KR100440678B1 - Fabrication method of hard ferrite using mill scale added oxidant - Google Patents

Abstract

The present invention relates to a method for producing a hard ferrite magnetic powder by 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 a mill scale with a small amount of sodium nitrate or potassium nitrate or ammonium nitrate in advance. It is to provide a method for producing a hard ferrite magnetic powder which can be mixed to improve the magnetic properties by improving the oxidization degree and millability of the mill scale.

The present invention for achieving the above object,

First milling the mill scale from which foreign substances have been removed;

Mixing the oxidant with the millscale powder,

Oxidizing the millscale powder to which the oxidizing agent is added,

Second milling the oxidized millscale powder to a predetermined particle size,

The technical gist of the present invention relates to a method for producing a hard ferrite magnetic powder using a mill scale comprising mixing the pulverized mill scale with one type of strontium carbonate or barium carbonate as a secondary raw material and calcining the mixed powder.

Description

Fabrication method of hard ferrite using mill scale added oxidant}

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, an oxidizing agent before oxidizing mill scale. A small amount of sodium nitrate or potassium nitrate or ammonium nitrate is mixed with a mill scale in advance, and a method for producing a hard ferrite magnetic powder capable of improving magnetic properties by improving the oxidization and grinding properties of the mill scale.

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 wetted by adding strontium carbonate (SrCO ₃ ) or barium carbonate (BaCO ₃ ) as a main raw material with iron oxide (α-Fe ₂ O ₃ ), a by-product of the cold rolling process of steel mills. After mixing by dry method and drying, Sr-ferrite (SrO · 6Fe ₂ O ₃ ) or Ba-ferrite (BaO · 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.

Since 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 soft ferrite magnets but also for the production of pigments and cosmetics, development of alternative raw materials due to the insufficiency of iron oxide supply has been difficult. Was required. The most prominent alternative to hard ferrite permanent magnets is mill scale, which is very cheap and easy to obtain.

Mill scale is mainly iron scrap produced in the production of coils or rebars in the hot rolling or rolling process of the steel manufacturing process, the shape of the plate 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 about 70% in the mill scale should be effectively oxidized to about 98% or more with an 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 strontium carbonate or barium carbonate as raw materials and calcined to form hard ferrite magnetic powder. Referring to Korean Laid-Open Patent Publication No. 1997-23480 in the prior art with reference to FIG. 1 (excluding the oxidizing agent addition process) 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 the subsidiary materials strontium carbonate and barium carbonate. And, through the dehydration process through a calcination reaction is made of hard ferrite magnetic powder. The ferrite magnetic powder is further made into magnetic powder particles having a particle size of 1 μm or less through coarsely pulverized and finely ground processes, and is made of anisotropic hard ferrite permanent magnets through a molding process and a sintering process in a magnetic field.

However, the prior art has a problem that it is difficult to oxidize and crush the mill scale to the iron oxide level compared to the hard ferrite manufacturing method using iron oxide, it is difficult to produce a hard ferrite of high characteristics.

Therefore, the present invention provides a method for producing a hard ferrite magnetic powder which can improve the magnetic properties by mixing a small amount of sodium nitrate or potassium nitrate or ammonium nitrate as an oxidizing agent in advance with a mill scale to improve the oxidization and grinding properties of the mill scale. Its purpose is.

1 is a conventional hard ferrite manufacturing process and manufacturing process diagram of the present invention

(Except conventional-oxidizer addition process, this invention-oxidizer addition process included)

Method for producing a hard ferrite magnetic powder of the present invention for achieving the above object,

First milling the mill scale from which foreign substances have been removed;

Mixing the oxidant with the millscale powder,

Oxidizing the millscale powder to which the oxidizing agent is added,

Second milling the oxidized millscale powder to a predetermined particle size,

It comprises a step of mixing and calcining the milled millscale powder in the appropriate molar ratio with strontium carbonate or barium carbonate as an auxiliary material.

