With a rotary shaft seal, the medium to be sealed can be fluid (grease), liquid or gaseous. Usually the medium the be sealed is lubricating oil and lubricating grease. In addition to the main requirement for good sealing, further demands are placed upon radial shaft seals like, operational reliability, long working life, simple fitting, compatibility towards the media to be sealed and low friction.
The importance given to the following factors in each individual case, and the operating conditions, are critical when selecting a seal:
- the medium to be sealed
- the surface speed
- the temperature
- the pressure
- exposure to external dirt
The function of the radial shaft seal in sealing rotating shafts against the housing assembly is divided into two parts:
- Static sealing and ensuring an interference fit between the O.D. covering of the radial shaft seal and the housing bore
- Static and dynamic sealing between the lip of the radial shaft seal and the shaft
The radial shaft seal is subjected to the complex interactions between the material of the seal, the rotating surface of the revolving shaft, and the medium as well as to its surroundings, which are determined by the working conditions. Thus a number of influencing factors affect the sealing behavior and the life of the radial shaft seal, and these factors must be taken into account in the configuration of the seal contact as well as in the design and the choice of the radial shaft seal.
Static Tightness/Seating in the Bore
The O.D. covering of the radial shaft seal, also called the press-fit part of the radial shaft seal, has the task of making a static seal between this seating and the housing bore. Over and above that, the O.D. covering must allow optimum assembly of the radial shaft seal to be carried out.
To fulfill this task, radial shaft seals are employed using different designs of the press-fit parts, depending on the design of the seal contact area, and also on the fitting and working conditions. To ensure trouble-free assembly, the O.D. covering is provided with suitable chamfer or radii, as well as press-fit allowances to a nominal outside diameter.