Ripple Test
Ripple formation (or oscillation wear) can occur in bearings that rarely or never rotate. This impairment is caused at a standstill with dynamic bearing loads, for example due to machine vibrations. These dynamic bearing loads generate relative motion in the Hertzian contact area due to elastic and plastic deformations. This can give rise to a combination of the damage mechanisms of adhesion, abrasion, surface breakdown and tribological-chemical reaction, which leads to the ripple formation. A ripple test is conducted to examine lubricants as to their protective suitability against rippling and corrosion. The inner rings of a greased four-point bearing are attached to a vertically installed axis. The outer rings are seated in the housing. A servo-hydraulic linear cylinder introduces a sinusoidal axial load of ±70 kN via the outer ring. Furthermore, a constant flow of water with 6 ml/min, 1% salt content passes through the bearing. Two pins attached to the bearing cages prevent the bearing from rotating. The ripples are examined after 1 million load changes at a frequency of 10 Hz which equates to a test run time of approximately 28 hours and their depth is measured using a roundness measuring instrument.