Pump seals, turbine seals, shaft seals and other similar seal applications may find it necessary to use a seal component which has very high heat generative properties. For instance, carbon seals often are used in dynamic machines which have rotary components. Such materials as carbon are somewhat brittle and produce very high heat under friction conditions. Consequently, such carbon seals have been limited to low speed uses because of heat transmission problems. There has been difficulty in transmitting heat away from carbon seals by known assembly procedures.
Carbon seals, rings and the like heretofore have been held in place by adhesives or, in some cases, mechanically by clamping, shrink fitting or retained with the use of grooves, snap rings, splines, etc. Adhesives and mechanically held mechanisms create problems due to the inherent characteristics of carbon or carbon/graphite material.
Such seals are brittle, fragile and transmit frictional heat. They are desirable because of their very low coefficient of thermal expansion, but they have a very high thermal conductivity. When a carbon seal is used in conjunction with a high speed rotating component, for instance, the seal generally is fastened to a stationary component or housing at a particular position relative to the rotating component. Typically, the housing is made of metal and the carbon seal is attached to the metal housing. Since the carbon seal is an excellent conductor of heat, the heat which is generated at the sealing surface propagates quickly through the seal to the surface that is attached to the stationary housing.
If the carbon seal is bonded to the housing with a substance that is heat sensitive, as with most adhesives, the heat traveling from the source proximate the rotating shaft toward the stationary housing can adversely affect the bonding characteristics of the adhesive. Although most adhesives are desirable for withstanding harsh environments, they also act as insulators and will not allow the heat to dissipate. As a result, the frictional heat builds up until the sheer strength of the adhesive breaks down, allowing the carbon seal to rotate and destroy itself.
Grooves, splines or other geometric, mechanical fastening systems often cause cracks in the seal due to the brittle nature of the material, such as carbon.
With shrink fit systems, if the carbon part is held too tight, strain is created and the carbon material will easily break. The tolerance problems of shrink fit systems are impractical in most applications. If the shrink fit is at a minimum, when the heat reaches the surrounding housing, the housing will expand due to its coefficient of thermal expansion, resulting in a loosening of the seal itself. Maintaining tight tolerances simply is impractical and far too costly with most applications.
This invention is directed to solving the above problems and satisfying a need for a new and improved seal assembly and method of fabricating a seal which uses a high heat generative, usually brittle, material such as carbon or the like.