Graphite packing is precision-braided from graphite yarn reinforced with various materials, such as high-strength fibers or metal wires (including steel, copper, or nickel wire, as well as carbon fiber, pre-oxidized fiber, or glass yarn). It is designed for dynamic sealing applications under high-temperature and high-pressure conditions. With the exception of a few strong oxidizing agents, it is suitable for sealing media such as hot water, superheated steam, heat-transfer fluids, ammonia solutions, hydrocarbons, and cryogenic liquids. It is primarily used for sealing valves, pumps, and reactors in environments characterized by high temperatures, high pressures, and corrosive media. It serves as a versatile, universal sealing packing.
The production of graphite packing involves a continuation of the solid-phase carbonization process, during which non-carbon elements-predominantly nitrogen-are almost entirely removed from the carbon fibers, resulting in graphite fibers with a carbon content approaching 100%. The release of nitrogen is the result of further condensation reactions among small, hexagonal carbon-lattice planes. Approximately 6% to 7% of the nitrogen is eliminated during the graphitization process, leaving behind numerous pore defects and channels-a phenomenon that causes the porosity to reach its peak during this stage. At approximately 2200°C, nitrogen is almost completely removed, causing porosity to reach its maximum value. Beyond 2200°C, the porosity drops sharply while the density increases significantly. The condensation and denitrogenation of small aromatic rings are the primary reactions occurring during the formation of graphite packing, leading to substantial changes in the fiber's elemental composition, porosity, and density.
Graphite packing is highly effective for static sealing in environments involving weak acids and bases, liquid ammonia, water, or various oils, offering excellent corrosion resistance. This type of fiber-based packing features high thermal conductivity and resistance to acids and bases; it is suitable for sealing pumps, valves, and reactors handling a wide range of solvents, gasoline, water, and liquid nitrogen. (Certain variants also offer high-temperature resistance, making them suitable for both dynamic and static sealing applications under high-speed operating conditions.) PTFE (polytetrafluoroethylene) packing is manufactured using pure PTFE dispersion resin. The resin is first processed into an unsintered film, which is then twisted into strands and braided to form the packing. This type of PTFE packing contains no additives and is well-suited for use in valves-particularly those handling highly corrosive media or operating in environments that demand a high degree of cleanliness, such as in the food, pharmaceutical, papermaking, and chemical fiber industries. It is not, however, suitable for use in water pumps.
