Part 1: Classification by Structural Type

The structural design of a plain bearing bushing dictates how loads are distributed and how the bearing integrates into the housing assembly.

+-----------------------------------------------------------------------+
|                       PLAIN BEARING TYPES                             |
+-------------------++-------------------++------------------------------+
| Cylindrical Sleeve| Flanged Bushings   | Thrust Washers / Thrust Plates|
| (Pure Radial Load)| (Radial + Axial)   | (Pure Axial Load)            |
+-------------------++-------------------++------------------------------+

1. Cylindrical Sleeve Bushings (Plain Cylinders)

• Design: A straight cylindrical sleeve with smooth inner and outer diameters.

• Load Direction: Designed strictly for radial loads acting perpendicular to the shaft axis.

• Applications: Hydraulic cylinders, automotive suspensions, linkage pivots, electric motors.

2. Flanged Bushings

• Design: A cylindrical body with an integrated shoulder (flange) at one end.

• Load Direction: Handles combined radial loads and single-direction axial thrust loads.

• Applications: Gearboxes, agricultural machinery pivots, steering assemblies where axial locating is required without adding a separate washer.

3. Thrust Washers and Sliding Plates

• Design: Flat circular rings (thrust washers) or rectangular flat strips (sliding plates).

• Load Direction: Handles pure axial loads parallel to the shaft or flat sliding linear guidance.

• Applications: Kingpin assemblies, crane booms, heavy-duty door hinges, machine tool ways.

4. Spherical Plain Bearings

• Design: An inner ring with a spherical outer surface mating with a correspondingly spherical inner surface on the outer ring.

• Load Direction: Handles heavy radial loads while accommodating angular misalignment and tilting movements.

• Applications: Hydraulic cylinder end-eyes, heavy construction equipment linkages, suspension wishbones.

5. Split / Wrapped vs. Solid Machined Bushings

• Wrapped (Clenched Seamless): Formed from flat strips of laminated material with a split seam. Cost-effective, thin-walled, easy to press-fit into standard housings.

• Solid Machined: Turned or cast from solid metal stock. Ideal for heavy shock loads, thick-wall requirements, or custom dimensional tolerances.

Part 2: Classification by Material Composition

The material composition determines the tribological performance, wear rate, temperature tolerance, and self-lubricating properties of the bushing.

+-----------------------------------------------------------------------+
|                     BUSHING MATERIAL CLASSES                          |
+-----------------+-------------------+-------------------+-------------+
| Metal-Polymer   | Solid Bronze /    | Filament Wound    | Thermoplastic|
| Composites      | Graphite Plugged  | Fiber Reinforced  | Plastics    |
+-----------------+-------------------+-------------------+-------------+

1. Metal-Polymer Composite Bearings (Laminated)

• Structure: Steel or bronze metal backing + porous bronze sintered interlayer + self-lubricating polymer surface overlay.

• Sub-Types:

  • PTFE-Lined (Dry Running): Designed for maintenance-free operation under dry sliding conditions. Low friction coefficient (

    
    0.02−0.12

     

    $0.02-0.12$

    ).

  • POM-Lined (Marginal Lubrication): Features grease retention pockets on the sliding surface. Designed for applications with initial grease fill and infrequent relubrication.

• Key Characteristics: High load capacity in a compact wall thickness (

  
  1.0 mm−2.5 mm

   

  $1.0\text{ mm}-2.5\text{ mm}$

  ), excellent dimensional stability, wide temperature tolerance.

2. Solid Bronze and Machined Brass Bushings

• Structure: Cast or extruded high-density copper alloys (e.g., CuSn8, CuSn10, Aluminum Bronze).

• Sub-Types:

  • Oil-Grooved Bronze: Requires continuous or periodic liquid/grease lubrication via engineered surface grooves.

  • Solid Lubricant / Graphite-Plugged Bronze: Features embedded graphite or PTFE plugs inside a bronze matrix. Provides self-lubrication under high-temperature and high-load conditions where oil breaks down.

• Key Characteristics: High resistance to severe shock loads, edge loading, and abrasive environments.

3. Filament Wound Fiber-Reinforced Composite Bearings

• Structure: High-strength glass fibers woven with continuous self-lubricating liners (e.g., PTFE/epoxy matrix) cured into a rigid tube.

