When blast furnaces are forced to run at high speed, one way of reducing their downtime, increasing their productivity, and lowering the cost of making pig iron is to improve the durability of the tuyeres. Experience shows that the main causes of tuyere failure are crack formation, wear, and burn-throughs. The durability of a tuyere and the type of problems encountered with it are significantly affected by the sophistication of the smelting technology that is used and the quality of the charge materials. Most tuyeres do not last longer than three months when the supply of raw materials to the furnace is unstable, and 20% of tuyeres (out of the total number that are replaced) have lasted less than half a month under such conditions. The amount of furnace downtime necessitated by the replacement of failed tuyere parts has reached 2.0-2.5% of nominal operating time, which has seriously hurt furnaces' technical-economic indices. Stabilization of the operation of blast furnaces at EZRAZ ZSMK has allowed the combine to work on improving the durability of the tuyeres by redesigning them, improving the quality of the work done in making them, and applying protective coatings (by plasma deposition, electron-beam hard facing, etc.). The combine's introduction of a new technology for making tuyeres and the strengthening of these pieces of equipment while ensuring a satisfactory cooling rate have made it possible to reduce the incidence of tuyere failure due to cracking. The number of tuyere replacements has declined during both normal and high-speed operation of the furnaces, which has in turn elevated tuyere service life to an average of 5-7 months and a maximum of 14-15 months.Having blast-furnace tuyeres that are durable reduces downtime, increases productivity, and lowers the cost of making pig iron during periods when the furnace is forced to operate at higher-than-normal smelting rates.Experience with the use of the tuyeres at the combine has shown that most of the damage done to tuyeres comes from cracks, wear, and burn-throughs. By cracks, we mean fractures of the tuyeres along the weld or base metal (copper). The wear that the tuyere undergoes is for the most part uniform (and occurs primarily in the tuyere's "snout" region). Burnthroughs occur when the tuyere is destroyed by the action of the molten pig iron.It has been established that the durability of tuyeres and the types of defects that take them out of service are influenced chiefly by the sophistication of the smelting technology that is used and the quality of the iron-bearing materials and coke in the charge. Studies have found a correlation (correlation coefficient 0.69, reliability criterion of the relationship 2.96) between the number of burned tuyeres and several parameters of the smelting operation: N = -1.29 + 6.02[Si] + 5.41B Σ -0.34Fe snt + 0.3M 10 , where N is the number of burnt tuyeres; [Si] is the silicon content of the pig iron, %; B Σ is the absolute value of slag basicity (CaO + MgO)/SiO 2 ; Fe snt is the iron content of the charge, %; and ...

Results of study of scull and lining composition from the hearth of blast furnace No. 2 of JSC EVRAZ ZSMK after stop for capital overhaul quoted. It was determined, that due to microprobe chemical analysis data, considerable quantity different minerals and metals can be discovered in the scull and in the lining. But chemical analysis of averaged samples and their X-ray structure analysis allows to state, that the scull is formed during crystallization of heat products – cast iron and slag. Therefore the scull base is the following:– metal, in the content of which α-Fe prevails with iron carbides (Fe3C) inclusions, complicated carbides of variable composition (FeхSiyCz), iron and graphite sulfides and phosphides, as a rule, of laminar structure;– graphite in the form of separate phase;– slag components, melilite and anorthite being the base of them (minerals, formed during crystallization of slag of blast furnace heat).At the level of hot metal tap hole and higher the scull and lining are saturated by alkaline metals accompanied by forming leucite, caliofilite, calcilite, zinc (zinc oxide, ganit, willemite in samples), sulphur with forming of sulphides, phosphor (iron phosphides in metal, apatite in slag). Lower the level of tap hole the number of slag inclusions in the scull is not considerable, zinc and alkaline metals were not discovered.In all the samples content of silicon, silicon carbide, carbides, nitrides, titanium carbonitrides in total does not reach level of 5%.

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