Soderberg electrodes are a key component in the submerged electric-arc furnaces (EAFs) that produce pig metal and ferroalloys. These carbon-based products are made from electrically calcined oil coke, calcined pitch, and calcined anthracite. They can be shaped into cylinders eggs or briquettes before being fed into EAF columns to undergo the baking procedure. This leads to the development of carbon-based electrodes with improved mechanical strength and thermal conductivity.
A successful Soderberg-type electrode requires a unique recipe that balances the performance and performance of various constituents including binder (binder), softener (softener) and additives. The ingredients must be able withstand the high temperatures found in the melting zone, and they must also have enough plasticity so that the composition remains fluid when it rises up into the sintering region. It must be able, at the same time to withstand all the stresses that come with the sintering or cooling process.
The composition must also be able to retain its fluidity when it is cooled and must not separate into the individual components. The addition of a resin such as novolak phenolic is often used to achieve this, although the optimum amount and type of resin must be carefully selected to avoid degradation of the carbon aggregates at elevated temperature.
Despite these challenges it is possible develop electrode pastes that have excellent properties. They include a low-carbon content, good thermal stabilities and the ability of being moulded in various shapes and sizes. Such compositions have the added advantage of being cost-effective as they are made from readily accessible raw materials.
As the paste is poured into a smelting chamber its thermal properties change rapidly. The thermal conductivity is reduced to 0.5 Wm-1 *K-1 at 673K (400degC) but remains constant up until the baking-isotherm temperature of 873K (1073 degC).
Above this point the material begins to become liquid again, indicating it has passed through sintering and is now being converted into solid electrodes. The thermal resistance increases rapidly with temperature. It reaches about 2.8W m-1*K-1 around 1173 K (2880 degC).
In order to improve the reliability of these thermodynamic predictions, it is important to know exactly how the material behaves as it passes through the various temperatures zones within an EAF column. In order to obtain accurate data on the material's behaviour, a detailed analysis of thermomechanical properties has been performed. The thermal properties of electrode paste are measured by a hot disc enclosed by samples of electrode paste that are accommodated in a sample holder. The measured data is compared with the calculated thermal conductivity graphs derived from published experimental data. The results confirm that the thermal conductivity of the electrode paste increases with temperature after passing through the sintering and baking zones. The increase of thermal conductivity can be attributed to the fact graphite becomes ordered during baking.
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