Axial displacement

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Verifying the axial displaceability

1. Determine the required axial displacement

  • Thermal expansion of the shaft can be estimated using
    sreq = α L ΔT
  • Considering other effects may require advanced calculation or simulation.

2. Determine the maximum misalignment

  • Estimate the misalignment of the housing seats based on specified tolerances.
  • Considering other effects may require advanced calculation or simulation.

3. Check the permissible axial displacement

Check the permissible axial displacement in both directions, depending on the bearing used:

  • open bearing (fig. 1)
  • full complement bearing with a retaining ring (fig. 2)
  • sealed bearing (fig. 3)

sreq < s1 - β k1 B

or

sreq < s2 - β k1 B

If sreq is too large, consider offset mounting.

4. Check the internal clearance

  • Determine the clearance reduction caused by axial displacement.
    Clearance reduction caused by axial displacement
  • Determine the amount of clearance reduction from other effects (→ Bearing clearance).
Symbols
Bbearing width [mm]
Cred
reduction of radial clearance as a result of an axial displacement from a centred position [mm]
k1
misalignment factor (→ product tables)
LLength of the shaft that is subjected to the temperature raise [mm]
s1axial displacement limit in bearings with a cage (fig. 1) or in full complement bearings (fig. 2) when displacing away from the retaining ring [mm] (→ product tables)
s2axial displacement limit in sealed (fig. 3) and full complement bearings (fig. 2) when displacing toward the seal or retaining ring respectively [mm] (→ product tables)
sreqrequired axial displacement from a centred position [mm]
αthermal coefficient of expansion [°C–1]
= 12 x 10–6 for steel
βmisalignment [°]
ΔTtemperature difference [°C]
Calculation example
Application (fig. 4)
  • Bearing C 3040
    - d = 200 mm
    - D = 310 mm
    - B = 82 mm
    - Normal clearance: min. 170 μm
    - s1 = 15,2 mm
    - k1 = 0,123
    - k2 = 0,095
    - interference fit on the shaft: p6, max. probable interference 101 μm
  • Temperature range for the shaft: 20 to 90 °C [70 to 195 °F]
  • Max. misalignment: 0,46°

Verifying the axial displacability

  1. Required axial displacement
    sreq = 12 x 10-6 x 3000 x (90 - 20) = 2,5 mm
  2. Max. misalignment
    Input provided: 0,46°
  3. Checking the permissible axial displacement
    2,5 < 15,2 - 0,46 x 0,123 x 82 ≈ 10,5
    → okay
  4. Checking the internal clearance
    Calculation example
    Clearance reduction from interference fit on the shaft (→ Bearing clearance)
    For d/D = 0,65 → 0,87 x 101 = 87 μm

    Min. residual internal clearance when the bearing is displaced
    170 - 87 - 7 = 76 μm
    → okay
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