Hereinafter, the present invention will be described in detail.

In the technical field of producing hard ferrite powder, a process of oxidizing by-products such as mill scale to be pulverized into high purity iron oxide and then mixing subsidiary materials (barium carbonate or strontium carbonate) is formulated. However, it is difficult to oxidize and grind mill scale to iron oxide level and to grind it.

The inventors of the present invention show that, unlike the conventional method, a small amount of oxidizing agent is first mixed with a mill scale, and then oxidized to improve the degree of oxidation of the mill scale. This improvement has been found. The production process of the present invention completed based on this finding will be described in detail.

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.

The mill scale from which foreign matters 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.

A small amount of oxidant is mixed into the first milled millscale. The oxidizing agent can be used as long as it can be removed in the oxidation process in the form of a solid powder that is easily mixed with a mill scale, which is a solid powder, rather than a liquid oxidizing agent. A typical example is nitrate, which is inexpensive and volatilized and removed during oxidation. The nitrate is one selected from the group of sodium nitrate, potassium nitrate and ammonium nitrate. The mixing amount of the oxidizing agent is preferably 0.05 to 5 parts by weight based on 100 parts by weight of the mill scale. If the amount of the oxidizing agent is less than 0.05 parts by weight, the amount of the oxidant is too small to improve the oxidization and pulverization of the mill scale, and if it is more than 5 parts by weight, the oxidant is relatively expensive compared to the mill scale, the economical efficiency. Mixing of the oxidant to the mill scale may be carried out while charging the pulverized mill scale into the hopper while adding a small amount of oxidant at a constant rate.

The mill scale powder to which the oxidizing agent is added is oxidized to make the mill scale more than about 98% of the α-Fe ₂ O ₃ component. Oxidation treatment conditions at this time are carried out at a temperature of about 500 ~ 800 ℃. If the heat treatment temperature is lower than 500 ° C, satisfactory levels of iron oxide (Fe ₂ O ₃ ) are not obtained. If the heat treatment temperature is higher than 800 ° C, the process cost increases and the mill scale partially melts, which adversely affects the efficiency of the grinding operation. Can be crazy

The oxidized powder is then milled second. Secondary grinding is preferably pulverized to about 3 μm or less. The present inventors have confirmed that the pulverized property of the oxidized powder is improved due to the increase in the degree of oxidation compared to the conventional due to the addition of the oxidizing agent. Therefore, at the same time, the powder to which the oxidant is added can be pulverized even more.

The secondary milled mill scale is mixed with strontium carbonate or barium carbonate as a subsidiary material by a wet dispersion mixing process, and the mixing ratio is 1 in which the hard ferrite phase exhibiting magnetic properties is (Ba, Sr) O.6Fe ₂ O ₃ . In consideration of the mole side feed and the 6 moles of iron oxide, the sub raw material and the oxidized mill scale are mixed in a molar ratio of 1: 5.6 to 6.1. The powder mixed with the subsidiary materials in a suitable molar ratio 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

A mill scale having a composition of Table 1 is introduced into a mill scale on a 20 mm level, and then filtered through the lower vibrating screen to remove this material and the like to obtain only a 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. The mill scale primary grinding is stored in the feed hopper at a constant speed through a conveyer such as a screw conveyor or bucket elevator. At this time, the oxidizing agent sodium nitrate (NaNO3) When the addition amount was changed with respect to the part, it was added at a constant speed so as to mix with the mill scale grinding powder in the hopper.

Mill scale powder containing sodium nitrate, an oxidizing agent, was used in a rotary kiln to oxidize the mill scale's FeO component to at least 98% of α-Fe ₂ O ₃ . Oxidation was carried out continuously for about 1 hour. During oxidation, these substances, such as oils attached to the surface of the mill scale, were also volatilized and removed. The oxidized mill scale 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).

