Operation of Journal Bearings

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Operation of Journal Bearings

• IMT 161/121
• Drive Systems
• Chapter 2

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Journals

• Journals are the parts of a shaft that is
  supported by bearings.
• Journals are always machined smooth and true.

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Journal Bearings
Bearing support block
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Journal Bearings

• Guides and supports a rotating shaft.
• Confines radial motion of a shaft.
• Formed in a cylindrical shape or a portion of a
  cylinder.
• Can be anti-friction or plain bearings.
• Can be made of many different materials.

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Plain Journal Bearings

• Advantages compared to anti-friction bearings
• 1. Less radial space required.
• 2. Quiet operation.
• 3. Less likely to be damaged by contamination.
• 4. Better resistance to overloading and shock
  loads.
• 5. Lower original cost (generally).

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Plain Journal Bearings

• Can be stored indefinitely without deteriorating.
• Require good lubrication practices.

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Lubrication

• When the shaft is rotating, a thin film of lube
  prevents metal to metal contact between the
  bearing surface and the shaft surface.
• Full film lubrication is when there is NO metal
  to metal contact.

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Lubrication

• When the shaft is not turning, there will be
  metal to metal contact.
• As the shaft starts to turn, boundary lubrication
  is achieved.
• Boundary lubrication means there is some
  separation of metal surfaces but metal to metal
  contact occurs at high spots.

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Lubrication
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Lubrication

• Two types of lubricants are used with PJB.
• 1. Oil--the measure of an oils ability to flow
  is viscosity. Slow flowing oils have a high
  (thick) viscosity.

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Lubrication

• 2. Grease--used where oil leakage may be a
  problem. The hardness (or softness) of a grease
  is expressed by the term consistency.

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Lubrication

• Thick (hard) grease may not properly coat a
  bearing surface, leaving bare spots.
• Thin (soft) grease may run off a bearing surface
  leaving no lubricant film.

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Lubrication

• Improper lubrication means too much, not enough
  or the wrong kind of lubricant.
• Good lubrication means the right amount of the
  right type in the right place at the right time.

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Lubrication

• Check the manufacturers specifications for the
  right type and amount of lubricant.

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Lubrication Grooves

• PJB often have lubrication grooves on the inside
  surfaces.
• Grooves are not generally positioned in the lower
  1/3 of the bearing. This would disrupt the full
  film lube.
• Grooves are generally located in the areas of
  least resistance.

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Lubrication Grooves

• Depth of oil grooves is generally 1/3 the wall
  thickness.
• Width of oil grooves is generally twice the depth.

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Lubrication Grooves

• Grease grooves are usually wider and deeper than
  oil grooves.
• Edges of grooves are beveled to aid in lube
  dispersion.

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Lubrication Grooves

• The simplest of groove patterns are axial and
  circumferential.
• Some grooves are variations/combinations of axial
  and circumferential grooves.

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Grooves
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Grooves
Bearing inserts
Shaft
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Oil Groove
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Seals

• Prevent contamination from entering the bearing
  area.
• Prevent lubrication leakage.
• Not all bearings are sealed.
• Can be made of felt or synthetic rubber.
• Many styles, materials and designs.

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Seals
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Nomenclature
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Nomenclature
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Types of Plain Journal Bearings

• Solid --one piece, can be called bushings or
  sleeve bearings.
• Bushings are generally thin walled are pressed
  into place.
• Sleeve bearings are usually thick walled.
• Split--generally two equal sized pieces.
• Multi-part--generally, 4 pieces.
• Partial--generally a half-bearing.

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Types of Plain Journal Bearings

• Matching halves--Must be used in pairs, saw cut
  from a solid bearing.
• Precision halves--are interchangeable because
  they are made to close tolerances

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Types of Bearings
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Bearing Types
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Materials

• Bronze.
• Hard drawn bronze.
• Cast bronze.
• The solid bronze sleeve bearing is considered to
  be the most reliable of all types of bearings
  available.

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Solid Bronze Sleeve Bearing
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Materials

• Split bearings are often made by lining steel,
  cast iron or bronze shells with a low friction
  material.
• Babbitt.
• Bimetal construction.
• Precision inserts fit into accurately machined
  shells.
• Tri-metal construction.

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No Glasses
Fire
Babbitt
Drive box
Molten babbitt
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Precision Inserts
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Materials

• Crush and spread.

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Materials

• Crush is the extra amount of lining material that
  makes each insert half slightly larger than a
  half circle. Helps clamp the insert into the
  bearing seat.
• Spread is the slight increase in diameter of the
  insert across the open-end width, requires the
  insert to be lightly forced into place.

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Crush and Spread
Insert
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Design and Selection

• Each type of bearing has advantages and not all
  bearings are good for all applications.
• Criteria for choosing a bearing
• 1. Load.
• 2. Clearance.
• 3. How the bearing can be installed.
• 4. Alignment stability.

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Design and Selection

• 5. Shaft size and speed
• 6. Lubrication method and type
• 7. Environment of equipment
• 8. Operating temperature
• 9. Maintenance practices
• 10. Duty cycle

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The End!!!!