PRODUCING METHOD OF SINTER
BACKGROUND OF THE INVENTION Field of the Invention
[0001]
The present invention relates to a producing method of iron ore sinter which is used as a raw material in iron making, and particularly, to a producing method of sinter for improving product yield and strength of the upper portion of a feed bed which is formed in a sintering pallet.
Priority is claimed on Japanese Patent Application No. 2008-238448 filed on September 17,2008, the content of which is incorporated herein by reference.
Description of Related Art
[0002]
In recent years, among iron ores from Australia that are the main iron ores used in Japan, high-quality hematite ores are depleting, and in the present situation, pisolite ore deposit, Marra Mamba iron formation, and the high phosphorus Brockman iron formation are being developed.
[0003]
The iron ores which are produced from the Marra Mamba iron formation and the high phosphorus Brockman iron formation have a smaller particle size and a higher amount of combined water than high-quality hematite ore. For this reason, these iron ores cause a decrease in bed permeability and deterioration in sintering during sintering.
[0004]
The existing pisolite ore which is produced in the pisolite ore deposit is an ore
with high combined water. 90% of the iron ores which are produced in the pisolite ore
deposit, the Marra Mamba iron formation and the high phosphorus Brockman iron
formation are iron ores having a combined water content equal to or greater than 4
mass%.
[0005]
The influence on the sintering operation of a case in which a large amount of ores with high combined water are blended as a sintering feed will be described below.
[0006]
In general, production of sinter using a downward suction type sintering machine is performed as follows.
[0007]
Raw materials for iron ore sintering include an iron-containing raw material such as dust that is generated in steel works and iron ore that is a primary raw material, an auxiliary raw material such as limestone and serpentine that are necessary for sintering reaction, and a solid fuel such as coke breeze as a heat source. These raw materials are blended, and are used as the sintering feed.
[0008]
Before being charged into a downward suction type sintering machine, the sintering feed is mixed and granulated by using a mixing and granulation machine such as a drum mixer with water addition and is thus processed into a shape of granules. The granules are composed of nuclei (nuclei particles) with a particle diameter equal to or larger than 1 mm and adhering fines which are adhered therearound and have a particle diameter equal to or smaller than 0.5 mm.
[0009]
By charging the granulated sintering feed into the sintering machine,
permeability of the bed in a sintering pallet being maintained, the sintering reaction of
the sintering feed is promoted, and high productivity can be ensured.
[0010]
The granulated sintering feed is charged into the sintering pallet from a charging apparatus and forms a packed bed of feed. After that, by ignition, the coke breeze on the surface of the feed bed starts to burn. With the air suction to the lower portion of the sintering machine, the combustion zone of the coke moves to the lower side of the feed bed.
[0011]
The sintering reaction sequentially proceeds from the upper layer to the lower layer of the bed by the combustion heat of the coke and the sintering completes by the time the sintering pallet reaches the discharge end. The sinter cake (lump) in the sintering pallet is discharged at the end and then is crushed into a predetermined particle size for a blast furnace to be a sinter.
[0012]
Since the sinter powder which is generated in the production of sinter and has a particle diameter smaller than the predetermined particle diameter cannot be used as a sinter for a blast furnace, it is blended as return fines in the sintering feed and is sintered once again.
[0013]
The sintering reaction mainly starts around 1200°C by the following initial melt generation and proceeds with a subsequent assimilation. That is, through the reaction of Fe2O3 in the iron-containing raw material and CaO in the limestone, an initial melt of calcium ferrite (CaO-Fe2O3) is generated. After that, the assimilation proceeds as the components in the iron ore and the components in the auxiliary raw material dissolve in
this initial melt.
[0014]
This sintering reaction is an extremely rapid reaction which is completed in a few minutes from the generation of the initial melt. This reaction has an influence on the product yield and productivity of the sinter, and on the quality thereof such as strength.
[0015]
For example, if the sintering reaction proceeds excessively and thus the amount of the generated melt increases excessively, the permeability in the sintered layer deteriorates in the sintering operation. Since deterioration in this permeability causes sintering unevenness, the product yield and productivity decrease and the quality, such as the strength, also deteriorates.
[0016]
On the other hand, when the sintering reaction does not proceed sufficiently, the melt is reduced for bonding un-melted portions such as relict ore (residual original ore) to each other, and thus the product yield decreases and the quality of the sinter such as the strength and the reduction disintegration (RDI) deteriorates.
[0017]
This sintering reaction has a large influence on sinterability (the ability of assimilation) attributed to the mineral composition and the other properties of the iron ore, which is a primary raw material accounting for 60% or more thereof in the feed, and granularity (the ability of granulation) influencing the permeability of the feed bed.
[0018]
When an iron ore with high combined water such as pisolite ore is blended, the combined water derived from the goethite structure in the iron ore starts to dehydrate
around 300°C, which caused cracks in the goethite structure during this period.
[0019]
Accordingly, either pores are formed in the initial melt, or a bonded phase generates, which is coagulated when the formed pores remain, or un-melted original ore including cracks remains. As a result, the sinter becomes fragile with a porous structure and thus the product yield of the sinter decreases and the quality such as the strength deteriorates.
[0020]
In addition, when iron ore having a large amount of combined water and a small particle size, such as Marra Mamba ore and High Phosphorus Brockman ore, is blended in a sintering feed, in addition to the above-described problems caused by the combined water, granularity is worsened. Accordingly, it becomes difficult to generate strong granules, and disintegration occurs easily when the granules are conveyed or are charged into the pallet.
[0021]
Accordingly, when the feed is charged into the pallet, the un-granulated fine iron ore particles or the fine ones of iron ore which are generated due to the disintegration are segregated and distributed on the upper layer side of the feed bed, and thus the permeability in the upper layer decreases. In addition, since the goethite structure including combined water is brittle, a large amount thereof exists in iron ore particles of small diameter.
[0022]
Accordingly, the fine particles of iron ore which are segregated and distributed on the upper layer side of the feed bed pose a problem attributed to the combined water.
[0023]
In general, in the production of sinter using a downward suction type sintering
machine, the suction of the air of room temperature decreases the temperature of the
surface portion of the feed bed after ignition. Accordingly, a decrease in the product
yield of the sinter in the upper layer and a deterioration in the quality such as strength
have been conventional problems.
[0024]
These problems concerning the product yield and the quality such as strength of the sinter in the upper layer frequently occur in the sintering operation of recent years in which iron ore with high combined water and fine iron ore are blended as a sintering feed.
[0025]
Up to now, a number of methods of improving the product yield and the quality such as the strength of the upper layer of a feed bed in the production of sinter using the downward suction type sintering machine have been proposed.
[0026]
For example, a method (for example, see Japanese Unexamined Patent Application, First Publication No. 2000-144266) of increasing the solid fuel in the upper layer of the feed bed has been proposed.