The milled second mill scale and barium carbonate were mixed in a 5.8: 1 molar ratio by wet mixing and dispersing, and then introduced into a calcination furnace after dehydration. In the rotary calcination furnace, the temperature of the ferritic reaction zone was maintained at 1250 ° C. and the oxygen concentration was maintained at 8% or higher. Ba-ferrite (BaO · 6Fe ₂ O ₃ ) calcining powder was prepared by the calcination process. 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.

The magnetic properties of Ba-ferrite prepared using a mill scale with improved oxidizing and pulverizing properties by adding a small amount of sodium nitrate, an oxidizing agent, in the present invention added as an oxidizing agent in the prepared Ba-ferrite using a BH tracer One result is shown in Table 2.

Oxidizer Compounding Ratio Magnetic properties Mill scale Sodium Nitrate Blend Residual magnetic flux density (G) Oe Maximum Magnetic Energy (MGOe) 100 parts by weight 0.00 parts by weight 3800 1850 3.40 0.05 parts by weight 3900 1950 3.50 1 part by weight 4000 2000 3.60 5 parts by weight 4020 2030 3.65 6 parts by weight 4020 2050 3.65

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, potassium nitrate (KNO ₃ ), which is an oxidizing agent, was weighed at 0.5 parts by weight based on 100 parts by weight of mill scale and charged at a constant speed so as to be mixed with the mill scale grinding powder in a hopper. The mill scale powder to which the oxidant was added was oxidized while mixing by rotational force continuously in a rotary furnace within a temperature range of about 600 to 800 ° C. The oxidized millscale powder was cooled with a screw cooler, charged into a vibratory mill, and dry pulverized secondly to 2 μm or less. The secondary milled mill scale and the subsidiary material strontium carbonate were mixed in a wet mixing ratio by 6.0: 1 molar ratio through a mixing process and introduced into a calcining furnace after 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 prepared by using a small amount of potassium nitrate as an oxidizing agent in the present invention, the oxidative property and the crushability are improved, the residual magnetic flux density is 4050 G or more, the intrinsic coercive force is 3000 Oe or more, High magnetic properties with a maximum magnetic energy of 4.1 MGOe were shown.

On the other hand, Sr-ferrite was manufactured in the same manner except that potassium nitrate (KNO ₃ ) was replaced with the same amount of ammonium nitrate. The magnetic properties of Sr-ferrite were more than 4050 G in residual magnetic flux density and 2950 intrinsic coercive force. It showed high magnetic properties similar to the case of using potassium nitrate above Oe and maximum magnetic energy of 4.05 MGOe.

As described above, the present invention has a useful effect in that the magnetic properties can be improved and mass-produced by producing a hard ferrite using a mill scale by adding a small amount of an oxidizing agent and improving the oxidizing property and the crushability.

Claims (8)

delete First milling the mill scale from which foreign substances have been removed; Mixing the nitrate oxidant with the millscale powder, Oxidizing the millscale powder to which the oxidizing agent is added, Second milling the oxidized millscale powder to a predetermined particle size, A method for producing a hard ferrite magnetic powder using a mill scale comprising the step of mixing the pulverized mill scale with one kind of strontium carbonate or barium carbonate as a secondary raw material and calcining the mixed powder. The method of claim 2, wherein the nitrate is sodium nitrate, potassium nitrate, or ammonium nitrate. The method according to claim 2 or 3, wherein the amount of the oxidizing agent is 0.05 to 5 parts by weight based on 100 parts by weight of the mill scale. The method of claim 2, wherein the first milling of the mill scale is 5 µm or less, and the second milling of the oxidized mill scale powder is 3 µm or less. . The method of claim 2, wherein the raw material strontium carbonate or barium carbonate and mill scale are mixed in a molar ratio of 1: 5.6 to 6.1. The method of manufacturing a hard ferrite magnetic powder using a mill scale according to claim 2, wherein the oxidation treatment is performed in a temperature range of 500 to 800 ° C. 3. The method of claim 2, wherein the calcination is performed at 1200 to 1300 ° C.