KR20140087361A - Method for reduction of iron powders - Google Patents

Abstract

An iron powder reducing method is disclosed. According to an embodiment of the present invention, the iron powder reducing method comprises a step of evenly mixing an iron powder having oxidized surfaces and a carbon powder; a step of making pellets from the mixed powder; a step of reducing the pellets by heating; and a step of separating the pellets into particles. The iron powder reducing method according to the present invention is capable of reducing production costs of the iron powder by replacing an expensive carbon powder with a cheap carbon powder.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for reducing iron powders,

More particularly, the present invention relates to a method for reducing an iron-based powder, and more particularly, to a method for reducing an iron-based powder by uniformly mixing an oxidized iron-based powder with carbon powder and forming a pellet through uniaxial molding to induce mutual reaction at a high temperature, The present invention relates to a reduction method of an iron-based powder having an economical efficiency.

Recently, the use of iron-based powder, which is used as a main raw material for components, has been rapidly increasing due to the development of complex sintering parts industry required for automobiles and machines.

Parts for sintering is physically in the molded body obtained by then filling the mold interior with the shape of the part to be prepared mixing together raw material for iron-based powder with a lubricant and alloying powder, and added to 4 ~ 7 ton of / cm ² pressure compression molding And a high-temperature heat treatment is performed in a non-oxidizing atmosphere to obtain a sintered part having desired characteristics to impart mechanical properties.

In particular, in order to manufacture sintered parts for automobiles, the iron-based powder as a raw material must have adequate quality such as proper particle size, flowability, apparent density, molding density and cleanliness, so that a high-density sintered body can be mass-produced without defects.

The powders produced by the water injection process have an unavoidable oxide layer on the surface due to the reaction of Fe + H2O → FeO + H2 by contact with the molten liquid droplets at a high temperature exceeding 1,500 ° C and the jet / cooling water. Further, the internal structure becomes a structure having a high hardness value due to the quenching effect in the process of immersing in a large amount of water. Therefore, it is possible to obtain the powder having excellent moldability as described above through an annealing process for removing the oxide layer and softening the internal structure.

Conventionally, a process capable of simultaneously removing the oxide layer and softening internal structure has been applied by maintaining a hydrogen atmosphere in a continuous furnace heated to a temperature range of 800 to 1,000 ° C. However, There is a problem that the process cost is increased due to the use of a large amount of hydrogen.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems,

The present invention provides an iron-based powder reduction method capable of reducing the process cost by using carbon powder such as graphite as a reducing agent instead of using conventional hydrogen.

In addition, by using the rapid reaction rate between the carbon powder and the surface oxide layer of the iron-based powder, it is possible to reduce the process time compared with the conventional hydrogen reduction process, thereby reducing the reduction of the iron- Method.

To achieve the above object, a method for reducing iron-based powder according to an embodiment of the present invention includes uniformly mixing an oxidized iron-based powder and a carbon powder, pelletizing the mixed powder, Heating and reducing the pellet, and disposing the reduced pellet.

The iron-based powder whose surface is oxidized may be one produced by a water jet process.

The carbon content of the carbon powder may be 85 wt% or more.

The carbon powder may be graphite or coal powder.

The mixing time of the iron-based powder and the carbon powder may be 10 to 30 minutes.

The pelletizing step may be performed by uniaxial molding by a high-pressure press.

The molding pressure of the uniaxial molding may be 100 to 1,000 MPa.

The size of the pellets may be 20 mm or less in diameter and 50 mm or less in thickness.

The reducing step may be performed by heating at 750 to 1,100 ° C in a continuous high temperature furnace.

The method for reducing iron-based powder according to the present invention has the following effects.

First, unlike hydrogen, surface-reducing agent of iron-based powder can be reduced in cost by mixing a low-cost carbon powder with an iron-based powder and reducing it through mutual reaction.

Second, when mixing iron powder and carbon powder, pelletization using a high-pressure press increases the contact area, thereby increasing the reaction surface area to increase the reduction rate, thereby increasing the productivity and reducing the manufacturing cost accordingly have.

1 is a process diagram of a method for reducing iron-based powder according to an embodiment of the present invention.
2 is a schematic diagram of a method for reducing iron-based powder according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a method of reducing iron-based powder according to a preferred embodiment of the present invention will be described.

1 is a process diagram of a method for reducing iron-based powder according to an embodiment of the present invention. 2 is a schematic diagram of a method for reducing iron-based powder according to an embodiment of the present invention.

Referring to FIGS. 1 and 2, an embodiment of the present invention includes a method of uniformly mixing a surface iron oxide powder and a carbon powder using a powder mixing apparatus (S10), mixing the powder with a high- A step (S20) of pelletizing the formed pellets, a step (S30) of charging the formed pellets into a continuous high-temperature furnace, and a step (S40) of applying a shock to the pellets after reduction.

