Tough and durable: Rolling bearing cages with DLC coating

NKE Austria GmbH introduces rolling bearing cages with DLC (Diamond-like Carbon) coating. These steel cages coated with DLC are tougher and last longer than the standard, uncoated brass variants, and are ideally suited to harsh operating conditions. Other bearing components besides cages can also be treated with the amorphous carbon coating.

As part of its continuous effort to improve the performance capabilities of its rolling bearings, NKE researches surface coating technologies and uses alternative cage materials. Bearings that are used in machines with high radial accelerations, centrifugal forces or vibrations are typically equipped with inner-ring or outer-ring guided, primarily one-piece, solid brass cages in order to minimise any undesirable effects the cage may have on the motion characteristics of the rolling elements. Examples of typical applications include big end bearings, fast accelerating gearboxes or generator systems. Although solid brass cages are an acknowledged standard, they are still subject to certain operating limits. In applications with heavy loading, excessive wear, abrasion of the cage guide surfaces or even mechanical failure can occur.

In order to improve the performance of radial cylindrical roller bearings and radial deep groove ball bearings in particular, for demanding operating conditions NKE uses a cage made from high strength material with an amorphous carbon coating, the DLC coating with NKE suffix SQ202. This increases resistance to breakage and lowers the coefficient of friction between the rolling bearing shoulders and the cage, helping to prevent premature wear or abrasion especially in applications where lubrication is difficult. The material of choice for the cage is steel, and depending on the design of the bearing the cage may be machined solid steel with inner or outer ring guidance. These cages are identified accordingly with the suffixes F(P)A or FPB.

The coating itself must satisfy the following requirements: it must be hard and wear-resistant, and adhere to the surface for the entire operating period. Due to its low coefficient of friction and good sliding properties, the coating provides protection from adhesive wear and withstands lubricant starvation conditions. One of the most important properties of the coating is that it prevents wear and thus also the abrasion particles that become trapped by the lubricating grease in the bearing. The wear process cannot be entirely stopped, but the coating improves the steel cages‘ resistance to wear significantly, preventing scuffing on the cage support surfaces. It helps to prolong the service life of bearings significantly in extreme operating conditions. The use of the coating is not restricted to cages – practically all NKE bearing components made from steel can be supplied with this surface treatment.

The coating has undergone application-specific tests carried out jointly with a customer, and very positive results were obtained. The service life of bearings was extended considerably, and mechanical failures were eliminated altogether. When compared directly with uncoated brass cage variants, the steel cages with the SQ202 coating offer clearly superior performance in terms of wear and strength in harsh application environments.

NKE
www.nke.at