KR100428559B1 - Simple fabrication method of hard ferrite powder using mill scale - Google Patents

Abstract

The present invention relates to a method for producing a hard ferrite magnetic powder using mill scale as a by-product of a steel mill hot rolling process as an alternative raw material for iron oxide, and an object thereof is to prepare an oxidation treatment by mixing strontium carbonate or barium carbonate as a sub raw material with mill scale. By mixing while grinding, separate wet dispersion mixing process and dehydration process are omitted, which simplifies the manufacturing process and improves productivity, and provides a method for producing a hard ferrite magnetic powder that can improve magnetic properties by uniform mixing. have.

The present invention for achieving the above object,

Pulverizing the mill scale from which foreign substances have been removed;

Mixing barium carbonate or strontium carbonate with millscale powder,

Oxidizing the mixed powder,

Mixing the oxidized mixed powder while grinding to a predetermined particle size; and

The technical gist of the present invention relates to a method for producing a hard ferrite magnetic powder in a mill scale by a simple process comprising calcining the pulverized mixed powder.

Description

Simple fabrication method of hard ferrite powder using mill scale}

The present invention relates to a method for producing a hard ferrite magnetic powder using mill scale, a by-product of a steel mill hot rolling process, as a raw material of iron oxide, and more specifically, to prepare an auxiliary raw material before oxidizing the mill scale. The present invention relates to a method for producing a hard ferrite magnetic powder which is mixed by performing oxidation treatment and pulverization, thereby simplifying the production process and improving magnetic properties by uniform mixing.

Hard ferrite permanent magnets are energy-efficient and chemically stable for the price, making them the largest product in the permanent magnet market worldwide. The general manufacturing method of hard ferritic permanent magnet is made by adding barium carbonate (BaCO ₃ ) or strontium carbonate (SrCO ₃ ) as a _secondary raw material by using iron oxide (α-Fe ₂ O ₃ ), a by-product of the cold rolling process of a steel mill. After mixing by wet method and drying, Ba-ferrite (BaO · 6Fe ₂ O ₃ ) or Sr-ferrite (SrO · 6Fe ₂ O ₃ ) magnetic phase is made through ferrite reaction in the calcination process, and coarsely pulverized B. After making the fine powder of magnetic powder of about 1 ㎛ level through the pulverization process, the highly anisotropic hard ferrite permanent magnet of high characteristics is completed through the molding process and the sintering process in the magnetic field.

Iron oxide, which is used as a main raw material for hard ferrite permanent magnets, is widely used not only as a main raw material for the manufacture of soft ferrite magnets but also for the production of pigments and cosmetics, and thus, alternative raw materials are required due to the insufficiency of iron oxide. The most prominent alternative raw material is wheat scale, which is very cheap and easy to obtain.

Mill scale is mainly iron scrap produced when producing coils or rebars in the hot rolling or rolling process of steel manufacturing process, and its shape is plate-shaped and the particle size is maintained about 20mm or less. In addition, 70% or more of the components of the mill scale are composed of Fe, 30% or more of fully oxidized Fe ₂ O ₃ and 70% or less of unoxidized FeO, and other components include Mn _2. O ₃ , SiO ₂ , CaO and the like are contained. At present, mill scale is mainly used as blast furnace coolant.

In order to use this mill scale as a main raw material for the manufacture of hard ferrite permanent magnets, two technical prerequisites are required. First, the unoxidized FeO component contained in the mill scale about 70% should be effectively oxidized more than 98% to the α-Fe ₂ O ₃ component such as iron oxide. Next, the average particle size of the mill scale of 20 mm level should be effectively crushed to a level of 3 μm or less similar to iron oxide.

Recently, the technique of using mill scale as a main raw material of a hard ferrite permanent magnet instead of iron oxide is disclosed in Korean Patent Laid-Open Publication Nos. 1997-23480 and 1990-15187. These prior arts are all oxidized mill scale to obtain iron oxide, and then mixed with subsidiary barium carbonate or strontium carbonate and calcined to form hard ferrite powder. Korean Patent Publication No. 1997-23480 of the prior art will be described with reference to FIG. 1 as follows.

The prior art includes the steps of removing this material from a mill scale having a particle size of 20 mm or less to obtain a pure mill scale, taking a predetermined amount of the pure mill scale and dry grinding it first, and subjecting the mill scale powder to 98% α-Fe. Oxidative heat treatment (about 600 to 800 ° C.) with ₂ O ₃ components, followed by dry grinding of the oxidized mill scale to adjust the particle size to 3 μm or less, and then wet mixing and mixing the barium carbonate or strontium carbonate as subsidiary materials. And, through the dehydration process through a calcination reaction is made of hard ferrite magnetic powder. Eferrite magnetic powder is again made of magnetic powder fine particles of 1 μm or less through coarsely pulverized and pulverized processes, and is made of anisotropic hard ferrite permanent magnet through a molding process and a sintering process in a magnetic field.

However, the above prior art has a problem that the manufacturing process before the calcination process is very complicated as well as the production of high-quality hard ferrite, compared to the hard ferrite manufacturing method using iron oxide.

