Understanding Complex Material Analysis

Bearings

• Two basic types of bearings are used: friction and anti-friction bearings
• Friction bearings have a sliding contact between a shaft and the bearing
• Friction bearings use a special low-friction material lining a rigid housing
• Anti-friction bearings have a rolling contact between the shaft and bearing, using balls, needles or rollers
• Bearing housings are the outer casing
• Common materials for housings are cast iron, cast steel and fabricated steel
• Bearing dimensions are important for installation and alignment
• Bearing styles are chosen based on load, speed and direction of pull
• Solid bearings are used for low speed and load
• Split bearings differ in their housings

Bearing Housings

• Housings are sometimes called pillow blocks
• Parts of a friction bearing include: base, base bolt slots, cap, and cap bolt holes
• Common bearing housing sizes are fractional, not decimal
• Bearing size, design and service weight from the same supplier will usually have the same shaft centre dimension.

Styles of Bearings

• Types of flat bearings include solid and split bearings
• Solid bearings are frequently mounted in an inverted position and must be slid on or off the shaft
• Split bearing designs vary depending on manufacturer
• The choice of a bearing depends on load, rotational speed, and direction of pull
• Angle bearings are used when the load is applied parallel to or at a slight angle to the horizontal or when the bearing is mounted on a vertical support

Liner Materials

• Common metallic liner materials are babbitt, brass, bronze, and aluminum
• Common non-metallic liner materials are nylon, polyurethane, and phenol laminates
• Babbitt is a common anti-friction lining material for bearings
• Babbitt melts at a temperature of about 288°C (550°F)

Liner Materials (cont)

• Babbitt alloys commonly contain tin, copper, antimony and lead, with varying proportions
• Using mandrels to pour babbitt, which are short smooth pieces of shaft of the required diameter to hold the bearing securely in position during pouring

Bearing Installation and Removal

• Bearings are installed square on the shaft
• Shaft and housing checks should include diameter, roundness, deflection, surface damage, and cracks before installation
• Push fit bearings can be installed by hand
• Interference fit bearings are tightened on the shaft to reduce clearance when installed
• For clearance in bearings, shims are used to adjust space or gap between the shaft and bearing

Bearing Installation and Removal (cont.)

• When removing a bearing, use a puller
• Use caution when heating or cooling bearings
• Always select a proper fit to avoid damage or binding when removing or installing

Thrust Control

• The thrust of a shaft is controlled by the shaft shoulder and a collar.
• The liner material for end thrust of bearings can be solid babbitt, brass or bronze.
• There are multiple methods for dealing with thrust.

Kingsbury Thrust Bearings

• A special thrust bearing design for high speeds and heavy loads
• The design consists of a pair of rings: a revolving ring with a flat contact surface, and a stationary ring with multiple flat contact surfaces of a low-friction material
• Types of Kingsbury bearing systems include fixed pad, and tilting pad bearing systems

Angle Bearings

• Used in situations where the load is applied parallel to or at a slight angle to the horizontal, or mounted on a vertical support

Integrated Bearings

• Some heavy-duty machines utilize a base that's cast as an integral part of the machine itself rather than as a separate unit.

Joint Design

• Three general styles for bearing joints - flat joints, with a gib, and with an angle joint

Liner Materials (Cont.)

• Softer than the shaft material, so slightly deforms under heavy loads
• Wear-resistant (important to minimize wear)

Bearing Clearance

• Amount of clearance between the shaft and the bearing cap is important to prevent clamping or binding
• Clearance must be checked to prevent damage or friction
• Shims are used to adjust clearance
• P numbers classify bearing tolerance

Installing Tapered Bore Bearings

• Sleeve adapters allow for placement of a tapered bore bearing at any point on the shaft.
• The sleeve is slotted for expansion and contraction, has a threaded end which is used with a locknut for fastening
• Use caution to avoid damage to the bearing and shaft when tightening any mounted sleeve and/or locknut

Mounting Tapered Bore Bearings (Hydraulic)

• Using a hydraulic nut, the fitting is performed

Bearing Removal

• For destructive bearing removal, an oxyacetylene torch may be used

Pillow Block Installation and Removal

• Split housings typically consist of a base and a cap
• Vertically split housings use a one-piece ring and a base with separate end covers
• Common bearing designs are single-groove ball bearings, double-taper roller bearings, and spherical or concave roller bearings

Floating and Fixed Bearings

• To prevent end-float, one bearing must be fixed axially in the housing
• Floating bearings allow for movement to compensate for shaft expansion

Thrust Control Methods (Angular Contact Bearings)

• Thrust control in angular contact bearings can be achieved through a back-to- back, face-to-face, or tandem arrangement (of paired bearings)