Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1985-08-15
1988-02-02
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75257, C22B 120
Patent
active
047227508
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to new agglomerated ores and a producing method therefor. Objective ores have excellent properties at high temperatures, high RI, low RDI and high producing yield. These ores are produced from fine powder iron ores having so wide range of grain sizes to an extent that they are not always suitable to sintering nor pellets. The invention is to provide a producing method which enables to carry out induration by means of a blower of low faculty.
BACKGROUND OF THE INVENTION
In general, the fine powder ores as raw materials for sintering or pelletizing have ranges of proper grain sizes. For example, in a sintering process of DL type, grains are mixed in a mixer of drum type, but since a pelletizing time is short, perfect agglomeration of ores could not be performed. Therefore, for maintaining permeability, such a condition is burdened that the grain sizes of raw iron ore of not more than 125 .mu.m should be below 20%, preferably not more than 10%. Notwithstanding said conditions, the blower faculty of around 1500 to 2000 mmAq is required during sintering, because of bad permeability in the sintered bed. Further, because products are crushed and regulated in grain size, yield is undesirable, and 70% at the most. Sources of SiO.sub.2 are added such that the content of SiO.sub.2 in the product is about 5 to 7% in order to increase bonding power, and strength of the sintered ores is maintained, but on the other hand, amount of generating slags within the furnace is increased, and RI (Reduction Index) is generally decreased as 60 to 70%.
In a travelling grate typed pellet sintering process, the powder iron ores should be pelletized more than 10 mm.phi. in a preceding process. Therefore, with respect to the grain sizes of the raw powder iron ores, those of not more than 44 .mu.m is necessarily 60 to 90%, preferably more than 80%, for smoothly performing pelletization. The obtained pellets are good in reducing nature. However, since they are relatively large in grain diameter, the reduction does not reach to nuclei of the pellets in the shaft zone of a furnace, so that there remain non-reduced parts which are low in melting points, thereby to widen softening and melting zones at high temperature range within the furnace, and bad influences are given to the operation. Being low in the amount of containing veinstones, swelling phenomena occur and are pulverized within the shaft zone. In addition, the pellets are like ball and are not bonded one another but each independent. When charging into the furnace, they gather to a center part from the circumference thereof, so that the gas flowing distribution is disturbed and cannot be effectively used to the reduction.
The present invention has been realized to solve the above mentioned problems. The agglomerated ores by the invention have excellent properties at high temperatures, high RI, low RDI (shutter index) and high production yield. These ores are produced from the fine iron ores having so wide range of grain sizes that they are not suitable to sintering and pelletization. The invention is to provide the producing method which enables to carry out induration by means of the blower of the low faculties.
DISCLOSURE OF THE INVENTION
The invention will be explained in detail. The raw iron ores for sintering are crushed if exceeding 5 mm of the grain size, and main grain sizes are not more than 5 mm. Mini-pellets comprise such iron ores, and the agglomerated ores are produced by indurating the mini-pellets.
Thus, since the powder iron ores are prepared as pellets when the induration is carried out, they are permeable and so the small blowing faculties are sufficient. The conventional pellets are, as mentioned above, produced by merely pelletizing and indurating the powder iron ores, and when charging them into the furnace, they flow toward the center part from the circumferential of the furnace. The inventors made contrivances in this respect and produced new ores by bonding the pellets one another as seen in FIG. 1, so that they
REFERENCES:
patent: 3868246 (1975-02-01), Boss
patent: 4082540 (1978-04-01), Sasaki
Fukuya Hiroshi
Iwata Yoshihito
Saito Hiroshi
Sakamoto Noboru
Andrews Melvyn J.
Kojima Moonray
Nippon Kokan Kabushiki Kaisha
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