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JP2006253509

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DESCRIPTION JP2006253509
PROBLEM TO BE SOLVED: To provide a highly reliable magnetostrictive element which can
withstand use under continuous conditions even when it is used as an acoustic element without
occurrence of falling off, cracking, chipping and the like due to a stretching operation and the
like. A magnetostrictive element has a magnetostrictive element body made of a magnetostrictive
material, and a resin film that covers the magnetostrictive element body. The processingdeteriorated layer substantially does not remain on the surface of the magnetostrictive element
body. The magnetostrictive element includes a sintering step of sintering the raw material alloy
powder, an outer peripheral processing step of processing the outer periphery of the sintered
body, an etching processing step of etching the surface of the sintered outer peripheral
processed body, and a resin coating film covering the surface. Although manufactured through a
resin coating process, the conditions of the outer periphery processing step are set so that the
thickness of the process-altered layer after the outer periphery processing step is 15 μm or less.
For example, in the outer periphery processing step, the amount of grinding per one operation is
less than 150 μm. [Selected figure] Figure 5
Magnetostrictive element and method of manufacturing the same
[0001]
The present invention relates to, for example, a magnetostrictive element used as an acoustic
element for driving a diaphragm or the like, and further relates to a method of manufacturing the
same.
[0002]
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1
For example, since the giant magnetostrictive material composed of a Tb-Dy-Fe-based
intermetallic compound or the like has high magnetostriction characteristics as compared to the
conventional ferrite-based magnetostrictive material or the like, its demand tends to be further
expanded.
Specific applications include linear actuators, vibrators, pressure torque sensors, vibration
sensors, gyro sensors and the like. When used as a linear actuator or vibrator, the
magnetostrictive element changes its dimension with the change of the applied magnetic field,
and generates a driving force. When used as a pressure torque sensor, a vibration sensor, a gyro
sensor, etc., the magnetostrictive element changes its magnetic permeability with a change in
external force, and pressure, torque, vibration, etc. are detected by sensing this.
[0003]
Under such circumstances, in recent years, application to the acoustic field has attracted
attention as a use of a magnetostrictive element using a magnetostrictive material. The
magnetostrictive actuator formed of the giant magnetostrictive material has excellent
characteristics such as large magnetostriction displacement (about 1100 ppm), high-speed
response (nanosecond scale), and large driving force (for example, 220 kgf / cm <2>), It is
expected that an excellent acoustic element will be realized by utilizing the characteristics (see,
for example, Patent Document 1 and Patent Document 2).
[0004]
Heretofore, dynamic speakers that vibrate a diaphragm with a magnet and a coil to vibrate air
are generally used as speakers, and ceramic speakers and the like that use the piezoelectric effect
of ceramics have also been developed. On the other hand, if high-speed response and large
driving force of the magnetostrictive actuator are used to effectively transmit this to a diaphragm
such as a flat panel or an acoustic plate, a high-performance speaker exceeding conventional
speakers is obtained. It is considered to be realized. JP 2004-266307 A JP JP 2004-3204421 A
[0005]
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2
By the way, in order for the magnetostrictive element (magnetostrictive actuator) to fully exhibit
its features (large magnetostrictive displacement, high-speed response, large driving force), the
occurrence of the magnetostrictive element itself from falling off, cracking or chipping is avoided.
There is a need to. For example, if the magnetostrictive element itself falls off or breaks or breaks
due to the expansion and contraction of the magnetostrictive element during long-term
continuous operation using an audio signal application, when it is used as a speaker, problems
occur in voice and sound quality. There is a risk of getting tired.
[0006]
In order to avoid such a problem, it is necessary to determine the optimum process conditions
from which the generation sources such as dropouts, cracks, and chips are removed in the
manufacturing process of the magnetostrictive element, and to manufacture the magnetostrictive
element under the conditions. It is. This is considered to be able to provide a highly reliable
magnetostrictive element (sound element) that can withstand use under continuous conditions.
[0007]
The present invention has been proposed in view of such conventional circumstances. That is, the
present invention provides a highly reliable magnetostrictive element that can withstand use
under continuous conditions even when used as an acoustic element without occurrence of
detachment, cracking, chipping, and the like due to expansion and contraction operations and the
like. In addition, it aims at providing the manufacturing method.
