was 0.5041. Thus, in comparison with the magnetostrictive element that has not been chamfered, the average value itself of the detected inductance change ΔL is also higher in the magnetostrictive element that has been chamfered. Can be confirmed.

Moreover, the external appearance of the magnetostrictive element 10 of the Example which performed coating, and the magnetostrictive element main body 11 before a coating was observed. FIG. 7 is a photograph thereof.
As shown in FIG. 7 (a), a large number of holes are observed on the surface of the uncoated magnetostrictive element body 11, but as shown in FIG. In the element 10, it can be observed that these holes are blocked by the coating agent 15.

In the above embodiment, a thermosetting epoxy resin is used for the coating layer of the magnetostrictive element. However, other coating agents may be appropriately used as long as they have required heat resistance, strength, and rust prevention. it can.
Even when an epoxy resin is used, the coating process is not limited to the above-described example, and can be appropriately changed to another configuration.
Furthermore, it is preferable to appropriately change the thickness of the coating layer, the viscosity of the epoxy resin, and the like depending on the coating agent used.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a figure which shows the magnetostriction element in this Embodiment, (a) is a perspective view of a magnetostriction element, (b) is sectional drawing of the magnetostriction element which chamfered the outer periphery part, (c) is R process of an outer periphery part 2 is a cross-sectional view of the magnetostrictive element. It is a figure which shows the flow of the process for forming the coating layer of a magnetostriction element. It is a figure which shows the magnetostriction element in the process of coating a magnetostriction element. It is sectional drawing which shows the structure of a pressure sensor. It is a figure which shows the result in an Example and shows the relationship between the applied pressure and the variation | change_quantity of an inductance in the magnetostrictive element which did not perform chamfering, and the magnetostrictive element which performed chamfering. It shows the distribution of the amount of change in inductance between the magnetostrictive element that has not been chamfered and the magnetostrictive element that has been chamfered. (A) is a photograph showing the magnetostrictive element body before coating, and (b) is a photograph showing the magnetostrictive element after coating. It is sectional drawing which shows the magnetostrictive element in which the level | step difference produced.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Magnetostrictive element, 11 ... Magnetostrictive element main body (sintered body), 12 ... Pressure surface (1st surface), 12a, 13a ... Outer peripheral edge part, 13 ... Pressure surface (2nd surface), 15 ... Coating layer , 100: Pressure sensor (sensor), 102: Coil

Claims (10)

When pressure is applied, the magnetic permeability changes, the first surface and the second surface are substantially parallel to receive the pressure, and at the outer peripheral edge of the first surface and the second surface A magnetostrictive element body formed with a chamfered portion or an R portion;
A coating layer formed so as to cover the surface of the magnetostrictive element body;
A magnetostrictive element comprising:   The magnetostrictive element according to claim 1, wherein the coating layer is formed of an epoxy resin.   The magnetostrictive element according to claim 1 or 2, wherein a dimension of a chamfered portion or an R portion of an outer peripheral edge portion of the first surface and the second surface is 0.1 to 0.4 mm. A magnetostrictive element whose permeability changes when pressure is applied;
A coil provided on the outer peripheral side of the magnetostrictive element,
The magnetostrictive element is made of a sintered body, has a first surface and a second surface that are substantially parallel to receive the pressure, and an outer peripheral edge portion of the first surface and the second surface. A sensor comprising: a magnetostrictive element body having a chamfered portion or an R portion formed thereon; and a coating layer formed so as to cover a surface of the magnetostrictive element body.   The sensor according to claim 4, wherein the coil outputs an electric signal corresponding to an external force in a direction in which the magnetostrictive element is compressed. Chamfering or R processing the outer peripheral edge of a sintered body formed using a magnetostrictive material as a raw material;
Covering the surface of the sintered body with a thermosetting coating agent;
Thermally curing the coating agent;
A method of manufacturing a magnetostrictive element comprising: The step of covering the surface of the sintered body with the coating agent includes the step of covering the surface of the sintered body with a first coating agent,
And a step of covering the surface of the sintered body with a second coating agent having a higher viscosity than the first coating agent. Covering the surface of the sintered body formed using a magnetostrictive material as a raw material with a first coating agent having a predetermined viscosity;
Covering the surface of the sintered body with a second coating agent having a higher viscosity than the first coating agent;
A method of manufacturing a magnetostrictive element comprising:   The method of manufacturing a magnetostrictive element according to claim 8, wherein the first coating agent and the second coating agent are made of the same material. In the step of covering the surface of the sintered body with the first coating agent, the sintered body is immersed in the first coating agent,
The method for manufacturing a magnetostrictive element according to claim 8 or 9, wherein in the step of covering the surface of the sintered body with the second coating agent, the second coating agent is sprayed onto the sintered body. .

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