JP3985695B2 - Method for evaluating the degree of orientation of anisotropic magnetic materials - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating the degree of orientation of an anisotropic magnetic material.
[0002]
[Prior art]
In general, an anisotropic magnet is obtained by crushing a magnetic material having anisotropic magnetic anisotropy (anisotropic magnetic material) to a single crystal grain size to obtain a material powder. Anisotropy in which the axis of easy magnetization of material particles is oriented in a fixed direction by compressing the raw material obtained by mixing (magnetic orientation) in a magnetic field or mechanically rolling with a forming roller (mechanical orientation) It is manufactured by producing a magnetic green compact and subjecting the anisotropic green compact to a hardened material by firing or the like.
[0003]
As described above, since anisotropic magnetic materials are used with the easy axis of magnetization easily exhibiting magnetic properties oriented in a certain direction, the degree of orientation of the anisotropic compact before magnetization is varied. The magnetic properties of the final product (sintered magnet or bonded magnet) after magnetization are greatly changed, leading to the generation of defective products. Therefore, accurately grasping the degree of orientation of the anisotropic green compact before magnetization, which is a raw material of the anisotropic magnet, is extremely important in terms of quality maintenance and design management of the anisotropic magnet.
Therefore, conventionally, there is a case where a method for evaluating the degree of orientation of the green compact by analyzing the crystal structure of the anisotropic green compact using an X-ray diffraction apparatus (see Patent Document 1). ).
[0004]
[Patent Document 1]
JP-A-11-195516 (column [0054])
[0005]
[Problems to be solved by the invention]
However, when the degree of orientation of the anisotropic green compact is evaluated using the X-ray diffractometer, it is necessary to measure the analytical strength of a plurality of crystal planes, and the measurement time becomes very long. End up. For this reason, it is very difficult to incorporate the diffraction device into a production line for anisotropic magnets, evaluate the degree of orientation of the anisotropic green compact, and remove defective products from the line. In the first place, since the X-ray diffractometer is very expensive, in order not to raise the facility cost more than necessary, the X-ray diffractometer is used only for evaluating the degree of orientation of the anisotropic green compact before magnetization. It is not a good idea to introduce equipment.
[0006]
On the other hand, it is also possible to measure the hysteresis loop of the anisotropic green compact with a BH tracer or a vibrating sample magnetometer and evaluate the magnetic orientation degree of the anisotropic green compact based on this loop. However, in this case, it is necessary to magnetize the anisotropic compact once, and it is difficult to completely demagnetize the anisotropic compact after the magnetization. The degree of orientation of the anisotropic green compact cannot be easily evaluated.
[0007]
In view of such circumstances, the present invention makes it possible to easily evaluate the degree of orientation of an unmagnetized anisotropic green compact, which is a raw material for an anisotropic magnet, in a short time. The purpose is to enable easy maintenance and design management.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following technical means.
That is, the method of the present invention is a method for evaluating the degree of orientation of an anisotropic magnetic material comprising the following steps.
[0009]
(A) First step of measuring volume fraction and remanent magnetization of at least one reference green compact obtained by completely magnetically orienting a material powder made of an anisotropic magnetic material in a predetermined direction (b) Volume fraction and remanent magnetization A second step of plotting the measurement data of the reference green compact in two-dimensional coordinates with the variable as a variable, and connecting the point and the origin or a plurality of points to determine a magnetization reference line (c) the material powder in a predetermined direction A third step (d) of measuring the volume fraction and the residual magnetization of the green compact to be measured, wherein the measurement data of the green compact to be measured is plotted on the two-dimensional coordinates, and the residual magnetization of the measurement data is A fourth step of estimating the degree of orientation of the green compact to be measured from the degree of separation from the magnetization reference line.
According to the present invention, the magnetization reference line is determined in advance based on the measurement data of the reference green compact obtained by completely magnetically orienting the material powder, and the residual magnetization of the green compact to be measured is the magnetization reference. Since the degree of orientation of the green compact to be measured is specified from the degree of separation from the properties, the residual magnetization and volume ratio of the green compact to be measured are measured and compared with the magnetization reference line. The degree of orientation of the green compact to be measured can be evaluated. For this reason, the orientation degree of the green compact to be measured can be evaluated in an unmagnetized state in a short time without using an expensive apparatus such as an X-ray diffraction apparatus.
[0011]
In the method of the present invention, the residual magnetization can be measured with a vibrating sample magnetometer, and the volume ratio can be measured with a thermal analyzer. Such magnetometers and thermal analyzers are generally already owned by magnet manufacturers and their developers, and therefore are preferable in that they do not cause an increase in equipment costs when implementing the method of the present invention.