[0027]
In addition, a method (for example, see Japanese Unexamined Patent Application, First Publication No. 2000-328148, Japanese Unexamined Patent Application, First Publication No. 2001-234257, Japanese Unexamined Patent Application, First Publication No. 2001-271122, Japanese Unexamined Patent Application, First Publication No. 2001-335849, and Japanese Unexamined Patent Application, First Publication No. 2002-130957) of charging a high FeO ferromagnetic
raw material such as return fines, mill scale or magnetite and a granulated material of a
ferromagnetic raw material and a carbon material into the surface portion of the feed bed
by a charging device using magnetism has also been proposed.
[0028]
In addition, a method (for example, see Japanese Unexamined Patent Application, Second Publication No. S60-47887) of charging iron ore having high-melting behavior into the upper layer of the feed bed and charging iron ore having low-melting behavior into the lower layer portion thereof in consideration of the assimilation melting properties of the iron ore which is blended in the sintering feed has also been proposed.
[0029]
That is, in order to increase the temperature of the surface portion of the feed bed after ignition, the solid fuel in the surface portion of the feed bed is increased, or a ferromagnetic raw material, iron ore having high-melting behavior or the like containing a large amount of FeO which easily generates a melt (CaO-SiOV2-FeO) with CaO and SiO2 in the auxiliary raw material in the surface portion of the feed bed is charged. The object of these methods is to improve the product yield and the quality such as strength of the sinter in the upper layer of the feed bed.
[0030]
However, according to these methods, since it is difficult to properly control the heat input of the upper layer of the feed bed and the melt formation, the heat input is too high or the amount of the melt increases excessively. Accordingly, the permeability in the entire feed bed deteriorates and thus problems occur in that productivity decreases and the quality, such as the reducibility of sinter, deteriorates.
[0032]
In view of the above-described problems of the conventional technique, an
object of the invention is to provide a producing method of sinter, which includes
selective charging a brand of iron ore having excellent melt penetrability into a fine
region into the upper layer of a feed bed in a producing method of sinter by using a
downward suction type sintering machine in order to prevent an excessive increase in the
amount of the melt of the upper layer of the feed bed to thereby improve the product
yield and the strength of the upper layer of the feed bed and improve the productivity of
sinter without a deterioration in permeability in the entire feed bed or a decrease in
quality such as reducibility of sinter.
SUMMARY OF THE INVENTION
[0033]
The inventors extensively studied methods of improving the product yield and the strength of the upper layer of a feed bed which is formed in a sintering pallet in the production of sinter.
[0034]
As a result, an improvement was confirmed in the product yield and the strength of the sinter in the upper layer of the feed bed by the selective charging of iron ore, of which the melt penetration length, as measured by a test of evaluating melt penetration into an iron ore powder, is equal to or longer than 4.0 mm, among a plurality of brands of iron ore constituting the sintering feed, into a predetermined range of the upper layer of the feed bed which is formed in the sintering pallet.
[0035]
In addition, it was found that according to this method, as compared to the method of increasing a solid fuel or an FeO source in the upper layer of the feed bed or
the method of charging iron ore having high-melting behavior into the upper layer of the
feed bed, which have been conventionally proposed, the product yield and the strength of
sinter in the upper layer of the feed bed can be improved without a decrease in
permeability in the entire feed bed due to the excessive generation of a melt in the upper
layer of the feed bed.
[0036]
The present invention is achieved based on the above-described finding and the main points of the present invention are as follows.
[0037]
(1) A producing method of a sinter which includes blending an iron-containing
raw material including a plurality of brands of iron ores, an auxiliary material, a solid
fuel, and return fines as a sintering feed, mixing and granulating the sintering feed,
charging the sintering feed onto a sintering pallet, and sintering the sintering feed
includes: charging a high melt-penetrable iron ore that is selected or blended from the
plurality of brands of iron ores so that a weighted average value of melt penetration
lengths thereof is equal to or greater than 4.0 mm, on the basis of the melt penetration
lengths of the iron ores which are measured for each brand, into an upper layer, wherein
an ratio of an upper layer thickness to an total bed height is in the range of 5 to 12%, the
upper layer thickness being measured from an upper surface of a feed bed which is
formed on the sintering pallet; charging the other iron ores into a lower layer of the feed
bed; and charging the auxiliary raw material, the solid fuel, and the return fines into the
upper layer and the lower layer of the feed bed.
[0038]
(2) In the producing method of a sinter according to (1), an Al2O3 content in the
high melt-penetrable iron ore may be equal to or lower than 0.6 mass%.
[0039]
(3) In the producing method of a sinter according to (1), in addition to the high
melt-penetrable iron ore, as the iron-containing raw material, a domestic scale may be
charged into the upper layer in which the ratio of the upper layer thickness to the total
bed height is in the range of 5 to 12%, the upper layer thickness being measured from the
upper surface of the feed bed.
[0040]
(4) In the producing method of a sinter according to (1), the solid fuel and the
return fines may be charged into the upper layer and the lower layer of the feed bed at the
same blending ratio.
[0041]
(5) In the producing method of a sinter according to (1), regarding the auxiliary
raw material which is charged into the feed bed, a blending ratio in the upper layer may
be equal to or lower than a blending ratio in the lower layer.
[0042]
(6) In the producing method of a sinter according to (1), the high
melt-penetrable iron may be blended with the auxiliary raw material, the solid fuel and
the return fines, mixed and granulated, and then charged into the upper layer of the feed
bed; and the other iron ores may be blended with the auxiliary raw material, the solid fuel
and the return fines, mixed and granulated, and then charged into the lower layer of the
feed bed.
[0043]
(7) In the producing method of a sinter according to (6), the high
melt-penetrable iron ore as the iron-containing raw material may be blended with the
domestic scale, blended with the auxiliary raw material, the solid fuel and the return fines,
mixed and granulated, and then charged into the upper layer of the feed bed.
[0044]
According to the present invention, in a producing method of a sinter by using a downward suction type sintering machine, the melt penetration penetrability into a fine region of each of the brands of iron ores which is blended in a sintering feed is evaluated, and a brand of iron ore having excellent melt penetration penetrability into the fine portion is selected from among the brands of iron ores on the basis of this evaluation result and is selectively charged into the upper layer of a feed bed. In this manner, the product yield and the strength of the upper layer of the feed bed can be improved and the productivity of the sinter can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045]
FIG. 1 is a microscopic diagram showing the cross sectional structure of a granule of sintering feed, taken from a sintering machine.
FIG. 2 is a graph showing the relationship between the melt penetration length of iron ore and the SI strength of sinter obtained in a sintering operation of a commercial machine.
FIG. 3 is a graph showing the relationship between the melt penetration length of iron ore and the product yield of sinter in the sintering operation of the machine.
