When it comes to packings, it’s easy for folks to confuse graphite and carbon fiber packings. For many manufacturers, the two are used almost interchangeably as they are both used in the manufacture of braid packings.
Carbon fiber has strength and toughness and carbon fiber packings are usually tougher than graphite and can handle high compressive loads.
Graphite packing fibers don’t quite have the strength of carbon, but have better lubrication and can operate at higher speeds. Another benefit of graphite is that it has better thermal conductivity, which helps dissipate frictional heat.
When it comes to materials used in sealing applications, both carbon and graphite fibers can be quite effective. But if a company is looking for materials that can effectively seal at high temperatures, an easy solution is to use flexible graphite.
Flexible graphite is 95-99% carbon and is one of the softest materials on the Mohs Hardness Scale, despite being formed with the same elemental carbon as diamond. Think of flexible graphite as a deck of new playing cards that have been fused together.
When flexible graphite is unexpanded, it has good lubricity, but doesn’t seal as well. When it is expanded and recompressed however, it becomes flexible. When flexible graphite does indeed become flexible it is resistant to high heat and solvents, acids and other chemicals. Flexible graphite is also very resistant to corrosion and it takes on a the shape of whatever it’s compressed, making it a go-to material for sealing.
But just how is flexible graphite made flexible? Using strong oxidizers like acids, bonds are weakened between the layers of graphite. Once the layers (think back to the deck of cards) are dried and exposed to heat, they separate and can be formed into shapes.
Flexible graphite has many positive benefits, but compressing the reheated graphite can weaken its tensile strength. So when it comes to turning the flexible graphite into braided packings, it requires some creativity. Many manufacturers will emboss a variety of fiber into a sheet of flexible graphite to provide the lacking tensile strength.
Flexible graphite can be used for packing and doesn’t require the use of blocking agents, making it an extremely effective sealer for emissions of things such as volatile organic compounds or VOCs. Braided flexible graphite packing can also be used in sealing different types of rotating equipment such as mixers, agitators and pumps that are designed to be leak-free.