In the evaluation method of the present invention, the measured values of remanent magnetization and volume fraction were used, for example, when rubber magnets were manufactured, rubber / additive / magnetic powder kneading or magnetic powder arrangement This is because distortion is introduced into the magnetic powder by the rolling forming, and it is difficult to obtain true saturation magnetization. Further, there is a variation in the amount of magnetic powder depending on the portion of the rubber magnet, and the mixing ratio of the magnetic powder cannot be used as it is.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In order to carry out the orientation degree evaluation method according to the present invention, first, a reference powder 1 is prepared by completely magnetically orienting a material powder made of an anisotropic magnetic material such as ferrite in a predetermined direction. The volume ratio xp and the residual magnetization yp of the green compact 1 are measured using a thermal analyzer and a vibrating sample magnetometer.
[0013]
In addition, the reference green compact 1 which is completely magnetically oriented is prepared by, for example, putting a weighed mixture of material powder and wax made of anisotropic magnetic material into a container and heating it, and applying a strong magnetic field in a state where the wax is melted. It can be made by cooling and curing in that state.
Then, as shown in FIG. 1 (a), the measurement data P of the reference green compact 1 is plotted on two-dimensional coordinates with the volume ratio X and the residual magnetization Y as variables, and as shown in FIG. 1 (b). The magnetization reference line L is determined by connecting the point P and the origin. Although not shown in FIG. 1, a plurality of measurement data P may be plotted using a plurality of reference green compacts 1, and the magnetization reference line L may be determined by connecting adjacent points P.
[0014]
Next, the measured powder 2 is produced by orienting the same material powder as in the case of the reference green compact 1 in a predetermined direction, and the volume ratio xr and residual magnetization yr of the measured green powder 2 are measured. .
The green compact 2 to be measured is prepared by, for example, kneading a weighed mixture of material powder made of anisotropic magnetic material and rubber powder, and rolling the kneaded magnetic powder-containing rubber at a predetermined reduction rate. The material powder can be produced by mechanical orientation in a rubber sheet.
[0015]
Then, as shown in FIG. 1C, the measurement data R of the green compact 2 to be measured is plotted on the two-dimensional coordinates described above, and the residual magnetization yr of the measurement data R is detached from the magnetization reference line L. The degree of orientation of the green compact 2 to be measured is specified according to the degree to which it is present. The degree of separation from the magnetization reference line L in this case means the residual magnetization yr ′ (complete magnetic field) on the magnetization reference line L when the volume ratio X is the volume ratio xr of the green compact 2 to be measured. This means the ratio yr / yr ′ of the residual magnetization yr of the green compact 2 to be measured with respect to the residual magnetization in the case of orientation, and can be regarded as the degree of orientation of the green compact 2 to be measured by this ratio yr / yr ′.
[0016]
The reason is that, as will be apparent from the experimental examples described later, since the residual magnetization Y of the magnetic anisotropic compact is proportional to the amount of magnetic powder (volume ratio X), it is assumed that the residual magnetization Y is proportional to the degree of orientation. Because it can.
If the orientation degree evaluation method according to the present invention is used, in the anisotropic magnet production line, the crystal orientation of the anisotropic compact immediately after being magnetically or mechanically oriented is evaluated. , It is possible to detect pressure setting mistakes and molding equipment failures in the molding process of magnetic anisotropic compacts at an early stage, which can eliminate defective products, so that defective products flow into subsequent sintering and magnetizing processes. Can be prevented in advance.
[0017]
In addition, an orientation evaluation device using the method of the present invention is arranged between the magnetic anisotropic green compact molding device and the subsequent device, and these devices are connected online, so that the operation status of the molding device is almost the same. It becomes possible to grasp in real time, and the operation of the molding apparatus can be immediately stopped based on the evaluation of the magnetic anisotropic green compact. For this reason, the response time to the malfunction of the molding apparatus is greatly shortened, and the occurrence of defective products can be reduced.
Furthermore, if the evaluation method of the present invention is used, the degree of orientation of the green compact to be measured can be evaluated in a short time without using an expensive apparatus such as an X-ray diffractometer. Therefore, the total number of anisotropic green compacts can be inspected without reducing production efficiency, and the design management of anisotropic magnets can be simplified.
[0018]
On the other hand, with an anisotropic magnet that needs to perform multipolar magnetization, complete demagnetization is difficult even if the magnet is once demagnetized for evaluation of the degree of orientation. For this reason, when multipolar magnetization is finally performed, the degree of magnetization increases in the direction of magnetic field application in the evaluation of the orientation degree, and the symmetry of magnetization cannot be ensured. In this regard, the use of the method of the present invention is particularly effective in evaluating the degree of orientation of the magnetic anisotropic compact when producing a multipolar magnet.
[0019]
The above-described embodiments are all illustrative and not restrictive. The scope of the present invention is defined by the claims, and all modifications within the scope equivalent to the configurations described therein are also included in the present invention.