FIG. 4 is a diagram showing a measurement position for the melt penetration length in a tablet sample after sintering.
FIG. 5 is a graph showing the comparison of the melt penetration lengths of the main brands of iron ores.
FIG. 6 is a graph showing the relationship between the melt penetration length of
iron ore and the strength index (+0.5 mm%) obtained by a drop test of sintered tablets.
FIG. 7 is a graph showing the relationship between the ratio of the thickness of an upper layer and the SI strength of sinter by sintering pot test.
FIG. 8 is a graph showing the relationship between the ratio of the thickness of the upper layer and the product yield of sinter by sintering pot test.
FIG. 9 is a graph showing the relationship between the melt penetration length of iron ore and the Al2O3 content.
FIG. 10 is a graph showing the relationship between the ratio of limestone in the upper layer and the product yield of sinter by sintering pot test.
FIG. 11 is a graph showing the relationship between the ratio of limestone in the upper layer and the SI strength of sinter by sintering pot test.
FIG. 12 is a diagram showing charging conditions of a sintering feed by sintering pot test for the examples.
FIG. 13 is a diagram showing an example of a method of charging high melt-penetrable iron ore and the other iron ores into an upper layer and a lower layer of a feed bed, respectively.
DETAILED DESCRIPTION OF THE INVENTION [0046]
First, the technical concept of the present invention will be described. [0047]
FIG. 1 is a microscopic diagram showing the cross sectional microstructure of a granule of a sintering feed, taken from a feed bed in a sintering machine. [0048] In a sintering process, an initial melt is generated in a region in which iron ore
(Fe2O3) and limestone (CaO) are in contact with each other. However, as shown in FIG.
1, according to the micro-observation of an adhered fine region (fine region) of a granule
(formed of a nucleus which has a particle diameter equal to or greater than 1 mm and an
adhered fine region which is adhered therearound and has a particle diameter equal to or
smaller than 0.5 mm) of the sintering feed, iron ore (Fe2O3) and limestone (CaO) are
distributed heterogeneously. Accordingly, the number of regions is small where these
are in contact with each other.
[0049]
For this reason, in the sintering process, the following sintering reaction proceeds. That is, an initial melt of calcium ferrite (CaO-Fe2O3) is generated in a region in which iron ore (Fe2O3) and limestone (CaO) in the adhered fine region of the granule of the sintering feed are in contact with each other. After that, the initial melt penetrates into the adhered fine region, comes into contact with the iron ore and auxiliary raw material therearound, is assimilated and coalesces repeatedly. In this manner, the amount of the melt increases and a bonded phase of sinter is formed.
[0050]
The inventors have found that a behavior penetrating into the feed bed of the initial melt generated in the sintering process, that is, the melt penetration penetrability, depends on the mineral structure of iron ore and has a large influence on the formation of a bonded phase of sinter (see ISIJ-Int. 43 (2003), p. 13 84)
[0051]
The temperature of an upper layer of the feed bed during the sintering operation easily decreases and the period of time from the initial melt formation from iron ore (Fe2O3) and limestone (CaO) to the completion of the sintering reaction (assimilation) is short. For this reason, the inventors conceived that in order to improve the product
yield of the sinter in the upper layer of a feed bed, it is effective to selectively charge the
iron ores of high melt penetration penetrability into the upper layer of the bed. Thereby,
it is possible to allow initial melt to rapidly penetrate into a fine region of the raw
material and to promote an assimilation.
[0052]
The present invention bases on this technical concept, and includes a producing method of iron ore sinter by blending an iron-containing raw material including a plurality of brands (iron ore brands) of iron ore, an auxiliary material (such as limestone), a solid fuel (such as coke), and return fines as a sintering feed, mixing and granulating the sintering feed, charging the sintering feed onto a sintering pallet, and sintering the sintering feed. The method features that an evaluation test of melt penetration is performed on each of the brands of iron ore, one or more kinds of iron ore is selected or blended from the plurality of brands of iron ore on the basis of the measured values of melt penetration lengths of the respective brands so that the melt penetration length is equal to or longer than 4.0 mm, and the selected or blended ore is charged into an upper layer so that a ratio of the upper layer thickness to the total bed height is in the range of 5 to 12%, the upper layer thickness measured from the upper surface of the feed bed (ratio of the thickness of the upper layer) which is formed on the sintering pallet.
[0053]
In the present invention, the melt penetration penetrability (ease of spread when an initial melt penetrates into an iron ore powder having a particle diameter equal to or smaller than 0.5 mm) of iron ore and the melt penetration length (penetration distance of a melt into an iron ore powder) can be evaluated and measured by the evaluation test (hereinafter, referred to as the "iron ore melt penetration evaluation test") the inventors proposed in Japanese Unexamined Patent Application, First Publication No. 2002-62290
and the like.
Regarding this melt penetration length, when two or more brands of iron ore are blended as iron ore of the sintering feed, a weighted average value of the measured melt penetration lengths of the respective brands of iron ore is used for simplification in measurement. Since then, when iron ore is used in which two or more brands of iron ore are blended, the weighted average value thereof is also represented as the melt penetration length. Further, a plurality of brands of iron ore may be blended and the melt penetration length of the blended iron ore may be measured as one brand of iron ore.
In addition, in the present invention, although the melt penetration length is evaluated by the above-described melt penetration evaluation test of the present invention, the melt penetration may be evaluated by another evaluation test and converted into the melt penetration length of the present invention. For example, the evaluation may be performed with changes in the molding pressure in the above-described iron ore melt penetration evaluation test, the size and shape of iron ore tablets and initial melt tablets, the sequence of the test and the like and the evaluation result may be converted into the melt penetration length of the present invention. In addition, for example, the period of time during which the melt penetrates by a predetermined distance may be measured and converted into the melt penetration length of the present invention, and any physical quantity such as a penetration weight or a temperature change due to an assimilation may be employed if it can be converted into the melt penetration length of the present invention.
[0054]
The iron ore melt penetration evaluation test of the present invention is performed in the following manner to measure the melt penetration length.
[0055]
An iron ore sample, the particle size of which is controlled so that the proportion of particles having a particle diameter of 0.25 to 0.5 mm is 50 mass% and the proportion of particles having a particle diameter equal to or smaller than 0.25 mm is 50 mass%, is sufficiently mixed. After that, by using a metallic mould, the iron ore sample is press-formed at a molding pressure of 4 MPa into an iron ore tablet (porosity (open porosity) due to a mercury intrusion technique: about 30%) having a diameter of 15 mm and a height of 5 mm.
