Coal-tar pitch based needle coke producers in China are now faced with the contradictory quality issues
Recently, we have frequently encountered with articles on coal-tar pitch
based needle coke and its utilization as the raw material of the graphite
electrode production in Chinese conferences/workshops.
The technology to produce coal-tar pitch based needle coke was established in the late 70s in Japan. In these several years, the production of such needle coke has been challenged by several companies in China and some have initiated to produce commercially.
At the moment, they have been faced with oversupply issues due to the worse economic situation and quality problem ascribed to the raw material for the production of larger diameter graphite electrode over 24 /28 inches.
In China, larger diameter graphite electrodes and these connecting pins are still produced by using imported premium grade needle coke. On the other hand, Chinese needle coke is only available for the production of rather smaller diameter graphite electrodes under 20 inches. These have been used in smaller Electric Arc Furnace (EAF) and Ladle Furnace (LF) which does not require severe thermal properties of the electrode.
We indicate two points of view in order to apply domestic needle coke in China to larger diameter electrode production.
Firstly, larger grain size needle coke is essential. Although it may be possible to produce larger diameter electrode by using smaller size needle coke, only poor thermal shock resistance (TSR) of the resultant electrode is exhibited.
The graphite electrode by smaller needle coke grain shows higher bulk density and mechanical strength, however, indicates lower TSR. Larger needle coke grain improve TSR of the manufactured electrode due to its lower CTE.
Secondly, it is well known that the puffing property strongly depends on the needle coke grain size and CTE. Although smaller needle coke grain contributes to lower the puffing property of the manufactured electrode, the TSR of the electrode become lower as mentioned above.
Accordingly, with increasing demand to produce larger diameter graphite electrode using domestic raw materials, it will become more important to solve the contradictory issue which is caused by grain size, CTE and puffing property.
Close association between the needle coke supplier and the electrode manufacturer will be effective to overcome such a issue.