Machine Design

Bearing works three times longer with new material

Cronidur bearings are suitable for pumps where a flame-resistant fluid serves both as pressure agent and as lubricant for the bearings. Here, in the mixed-friction range, they reach about 10 to 20 times the service life of standard bearings.

A new material called Cronidur, first used in space applications, works well in bearings. Machine-tool spindle manufacturer, Spindeltechnologie Weiss GmbH, Schweinfurt, Germany, has fitted its high-speed, heavy-duty motor spindles with FAG spindle bearings made of Cronidur. This lets the spindle manufacturer offer bearings with three times the usual service life. The hybrid spindle bearings have Cronidur rings and ceramic rolling elements. The new rolling bearing steel comes from a family of high-nitrogen steels characterized by its extreme hardness of more than Rc 58. The material also exhibits a high-temperature hardness, corrosion resistance, tolerance to starved lubrication, mixed-friction conditions, and contamination particles in the lubricant. "The increased operational reliability of the hybrid bearing pays off with a longer service life and more machine uptime," says Siegfried Weiss, the owner of the company.

Standard bearings in machine spindles have service lives limited by wear, but overloading and material fatigue play a part. The hybrid spindle bearings feature considerably lower wear rates than the conventional material combinations, such as bearing rings made of field-proven 100Cr6 rolling-bearing steel and ceramic rolling elements. Under identical conditions, bearings made of the recent material have service lives about three times longer. In contact areas, the recent hybrid bearings carry a 25% higher contact load, thus providing better prevention of fatigue damage. This also means the material accommodates higher short-term loads without causing permanent bearing damage than was possible with traditional bearings. Field tests with high-performance, high-speed spindle units proved the statements.

The new material provides another advantage: should damage occur, it progresses more slowly than in standard bearings, which simplifies diagnosis and maintenance.

Rolling-element bearings of the new material were first used in aircraft and aerospace applications because of the unusual combination of good fatigue strength and corrosion resistance. The bearings are used in Space-Shuttle-fuel pumps and as rotor-head bearings in the latest Sikorsky helicopter, the S-92 Helibus. The material is also finding work in conventional applications such as chainsaws and machine tools.

This information provided by FAG Bearings Corp., Danbury, Conn.

TAGS: Materials
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