[0056]
Meanwhile, regarding an initial melt source, a Fe2O3 reagent and a CaO reagent are blended so as to obtain a composition of 26 mass% of CaO and 74 mass% of Fe2O3, which is close to the eutectic composition of a binary phase diagram of CaO-Fe2O3, and are mixed by an automatic mortar for 20 minutes. After that, as in the case of the iron ore tablet, the initial melt source is pressed at a molding pressure of 4 MPa by using a metallic mould into a tablet having a diameter of 5 mm and a height of 5 mm.
[0057]
Further, the combination of the iron ore tablet and the initial melt source tablet thereon is placed in a cylindrical crucible (inner diameter 20 mm, height 15 mm) made of Ni and is heated in the air flow in an electric furnace. After the sintering, the melt penetration length is measured through the observation of the cross-section of the tablet.
[0058]
For the measurement of the melt penetration length in the tablets after the sintering, the tablet is cut vertically at the center portion in the radial direction of the tablet, the cut surface is polished and the mineral structure of the cut surface shown in FIG. 4 is observed by an optical macroscope. It is preferable that in the photograph of
the cross-section, the penetration length be measured at the three points, which are the
center portion (3) shown in FIG. 4 in the width direction (in the radial direction of the
tablet) of the region into which the melt penetrates and the intermediate points (2) and (4)
which are between the center portion (3) and the outer ends (1) and (5), respectively, and
the melt penetration length be obtained from the average value of the measured values.
[0059]
In the above-described evaluation test, the heat pattern of the tablet sintering is set to be similar to that of a sintering machine. That is, the tablet is heated for 1 minute from 1100°C to 1290°C (maximum temperature), and then is cooled for 3 minutes from 1290°C to 1100°C and immediately picked out to the outside of the furnace to be air-cooled.
[0060]
In the practical sintering operation using an iron-containing raw material including a plurality of brands of iron ore, FIG. 2 shows the relationship between the melt penetration length of the iron ore and the SI strength of the sinter and FIG. 3 shows the relationship between the melt penetration length of the iron ore and the product yield of sinter.
[0061]
SI, which is an index showing the strength of sinter, is measured by sampling 10 kg of sinter having particle diameter of 10 to 25 mm from the sinter after the product yield measurement and dropping it 4 times from a height of 2 m. This SI indicates a ratio (mass%) of mass (kg) of sinter after dropping which has a particle diameter equal to or larger than 5 mm to the mass (kg) of sinter before dropping.
[0062]
The product yield of sinter is measured by dropping a sinter cake (lump) 5 times
from a height of 2 m. This product yield of sinter indicates a ratio (mass%) of mass
(kg) of sinter (however, excluding bedding ore) after dropping which has a particle
diameter equal to or larger than 5 mm to mass (kg) of a sinter cake (lump) (however,
excluding bedding ore) before dropping.
[0063]
According to FIGS. 2 and 3, it is found that when the melt penetration length increases in the sintering feed including a plurality of brands of iron ore, the product yield and the SI of sinter are improved.
[0064]
That is, these results show that the method of controlling the blending of the respective brands of iron ore in the sintering feed on the basis of the melt penetration length as an index of melt penetration ability of iron ore is effective at improving the product yield and the strength of sinter produced by a practical machine.
[0065]
As shown in FIGS. 2 and 3, in a live sintering operation, the SI strength of sinter is required to be equal to or greater than 90.5% and the product yield is required to be equal to or greater than 80.0%.
[0066]
Next, in the present invention, the proper range of the melt penetration ability of iron ore which is necessary to improve the strength and the product yield (SI strength: equal to or greater than 90.5%, product yield: equal to or greater than 80.0%) of the sinter in the upper layer of a feed bed, that is, the melt penetration length which is measured by the melt penetration evaluation test, will be described.
[0067]
Table 1 shows the chemical compositions of the main brands of iron ore which
are blended in a sintering feed, and melt penetration lengths which are measured by the
melt penetration evaluation test.
[0068]
[Table 1]
(Table Removed)
[0069]
In Table 1 , B(a) and B(b) are ores from Brazil, H(a) and H(b) are hematite ores from Australia, and M(a) and M(b) are Marra Mamba ores from Australia. HP(a) and HP(b) are high phosphorus ores from Australia, P(a) and P(b) are pisolite ores from
Australia, HPM is a pre-blended ore from Australia, and 1(a) and 1(b) are ores from India.
In addition, S1 and S2 are domestic scales.
[0070]
FIG. 5 is a graph showing the comparison of the melt penetration lengths of the main brands of iron ore shown in Table 1. The Table 1 and FIG 5 show that either of ores B(a) or B(b) from Brazil are equal to or longer than 4.0 mm in the melt penetration lengths among the main brands of iron ores.
[0071]
Meanwhile, the figure shows that hematite ores H(a) and H(b) from Australia, high phosphorus ores HP(a) and HP(b) from Australia and pisolite ores P(a) and P(b) from Australia are equal to or shorter than 2.0 mm in the melt penetration length.
[0072]
In addition, the figure shows that the melt penetration lengths of pre-blended ore HPM from Australia, Marra Mamba ores M(a) and M(b) from Australia and 1(a) and 1(b) from India are in a range longer than 2.0 mm and shorter than 4.0 mm.
[0073]
The Australian pisolite ores P(a) and P(b) are known as an iron ore having high-melting behavior, i.e. they are easily assimilated and melted in the sintering reaction. However, this figure shows that the Australian pisolite ores P(a) and P(b) have a short melt penetration length equal to or shorter than 2.0 mm and are poor in melt penetration penetrability. In addition, the domestic scales S1 and S2 show different melt penetration lengths.
[0074]
Next, by using the plurality of brands of iron ores of Table 1, which are different from each other in melt penetration ability, the improvement effect of the strength and the product yield of sinter when these iron ores were selectively charged into the upper layer of a sintering feed bed was confirmed by the tablet sintering test.
[0075]
As samples for the tablet sintering test, the plurality of brands of iron ores shown in Table 1 were crushed so that the particle size was controlled to contain 50 mass% of iron ore having particle diameter of 0.25 to 0.25 mm and 50 mass% of iron ore having particle diameter equal to or smaller than 0.25 mm. Limestone of 0.25 mm or less was mixed to these respective iron ores so that the concentration of CaO was 10 mass%.
[0076]
These samples were press-formed into tablets (porosity of about 30%) having a diameter of 8 mm and a height of 10 mm at a molding pressure of 4 MPa by using a metallic mould.
[0077]
In the tablet sintering test, the sample tablets were put in a cylindrical crucible made of Ni and having an inner diameter of 20 mm and a height of 15 mm and were sintered in the air flow in an electric furnace. For the tablet sintering conditions, a sintering heat pattern was set to be similar to that of a sintering machine. That is, the tablets were heated for 1 minute from 1100°C to 1290°C (maximum temperature), and then were cooled for 3 minutes from 1290°C to 1100°C and immediately picked out to the outside of the furnace to be air-cooled.
