Rotary Seals - Trelleborg Sealing Solutions - #19

In order to achieve an optimum sealing solution, it is also necessary to select suitable material pairing between the seal and the mating surface.

The functional reliability and service life of a seal depend to a very great extent on the quality and surface finish of the mating surface to be sealed. Scores, scratches, pores, concentric or spiral machining marks are not permitted. Higher demands must be made on the surface finish of dynamic mating surfaces than to static mating surfaces.

The characteristics most frequently used to describe the surface microfinish, R_a,R_z and R_max, are defined in ISO 4287. These characteristics alone, however, are not sufficient for assessing the suitability in seal engineering. In addition, the material contact area R_mr in accordance with ISO 4287 should be considered. The significance of these surface specifications is illustrated in Figure 5. It shows clearly that specification of R_a or R_z alone does not describe the profile form accurately enough and is thus not sufficient for assessing suitability in seal engineering.

The material contact area R_mr is essential for assessing surfaces, as this parameter is determined by the specific profile form. This in term is directly depending on the machining process employed.

Figure 5 Profile forms of surfaces

The running surface for oil seals is specified in DIN 3760/61. The surface should meet the following requirements:

Surface roughness R_a = 0.2 to 0.8 |jm

R_z = 1 to 4 |jm R_max = 6.3 |jm

Hardness 55 HRC or 600 HV,

hardness depth min. 0.3 mm

Latest information available atwww.tss.trelleborg.com Edition April 2007

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