[0008]
In order to achieve the above object, the magnetostrictive element of the present invention has a
magnetostrictive element body made of a magnetostrictive material, and a resin coating that
covers the magnetostrictive element body, and the surface of the magnetostrictive element body
is substantially It is characterized in that no processing-deteriorated layer remains.
[0009]
Although it has conventionally been known that a single crystal growth method is effective as a
method of manufacturing a giant magnetostrictive material, the single crystal growth method has
04-05-2019
3
the disadvantage that productivity is extremely low and the degree of freedom in shape is also
greatly restricted. There is.
Therefore, powder metallurgy is currently adopted because the disadvantages of the single
crystal growth method are improved and low-cost manufacturing is possible. Basically, a sintered
compact (magnetostrictive element) by powder metallurgy is weighed and mixed with a raw
material alloy powder, is pressure-formed into a predetermined shape, and is sintered with
respect to the obtained molded body, if necessary It is manufactured by post processing.
[0010]
In the case of producing a magnetostrictive element by the powder metallurgy method,
machining (peripheral processing) to a desired element shape is required after the firing process
due to the mold shape and the like at the time of molding. Then, after the outer periphery
processing is performed, a process-altered layer is formed on the peripheral surface of the
magnetostrictive element.
[0011]
The inventors of the present invention have studied repeatedly, and if this process-altered layer
is a cause of generation of cracks, and the process-altered layer remains on the surface of the
magnetostrictive element, for example, falling off, cracking or chipping along with expansion and
contraction. It has been found that etc occur. In the magnetostrictive element of the present
invention, since this process-deteriorated layer does not remain (is substantially zero), dropping
off, cracking, chipping and the like do not occur, and the displacement characteristics and the
like are not changed. In addition, since the processing-deteriorated layer does not remain, a gap
or the like is not formed between the resin film and the magnetostrictive element body, and a
rustproof effect, oxidation resistance, and the like are also guaranteed.
[0012]
The presence or absence of the formation of the processing-altered layer can be controlled by the
process conditions at the time of peripheral processing, and the manufacturing method of the
present invention defines this. That is, in the method of manufacturing a magnetostrictive
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4
element according to the present invention, a sintering step of sintering the raw material alloy
powder, an outer peripheral processing step of outer peripheral processing on the sintered body,
and an etching processing step of etching the surface of the outer peripheral processed sintered
body And a resin coating step of covering the surface with a resin film, wherein the condition of
the outer periphery processing step is set so that the thickness of the damaged layer after the
outer periphery processing step is 15 μm or less.
[0013]
In the outer periphery processing of the magnetostrictive element main body, for example, when
grinding is performed under severe conditions where the amount of grinding per time is large,
the surface of the magnetostrictive element main body is damaged, and the process-altered layer
extends deep into the surface. On the other hand, when the grinding is performed under gentle
conditions where the amount of grinding per time is small, the surface of the magnetostrictive
element main body is less damaged, and the thickness of the damaged layer is reduced. As
described above, if the conditions of the outer periphery processing step are set so that the
thickness of the damaged layer after the outer periphery processing step is 15 μm or less, the
remaining operation damaged layer is rapidly removed in the next etching step, Eventually, the
processing-deteriorated layer does not substantially remain on the surface of the
magnetostrictive element body.
[0014]
In order to make the thickness of the damaged layer after the outer periphery processing step be
15 μm or less, for example, the grinding amount per one operation may be less than 150 μm in
the outer periphery processing step. In the etching step, the etching amount is t + 5 μm to t + 10
μm, where t is the thickness of the processing-altered layer formed in the outer periphery
processing step after the outer periphery processing step. And almost completely eliminated. In
this state, if the resin is coated so that the thickness of the resin film is 15 μm to 25 μm in the
resin coating process, the resin film is formed with good adhesion.
[0015]
According to the magnetostrictive element of the present invention, there is no occurrence of
detachment, cracking, chipping, and the like due to the expansion and contraction operation, etc.,
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and a highly reliable magnetostrictive element that can withstand use under continuous
conditions even when used as an acoustic element. It is possible to provide an element. In
addition, since the resin film as the protective film is formed in the state where there is no
processing-deteriorated layer, it is possible to sufficiently secure the antirust effect and the
oxidation resistance etc. Also in this respect, the magnetostriction is excellent in reliability. It is
possible to provide an element.