[0078]
In the evaluation of the strength of the sintered tablets after the sintering, a drop test was performed of dropping a 300 g iron weight 3 times per one sintered tablet. The samples (sintered tablets) after the drop were mixed and then classified by a 0.5 mm
sieve. As a strength index (+0.5 mm%), a mass percentage of the samples having a size
equal to or larger than 0.5 mm to the mass of all the samples was used.
[0079]
In a practical sintering operation, the SI strength of sinter is required to be equal to or greater than 90.5% and the product yield is required to be equal to or greater than 80.0%.
[0080]
In order to establish the strength correlation of the sintered tablets to sinter, the plant sinter the SI strength of which was equal to or greater than 90.5% and the product yield was equal to or greater than 80.0%, was sampled in advance and the above-described drop test was performed thereon. In this drop test, tablet samples were processed in the same shape as that of sinter for a pot test, that is, a tablet shape having a diameter of 8 mm and a height of 10 mm. The strength index (+0.5 mm%) measured in this drop test was applied to the correlation.
[0081]
The strength index (+0.5 mm%) measured by the above-described drop test by using the sinter was 88%. Here, the SI strength of the sinter was equal to or greater than 90.5% and the product yield was equal to or greater than 80.0%. Accordingly, in the strength evaluation of the sintered tablets, the sintered tablets satisfying the strength index (+0.5 mm%) of the drop test of 88% or greater were judged to be excellent in strength and product yield of sinter.
[0082]
FIG. 6 shows the relationship between the melt penetration lengths of the brands of iron ore obtained by the tablet sintering test and the strength index (+0.5 mm%) obtained by the drop test.
[0083]
As shown in FIG. 6, equal to or longer than 4.0 mm in the melt penetration length is required to achieve 88% or greater in the strength index (+0.5 mm%) of the drop test, which realizes a target strength (SI equal to or greater than 90.5%) of sinter in practice.
[0084]
Specifically, the Brazilian ores B(a) and B(b), shown in Table 1, were exemplified as the iron ore brands having a melt permeability corresponding to the melt penetration length equal to or longer than 4.0 mm.
[0085]
In the present invention, in order to improve the strength and the product yield (SI strength equal to or greater than 90.5%, product yield equal to or greater than 80.0%) of sinter in the upper layer of a sintering feed bed, one or more kinds of iron ore is charged into a predetermined range of the upper layer of the sintering feed bed so that the melt penetration length of the upper layer is equal to or longer than 4.0 mm.
[0086]
As described above, when the iron ore which is charged into a predetermined range of the upper layer of the sintering feed bed includes two or more brands of iron ores, a blending ratio of the two or more brands of iron ores is controlled so that the weighted average value of the melt penetration lengths of the respective brands of iron ores which are measured by the melt penetration evaluation test is equal to or greater than 4.0 mm.
Hereinafter, the one or more kinds of iron ores which are selected or blended so that the melt penetration length is equal to or longer than 4.0 mm will be defined as high melt-penetrable iron ore.
[0087]
FIG. 7 shows the relationship between the ratio of the thickness of the upper layer which is charged with high melt-penetrable iron ore and the SI strength of sinter. Similarly, FIG. 8 shows the relationship between the ratio of the thickness of the upper layer and the product yield of sinter.
[0088]
SI, which is an index showing the strength of sinter, is measured by sampling 10 kg of sinter having a particle diameter of 10 to 25 mm from sinter after the below product yield measurement and dropping it 4 times from a height of 2 m. This SI indicates a ratio (mass%) of mass (kg) of sinter after dropping which has a particle diameter equal to or greater than 5 mm to the mass (kg) of sinter before dropping.
[0089]
The product yield of sinter is measured by dropping a sinter cake (lump) 5 times from a height of 2 m. This product yield of sinter indicates a ratio (mass%) of mass (kg) of sinter (however, excluding the bedding ore) after dropping which has a particle diameter equal to or larger than 5 mm to the mass (kg) of a sinter cake (lump) (however, excluding the bedding ore) before dropping.
[0090]
FIGS. 7 and 8 show test results when high melt-penetrable iron ore and the other iron ores are charged into an upper layer (A portion) and a lower layer (B portion) of a sintering pot, shown in FIG. 12, having a height of 600 mm and a diameter of 300 mm, and are sintered. Limestone, coke and return fines are blended so that 5.01 mass% of SiO2, a ratio of CaO/ SiO2 of 1.89 and 4.3 mass% of coke remain constant in the sintering feed as an average value of the upper layer (A layer) and the lower layer (B layer). These sintering feeds are used after being granulated to have 7.0 mass% of
granulation moisture. Herein, the other iron ores means iron ores excluding the iron ore
charged into the upper layer.
[0091]
Regarding the sintering conditions of this sintering pot test, the total bed height is 600 mm, the suction negative pressure is 14.7 KPa and the sintering time is 27 minutes.
[0092]
The strength and the product yield of the sinter in this sintering pot test were evaluated on the basis of 77% of the SI strength of sinter and 76% of the product yield. These values were obtained by performing the sintering pot test thereon with the use of the sintering feeds under the blending conditions shown in Table 2, confirming in advance that the SI strength of the sinter is equal to or greater than 90.5% and the product yield is equal to or greater than 80.0% in practice. Accordingly, these values can realize the SI strength (equal to or greater than 90.5%) of sinter and the product yield (equal to or greater than 80.0%) which are targets of the practical sintering operation.
[0093]
That is, in the sintering pot test, it was evaluated that when the SI strength of sinter is equal to or greater than 77% and the product yield is equal to or greater than 76%, the strength and the product yield of the sinter are excellent.
[0094]
As shown in FIGS. 7 and 8, in order to achieve 77% or greater of the SI strength of sinter of the above-described sintering pot test and 76% or greater of the product yield, the ratio of the thickness of the upper layer (ratio of the upper layer thickness of the feed bed to the total bed height) which is charged with high melt-penetrable iron ore is required to be in the range of 5 to 12%.
[0095]
When the ratio of the thickness of the upper layer which is charged with high melt-penetrable iron ore is lower than 5%, the improvement effect of the product yield, the strength and the production rate of sinter in the upper layer of the feed bed by selective charging of iron ore having excellent melt penetrability cannot be sufficiently obtained.
[0096]
When the ratio of the thickness of the upper layer which is charged with high melt-penetrable iron ore is higher than 12%, as described later, granularity of the iron ore having high melt penetrability is low, granules are disintegrated when being charged into a sintering machine and in the course of sintering, permeability in the feed bed decreases easily. Accordingly, sinterability of the entire feed bed deteriorates, and the product yield, the strength and the production rate of sinter deteriorate.
[0097]
In addition, as described later, the iron ore having high melt penetrability is iron ore which has a low Al2O3 content and is relatively expensive. Accordingly, it becomes a cause of an increase in the production costs of sinter.
