The working principle of the Basic rotary seal
The surface between the sealing edge and the shaft is the most important. The sealing effect is achieved by pre-loading the sealing lip, making its internal diameter slightly smaller than the shaft diameter. The garter spring provides constant mechanical pressure and maintains the radial force to the shaft, flattening the sealing edge to defined width. Sealing is the result of the surface tension of the hydrodynamic oil layer between the seal flattened area and the shaft. Oil thickness must be between 1 and 3 micro millimeters as to avoid leakage. The meniscus acts as an interface between the outside air and the fluid. Any break in the meniscus will result in leakage. This can happen if the shaft contains scratches along the seal path.
The metal case
The metal insert or case is used to give the seal strength and rigidity. It is usually made of cold rolled steel in accordance with the standard DIN 1624. Stainless steel can be used to avoid rust or chemical corrosion attack. Chromium-Nickel AISI 304 (DIN 1.4301 - V4A), Chromium-Nickel Molybdenum AISI 316 (DIN 1.4401 - V4A).
The garter spring
The garter spring maintains the radial force exerted by the sealing lip around the shaft surface. It is usually made of SAE 1074 spring harmonic steel wire (DIN 17223) or AISI 302 chromium nickel stainless steel wire (DIN 1.4300).