Applications involving extreme temperatures are challenging for many gasket materials. In high temperature applications, non-graphite gasket materials, such as Nitrile, Silicone, PTFE, and others, will only support temperatures up to a certain level, while applications involving low temperatures bring similar challenges for other materials. In either case, selection of the appropriate material is essential for achieving seals that are effective, reliable and safe.
High temperature applications
Nitrile gaskets will service application temperatures up to about 95°C (203°F), while Silicone and PTFE will service application temperatures up to 200°C (392°F) and 260°C (500°F) respectively. For applications involving temperatures higher than these, gaskets made from graphite sheet are the preferred choice.
Graphite, a form of carbon, is an inert material which resists chemical attack even at high temperatures. Since it is an inert material, graphite will not react with, or contaminate, other substances. Graphite also has a low coefficient of friction which is useful in joint sealing applications – gaskets made from graphite sheet readily adapt to loading forces as flange faces are tightened.
Standard-grade graphite gaskets will support temperature ranges of -240°C (-400°F) to 450°C (850°F) in an oxidizing atmosphere, as well as pressures up to 2000 psi. Because high-purity graphite sheet can become brittle in strongly oxidizing atmospheres, oxidation-resistant graphite is preferred for applications where powerful oxidizing agents are present. In applications involving higher pressures, graphite sheet reinforced with metal core inserts to provide additional strength and stability is the preferred material.
For servicing high temperature applications, CRG offers flexible gaskets cut from a range of graphite sheet materials. These include gaskets made from high-purity and oxidation-resistant graphite, as well as those made with a foil insert, tanged core, or Mylar film insert. The latter types offer extra strength and stability in high pressure applications. For applications involving severe temperatures and pressures, CRG can also supply gaskets made from Teadit GR1700 Sigraflex APX2 Hochdruck material. This high-strength, multilayer material, which is superior to standard grades of graphite foil, can support a maximum service temperature of 650°C (1202°F) and a working pressure resistance of 3600 psi.
Low temperature applications
Sealing applications involving low temperatures can be problematic to service. At low temperatures, many standard gasket materials harden and stiffen, becoming less compliant as a load is applied. In addition, at low temperatures, many gasket materials can acquire a compression set and begin to leak.
For servicing low temperature and cryogenic applications, two types of gasket materials are preferred: silicone and PTFE. Because each material has different grades and variants, it is always wise to check carefully with your gasket supplier as to which grade is best for a specific low temperature application.
Silicone gaskets will generally remain flexible and compliant at application temperatures down to -60°C (-76°F), while some types, such as phenyl-based silicone, will service application temperatures as low as -90°C (-130°F). Fluorosilicone (FVMQ) gaskets can be used in oil and fuel applications with service temperatures down to -75°C (-103°F).
PTFE (Teflon™) gaskets are the preferred choice for cryogenic service. PTFE gaskets will service temperatures down to -185°C (-300°F). While PTFE gaskets will not harden or stiffen at these low temperatures, the material can tend to creep.
CRG has over 30-years of experience in manufacturing precision-cut flexible graphite gaskets for extreme temperature applications. These gaskets are produced from the highest quality materials supplied by our supply chain partners, including Teadit, Garlock and others. All gaskets we manufacture are made to customer specifications and requirements, using the latest manufacturing processes in our ISO 9001-certified production facility. If required, we can supply gaskets made from flexible graphite sheet with or without pressure sensitive adhesive (PSA) backing.
For further information on the extreme temperature graphite gaskets we can supply, please contact our sales department at crg@canadarubbergroup.com.