The expanded graphite comes from the hot expansion of the graphite powder. The expanded graphite is qualified by high carbon content C, greater than 98, 00% for the industrial grade graphite and up to 99.85% for nuclear grade. From a chemical point of view the mineral expanded graphite shows, even after the refining treatment, residual elements such as halogens, sulfur and heavy metals that are responsible for the potential stem and flange corrosion. Their minimization qualifies the high quality or industrial grade. Finally the expanded graphite can be enriched with the inhibitors of corrosion and/or retardants of oxidation.
The tensile strength and the Young module of the expanded graphite strands are considerably lower than those of the carbon yarns. For this reason, for a safe use of the product, often the expanded graphite strands are reinforced with continuous filament of Inconel. This technique, rather inefficient, has been integrated with the knitted reinforcement.
The manufacturing of expanded graphite packing can include or not the impregnation. The corrosion inhibitor and the micronized graphite at this stage are adducted on the strands. Finally the packinga are calibrated to the right size.
The expanded graphite packings Carrara are grouped into three range:
The Performer packings are GR80SGR , GR80SGR OXY and GR8622 , the three most experienced and qualified packings for valve applications. These packings are made with a special knitted reinforced graphite strands for which the graphite complies the EN 14772 (weight loss test). These packings are qualified ISO 15848, VDI 2440, API 622, Fire Test API 589 and BAM for Oxygen Service. It is a Premium product the packing style GR8048, engineered both for valve and pump applications. In the Basic range for general applications are the styles GR81SGR, GR48 and GR48R.