[0016]
Further, according to the manufacturing method of the present invention, the formation of the
damaged layer is minimized by optimizing the conditions of the outer periphery processing step,
so that this is almost completely removed by the subsequent etching step or the like. Thus, it is
possible to manufacture a magnetostrictive element excellent in reliability, in which the dropout,
the crack, the chipping and the like do not occur due to the expansion and contraction operation
and the like. Moreover, since resin coating is performed in the state which does not have the said
process degradation layer, it is possible to form the resin film excellent in adhesiveness.
[0017]
Hereinafter, a magnetostrictive element to which the present invention is applied and a method
of manufacturing the same will be described in detail with reference to the drawings.
[0018]
The magnetostrictive element 1 of the present invention is formed, for example, by covering the
surface of the magnetostrictive element body 2 with a resin film 3 as shown in FIG.
Here, the processing-deteriorated layer does not remain on the surface of the magnetostrictive
element main body 2, and it is in a state where separation, cracking, chipping, and the like do not
occur due to the expansion and contraction operation and the like. The presence or absence of
the process-altered layer can be confirmed, for example, by observing the cross section of the
magnetostrictive element body with an electron microscope or the like, and when the processaltered layer remains, machining marks are clearly observed by machining. Ru.
[0019]
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6
The magnetostrictive element 1 is formed of a so-called super-magnetostrictive material, and
therefore has an excellent feature that the magnetostrictive displacement is large, the high-speed
response is excellent, and the large driving force is provided. Specifically, the supermagnetostrictive material is, for example, RTy (wherein R is one or more types of rare earth
elements, T is one or more types of transition metals, and y is 1 <y <4. It is obtained by sintering
the alloy powder of the composition shown.
[0020]
Here, R represents one or more selected from the lanthanoid series containing Y and the rare
earth elements of the actinide series. Among these, as R, particularly, rare earth elements such as
Nd, Pr, Sm, Tb, Dy, Ho and the like are preferable, Tb and Dy are more preferable, and these can
be used by mixing. T represents one or more transition metals. Among these, as T, particularly,
transition metals such as Fe, Co, Ni, Mn, Cr, Mo and the like are preferable, and these can be
mixed and used.
[0021]
Among the alloys represented by RTy, an RT2 Laves type intermetallic compound in which y = 2
is suitable for the magnetostrictive element because it has a high Curie temperature and a large
magnetostriction value. Here, when y is 1 or less, the RT phase precipitates in the heat treatment
after sintering, and the magnetostriction value decreases. In addition, when y is 4 or more, the
RT3 phase or RT6 phase increases, and the magnetostriction value decreases. For this reason, y
is preferably in the range of 1 <y <4 in order to increase the phase rich in RT2.
[0022]
R may be a mixture of two or more types of rare earth elements, and in particular, a mixture of
Tb and Dy is preferably used. Specifically, in the alloy represented by TbaDy1-a, a is more
preferably in the range of 0.27 <a ≦ 0.50. As a result, in the alloy (TbaDy1-a) Ty, the saturation
magnetostriction constant is large, and a large magnetostriction value is obtained. Here, when a
is 0.27 or less, a sufficient magnetostriction value is not shown at room temperature or less, and
conversely, when it exceeds 0.50, a sufficient magnetostriction value is not shown near room
04-05-2019
7
temperature.
[0023]
T is particularly preferably Fe, and Fe forms a (Tb, Dy) Fe2 intermetallic compound with Tb and
Dy to obtain a sintered body having a large magnetostriction value and high magnetostriction
characteristics. At this time, although part of Fe may be replaced with Co or Ni, Co increases the
magnetic anisotropy but lowers the magnetic permeability, and Ni lowers the Curie temperature,
resulting in normal temperature. Decrease the magnetostriction value in high magnetic fields.
Therefore, Fe is preferably 70% by mass or more, and more preferably 80% by mass or more.
