"Progressive loss of material from the surface of a solid body brought about by mechanical causes, i.e. contact with, and relative movement of, an adjacent solid, liquid or gaseous body." (DIN 50 320, December 1979).

Adhesion wear on a seal face (SEM picture)


Wear on a seal face (cast chromium) caused by solid matter in the sealing gap


Wear rate of a carbon stationary seat as a function of running time

Wear arises in a mechanical seal on its sliding faces, torque transmission elements and dynamically loaded secondary seals. When assessing wear on seal faces and stationary seats, consideration must always be given to the process medium. Wear on sliding faces is greater during a mechanical seal's running-in period. This is owed to the mutual adaptation of the sliding faces under operating conditions. Sliding face wear caused by mixed and boundary friction friction types leave the sliding faces with a uniform appearance; the leakage rate is minimal. In the case of abrasion wear, the softer face material is worn by solid matter that has worked its way into the sealing gap. The edges of thermal stress cracks can also exert a highly abrasive effect. Crystalline solids – embedded in the softer material – can cause wear on the harder material. With wear of this type, the sliding faces display pronounced scores. Adhesion wear is promoted by dry running. The forces of adhesion lead to local overstepping of the permissible shear stresses; material is detached from the surface. Deformation wear results from warping of the sliding faces and is characterized by an irregular development profile. With abrasive jet wear (erosion), material is washed out of the seal rings as the result of high flow velocities. Cavitation wear occurs in the outer zone of the sealing gap. At high speeds there is a possibility of the vaporization pressure being reached locally. The vapour bubbles thus formed are compressed under high pressure, and the resultant knocking produces a sponge-like damage profile. Shaft wear under O-rings is caused by axial movements of the O-ring in combination with particles of dirt which lodge in the wedge-shaped gap between O-ring and shaft or which become embedded in the O-ring. For wear at the torque input, see deflections.

Erosion and cavitation wear on a seal face