The surface iron oxide powder and the carbon powder are uniformly mixed using a powder mixing apparatus. (S10) The surface iron oxide powder can be an iron-based powder having a constant oxide layer formed on the surface thereof and manufactured by an aqueous spraying process. The water injection process is a process of spraying a high-pressure water of 100 bar or more through a special nozzle through a special high-pressure pump onto a free-falling steel stream and pulverizing it. The water injection method may be V-jet, Annular, Straight type, The temperature of the molten steel may range from 1,500 to 1,650 ° C.

The surface iron oxide powder produced in the water injection process may be water-less than 0.1 wt% through dehydration and drying process after water spraying.

The carbon powder to be mixed may be graphite or coal powder, and the carbon content is preferably 85 wt% or more. Generally, graphite or coal powder contains ash components in addition to carbon components. The constituent materials of ash generally include oxides such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MgO, CaO, K ₂ O, Na ₂ O, TiO ₂ and P ₂ O ₅ .

When the carbon content is less than 85 wt%, the oxides should be separated by magnetic separation after the reduction and destruction process is completed. However, in order to drop the oxide to below the regulation value of 0.15 wt% The process becomes complicated and the process time may become longer.

A V-mixer, a double-cone mixer, or the like may be used as the apparatus used in the mixing process, but the present invention is not limited thereto as long as the powders can be uniformly mixed.

The time required for the mixing process is preferably 10 to 30 minutes. When the mixing time is less than 10 minutes, the uniformity of the mixed powder is lowered, and after the pelletization, the carbon powder is unevenly distributed in the pellets, making it difficult for the reduction reaction to completely take place. Thus, the surface oxide layer of the iron- A problem may arise. When the mixing time exceeds 30 minutes, the uniformity improvement of the powder is not further improved.

When the mixing is completed, the mixed powder is pelletized by uniaxial pressing using a high-pressure press apparatus. (S20)

The pelletization of the mixed powder not only suppresses the scattering of the powder in the subsequent process but also facilitates the reduction process because the contact area between the surface oxide layer of the iron-based powder and the carbon powder is widened.

It is preferable that the molding pressure in the high-pressure press apparatus at the time of uniaxial molding is 100 to 1,000 MPa. When the molding pressure is less than 100 MPa, the molding pressure is too low, so that the mixed powder compact recovered from the high-pressure press is not strong enough to maintain its shape and can be destroyed before the reduction process. This is because scratches may be applied to the inner wall of the press mold or plastic deformation or destruction of the mold may occur due to high pressure.

The size of the pellet is preferably 200 mm or less in diameter and 50 mm or less in thickness. If the diameter of the pellet exceeds 200 mm, the load applied to apply the desired pressure in the high-pressure press increases as the diameter increases, so that the high-pressure press apparatus becomes excessively large, and the equipment cost and space can be wasted. If the thickness of the pellet exceeds 50 mm, the reaction between the surface oxide layer of the iron-based powder and the carbon powder at the center of the pellet does not occur smoothly and the reaction is not terminated, so that the desired oxygen and carbon content can not be obtained in the final product.

After the pellet is formed, it is charged into a continuous high-temperature furnace to be reduced (S30)

The temperature inside the continuous high-temperature furnace is preferably 750 to 1,100 ° C. When the temperature inside the high-temperature furnace is less than 750 ° C, the reaction rate between the surface oxide layer of the iron-based powder and the carbon powder is slowed, and the process time exceeds 1 hour, so that the productivity improvement effect may be insufficient compared to the conventional hydrogen reduction process. If the temperature inside the high-temperature furnace is higher than 1,100 ° C, sintering occurs between the powders, excessive time is taken for the refining process, and the average size and shape of the reduced iron-based powder particles are changed, .

After the reduction process is completed, impact is applied to the pellets collected (S40)

In the refining process, a shock is applied to separate weakly bound iron particles from each other in a high-temperature reduction process. When the iron particles having a size of 60 to 80 mesh are disposed at the lower portion thereof, .

Hammer crusher, Jaw crusher, Roll crusher and the like can be used as the device used in the deburring process, but the present invention is not limited thereto.

The recovered iron-based powder collected in the collection vessel may further include a step of separating the impurities additionally in accordance with the difference in density through a centrifugal separator.

Hereinafter, a method for reducing iron-based powder according to the present invention will be described in more detail with reference to examples.

