Improving the endurance of graphite-containing submerged nozzles for CCM

Abstract

The main causes of erosion of graphite-containing submerged nozzles in the slag belt in operation of continuous casting machines and results of industrial tests of experimental articles of different compositions are described. It is shown that the materials can be arranged in the following series in accordance with their endurance: A1203 -C -SiC -BN ~ ZrO2 -C -SiC ---> A1203 -C -SiC.The efficiency of continuous steel casting is determined by the quality of the cast preform, which depends to a considerable degree on the stability of the process, i.e., the possibility of sustaining a constant casting rate for a long time. Submerged nozzles of a corundum-graphite composition are suitable for casting any grade of steel, but their service life is restricted by erosion of the wall of the submerged nozzle in the slag belt, thermal cracking of the nozzle walls, and blocking of the channel and the tap holes by aluminum oxide and calcium aluminate [1].The process is completely stopped or the casting rate is changed considerably when the submerged nozzle is being replaced, which creates a number of problems. First, this causes a loss of steel production, second, the part of the ingot formed in the period when the nozzle is being replaced (30 -90 sec) is rejected, and third, the cyclic fluctuations of the load exerted on the bearings of the rolls of a curvilinear CCM, which are an order of magnitude higher than the fluctuations in casting at a constant rate, damage the bearings and rolls. In addition, the closing of the tapping channel of the intermediate ladle during the replacement of the nozzle causes blocking of the channel and requires its burning through in oxygen. This worsens the quality of the continuous ingot, enriching it with endogenous inclusions, and creates an emergency situation on the casting platform.The present article is devoted to results of an investigation of corundum-graphite submerged nozzles with a slag belt made of various erosion-resistant refractory materials.St. Petersburg Institute of Refractories, St. Petersburg, Russia.The operating conditions and the factors affecting the wear of the slag belt of a submerged nozzle at the level of a metal meniscus covered by a slag-forming mixture (SFM) are presented in Fig.

Competitiveness of products: A key to success in an incipient market economy

“…In the slag belt the nozzle makes contact with fluorine-and alkali-containing slag [2], whereas the channel of an immersion nozzle is blocked by alumina-containing inclusions [3], which reduces the service life. The BKO has installed a technolog'y for manufacturing two-layer and three-layer immersion nozzles.…”