• Key Characteristics: Exceptional dynamic load capacity, non-conductive (electrical isolation), high resistance to corrosion and moisture absorption, ideal for outdoor or submerged environments.

4. Engineering Thermoplastic Bushings

• Structure: Homogeneous injection-molded polymers (e.g., POM, PEEK, Nylon, PTFE) blended with solid lubricant additives and reinforcing fibers.

• Key Characteristics: 100% corrosion proof, lightweight, low vibration transmission, chemically inert. Suitable for food processing, medical equipment, and chemical exposure.

5. Sintered Metal (Oil-Impregnated / Powder Metallurgy)

• Structure: Pressed and sintered bronze or iron powder forming a porous structure impregnated with liquid lubricating oil (typically 15–20% by volume).

• Key Characteristics: Cost-effective for high-volume automated production, maintenance-free at moderate speeds and light-to-medium loads.

Part 3: Material Performance Selection Matrix

When selecting a bushing material, engineers evaluate the permissible specific pressure limit (

P

$P$

), velocity upper limit (

V

$V$

), 

PV

$PV$

 factor limit, and operating temperature range:

P

$P$

V

$V$

PV

$PV$

140−250

$140-250$

60−100

$60-100$

2.0−2.5

$2.0-2.5$

1.5−2.0

$1.5-2.0$

−195 to +280

$-195\text{ to }+280$

120−200

$120-200$

2.5−3.0

$2.5-3.0$

2.8−3.0

$2.8-3.0$

−40 to +130

$-40\text{ to }+130$

80−120

$80-120$

0.5−1.0

$0.5-1.0$

1.0−1.5

$1.0-1.5$

−40 to +150

$-40\text{ to }+150$

100−230

$100-230$

0.4−0.6

$0.4-0.6$

1.5−2.0

$1.5-2.0$

−50 to +400

$-50\text{ to }+400$

140−210

$140-210$

0.1−0.3

$0.1-0.3$

1.2−1.6

$1.2-1.6$

−100 to +160

$-100\text{ to }+160$

30−80

$30-80$

1.0−3.0

$1.0-3.0$

0.3−0.8

$0.3-0.8$

−50 to +250

$-50\text{ to }+250$

20−35

$20-35$

2.5−5.0

$2.5-5.0$

0.5−1.0

$0.5-1.0$

−10 to +90

$-10\text{ to }+90$

Part 4: Engineering Selection Protocol

To select the correct plain bearing bushing for an industrial application, follow this systematic procedure:

1. Determine Motion and Geometry Type:

   • If load is strictly perpendicular to shaft 

     
     →

      

     $\to$

      Cylindrical Bushing.

   • If load has radial and axial components 

     
     →

      

     $\to$

      Flanged Bushing.

   • If angular misalignment exists 

     
     →

      

     $\to$

      Spherical Plain Bearing.

2. Calculate Specific Load (

   
   P

    

   $P$

   ) and Velocity (

   
   V

    

   $V$

   ):

   
   P=Fdi⋅B[MPa],V=π⋅di⋅n60000[m/s]

    

   P=di​⋅BF​[MPa],V=60000π⋅di​⋅n​[m/s]

3. Evaluate Operating 

   
   PV

    

   $PV$

    Value:
   Verify that 

   
   PVactual≤PVallowable_limit⋅CT⋅CL⋅CM

    

   PVactual​≤PVallowable_limit​⋅CT​⋅CL​⋅CM​

   .

4. Assess Environmental & Lubrication Factors:

   • Dry / No-Maintenance Required? 

     
     →

      

     $\to$

      PTFE Metal-Polymer, Filament Wound, or Engineering Plastic.

   • Extreme High Temperature (

     
     >200∘C

      

     >200∘C

     )? 

     
     →

      

     $\to$

      Graphite-Plugged Bronze or Unfilled PTFE Composite.

   • Corrosive or Marine Environment? 

     
     →

      

     $\to$

      Filament Wound Composite, Stainless Backed Composite, or Plastic.

   • Heavy Shock Load / Agricultural Equipment? 

     
     →

      

     $\to$

      Solid Machined Bronze or Filament Wound Fiber.