[0024]
On the other hand, the resin film 3 has a function as a protective film, and can be formed of any
resin. However, it is preferable to have stretchability so as not to constrain the displacement of
the magnetostrictive element body 2, and to ensure high strength to withstand high stress,
flatness for accurate displacement transmission, and adhesion strength with the magnetostrictive
element body 2. The adhesion, the water resistance, the heat resistance, etc. to exert the antirust
effect are also required. As a resin material which satisfies these requirements, an epoxy resin
etc. can be mentioned, for example. For example, acrylic resin can not be used because the
surface part melts and adheres. Polyimide resins can not be used because of element oxidation
(occurrence of rust). It is preferable to avoid using silicone resin, as it is a factor that lowers the
magnetostriction value in the reliability test.
[0025]
The thickness of the resin film 3 may be a thickness sufficient to sufficiently secure the antirust
effect and the oxidation resistance. For example, in the case of the resin film made of the epoxy
resin, it is preferable to be about 15 μm to 25 μm. . If the thickness of the resin film 3 is too
thin, it may be difficult to obtain a sufficient antirust effect and oxidation resistance. On the
contrary, if the thickness of the resin film 3 is too thick, accurate transmission of displacement
may be difficult.
[0026]
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8
By constructing the magnetostrictive element 1 as described above, it is possible to withstand use
under continuous conditions even when it is used as an acoustic element, without falling off,
cracking, chipping, etc. occurring due to the expansion and contraction operation etc. It is
possible to make a magnetostrictive element with high reliability. In addition, the occurrence of
rusting of the magnetostrictive element body 2 and the deterioration of the magnetostrictive
characteristics due to oxidation can be suppressed by the resin film 3, so that it is possible to
realize a magnetostrictive element excellent in long-term reliability.
[0027]
Next, a method of manufacturing a magnetostrictive element without a processing-deteriorated
layer as described above will be described. FIG. 2 shows an example of the manufacturing
process of the magnetostrictive element by the powder metallurgy method. As shown in FIG. 2,
basically, the magnetostrictive element is pretreated with three types of raw materials A, B and C,
respectively, and then mixed and formed, forming step 11, sintering step 12, barrel processing
step 13, outer periphery It manufactures by passing through processes, such as a process
process 14, an etching process 15, an aging treatment process 16, and a resin coating process
17.
[0028]
First, the raw material A, which is a part of the raw material, is heat-treated (annealed) under a
predetermined condition and then subjected to a pulverizing process on the Tb-Dy-Fe-based alloy
having a predetermined composition. An alloy having a composition of Dy2Fe as the raw material
B is subjected to hydrogen absorption treatment and then pulverized. As a raw material C, Fe is
subjected to a reduction treatment to remove oxygen in a hydrogen gas atmosphere.
[0029]
Here, it is preferable that a part of these alloy powders be subjected to hydrogen storage
treatment. Storing hydrogen in the alloy powder causes distortion, and internal stress causes
cracking. For this reason, the mixed alloy powder is subjected to pressure when forming a
compact, and is crushed and refined internally, whereby a dense dense sintered body can be
04-05-2019
9
obtained when sintered. Furthermore, since rare earth elements such as Tb and Dy are easily
oxidized, an oxide film having a high melting point is formed on the surface to suppress the
progress of sintering even if there is a slight amount of oxygen. There is also an advantage that it
becomes difficult to oxidize. The alloy powder to be subjected to the hydrogen storage treatment
is preferably, for example, a composition represented by DybT (1-b) and b is 0.37 ≦ b ≦ 1.00. In
the formula, T may be Fe alone or one in which a part of Fe is replaced by Co or Ni. Therefore,
among the above-described raw materials, it is optimal to use the raw material B as an alloy
powder to be subjected to a hydrogen storage treatment.
[0030]
Next, predetermined amounts of the raw material A, the raw material B, and the raw material C
described above are weighed, crushed and mixed, and molded in a magnetic field to produce a
molded body (molding step 11). At this time, the composition of the whole raw material alloy
powder after mixing is, for example, Tb 0.34 Dy 0.66 Fe 1.88.
[0031]
Subsequently, the formed body is placed in a sintering furnace, heat-treated under predetermined
conditions, and sintered to prepare a sintered body (sintering step 12). Sintering is carried out by
raising the temperature of the molded body in a sintering furnace and then raising the
temperature to a predetermined temperature, maintaining the predetermined temperature (stable
temperature) substantially constant, and lowering the temperature.
