Primary aluminum smelting is conducted according to the Hall-Héroult process, which describes the reduction of oxidized aluminum (Al2O3) through electrolysis occurring within an industrial cell. The cell comprises a salt bath where liquidized aluminum is extracted from molten mixtures of alumina and cryolite using electrodes engineered from coke. These components penetrate the walls of the reduction cell, representing a potential point of mechanical weakness.
Various insulation materials are used to hermetically seal external cathode bars. These must contend with persistently severe thermodynamic conditions and the constant risk of chemical attack. Hard refractory oxides and ceramics must exhibit sufficient thermal shock resistance to withstand thermal spalling, which can cause immediate seal failure. Lightweight ceramic fibers may require additional surface treatment to withstand shrinkage due to chemical attack.
The environment of a Hall-Héroult reduction cell is extreme, operating at temperatures of up to 1000°C (1832°F) continuously. Refractory linings, anodes, and cathodes all gradually degrade due to these demanding operating conditions. This necessitates a novel arrangement of insulation materials to suitably reduce ongoing expenditure and prolong the life cycle of the reduction cell.
THERMOPAK® Insulation Materials
THERMOPAK® Insulation Materials cover a substantial range of custom-built components for novel sealing applications. These include a more efficient external cathode bar seal boot which outperforms a more traditional design and is engineered to resist myriad forms of thermodynamic stress including: extreme temperatures; chemical attack; expansion and contraction issues; abrasion; and more. These unique insulation materials are designed to a patented four-part composite design, comprising:
- ARMATEX SBQF® 100: a silicone-coated refractory fabric with exceptional thermal qualities and superb resistance to chemical attack.
- ARMATEX TAF® 18: an additional exterior fabric that provides the hermetic seal and provides additional resistance to initial expansion/contraction phenomena.
- THERMOSEAL® 1000SF: a high-strength refractory cement for bonding the cathode bar seal boot, with a high tolerance for expansion/contraction.
- THERMOSEAL® M22: a final moldable insulation material that completes the hermetic seal by filling the remaining voids of the cathode bar.
Cathode Bar Seal Boots from Mid-Mountain Materials, Inc.
Mid-Mountain is one of the world’s leading suppliers of insulation materials for refractory environments. We specialize in fabricated and moldable sealing products for primary and secondary aluminum production, with a range of protective materials designed to reduce waste and emissions to forefront efficiency in demanding industrial sectors.
If you would like to learn more about how Mid-Mountain Materials, Inc. is enabling new levels of performance in the aluminum industry, read our previous blog post: Tray Pads for Secondary Aluminium Plants and Rolling Mills. Or, contact us directly if you have any questions.