Improving the Durability of Blast-Furnace Tuyeres

Abstract

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 ...

Problems and prospects of surfacing copper and copper parts by wear-resistant layers (Review)

“…У роботі [17] відзначено, що застосування плазмового способу нанесення захисних покриттів різного складу на мідну основу дозволяє підвищити зносостійкість у порівнянні із чистою міддю в 1,5…3,0 рази. Однак треба відзначити, що застосовування тонких покриттів (0,5…0,7 мм) в умовах значного газоабразивного зношування не дає змоги значно підвищити довговічність таких деталей.…”

Hardfacing of Copper

“…3. Copper crystalliser sprayed with XuperCoat™ composite using the HVOF method [16] Work [17] informs that the use of plasma spraying when surfacing copper with protective layers having various chemical compositions increases wear resistance by between 1.5 and 3.0 times in comparison with that of pure copper. However, it should be noted that the use of thin coatings (between 0.5 mm and 0.7 mm) under conditions of intense gas-abrasive wear does not significantly increase the service life of elements.…”

“…More detailed information can be found on the plasma powder surfacing of copper and its alloys with cobalt and nickel alloys [25]. It should be noted that the above-named method enables the relatively low melting of the base material [4,17,25,26].…”

“…Reference publications also contain information concerning the electron beam surfacing of copper with layers having a thickness restricted within the range of 1.5 mm to 2.0 mm [17,27]. The aforesaid technology enables the favourable penetration of copper surface with a layer based on refractory metal carbides.…”

“…Specialist methods enabling the making of bimetallic steel-copper joints include explosion welding, pressure welding, friction stir welding etc. [11,12,17,28]. Although the above-named processes enable the obtainment of reliable joints, their application in the deposition of wear resistant layers is often limited by the shape and dimensions of elements (products).…”