[0098]
From the above-described reasons, in order to sufficiently improve the product yield and the strength of the upper layer of a feed bed (SI strength equal to or greater than 90.5%, product yield equal to or greater than 80.0%) without a decrease in permeability in the entire feed bed, high melt-penetrable iron ore, which is selected or blended among a plurality of brands of iron ores so that a weighted average value of melt penetration lengths is equal to or greater than 4.0 mm, is charged into the upper layer which is in the range of 5 to 12% regarding to the ratio of the upper layer thickness to the total bed
height from the upper surface of a feed bed, the other iron ores are charged into the lower
layer of the feed bed, and an auxiliary raw material, a solid fuel and return fines are
charged into the upper layer and the lower layer of the feed bed. The blending ratio of
the auxiliary raw material, the solid fuel and the return fines is the same in the upper
layer and in the lower layer of the feed bed as long as they are not particularly specified.
[0099]
In addition, the domestic scales S1 and S2 may be added to the high melt-penetrable iron ore to be charged into the upper layer as an iron-containing raw material having the ratio of the thickness of the upper layer in the range of 5 to 12%. Similarly, the above-described scales Sl and S2 may be added to the other iron ores to be charged into the lower layer as an iron-containing raw material. Hereinafter, only the high melt-penetrable iron ore or the iron-containing raw material including the high melt-penetrable iron ore and the scales is defined as a high melt-penetrable iron-containing raw material. In addition, only the other iron ores or the iron-containing raw material including the other iron ores and the scales is defined as the other iron-containing raw material.
[0100]
FIG. 9 shows the relationship between the melt penetration lengths of the respective brands of iron ores and the Al2O3 content. As shown in FIG 9, the melt penetration length is associated with the Al2O3 content, and it is preferable that an iron ore brand having an Al2O3 content equal to or less than 0.6 mass% be selected as an iron ore having a melt penetration length equal to or longer than 4.0 mm.
[0101]
The melt penetrability of iron ore is also influenced by the structure of pores and the like of the iron ore as well as the Al2O3 content. However, as the Al2O3 content in
the iron ore increases, the Al2O3 content in the assimilated melt also increases.
Accordingly, the viscosity of the melt increases and the melt penetrability decreases.
[0102]
Accordingly, in the present invention, it is preferable that the Al2O3 content of the iron ore be equal to or less than 0.6 mass%, which is charged into the upper layer of a feed bed and has a melt penetration length equal to or longer than 4.0 mm.
[0103]
Further, as described above, it is necessary to prevent an excessive increase in the amount of the melt of the upper layer of the feed bed in order to maintain the feed bed in the entire feed bed. In addition, it is preferable that the auxiliary raw material be reduced in order to reduce costs. Accordingly, the influence on the sinterability of the ratio of the auxiliary raw material which is necessary for the formation of the melt, limestone in particular, in the upper layer, was examined.
[0104]
FIG. 10 shows the relationship between the ratio of limestone in the upper layer and the product yield of sinter in the sintering pot test. FIG. 11 shows the relationship between the ratio of limestone in the upper layer and the SI strength of sinter in the sintering pot test. In the examples of the present invention, as high melt-penetrable iron ore in the upper layer, the Brazilian ore B(b) was used and the ratio of the thickness of the upper layer was 11.7%. In addition, the sintering feeds having the blending ratios shown in Table 2 were used.
[0105]
As shown in FIGS. 10 and 11, by using high melt-penetrable iron ore as the iron ore in the upper layer, SI and the product yield were improved. Further, by decreasing the ratio of limestone in the upper layer, SI and the product yield increased.
Accordingly, regarding the auxiliary raw material which is charged into the feed
bed, it is preferable that the blending ratio of the auxiliary raw material in the upper layer
be equal to or lower than the blending ratio of the auxiliary raw material in the lower
layer from the point of view of a reduction in costs.
[0106]
In the present invention, the method of charging a high melt-penetrable iron-containing raw material and the other iron-containing raw material into the upper layer of a feed bed and the lower layer of the feed bed on a sintering pallet, respectively, is not particularly limited. However, for example, a method shown in FIG 13 is used.
[0107]
In a charging apparatus of a downward suction type sintering machine, a first surge hopper (for the other iron-containing raw material) 1 and a second surge hopper (for high melt-penetrable iron-containing raw material) 2 are disposed in series in the longitudinal direction of the machine. From this first surge hopper 1, a sintering feed 3 including return fines, coke, limestone, and the other iron-containing raw material but excluding the high melt-penetrable iron-containing raw material, is charged onto a sintering pallet 4 and thus a lower layer 5 of a feed bed is formed. After that, from the second surge hopper 2, a sintering feed 6 including the high melt-penetrable iron-containing raw material, limestone, coke and return fines is charged and thus an upper layer 7 of the feed bed can be formed on the lower layer 5.
[0108]
The sintering feed 6 including the high melt-penetrable iron-containing raw material, limestone, coke and return fines and the sintering feed 3 including the other iron-containing raw material, limestone, coke and return fines are mixed and granulated by using granulation machines 8 and 9 which may be drum mixers and pan pelletizers,
respectively, to form granules. After that, the respective sintering feeds are supplied to
the second surge hopper (for high melt-penetrable iron-containing raw material) 2 and
the first surge hopper (for the other iron-containing raw material) 1.
[0109]
In addition, as described above, the sintering feed 6 including the high melt-penetrable iron-containing raw material, limestone, coke and return fines and the sintering feed 3 including the other iron-containing raw material, limestone, coke and return fines are blended so that limestone, coke and return fines are blended at a predetermined blending ratio.
[0110]
[First Example]
Hereinafter, the advantage of the present invention will be described with the examples.
As a sintering feed, on the basis of the average blending condition in the practical operation, which is shown in Table 2, a sintering pot test was performed by using a sintering pot having a height of 600 mm and a diameter of 300 mm as shown in FIG. 12.
[0111]
[Table 2]

(Table Removed)
[0112]
It is confirmed in advance that when the practical sintering operation is performed by using the sintering feeds having the blending conditions shown in Table 2, the SI strength of sinter is equal to or greater than 90.5% and the product yield is equal to or greater than 80.0%.
[0113]
In addition, the production rate in the sintering pot test and the product yield, the SI strength, the reduction disintegration index (RDI) and the reduction ratio JIS-RI (%) of sinter were measured. The results thereof are shown in Table 3 together with the production conditions. The production rate indicates a value which is obtained by dividing the mass (t) of the sinter which has a particle diameter equal to or larger than 5 mm, excluding bedding ore, by a pot area (m ) and a sintering time (day).
