Graphite is manufactured using two main steps. The first one involves the manufacturing of synthetic graphite. Secondly, the resulting material is impregnated with phenolic resin to make it inaccessible and also improve its mechanical characteristics. Using high-quality graphite ensures that the manufacturers can uphold high standards of production. On most occasions, graphite from Japan, Europe, and the United States of America is used.
In essence, any Graphite Materials that are used are homogenous and have a small grain structure. Excellent characteristics such as pore size distribution and optimal grain ensure that the final product is free from structural anomalies such as impurities, large pores, cracks, and most importantly, impurities.
Manufacturing Process of Synthetic Graphite
Natural graphite does not occur in large quantities. Nonetheless, numerous ways exist through which artificial graphite can be manufactured in large numbers in factories. Statistics indicate that a total of 132,000 tonnes of graphite valued at $495 million was produced in 2006. However, modern technological advancements have increased production due to the use of state-of-the-art equipment.
The manufacture of synthetic graphite entails various processes. For instance, an elaborate process will be required in powder preparation, graphitization, rebaking, densification, baking, and shape forming. These processes are explained below:
1. Power and Paste Preparation– the first process starts by loading the necessary raw materials into silos. Such raw materials include secondary graphite scrap, natural graphite, carbon black, pitch coke, and petroleum coke. After that, the materials are then ground in ball mills and crushers. Their particle grounding then groups the resulting powder. Finally, binders such as petroleum pitch are used to blend the powder before taking it to the second phase.
2. Shape Forming– the paste that results from the binding is then compacted using techniques such as cold isostatic pressing, vibro-molding, or extrusion. Extrusion involves passing the pasty mixture through an opened die. The process results in a long product like tubes, long plates, bars, and rods that can, later on, be cut into desired lengths.
3. Baking– high temperatures running from 900-1200 degrees Celsius is used to heat the compacted mixture in an anaerobic surface. As such, the decomposition of the binder into its elemental parts results in the occurrence of carbon. The powder particles that are formed during the process are then bound together with the carbon formed. The pores formed due to the carbonization process have a volume that is determined by the binder quantity.
4. Pitch Impregnation– the process involves the impregnation of the carbon parts with pitch and their rebaking to reduce porosity. Industry experts recommend that the process of pitch impregnation and baking be repeated several times in a month to get high-density graphite grades.
5. Graphitization– it is the second last stage of synthetic graphite manufacturing. It involves the heating of the rebuked, shaped and pitch impregnated in an anaerobic environment in temperatures of more than 2700-3000 degrees Celsius — amorphous precursor carbon forms as a result of graphitization resulting in the formation of crystalline graphite.
6. Quality Checks– a series of tests are used to authenticate the quality of the crystalized graphite.
At this stage, the graphite has excellent outstanding thermal conductivity and good corrosion resistance. Nonetheless, the resultant product is made previous through phenolic resin impregnation.