JPH03248504A - Bond type permanent magnet - Google Patents

Abstract

PURPOSE:To relieve deterioration of magnetic characteristics in molding by using powder which has an average aspect ratio of 2.5 or less and a diameter of 40mum or more in grain size at 90% or more in weight ratio. CONSTITUTION:The title magnet is constituted of a magnetic powder which has an average aspect ratio of 2.5 or less and a diameter of 40mum or more in grain size at 90% or more in weight ratio. That is, the process of molding bond type permanent magnets holds a close relation between the aspect ratio of a stock magnetic powder and a magnet which can obtain its grain size. A grain size falling short of 40mum deteriorates coercive force and angularity of hysteresis curve and further raises a problem of corrosion resistance: particularly, a weight ratio of 10% or more of magnetic powder whose grain size falls short of 40mum causes deterioration in characteristics. Control of the average aspect ratio of a magnetic powder is effective in improving magnetic characteristics of a bond type magnetic and allows improvement in the orientation of the magnetic powder. This process can relieve deterioration in magnetic characteristics in molding to provide bond type permanent magnets having excellent magnetic characteristics.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a bond type permanent magnet.

(Prior art) Ferrite-based, SmCo-based, NdFeB-based, etc. are known as bonded permanent magnets, and powders of these alloys are usually mixed with resin by compression molding, injection molding, etc. Manufactured.

However, even when the same raw material magnetic powder is used, variations occur in the magnetic properties obtained due to the manufacturing process, etc., and when manufacturing anisotropic bonded magnets to improve magnetic properties, especially the maximum energy product. There are also variations in the orientation of the magnetic powder. As a result, the quality of the final product is inconsistent.

In particular, in the case of NdFeB bonded magnets, cracks and chips in the magnetic powder during molding cause significant deterioration of the coercive force and squareness of the magnet's hysteresis curve, which poses a major problem in quality control of the final product. ing. Furthermore, when manufacturing anisotropic bonded magnets, a common method is to apply a magnetic field to magnetic powder to make it anisotropic, but at this time, the magnetic powder causes mechanical interaction with each other. , there is a problem that the desired degree of orientation cannot be obtained.

(Problems to be Solved by the Invention) Conventional bonded permanent magnets have a problem in that the orientation of magnetic powder varies, making it impossible to obtain magnets of stable quality.

An object of the present invention is to provide a bonded permanent magnet that reduces deterioration of magnetic properties during molding, achieves good orientation when anisotropic, and has good magnetic properties.

[Structure of the invention] (Means and effects for solving the problem) The present invention provides particles having an average aspect ratio of 2.5 or less and a particle size of 4.
This is a bond type permanent magnet characterized by being made of magnetic powder in which 90% or more by weight of magnetic powder has a particle size of 0 μm or more. Here, the aspect ratio refers to the maximum width of the magnetic powder, that is, the length in the major axis direction and the short width perpendicular to this major axis, although the individual shapes of the magnetic powders normally used in bonded magnets are not constant. It is defined by the ratio of the maximum width in the axial direction and the geometric mean of the minimum width.

The present inventors have discovered that there is a close relationship between the aspect ratio and particle size of the magnetic powder used as a raw material in the manufacturing process of a bonded permanent magnet, particularly in the molding process, and the magnet obtained.

First, when the aspect ratio exceeds 2.5, the following problems occur.

(1) Regardless of whether the target product is an isotropic bonded magnet or an anisotropic bonded magnet, the magnetic powder is often cracked or chipped due to pressure during molding, and the magnetic properties are significantly deteriorated.

(2) When the intended product is an anisotropic bonded magnet, the magnetic powder is not sufficiently oriented by the application of a magnetic field, etc., and initial magnetic properties cannot be obtained.

These problems can be improved by controlling the average aspect ratio of the raw magnetic powder. in this case,
The average aspect ratio of the magnetic powder is desirably 2.5 or less, preferably 2 or less.