Therefore, in the present invention, by mixing strontium carbonate or barium carbonate, which is an auxiliary material, with mill scale first, while performing oxidation treatment and pulverization, a separate wet dispersion mixing process and a dehydration process are omitted, thereby simplifying the manufacturing process to improve productivity. It is an object of the present invention to provide a method for producing a hard ferrite magnetic powder capable of improving magnetic properties by uniform mixing.

1 is a production process comparison of the conventional manufacturing method and the manufacturing method of the present invention

Method for producing a hard ferrite magnetic powder of the present invention for achieving the above object, the step of grinding a mill scale from which foreign substances are removed,

Mixing barium carbonate or strontium carbonate with millscale powder,

Oxidizing the mixed powder,

Mixing the oxidized mixed powder while grinding to a predetermined particle size; and

And calcining the ground mixed powder.

Hereinafter, the present invention will be described in detail.

In the technical field for producing hard ferrite powder, a process of oxidizing by-products such as mill scale to make high-purity iron oxide and then mixing subsidiary materials (barium carbonate or strontium carbonate) is formulated. Therefore, in order to mix the subsidiary materials with iron oxide, a separate wet dispersion mixing process and a dehydration process were involved, and the manufacturing process was complicated.

Unlike conventional stereotypes, the present inventors found that, after mixing subsidiary materials with mill scale first and then oxidizing, the mill scale is well oxidized even in a mixed powder state. It was also found that the magnetic properties were improved by mixing sufficiently uniformly in the secondary grinding process.

As a result, it was found that the wet dispersion mixing process and the dehydration process accompanying the mixing of the subsidiary materials and iron oxide can be omitted.

Based on this finding, the manufacturing process of this invention completed is demonstrated concretely.

First, a plate mill scale generated as a by-product in the hot rolling or rolling process of a steel mill is obtained, and foreign substances are filtered out from the mill scale. Removal of debris is usually done on a vibrating screen.

Millske, from which foreign substances have been removed, is pulverized, that is, dry pulverized. At this time, the particle size is set to about 12 μm or less and preferably 5 μm or less as in the usual method. If the particle size is too large, unoxidized FeO and Fe ₃ O ₄ components are present in the particles, which requires a lot of time during oxidation and secondary grinding.

The subsidiary material (barium carbonate or strontium carbonate) is mixed with the first milled mill scale. Mixing causes the milled millscale to be loaded at a constant rate while also loading the side materials together. In this case, the ratio of the sub-material and the mill scale is 1: 5.6-in consideration of the fact that the hard ferrite phase exhibiting magnetic properties is stoichiometrically (Ba, Sr) O.6Fe ₂ O ₃ , one mole of raw material and 6 mole of iron oxide. Mix at a molar ratio of 6.1.

The mixed powder of mill scale and subsidiary materials is oxidized so that the mill scale is 98% or more of α-Fe ₂ O ₃ component. Oxidation treatment conditions at this time are carried out at a temperature of about 600 ~ 800 ℃. If the heat treatment temperature is less than 600 ℃, satisfactory level of iron oxide (Fe ₂ O ₃ ) is not obtained. If the heat treatment temperature is higher than 800 ℃, the process cost increases and the mill scale partially melts, which adversely affects the efficiency of the grinding operation. Can be crazy

Then, the oxidized mixed powder is pulverized second. Secondary grinding is preferably pulverized to about 3 μm or less. During secondary grinding, the subsidiary materials and the oxidized mill scale are effectively mixed so that no additional wet dispersion mixing process is required. The inventors have found that the oxidized mixed powder has better grinding characteristics than the conventional iron oxide due to the addition of subsidiary materials. Therefore, the mixed powder can be pulverized even more at the same time.

The secondary milled mixed powder is calcined according to a conventional method. Calcination is usually performed at a temperature range of about 1200 to 1300 ° C.

The hard ferrite calcined powder prepared as described above is manufactured as a hard ferrite permanent magnet through a process of [crude grinding] → [pulverization] → [molding in the magnetic field] → [dry] → [sintering] → [processing]. . This process after the calcination process is the same as a general manufacturing process using a conventional iron oxide.

Hereinafter, the present invention will be described in detail through examples.

Example 1

The mill scale having the composition shown in Table 1 was put into a hopper with a vibrator, and the mill scale of 20 mm level was filtered out of the lower vibrating screen to remove this material and the like to obtain only pure mill scale.

Chemical composition (% by weight) Fe ₂ O ₃ FeO SiO ₂ CaO Mn ₂ O ₃ CuO NiO Al ₂ O ₃ T.Fe 33.50 65.02 0.20 0.07 0.95 0.05 0.07 0.06 73.97

Pure mill scale was put into a first vibrating mill using a screw conveyor and first dry pulverized to obtain a pulverized powder having a level of about 5 μm. Mill scale primary pulverization is stored in the feed hopper at a constant speed through a feeder such as a screw conveyor or bucket elevator. At this time, the subsidiary material barium carbonate (BaCO ₃ ) is added at a molar ratio of 5.8. Weighed and fed at a constant rate to mix with mill scale mill in the hopper.

