No abstract

The composition and fabrication technology of a repair mixture consisting of unmolded corundum with a TiB 2-C composite coating wettable with aluminum for repairing local fractures of bottom blocks without interrupting electrolysis have been developed. The proposed technical solution makes it possible to decrease the bottom wear and prolong the service life of an aluminum electrolyzer by six months. To fabricate a repair mixture with an optimal composition, the titanium diboride powder with a refractory powderlike binder in ratio 50 : 50 (wt %) is used. Unmolded corundum is coated with this mixture of a binder and titanium diboride. This material is dried at 150°C and thermally treated in a carbon bed at t = 700-900°C. Calcination in a reducing gas atmosphere results in the formation of the TiB 2-C composite material with a carbon content of 15-20 wt % on the unmolded corundum surface. The qualitative evaluation of the properties of the developed composite coating shows that it has rather high hardness, wear resistance, and adhesion to the base after calcination. To perform pilot tests, the repair mixture is poured with molten aluminum, which gives the platelike repair mass of the Al-TiB 2-C composition. Pilot tests of the repair mass using an RA-400 operating electrolyzer at the pilot shop of OAO RUSAL-Sayanogorsk show that the bottom wear decreases within three months after the repair of the local fracture with uninterrupted electrolysis. This fact is evidenced by a 13% decrease in an average fracture depth with a stable current force of 4.7-4.8 kA/bloom after the repair. Thus, the local use of the repair mass retards the overall wear of the cathodic surface and makes it possible to prolong the service life of the electrolyzer.

The paper presents the developed composition and technology for obtaining a repair mixture consisting of lumped corundum with a TiB2–C composite coating wettable with aluminum for restoration of local bottom block fractures without electrolyzer stops. The proposed technical solution made it possible to reduce bottom wear and increase aluminum electrolyzer service life by 6 months.A mixture of titanium diboride powder and a refractory powder-like binder in a ratio of 50 : 50 (wt.%) was used to obtain the repair mixture with an optimal composition. Then the lumped corundum was coated with the obtained mixture, dried at 150 °C and after that heat-treated under a carbon-bed at t= 700÷900 °C. As a result of reducing firing the TiB2–C composite material with a carbon content of 15–20 wt.% was formed on the surface of lumped corundum. A qualitative evaluation of the properties of the developed composite coating shows that the coating has a sufficiently high hardness, wear resistance and adhesion to the substrate after the heat treatment. For pilot testing, the repair mixture was covered with molten aluminum to obtain an Al–TiB2–C repair mass in the form of plates. The pilot testing of the repair mass on the 400 kA operating electrolyzer in the RUSAL-Sayanogorsk pilot shop showed that the bottom wear have slowed down 3 months after the local fractures were restored without electrolysis bath stops. This fact is evidenced by a 13 % decrease in the average depth of fractures with a stable current value of 4,7–4,8 kA/bloom after repair. Thus, the locallyused repair mass slowed that the overall wear of the cathode surface and allowed to extend the electrolyzer life.