Furthermore, if the powder particle size of the raw material magnetic powder is less than 40 μm, the effect of improving magnetic properties becomes small. In particular, when the raw material magnetic powder is, for example, NdFeB-based, as the powder particle size becomes smaller, the coercive force and the squareness of the hysteresis curve of the magnet deteriorate, and furthermore, there are problems in terms of corrosion resistance. arise. Therefore, it is desirable that the particle size of the magnetic powder is 40 μm or more.

In particular, magnetic powder with a particle size of less than 40 μm accounts for 10% by weight.
If it exceeds this, the characteristics of the bonded permanent magnet will deteriorate. Therefore, the particle size of 90% or more of the magnetic powder by weight is 40μ
It is desirable that it is more than m.

The effect of the above-mentioned selected magnetic powder varies depending on the type of magnetic powder used as the raw material.

In particular, when the raw material magnetic powder is NdFeB-based, the deterioration of the surface layer due to cracking or chipping is directly linked to the deterioration of the coercive force and squareness, so controlling the average aspect ratio of the magnetic powder is It is extremely effective in improving the magnetic properties of magnets. Furthermore, in the production of NdFeB-based anisotropic bonded magnets, the orientation of the magnetic powder can be greatly improved by controlling the average aspect ratio of the magnetic powder.

Regarding the method for manufacturing a bonded permanent magnet of the present invention, NdF
An example will be explained in which an eB-based sintered alloy is used as a starting material.

First, in terms of atomic fraction, 8 to 30% R (R is at least one element selected from rare earth elements including Y), 2
A permanent magnet alloy is produced which consists of ~28% B, 0.1~13% M (M is at least one element of Ag or Ga), and the balance essentially consists of one or more of Fe or Co.

Next, the permanent magnet alloy is crushed using a crushing means such as a ball mill. At this time, in order to facilitate molding and sintering in the post-process and to improve magnetic properties, the average particle size of the powder should be 2 to 2.
It is desirable that the powder be finely pulverized to a particle size of 10 μm. When this particle size exceeds 10 μm, the coercive force (iHc) decreases, while when it becomes less than 2 μm, the residual magnetic flux density (Br
), etc., resulting in a decrease in magnetic properties.

Finely pulverized permanent magnet alloy powder is press-molded into a desired shape. At the time of molding, no magnetic field may be used, or a magnetic field of, for example, about 15 koe is applied to perform the orientation treatment, as in the case of producing a normal sintered magnet. Subsequently, for example,
The molded body is sintered at 1000 to 1140°C for about 0.5 to 5 hours. This sintering is desirably performed in an inert gas atmosphere such as Ar gas or in vacuum so as not to increase the oxygen concentration in the alloy. In this case, it is desirable that the oxygen partial pressure be 1 torr or less.

The sintered body thus obtained was crushed to a powder particle size of 40 μm.
or more magnetic powder. In this case, a certain amount of magnetic powder having a particle size of less than 40 μm may be mixed in. The obtained magnetic powder is subjected to a spheroidization treatment using an inert gas stream or an organic solvent liquid stream to adjust the average aspect ratio to 2.5 or less, preferably 2.0 or less. The powder subjected to the spheroidization treatment is made to have a particle size of 40 μm or more by a method such as classification.

In this case, the amount of powder with a particle size below 40 μm is less than 10% by weight.

The powder thus obtained is subjected to aging treatment at a temperature range of 500 to 800° C. for about 0.1 to 10 hours. If the temperature of this aging treatment is lower than 500°C or higher than 800°C, the coercive force will decrease or the squareness will deteriorate, and the magnetic properties will deteriorate significantly. Therefore, the temperature of this aging treatment is 500~
A range of 800°C is preferred.

By performing a first stage aging treatment at 550 to 1150° C. before this aging treatment, a powder having a larger coercive force can be obtained. This first stage aging treatment will not produce any significant effect if the temperature is lower than 550°C or higher than 1150°C.

The thus treated powder is kneaded with a resin such as epoxy or nylon and molded into a desired shape to obtain a bonded permanent magnet. By applying a magnetic field during molding,
It can be made anisotropic.