Mill scale / barium carbonate powder is used for 1 hour in the temperature range of 600 ~ 800 ℃ by using rotary kiln to oxidize Fe scale of mill scale to more than 98% α-Fe ₂ O ₃ component. It was oxidized while mixing by rotational force continuously. During oxidation, these substances, such as oils attached to the surface of the mill scale, were also volatilized and removed.

The oxidized mill scale / barium carbonate mixed powder was cooled with a screw cooler and introduced into a second vibratory mill, and pulverized dry to have a particle size of 3 μm or less. The vibration mill has two chambers (chamber) at the top and bottom, the upper chamber has a steel bar (pulverization medium) and the lower chamber is filled with a steel ball (steel ball). In vibratory mills, not only mill scale secondary grinding but also low cost barium carbonate with large particles are possible. Importantly, it is possible to improve the magnetic properties of the Ba-ferrite calcined powder because of the uniform mixing of the mill scale and barium carbonate.

The mixed powder of the second milled mill scale and barium carbonate was immediately put into the calcination furnace without a separate dispersion mixing process and a dehydration process. Temperature interval the ferrite formation reaction takes place in a rotary calcination keep 1250 ℃ had been held more than 8% oxygen concentration, through the calcination process Ba- ferrite (BaO · 6Fe ₂ O ₃₎ to prepare a calcined powder in a simple manner It was possible. The manufacturing process after calcination was carried out in the same manner as in the general manufacturing process using a conventional iron oxide. The calcined powder was pulverized dry to a 3.5 μm particle size, and pulverized to a particle size of about 1.1 μm wet in a ball mill. The pulverized slurry was continuously dehydrated in a dehydrator to around 61% concentration and then molded in a magnetic field into the desired form using a press. The molded body was dried at 70 ° C. and then sintered at 1220 ° C./24 hours in a sintering furnace to produce anisotropic Ba-ferrite.

As a result of evaluating the magnetic properties of Ba-ferrite manufactured using mill scale in the present invention using a BH tracer, the residual magnetic flux density is 3900 G or more, the intrinsic coercive force is 1950 Oe or more, and the maximum magnetic energy is 3.5 MGOe. High magnetic properties were shown above.

Example 2

The first milled powder of the mill scale prepared as in Example 1 was stored in the feed hopper at a constant speed through the feeder. At this time, the secondary raw material strontium carbonate (SrCO ₃ ) was weighed in a 6.0 molar ratio, and was introduced at a constant speed so as to be mixed with mill scale pulverized powder in a hopper. The mill scale / strontium carbonate mixed powder was oxidized while mixing by rotational force continuously in a rotary furnace within a temperature range of about 600 to 800 ° C. The oxidized mill scale / strontium carbonate mixed powder was cooled with a screw cooler, charged into a vibrating mill, and dry pulverized secondly so as to have a thickness of 2 μm or less. The second milled mill scale / strontium carbonate mixture was directly put into the calcination furnace without separate dispersion mixing and dehydration. The reaction temperature of the rotary calcination furnace was maintained at 1230 ℃ and maintained an oxygen concentration of more than 8%, through the calcination process Sr-ferrite (SrO.6Fe ₂ O ₃ ) calcined powder was prepared.

The manufacturing process after calcination was carried out in the same manner as in the general manufacturing process using a conventional iron oxide. The calcined powder was dry pulverized to a 3.5 μm particle size and finely pulverized to about 0.9 μm particle size in an attritor. The pulverized slurry was continuously dehydrated in a dehydrator to around 61% concentration and then molded in a magnetic field into the desired form using a press. The molded body was dried at 70 ° C. and then sintered at 1220 ° C./24 hours in a sintering furnace to produce anisotropic Sr-ferrite.

As a result of evaluating the magnetic properties of the Sr-ferrite manufactured using the mill scale in the present invention, the residual magnetic flux density was 4000 G or more, the intrinsic coercive force was 2900 Oe or more, and the high magnetic energy was 4.0 MGOe or more.

As described above, the present invention has a useful effect of manufacturing hard ferrite by using a mill scale in a simple manufacturing process and economically producing both productivity and magnetic properties at the same time.

Claims (6)

delete Grinding the mill scale to which foreign substances are removed to 5 μm or less, Mixing barium carbonate or strontium carbonate with the milled millscale powder, Oxidizing the mixed powder; Mixing the oxidized mixed powder while grinding to a predetermined particle size; and A method for producing a simplified hard ferrite magnetic powder using a mill scale comprising calcining the pulverized mixed powder. Pulverizing the mill scale from which foreign substances have been removed; Mixing barium carbonate or strontium carbonate to the milled millscale powder, wherein the barium carbonate or strontium carbonate and mill scale are mixed at a molar ratio of 1: 5.6 to 6.1, Oxidizing the mixed powder; Mixing the oxidized mixed powder while grinding to a predetermined particle size; and A method for producing a simplified hard ferrite magnetic powder using a mill scale comprising calcining the pulverized mixed powder. delete The method of claim 2 or 3, wherein the pulverizing and mixing of the oxidized powder are mixed while pulverizing the powder to 3 μm or less. The method of claim 2 or 3, wherein the calcining is performed at 1200 to 1300 ° C.