Opinion ID: 778819
Heading Depth: 3
Heading Rank: 2

Heading: Cell Relining

Text: 7 The lining of the cell is located in the cell shell and consisted of cathode blocks made of carbon materials, collector bars, refractory brick made of a lightweight silicate material, castable refractory, steel plate, insulation board, carbon sidewall blocks, carbon lining paste, and various nuts and bolts. The cell lining of each LCD cell consisted of eight cathode blocks that were 60 inches × 18 inches × 14 inches; two that were 60 inches × 15 inches × 14 inches; one that was 60 inches × 17 inches × 14 inches; two that were 30 inches × 18 inches × 14 inches; and two that were 30 inches × 17 inches × 14 inches. The average life of the cell lining was three years. 4 8 Cells were monitored by Vanalco in two ways. One involved measuring the iron content of the molten aluminum within each cell twice a week. If the iron content increased above a certain level, it was a sign that the cell lining had eroded to expose the steel collector bars or the shell. Failure to replace the cell lining in this circumstance would cause the cell to eventually rupture, spilling molten metal onto the floor. In addition, the voltage of the cells was monitored to ensure that the cells were running efficiently. If the voltage could not be maintained at a designated level or within a specified range, it was an indication that there was something wrong with the cell lining. In this situation, if all other attempts to improve the operation of the cell failed, the cell would be bypassed and removed from service for relining. 9 Once the cell was shunted, the relining process involved removing the carbon anodes, cooling the cell for 20 hours, then adding water to further cool the cell and soften the lining materials. The superstructure and shields were then removed, and the superstructure was taken to the potlining area for any necessary repairs. The cell lining crew then removed the cooled, solidified electrolyte and solid aluminum metal from the cell cavity, and the cell was dug with pot diggers to extract the remaining cell lining. The shell and cradle of the cell were removed and taken to the shell repair area with a crane and wagon. In the shell repair area, the shell and cradle were straightened and necessary welding repairs were made. The repaired shell and cradle were put in a vacant spot in the cell line, which was usually different from their original location. 10 The replacement lining was installed in layers. First, the bottom of each cell was lined with two layers of insulating block cemented together. The cell lining crew then placed a layer of sheet metal on top of the insulating block, which formed a vapor barrier. Two layers of heavy refractory fire brick were added on top of the vapor barrier and the cathode blocks with embedded collector bars were placed in rows on top of the refractory fire brick. The cell lining crew then installed the carbon sidewall blocks around the sides of the shell to cover the area from the top of the cathode blocks to the top of the shell. Finally, the crew installed a ramming paste around and between the cathode blocks to create a solid and smooth cell cavity. 11 After the lining was replaced, the collector bars were attached to the ring bus, the superstructure was reinstalled on top of the cell, new anodes were hung from the superstructure, and cell shields were reinstalled over the shell. At this point, the cell was reconnected to the cell line, although it was not immediately placed back into service. Instead, it remained empty for approximately 48 hours while the new lining and cathode blocks baked. The average time for a cell to be out of service for relining was 15 days. 12 During the 1992-1993 period, the cost for the replacement of cell lining, including labor and allocable overhead expenses, was $17,933. 5 In addition, Vanalco incurred approximately $5,401 per cell to tear out the old cell lining, as well as miscellaneous expenses. Vanalco replaced 206 cell linings in 1992 and 192 cell linings in 1993. Vanalco employed a cell lining crew of 22 to 26 workers. It reported a repair expense for relining of $4,411,245 in 1992 and $4,224,991 in 1993.