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Glossary R


Glossary R

Ra:
The average of all peaks and valleys from the mean line within cut-off (.10” or .254 mm). Ra does not describe the surface profile (texture) and two shafts with the same Ra value can have very different surface characteristics.

Rate, Leakage:
The quantity of fluid passing through a seal in a given length of time.

Rate, Spring:
The force, independent of initial tension, which is required for extending the working length of a spring a unit distance.

Rate, Wear:
The amount of seal contact surface wear per unit of time.

Relaxation, Stress:
A characteristic of an elastomer wherein a gradual increase in deformation is experienced under constand load, after the initial deformation.

Resilience:
In elastomer or rubber like materials subjected to and relieved of stress, resilience is the ratio of energy given up on recovery from the deformation to the energy required to produce the deformation. Resilience for an elastomer is usually expressed in percent.

Resistance, Cold:
The ability of a seal or sealing material to withstand the effects of a low temperature environment without loss of serviceability.

Resistance, Heat:
The ability of a seal or sealing material to resist the deteriorating effects of elevated temperatures.

Resistance, Ozone:
The ability of a material to withstand the deteriorating effects of ozone (surface cracking).

Rib:
A long, narrow projection which is normally triangular in cross-section and which is molded into the outside lip surface of a helix seal. It is oriented at an angle to the shaft axis. One end of the rib forms part of the seal-lip contact surface.

Rough Trim:
A trimmed surface with irregularities on the outside and inside lip surfaces in the immediate vicinity of the contact line.

Roughness:
Irregularities in shaft surface texture which result from the production process.

Roughness, Axial Surface:
Surface roughness of a shaft measured in a direction parallel with the centerline axis.

Roughness, Circumferential Surface:
Surface roughness of a shaft measured in a direction (plane) normal to the centerline axis.

Run-In:
The period of initial operation during which the seal-lip wear rate is greatest and the contact surface is developed.

Runout, Dynamic:
Twice the distance the center of the shaft is displaced form the center of rotation and expressed in TIR. That runout to which the seal lip is subjected due to the outside diameter of the shaft not rotating in a true circle.

RZ(din):
Average peak to valley height.

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