Kingsbury Engineering Staff

This paper, co-authored by Kingsbury's R&D Manager, Scan DeCamillo, presents experimental temperature data on the LEG (Leading Edge Groove) journal bearing for both "on pad" and "between pad" loading conditions and for different bearing clearances. The experimental results are compared with data from a computer model of the LEG bearing. In addition, the paper discusses results obtained from bidirectional testing of the LEG, and describes a technique for reducing power losses of the bearing.

For the complete paper with associated illustrations, 

Articles

Machine Improvements from Directed-Lube Journal Bearings

Advantages of Leading Edge Groove (LEG) lubrication technology

Kingsbury's equalized LEG thrust bearings are fitted with leveling plates to ensure optimum load distribution and trouble free operation, while taking advantage of other features such as offset pivots to achieve the best possible performance. Other key features make the LEG bearing superior to other directed lubrication bearings in use today: Oil feed tubes connecting the base rings to the shoes ensures that cool oil does not bypass the film. The LEG feature is an integral part of the shoes, delivering oil immediately to the film. Large oil flow passages eliminate the possibility of clogging that can occur in nozzles. No oil seal rings are required, lowering power loss and simplifying design and installation. The LEG does not require special, higher pressure lube systems to deliver oil to the film.

For the complete paper with associated illustrations,

Performance Comparison of LEG and Flooded Bearings

Kingsbury's very popular brochure, "General Guide To Hydrodynamic Bearings," covers the background and invention of the tilting pad fluid film bearing, the types of fluid film bearings in common use and a comprehensive section on the diagnosis and troubleshooting of bearing problems. This booklet provides a very good overview of bearing failure modes, but due to size constraints, it cannot cover all known issues. This current page therefore includes information about other types of bearing failures and serves as an addendum to the HB brochure.

Any machinery engineers viewing this page or the companion PDF who do not find information concerning the issues that they are encountering in their own test stands or field applications are encouraged to contact Kingsbury's engineering department for assistance.

More Causes and Remedies of Fluid Film Bearing Failure

Kingsbury's CH Bearing System consists of a NDE unit featuring a flange-mounted housing with an equalized thrust bearing and a journal bearing shell, and a DE unit without a thrust bearing. The CH System is unique because it is completely self-contained, thereby eliminating the need for an external lube skid, emergency pump, accumulator, rundown tank or other special arrangements for oil lubrication.

Since no separate lubrication system is required, the cost savings are significant. Lubrication of the bearings is autonomous, as the NDE unit acts as a viscosity pump driven by shaft rotation. The system's oil circulator, working in tandem with the rotating collar, draws oil up from the sump as soon as the pump is switched on and therefore assures lubrication whenever the machine is in operation.

Thrust & Journal Bearing System

A temperature sensor mounted at the 75/75 position can provide the critical shoe temperature for that one, fixed location, but cannot indicate the temperature pattern over the entire shoe surface. In order to demonstrate the localized nature of the critical temperature region, we rely on isotherms (lines of constant temperature) based upon an array of 9 thermocouples evenly distributed across the shoe surface, plus a tenth thermocouple at the 75/75 location. The sensors are embedded in the babbitt material, approximately 0.03" (0.76 mm) below the shoe working surface. Values from all ten thermocouples are curve-fit in the circumferential and radial directions to obtain intermediate temperature values at other locations on the shoe. These combined measured and intermediate temperatures are plotted as isotherms in the accompanying illustrations.

The isotherms shown here demonstrate the changing temperature patterns which develop under various operating conditions.

Fluid Film Shoe Temperature Patterns

Any change in load, shaft speed, oil flow, oil inlet temperature, or bearing surface finish affects bearing temperature. In turn, excessively high temperatures in the shoe babbitt metal can lead to costly bearing failures caused by wiping of the babbitt.

As you would expect, computer programs are available which analyze oil film pressure, oil temperature, oil viscosity, and shoe deflection. However, these programs yield temperature predictions which are dependent upon several assumptions regarding film shape, hot oil carry-over, and average viscosity.

Fortunately, a more reliable method of assessing bearing performance exists. We offer shoes with built-in temperature sensors so you can continually monitor the shoe's surface temperature. This way, metal temperature (the most accurate indicator of the bearing condition) is known at a glance. Remember, discharge oil temperature is indicative only of the inlet oil temperature and the friction power loss in the bearing.

Temperature Measurement in Fluid Film Bearings

Since 1912, we have gained unequaled experience in designing and manufacturing thrust bearings. This section details design features which we developed to improve your machine's performance.

For Kingsbury thrust bearings to operate safely and efficiently, continuous self-renewing oil films must be present between the shoes and collar.

The oil supplied to the bearing should be cooled and filtered, so that the average particle size is less than the bearing's minimum film thickness. The typical oil flow path is shown below.

To understand end play, or axial clearance, picture a double thrust bearing (one on each side of the collar). End play is the distance the thrust collar can be moved between the bearings during intallation while applying load to either bearing.

 End play isn't an exact dimension. The shaft's maximum end play is limited to the smallest clearance between the stationery and rotating machine elements, while the shaft's minimum end play must be sufficient to prevent excessive power loss in the unloaded thrust bearing.

Any time a double thrust bearing is installed, end play must be provided to allow for an oil film to form in each bearing, and thermal expansion of the bearing elements.

Using Kingsbury Design Features

Once you have selected the correct thrust bearing style and size, you may want to estimate the babbitt temperature of the operating bearing. This is a good design practice when:

Collar surface speed exceeds 15,000 feet per minute (76.2 m/s)

Inlet oil temperature exceeds 120°F (50°C) or

Specifications limit maximum allowable temperature

To estimate the babbitt temperature at the recommended 75/75 position, use the graph on this page for steel shoes. If the temperature exceeds 265°F (130°C), you may be able to reduce it to a more acceptable level by substituting chrome-copper-backed shoe or offset-pivot steel shoes. Consult the graph below to determine if this is the case. For those applications where the babbitt temperature still exceeds 265°F (130°C), contact our Engineering Department for additional suggestions.

How to Estimate Babbitt Temperature

We have conducted experimental tests on a variety of oil discharge configurations. The results? We have found that overall bearing power loss and performance are affected by:

The clearance between the rotating thrust collar and the stationary housing, and

For high speed applications, our recommended discharge dimensions have been incorporated in a separate bearing accessory called an oil control ring. The oil control ring fits into the housing as a stationary shroud that provides proper clearance around the rotating thrust collar, and includes a properly sized tangential discharge opening. You can find bearing housing dimensions for oil control ring installation on the following pages.

Oil Discharge Configurations in Fluid Film Bearings

Changes in load, shaft speed, oil flow, oil inlet temperature, or bearing surface finish can affect bearing surface temperatures. At excessively high temperatures, the shoe babbitt metal is subject to wiping, which causes bearing failure.

Consequently, for critical applications, we recommend using shoes with built-in temperature sensors so you can monitor actual metal temperatures under all operating conditions.

Either thermocouples (TCs) or resistance temperature detectors (RTDs) can be installed in the shoe body near the shoe body/babbitt interface. See figure below for Kingsbury's recommended location.

If your bearing is subject to critically high loads, continual thrust measurement will give you a vital indication of machine and bearing condition. To measure thrust, we can install a strain gauge load cell in one or more of the upper leveling plates or thrust shoe.