[0032]
The temperature rising rate in the temperature rising process is preferably 3 to 20 ° C./min. If
the temperature rise rate is less than 3 ° C./min, productivity is low, and if the temperature rise
rate exceeds 20 ° C./min, the temperature of the raw material powder formed in the furnace
will not be uniform and there is a possibility that segregation or heterophase may occur. It is
because there is.
[0033]
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10
Moreover, it is preferable to make a stable temperature into the range of 1150-1240 degreeC. If
the stable temperature is less than 1150 ° C., a stable time is required to remove internal strain
for a long time, and it becomes inefficient. Conversely, if the stable temperature exceeds 1240 °
C., the alloy represented by RTy Since the temperature is close to the melting point, there is a
possibility that the sintered body itself may be melted, or there may be a possibility of
precipitation of another phase such as RT3 phase.
[0034]
The sintering atmosphere is basically carried out in an inert gas atmosphere using an inert gas
such as argon gas alone, but hydrogen gas is introduced into the sintering furnace together with
the inert gas during sintering. Preferably, part of the sintering is carried out in a mixed
atmosphere containing hydrogen gas and an inert gas. Specifically, first, the temperature in the
sintering furnace is raised to an inert gas sole atmosphere to completely release the hydrogen
gas contained in the formed body (the raw material alloy powder or the like subjected to the
hydrogen storage treatment). Next, the raw material alloy powder is activated by starting the
introduction of hydrogen gas and setting the inside of the sintering furnace to a mixed gas
atmosphere of hydrogen gas and an inert gas. Here, it is important for the densification of the
sintered body to be a mixed gas atmosphere of hydrogen gas and inert gas. Finally, the
introduction of hydrogen gas is stopped, and the inside of the sintering furnace is again brought
into an inert gas sole atmosphere to complete the sintering.
[0035]
During the above sintering process, at least one of a temperature zone of 650 ° C. or higher and
a stable temperature zone of 1150 ° C. or more and 1240 ° C. or less during the temperature
raising process is a mixture of hydrogen gas and inert gas in the sintering furnace. Gas
atmosphere. Specifically, when expressed as hydrogen gas: argon (Ar) gas = X: 100-X, it is
preferable to set X (volume%) to 0 <X <50. Since argon gas is an inert gas and does not oxidize
the rare earth element R, it can be mixed with hydrogen gas to obtain an atmosphere having a
reducing action. In order to obtain the reducing action, it is preferable to make X (volume%)
larger than 0, and since the reducing action is saturated when the hydrogen gas becomes
excessive, it is preferable that X <50. Further, by setting the mixed gas atmosphere of a hydrogen
gas and an inert gas in a temperature zone of 650 ° C. or more in the temperature raising
process, the oxidation due to the remaining trace amount of oxygen can be prevented.
04-05-2019
11
[0036]
In particular, with regard to temperature control during sintering and atmosphere control, it is
preferable to set the introduction start temperature of hydrogen gas to 900 ° C. to 1000 ° C.,
and the introduction end temperature of hydrogen gas to 1150 ° C. to 1200 ° C. It is
preferable to do. Furthermore, when the mixing ratio of hydrogen gas and argon gas is expressed
as hydrogen gas: argon (Ar) gas = X: 100-X in volume ratio, it is more preferable to set 10 <X
<50.
[0037]
Although it is conceivable to carry out all the sintering in an inert gas atmosphere alone, it is
difficult not only to achieve high densification but also to completely remove oxygen only with
the inert gas alone, and it is difficult to carry out the sintering process. Significantly lower the
properties. The rare earth element R reacts very easily with oxygen to form a stable rare earth
oxide, but although this rare earth oxide has low magnetism, it does not exhibit magnetic
properties that would make it a practical magnetic material. It is. Therefore, it is preferable to
perform sintering in a mixed gas atmosphere of hydrogen gas and inert gas from the viewpoint
of preventing oxidation of the rare earth element. Moreover, the atmosphere at the time of
sintering can be arbitrarily changed according to sintering object, for example, may be a vacuum
atmosphere.
[0038]
For example, as shown in FIG. 3A, the surface of the sintered body 21 obtained by the sintering
step 12 is in a state in which asperities are formed. Therefore, in the next barrel processing step
13, so-called barrel polishing is performed to polish and planarize the surface asperities. FIG. 3B
shows the state of flattening by the barrel processing step 13.