[0114]
[Table 3]
(Table Removed)

[0115]
The SI strength of the sinter is measured by sampling 10 kg of sinter having a particle diameter of 10 to 25 mm from the sinter after the below product yield measurement and dropping it 4 times from a height of 2 m. This SI indicates a ratio (mass%) of the mass (kg) of the sinter after dropping which has a particle diameter equal to or larger than 5 mm to the mass (kg) of the sinter before dropping.
[0116]
The product yield of the sinter is measured by dropping a sinter cake (lump) 5 times from a height of 2 m. This product yield of the sinter indicates a ratio (mass%) of the mass (kg) of the sinter (however, excluding bedding ore) after dropping which has a particle diameter equal to or larger than 5 mm to the mass (kg) of a sinter cake (lump) (however, excluding bedding ore) before dropping.
[0117]
The reduction disintegration index (RDI) of the sinter is measured in accordance with a test method specified in JIS M 8720. That is, 500 g of sinter having a particle diameter of 15 to 19 mm is sampled and reduced at 550°C for 30 minutes in a mixed gas of 70% of N2 and 30% of CO. After that, the reduced sinter is charged into a drum and subjected to a rotation test 900 times in 30 minutes. The ratio (mass%) of the mass (g) of a sinter powder after the rotation which has a particle diameter equal to or smaller than 3 mm to the mass (g) of the reduced sinter before the rotation is the reduction disintegration index (RDI).
[0118]
The JIS reduction ratio (JIS-RI) of the sinter is measured in accordance with a test method specified in JIS M 8713. That is, 500 g of sinter having a particle diameter of 19 to 21 mm is sampled and reduced at 900°C for 180 minutes in a mixed gas of 70%

of N2 and 30% of CO. The ratio (mass%) of a reduced amount (g) of the mass of the
sinter due to the reduction to the mass (g) of the oxygen which is included in iron oxide
in the sinter before the reduction is the JIS reduction ratio (JIS-RI).
[0119]
Regarding the high melt-penetrable iron-containing raw material which is charged into the upper layer of a feed bed, the high melt-penetrable iron-containing raw material, limestone, return fines and coke were mixed and granulated to form granules, and were charged into the A portion (the upper layer of the feed bed) shown in FIG. 12. The blending ratio of limestone, coke and return fines is the same as the blending ratio of all the raw materials.
[0120]
In addition, as described above, the other iron-containing raw material, limestone, return fines and coke were mixed and granulated to form granules, and were charged into the B portion (the lower layer of the feed bed) shown in FIG. 12. The ratio of the coke, limestone (CaO) and return fines is the same in the A portion as in the B portion of the sintering feed bed.
[0121]
In addition, the high melt-penetrable iron-containing raw materials for charging into the A portion are Brazilian ores B(a) and B(b) which are shown in Table 1 and which are different from each other in melt penetration length, Australian pisolite ores P(a) and P(b) which are different from each other in melt penetration length, the iron ore which is prepared by mixing them, an Australian pre-blended ore HPM, and domestic scales S1 and S2 which are different from each other in melt penetration length.
[0122]
In this embodiment, the B portion was charged in a layer thickness of 530 mm

from a grate surface of the sintering pallet, and on the B portion, the A portion was
charged in a layer thickness of 70 mm (a ratio of the upper layer thickness to the total bed
height (600 mm): 11.7%).
[0123]
In addition, in the blended raw materials of the A portion and the B portion, 5.01 mass% of SiO2, a ratio of CaO / SiO2 of 1.89 and 4.3 mass% of coke (which are each the same ratio as that of all the sintering feeds) remained constant, and as the granulation conditions, granulation moisture was 7.0 mass%. Further, regarding the sintering conditions of this sintering pot test, the total bed height was 600 mm, the suction negative pressure was 14.7 KPa, and the sintering time was 27 minutes. The test results shown in Table 3 are average values of the measured values of n=2 times.
[0124]
Reference example 1 is a base test in which the plurality of brands of iron ores which are shown in Table 2 as sintering feeds are uniformly charged in the bed thickness direction. The SI strengths, product yields, production rates and the like of the sinter of the following examples and comparative examples were evaluated on the basis of Reference example 1.
[0125]
Example 1 is an example in which the Brazilian ore B(a) which is shown in Table 1 and has a melt penetration length of 4.65 mm is selectively charged into the A portion (the upper layer of the feed bed) and the remaining iron-containing raw material (the other iron-containing raw materials) is charged into the B portion (the lower layer of the feed bed).
[0126]
Example 2 is an example in which the Brazilian ore B(b) which is shown in

Table 1 and has a melt penetration length of 4.22 mm is selectively charged into the A
portion and the remaining iron-containing raw material is charged into the B portion.
[0127]
In Examples 1 and 2, the product yield and the SI strength of the sinter were improved and the production rate was improved as compared with Reference example 1 without deterioration of the reduction disintegration RDI and the reduction ratio JIS-RI.
[0128]
Example 3 is an example in which the Brazilian ore B(a) which is shown in Table 1 and has a melt penetration length of 4.65 mm and the Australian pisolite ore P(a) which has a melt penetration length of 1.12 mm are mixed at a mixing ratio P(a):B(a) of 15:85 and selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.
[0129]
The melt penetration length (weighted average value of the melt penetration lengths of B(a) and P(a) in accordance with the mixing ratio) of the iron ore mixture of B(a) and P(a) selectively charged into the A portion in Example 3 was 4.12 mm. Accordingly, the product yield and the SI strength of the sinter were improved and the production rate was improved as compared with Reference example 1 without deterioration of the reduction disintegration RDI and the reduction ratio JIS-RI.
[0130]
Example 4 is an example in which the Brazilian ore B(a) which is shown in Table 1 and has a melt penetration length of 4.65 mm and the domestic scale S1 which has a melt penetration length of 4.21 mm are mixed at a mixing ratio B(a):S of 85:15 and selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.

[0131]
Example 5 is an example in which the Brazilian ore B(a) which is shown in Table 1 and has a melt penetration length of 4.65 mm and the domestic scale S2 which has a melt penetration length of 1.66 mm are mixed at a mixing ratio B(a):S2 of 85:15 and selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.
[0132]
The melt penetration length (weighted average value of the melt penetration lengths of B(a) and S1 in accordance with the mixing ratio) of the iron ore mixture of B(a) and S1 selectively charged into the A portion in Example 4 was 4.28 mm. Accordingly, the product yield and the SI strength of the sinter were improved and the production rate was improved as compared with Reference example 1 without deterioration of the reduction disintegration RDI and the reduction ratio JIS-RJ.
In addition, the melt penetration length (weighted average value of the melt penetration lengths of B(a) and S2 in accordance with the mixing ratio) of the iron ore mixture of B(a) and S2 selectively charged into the A portion in Example 5 was 4.28 mm. Accordingly, the product yield and the SI strength of the sinter were improved and the production rate was improved as compared with Reference example 1 without deterioration of the reduction disintegration RDI and the reduction ratio JIS-RI.