Further, in the above example, a sintered alloy was used as the permanent magnet alloy, but when obtaining an isotropic magnet, magnetic field orientation and sintering may be omitted and an ingot may be used.

(Example) Examples of the present invention will be described below.

(Example 1) First, in terms of atomic fraction, 14.5% Nd, 17% Cos
A mixture of 1% Gas, 5% to 5% 81% Fe, and arc melting was performed using a water-cooled copper boat in an Ar atmosphere. The obtained alloy was coarsely ground in an Ar atmosphere, and further finely ground to an average particle size of 3.0 μm using a jet mill.

This fine powder was filled into a predetermined mold and compression molded at a pressure of 2 ton/c- while applying a magnetic field of 20 kOe.

This compact was sintered at 1600° C. for 1 hour in an Ar atmosphere, pulverized to an average particle size of 400 μm, and then subjected to spheroidization treatment under an Ar flow to adjust the average aspect ratio of the powder to 1.6. The powder that has been subjected to the spheroidization treatment is classified using a sieve, and after removing powder with a powder particle size of less than 40 μm,
Aging treatment was performed at 900°C for 1 hour. After this powder was rapidly cooled to room temperature, it was further aged at 600°C for 3 hours.

The obtained magnetic powder was kneaded with liquid epoxy resin (3 wt%), and compression molded at a pressure of 4 ton/cJ in a direction perpendicular to the direction of the magnetic field while applying a magnetic field of 18 koe.

The residual magnetic flux density (Br) and coercive force (
iHC), and the maximum energy product (BHmax) was measured. As a result, Br-94kG% 1Hc=11.2kO
e, BH+++ax -17,9MGOe. In addition, the residual magnetic flux density (Br=) in the direction perpendicular to the orientation direction was measured, and the degree of orientation was evaluated using the following equation (1).
A good value of A-89% was obtained.

A (%) −Br/ (Br +Br −) X
100.(L) (Comparative Example 1) A bonded permanent magnet was manufactured in the same manner as in Example 1, except that the average aspect ratio of the raw material magnetic powder was 3.1. The magnetic properties and degree of orientation of the obtained magnet were measured. As a result, Br-8,6kGSiHc-8,8kO
e, BHmax = LLIMGOe. Moreover, the degree of orientation was A-75%. It can be seen that these results are all inferior to Example 1.

(Example 2) The composition of the raw material alloy is 14% Nd and 16% C in atomic fraction.
A bonded permanent magnet was produced in the same manner as in Example 1, except that the remaining part of 81 was essentially Fe, and the compression molding was carried out in the absence of a magnetic field. Manufactured. The magnetic properties of the obtained magnet were measured. As a result, B
r = 6.3kG.

i Hc =10.8k Oe, B Hmax -8
, 2MGOe.

(Comparative Example 2) A bonded permanent magnet was manufactured in the same manner as in Example 2, except that the average aspect ratio of the raw material magnetic powder was 3.0. The magnetic properties of the obtained magnet were measured. the result,
Br-5,8kGS 1Hc-8,1kOe, BHma
x −5,5MGOe, and the squareness is also deteriorated compared to Example 2.

(Comparative Example 3) A bonded permanent magnet was manufactured in the same manner as in Example 1, except that the raw material magnetic powder had a particle size of 40 μm at a weight ratio of 40%. The magnetic properties of the obtained magnet were measured. As a result, Br-7,6kG, i Hc −
6,5koe, BHa+ax -7,8M G Oe
Met. Compared to the magnet of Example 1, this magnet has significantly deteriorated squareness and greatly deteriorated magnetic properties.

[Effects of the Invention] As described above, according to the present invention, deterioration of magnetic properties during molding is reduced, good orientation is achieved when anisotropy is made, and a bond having good magnetic properties is produced. type permanent magnet can be provided.

Claims (1)

[Claims] A bonded permanent magnet comprising magnetic powder having an average aspect ratio of 2.5 or less and a weight ratio of 90% or more of the particles having a particle size of 40 μm or more.