[0039]
The sintered body 21 (magnetostrictive element) formed as described above is formed into a
predetermined shape in the forming step 11 and sintered in a form reflecting the shape.
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12
However, due to the convenience of the mold at the time of molding, etc., it is difficult to match
the details to the desired shape. For example, in the case of producing a magnetostrictive element
having a cylindrical shape, when molds having a semicircular cross-section are butted, sharpshaped portions abut each other, causing disadvantages such as breakage of the molds. . In such
a case, the molds are stopped and molded before the molds are butted, and as a result, not a
complete cylinder, but two flat surface portions are formed along the axial direction. In such a
case, it is necessary to adjust the shape of the sintered body (magnetostrictive element) by
mechanical processing.
[0040]
The outer periphery processing step 14 performs this. In the outer periphery processing step 14,
for example, grinding is performed by passing the sintered body 21 (magnetostrictive element)
between a pair of rotating grindstones to prepare a predetermined shape. However, after this
mechanical grinding, a damaged layer 22 is formed as shown in FIG. 3 (c). The process-altered
layer 22 can be confirmed, for example, by observing the cross section of the sintered body 21
with an electron microscope or the like.
[0041]
The damaged layer is to be removed in the next etching step 15. However, if the thickness of the
processed grinding layer 22 becomes large, the damaged layer due to mechanical grinding is
completely removed even after the etching step 15. There is a risk that it will become impossible.
Also, if the etching time is increased, for example, in the etching step 15 in order to remove the
thick work-affected layer 22, so-called grain boundary etching may proceed and the surface
properties may be impaired.
[0042]
Therefore, in the present invention, by making the grinding conditions in the outer periphery
processing step 14 appropriate, the thickness of the process-altered layer 22 can be suppressed,
and the process-altered layer 22 can be sufficiently removed even under normal etching
conditions. . As a result of repeated studies by the present inventor, it was found that the
thickness (depth) of the process-altered layer 22 is proportional to the amount of grinding per
grinding in grinding. Specifically, by setting the grinding amount per time to 150 μm or less, the
04-05-2019
13
thickness of the process-altered layer 22 can be set to 15 μm or less, and the process-altered
layer is reliably removed in the next etching step 15 Can. In addition, when the amount of
grinding per time is made into the said range, sufficient grinding may be difficult by one
grinding. In such a case, the grinding may be performed a plurality of times under the above
conditions. If the grinding amount per one operation is 150 μm or less, the thickness of the
damaged layer 22 does not increase even if grinding is performed a plurality of times. This is
because the damaged layer 22 formed by the previous grinding is removed by the next grinding.
[0043]
After the outer periphery processing step 14, the processing-altered layer 22 is etched away in
an etching step 15. In the etching step 15, the purpose is to completely remove the damaged
layer 22. Therefore, as the etching conditions at this time, the depth d to be etched away shown
by the broken line in FIG. It needs to be larger than the thickness t of 22. Preferably, it is
performed so as to be t + 5 μm to t + 10 μm. As a result, the damaged layer 22 is almost
completely removed. However, as described above, when the etching amount exceeds 20 μm,
grain boundary etching proceeds more than necessary, so the etching amount is preferably 20
μm or less.
[0044]
By the etching, as shown in FIG. 3E, the damaged layer is removed, and the surface of the
sintered body 21 is flattened. In addition, although etching is performed using nitric acid
aqueous solution etc., for example, it is not restricted to this.
[0045]
After the etching step 15, an aging treatment step 16 is performed, and a resin coating step 17 is
performed. The aging treatment step 16 is for imparting stable magnetic characteristics by
holding the sintered body 21 at a predetermined temperature for a fixed time in a predetermined
inert atmosphere, for example, at 860 ° C. in an argon atmosphere. I just have to keep time.
[0046]
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14
In the resin coating process 17, a predetermined resin material, for example, an epoxy resin, is
applied to the surface of the sintered body 21 by any application method such as dipping or
spraying, and as shown in FIG. Form 23. The thickness of the resin film 23 is, for example, 15
μm to 25 μm.
[0047]
As described above, a magnetostrictive element without a process-deteriorated layer is produced.