[0133]
On the other hand, Comparative example 1 is an example in which the Brazilian ore B(b) which is shown in Table 1 and has a melt penetration length of 4.22 mm and the Australian pisolite ore P(b) which has a melt penetration length of 1.23 mm are mixed at a mixing ratio P(b):B(b) of 45:55 and selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.

[0134]
The melt penetration length (weighted average value of the melt penetration lengths of B(b) and P(b) in accordance with the mixing ratio) of the iron ore mixture of B(b) and P(b) selectively charged into the A portion in Comparative example 1 was small, that is, 2.87 mm. Accordingly, the product yield and the SI strength of the sinter decreased and the production rate also decreased as compared with Reference example 1.
[0135]
Comparative example 2 is an example in which the Australian pisolite ore P(a) which is shown in Table 1 and has a melt penetration length of 1.12 mm is selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.
[0136]
Comparative example 3 is an example in which the Australian pisolite ore P(b) which is shown in Table 1 and has a melt penetration length of 1.23 mm is selectively charged into the A portion and the remaining iron-containing raw material is charged into the B portion.
[0137]
In both Comparative examples 2 and 3, the melt penetration lengths of the iron ores P(a) and P(b) selectively charged into the A portion were small, that is, 1.12 mm and 1.23 mm, respectively. Accordingly, the product yield and the SI strength of the sinter decreased and the production rate also decreased as compared with Reference example 1.
[0138]
[Second Example]
Next, under the same conditions as in Example 1 carried out in [First Example], that is, under the same conditions except for the ratio (ratio of the upper layer thickness

to the total bed height from the upper surface) of the thickness of the upper layer of the
Brazilian ore B(a) which is charged into the A portion (the upper layer of the feed bed),
only the ratio of the thickness of the upper layer was changed and the test was performed
in the same manner. The conditions of Reference example 1 is the same conditions as
the conditions of [First Example].
[0139]
In addition, as in [First Example], the production rate in a sintering pot test, and the production yield and the SI strength of the sinter were measured. The results thereof are shown in Table 4.
[0140]
[Table 4]
(Table Removed)
[0141]
In the cases of Examples 1 to 3 in which the Brazilian ore B(a) is charged into
the A portion so that the ratio of the thickness of the upper layer is in the range of 5 to
12%, the product yield and the SI strength of the sinter were improved and the
production rate was improved as compared with Reference example 1 without
deterioration of the reduction disintegration RDI and the reduction rate JIS-RI.
[0142]
In the cases of Comparative examples 1 and 2 in which the Brazilian ore B(a) is charged into the A portion so that the ratio of the thickness of the upper layer is lower than 5% and Comparative examples 3 and 4 in which the Brazilian ore B(a) is charged into the A portion so that the ratio of the thickness of the upper layer is higher than 12%, the product yield and the SI strength of the sinter decreased and the production rate also decreased as compared with Reference example 1.
[0143]
As described above, according to the present invention, in a producing method of sinter by using a downward suction type sintering machine, melt penetrability into a fine region of each of the brands of iron ores which are blended in a sintering feed is evaluated, and the brand iron ore having excellent melt penetrability into the fine region is selected from among the brands of iron ores on the basis of this evaluation result and is selectively charged into the upper layer of a feed bed. In this manner, the product yield and the strength of the upper layer of the feed bed can be improved and the productivity of the sinter can be improved. Accordingly, the applicability of the present invention in the steel industry is high. [Reference Symbol List]
[0144]
1: FIRST SURGE HOPPER (FOR THE OTHER IRON-CONTAINING RAW MATERIAL)
2: SECOND SURGE HOPPER (FOR HIGH MELT-PENETRABLE
IRON-CONTAINING RAW MATERIAL)
3: SINTERING FEED INCLUDING THE OTHER IRON-CONTAINING RAW MATERIAL, AUXILIARY RAW MATERIAL, COKE AND RETURN FINES
4: SINTERING PALLET
5: LOWER LAYER OF FEED BED
6: SINTERING FEED INCLUDING HIGH MELT-PENETRABLE IRON-CONTAINING RAW MATERIAL, AUXILIARY RAW MATERIAL, COKE AND RETURN FINES
7: UPPER LAYER OF FEED BED
8: GRANULATION MACHINE
9: GRANULATION MACHINE

What is claimed is:
1. A producing method of a sinter which includes blending an iron-containing raw
material including a plurality of brands of iron ores, an auxiliary material, a solid fuel,
and return fines as a sintering feed, mixing and granulating the sintering feed, charging
the sintering feed onto a sintering pallet, and sintering the sintering feed, the method
comprising:
charging a high melt-penetrable iron ore that is selected or blended from the plurality of brands of iron ores so that a weighted average value of melt penetration lengths thereof is equal to or greater than 4.0 mm, on the basis of the melt penetration lengths of the iron ores which are measured for each brand, into an upper layer, wherein an ratio of an upper layer thickness to an total bed height is in the range of 5 to 12%, the upper layer thickness being measured from an upper surface of a feed bed which is formed on the sintering pallet;
charging the other iron ores into a lower layer of the feed bed; and charging the auxiliary raw material, the solid fuel, and the return fines into the upper layer and the lower layer of the feed bed.
2. The producing method of a sinter according to claim 1,
wherein an Al2O3 content in the high melt-penetrable iron ore is equal to or lower than 0.6 mass%.
3. The producing method of a sinter according to claim 1,
wherein in addition to the high melt-penetrable iron ore, as the iron-containing raw material, a domestic scale is charged into the upper layer in which the ratio of the

upper layer thickness to the total bed height is in the range of 5 to 12%, the upper layer
thickness being measured from the upper surface of the feed bed.
4. The producing method of a sinter according to claim 1,
wherein the solid fuel and the return fines are charged into the upper layer and the lower layer of the feed bed at the same blending ratio.
5. The producing method of a sinter according to claim 1,
wherein regarding the auxiliary raw material which is charged into the feed bed, a blending ratio in the upper layer is equal to or lower than a blending ratio in the lower layer.
6. The producing method of a sinter according to claim 1,
wherein the high melt-penetrable iron ore is blended with the auxiliary raw material, the solid fuel and the return fines, mixed and granulated, and then charged into the upper layer of the feed bed; and
the other iron ores are blended with the auxiliary raw material, the solid fuel and the return fines, mixed and granulated, and then charged into the lower layer of the feed bed.
7. The producing method of a sinter according to claim 6,
wherein the high melt-penetrable iron ore as the iron-containing raw material is
blended with the domestic scale, blended with the auxiliary raw material, the solid fuel
and the return fines, mixed and granulated, and then charged into the upper layer of the feed bed.