Cathode Bars: Introducing a more efficient sealing system to improve cell life and efficiency - Tony Carroll, International Aluminum Industry Sales and Product Development at Mid-Mountain Materials, Inc.

One of the most critical areas determining cell life reduction and productivity over that life is the efficient sealing or lack of good sealing at the cathode bar penetrations on each cell. Engineers and product developers have worked for years to improve the sealing solutions in this critical application to lengthen reduction cell life and avoid premature failure or the inevitable declining productivity of cells that have not been suitably sealed during rebuild operations.

Mid-Mountain Materials, Inc. has worked to develop creative products and solutions for this application for almost half a century. This has culminated in the design and implementation of two systems proving to be very highly efficient sealing systems for cathode bars in the worldwide aluminium industry.

Mid-Mountain’s sealing solutions for cathode bars utilise their THERMOSEAL® M44 moldable, but the two methods differ in the external containment method for the moldable. With unique advantages to both systems, it comes down to preference, but regardless of which system is chosen, both achieve exceptional sealing results for the life of the reduction cell.

Mid-Mountain’s patented THERMOPAK® Cathode Bar Seal Boot solution incorporates a custom-designed external boot fabricated using automated sewing machines and coated fabrics manufactured by Mid-Mountain. Vertical integration is key to the success of this solution as Mid-Mountain manufactures all Cathode Bar Seal Boot components to the standards of ISO 9001-2015.

THERMOPAK® Cathode Bar Seal Boots are manufactured from Mid-Mountain’s exclusive ARMATEX® SBQF100 refractory impregnated fabric as the inner side of the boot, which adheres to the sidewall of the pot using Mid-Mountain’s THERMOSEAL® 1000SF cement. The outer side of the boots uses ARMATEX® SRF22 fabric as a hydrofluoric atmosphere-resistant enclosure for the THERMOSEAL® M44 moldable to achieve a hermetic seal for the life of the pot. 

The key advantage of this sealing system is that it does not require any welding or metal fabrication so that any maintenance employee can install the system easily. Another advantage is its tolerance of the initial expansion and movement of the cathode bars during start-up due to heat expansion. Competitive, fast, and simple installation, offering excellent sealing for the life of the pot, has made Mid-Mountain’s patented THERMOPAK® Cathode Bar Seal Boots a preferred sealing system for a variety of aluminium smelters.

The second sealing system Mid-Mountain has developed also utilises their THERMOSEAL® M44 moldable in conjunction with external steel packing glands, which are welded to the exterior of the cells at the cathode bar protrusions. The packing glands are filled using a pneumatic bucket pump to fill the cavity under pressure. This process ensures complete filling of the void while forcing the moldable into even the smallest cracks and voids for excellent sealing. This system requires minimal metal fabrication and welding while providing excellent sealing of the cathode bar penetrations for the life of the pot.

Mid-Mountain uses computer-controlled automated dosing and mixing equipment to maintain the tightest specification ranges available on THERMOSEAL® M44 moldable. Tighter specification ranges result in more consistent wet and dry densities to ensure the lowest air permeability and the highest resistance to sodium penetration, resulting in the best lifetime seal for the reduction cell. The use of the bucket pump is also very productive, as each seal can be completed in less than a minute with consistently good results and practically no product waste once the flow nozzle is mastered.

Mid-Mountain’s half-century of product development and improvement continues to have a positive impact on aluminium smelter performance around the world.