Effective Presentation Techniques Quiz

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
• A special, low-friction material lines a rigid housing
• The lining directly contacts and supports the shaft
• The shaft slides over the liner material, separated by a thin film of lubricant
• The area of contact is relatively large
• Pressure on the bearing material is usually low
• Anti-friction bearings have a rolling contact between the shaft and bearing
• Using balls, needles, or rollers
• The area of contact is very small
• The pressure on the rings and balls or rollers is quite high

Bearing Housings

• The housing is the outer casing
• For friction bearings, the housing includes the base, base bolt slots, the cap, and the cap bolt holes
• Housings are made of one of the following materials:
  • Cast iron (for light to medium loads)
  • Cast steel (for light to heavy loads)
  • Fabricated steel (for special jobs)

Dimensions of Friction Bearings

• Bearings have nominal sizes (e.g., "27/16" bearing")
• Bore diameter (ID) is important
• Dimension from the base to the shaft center (the eye of the bearing) is important for installation and alignment
• Bearings from the same supplier, of the same size, design, and service weight, have identical shaft center dimensions
• Values for dimensions may vary between suppliers

Styles of Friction Bearings

• Choice depends on load, rotational (or rubbing) speed, direction of pull, and support design
• Regular (or flat) bearings:
  • Solid bearings
  • Split bearings

Angle Bearings

• Used for drives where the load is parallel or at a slight angle to the horizontal/mounted on a vertical support

Integrated Bearings

• Some heavy-duty machines have the bearing base cast as an integral part of the machine
• Babbitted or fitted with shells or liners

Joint Design

• Bearing joints are designed as flat joints, with a gib in the joint, or with an angle joint
• Flat joints:
  • Bolts hold the cap in alignment
  • Sections of the joint may be completely level or at an angle

Liner Materials

• Journal bearings and pillow block bearings are commonly used for low- to medium-speed, light- to heavy-loads
• They use liners with:
  • Softer, deforming material
  • Low coefficient of friction
  • Wear-resistance
  • Good heat conductivity
  • Readily availability
• Metallic Liner Materials:
  • Babbitt
  • Brass (copper/zinc alloy)
  • Bronze (copper/tin alloy)
  • Aluminum
  • Sintered bronze (oiliteTM)
• Nonmetallic Liner Materials:
  • Nylon
  • Polyurethanes
  • Phenol laminates (e.g., Celoron™, Micarta™)

Babbitt

• Common anti-friction lining material for bearings
• Melts at approximately 288°C (550°F) or less
• Fills cracks
• Has a smooth surface for the shaft
• Can be used in badly worn bearing housings

Using Mandrels to Pour Babbitt

• A mandrel is a dummy shaft
• Used to shape and size bearings
• Fitted with side pieces to help with positioning

Pouring Babbitt

• Done by a designated millwright
• Safety precautions should be observed

Fitting a Babbitt Bearing

• The babbitt fits the shaft and allows no clearance for lubricant
• Surface finish and area of contact need to be checked
• Running clearance, lubrication entry, and grooves need to be considered

Hand Tools for Fitting Bearings

• May be commercially produced or made in the plant
• Curved and straight scrapers
• Flat files or machinist's files
• Triangular files

The Fitting Process

• Bearing corners are relieved (to prevent binding)
• The top edge is chamfered
• Oil grooves are cut for lubricant entry

Clearance in a Bearing

• Needs to be a small amount so the shaft does not bind when assembled
• Shims to adjust clearance

Amount of Clearance

• Depends on the machine design and company policy
• Use feeler gauges to check clearance
• Use Plastigage™ to check clearance
• Refer to manufacturer's specifications

Bearings with Relieved Corners

• Bearings with relieved corners prevent the shaft from binding

Bearing Shims

• Made of a material that does not compress (e.g., sheet packing, tin plate, or brass shim stock)
• Slip-in shims can be used in gib-style blocks or any split block
• It may be necessary to take the bearing cap off to adjust the amount of shim

Metallic Liner Materials

• Must have a low coefficient of expansion
• Dimensionally stable in the presence of water
• May react chemically with water, mild acids, etc.

Thrust Control

• Thrust (axial force) is controlled by shaft collars, thrust washers, or other components
• Shaft shoulders and collars adjust axial displacement

Kingsbury Thrust Bearings

• Design consists of:
  • A revolving ring
  • A stationary ring made of low-friction materials (brass, bronze, tinned babbitt)
• Various styles, including fixed pad and floating pad
• Used for high-speed and heavy loads

Guide Bearings

• Used as positioning devices or guides for linear motion
• Often have a thin layer of bearing material for reduced friction
• Used in machine tools and gas compressors

Pivoted Shoe Bearings

• Used for high peripheral speeds and shaft stabilization
• The shoes are cylindrical to fit in grooves of the retaining ring
• Similar operation to flat, tilting pad Kingsbury bearings

Rolling Elements

• Classified by three basic styles:
  • Ball bearings
  • Roller bearings (cylindrical, tapered, spherical, needle)
• Spherical roller bearings:
  • Surfaces of rollers are curved across their width.

Bearing Installation Methods and Removal

• Multiple methods are available for mounting bearings, for instance, using sleeves or hydraulics to install, using various tools for removal or using various types of pressing to obtain a fit

Pillow Block Installation and Removal

• Split housings:
  • Have a base and cap separated in a horizontal manner, with mate marks (for alignment)
• Vertically split:
  • Have a one-piece ring and a base
• One-piece:
  • Bearings can be slipped over the shaft and bolted in place

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