Journal Bearing

Definition

What is the definition of bearing?

A friction-reducing device that allows one moving part to glide past another moving part. Bearings

operate using a sliding or rolling mechanism.

What is the definition of journal?

The shaft of a journal bearing. The journal is softer than the outer casing of the bearing.

What is the definition of journal bearing?

A type of plain bearing designed to reduce friction by supporting radial loads. Journal bearings are

often used when the load is light and motion is relatively continuous, such as in crankshafts. Journal

bearings are also called radial or sleeve bearings.

What is the definition of lubricant?

A substance used to reduce friction between two surfaces in relative motion. Oil and grease are

common industrial lubricants.

Application hydrodynamic bearing in industry:

Hydroelectric generators

Steam turbine

High speed blowers

Dredged pumps

Electric motor

Oil pumps

Pulp refines

Air preheated

Extrudes

Hydraulic turbine

Gas turbine

Boiler feed pumps

Rock crusher

Cooling pump

Types of hydrodynamic bearing :

Journal Bearings

Tilting pad journal bearings offer the maximum rotor Stability thanks to their exceptional stiffness and

Damping characteristics. This makes them ideal for use in high speed machinery operating under low to

high loads, e.g. turbines, turbo compressors, pumps and high-speed gearboxes. Available in both flooded

and directed lubrication designs, their overall load capacity is determined by the oil temperature generated

and to control this, several alternatives are offered:

• Optimized lubrication systems which reduce power

losses and temperature, including our directed

lubrication and patented advantage system

• Offset pivoting of pads to reduce the temperature

generated at the sliding surface

• A choice of pad material to permit higher operating

temperatures and improved heat conductivity

Other design options available include hydrostatic lift to

prevent abrasive wear during slow speed and high load

conditions, spherical support systems to permit rotor

deflection angles of up to 0.15° without the risk of edge

loading and wear.

Thrust Bearings

Tilting pad thrust bearings provide a greater load carrying capacity, compared to thrust plate and taper land

bearings. These are offered in flooded, directed and our patented OCITM lubrication configuration. Thrust

bearings are available in a wide range of sizes and pad configurations from our standard catalogue or as a

custom designed solution.

Self equalising bearings are offered to accommodate thrust collar alignment, required for example on API

compliant applications. The equalising link system automatically adjusts to accommodate geometrical

misalignments up to 0.1°. This self equalising function creates an even load and therefore an equal

minimum oil film thickness on each pad. As all tilting pads are loaded equally, they offer greater

operational safety than standard thrust bearings.

Combined Bearings

Our combined bearings provide tailored solutions for special applications with restricted assembly and

mounting conditions and are designed to meet customer specific requirements in terms of performance and

running conditions.

Available in any arrangement of fixed geometry and tilting pad designs, the compact cartridge design

provides axial and radial rotor support whilst minimizing the space requirements. Reduced space permits

shorter rotor and stiffer rotor designs or additional compression stages to be included.

Pedestal Bearings

For a variety of applications including electric motors,generators, and line shafts. Designed with tilting pad

or fixed geometry journal bearings, a thrust bearing can be included to support axial loads. Assemblies can

be selected from our standard range of bearings or custom designed to meet specific customer requirements

such as insulated bearing assemblies. Shaft sizes range from 100mm (4”) up

to 625mm (25”).. Bearing lubrication is achieved by oil rings or pressure fed lubrication. Hydrostatic

lubrication and performance monitoring provisions are also available.

Low-speed pins and bushings are a form of journal bearing in which the shaft or shell generally does not

make a full rotation. The partial rotation at low speed, before typically reversing direction, does not allow

for the formation of a full fluid film and thus metal-to-metal contact does occur within the bearing. Pins

and bushings continually operate in the boundary lubrication regime. These types of bearings are typically

lubricated with extreme pressure (EP) grease to aid in supporting the load. Solid molybdenum disulfide

(molly) is included in the grease to enhance the load-carrying capability of the lubricant. Many outdoor

construction and mining equipment applications incorporate pins and bushings. Consequently, shock

loading and water and dirt contamination are often major factors in their lubrication.

Dry journal bearings consist of a shaft rotating in a dry sleeve, usually a polymer, which may be blended

with solids such as molybdenum, graphite, PTFE or nylon. These bearings are limited to low-load and low-

surface speed applications. Semi lubricated journal bearings consist of a shaft rotating in a porous metal

sleeve of sintered bronze or aluminium in which lubricating oil is contained within the pores of the porous

metal. These bearings are restricted to low loads, low-to-medium velocity and temperatures up to 100°C

(210°F).

Tilting-pad or pivoting-shoe bearings consist of a shaft rotating within a shell made up of curved pads.

Each pad is able to pivot independently and align with the curvature of the shaft. A diagram of a tilt-pad

bearing is presented in Figure 1. The advantage of this design is the more accurate alignment of the

supporting shell to the rotating shaft and the increase in shaft stability which is obtained

Journal bearings are meant to include sleeve, plain, shell and

Babbitt bearings. The term Babbitt actually refers to the layers of softer

metals (lead, tin and copper) which form the metal contact surface of the bearing shell. These softer metals

overlay a stronger steel support shell and are needed to cushion the shell from the harder rotating shaft.

Simple shell-type journal bearings accept only radial loading, perpendicular to the shaft, generally due to

the downward weight or load of the shaft. Thrust or axial loads, along the axis of the shaft, can also be

accommodated by journal bearings designed for this purpose. Figure 1 shows a tilt-pad bearing capable of

accepting both radial and thrust loads.

It is important to understand that the rotating shaft is not cantered in the bearing shell during normal operation. This offset distance is referred to as the eccentricity of the bearing and creates a unique location for the minimum oil film thickness, as illustrated in Figure 3.

The ISO grade number indicated is the preferred grade for speed and temperature range. ISO 68- and 100-grade oils are commonly used in indoor, heated

applications, with 32-grade oils being used for high-speed (10,000 RPM) units and some outdoor low-temperature applications. Note in the table that the higher the bearing speed, the lower the oil viscosity required; and that the higher the operating temperature of the unit, the higher the oil viscosity that is required. If vibration or minor shock loading is possible, a higher grade of oil than the one indicated in Table 1 should be considered.

Bearing Speed Bearing / Oil Temperature (°C)

(rpm) 0 to 50 60 75 90

300 to 1,500 - 68 100 to 150 -

~1,800 32 32 to 46 68 to 100 100

~3,600 32 32 46 to 68 68 to 100

~10,000 32 32 32 32 to 46

References

Encyclopedia of Tribology (Tribology Series, 15), ISBN 0444884017, 1990; T. Someya (Editor),

Journal-Bearing Databook, ISBN 038717074X,

Hydrodynamic journal bearing test and analysis, Volume 1517

NASA contractor report

Hydrodynamic Journal Bearing Test and Analysis, Richard J. Rossbach

Hydrodynamic Bearings: Applications And Implications To Machine-Failure Prevention

Kristin L. Wood Dean Neikirk, Ilene Busch-Vishniac, William Weldon, Chin-

Seng Chu, Youndmin Kim, Vikas Gupta, William Maddox, and David Masser

Departments of Mechanical and Electrical Engineering

The University of Texas, Austin, TX 78712

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