Flexible Graphite is often used in industries which have high temperature, or chemical applications. Because Flexible graphite is (generally 98% or above) a homogeneous carbon based product, it contains no rubber (which degrades with age) or metal (unless added later for strength).
Flexible graphite is manufactured by adding and acid (usually Nucleic or sulfuric) to a ground graphite. The result is that graphite "pops" to many times its original size, into what resembles silver/grey worms. Those flexible graphite worms are then placed into a hopper which feeds a gasket sheeter to produce gasket sheets of flexible graphite.
Generally the sheet is compressed to 70 ft. lbs. however 90 foot lb. material is also produced. If the flexible graphite is being produced for braided packing, the process is slightly different. The worms are feed from a hopper down to a protrusion press, which combines the flexible graphite with a fiberglass thread, which gives the resulting yarn enough tensile strength to be pulled through a braiding machine.
The choice of chemical used to expand the graphite into worms is important. Quality manufacturers will use nucleic acid as opposed to sulfuric acid. The reason this is important is that if manufactured using sulfuric acid, the resulting product will have a high sulfur content. Flexible graphite with a high sulfur content will cause pitting on metal flanges making them more difficult to seal in the long run. The higher quality flexible graphite materials generally come from USA, German and Japanese sources. Specifying Grafoil® flexible graphite will ensure you get a quality material.
The flexible graphite sheet material is either rolled into a continuous roll, or cut to standard sheet sizes. The most common sizes are 39.4" x 39.4" (meter x meter), or 60" x 60". The thickness of the sheet can range from .005" to 1" thick via a laminating process. The most common thickness as in most of the gasket world is 1/16", 1/8", 1/32", 1/64th& ¼".
Because flexible graphite has such poor tensile strength, it is often combined with metal.
Nothing is more frustrating than carefully cutting a large gasket, and then having it break in half when you pick it up off the table. To combat this two common forms of metal are added to the core of the flexible graphite. (1) A .002" stainless steel foil which is laminated within the sheet using glue to adhere it. In most applications this works great, but in some applications that get hot the glue that was added can "gas off" contaminating the product you are producing. To overcome this issue, the stainless steel foil containing sheet can be placed in an oven prior to installation causing it to gas off in the oven rather than in your process. The second (2) method of overcoming off gassing is to use a stainless steel insert that mechanically bonds itself to the flexible graphite. This insert need to be stronger (thicker), so it is .004" thick, and will either have a triangular or starburst pattern that bites into the flexible graphite. This product does not have to be off gassed in an oven because no glue is used.
Industries have grown to rely on flexible graphite as an exceptional sealing material. Flexible graphite is versatile and capable of meeting most industrial requirements with ease. It can easily compensate most to irregularities found in surfaces making it an exceptional sealing material. Another advantage of using flexible graphite is that it easily blends with carbon yarns, or metals such as wire mesh or sheet to provide strength. It has a great PH range that varies from 0 to 14 which makes it extremely resistant to most types of chemicals. Be it corrosive or acidic, the material can withstand the long run and act as an efficient sealing component. Because they are used in its production, the common acids that it should not be used with are sulfuric and nucleic acids. Most everything else (consult American Seal & Packing if you have doubts) can be sealed using flexible graphite as the sealant.
Because of flexible graphite's versatile nature, it is used in a wide range of applications including internal combustion, chemical seals, heat exchangers, exhaust, pipe flanges, oil and gas refining, power generation, pump and valve seals, sealing about any fluid transfers and other types of industrial usage.
When choosing flexible graphite, the buyer should consider multiple factors including the thickness of the product, the combination of materials used and its shape. Because flexible graphite is soft and conformable it seals better than any other material. When valve manufactures need a valve stem to seal against VOC's (Volatile Organic Compounds) as required by the Environmental Protection Agency (USA), or a valve has to be "Fire Safe" flexible graphite is doing most of the sealing. Often in combination sets utilizing various shapes materials and densities.
There are different grades of materials available including Automotive, Industrial and Nuclear grades. Flexible graphite can be added to spiral wound gaskets, KammProfile gaskets, jacketed gaskets, heat exchanger gaskets, eyeleted gaskets, and a wide range of braided and die formed shapes.
Some of the typical characteristics of flexible graphite is that it is resistive to fire, flexible, has good resistance against most chemicals and are also reliable when it comes to handling high temperature applications. They are often used in gasketing chemicals, as a heat shield and also as a noise reducing component. The sealant can also be used in electronic applications when you need to shield your components from EMI and RFI. Flexible graphite also has great thermal and electrical conductivity, and is commonly used as heat sinks in computer and other applications.