For example, the method of the present invention can be applied not only to the measured green compact 2 that is mechanically oriented but also to the green compact 2 that is magnetically oriented. However, when an anisotropic compact is compression-molded by magnetic field orientation, it is often produced by applying a sufficiently strong magnetic field, so that almost perfect orientation is often performed. Therefore, it can be said that it is less necessary to evaluate the degree of orientation than in the case of mechanical orientation.
[0020]
【Example】
In order to demonstrate the usefulness of the method of the present invention, an evaluation experiment of the degree of orientation was performed on the actually measured green compact. The specifications of the reference green compact 1 and the green compact 2 to be measured used in this experiment are as follows.
[0021]
[Standard compact]
・ Magnetic powder:
Toda Kogyo Co., Ltd. FH-800 (trade name)
Strontium ferrite for mechanical orientation (SrO · 6Fe2O3)
A mixture of the above magnetic powder and wax was put in a container and heated, and a magnetic field of 22 kOe was applied in a state where the wax was melted, and then cooled and cured in that state.
[0022]
[Measured compact]
・ Magnetic powder:
Same as for standard green compact.
・ Rubber material:
NBR
・ Rolling conditions:
A mixture of the above magnetic powder and rubber powder is kneaded, and the kneaded magnetic powder-containing rubber is set at an initial roll interval of 4.8 mm and a sheet width of about 150 mm, and rolled with various reduction ratios. The magnetic powder was produced by mechanical orientation in a rubber sheet.
[0023]
[Type of specimen]
Four types of specimens having magnetic powder addition amounts (volume ratios) of 38, 45, 54, and 65% by weight (mass%), respectively, were prepared. Rolling was performed while changing the roll interval / initial roll interval to 1.0, 0.62, 0.42, and 0.25, respectively, and the residual magnetization in that case was measured as a vibrating sample magnetometer (VSM-3 manufactured by Toei Kogyo Co., Ltd.). ).
[0024]
The relationship between each variable obtained as a result is shown in FIGS.
Among these, as shown in FIG. 2, when the rolling reduction is 0.25, that is, when a rubber sheet containing magnetic powder is rolled to a thickness of 1/4, the line of the reference green compact that is completely magnetically oriented. In this case, the degree of orientation due to the mechanical orientation is almost perfect. Further, the remanent magnetization decreases as the rolling reduction approaches 1.0 (non-rolled state).
[0025]
On the other hand, as shown in FIG. 3, even if the addition amount (volume ratio) of the magnetic powder is changed, the relationship between the rolling reduction and the degree of orientation is maintained in a substantially constant state. Therefore, it can be seen that the degree of orientation of the green compact can be specified by the ratio of the residual magnetization of the green compact to be measured to the residual magnetization on the magnetization reference line in the case of a certain volume ratio.
[0026]
【The invention's effect】
As described above, according to the present invention, generally, an unmagnetized magnetic material that becomes a raw material of an anisotropic magnet can be used without using a special device other than a device already owned by a magnet manufacturer or developer. Since the degree of orientation of the anisotropic green compact can be easily evaluated in a short time, generation of defective anisotropic magnets can be suppressed, and design management of the magnets can be further simplified.
[Brief description of the drawings]
FIG. 1 is a graph for showing an orientation degree evaluation method according to the present invention in time series.
FIG. 2 is a graph showing the relationship between the volume fraction of magnetic powder and residual magnetization.
FIG. 3 is a graph showing the relationship between the rolling reduction and the degree of orientation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reference green compact 2 Measuring green compact L Magnetization reference line xp Volume ratio yp of standard green compact Residual magnetization xr of standard green compact Volume ratio yr of green compact to measure Residual magnetization P of green compact to be measured Measurement data R Measurement data

Claims (3)

A method for evaluating the degree of orientation of an anisotropic magnetic material comprising the following steps (a) to (d).
(A) First to measure the volume fraction (xp) and the residual magnetization (yp) of at least one reference green compact (1) obtained by completely magnetically orienting a material powder made of an anisotropic magnetic material in a predetermined direction. Step (b) The measurement data (P) of the reference green compact (1) is plotted on two-dimensional coordinates with the volume fraction (X) and the residual magnetization (Y) as variables, and the point (P) and the origin or plural A second step (c) for determining the magnetization reference line (L) by connecting the points (P) to the volume ratio (xr) of the green compact (2) to be measured formed by orienting the material powder in a predetermined direction; Third step (d) of measuring the residual magnetization (yr) Plotting the measurement data (R) of the green compact (2) to be measured on the two-dimensional coordinates, and the residual magnetization (yr) of the measurement data (R) Degree of orientation of the green compact (2) to be measured from the extent to which it is separated from the magnetization reference line (L) The fourth step to identify The method for evaluating the degree of orientation of an anisotropic magnetic material according to claim 1, wherein the residual magnetization is measured with a vibrating sample magnetometer. The method for evaluating the degree of orientation of an anisotropic magnetic material according to claim 1 or 2, wherein the volume ratio is measured by a thermal analyzer.

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