NoWear coated bearings
NoWear is a wear-resistant carbon coating that can be applied to the rolling elements and inner ring raceway(s) of a bearing (designation suffix L7DA) or only the rolling elements (designation suffix L5DA) (fig. 1). A physical vapour deposition process applies the wear-resistant carbon coating ranging from 1 to 3 μm depending on the size of the bearing. The hardness of the coating is 1 200 HV10.
NoWear coated bearing surfaces retain the toughness of the underlying material while adopting the hardness, improved friction properties and wear-resistance of the coating.
During the running-in period, minute amounts of the coating material are transferred to the counter surfaces. This transfer reduces friction and improves resistance against wear and smearing, even in bearings where only the rolling elements are coated.
NoWear coated bearings are designed to extend service life, relubrication intervals and to withstand severe operating conditions including:
- increased risk of smearing
- insufficient lubricating film for undisturbed bearing operation (κ < 1)
- sudden load variations
- light loads
- rapid speed changes
- vibration and oscillations
high operating temperatures
NoWear coated bearings open up new possibilities to existing applications operating under severe conditions. They do not require major design changes and provide new design possibilities. Typical applications where NoWear coated bearings are used include:
- paper machines
- marine and offshore applications
- hydraulic pumps
For demanding applications where NoWear coated bearings are being considered, several operating parameters must be taken into consideration and weighed against each other. Therefore, SKF recommends contacting the SKF application engineering service prior to selecting NoWear coated bearings.
NoWear coated bearings are not intended for vacuum or other completely dry running applications. The coating does not act as a barrier against oxygen and is therefore not recommended as a corrosion inhibitor.
Bearing service lifeThe extended bearing service life that NoWear can provide in high-speed, lightly loaded applications is difficult to calculate and depends on a variety of factors. However, experience has shown a multifold improvement in bearing service life.
For greased bearings that operate at speeds near or above the permissible speed, or at high temperatures that shorten the grease life, using NoWear extends relubrication intervals.
When the objective is to extend bearing service life in applications with heavy loads and marginal lubrication conditions, NoWear can be a solution. However, NoWear cannot protect the bearing against spalling as a result of constant heavy loads. Under heavy loads the maximum shear stresses are located below the coating within the bearing steel, which still has the properties of standard steel.