500 kg of the iron-based powder prepared by spraying high-pressure water of 150 bar into free-falling molten steel was dewatered and dried to completely remove water and then charged into a double-cone mixer. Then, graphite with a carbon content of 98 wt% 7 kg of the powder was further charged into the mixer, followed by mixing at a rotation speed of 30 rpm for 20 minutes.

The powder was recovered from the mixer, charged into a cylindrical mold having a diameter of 150 mm, uniaxially molded at a pressure of 200, 400, 600 and 800 MPa using a high-pressure press to obtain pellets. Various pressure conditions are set to confirm the reduction effect according to the contact area between the surface iron oxide powder and the graphite powder. Regardless of the applied molding pressure, the pellet size was adjusted to 150 mm in diameter and 40 mm in height by controlling the amount of powder charged into the mold.

The molded pellets were charged to a high temperature furnace capable of continuous operation by applying a conveyor belt. In order to confirm the effect of temperature on the reduction reaction in the high temperature furnace, the reduction process was performed by controlling the temperature to 750, 850, 950 ℃.

In order to specifically calculate the effect according to an embodiment of the present invention, the reduction process according to an embodiment of the present invention is performed, and at the same time, the reduction process of the iron-based powder according to the prior art is performed in a hydrogen atmosphere, The effects (Table 1) and economic efficiency (Table 2) were compared.

The initial oxygen content of the iron-based powder produced by the water jet process was 2.01 wt%, and the carbon content was 0.02 wt%.

division Molding pressure
(MPa) Reduction temperature
(° C) After reduction
Carbon content
(wt%) After reduction
Oxygen content
(wt%) Reduction time
(minute) Inventory 1
200 750 0.004 1.32




30 Inventory 2 850 0.002 1.16 Inventory 3 950 0.002 0.77 Honorable 4
400 750 0.003 1.18 Inventory 5 850 0.002 0.83 Inventory 6 950 0.002 0.55 Honorable 7
600 750 0.003 0.79 Honors 8 850 0.003 0.41 Proposition 9 950 0.002 0.14 Inventory 10
800 750 0.002 0.64 Exhibit 11 850 0.003 0.15 Inventory 12 950 0.001 0.10 Comparative Example 1
- 750 0.004 0.98
60 Comparative Example 2 850 0.003 0.59 Comparative Example 3 950 0.002 0.12

As shown in Table 1, in the case of Inventive Examples 9, 11 and 12, it was confirmed that the limits of carbon and oxygen content required in the final product are 0.003 wt% and 0.15 wt%, respectively. In the conventional reduction process using hydrogen, only Comparative Example 3 satisfied the limits of the carbon and oxygen content.

In case of Examples 9, 11 and 12, it was found that the time required for the reduction was 30 minutes, which was reduced to half compared with 60 minutes of the conventional process, and the productivity was doubled.

As productivity improves, the amount of LNG gas consumed to maintain the temperature of the reducing furnace is reduced to half per unit production, thus reducing energy consumption during heating.

Cost factor Comparative Example 3 Examples 9, 11, 12 Raw material cost Hydrogen (unit price 650 won / Nm ³ )
25kg per 1Nm ³ Reduction of surface iron oxide
→ KRW 2.6 million / ton Graphite powder (unit price 700 won / kg)
71kg per 1kg Reduction of surface iron oxide
→ 10 million won / ton Reduction cost Surface iron oxide 5 ton / hour
LNG (price of 286 won / Nm ³ )
LNG 480Nm ³ / hour use
→ 2.8 million won / ton Surface iron oxide 10 ton / hour
LNG (price of 286 won / Nm ³ )
LNG 480Nm ³ / hour use
→ 14,000 Yuan / ton Sum 5.4 million Yuan / ton 2.4 million won / ton

As shown in Table 2, when compared with the process of reducing pellets formed by mixing the surface iron oxide powder with the graphite powder as shown in one embodiment of the present invention using conventional hydrogen, The total reduction of KRW 14,000 / tonne can be saved by KRW 30,000 / ton.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (6)

Uniformly mixing the surface-oxidized iron-based powder and the carbon powder;
Pelletizing the mixed powder through uniaxial molding;
Heating and reducing the pellet; And
Disposing the reduced pellet;
Based powder. The method of claim 1,
Wherein the carbon powder has a carbon content of 85 wt% or more. The method of claim 1,
Wherein a mixing time of the iron-based powder and the carbon powder is 10 to 30 minutes. The method of claim 1,
Wherein the uniaxial forming pressure is 100 to 1,000 MPa. 5. The method according to any one of claims 1 to 4,
Wherein the size of the pellet is 20 mm or less in diameter and 50 mm or less in thickness. The method of claim 5,
Wherein the reducing step is performed by heating at 750 to 1,100 ° C in a continuous high temperature furnace.

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