However, the magnetostrictive element produced is free from occurrence of falling off, cracking,
chipping, etc. due to the expansion and contraction operation, large magnetostrictive
displacement, high speed response, large driving force, etc. Since it has, it is possible to utilize as
an element for sound.
[0048]
FIG. 4 shows an example of an acoustic device (speaker) using a magnetostrictive element.
The acoustic device comprises a magnetostrictive actuator unit 31 and a diaphragm 32. The tip
of an actuator rod 33 provided on the magnetostrictive actuator 31 vibrates the diaphragm 32 to
generate sounds such as voice and music. For the diaphragm 32, for example, an optional flat
panel, an acoustic plate or the like can be used.
[0049]
The magnetostrictive actuator unit 31 incorporates a magnetostrictive element 35, a drive coil
36, and a preload spring 37 for supporting the actuator rod 33 in addition to the actuator rod 33
in the outer case 34. The actuator rod 33 The magnetostrictive element 35 is disposed in such a
manner as to abut on the proximal end face of the magnetic sensor. The magnetostrictive
element 35 expands and contracts (displaces) in accordance with the magnetic field generated by
the supply of the electric signal to the drive coil 36, and transmits the displacement to the
diaphragm 32 through the actuator rod 33, whereby the input electric The signal is converted to
an acoustic signal (sound).
[0050]
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15
In the acoustic device of the above-mentioned structure, by using the magnetostrictive element of
the present invention as the magnetostrictive element 35, a highly reliable acoustic device which
does not change the element appearance characteristic or the element displacement
characteristic by continuous operation is realized. Is possible.
[0051]
Next, specific examples of the present invention will be described based on experimental results.
[0052]
First, the magnetostrictive element body was formed as follows.
That is, Tb, Dy and Fe were weighed as the raw material A and melted in an inert gas (Ar gas)
atmosphere to produce an alloy having a composition of Tb0.4Dy0.6Fe1.95.
Then, the raw material A is heat-treated by annealing at 1170 ° C. (stabilizing time 20 hours) to
make the concentration distribution of each metal element uniform at the time of alloy
production and to eliminate the deposited heterophase. The powder was crushed to obtain coarse
powder.
[0053]
Moreover, Dy and Fe were weighed as the raw material B, and were melted in an inert gas (Ar
gas) atmosphere to produce an alloy having a composition of Dy 2.0 Fe. Then, this alloy was
heat-treated at 150 ° C. (stabilizing time of 1 hour) in a hydrogen atmosphere (hydrogen
concentration 80%) to occlude hydrogen of about 18,000 ppm, whereby the alloy was crushed to
obtain coarse powder. The coarse powder was passed through a 2 mm mesh sieve to remove
coarse powder having a particle size of 2 mm or more. Furthermore, using Fe powder as the raw
material C, the Fe powder was subjected to reduction treatment (300 ° C., stabilization time: 1
hour) for removing oxygen in a hydrogen gas atmosphere.
[0054]
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Next, after weighing the obtained raw materials A, B and C, they were mixed and further finely
pulverized by 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 placed in a mold and molded at a molding
pressure of 5 to 8 ton / cm <2> in a magnetic field of 12 kOe to obtain a molded body. At this
time, when the alloy powder was filled in the mold, the alloy powder was moved through a pipe
filled with nitrogen gas. The magnetic field was applied in the direction perpendicular to the
pressure direction (so-called transverse magnetic field). The shape and size of the molded body
were cylindrical with a diameter of 3.8 mm and a length of 34 mm.
[0055]
The obtained molded product is put in a sintering vessel, heated in a furnace, and fired in a
mixed atmosphere of 35% by volume hydrogen and 65% by volume Ar in a stable temperature
zone of 1150 ° C. to 1230 ° C. , A sintered body was obtained. Furthermore, barrel polishing
was performed on this sintered body.
[0056]
Next, outer periphery processing was performed on this sintered body. The outer periphery
processing was performed by grinding the surface of the sintered body by 300 μm. At this time,
the processing conditions were changed to observe the appearance of the processing-altered
layer. As processing conditions, when 300 μm is ground at one time (condition A), when one
grinding amount is 150 μm and two grindings are performed (condition B), and one grinding
amount is 100 μm three times There are three types of grinding (condition C).
