Tham khảo tài liệu 'volume 18 - friction, lubrication, and wear technology part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Seals are usually classified as being either static or dynamic which refers to the motion the seal experiences rather than the presence or absence of pressure fluctuations. A dynamic seal has a surface that is in motion usually sliding relative to the contacting surface. This type of seal can experience either rotary or reciprocating motion or a combination of both. Static seals are available in many variations. The most frequently used static seals are probably O-rings gaskets and packing. O-rings Fig. 1 are also occasionally used as dynamic seals and are effective as seals when used within their recommended range. Fig. 1 Mechanical face seal O-rings are made from a variety of polymer materials including natural neoprene and nitrile rubbers. They are generally limited to a temperature range from 0 to 93 C 32 to 200 F because of their material composition. Chemical compatibility between the seal material and the fluid being sealed is an important design requirement. The surface finishes of the groove containing the O-ring and the mating surface are also significant in determining seal life and effectiveness. Another design requirement is the amount of compression. The catalogs of O-ring manufacturers provide definitive tables of groove size versus O-ring size and can determine compression which is generally from 10 to 15 . Gaskets Fig. 1 are used as seals between static machine joints and are the least expensive most effective choice for many applications. They are available in a variety of materials ranging from cork to metals such as copper. Some such as room-temperature vulcanizing RTV silicone rubber can be formed in place. Many contain asbestos which is being phased out because of environmental and health risks. The material selection and joint design of gaskets are driven by operating temperature range chemical compatibility and differential pressure. Typical applications are an engine head to block steam turbine upper to lower housing and bearing pillow .
