A New Bearing From A Technological Alliance

Tilt-pad Fluid-film Bearing Outperforms Flooded & Spray Feed Technologies

Kingsbury, Inc. of Philadelphia, PA USA and Coleherne, Ltd of Cheshire, England have combined technical and marketing skills to provide one of the most significant advances in bearing technology since the invention of the tilt-pad thrust bearing over 80 years ago. Internationally recognized as the most trusted name in fluid film bearings, Kingsbury brings its engineering leadership to Coleherne, one of Europe's most familiar bearing service providers. The result is the successful achievement of new technical innovation called the KingCole bearing.

KingCole incorporates a new, highly efficient Leading Edge Groove (LEG) lubrication system into a bearing style familiar to all of Europe. The LEG system lowers frictional losses and lube oil requirements with accompanying reduction in oil film temperatures - features which contribute to overall installation economy.

Important design features, such as a 360º pad pivot arrangement as well as conservative load ratings, allow users to confidently specify the KingCole in tough applications.

The KingCole can be specified for either new or retrofit installations as one-to-one replacement in existing applications, reducing downtime and ensuring an exact fit. ISO standards are used for all dimensional tolerances.

Advantages Of LEG Technology

Leading Edge Groove (LEG) technology, introduced by Kingsbury in 1984, has revolutionized the world of thrust bearings. The creation of these new thrust bearings has made it possible for the world's leading equipment manufacturers to simultaneously increase bearing capacity, reduce friction losses, and hold white metal temperatures within acceptable limits. When compared to a standard thrust bearing, the advanced design KingCole LEG bearing can:

• Reduce operating temperatures at the 75/75 location by 8º to 27ºC, depending on shaft speed.
  
• Provide a load carrying capacity increase of 15-20%, based on that temperature reduction.
  
• Operate at oil flow rates as much as 60% lower, with an accompanying reduction in friction losses of 40%.
  

The KingCole's LEG bearing design has proven itself through exhaustive testing and field research to represent the most reliable and efficient advancement in directed lubrication technology. Yet the design concept is remarkably - and elegantly - simple.

The bearing pads and carrier ring are constructed so that cool undiluted inlet oil flows from the leading edge groove in the bearing pad directly into the oil film. The cool oil in the oil film wedge insulates the white metal face from the hot oil carryover that adheres to the rotating collar.

In contrast to the KingCole LEG bearing, the oil for spray-fed bearings is injected not directly onto the bearing surfaces but between them. This can result in uneven bearing lubrication and the need to supply impractically high pressure to get true effective scouring of the hot oil carryover adhering to the thrust collar. There is also a tendency of the small jet holes to clog with foreign material, further hampering distribution. Greater friction, higher operating temperatures, and more power loss are the ultimate result.

Friction power loss is lower than both flooded and spray feed bearings due to the reduced oil flow. The flow of cool oil over the leading edge lowers pad surface temperatures, increasing the KingCole's capacity.

Product & Component Description

While the general arrangement of the KingCole appears to be very familiar, certain key features provide advantages over the more common tilt-pad bearings in use today.

Pads All KingCole bearing pads are provide with Leading Edge Groove (LEG) lubrication grooves to improve oil flow, reduce power loss, reduce friction and reduce pad temperatures. Bearings are designed to the proper rotation direction rather than a style which accommodates either clockwise or counterclockwise rotation. This feature means that performance is assured according to design tolerances rather than on averages.

Standard materials of construction of pad body are low carbon steel with high tin content white metal face, although material selection can be engineered to meet unusual requirements.

KingCole utilizes a distinctive raised "button" on the back of the pad to allow for full 360º pivot, rather than the more familiar strip which allows pad tilt in only one direction. Pad buttons are made of carbon tool steel, heated to 52 to 57

Rockwell C to ensure no flattening of the sphere. Tests indicate that this feature lowers the spread of temperatures from pad to pad.

Carrier rings Carrier rings are constructed to exacting tolerances and are normally provided in halves to allow simple installation in tough-to-reach applications.
Standard material of construction is low carbon steel with tensile strength of 483 MPA.

Lubrication ports from the carrier ring provide oil directly into the bearing pads, ensuring even pressure and distribution.

Pad retention Pads are held in position by a retaining fastener which can be removed easily to facilitate service or replacement. This is similar to designs common in most European bearing applications.

Oil feed tube The oil feed tube, connecting the base ring and pad, is uniquely designed so that the pad is free to pivot. This allows freedom of movement in the pad and eliminates the possibility of leakage as all oil is fed directly to the pad face.

LEG Bearing Housing Requirements

The bearing housing requirements for the KingCole LEG bearing are similar to those of standard thrust bearings. Oil seals at the back of the carrier rings are not required as the inlet oil is confined to passages within the base ring assembly. Fresh oil enters the bearing through an annulus located at the bottom of the base ring. The discharge space should be large enough to minimize contact between the discharged oil and the rotating collar. The discharge oil outlet should be amply sized so that oil can flow freely from the bearing cavity.

A tangential discharge opening is recommended, equal in diameter to 80% of the recommended collar thickness. If possible, the discharge outlet should be located in the bottom of the bearing housing. Alternately, it should be located tangential to collar rotation.

Instrumentation

KingCole bearings can be instrumented in the same manner as European standard thrust bearings.

Temperature Changes in load, shaft speed, oil flow, oil inlet temperature, or bearing surface finish can affect bearing surface temperatures. At excessively high temperatures, the pad white metal is subject to wiping which causes bearing failure. While computer predictions of acceptable operating temperatures are based on typical empirical data, the algorithms used do include assumptions about the nature of the oil film shape, amount of hot oil carryover, and average viscosity. Consequently, for critical applications, built-in temperature sensors are recommended to monitor white metal temperatures under all operating conditions. Either thermocouples or resistance temperature detectors (RTDs) can be installed in contact with the white metal or in the pad body near the pad body/white metal interface.

Thrust loads For bearings subject to critically high loads, continual thrust measurements can provide a vital indication of machine and bearing condition. To allow thrust measurement, a strain gauge load cell can be installed in one or more places in the bearing.

Load cells can be installed in LEG bearings in place of the pad support. Complete measuring instrumentation and recorders can also be provided.