[0057]
The cross-sectional SEM photograph at the time of grinding on each condition is shown in FIG.5
(a)-(c). Under the condition A, as shown in FIG. 5 (a), the depth of the damaged layer is 25 μm,
and under the condition B, the depth of the damaged layer is 17 μm as shown in FIG. 5 (b). On
the other hand, under the condition C, as shown in FIG. 5C, the depth of the damaged layer is
greatly reduced to 7 μm.
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[0058]
Next, the sintered body processed on the outer periphery under each of these conditions was
etched to remove the process-altered layer on the surface. The etching was performed using an
aqueous nitric acid solution (concentration: 1.8%) as the etching solution, with the etching time
being 5 minutes and 15 seconds. The cross-sectional SEM photograph after an etching is shown
to FIG. 6 (a)-(c). In the case of condition A [FIG. 6 (a)] and condition B [FIG. 6 (b)], it can be seen
that the processing-deteriorated layer can not be removed under the above-mentioned etching
conditions and remains. On the other hand, under the condition C, as shown in FIG. 6C, all the
damaged layers are removed.
[0059]
Furthermore, a film of epoxy resin (S-No. 6, super anticorrosion primer C-7261 manufactured by
Nagashima Special Paint Co., Ltd.) was formed on the surface of the sintered body
(magnetostrictive element main body) manufactured under each condition. The formation of a
film was performed by spraying by a spray method. As a result, in the case of using the
magnetostrictive device main body having no process-altered layer manufactured by performing
the peripheral processing under the condition C, the abnormality is observed even if the
continuous operation test (68 ° C., 1 kHz, 1 W input, 1500 hours) is performed. It was not
recognized [see FIG. 7 (a)]. In addition, no change was observed in the displacement
characteristics before and after the test. On the other hand, when peripheral processing is
performed under conditions A and B and a magnetostrictive device main body with a processingaltered layer remaining on the surface, a change in displacement characteristics is observed in
1000 hours or less in a continuous operation test. An appearance abnormality was also observed
[see FIG. 7 (b)].
[0060]
On the other hand, in order to confirm the effect of the epoxy resin film, using the
magnetostrictive device body without the process-deteriorated layer prepared by performing the
peripheral processing under the condition C, the influence of the oxidation due to the presence or
absence of the epoxy resin film was investigated. Here, the state of change of the
magnetostriction value with the passage of time was examined under the environment of a
temperature of 85 ° C. and a relative humidity of 85%. The results are shown in FIG. In the
absence of the epoxy resin coating, a clear decrease in the magnetostriction value is observed,
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but in the case of the epoxy resin coating, the decrease in the magnetostriction value is hardly
observed.
[0061]
It is a schematic sectional drawing which shows an example of the magnetostriction element to
which this invention is applied. It is a flowchart which shows an example of the manufacturing
process of a magnetostriction element. It is a schematic diagram which shows the surface state of
the sintered compact in each process, (a) is after sintering, (b) is after barrel polishing, (c) is after
outer periphery processing, (d) is before etching, (e) Is after etching, and (f) is after resin coating.
It is a schematic sectional drawing which shows the structural example of an acoustic apparatus.
It is a cross-sectional SEM photograph which shows the difference of the processing-degraded
layer by the conditions of outer periphery processing, (a) shows condition A, (b) shows condition
B, (c) shows the processing-degraded layer by condition C (equivalent to an example). . It is a
cross-sectional SEM photograph which shows the difference of the process-degraded layer after
an etching, (a) is condition A, (b) is condition B, (c) shows the process-degraded layer by
condition C (equivalent to an Example). The vicinity of the interface between the magnetostrictive
element body and the epoxy resin film after the continuous operation test is shown. (A) is a crosssectional SEM photograph of a non-defective product after the continuous operation test, (b) is a
cross-sectional SEM photograph of the defective product after the continuous operation test is
there.
Explanation of sign
[0062]
Reference Signs List 1 magnetostrictive element, 2 magnetostrictive element body, 3 resin film,
11 forming step, 12 sintering step, 13 barrel processing step, 14 outer peripheral processing
step, 15 etching step, 16 aging step, 17 resin coating step, 21 sintered body, 22 Processdeteriorated layer, 23 resin film, 31 magnetostrictive actuator, 32 diaphragm, 33 actuator rod,
34 outer case, 35 magnetostrictive element, 36 drive coil, 37 preload spring
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